Understructure for electric vehicles

Abstract

To provide an electric vehicle understructure that can reduce LC-GHG per unit volume of the understructure for electric vehicles. [Solution] This understructure for electric vehicles comprises a battery housing, a floor module, a side sill, and brackets joined to these components, and the projected area of ​​the battery housing and the battery housing adjacent portion of the side sill, when viewed from the vertical direction of the reference plane, is S(m²). 2 ), the height of the side sill is H (m), and the total weight of the components of the electric vehicle understructure is W. TOTAL (kg), the total weight of the steel components of the electric vehicle's lower structure, which have a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or higher, is W. A When defined as, W TOTAL / SH is 180 or less, W A / W TOTAL The value is 0.10 or higher.

Description

Technical Field

[0001] The present invention relates to a structure (lower structure for an electric vehicle) that constitutes the lower part of an electric vehicle.

Background Art

[0002] Recently, from the perspective of preventing global warming, it has become more important to suppress the emission of greenhouse gases (hereinafter referred to as GHG) such as carbon dioxide (CO2). Under such circumstances, with the emergence of electric vehicles with lower GHG emissions than conventional internal combustion engine-powered vehicles, it is expected to reduce the GHG emissions from electric vehicles during driving. In addition, by adopting materials such as aluminum and carbon, which are excellent in weight reduction, as materials for electric vehicles, it is expected to reduce the GHG emissions from electric vehicles during driving.

[0003] Regarding the vehicle body of an automobile, for example, Patent Document 1 below discloses a vehicle body structure with excellent productivity. Also, regarding the floor module of an automobile, Patent Document 2 below discloses an integrated plate-shaped metal member used for a vehicle, and Patent Document 3 below discloses an automobile floor obtained by hot stamping. Furthermore, Patent Document 4 below discloses an automobile body capable of reducing the total amount of GHG generated during a series of life cycles from the manufacturing, use, and disposal of an automobile.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] Considering the lifecycle of electric vehicles, reducing GHG emissions solely during vehicle use (driving) is insufficient to reduce the total amount of GHGs emitted into the global environment. Furthermore, no studies have been conducted to date to reduce life cycle greenhouse gases (LC-GHGs, hereinafter referred to as life cycle GHGs or LC-GHGs) generated throughout the entire lifecycle of electric vehicle understructures, from manufacturing to use and disposal.

[0006] Therefore, the present invention aims to provide an electric vehicle substructure that can reduce LC-GHG per unit volume of the substructure for electric vehicles. [Means for solving the problem]

[0007] The gist of this disclosure is as follows:

[0008] (1) A first aspect of the present invention is an understructure for an electric vehicle having a battery housing, a floor module, a side sill, and a bracket joined to these members as components, wherein the projected area of ​​the battery housing and the battery housing adjacent portion of the side sill, which is the portion adjacent to the battery housing, when viewed from the vertical direction of a reference plane is S(m 2 ), the height of the side sill is H (m), and the total weight of the components of the electric vehicle understructure is W. TOTAL (kg), the total weight of the steel components of the electric vehicle's lower structure, which have a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or higher, is W. A When defined as, W TOTAL / SH is 180 or less, W A / WTOTAL A lower structure for an electric vehicle, where [a certain value] is 0.10 or more. (2) In the lower structure for an electric vehicle according to (1) above, when the weight of the steel material of the component parts of the lower structure for an electric vehicle is defined as W STEEL (kg), W STEEL / W TOTAL may be 0.56 or more. (3) In the lower structure for an electric vehicle according to (1) or (2) above, the battery housing includes a tray, a bottom plate, a frame, a cross member, a cooler, and an upper lid, and the floor module includes a floor cross member, a floor cross member extension, a floor panel, and components constituting the floor part, and the side sill may include a side sill outer, a side sill inner, and a side sill inner shock absorption member. (4) In the lower structure for an electric vehicle according to any one of (1) to (3) above, it may be provided with at least one of element technology A1 and element technology A2, and at least one of element technology B1, element technology C1, element technology C2, element technology D1, and element technology D2. The aforementioned element technology A1 has a chemical composition in mass percent of: C: 0.15~0.50%, Si: 0.0010~3.000%, Mn: 0.30~3.00%, Al: 0.0002~2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0~0.15%, Ti: 0~0.15%, V: 0~0.1 It contains 5%, Mo: 0~1.0%, Cr: 0~1.0%, Cu: 0~1.0%, Ni: 0~1.0%, B: 0~0.0100%, Ca: 0~0.010%, and REM: 0~0.30%, with the remainder being Fe and impurities, and by area percentage, a total of 10~30% ferrite and granular bainite, and martensite. A hot-stamped molded body having a metallic structure consisting of the remainder being one or more of bainite and tempered martensite, wherein in the texture from the surface to a position 1 / 4 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 1.8, and in the texture from a position 1 / 4 of the plate thickness from the surface to a position 1 / 2 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 2.3. The aforementioned element technology A2 has a chemical composition in mass percent of C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder being Fe and impurities, and containing a total area percentage of 90% or more of martensite and bainard. A hot-stamped molded body having a metallic structure including thread and tempered martensite, wherein in the texture from the surface to a position 1 / 4 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 1.8, and in the texture from a position 1 / 4 of the plate thickness from the surface to a position 1 / 2 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 2.3. The element technology B1 is a press-formed part in which a plurality of partial blanks made of steel plates are joined together, and at least two of the partial blanks are joined at a plurality of joint portions in an overlapping portion formed by partially overlapping, and in a cross section perpendicular to the surface of the partial blank including the center of the joint portion of the outermost partial blank, at a position 1 / 4 of the plate thickness from the surface of the partial blank that is in contact with other partial blanks, when the Vickers hardness at a position that is 15 mm or more away from the center of the joint portion and is not joined is Hvm, a portion of the plurality of joint portions has a Vickers hardness difference of ΔHv, which is the difference between the maximum hardness and the minimum hardness in a range of 5 mm toward the base material from the end of the joint portion, less than 0.2 Hvm, preferably 0.1 Hvm or less, and the other joint portions of the plurality of joint portions have a ΔHv of 0.2 Hvm or more. The element technology C1 is a structural member comprising a first member and a second member, wherein one of the first member and the second member includes a member body including a curved portion that curves in a plan view of the structural member, and a flange provided continuously with the member body, wherein the flange is joined to the other of the first member and the second member to form a hollow cross section together with the other of the first member and the second member, and the rate of reduction in plate thickness in the curved portion of the member body, based on the plate thickness of the flange, is 30% or more. The aforementioned element technology C2 is a material comprising a first blank and a second blank superimposed on the first blank, wherein the first blank and the second blank are not joined in the regions of the material that will become the first structural member and the second structural member; and a first structural member manufactured by a manufacturing method comprising: holding the material with a first mold and a second mold and supplying fluid between the first blank and the second blank to deform the material in the hollow space formed by the first mold and the second mold to form a first molded product including the first structural member from the first blank and a second molded product including the second structural member from the second blank; and a second structural member which is separate from the first structural member. The element technology D1 is a structural member comprising a lid for a battery case, a top plate facing the lid at a distance from it, two vertical walls connected to the top plate via their respective edges, and two flanges connected to the vertical walls on the opposite side of the top plate and joined to the lid, and a cross member extending in the width direction of the lid, wherein the rate of reduction in plate thickness at the center of the top plate, based on the plate thickness of the flanges, is 2.0% or more and 30.0% or less. The element technology D2 includes a plate-shaped first member, a flange portion disposed on one surface of the first member, and a main body portion having a convex shape relative to the flange portion, and a plurality of second members that together with the first member form a refrigerant flow path. A cooling member comprising the following features: the total area of ​​the region on the surface of the first member in which the refrigerant flow path is provided is 50% or more and less than 90% of the area of ​​the smallest rectangle that circumscribes the second member within the range of the surface; at each side edge in the width direction of the first member, at least one of the second member protrudes outward from the first member; and in each of the second members, the rate of reduction in plate thickness at the center of the main body portion, based on the plate thickness of the flange portion, is 5.0% or more. (5) The lower structure for electric vehicles described in (4) above may include at least one of the element technology A1 and the element technology A2, and the element technology B1. (6) The lower structure for electric vehicles described in (4) above may include at least one of element technology A1 and element technology A2, and at least one of element technology C1 and element technology C2. (7) The substructure for electric vehicles described in (4) above may include at least one of element technology A1 and element technology A2, and at least one of element technology D1 and element technology D2. (8) The substructure for electric vehicles described in (4) above may include at least one of element technology A1 and element technology A2, element technology B1, at least one of element technology C1 and element technology C2, and at least one of element technology D1 and element technology D2. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide an electric vehicle understructure that can reduce LC-GHG per unit volume of the understructure for electric vehicles. [Brief explanation of the drawing]

[0010] [Figure 1] This is a characteristic diagram showing the environmental impact (GHG emissions) during manufacturing for each material used in the understructure of electric vehicles. [Figure 2] This is a perspective view showing the lower structure for an electric vehicle according to this embodiment. [Figure 3] This is a cross-sectional view of the side sill. [Figure 4] This is a schematic diagram illustrating the projected area S. [Figure 5A] This graph shows the examples, with WA / WTOTAL plotted on the horizontal axis and WTOTAL / SH (kg / m3) plotted on the vertical axis. [Figure 5B] This graph shows the examples, with WA / WTOTAL plotted on the horizontal axis and LC-GHG / SH (kg, CO2-eq / m3) plotted on the vertical axis. [Figure 6] This is a schematic diagram showing the appearance of a single-door car. [Figure 7] This diagram illustrates the conventional press-formed manufacturing process for TWB parts. [Figure 8] This is a schematic diagram illustrating the structure of a blank for press forming door rings. [Figure 9] This is a conceptual diagram showing the stress analysis results of the overlapping section of the lower A-pillar. Figure 9(a) is a conceptual diagram showing the stress state of the lower A-pillar as viewed from the outside, and Figure 9(b) is a conceptual diagram showing the stress state of the rocker as viewed from the inside, using contour plots. [Figure 10] This is a conceptual diagram showing an example of spot welding points on the overlapping section of the lower A-pillar. Figure 10(a) shows an example of spot welding point locations on the overlapping section of the lower A-pillar, and Figure 10(b) is an explanatory conceptual diagram showing the parts of these spot welding points that have a risk of fracture enclosed by solid lines, and the parts that do not have a risk of fracture enclosed by dotted lines. [Figure 11] This is a conceptual diagram showing the spot welding positions of the overlapping sections determined by simulation analysis. Figure 11(a) shows examples of spot welding at the overlapping sections (L-shaped) of the A-pillar lower and the B-pillar lower, as viewed from the outside, and Figure 11(b) is a conceptual diagram showing the same section as viewed from the inside. [Figure 12]Figure 11 is a conceptual diagram showing the stress state after hot pressing of the integrated blank, obtained through FEM simulation. Figure 12(a) is a conceptual diagram showing the stress state at the overlapping section (L-shape) of pillar lower A and pillar lower B (T-shape) as viewed from the outside, while Figure 12(b) shows the same as viewed from the inside. [Figure 13] This diagram illustrates the press molding process for manufacturing components related to TWB, a component technology. [Figure 14] This is an explanatory diagram illustrating the softened area of ​​the heat-affected zone (HAZ) caused by spot welding. [Figure 15] This is a conceptual diagram illustrating an example of applying elemental technologies to an automobile floor module. [Figure 16] This is a conceptual diagram showing the overlap welding positions of the overlapping sections determined by simulation analysis, and illustrating an example where overlap welding is performed instead of spot welding as shown in Figure 11. Figure 16(a) shows examples of overlap welding at the overlapping sections (L-shaped) of the A-pillar lower and the B-pillar lower, as viewed from the outside, and Figure 16(b) is a conceptual diagram showing the same thing as viewed from the inside. [Figure 17A] Figure 17A is a perspective view showing the schematic configuration of a structural member according to the first embodiment. [Figure 17B] Figure 17B is an exploded perspective view of the structural member shown in Figure 17A. [Figure 18] Figure 18 is a perspective view showing the schematic configuration of the mold according to the first embodiment. [Figure 19] Figure 19 is a cross-sectional view of the mold shown in Figure 18, taken along line III-III. [Figure 20] Figure 20 shows an example of a mold different from that shown in Figure 19. [Figure 21A] Figure 21A is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 21B] Figure 21B is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 21C]Figure 21C is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 21D] Figure 21D is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 21E] Figure 21E is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 22] Figure 22 is a partial cross-sectional view of the structural member shown in Figure 17A. [Figure 23] Figure 23 is a perspective view showing the schematic configuration of a structural member according to the second embodiment. [Figure 24A] Figure 24A is a schematic diagram illustrating the manufacturing method of a structural member according to the second embodiment. [Figure 24B] Figure 24B is a schematic diagram illustrating the manufacturing method of a structural member according to the second embodiment. [Figure 24C] Figure 24C is a schematic diagram illustrating the manufacturing method of a structural member according to the second embodiment. [Figure 24D] Figure 24D is a schematic diagram illustrating the manufacturing method of a structural member according to the second embodiment. [Figure 25] Figure 25 is a perspective view showing the schematic configuration of a structural member according to the third embodiment. [Figure 26A] Figure 26A is a schematic diagram illustrating the manufacturing method of a structural member according to the third embodiment. [Figure 26B] Figure 26B is a schematic diagram illustrating the manufacturing method of a structural member according to the third embodiment. [Figure 26C] Figure 26C is a schematic diagram illustrating the manufacturing method of a structural member according to the third embodiment. [Figure 26D] Figure 26D is a schematic diagram illustrating the manufacturing method of a structural member according to the third embodiment. [Figure 27] Figure 27 is a perspective view showing the schematic configuration of a structural member according to the fourth embodiment. [Figure 28A] Figure 28A is a schematic diagram illustrating the manufacturing method of a structural member according to the fourth embodiment. [Figure 28B] Figure 28B is a schematic diagram illustrating the manufacturing method of a structural member according to the fourth embodiment. [Figure 28C] Figure 28C is a schematic diagram illustrating the manufacturing method of a structural member according to the fourth embodiment. [Figure 28D] Figure 28D is a schematic diagram illustrating the manufacturing method of a structural member according to the fourth embodiment. [Figure 29] Figure 29 is a perspective view showing the schematic configuration of the structural members in the first embodiment. [Figure 30] Figure 30 is a cross-sectional view of the side frame included in the structural member shown in Figure 29. [Figure 31] Figure 31 is a cross-sectional view of a cross member included in the structural member shown in Figure 29. [Figure 32] Figure 32 is a perspective view showing the schematic configuration of the mold in the first embodiment. [Figure 33A] Figure 33A is a cross-sectional view of the mold shown in Figure 32. [Figure 33B] Figure 33B is another cross-sectional view of the mold shown in Figure 32. [Figure 34A] Figure 34A is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 34B] Figure 34B is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 34C] Figure 34C is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 34D] Figure 34D is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 34E] Figure 34E is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 34F] Figure 34F is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 34G] Figure 34G is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 35]Figure 35 is a perspective view showing the schematic configuration of the structural members in the second embodiment. [Figure 36A] Figure 36A is a schematic diagram illustrating the manufacturing method of a structural member according to the second embodiment. [Figure 36B] Figure 36B is a schematic diagram illustrating the manufacturing method of a structural member according to the second embodiment. [Figure 36C] Figure 36C is a schematic diagram illustrating the manufacturing method of a structural member according to the second embodiment. [Figure 37] Figure 37 is a perspective view showing the schematic configuration of the structural members in the third embodiment. [Figure 38A] Figure 38A is a schematic diagram illustrating the manufacturing method of a structural member according to the third embodiment. [Figure 38B] Figure 38B is a schematic diagram illustrating the manufacturing method of a structural member according to the third embodiment. [Figure 39] Figure 39 is a perspective view showing the schematic configuration of the structural members in the fourth embodiment. [Figure 40A] Figure 40A is a schematic diagram illustrating the manufacturing method of a structural member according to the fourth embodiment. [Figure 40B] Figure 40B is a schematic diagram illustrating the manufacturing method of a structural member according to the fourth embodiment. [Figure 41] Figure 41 is a perspective view showing the schematic configuration of the structural members in the fifth embodiment. [Figure 42A] Figure 42A is a schematic diagram illustrating the manufacturing method of a structural member according to the fifth embodiment. [Figure 42B] Figure 42B is a schematic diagram illustrating the manufacturing method of a structural member according to the fifth embodiment. [Figure 42C] Figure 42C is a schematic diagram illustrating the manufacturing method of a structural member according to the fifth embodiment. [Figure 43] Figure 43 is a cross-sectional view showing the schematic configuration of the structural member in the sixth embodiment. [Figure 44A] Figure 44A is a schematic diagram illustrating the manufacturing method of a structural member according to the sixth embodiment. [Figure 44B] Figure 44B is a schematic diagram illustrating the manufacturing method of a structural member according to the sixth embodiment. [Figure 44C] Figure 44C is a schematic diagram illustrating the manufacturing method of a structural member according to the sixth embodiment. [Figure 45] Figure 45 is a cross-sectional view showing an example of a structural member in the seventh embodiment. [Figure 46] Figure 46 is a cross-sectional view showing another example of a structural member in the seventh embodiment. [Figure 47A] Figure 47A is a schematic diagram illustrating the manufacturing method of a structural member according to the seventh embodiment. [Figure 47B] Figure 47B is a schematic diagram illustrating the manufacturing method of a structural member according to the seventh embodiment. [Figure 47C] Figure 47C is a schematic diagram illustrating the manufacturing method of a structural member according to the seventh embodiment. [Figure 48] Figure 48 is a cross-sectional view of the mold according to the eighth embodiment. [Figure 49A] Figure 49A is a schematic diagram illustrating the manufacturing method of a structural member using the mold shown in Figure 48. [Figure 49B] Figure 49B is a schematic diagram illustrating the manufacturing method of a structural member using the mold shown in Figure 48. [Figure 50] Figure 50 is a perspective view showing the schematic configuration of a structural member according to the embodiment. [Figure 51] Figure 51 is a cross-sectional view of the structural member shown in Figure 50, taken along line II-II. [Figure 52A] Figure 52A is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 50 and 51. [Figure 52B] Figure 52B is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 50 and 51. [Figure 52C] Figure 52C is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 50 and 51. [Figure 52D]Figure 52D is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 50 and 51. [Figure 52E] Figure 52E is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 50 and 51. [Figure 53] Figure 53A is a partial cross-sectional view of a structural member manufactured by the manufacturing method shown in Figures 52A to 52E. [Figure 54] Figure 54 is a partial cross-sectional view of a structural member manufactured by the manufacturing method shown in Figures 52A to 52E, and is different from the structural member shown in Figure 53. [Figure 55] Figure 55 is a perspective view showing the schematic configuration of the cooling member according to the first embodiment. [Figure 56] Figure 56 is a cross-sectional view of the cooling member shown in Figure 55, taken along line II-II. [Figure 57A] Figure 57A is a perspective view showing the schematic configuration of the mold according to the first embodiment. [Figure 57B] Figure 57B is another perspective view showing the schematic configuration of the mold according to the first embodiment. [Figure 58] Figure 58 is a partial longitudinal cross-sectional view of the mold according to the first embodiment. [Figure 59] Figure 59 shows an example of a different mold from Figure 58. [Figure 60] Figure 60 is a partial cross-sectional view of a mold according to the first embodiment. [Figure 61A] Figure 61A is a schematic diagram illustrating the manufacturing method of the cooling member according to the first embodiment. [Figure 61B] Figure 61B is a schematic diagram illustrating the manufacturing method of the cooling member according to the first embodiment. [Figure 61C] Figure 61C is a schematic diagram illustrating the manufacturing method of the cooling member according to the first embodiment. [Figure 61D] Figure 61D is a schematic diagram illustrating the manufacturing method of the cooling member according to the first embodiment. [Figure 61E] Figure 61E is a schematic diagram illustrating the manufacturing method of the cooling member according to the first embodiment. [Figure 61F] Figure 61F is a schematic diagram illustrating the manufacturing method of the cooling member according to the first embodiment. [Figure 61G] Figure 61G is a schematic diagram illustrating the manufacturing method of the cooling member according to the first embodiment. [Figure 62A] Figure 62A is a partial cross-sectional view of a cooling member manufactured by the manufacturing method according to the first embodiment. [Figure 62B] Figure 62B is a perspective view of a cooling member manufactured by the manufacturing method according to the first embodiment. [Figure 63] Figure 63 is a bottom view of the cooling member according to the second embodiment. [Figure 64A] Figure 64A is a schematic diagram showing a method for manufacturing a cooling member according to the second embodiment. [Figure 64B] Figure 64B is a schematic diagram showing a method for manufacturing a cooling member according to the second embodiment. [Figure 65] Figure 65 is a bottom view of the cooling member according to the third embodiment. [Figure 66A] Figure 66A is a schematic diagram showing a method for manufacturing a cooling member according to the third embodiment. [Figure 66B] Figure 66B is a schematic diagram showing a method for manufacturing a cooling member according to the third embodiment. [Figure 67] Figure 67 is a perspective view of the cooling member according to the fourth embodiment. [Figure 68] Figure 68 is a cross-sectional view of the cooling member shown in Figure 67, taken along line XIV-XIV. [Figure 69A] Figure 69A is a schematic diagram showing a method for manufacturing a cooling member according to the fourth embodiment. [Figure 69B] Figure 69B is a schematic diagram showing a method for manufacturing a cooling member according to the fourth embodiment. [Modes for carrying out the invention]

[0011] As mentioned above, considering the lifecycle of electric vehicles, reducing GHG emissions solely during vehicle use (driving) is insufficient to reduce the total amount of GHGs emitted into the global environment. Furthermore, since the understructure of electric vehicles accounts for approximately 3-10% of the total vehicle weight, reducing GHG emissions associated with the understructure of electric vehicles has a significant impact on overall energy consumption. Currently, the focus is on making electric vehicles lighter by using multi-material construction with materials such as aluminum and carbon, but the inventors of this invention... 1. GHGs generated during the manufacturing of materials for the understructure of electric vehicles (hereinafter referred to as "material manufacturing GHGs") 2. GHG generated during the manufacturing process of the understructure for electric vehicles (hereinafter referred to as "process GHG") 3. The contribution of the understructure of the electric vehicle to the GHG generated when generating electricity used when the electric vehicle is running (hereinafter referred to as "GHG during operation"), and, 4. GHG generated during the disposal of understructures for electric vehicles (hereinafter referred to as "disposal GHG") The inventors focused on these four types of GHGs and investigated ways to reduce their total amount.

[0012] In this specification, the term "understructure for electric vehicles" refers to a group of structural members including the floor of the electric vehicle body and the skeletal components joined thereto. Battery Furthermore, in this specification, GHGs, including CO2 generated during the lifecycle (including CO2 generated when electricity is generated for use during driving), are referred to as LC-GHG, and the amount of CO2 is defined as the sum of GHGs other than CO2, converted to equivalent mass. Other GHGs besides CO2 include ozone-depleting substances such as methane, nitrous oxide, and chlorofluorocarbons (CFCs). The CO2 equivalent mass is calculated using the conversion factors listed in Tables 1A, 1B, and 1C, which are set for each category of material, process, and use. "CO2 equivalent" is also called "CO2 equivalent mass," and in this specification, "CO2 equivalent," "CO2 equivalent mass," and "CO2 conversion amount" are defined as having the same meaning. "CO2 equivalent mass" is calculated by weighting the CO2 equivalent mass of gases other than CO2, such as methane CH4 (greenhouse effect per unit mass is 25 times that of CO2: global warming potential 25) and nitrous oxide N2O (greenhouse effect per unit mass is 298 times that of CO2: global warming potential 298), by their global warming potentials.

[0013] [Table 1A]

[0014] [Table 1B]

[0015] [Table 1C]

[0016] (Material manufactured by GHG) As a material, steel has the lowest GHG emissions per unit weight compared to other materials. Figure 1 is a characteristic diagram showing the environmental impact (GHG emissions) during manufacturing for each material used in the understructure of electric vehicles. The vertical axis shows the materials used in the understructure of electric vehicles: ordinary steel plate, high-strength steel plate, aluminum, and carbon fiber reinforced plastic (CFRP). The horizontal axis shows the GHG emissions per equivalent function [kg-CO2 equivalent / kg-equivalent component]. As shown in Figure 1, steel materials (regular steel plates, high-strength steel plates) have significantly lower GHG emissions compared to other materials (aluminum, carbon fiber reinforced plastics), and it is clear that primarily using steel materials as the material for the understructure of electric vehicles will greatly contribute to the reduction of LC-GHG.

[0017] (Process GHG) In the manufacturing of understructures for electric vehicles, GHGs are mainly generated during processes such as welding, heating, and painting. Therefore, by designing appropriate processes while ensuring the performance required for understructures for electric vehicles, it is possible to contribute to the reduction of LC-GHGs.

[0018] (GHG during driving) By reducing the weight of the understructure of electric vehicles, the power consumption rate of electric vehicles can be improved. Therefore, reducing the weight of the understructure of electric vehicles can contribute to the reduction of LC-GHG (Life Cycle Gas).

[0019] (GHG at disposal) Steel can contribute to a reduction of 1.60 kg-CO2eq of GHGs per kilogram through scrap recycling. Compared to aluminum, the reduction effect per kilogram of emissions from steel is smaller, but when using high-strength steel, the weight required to obtain the necessary strength is smaller, so it can be said that using high-strength steel can contribute to the reduction of LC-GHGs. In other words, GHGs at the time of disposal, similar to GHGs in material manufacturing, can be reduced by primarily using steel materials as components for the understructure of electric vehicles, thereby contributing to the reduction of LC-GHGs.

[0020] As mentioned above, reducing LC-GHG requires reducing total GHG emissions from four perspectives. For example, there is a trade-off relationship between "GHG from material manufacturing and disposal" and "GHG during operation." Furthermore, generally, manufacturing lightweight and high-performance parts tends to increase "process GHG," and there is a trade-off relationship between "process GHG" and "GHG during operation." While methods for reducing GHGs at each stage of the lifecycle have been considered and discussed, optimal examples of material selection and process design for reducing LC-GHGs have not been disclosed.

[0021] The inventors focused on reducing LC-GHG by considering the above four categories of GHG, including trade-off relationships, and found that by controlling the weight of components per predetermined volume and the weight of high-strength components with a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or higher to an appropriate range, it is possible to reduce LC-GHG of the understructure for electric vehicles while satisfying the required strength (collision resistance).

[0022] The following describes, with reference to the figures, an electric vehicle substructure according to an embodiment of the present invention based on the above findings. However, these descriptions are intended to be merely illustrative of preferred embodiments of the present invention and are not intended to limit the present invention to such specific embodiments.

[0023] The lower structure 100 for electric vehicles according to this embodiment is applied to the body of an electric vehicle, which is composed of a monocoque frame equipped with shock-absorbing skeletal members. Figure 2 shows an exploded perspective view of the lower structure 100 for an electric vehicle according to this embodiment. As shown in Figure 2, the understructure 100 for an electric vehicle includes a battery housing 10 that houses a battery 50, a floor module 20 provided on top of the battery housing 10, a pair of side sills 30 provided on the sides of the battery housing 10, and brackets (not shown) that are joined to these members.

[0024] As shown in Figure 2, the battery housing 10 includes, for example, a bathtub-shaped tray 11 on which the battery 50 is placed, a bottom plate 12 positioned below the tray 11, a rectangular frame 13 surrounding the sides of the tray 11, a cross member 14 connected to the frame 13 to improve the strength of the battery housing 10, a cooler 15 for cooling the battery 50, and a top cover 16 positioned above the tray 11. Furthermore, the top cover 16 may be configured to also serve as part of the floor module 20.

[0025] As shown in Figure 2, the floor module 20 includes, for example, a floor panel 21 that constitutes the floor surface of the passenger compartment, a floor cross member 23 positioned on the upper part of the floor panel 21 so as to extend in the vehicle width direction of the passenger compartment, floor cross member extensions 25 joined to both ends of the floor cross member 23, and components 27 that constitute the floor portion. In the example shown in Figure 2, the components 27 that make up the floor section are the floor tunnel 27a, the side floor panel 27b, and the floor side member 27c.

[0026] Each of the pair of side sills 30 includes, for example, a side sill outer 31, a side sill inner 33, and a side sill internal shock absorbing member 35. In the example shown in Figure 3, the side sill outer 31 and the side sill inner 33 are joined together to form a closed cross-section, and the side sill internal impact absorbing member 35 is provided inside this closed cross-section. Figure 4 is a schematic plan view showing the positional relationship between the battery housing 10 and the side sills 30. As shown in Figure 4, the side sills 30 are provided on both edges in the width direction of the battery housing 10. The side sills 30 extend in the front-rear direction beyond the front and rear ends of the battery housing 10. In this application, the portion of the battery housing 10 and the side sill 30 adjacent to the battery housing 10 when viewed from a direction perpendicular to the reference plane is referred to as the battery housing adjacent portion 301. The "portion of the battery housing 10 and the side sill 30 adjacent to the battery housing 10" is the portion of the side sill 30 whose longitudinal position is between the front end and the rear end of the battery housing 10.

[0027] In the electric vehicle understructure 100 according to this embodiment, it is possible to reduce LC-GHG of the electric vehicle understructure by controlling the weight of the components per unit volume and the weight of high-strength components with a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or higher to an appropriate range.

[0028] in particular, The projected area of ​​the battery housing 10 and the adjacent part 301 of the battery housing when viewed from the vertical direction of the reference plane is S(m²). 2 ), The height of the side sill 30 is H (m), The total weight of the components of the understructure 100 for electric vehicles is W TOTAL (kg), The total weight of the steel components of the understructure 100 for electric vehicles, which have a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or higher, is W. A When defined as, W TOTAL / SH(kg / m 3 ) is 180 or less, W A / W TOTAL (-) is 0.10 or higher By satisfying these conditions, it becomes possible to reduce LC-GHG in the understructure of electric vehicles.

[0029] Projected area S(m 2 As shown in Figure 4, the distance Ls (m) in the front-to-back direction of the battery housing adjacent portion 301 and the distance Ws (m) between the widthwise edges of the pair of side sills 30 are used. If the battery housing 10 is not a perfect rectangle, the distance Ls is defined as the distance at the point where the front-to-back distance of the battery housing adjacent portion 301 is maximum. If the distance between the widthwise edges of a pair of side sills 30 is not constant, the distance Ws is defined as the distance at the point where the widthwise edges of the pair of side sills 30 are closest. H(m) is the height of the side sill 30. 2 ) is the height distance when the side sill 30 is installed on the vehicle body. If the height distance of the side sill 30 is not constant, the height H is defined as the distance at the point where the height distance is maximum.

[0030] No conventional understructure for electric vehicles has met the above conditions, and these conditions would not have been easily conceived without the aforementioned knowledge of the inventors. The reference plane of the battery housing 10 is the plane perpendicular to the vehicle height direction in the understructure of the electric vehicle when it is attached to the vehicle body.

[0031] W TOTAL The value of tends to increase with larger vehicle bodies. For this reason, in this application, W corresponds to a predetermined volume which is the product of the projected area S of the battery housing adjacent portion 301 of the electric vehicle lower structure 100 and the side sill 30 and the height H of the side sill 30. TOTAL The core is W TOTAL / SH(kg / m 3 ) is used as an indicator. W TOTAL / SH(kg / m 3 If the value of ) is 180 or less, weight reduction in proportion to the size of the understructure for electric vehicles has been achieved, making it possible to reduce GHG during driving. From the perspective of reducing GHG during driving, W TOTAL A smaller / SH value is better, preferably 175 or less, and more preferably 170 or less. W TOTAL The lower limit of / SH is set based on the required safety performance. TOTAL For the purpose of ensuring rigidity as a lower structure for electric vehicles and achieving both safety performance, a value of, for example, 150 or higher is sufficient.

[0032] W A / W TOTAL If the value is 0.10 or higher, it indicates that a high proportion of the components used in the understructure of electric vehicles are high-strength components with a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or higher, making it possible to reduce GHG emissions from material production. From the perspective of reducing GHGs in material manufacturing, W A / W TOTAL A higher value is better, preferably greater than 0.40, and more preferably greater than 0.45. Furthermore, from the perspective of reducing material manufacturing GHGs, the weight of components with a plate thickness of 1.3 mm or less and a minimum Vickers hardness of HV230 or higher should be reduced to W B When that happens, W B / WTOTAL The value of is preferably 0.2 or higher, and more preferably 0.4 or higher. Furthermore, in order to reduce LC-GHG in the understructure of electric vehicles, it is preferable to increase the proportion of steel material used in the understructure of electric vehicles. For this reason, the weight of the steel material in the components of the understructure of electric vehicles is W STEEL When defined as (kg), W STEEL / W TOTAL It is preferable that the ratio is 0.56 or higher, and more preferably 0.62 or higher.

[0033] The method for measuring Vickers hardness is as follows: Samples with cross-sections perpendicular to the plate surface are taken from the flat parts of each section, and these cross-sections are prepared as measurement surfaces, which are then used for hardness testing. The method for preparing the measurement surfaces is carried out in accordance with JIS Z 2244:2009. After polishing the measurement surface with silicon carbide sandpaper from #600 to #1500, the measurement surface is finished to a mirror surface using a liquid in which diamond powder with a particle size of 1 μm to 6 μm is dispersed in a diluent such as alcohol or pure water. The hardness test is carried out in accordance with the method described in JIS Z 2244:2009. Using a micro-Vickers hardness tester, 30 measurements are taken at 3 / 8 of the plate thickness of the sample with a load of 1000 gf, at intervals of at least 3 times the indentation, and the average value of these measurements is taken as the hardness at the center of the plate thickness.

[0034] In this application, (1) At least one of element technology A1 and element technology A2, (2) At least one of element technology B1, element technology C1, element technology C2, element technology D1, and element technology D2, By applying this to the components of the understructure 100 for electric vehicles, the weight ratio of steel materials in the electric vehicle body is increased, reducing the above-mentioned material manufacturing GHGs, and the weight reduction of the vehicle body reduces GHGs during operation, resulting in a significant reduction in LC-GHG compared to conventional vehicle bodies. Specifically, the battery LC-GHG per predetermined volume, which is the product of the projected area S and the height H of the side sill 30, is 3000 kg CO2 eq / m³.3 The following can be achieved. Each of the elemental technologies will be discussed later.

[0035] At least one of the aforementioned element technology A1 and element technology A2, The aforementioned element technology B1, It is even more preferable to apply this. At least one of the aforementioned element technology A1 and element technology A2, At least one of the element technology C1 and the element technology C2, It is even more preferable to apply this. At least one of the aforementioned element technology A1 and element technology A2, At least one of the element technology D1 and the element technology D2, It is even more preferable to apply this. At least one of the aforementioned element technology A1 and element technology A2, The aforementioned element technology B1, At least one of the element technology C1 and the element technology C2, At least one of the element technology D1 and the element technology D2, It is even more preferable to apply this.

[0036] In this specification, an electric vehicle is defined as an electric vehicle that excels in side-impact safety. A vehicle for public road use is one that meets the safety standards of each country's regulations (type approval) and demonstrates superior crash safety performance in the side impact and pole side impact tests of the New Car Assessment Programme (NCAP), which is a national assessment test. It should be noted that the aforementioned assessment tests are more stringent than the national regulations, and if the battery protection evaluation results for the side impact and pole side impact tests are equivalent to those of a vehicle with good performance in those tests, it can be said that the vehicle is perfectly capable of being driven on public roads. The body of an electric vehicle to which the understructure for electric vehicles is applied is not limited to a vehicle body having a monocoque frame structure, but may also be a vehicle body with a ladder frame structure. Furthermore, vehicle types for use on public roads include passenger cars and commercial vehicles such as sedans, hatchbacks, station wagons, minivans, and pickup trucks. Furthermore, vehicles used on public roads include trucks and other vehicles that carry cargo.

[0037] (Examples) The present disclosure will be specifically explained below with reference to examples of embodiments. The conditions in the embodiments are merely examples adopted to confirm the feasibility and effectiveness of the present disclosure, and the present disclosure is not limited to the conditions in the embodiments. The present disclosure may adopt various conditions as long as they do not depart from its essence and achieve its objectives.

[0038] Tables 2A and 2B show the elemental technologies applied to the understructure of electric vehicles in the examples and comparative examples. Table 3 also shows the various characteristic values ​​of each electric vehicle substructure, including W A / W TOTAL , S(m 2 ), H(m), W TOTAL (kg), W TOTAL / SH(kg / m 3 ), and W STEEL / W TOTAL This shows the value.

[0039] [Table 2A]

[0040] [Table 2B]

[0041] [Table 3]

[0042] The weight W shown in Table 3 TOTAL and W A and W STEEL The weights were determined by disassembling the understructure for electric vehicles and measuring and analyzing the shape and weight data. The weights in some comparative examples and inventive examples were determined by measuring and analyzing the design and development data obtained using CAD (Computer-Aided Design). The hardness HV was determined as follows. Samples with cross-sections perpendicular to the plate surface were taken from the flat areas of each section, and these cross-sections were prepared as measurement surfaces. These measurement surfaces were then subjected to hardness testing. The method for preparing the measurement surfaces was carried out in accordance with JIS Z 2244:2009. After polishing the measurement surfaces with silicon carbide sandpaper ranging from #600 to #1500, the measurement surfaces were polished to a mirror finish using a liquid in which diamond powder with a particle size of 1 μm to 6 μm was dispersed in a diluent such as alcohol or pure water. The hardness testing was carried out according to the method described in JIS Z 2244:2009. Using a micro-Vickers hardness tester, 30 measurements were taken at 3 / 8 of the plate thickness of the sample, with a load of 1000 gf, at intervals of at least 3 times the indentation distance, and the average value of these measurements was taken as the hardness at the center of the plate thickness.

[0043] Table 4 shows the examples of inventions and comparative examples, respectively. • Total GHG emissions LC-GHG (kg, CO2-eq), and, • LC-GHG / SH (kg, CO2-eq / m³) 3 ) The calculated value is shown.

[0044] [Table 4]

[0045] Total GHG emissions are calculated by summing the CO2 equivalent mass from the above-mentioned material manufacturing GHGs, process GHGs, driving GHGs, and disposal GHGs, and correspond to LC-GHG emissions. Total GHG emissions are calculated using the method described later.

[0046] The characteristic values ​​for each of the Invention Examples 1-11 were obtained by the inventors by measuring and analyzing the lower structure for an electric vehicle constructed by the inventors using the elemental technologies described above. Furthermore, the characteristic values ​​for Comparative Examples 1-4 were obtained by the inventors by measuring and analyzing the vehicle bodies of commercially available electric vehicles used on public roads. Furthermore, the analysis of LC-GHG emissions is as follows: "Roland Geyer, Parametric Assessment of Climate Change Impacts of Automotive Material Substitution, Environmental Science & Technology 2008 42 (18), 6973-6979, DOI: 10.1021 / es800314w" It was carried out based on the following.

[0047] (Calculation of GHG emissions from material manufacturing) The default settings of the GHG analysis software were used as the basic conditions. In these default settings, the rate of scrap charging into the blast furnace is 11.9%, and the usage rates of recycled materials using scrap are set to 5% for sheet metal, 85% for rods and wires, and 100% for cast iron, based on statistical data. Assuming these as base conditions, calculations were performed by inputting values ​​to achieve the various material compositions shown in Tables 1A, 1B, and 1C.

[0048] (Calculation of process GHG) The default settings of the GHG analysis software were used as the basic conditions. Assuming that the material yield in automotive parts production is 55% for steel sheets, 52% for aluminum alloy sheets, 75% for sheet metal, bars, and wire rods, and 80% for cast iron, aluminum extruded materials, and aluminum castings, the values ​​were entered to calculate the various material compositions shown in Tables 1A, 1B, and 1C.

[0049] (Calculation of GHG during driving) Electric vehicles were selected as the powertrain type for the target vehicle models. Based on the size and weight of each vehicle being analyzed, a corresponding mid-size electric vehicle was selected. The vehicle driving pattern was set to the following WLTP (Class 3b) mode. WLTP mode ·Average speed ···36.57km / h ·Maximum speed...97.4km / h • Running time: 1477 seconds • Distance traveled: 15.01 km The calculation assumed a driving range of 110,000 km and incorporated the weight reduction of the vehicle body to consider the resizing of the powertrain. Furthermore, the calculation assumed that the electric vehicle's power consumption during operation was based on electricity generated in Japan, and the inventors used the power consumption figures for the electric vehicle's understructure, obtained through analysis, as input.

[0050] (Calculation of GHG emissions at disposal) Based on the default settings of the software used for GHG analysis at the time of disposal, we assumed a recycling rate of 90.3% for steel materials and 78.6% for aluminum alloy materials.

[0051] The CO2 equivalent mass was calculated using coefficients that treat GHGs in the processes shown in Tables 1A, 1B, and 1C as CO2 equivalent mass, and the CO2 equivalent mass was determined using either weight or energy. These values ​​are the default settings of the GHG analysis software and are based on statistical data of GHG emissions for each substance and process. Following the above procedure, the CO2 equivalent mass was calculated from the material manufacturing GHG, process GHG, operating GHG, and disposal GHG, and the LC-GHG listed in Table 4 was calculated by summing them up.

[0052] In Invention Example 1-11, the proportion of steel used in the understructure of an electric vehicle was increased, and as a result of combining and applying the above-mentioned elemental technologies, W TOTAL Set / SH to 180 or less, and W A / W TOTALWe were able to achieve a value of 0.10 or higher. This allowed us to reduce LC-GHG in the understructure of electric vehicles.

[0053] On the other hand, in Comparative Examples 1-4, W A / W TOTAL The ratio is 0.08 or less (8% or less), and in order to ensure collision performance, W TOTAL It was necessary to increase the / SH value, and we were unable to fully achieve the reduction effect of GHG emissions during material production and operation.

[0054] Figure 5A shows the embodiment, with W on the horizontal axis. A / W TOTAL W on the vertical axis TOTAL / SH(kg / m 3 This is a graph plotting ). Figure 5B shows the embodiment, with W on the horizontal axis. A / W TOTAL The vertical axis is plotted as LC-GHG / SH(kg,CO2-eq / m³). 3 This is a graph showing the plotted values. These graphs confirm that, according to this embodiment, LC-GHG is significantly reduced compared to the conventional structure. Thus, according to this disclosure, W TOTAL / SH is 180 or less, W A / W TOTAL By using batteries with a coefficient of 0.10 or higher, it is possible to reduce LC-GHG in the understructure of electric vehicles.

[0055] (Example 2) Table 5 shows the results of crash tests conducted on the inventive example and comparative example. In Table 5, the crash test results are shown with evaluation values ​​A and B. In this evaluation, the test results for the IIHS side impact test are first disclosed, and numerical analysis of the side impact test was performed using the IIHS side impact analysis model for the vehicle body of Comparative Example 1, which has the highest crash safety performance rating, and the resulting intrusion amount was used as the standard (evaluation B). Furthermore, the vehicle bodies in Comparative Examples 1-4 are also certified (type approved) under the regulations of each country. The safety performance evaluation results for some of the vehicle bodies are described in comparison with Comparative Example 1. For Invention Example 1-11, numerical analysis was performed on a side-impact test in which only the understructure of the electric vehicle was replaced, and the safety performance was evaluated based on the relative amount of intrusion into the understructure of the electric vehicle and the energy absorbed during the collision. Vehicles that performed better than the highest-rated vehicle in the IIHS side impact simulation test (Comparative Example 1) were given a rating of A. Vehicles that performed similarly to the safety test results of Comparative Example 1 and did not experience any parts breaking were given a rating of B.

[0056] [Table 5]

[0057] As shown in Table 5, Invention Example 1-11 achieved results (rating A or B) in side impact tests that were equivalent to or better than those of vehicles that received a "good" rating in the IIHS side impact test.

[0058] Therefore, according to Invention Example 1-11, it is possible to reduce LC-GHG while satisfying the safety test results of a vehicle that received a "good" rating in the IIHS side impact test.

[0059] The following is an overview of the elemental technologies applied to the lower structure 100 for electric vehicles according to this embodiment. Furthermore, the reference numerals for components, formulas, embodiments, and examples in the description of each elemental technology are assigned to each elemental technology for the purpose of simplifying the explanation. Therefore, the same reference numeral may be assigned to different elemental technologies.

[0060] (Elemental Technology A1) Elemental technology A1 has a chemical composition in mass percent of: C: 0.15~0.50%, Si: 0.0010~3.000%, Mn: 0.30~3.00%, Al: 0.0002~2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0~0.15%, Ti: 0~0.15%, V: 0~0.15% It contains %, Mo: 0~1.0%, Cr: 0~1.0%, Cu: 0~1.0%, Ni: 0~1.0%, B: 0~0.0100%, Ca: 0~0.010%, and REM: 0~0.30%, with the remainder being Fe and impurities, totaling 10~30% by area percentage of ferrite and granular bainite, along with martensite, and bainite. A hot-stamped molded article having a metallic structure consisting of the remainder consisting of one or more inite and tempered martensite, wherein in the texture from the surface to a position 1 / 4 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 1.8, and in the texture from a position 1 / 4 of the plate thickness from the surface to a position 1 / 2 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 2.3.

[0061] Element technology A1 is a technology disclosed in International Publication No. 2021 / 230149. According to this element technology A1, it is possible to provide hot-stamped molded articles having excellent strength, bendability, and ductility.

[0062] (Element technology A2) Elemental technology A2 has a chemical composition in mass percent of C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder being Fe and impurities, and totaling 90% or more of martensite and bainai in terms of area percentage. This is a hot-stamped molded article having a metallic structure including t and tempered martensite, wherein in the texture from the surface to a position 1 / 4 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 1.8, and in the texture from a position 1 / 4 of the plate thickness from the surface to a position 1 / 2 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10>~{001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10>~{111}<-1-12> is less than 2.3.

[0063] Element technology A2 is a technology disclosed in International Publication No. 2021 / 230150. According to this element technology A2, it is possible to provide a hot-stamped molded article that has excellent strength and flexibility, as well as high load-bearing capacity.

[0064] (Element technology B1) Element technology B1 is a press-formed part in which a plurality of partial blanks made of steel plates are joined together, and at least two of the partial blanks are joined at a plurality of joint portions in an overlapping portion formed by partially overlapping, and in a cross section perpendicular to the surface of the partial blank including the center of the joint portion of the outermost partial blank, at a position 1 / 4 of the plate thickness from the surface of the partial blank that is in contact with other partial blanks, when the Vickers hardness at a position that is 15 mm or more away from the center of the joint portion and is not joined is Hvm, a portion of the plurality of joint portions has a Vickers hardness of ΔHv, which is the difference between the maximum hardness and the minimum hardness in a range of 5 mm toward the base material from the end of the joint portion, which is less than 0.2 Hvm, preferably 0.1 Hvm or less, and the other joint portions of the plurality of joint portions have a ΔHv of 0.2 Hvm or more.

[0065] According to element technology B1, a press-formed blank for press forming, which is formed by joining multiple partial blanks to form an integrated blank (TWB) having an overlapping portion in which at least two partial blanks are partially overlapped, can be press-formed (hot press-formed) in a way that suppresses cracking and other fractures.

[0066] This elemental technology will be explained using an automobile door ring as an example, which is one embodiment of this elemental technology (hereinafter simply referred to as "this elemental technology"). Figure 6 shows an external view of a single door ring 1 as an example of an automobile door ring. Even this door ring 1 alone is usually constructed by combining multiple types of steel plates. For example, the A-pillar 2 (also called the front pier) and B-pillar 3 (also called the center pillar) of the door link 1 may be constructed by combining a 2.0 GPa class high-strength steel plate at the top and a 1.3 GPa class high-strength steel plate at the bottom, which joins with the rocker 4, in order to ensure workability and toughness, from the viewpoint of securing interior space during a collision. When such parts are manufactured by press forming, a tailored blank (TWB) is manufactured by joining the partial blanks that will become the respective parts as press blank material, and this tailored blank is then press-formed to manufacture the parts that make up the door ring. The parts thus obtained are further welded to manufacture the door ring.

[0067] Figure 7 shows an overview of the manufacturing process for a typical TWB press-formed part (press-formed part).

[0068] Partial blanking process: This is the process of manufacturing partial blanks that will become parts of an integrated blank. Partial blanks are cut out from a specified steel plate (blanking), and then refined using laser trimming and other methods to produce the partial blanks.

[0069] Press blanking process: This process involves joining the obtained partial blanks to manufacture a press-formed blank (integrated blank). The method of joining the partial blanks is not particularly limited. For example, when butt welding partial blanks, laser welding or arc welding can be used. Also, when overlapping partial blanks, the overlapping portion can be joined by, for example, spot welding (resistance spot welding, laser spot welding, etc.), overlap welding (arc welding, laser welding), overlap fillet welding (arc welding, laser welding), brazing, friction stir welding (FSW), or friction pressure welding. A press-formed blank can be obtained by combining and joining predetermined partial blanks to form an integrated blank.

[0070] Hot press forming process: This is the process of hot press forming the obtained press-forming blank (integrated blank). By press forming the press-forming blank, a part or a part with a shape close to the part (near-net shape) can be obtained (the part obtained after the hot press process is called a press-formed product). The press forming method is not particularly limited, but when press forming a blank made of high-strength steel sheet (for example, a steel sheet with a high tensile strength of more than 590 MPa), hot press forming is preferable. Hot press forming is also called hot stamping (hot stamping method), and is a press forming method in which the blank (steel sheet) is heated to the austenite temperature range of approximately 900°C, and then pressed and rapidly cooled at the same time to perform quenching by martensitic transformation. Hot press forming has the characteristics that the press load can be reduced because it is formed at a high temperature, and because it undergoes martensitic transformation, it has the characteristics of being high strength after forming while having excellent shape retention. For these reasons, it is widely used for press forming of high-strength steel sheet.

[0071] Trimming process: This is a process for refining press-formed products (including those with a specific part shape and near-net-shape parts) that have been hot-press-formed. The method for refining the press-formed products is not particularly limited. For example, it may include processing (laser trimming) to remove burrs and other debris from the edges of the press-formed product to achieve a predetermined shape. In the case of near-net-shape press-formed products, it may also include processing to create the final part shape. If a press-formed product with the final shape can be obtained through hot-press forming, this trimming process can be omitted.

[0072] Post-pressing parts joining process: This is the process of joining other parts to the resulting press-formed product if further parts need to be attached. The method of joining the other parts is not particularly limited. For example, they may be joined by spot welding, arc welding, laser welding, brazing, etc. In addition, this process may be used to attach partial reinforcing materials to the press-formed product or to join parts that cannot be formed simultaneously during press forming. Of course, if there is no need to join other parts, this post-press part joining process can be omitted.

[0073] By going through these processes, the final target part (press-formed part) can be obtained. However, the manufacturing process for press-formed parts by TWB is not limited to the processes described above. Other necessary processes can be added.

[0074] Recently, there has been a demand for increased efficiency and lower costs in parts production, leading to a pursuit of larger parts and modules (parts made up of even smaller components combined together). For example, in the case of automotive door rings, instead of separately manufacturing and assembling the aforementioned A-pillars and B-pillars, there is a demand to manufacture the door ring as a single unit using press forming. Therefore, press forming blanks are needed for the single-unit press forming of door rings.

[0075] Figure 8 shows an example of a press-formed blank 30 for door ring 1 (Figure 8 is an example of a single door ring). The press-formed blank 31 in Figure 8 is constructed by joining together partial blanks corresponding to the upper A-pillar 31 (also called the upper A-pillar), lower A-pillar 32 (also called the lower A-pillar), upper B-pillar 33 (also called the upper B-pillar), lower B-pillar 34 (also called the lower B-pillar), and rocker 35. Each of the partial blanks may be made of the same type of steel or have different plate thicknesses. In the example shown in Figure 8, for example, the lower A-pillar 32 is made of 1.4 mm thick 1.5 GPa grade steel plate, the upper B-pillar 33 is made of 1.4 mm thick 2.0 GPa grade steel plate, the lower B-pillar 34 is made of 1.2 mm thick 1.0 GPa grade steel plate, the rocker 35 is made of 1.2 mm thick 1.5 GPa grade steel plate, and the upper A-pillar 31 is made of 1.4 mm thick 2.0 GGPa grade steel plate. These partial blanks are joined together to manufacture a press forming blank 30 (hereinafter sometimes referred to as an integrated blank).

[0076] In the example shown in Figure 8, for door ring 1, the lower A-pillar (A-pillar lower) 32 and rocker 35, the lower B-pillar (B-pillar lower) 34 and rocker 35, and the upper B-pillar (B-pillar upper) 33 and upper A-pillar (A-pillar upper) 31 are overlapped and joined together to manufacture door ring 1. Therefore, in order to manufacture such a door ring by press forming in one piece, a partial blank corresponding to the A-pillar lower 32 and a partial blank corresponding to the rocker 35 are overlapped to manufacture an integrated blank 30. Similarly, the partial blanks that make up the B-pillar lower 34 and rocker 35, and the B-pillar upper 33 and A-pillar upper 31 are overlapped to manufacture an integrated blank 30. Figure 8 shows an overview of the configuration of the partial blanks for press forming of this door ring. The overlapping parts of the partial blanks are hatched in Figure 8. The overlapping portion 36 of the A-pillar lower 32 and rocker 35 is L-shaped, the overlapping portion 37 of the B-pillar lower 34 and rocker 35 is T-shaped, and the overlapping portion 38 of the B-pillar upper 33 and A-pillar upper 31 is also T-shaped.

[0077] In the example shown in Figure 8, the overlapping section consists of two partial blanks, but the number of overlapping partial blanks is not limited. For example, three or more partial blanks may be overlapped. The number should be determined according to the required characteristics and shape of the final manufactured part.

[0078] As described above, parts whose shape when viewed from directly above is generally L-shaped are called L-shaped, and those that are generally T-shaped are called T-shaped. When the cross-sectional shape is a three-dimensional structure such as a hat shape, such as the overlapping section 36 of the A-pillar lower 32 and rocker 35, and when viewed from above it becomes a complex shape such as an L-shape or T-shape, the material flow behavior at the corner becomes complex. Therefore, cracks are likely to occur during press forming of the integrated blank.

[0079] [Overlapping section] When a single blank is manufactured by joining the entire overlapping section, fracture (cracks, breaks, etc.) may occur at the overlapping section after press forming. Observation of the fractured area revealed that fractures often occur where the thickness reduction due to press forming is significant. Therefore, we proceeded with an analysis of the cause of fracture, which led to this elemental technology.

[0080] The joining method for overlapping sections of partial blanks and for joining parts after pressing is not particularly limited. For example, resistance welding (resistance spot welding, projection welding, seam welding, etc.), arc welding (overlap arc welding, overlap fillet arc welding), laser welding (overlap laser welding, overlap fillet laser welding, laser spot welding), friction stir welding (FSW), friction welding, brazing, etc. can be applied. Furthermore, mechanical fastening methods can also be applied for joining parts after pressing. In the following explanation of this elemental technology, the case where spot welding (resistance spot welding) is applied as the joining method will be used as an example. This elemental technology is not limited to the form described below. In particular, the joining method is not limited to spot welding, and the various joining methods described above or similar joining methods can be applied, and by substituting spot welding with other joining methods in the explanation, the application of other joining methods can be understood.

[0081] The cause of fracture can be analyzed using simulation methods such as the Finite Element Method (FEM). The inventors performed an analysis using FEM. Figure 9 shows the analysis results for the L-shaped overlapping section 36 of the A-pillar lower 32 and the rocker 35. Figure 9(a) shows the stress state of the A-pillar lower 32 as viewed from the outside, and Figure 9(b) shows the stress state of the rocker 35 as viewed from the inside, as shown in the contour plot. The area where the fracture actually occurred is enclosed by an ellipse and corresponds to the darker area in the contour plot. Comparing these, it was confirmed that the fracture actually occurred in the area where the simulation indicated high shear stress and a fracture state.

[0082] From these analysis results, it was found that the factors contributing to fracture were (i) the significant difference in material inflow behavior of the partial blank when the overlapping section deforms, and (ii) the restriction of material inflow behavior due to spot welding. Here, material inflow refers to the deformation (movement) of the material due to press forming, and material inflow behavior refers to the deformation behavior of the material at a specific location, specifically how far and in which direction it deforms (moves) before and after press forming.

[0083] When the difference in material flow between partial blanks becomes large (factor (i)), shear deformation occurs in the spot weld, and it is thought that a large concentration of deformation occurs near the spot weld. When material flow is restricted there (factor (ii)), deformations involving material flow, such as elongation flange deformation, do not occur. As a result, deformation becomes more likely to concentrate, and fracture is thought to occur.

[0084] Therefore, in order to prevent fracture of the integrated blank during press forming, the inventors focused on the material inflow behavior of partial blanks during hot press forming. Specifically, they first understood the material inflow behavior of each partial blank constituting the overlapping section through simulation, and divided the partial blanks into areas with small material inflow differences and areas with large material inflow differences. They then conceived that fracture during press forming could be prevented by spot welding the partial blanks only in the areas with small material inflow differences, and leaving the other areas unspot-welded, and proceeded with development based on this idea.

[0085] As a result, it was confirmed that even in areas with large differences in material inflow between partial blanks, such as areas where the flange stretches and deforms, no fracture occurred and hot press forming was performed without spot welding. In other words, even if the aforementioned factor (i) that the material inflow behavior of partial blanks differs significantly when the overlapping section deforms remains, it was confirmed that fracture can be suppressed by removing factor (ii) that restricts the material inflow behavior due to spot welding.

[0086] The difference in material flow rate between each section blank is the absolute value of the difference in movement vectors obtained as a result of press forming, where each point (position) corresponding to an arbitrary point (position) in the overlapping section before forming moves within the section blanks constituting the overlapping section. In other words, the movement vector of each point (position) in each section blank corresponding to an arbitrary point (position) in the overlapping section is determined from the point (position) after press forming, and the absolute value of the difference in movement vectors between the points (positions) of each section blank (the distance between the points (positions) after each movement) is determined as the difference in material flow rate (amount of displacement) at that point (any point in the overlapping section).

[0087] Let's look at a concrete example of a simulation. As mentioned earlier, we will use spot welding as an example, but other joining methods can be applied in a similar manner. For example, when press-forming the overlapping portion, assume that the partial blank is fixed (meaning it is joined by spot welding, etc.) at at least one point on the top surface (the part held down by the pad or die) (for example, the center of gravity of the overlapping portion or the center of gravity of the top surface) and perform a press-forming (hot press-forming) analysis (simulation analysis using FEM, etc.) of the integrated blank. In this analysis, the movement vector of each point is determined from the position of each point of the partial blank corresponding to an arbitrary point of the overlapping portion before and after the movement. The absolute value of the difference in the movement vectors of the corresponding points for each partial blank is obtained as the material inflow difference (slip amount) at that point. If the obtained material inflow difference (slip amount) is smaller than a predetermined limit value (as described later, for example, 1 mm, preferably 0.5 mm), then the material inflow difference is small and it can be used as a point (position) to spot-weld before press-forming. On the other hand, if the calculated difference in material inflow (deviation) is greater than a predetermined limit value, then because the difference in material inflow is large, spot welding should be done after press forming rather than before press forming.

[0088] The inventors investigated the relationship between the difference in material flow rate (slip amount) in a joint formed by hot pressing and the tensile shear strength (TSS) at room temperature. They found that if the difference in material flow rate (slip amount) in hot pressing is 0 to 1 mm (greater than 0 mm and 1 mm or less), the tensile shear strength (TSS) at room temperature becomes equal to or greater than the original TSS (TSS when the slip amount is 0 mm). Although the technical reason for this phenomenon has not been elucidated, it is speculated that when the slip amount is small (1 mm or less), a synergistic effect is obtained between the processing strain introduced by hot pressing and the hardening due to quenching.

[0089] Let's explain with a specific example of a test. A joint (test specimen) made by spot-welding two 1.5 GPa grade steel plates (1.2 mm thick) was heated to 900°C and held for 1 minute. Then, at 740°C, the steel plates were stretched to shift by a predetermined length (amount of displacement), and the specimen was then quenched. After that, the specimen was stretched at 1 mm / s at room temperature, and the amount of displacement between the two steel plates and the tensile shear strength (TSS) of the joint (spot-welded area) at room temperature were observed. As a result, if the amount of displacement of the steel plates while hot was between 0 and 1.0 mm, the TSS of the joint at room temperature was equivalent to or higher than that of a joint with a displacement of 0 mm (i.e., no hot deformation). On the other hand, when the amount of displacement exceeded 1.0 mm, the TSS tended to decrease. Specifically, under these test conditions, it was confirmed that the TSS was 102% of the TSS when the displacement was 0mm at 0.1mm, 105% at 0.3mm, 107% at 0.5mm, 102% at 0.7mm, 100% at 1.0mm, 90% at 1.2mm, 86% at 1.5mm, and 71% at 2.0mm. In other words, it was discovered for the first time that even in hot press forming (hot stamping), it is possible to guarantee tensile shear strength equivalent to or greater than that when no deformation occurs, even if a difference in material flow rate (displacement) of 0.0mm to 1.0mm occurs at the spot welding point.

[0090] Based on this new finding, when hot press forming an integrated blank by stacking partial blanks, it is advisable to set the limit value of the material flow rate difference (slippage) to 1.0 mm, preferably pre-set to 0.9 mm, 0.8 mm, 0.7 mm, 0.6 mm, or 0.5 mm.

[0091] There is no particular limitation on the points (locations) where the material flow rate difference is calculated. For example, the material flow rate difference at the points (locations) set as the final spot welding locations may be analyzed. Alternatively, for example, the analysis mesh may be made finer to find the region where the material flow rate difference is below a limit value. In this case, it is advisable to set the pre-press forming spot welding points (locations) within the region where the material flow rate difference is analyzed to be small.

[0092] Figure 10(a) shows an example of the spot welding locations (indicated by black circles (●) in the figure) of the overlapping portion 36 of the A-pillar lower 32 and rocker 35. When spot welding was performed at all welding points before press forming, stress concentration was observed at the actual fracture locations (areas enclosed by ellipses in Figures 9(a) and 9(b)), as shown in Figures 9(a) and 9(b).

[0093] Next, assuming that spot welding was performed only at the double-circled point (the point with a black circle inside a white circle) near the center of the overlapping section 36 shown in Figure 10(a), and that no spot welding was performed at all other welding locations (points indicated only by black circles (●)), press forming was simulated using FEM to determine the material inflow rate (movement vector) of the A-pillar lower 32 and rocker 35. Furthermore, the material inflow rate (movement vector) at the corresponding point of the partial blank constituting the overlapping section 36 was also determined for each node of the FEM, and the difference in material inflow rate (movement vector) of each partial blank (material inflow rate difference) was determined. The absolute limit of the difference in material inflow rate at the corresponding node (sometimes simply called the limit of the material inflow rate difference) was set to 1.0 mm as described above, and parts with a material inflow rate difference exceeding this were considered to be parts with a risk of fracture. As a result, the part 40 enclosed by a solid line in Figure 10(b) is the part 40 that was determined to have a risk of fracture when spot welding is performed and press forming is carried out.

[0094] When the difference in material inflow is small, there are no particular restrictions on the method for determining the region. As mentioned above, it is advisable to determine it based on analysis using simulations such as FEM, or based on actual values ​​from prior offline tests or actual press operations.

[0095] In addition to evaluating the difference in material inflow, the rate of plate thickness reduction may also be evaluated. For example, in the case of FEM simulation, the rate of plate thickness reduction for each element may be determined and added to the difference in material inflow mentioned above. This is because areas with a large rate of plate thickness reduction tend to concentrate deformation more easily in the spot weld area, thus increasing the risk of fracture. In this case, it is good to determine a limit value using the rate of plate thickness reduction. The limit value is set as an absolute value because there are cases where the plate thickness increases (for example, when wrinkles occur), in which case the rate of plate thickness reduction is expressed as a negative value. It is good to set the limit value of the absolute value of the rate of plate thickness reduction at 10%, and areas with a rate of plate thickness reduction above this should be considered areas with a high risk of fracture. Preferably, the limit value of the rate of plate thickness reduction should be 9%, 8%, 7%, 6%, or 5%. The rate of plate thickness reduction is a relatively easy indicator to grasp because it can be directly determined using FEM analysis, etc.

[0096] In Figure 10(b), the area enclosed by the solid line indicates the area 40 with a risk of fracture. Conversely, the area enclosed by the thick dotted line indicates the area 41 with a low risk of fracture. In this press forming process, spot welding was performed only at the spot welding points in the area 41 with a low risk of fracture (the area where the plate thickness reduction rate is below the limit value), thereby manufacturing an integrated blank. Needless to say, spot welding was not performed at the welding points in the other areas (the area 40 with a risk of fracture, enclosed by the solid line in Figure 10(b)).

[0097] Similarly, the overlapping portion 37 of the lower B pillar 34 and the rocker 35, and the overlapping portion 38 of the upper B pillar 33 and the upper A pillar 31 were determined to determine which parts would be spot-welded and which parts would not be spot-welded, and a press-formed blank 30 was manufactured. Figure 11 is a conceptual diagram showing the spot welding positions at the overlapping portions 36 and 37 of the lower A pillar 34 and the lower B pillar 34 and the rocker 35, as determined by simulation analysis. Figure 11(a) shows the spot welding positions at the overlapping portion 36 (L-shaped) of the lower A pillar 32 and the rocker 35, and the overlapping portion 37 (T-shaped) of the lower B pillar 34 and the rocker 35, as viewed from the outside of the rocker 35. Figure 11(b) shows the same object viewed from the inside, showing the spot welding positions at the overlapping portions 36 and 37 of the rocker 35. The individual blank sections were joined together to form a single, integrated blank, which was then hot-pressed to manufacture the press-formed part that would become the door ring.

[0098] Figure 12 schematically shows the stress state of the integrated blank 30 shown in Figure 11 after hot pressing, obtained by FEM simulation. Figure 12(a) shows the stress state at the overlapping portion 36 (L-shaped) of the A-pillar lower 32 and the overlapping portion 37 (T-shaped) of the B-pillar lower 34, as viewed from the outside. In Figure 12(a), the thick dotted line indicates the portion 41 with a low risk of fracture, and spot welding is performed only in this portion. Figure 12(b) shows the same object as viewed from the inside, showing the stress state at the overlapping portions 36 and 37 of the rocker 35. No fracture was observed in either overlapping portion of the actual integrated blank after hot press forming, i.e., in the press-formed part that becomes the door ring.

[0099] As an example of joining other than spot welding, Figure 16 shows an example of overlap laser welding. In the example in Figure 16, overlap laser welding was used instead of spot welding in Figure 11 when manufacturing the same integrated blank as in Figure 11. Similar to Figure 11, Figure 16(a) shows the welding positions (position of the weld line 42 of the overlap welding) at the overlapping portion 36 (L-shaped) of the A-pillar lower 32 and the rocker 35 and the overlapping portion 37 (T-shaped) of the B-pillar lower 34 and the rocker 35, when viewed from the outside of the rocker 35. In Figure 16(a), the thick dotted line indicates the portion 41 with a low risk of fracture, and overlap welding is performed only in this portion. Figure 16(b) shows the same object when viewed from the inside, showing the welding positions (position of the weld line 42) at the overlapping portions 36 and 37 of the rocker 35. The integrated blank, with each section blank joined in this way, was hot-pressed to manufacture a press-formed part that would become a door ring. In this case as well, the integrated blank is manufactured by overlap laser welding only in the parts 41 with a low risk of fracture, but the method of drawing the weld line 42 for the overlap welding is not particularly limited. Similar to determining the welding point for spot welding, the joint may be made at the end, the center, or both of the overlapping parts of the partial blanks. Figure 16 shows the stress state after hot pressing of the integrated blank 30 manufactured in this manner, as shown in the contour plot. A stress state almost equivalent to that obtained when the integrated blank was manufactured by spot welding (Figure 12) was obtained, and no fracture was observed in the overlapping parts of the partial blanks.

[0100] In summary, it is preferable to determine the material inflow rate (movement vector) of each blank portion in the overlapping section formed by press forming in advance, and to join the blank portions constituting the overlapping section only in the portion where the absolute value of the difference in material inflow rate at corresponding positions of each blank portion (the absolute value of the difference in movement vectors) is smaller than a predetermined limit value. The method for determining the difference in material inflow rate of the blank portions by simulation in advance is not particularly limited. For example, the deformation behavior of the material may be determined by FEM, or it may be determined by performing press forming tests on test pieces that simulate the actual overlapping section. Furthermore, for example, the rate of reduction in plate thickness before and after pressing at a specific position of the blank portion may be taken into further consideration during evaluation.

[0101] Whether the difference in material inflow is large can be evaluated using a predetermined limit value. There are no particular restrictions on how to set the predetermined limit value. It is advisable to set it based on prior analysis using simulations such as FEM or based on actual values. When evaluating using the plate thickness reduction rate, it is advisable to determine the limit value using the absolute value of the plate thickness reduction rate of the overlapping blank portion. The limit value is an absolute value because the plate thickness may increase (for example, when wrinkles occur).

[0102] In particular, as explained above, L-shaped sections such as the overlapping portion 36 of the A-pillar lower 32 and rocker 35, and T-shaped sections such as the overlapping portion 37 of the B-pillar lower 34 and rocker 35, are parts that undergo complex deformation (complex material inflow behavior), so the effect of applying this elemental technology is remarkable.

[0103] [Joining process in the post-press parts joining process] In integrated blanks, areas where the overlapping sections are not joined (e.g., by spot welding) remain unjoined even after press forming. This can result in insufficient strength and rigidity, potentially preventing the desired performance from being achieved. Therefore, it is advisable to join (e.g., by spot welding) the areas of the overlapping sections that were not joined during the press forming blank processing stage after press forming (after the pressing process).

[0104] Generally, after press-forming an integrated blank to obtain a press-formed product, additional parts are often joined to the press-formed product (post-press part joining process). Therefore, it is desirable that the post-press part joining process include a step to join (spot welding, etc.) the unjoined parts of the overlapping section (spot welding in the above example). This is because it can be efficiently achieved without adding new steps by joining the unjoined parts of the overlapping section as an extension of the conventional post-press part joining process. A press-formed product can be obtained by going through these steps.

[0105] Based on the above explanation, Figure 13 shows an overview of the manufacturing process for press-formed parts using TWB related to this elemental technology. Compared to the conventional manufacturing process (Figure 7), it differs in the following points: In the press blanking process, the material inflow behavior of the overlapping portion blank is analyzed in advance, and the portion exceeding a predetermined limit value is determined to be a fracture risk area, and the joining is performed only on the portion of the overlapping part that is outside the fracture risk area. Furthermore, the post-press part joining process includes a step to join the portion of the overlapping part that has not been joined (the remaining part).

[0106] [Press-formed parts] The part (press-formed part) obtained by the method described above is an integrated blank formed by joining multiple partial blanks made of steel plates, and is a press-formed part in which at least two partial blanks are partially overlapped in an overlapping section, and the partial blanks constituting the overlapping section are joined at multiple joints. Of the multiple joints in the overlapping section, some are applied before hot press forming, and the remaining ones (joints other than the partial ones) are applied after hot press forming. Therefore, in the case of joining by welding such as spot welding or overlap welding, or friction stir welding or friction pressure welding, the HAZ softened area that occurred before hot pressing is eliminated by the heat treatment in hot pressing. On the other hand, in the joints applied after hot press forming, such as welding or friction stir welding, the HAZ softened area remains because it has not been heat-treated by hot pressing. In other words, in the resulting part (press-formed part), the joints in the overlapping section have no HAZ softened area in some parts of the overlapping section, but have HAZ softened areas in other parts. Spot welding will be explained below as an example. In particular, the joining method is not limited to spot welding, as mentioned above.

[0107] HAZ softening refers to the phenomenon where the heat-affected zone (HAZ) in the base metal, located just outside the outer edge of the weld metal in spot welding nuggets or arc welding, becomes tempered and softer than the base metal. Similarly, in friction stir welding, friction pressure welding, and brazing, the softened area that forms in the heat-affected zone (HAZ) of the base metal just outside the outer edge of the joint is called HAZ softening. The following explanation will use spot welding as an example.

[0108] Figure 14 shows an example of the correspondence between the results of a cross-sectional investigation of a spot weld test specimen 90 and the hardness distribution of the spot weld 91 (near the spot weld point) and the base material 92 (corresponding to a partial blank). Unless otherwise specified, hardness refers to Vickers hardness. As can be seen in Figure 14, the spot weld, including the joint (nugget), has a hardness of about Hv500 because it is hardened (the hardness is almost the same within the spot weld point, so the hardness at the center of the spot weld point is considered representative). On the other hand, it can be seen that the hardness is softened to about Hv300 at a point about 1 mm away from the end (outer edge) of the spot weld nugget 93 (near the outer edge of the spot weld). This softened area is the HAZ softening area. Normally, the HAZ softening area occurs in a region within 5 mm of the end (outer edge) of the joint (nugget or weld metal).

[0109] Further away from the joint (nugget 93), the hardness converges to the hardness of the base material 92 (Figure 14 shows that it converges to a hardness of slightly less than Hv500). The hardness of the HAZ softened area relative to the center of the spot weld point 91 is, for example, 50 Hv or more less when the base material 92 is a 1.0 GPa grade steel plate, 100 Hv or more less when it is a 1.5 GPa grade steel plate, and 150 Hv or more less when it is a 2.0 GPa grade steel plate. Generally speaking, if we define Hvm as the hardness of the base material 92, that is, the hardness of the base material 92 in the area unaffected by spot welding, and define the maximum value and minimum value of the hardness measured within a radius of 12 mm from the center of the spot weld 91 (or within 5 mm outward (towards the base material) from the end of the joint as the minimum hardness, and define ΔHv as the difference between the maximum and minimum hardness, then if there is no HAZ softening, ΔHv should be less than 0.2 Hvm, preferably 0.1 Hvm or less. Conversely, if there is HAZ softening, ΔHv should be 0.2 Hvm or more, preferably 0.3 Hvm, 0.4 Hvm, or 0.5 Hvm or more.

[0110] The hardness distribution of the HAZ softened area can be determined by measuring the hardness (Vickers hardness) from the center of the spot weld outward along a straight line (hardness measurement line) parallel to the surface of the blank, at a position 1 / 4 of the thickness from the surface of the outermost blank that is in contact with other blanks, including the center of the joint (center of the spot weld) in the thickness direction cross-section of the outermost blank of the blanks. For example, it is good to measure the hardness distribution in the thickness direction cross-section of the outermost blank of the blanks that make up the overlapping section. First, as the base material hardness (hardness of the base material in a part unaffected by the spot weld), the hardness is measured at a position where there is no spot weld, at least 15 mm away from the center of the spot weld, and this hardness is defined as Hvm. Note that the outermost blank here refers to the blank on the upper surface side when the press-formed part is placed with the convex shape facing upward.

[0111] Next, the hardness of the spot weld can be determined by measuring the hardness from the outer edge of the spot weld point outwards, along the center line of the plate thickness of the partial blank, up to a range of 12 mm from the center of the spot weld point. In particular, for the range from 0.5 to 1 mm inside the outer edge of the spot weld point to 2 to 3 mm outside the outer edge, it is recommended to measure at a measurement interval (pitch) of 0.1 to 0.2 mm. This is because the minimum hardness of the HAZ softened area due to spot welding often exists within this range.

[0112] Spot welds without HAZ softening are performed before hot press forming. That is, they are spot welds in areas where the difference in material inflow between the partial blanks in the overlapping section is small. On the other hand, spot welds with HAZ softening are performed after hot press forming, and are spot welds in areas where the difference in material inflow between the partial blanks is large, such as areas where the flange undergoes stretch deformation due to press forming. In other words, in press-formed parts relating to this elemental technology, some of the multiple spot welds (at least one spot weld that was joined before hot press forming) have a ΔHv of less than 0.2Hvm. On the other hand, the other spot welds (spot welds other than the aforementioned some, at least one other spot weld that was joined after hot press forming) have HAZ softening and therefore have a ΔHv of 0.2Hvm or more.

[0113] Furthermore, as explained in the press forming method described above, the press-formed parts related to this elemental technology are press-formed parts that have been joined by spot welding or the like before press forming in the parts where the absolute value of the difference in material inflow between each part blank is smaller than a predetermined limit value, after the material inflow amount of each part blank has been determined in advance by press forming. In other words, some of the multiple spot welds described above (spot welds where △Hv is less than 0.2Hvm) are the parts that fall into this category, that is, the parts where the absolute value of the difference in material inflow is smaller than a predetermined limit value.

[0114] From the shape of the press-formed part, it is also possible to confirm whether spot welding was performed before press forming only in areas where the absolute value of the difference in material inflow between each blank is smaller than the limit value. For example, this can be done by performing a 3D shape measurement centered on the overlapping portion of the blanks in the press-formed part and obtaining shape data for that part. From the obtained 3D shape data, blank data for the overlapping portion before press forming can be created. For example, by using equipment such as AUTOFORM R.10 from AUTOFORM, data for the blanks to be used for press forming can be obtained from the shape data of the press-formed part. Using the obtained blank data, the difference in material inflow to each blank due to press forming can be analyzed by FEM or the like, as described in the manufacturing method of the press-formed part above. This makes it possible to determine whether spot welding without HAZ softening (spot welding performed before press forming) belongs to an area where the difference in material inflow due to press forming is smaller than the limit value. Similarly, it is possible to determine whether spot welding with HAZ softening (spot welding performed after press forming) belongs to an area where the difference in material inflow due to press forming is larger than the limit value.

[0115] The above explanation uses spot welding as an example. However, even with joining methods other than spot welding, such as arc welding and laser welding, where the base steel plate is heated and melted for joining, or friction stir welding, friction pressure welding, and brazing, where the base steel plate is heated but not melted, a HAZ (Heat-Aided Zone) softening occurs in the joined portion after hot press forming. For example, in the case of arc welding, a HAZ softening occurs in the base metal outside the outer edge of the weld metal. Similarly, in the case of friction stir welding, a HAZ softening occurs in the base metal outside the outer edge of the joined portion. Even with joining methods other than spot welding, as with spot welding, it is advisable to measure the Vickers hardness along a hardness measurement line located at a position 1 / 4 of the plate thickness from the surface of the partial blank that is in contact with other partial blanks, in a cross section perpendicular to the surface of the partial blank, including the center of the joined portion of the outermost partial blank.

[0116] For example, in the case of lap fillet welding or lap welding using arc welding or laser welding, it is advisable to define a hardness measurement line in a cross-section perpendicular to the weld line and measure the hardness distribution. In this case, the center of the joint should be the center of the hardness measurement line in the weld metal. In the case of friction stir welding, friction pressure welding, and brazing, it is advisable to measure the hardness distribution in the same way as in the case of spot welding.

[0117] The procedure for measuring the hardness distribution is the same as that for spot welding, so it is sufficient to follow that procedure. Specifically, in the blank portion to be measured, when the Vickers hardness at a position 15 mm or more away from the center of the joint (such as the weld metal) and not joined is taken as Hvm, the difference between the maximum and minimum Vickers hardness in the range within 5 mm outside the edge of the joint should be taken as ΔHv. In the joint portion (those that have been hot-pressed after joining), the HAZ softening has been eliminated, so ΔHv is less than 0.2 Hvm, preferably 0.1 Hvm or less, while in the other joint portion (joining portions other than the aforementioned portion, for example, those joined after hot pressing), the HAZ has softened, so ΔHv is 0.2 Hvm or more, preferably 0.3 Hvm, 0.4 Hvm, or 0.5 Hvm or more.

[0118] [Other examples] Figure 15 shows a schematic diagram of an embodiment applied to an automobile floor module 100. Conventionally, floor modules were manufactured by manufacturing parts separately and then overlapping and joining them (such as spot welding). However, by applying the blank manufacturing method related to this element technology, it was possible to manufacture an integrated blank (press-forming blank) for the front module 100 and then manufacture the floor module 100 by hot-pressing it all at once. At this time, the blank and blank manufacturing method related to this element technology were applied to the joining (such as spot welding) of the six overlapping sections 101. As a result, even when hot-pressed all at once, the floor module 100 could be obtained without any breakage at the overlapping sections 101.

[0119] As described above, the parts (press-formed parts) obtained by this elemental technology are free from cracks and have excellent impact resistance. Compared to conventional spot-welded assemblies, where all spot welding is performed either before or after hot press forming, the press-formed parts related to this elemental technology have the following advantages.

[0120] Compared to conventional parts where all spot welding is performed before hot press forming, press-formed parts using this elemental technology exhibit improved formability. As a result, the depth of the part can be increased, the angle of the vertical wall can be made steeper, and the full plastic bending moment of each cross-section can be increased. Furthermore, since excessive thickness reduction introduced at joints (such as spot welds) in areas with large material flow can be eliminated, it is possible to improve the collision resistance performance of the module.

[0121] Furthermore, press-formed parts related to this elemental technology eliminate HAZ softening, mainly in the top surface (for example, the top surface of a part with a hat-shaped cross-section), improving the bonding strength between components and thus improving the collision resistance performance of the module.

[0122] The above describes the press-formed blank, the method for manufacturing the press-formed blank, the press-formed part, and the method for manufacturing the press-formed part related to this elemental technology, using automobile door rings and floor modules as examples. The blanks, parts, and methods for manufacturing them related to this elemental technology are not limited to the embodiments used in the above description. This elemental technology can be applied to any TWB having an overlapping portion, without being limited by its type or structure.

[0123] (Element technology C1) Element technology C1 is a structural member comprising a first member and a second member, wherein one of the first member and the second member includes a member body including a curved portion that curves in a plan view of the structural member, and a flange provided continuously with the member body, wherein the flange is joined to the other of the first member and the second member to form a hollow cross section together with the other of the first member and the second member, and the rate of reduction in plate thickness in the curved portion of the member body, based on the plate thickness of the flange, is 30% or more.

[0124] According to elemental technology C1, it is possible to provide a structural member that is an integrated component having a hollow cross-section and can be molded with high productivity.

[0125] <First Embodiment> [Structural members] Figure 17A is a perspective view showing the schematic configuration of the structural member 10 according to this embodiment. Figure 17B is an exploded perspective view of the structural member 10. The structural member 10 is used, for example, in the body of an automobile. In this embodiment, the structural member 10 is a rear module for the vehicle body. In this case, the structural member 10 is provided at the rear and lower part of the body of an automobile or the like.

[0126] Referring to Figure 17A, the structural member 10 is a member having a hollow cross-section in at least a part of it. The structural member 10 comprises a first member 11 and a second member 12. The first member 11 and the second member 12 are each formed from one or more metal plates. For example, the first member 11 and the second member 12 are each formed from one or more steel plates. However, the first member 11 and the second member 12 may be formed from aluminum alloy plates or the like.

[0127] The first member 11 and the second member 12 are arranged vertically when the structural member 10 is assembled to the vehicle body. The first member 11 includes a member body 111 and a flange 112. The second member 12 includes a member body 121 and a flange 122.

[0128] As shown in Figure 17B, the member body 111 of the first member 11 has a convex shape on the opposite side of the second member 12. In this embodiment, the member body 111 includes a pair of side frames 111a and a cross member 111b. In the example in Figure 17B, the member body 111 includes one cross member 111b. However, the member body 111 may include multiple cross members 111b.

[0129] The side frames 111a and cross members 111b each have a hollow shape. In this embodiment, the side frames 111a and cross members 111b each have a hollow rectangular shape. Each side frame 111a extends in the longitudinal direction of the vehicle body when the structural member 10 is assembled to the vehicle body. The cross members 111b extend in the lateral direction of the vehicle body when the structural member 10 is assembled to the vehicle body. The cross members 111b extend from one side frame 111a to the other side frame 111a, connecting the side frames 111a together.

[0130] The member body 111 has at least one curved portion 111c. The curved portion 111c is the part of the member body 111 that is curved in a plan view of the structural member 10. More specifically, when the structural member 10 is viewed from the first member 11 side, the curved portion 111c curves inward as a concave or outward convex shape. In this embodiment, the curved portion 111c is provided at the connection point between each of the side frames 111a and the cross member 111b. That is, the curved portion 111c is the corner portion between each of the side frames 111a and the cross member 111b. When the structural member 10 is viewed from the first member 11 side, that is, in a top view of the first member 11, the curved portion 111c extends with a radius of curvature of, for example, 10 mm or more and 100 mm or less.

[0131] In the first member 11, the flange 112 is provided continuously with the member body 111. In this embodiment, the flange 112 is provided at the end of the member body 111 so as to surround the member body 111. The flange 112 is provided continuously with both the side frame 111a and the cross member 111b.

[0132] The first member 11 forms a hollow cross-section together with the second member 12 when the flange 112 is joined to the second member 12. In the present embodiment, a hollow space is formed between the member body 111 of the first member 11 and the member body 121 of the second member 12 by joining the flanges 112 and 122.

[0133] The member body 121 of the second member 12 has a convex shape on the opposite side of the first member 11. In the present embodiment, the member body 121 includes a pair of side frames 121a and a cross member 121b. In the example of the present embodiment, the member body 121 includes one cross member 121b. However, the member body 121 may include a plurality of cross members 121b.

[0134] The side frames 121a and the cross member 121b each have a hollow shape. In the example of the present embodiment, the side frames 121a and the cross member 121b each have a hollow rectangular shape. Each of the side frames 121a extends in the longitudinal direction of the vehicle body when the structural member 10 is assembled to the vehicle body. The cross member 121b extends in the lateral direction of the vehicle body when the structural member 10 is assembled to the vehicle body. The cross member 121b extends from one side frame 121a to the other side frame 121a and connects the side frames 121a to each other.

[0135] The side frame 121a of the second member 12 is arranged to face the side frame 111a of the first member 11. The side frames 111a and 121a have convex shapes on opposite sides of each other. In the present embodiment, the cross member 121b of the second member 12 is also arranged to face the cross member 111b of the first member 11. The cross members 111b and 121b have convex shapes on opposite sides of each other.

[0136] The member body 121 has at least one curved portion 121c. The curved portion 121c is a portion of the member body 121 that is curved in a plan view of the structural member 10. More specifically, when the structural member 10 is viewed from the second member 12 side, the curved portion 121c is curved concave inward or convex outward of the member body 121. In the example of the present embodiment, the curved portion 121c is provided at the connection portion between each of the side frames 121a and the cross member 121b. That is, the curved portion 121c is a corner portion between each of the side frames 121a and the cross member 121b. When the structural member 10 is viewed from the second member 12 side, that is, in a top view of the second member 12, the curved portion 121c extends with a radius of curvature of, for example, 10 mm or more and 100 mm or less.

[0137] In the second member 12, the flange 122 is provided continuously with the member body 121. In the present embodiment, the flange 122 is provided at the end of the member body 121 so as to surround the member body 121. The flange 122 is provided continuously with each of the side frames 121a and the cross member 12l b.

[0138] The flange 122 of the second member 12 is joined to the flange 112 of the first member 11. The flanges 112 and 122 are typically joined to each other by welding. It is preferable that the flanges 112 and 122 are intermittently joined by, for example, spot welding. However, the flanges 112 and 122 may be joined by continuous welding such as laser welding.

[0139] [Die] FIG. 18 is a perspective view showing a schematic configuration of a die 20 according to the present embodiment. The structural member 10 (FIGS. 17A and 17B) can be manufactured using the die 20.

[0140] Referring to Figure 18, the mold 20 comprises a first mold 21 and a second mold 22. The first mold 21 and the second mold 22 are a pair of molds. When the mold 20 is in use, the first mold 21 and the second mold 22 are mounted on a press or the like so that they can approach each other relatively. Hereinafter, the direction in which the first mold 21 and the second mold 22 approach each other will be referred to as the processing direction D. The processing direction D is, for example, the vertical direction.

[0141] The first mold 21 is a mold primarily for molding the first member 11 (Figures 17A and 17B). The first mold 21 includes a molding surface 211 and a flange surface 212. The molding surface 211 and the flange surface 212 are provided on the surface of the first mold 21 that faces the machining direction D relative to the second mold 22.

[0142] The molding surface 211 has a shape corresponding to the member body 111 of the first member 11 (Figures 17A and 17B). In this embodiment, the molding surface 211 includes a pair of side frame molding sections 211a and at least one cross member molding section 211b. The side frame molding section 211a is the portion of the molding surface 211 configured to mold the side frame 111a (Figure 17B). The cross member molding section 211b is the portion of the molding surface 211 configured to mold the cross member 111b (Figure 17B).

[0143] The flange surface 212 is positioned around the molding surface 211. The flange surface 212 is provided on the first mold 21 so as to surround the entire circumference of the molding surface 211 when viewed along the machining direction D.

[0144] At least one projection 213 is formed on the flange surface 212. The projection 213 protrudes from the flange surface 212 toward the second mold 22. In this embodiment, multiple projections 213 are formed on the flange surface 212. The projections 213 are located near the side frame molding portion 211a of the molding surface 211.

[0145] Each of the projections 213 has, for example, a circular shape when viewed along the machining direction D. However, when viewed along the machining direction D, the projections 213 may have a polygonal shape such as a triangular or quadrilateral shape. If the projections 213 have a shape other than circular, the projections 213 may be formed to be wider on the side closer to the molded surface 211.

[0146] Fluid is used in the manufacture of the structural member 10 (Figures 17A and 17B). Therefore, the first mold 21 further includes fluid channels 214. The fluid channels 214 are formed inside the first mold 21. The fluid channels 214 open into each of the protrusions 213. The fluid channels 214 are connected to a fluid supply source (not shown) provided outside the first mold 21. In the example of Figure 18, the first mold 21 is provided with multiple fluid channels 214 corresponding to multiple protrusions 213. Each fluid channel 214 can open into the side of the first mold 21. However, the multiple fluid channels 214 may be consolidated into a single system within the first mold 21 and then open into the back of the first mold 21, etc.

[0147] The second mold 22 is a mold primarily for molding the second member 12 (Figures 17A and 17B). In this embodiment, the second mold 22 is positioned above the first mold 21. The second mold 22 includes a molding surface 221 and a flange surface 222. The molding surface 221 and the flange surface 222 are provided on the surface of the second mold 22 that faces the processing direction D relative to the first mold 21.

[0148] The molding surface 221 has a shape corresponding to the member body 121 of the second member 12 (Figures 17A and 17B). That is, the molding surface 221 includes a pair of side frame molding sections 221a and at least one cross member molding section 221b. The side frame molding section 221a is the part of the molding surface 221 configured to mold the side frame 121a (Figure 17B). The cross member molding section 221b is the part of the molding surface 221 configured to mold the cross member 121b (Figure 17B).

[0149] The molding surface 221 of the second mold 22 forms a hollow space together with the molding surface 211 of the first mold 21. Therefore, when the mold 20 is in use, the molding surfaces 211 and 221 face the processing direction D. In addition, one or both of the molding surfaces 211 of the first mold 21 and the molding surface 221 of the second mold 22 have a concave shape in at least a part of them. In this embodiment, the molding surfaces 211 and 221 have a concave shape on opposite sides to each other. That is, in the first mold 21, the molding surface 211 is formed to be concave with respect to the flange surface 212. In the second mold 22, the molding surface 221 is formed to be concave with respect to the flange surface 222.

[0150] In the second mold 22, the flange surface 222 is positioned around the molding surface 221. The flange surface 222 is provided in the second mold 22 so as to surround the entire circumference of the molding surface 221 when viewed along the machining direction D.

[0151] In this embodiment, the mold 20 further includes convex sealing portions 23 and 24. The sealing portions 23 and 24 are provided on the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, respectively. While the first mold 21 and the second mold 22 are made of, for example, metal, the sealing portions 23 and 24 are made of, for example, an elastic material such as resin.

[0152] On the flange surface 212 of the first mold 21, the sealing portion 23 is provided so as to substantially surround the molding surface 211. In this embodiment, the sealing portion 23 also surrounds each projection 213. The sealing portion 23 may surround the molding surface 211 without interruption around its entire circumference, but for example, a portion of the sealing portion 23 may be interrupted at positions away from each projection 213. The sealing portion 23 may be interrupted in a range of, for example, 150 mm or less.

[0153] On the flange surface 212 of the first mold 21, the seal portion 24 is provided so as to substantially surround the seal portion 23. That is, the flange surface 212 is provided with a double layer of seal portions 23 and 24. The seal portion 24 may surround the seal portion 23 without interruption around its entire circumference, but for example, a portion of the seal portion 24 may be interrupted at positions away from each projection 213. The seal portion 24 may be interrupted in a range of, for example, 150 mm or less.

[0154] In the flange surface 222 of the second mold 22, the sealing portion 23 is provided so as to substantially surround the molding surface 221. The sealing portion 23 of the second mold 22 is provided so as to face the processing direction D relative to the sealing portion 23 of the first mold 21, and has a shape corresponding to the sealing portion 23 of the first mold 21. In the second mold 22 as well, the sealing portion 23 may surround the molding surface 221 without interruption around its entire circumference, or it may be interrupted in a range of, for example, 150 mm or less.

[0155] On the flange surface 222 of the second mold 22, the seal portion 24 is provided so as to substantially surround the seal portion 23. That is, the flange surface 222 is provided with a double layer of seal portions 23 and 24. The seal portion 24 of the second mold 22 is provided so as to face the processing direction D relative to the seal portion 24 of the first mold 21, and has a shape corresponding to the seal portion 24 of the first mold 21. In the second mold 22 as well, the seal portion 24 may surround the seal portion 23 without interruption around its entire circumference, or it may be interrupted in a range of, for example, 150 mm or less.

[0156] Figure 19 is a cross-sectional view of the mold 20 shown in Figure 18, taken along line III-III. Figure 19 shows one of the projections 213 provided on the first mold 21 of the mold 20, and its vicinity.

[0157] Referring to FIG. 19, the protrusion 213 includes a tip surface 213a and a side surface 213b. The tip surface 213a is the surface that is disposed farthest from the flange surface 212 among the protrusions 213. In the example of the present embodiment, the tip surface 213a is a flat surface that is substantially perpendicular to the processing direction D.

[0158] The side surface 213b connects the tip surface 213a to the flange surface 212. In the present embodiment, when viewed in a cross-section including the central axis of the protrusion 213, the side surface 213b is inclined with respect to the processing direction D such that the width of the protrusion 213 is larger on the base end side and smaller on the tip end side.

[0159] FIG. 20 is a diagram showing another example of the protrusion 213. In the example of FIG. 19, the side surface 213b of the protrusion 213 is an inclined surface that is inclined as a whole with respect to the processing direction D. However, in the example of FIG. 20, a step is provided on the side surface 213b at the base end side of the protrusion 213. That is, when viewed in a cross-section including the central axis of the protrusion 213, a portion 213c of the side surface 213b adjacent to the flange surface 212 is substantially parallel to the processing direction D. Therefore, in the portion 213c of the side surface 213b adjacent to the flange surface 212, the width of the protrusion 213 is substantially constant. The other portions of the side surface 213b may be inclined with respect to the processing direction D as in FIG. 19.

[0160] The flow path 214 can open at a portion of the side surface 213b of the protrusion 213 on the side of the molding surface 211. The flow path 214 preferably opens at a position closer to the tip of the protrusion 213 than the flange surface 212 in the protrusion 213. In the examples of FIGS. 19 and 20, the portion of the flow path 214 passing through the protrusion 213 is substantially parallel to the processing direction D. However, at least the portion of the flow path 214 passing through the protrusion 213 may be inclined with respect to the processing direction D. The flow path 214 can be inclined with respect to the processing direction D so as to intersect the side surface 213b of the protrusion 213 when viewed in a cross-section including the central axis of the protrusion 213. At least the portion of the flow path 214 passing through the protrusion 213 may be inclined at an angle greater than 0° and less than or equal to 60° with respect to the processing direction D when viewed in a cross-section including the central axis of the protrusion 213.

[0161] Near the projection 213, a relief portion 222a is formed on the flange surface 222 of the second mold 22. Viewed in a cross-section including the central axis of the projection 213, the relief portion 222a extends from the portion of the flange surface 222 facing the tip surface 213a of the projection 213 to the molding surface 221. The relief portion 222a has a concave shape relative to the rest of the flange surface 222.

[0162] The sealing portions 23 and 24 of the first mold 21 and the second mold 22 preferably have a shape that allows surface contact with the mating mold or its sealing portions 23 and 24. As shown in Figures 19 and 20, each of the sealing portions 23 and 24 may have, for example, a substantially rectangular cross-section. The width W of each of the sealing portions 23 and 24 may be 1.0 mm or more, and preferably 2.0 mm or more. The width W is preferably 5.0 mm or less, and more preferably 3.0 mm or less. The height H of each of the sealing portions 23 and 24 is, for example, 0.2 mm or more. The height H may be 0.5 mm or less.

[0163] [Method for manufacturing structural members] Next, a method for manufacturing the structural member 10 using the mold 20 will be described with reference to Figures 21A to 21E. The method for manufacturing the structural member 10 according to this embodiment comprises a preparation step and a molding step. The manufacturing method may further include a heating step.

[0164] (preparation process) As shown in Figures 21A and 21B, the preparation step involves preparing the material 30. The material 30 includes a first blank 31 and a second blank 32.

[0165] Referring to Figures 21A and 21B, the first blank 31 is a blank corresponding to the first member 11 (Figures 17A and 17B). The first blank 31 has at least one through hole 311. The through hole 311 is provided corresponding to the projection 213 (Figure 18) of the first mold 21. In this embodiment, since the first mold 21 is provided with multiple projections 213, the first blank 31 is also provided with multiple through holes 311 corresponding to these projections.

[0166] The second blank 32 is a blank corresponding to the second member 12 (Figures 17A and 17B). The second blank 32 is superimposed on the first blank 31 and joined together. The second blank 32 is superimposed on the first blank 31 so as to close each through hole 311.

[0167] The first blank 31 and the second blank 32 are joined at the portions corresponding to the flanges 112 and 122 of the structural member 10 (Figures 17A and 17B). The first blank 31 and the second blank 32 are typically joined by welding. Preferably, the outer peripheries of the first blank 31 and the second blank 32 are joined by intermittent welding, such as spot welding. That is, the outer peripheries may be joined substantially over the entire circumference by continuous welding, such as laser welding. However, no welds are provided in the portions of the first blank 31 and the second blank 32 that correspond to the relief portion 222a (Figure 19) of the second mold 22.

[0168] The first blank 31 and the second blank 32 may each be formed from a single metal sheet, or they may each include multiple metal sheets (subblanks). The metal sheet is, for example, a steel sheet. However, the metal sheet may also be, for example, an aluminum alloy sheet.

[0169] If multiple metal plates are present in the first blank 31 and / or the second blank 32, these metal plates may differ in at least one of their tensile strength and thickness. If the first blank 31 contains multiple metal plates, the metal plates are typically joined to each other by welding. Similarly, if the second blank 32 contains multiple metal plates, the metal plates are typically joined to each other by welding. The metal plates are joined, for example, by spot welding or laser welding. In each of the first blank 31 and the second blank 32, adjacent metal plates may be joined with their ends butted together or with their ends overlapping.

[0170] (Heating process) The heating process is carried out before the forming process. In the heating process, the prepared material 30 is heated. The material 30 is heated, for example, in a heating furnace. The heating temperature of the material 30 is determined according to the material of the first blank 31 and the second blank 32. If the first blank 31 and the second blank 32 are made of steel, the material 30 is heated to the austenite transformation completion temperature (A) of the first blank 31 and the second blank 32. c3 It is preferable to heat the material to a temperature of 900°C or higher. If the first blank 31 and the second blank 32 are made of steel, the material 30 is heated to, for example, 900°C or higher. However, the heating step is not necessarily required.

[0171] (molding process) In the molding process, the material 30 is molded using the first mold 21 and the second mold 22. If a heating process is performed, the heated material 30 is molded using the first mold 21 and the second mold 22 in the molding process.

[0172] Referring to Figure 21C, in the molding process, first, with the first mold 21 and the second mold 22 separated in the processing direction D, the material 30 is placed between the first mold 21 and the second mold 22. At this time, the material 30 is positioned so that each through hole 311 of the first blank 31 corresponds to the projection 213 of the first mold 21. In this embodiment, since the first mold 21 is positioned below the second mold 22, the material 30 is placed on top of the first mold 21.

[0173] Referring to Figure 21D, the first mold 21 and the second mold 22 are then brought relatively close together and closed. Specifically, with the projections 213 of the first mold 21 inserted into each through hole 311 of the first blank 31, the material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, and the projections 213 create a gap between the first blank 31 and the second blank 32. The projections 213 are inserted into the through holes 311 of the first blank 31 and lift the second blank 32 from the inside of the material 30, thus creating a gap between the first blank 31 and the second blank 32.

[0174] In this embodiment, since the tip surface 213a of the projection 213 is substantially flat, the projection 213 can make surface contact with the second blank 32 at its tip surface 213a. When the first mold 21 and the second mold 22 are closed, the material 30 is first sandwiched between the tip surface 213a of the projection 213 and the relief portion 222a of the flange surface 222 of the second mold 22. This allows the material 30 to be positioned.

[0175] When the first mold 21 and the second mold 22 are closed, the material 30 is held between the sealing portion 23 of the first mold 21 and the sealing portion 23 of the second mold. Also, when the first mold 21 and the second mold 22 are closed, the material 30 is held between the sealing portion 24 (Figure 18) of the first mold 21 and the sealing portion 24 (Figure 18) of the second mold. At the positions of the sealing portions 23 and 24, the material 30 is held more strongly than at other parts of the flange surfaces 212 and 222.

[0176] Referring to Figure 21E, after the material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, fluid is injected from the projection 213 into the gap between the first blank 31 and the second blank 32. The fluid is supplied from a fluid supply source (not shown) to the flow path 214, passes through the flow path 214, and flows out from the projection 213. This fluid causes the material 30 to expand in the hollow space formed between the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22.

[0177] Within the hollow space of the mold 20, the first blank 31 of the material 30 is expanded by the fluid and then pressed against the molding surface 211 of the first mold 21. The second blank 32 of the material 30 is expanded by the fluid and then pressed against the molding surface 221 of the second mold 22. This forms a hollow cross-section in the material 30. More specifically, a structural member 10 (Figures 17A and 17B) having hollow member bodies 111 and 121 is formed.

[0178] The fluid used for molding material 30 is not particularly limited. The fluid may be a liquid such as water, or a gas such as nitrogen gas or compressed air. The fluid may be a liquid or gas under high pressure, for example, 10 MPa or more. The temperature of the fluid may be appropriately determined according to the material of material 30, and may be, for example, room temperature. If a heating process is performed, i.e., when molding is performed by hot stamping, the fluid may be heated.

[0179] If a heating process is performed before the molding process, the first blank 31 and the second blank 32 are cooled and hardened by contact with the first mold 21 and the second mold 22, respectively.

[0180] Through such a molding process, the structural member 10 (Figures 17A and 17B) can be obtained. After the molding process, the outer periphery of the structural member 10 may be removed by laser cutting or the like. At least the portion of the structural member 10 in which the through hole 311 (Figure 21E) is provided is usually removed after the molding process.

[0181] Figure 22 is a partial cross-sectional view of the structural member 10 after the molding process. Figure 22 shows the cross-section (transverse plane) when the structural member 10 is cut along the thickness direction of the first member 11 and the second member 12 at the curved portions 111c and 121c (Figure 17B) of the member bodies 111 and 121. The transverse plane of the structural member 10 in Figure 22 also includes the welded portion 13 that joins the flange 112 of the first member 11 and the flange 122 of the second member 12. Preferably, the welded portion 13 is formed such that its welding center is located on the side of the first member 11 or the second member 12 side relative to the overlapping surface of the flanges 112 and 122.

[0182] In this embodiment, the member body 111 of the first member 11 includes a top plate 113 and a vertical wall 114. The vertical wall 114 connects the top plate 113 and the flange 112. At the position of the curved portion 111c (Figure 17B), the vertical wall 114 is curved inward in a concave shape in a plan view of the structural member 10.

[0183] The main body 121 of the second member 12 also includes a top plate 123 and a vertical wall 124. The top plate 123 is positioned opposite the top plate 113 of the first member 11. The vertical wall 124 connects the top plate 123 to the flange 122. At the position of the curved portion 121c (Figure 17B), the vertical wall 124 is curved inward in a concave shape towards the main body 121 of the structural member 10 in a plan view.

[0184] When the plate thickness reduction rate T1 is taken as the curved portion 111c (Figure 17B) of the member body 111, the plate thickness reduction rate T1 is 30% or more. The plate thickness reduction rate T1 depends on the material or molding height of the member body 111, but for example it is 50% or less, and preferably less than 45%. The plate thickness reduction rate T1 is the plate thickness reduction rate based on the plate thickness of the flange 112. That is, when the plate thickness of the flange 112 is t0 and the plate thickness at the curved portion 111c of the member body 111 is t, the plate thickness reduction rate T1[%] can be obtained by (t0-t) / t0×100. The plate thickness t0 is, for example, the plate thickness of the flange 112 measured at a position 2.0 mm or more away from the welded portion 13 on the free end side of the flange 112. The plate thickness t0 is substantially equal to the plate thickness of the first blank 31 before molding. The plate thickness t is, for example, the minimum value of the plate thickness measured at five or more points at 1 mm intervals in the cross-section of the structural member 10 when it is cut at the bottom of the curve of the curved portion 111c, specifically at the corner portion between the flange 112 and the vertical wall 114, and at the portion of the vertical wall 114 adjacent to the said corner portion.

[0185] When the plate thickness reduction rate T2 is taken as the curved portion 121c (Figure 17B) of the member body 121, the plate thickness reduction rate T2 is 30% or more. The plate thickness reduction rate T2 depends on the material or molding height of the member body 121, but is, for example, 50% or less, and preferably less than 45%. The plate thickness reduction rate T2 is the plate thickness reduction rate based on the plate thickness of the flange 122. The plate thickness reduction rate T2 can be obtained by the same measurement and calculation method as the plate thickness reduction rate T1. That is, when the plate thickness of the flange 122 is t0 and the plate thickness at the curved portion 121c of the member body 121 is t, the plate thickness reduction rate T2[%] can be obtained by (t0-t) / t0×100. The plate thickness t0 is, for example, the plate thickness of the flange 122 measured at a position 2.0 mm or more away from the welded portion 13 towards the free end side of the flange 122. The plate thickness t0 is substantially equal to the plate thickness of the second blank 32 before forming. The plate thickness t is, for example, the minimum value of the plate thickness measured at 1 mm intervals at five or more points in the cross-section of the structural member 10 when it is cut at the bottom of the curve of the curved portion 121c, at the corner portion between the flange 122 and the vertical wall 124, and at the portion of the vertical wall 124 adjacent to the said corner portion.

[0186] When a heating process is performed during the manufacturing of the structural member 10, the softening of the heat-affected zone (HAZ softening) is reduced in the weld 13 formed when the first blank 31 and the second blank 32 are joined. Specifically, in the cross-section of the structural member 10 including the weld center of the weld 13, the minimum value of the Vickers hardness of the heat-affected zone of the weld 13 is 70% or more of the Vickers hardness of the unwelded parts of the first member 11 and the second member 12. Preferably, in the said cross-section, it is 80% or more of the Vickers hardness of the first member 11 and the second member 12, and more preferably 90% or more. In each of the first member 11 and the second member 12, the minimum value of the Vickers hardness of the heat-affected zone is less than or equal to the Vickers hardness of the unwelded part.

[0187] Vickers hardness can be measured by the Vickers hardness test specified in JIS Z 2244-1:2020. Specifically, first, a test piece containing the first member 11, the second member 12, and the weld 13 is obtained from the structural member 10 by laser cutting or the like, at a position passing through the weld center of the weld 13. Then, the test piece is embedded in resin so that the cross section passing through the weld center of the weld 13 is positioned on the surface, and the cross section is polished. Subsequently, for each of the first member 11 and the second member 12, the Vickers hardness is measured in accordance with JIS Z 2244-1:2020, for example, with a test force of 0.49 N and a measurement interval (pitch) of 0.1 to 0.2 mm, at a position 1 / 4 of the plate thickness from the surface on the weld center side of the weld 13, up to a position 12.0 mm outward from the weld center. The minimum value of the measured Vickers hardness is taken as the minimum Vickers hardness of the heat-affected zone of the weld 13. Furthermore, for each of the first member 11 and the second member 12, the Vickers hardness is measured in accordance with JIS Z 2244-1:2020, for example, with a test force of 0.49 N, at a position at least 15.0 mm away from the welding center of the welded joint 13 and at a position half the thickness of the plate from the surface on the welding center side of the welded joint 13. This Vickers hardness is taken as the Vickers hardness of the non-welded parts of the first member 11 and the second member 12.

[0188] [effect] In this embodiment, a first mold 21 and a second mold 22 are used to manufacture a structural member 10 from a material 30 including a first blank 31 and a second blank 32. At least one projection 213 is formed on the flange surface 212 of the first mold 21. In this case, when the projection 213 is inserted into the through hole 311 of the first blank 31 and the material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, the projection 213 lifts the second blank 32 towards the second mold 22. As a result, a gap is created between the first blank 31 and the second blank 32. By injecting fluid from the projection 213 into this gap through the flow path 214 of the first mold 21, the material 30 can be expanded and molded into the shape of the molded surfaces 211 and 221.

[0189] In other words, in this embodiment, a fluid passage is formed simply by closing the first mold 21 and the second mold 22, so there is no need to separately perform preforming to secure the fluid passage. Therefore, using the first blank 31 and the second blank 32 which are joined together, a structural member 10 in which the first member 11 and the second member 12 are integrated can be molded with high productivity.

[0190] In this embodiment, the clamping force between the first mold 21 and the second mold 22 seals the outer periphery of the overlapping first blank 31 and second blank 32. Therefore, the outer periphery of the first blank 31 and second blank 32 does not need to be laser-welded all around, as in conventional hydroforming technology for sheet metal. The first blank 31 and second blank 32 can be joined at multiple points, for example, by spot welding. In this case, the man-hours and costs required to manufacture the structural member 10 can be reduced compared to when all-around laser welding is performed. Therefore, the structural member 10 having a hollow cross-section can be formed with greater productivity.

[0191] In this embodiment, the material 30 may be formed into the structural member 10 using hot stamping. That is, the material 30 can be subjected to a heating process before the molding process using the first mold 21 and the second mold 22. In this case, even if softening due to welding (HAZ softening) occurs in the heat-affected zone of the welded part 13 formed before the heating process, the HAZ softening can be reduced by heating to a high temperature of, for example, 900°C or higher in the heating process. For example, in the case of a high-strength material such as hot-stamped material, HAZ softening occurs due to welding, and the minimum value of the Vickers hardness of the heat-affected zone is about 60% of the Vickers hardness of the unwelded part. However, after the heating process, the minimum value of the Vickers hardness of the heat-affected zone of the welded part 13 becomes 70% or more of the Vickers hardness of the unwelded part of the first member 11 and the second member 12. As a result, the portion of the structural member 10 with relatively low strength is reduced, and the impact resistance performance of the structural member 10 can be improved.

[0192] In this embodiment, sealing portions 23 are provided on the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22. Each sealing portion 23 is positioned to surround the hollow space formed by the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22. The sealing portions 23 can improve the liquid-tightness or airtightness of the hollow space. Specifically, when the first mold 21 and the second mold 22 are closed, the sealing portions 23 of the first mold 21 and the sealing portions 23 of the second mold 22 strongly abut and clamp the first blank 31 and the second blank 32, making it difficult for fluid to enter between the first mold 21 and the first blank 31, and between the second mold 22 and the second blank 32, and also making it difficult for fluid to leak out around the hollow space. Therefore, the molding of the structural member 10 using fluid can be performed more effectively.

[0193] In this embodiment, sealing portions 24 are further provided on the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22. Each sealing portion 24 is arranged to surround the other sealing portions 23. The sealing portions 24 can further improve the liquid-tightness or airtightness of the hollow space. That is, when the first mold 21 and the second mold 22 are closed, in addition to the sealing portions 23, the sealing portions 24 of the first mold 21 and the sealing portions 24 of the second mold 22 strongly abut and clamp the first blank 31 and the second blank 32. As a result, fluid leakage is further suppressed, and the molding of the structural member 10 using fluid can be performed even more effectively.

[0194] In this embodiment, the projection 213 provided on the first mold 21 may have a step on its side surface 213b. That is, the portion 213c of the side surface 213b of the projection 213 adjacent to the flange surface 212 of the first mold 21 may be substantially parallel to the machining direction D in cross-sectional view. In this case, it is preferable that the size of the portion 213c is greater than or equal to the size of the through hole 311 of the first blank 31. As a result, when the projection 213 is inserted into the through hole 311 of the first blank 31, the through hole 311 is widened by the portion 213c. Consequently, the periphery of the through hole 311 is in strong contact with the side surface 213b of the projection 213 over its entire circumference, making it difficult for a gap to form between the periphery of the through hole 311 and the projection 213. Therefore, fluid from the projection 213 is less likely to enter between the first blank 31 and the first mold 21. Therefore, fluid can be supplied more reliably between the first blank 31 and the second blank 32, and the molding of the material 30 can be performed more effectively.

[0195] In this embodiment, it is preferable that the flow path 214 formed in the first mold 21 opens near the tip of the projection 213. Furthermore, it is preferable that at least the portion of the flow path 214 that passes through the projection 213 is inclined with respect to the processing direction D so as to intersect with the side surface 213b of the projection 213. This makes it difficult for fluid from the projection 213 to enter between the first blank 31 and the first mold 21, and facilitates the supply of fluid between the first blank 31 and the second blank 32. Therefore, the molding of the material 30 using fluid can be performed more effectively.

[0196] In this embodiment, a structural member 10 having a hollow cross-section is formed by expanding the material 30 with a fluid. In this case, a larger reduction in plate thickness than in normal press forming can be tolerated. Specifically, in normal press forming, when the plate thickness reduction rate reaches 30%, cracks, necking, etc. occur in the material 30, resulting in a molding defect. In contrast, in the manufacturing method according to this embodiment, even if the plate thickness reduction rate is large, cracks, necking, etc. are less likely to occur in the part of the material 30 that is formed by the fluid. In the structural member 10 according to this embodiment, in the member body 111 of the first member 11, the plate thickness reduction rate T1 at the curved portion 111c, where plate thickness reduction is most likely to occur, is 30% or more. Similarly, in the member body 121 of the second member 12, the plate thickness reduction rate T2 at the curved portion 121c, where plate thickness reduction is most likely to occur, is 30% or more. Even if the plate thickness reduction rates T1 and T2 are 30% or more, the member bodies 111 and 121 can be formed well without causing cracks, necking, etc.

[0197] <Second Embodiment> Figure 23 is a perspective view showing the schematic configuration of the structural member 10A according to this embodiment. The structural member 10A is a front module for the vehicle body. In this case, the structural member 10A is provided at the front and lower part of the vehicle body of an automobile or the like. However, the structural member 10A may be a subframe for the vehicle body. In this case, the structural member 10A is provided at the front or rear and lower part of the vehicle body of an automobile or the like. The subframe can have a configuration that is generally similar to that of the front module.

[0198] As shown in Figure 17B, in the structural member 10 according to the first embodiment, the side frame 111a of the first member 11 is connected by a cross member 111b at its longitudinal center. Similarly, in the structural member 10 according to the first embodiment, the side frame 121a of the second member 12 is connected by a cross member 121b at its longitudinal center. On the other hand, as shown in Figure 23, in the structural member 10A according to this embodiment, the side frame 111a of the first member 11 is connected by a cross member 111b at one end in its longitudinal direction. Similarly, in the structural member 10A, the side frame 121a of the second member 12 is connected by a cross member 121b at one end in its longitudinal direction. The cross members 111b and 121b are positioned, for example, at the rear ends of the side frames 111a and 121a when the structural member 10A is assembled to the vehicle body.

[0199] The structural member 10A according to this embodiment can also be manufactured using the same manufacturing method as the manufacturing method according to the first embodiment. Figures 24A to 24D are schematic diagrams illustrating the manufacturing method of the structural member 10A.

[0200] Referring to Figures 24A and 24B, in this embodiment as well, a material 30 including a first blank 31 and a second blank 32 is prepared. The basic configuration of the first blank 31 and the second blank 32 is as described in the first embodiment. However, because the shape of the structural member 10A (Figure 23) is different from that of the first embodiment, the first blank 31 and the second blank 32 have different shapes from the first blank 31 and the second blank 32 (Figures 21A and 21B) used in the manufacturing method according to the first embodiment.

[0201] The material 30 is subjected to a molding process similar to that of the first embodiment. The material 30 may be subjected to the molding process after the heating process described above. Referring to Figure 24C, in this embodiment as well, with the projection 213 of the first mold 21 inserted into the through hole 311 of the first blank 31, the material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, and the projection 213 creates a gap between the first blank 31 and the second blank 32. Then, fluid is injected into the gap from the projection 213, and the fluid causes the material 30 to expand between the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22.

[0202] In this embodiment, in the first mold 21 and the second mold 22, protrusions 213 are provided near the cross member molding sections 211b and 221b of the molding surfaces 211 and 221. In the cross member molding sections 211b and 221b, the material 30 expands due to the fluid supplied from the protrusions 213, and the first blank 31 and the second blank 32 are pressed against the first mold 21 and the second mold 22, respectively. Referring to Figure 24D, in the side frame molding sections 211a and 221a, the material 30 expands due to the fluid flowing from the cross member molding section 211b and 221b side (Figure 24C), and the first blank 31 and the second blank 32 are pressed against the first mold 21 and the second mold 22, respectively.

[0203] After the molding process, the outer periphery of the structural member 10A (Figure 23) may be removed by laser cutting or the like. At least the portion of the structural member 10A that has through holes 311 (Figure 24C) is usually removed after the molding process.

[0204] In this embodiment, immediately after the fluid molding process, flanges 112 and 122 are provided so as to surround the entire circumference of the member bodies 111 and 121. For example, the cross members 111b and 121b may be opened at both ends in the longitudinal direction by removing both ends of the cross members 111b and 121b that include the through holes 311. Alternatively, the side frames 111a and 121a may be opened at one end in the longitudinal direction by removing the ends of the side frames 111a and 121a that are opposite to the cross members 111b and 121b.

[0205] <Third Embodiment> Figure 25 is a perspective view showing the schematic configuration of the structural member 10B according to this embodiment. The structural member 10B is a front floor module for a vehicle body. In this case, the structural member 10B is provided at the front of the floor of a vehicle body such as an automobile.

[0206] As shown in Figure 25, in the structural member 10B, similar to other embodiments, the member body 121 of the second member 12 includes a pair of side frames 121a and a cross member 121b. The side frames 121a are connected by the cross member 121b at one end in their longitudinal direction. The member body 121 forms a hollow cross section together with the first member 11 when the flange 122 is joined to the first member 11.

[0207] In this embodiment, the first member 11 includes a floor panel 115 and a floor tunnel 116. The first member 11 may include at least one cross member 111b (Figures 17B and 23), as in other embodiments. When the structural member 10B is assembled to the vehicle body, the floor tunnel 116 is positioned in the left-right center of the floor panel 115 and extends in the front-rear direction. The floor tunnel 116 has a shape that protrudes toward the second member 12 side relative to the floor panel 115. If a cross member 111b is present in the first member 11, the cross member 111b may be positioned to face the cross member 121b of the second member. The portion of the flange 122 of the second member 12 that is continuous with each side frame 121a is joined to the floor panel 115. The portion of the flange 122 of the second member 12 that is continuous with the cross member 121b is joined to the floor panel 115 and the floor tunnel 116.

[0208] The structural member 10B according to this embodiment can also be manufactured using the same manufacturing method as the manufacturing method according to the other embodiments. Figures 26A to 26D are schematic diagrams illustrating the manufacturing method of the structural member 26B.

[0209] Referring to Figures 26A and 26B, in this embodiment as well, a material 30 including a first blank 31 and a second blank 32 is prepared. As in other embodiments, the first blank 31 and the second blank 32 are superimposed and joined together. However, in this embodiment, as shown in Figure 25, the shapes of the first member 11 and the second member 12 are significantly different, so the first blank 31 and the second blank 32 also have different shapes from each other.

[0210] The material 30 is subjected to a molding process similar to that of other embodiments. The material 30 may be subjected to the molding process after the heating process described above. Referring to Figure 26C, in this embodiment as well, with the projection 213 of the first mold 21 inserted into the through hole 311 of the first blank 31, the material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, and the projection 213 creates a gap between the first blank 31 and the second blank 32. Then, fluid is injected into the gap from the projection 213, and the fluid causes the material 30 to expand between the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22.

[0211] In this embodiment, in the first mold 21 and the second mold 22, protrusions 213 are provided near the cross member molding sections 211b and 221b of the molding surfaces 211 and 221. In the cross member molding sections 211b and 221b, the material 30 expands due to the fluid supplied from the protrusions 213, and the first blank 31 and the second blank 32 are pressed against the first mold 21 and the second mold 22, respectively. Referring to Figure 26D, in this embodiment, since the first member 11 (Figure 25) does not include a side frame, the side frame molding section 221a exists only in the second mold 22. At the location of the side frame molding section 221a, the material 30 expands due to the fluid flowing from the cross member molding section 211b and 221b side (Figure 26C), and the first blank 31 and the second blank 32 are pressed against the first mold 21 and the second mold 22, respectively. At the position of the side frame molding section 221a, the material 30 bulges mainly toward the second mold 22 side and does not bulge substantially toward the first mold 21 side. The portion of the first blank 31 that does not overlap with the second blank 32 is held between the first mold 21 and the second mold 22, as in normal press molding, and is molded into a shape that follows the molding surfaces 211 and 221.

[0212] After the molding process, the outer periphery of the structural member 10B (Figure 25) may be removed by laser cutting or the like. At least the portion of the structural member 10B in which the through hole 311 (Figure 26C) is provided is usually removed after the molding process. For example, the cross member 121b may be opened at both ends in the longitudinal direction by removing both ends of the cross member 121b. At this time, the left and right ends of the floor panel 115 including the through hole 311 can also be removed.

[0213] <Fourth Embodiment> Figure 27 is a perspective view showing the schematic configuration of the structural member 10C according to this embodiment. The structural member 10C is a center or rear floor module for a vehicle body. In this case, the structural member 10B is provided in the central or rear part of the floor of a vehicle body such as an automobile.

[0214] As shown in Figure 27, the structural member 10C comprises a plurality of second members 12F and 12R. When the structural member 10C is assembled to the vehicle body, the second member 12F is positioned in front of the second member 12R on the vehicle body. Each of the second members 12F and 12R includes a cross member 121b as the member body 121. A curved portion 121c is provided at one or both ends of the cross member 121b in the longitudinal direction. In this embodiment, the cross member 121b has a wide portion at both ends in the longitudinal direction. The corner between this wide portion and the other portion is the curved portion 121c. Flanges 122 are provided on both sides of the cross member 121b.

[0215] The flanges 122 of the second members 12F and 12R are joined to the first member 11, so that the main body 121 of each member 12F and 12R together with the first member 11 forms a hollow cross section. The first member 11 includes a floor panel 115 and a floor tunnel 116, as in the third embodiment. The first member 11 may include at least one cross member 111b (Figures 17B and 23), as in the other embodiments. The first member 11 may also include multiple cross members 111b, corresponding to the second members 12F and 12R.

[0216] Referring to Figures 28A and 28C, in this embodiment, a material 30 is prepared that includes a first blank 31 and a plurality of second blanks 32F, 32R. The second blanks 32F, 32R are blanks corresponding to the second members 12F, 12R (Figure 27), respectively. Through holes 311 are provided in the first blank 31 at positions corresponding to the second members 12F, 12R.

[0217] The material 30 is subjected to a molding process similar to that of other embodiments. The material 30 may be subjected to the molding process after the heating process described above. Referring to Figures 28C and 28D, in this embodiment as well, with the projection 213 of the first mold 21 inserted into the through hole 311 of the first blank 31, the material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, and the projection 213 creates a gap between the first blank 31 and the second blank 32. Then, fluid is injected into the gap from the projection 213, and the fluid causes the material 30 to expand between the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22. As a result, as shown in Figure 28C, the first blank 31 and the second blank 32F are pressed against the first mold 21 and the second mold 22, respectively. Furthermore, as shown in Figure 28D, the first blank 31 and the second blank 32R are pressed against the first mold 21 and the second mold 22, respectively.

[0218] After the molding process, the outer periphery of the structural member 10C (Figure 27) may be removed by laser cutting or the like. At least the portion of the structural member 10C in which the through-hole 311 (Figures 28C and 28D) is provided is usually removed after the molding process. For example, by removing both ends of the second members 12F and 12R, each cross member 121b may be opened at both ends in the longitudinal direction. At this time, the left and right ends of the floor panel 115, including the through-hole 311, can also be removed.

[0219] In the structural members 10A to 10C according to the second, third, and fourth embodiments, the plate thickness reduction rate T1 of the curved portion 111c and / or the plate thickness reduction rate T2 of the curved portion 121c have the same characteristics as in the first embodiment. Furthermore, in these embodiments, if a heating process is performed before the molding process, the minimum value of the Vickers hardness of the heat-affected zone of the welded portion 13 also has the same characteristics as in the first embodiment.

[0220] In the structural members 10A to 10C according to the second, third, and fourth embodiments, the first blank 31 is formed from one or more metal plates (subblanks), similar to the first embodiment. The second blanks 32, 32F, and 32R are also each formed from one or more metal plates (subblanks), similar to the first embodiment.

[0221] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0222] In the above embodiments, structural members 10, which is the rear module of the vehicle body, structural member 10A, which is the front module, and structural members 10B and 10C, which are the floor modules, were exemplified. However, the structural members manufactured by the manufacturing method according to this disclosure are not limited to the structural members 10, 10A to 10C exemplified in the above embodiments. The manufacturing method according to this embodiment can be applied to various structural members as long as the structural member includes a first member and a second member, and one of the first member and the second member forms a hollow cross-section with the other of the first member and the second member. The hollow member body and the flange continuous with the member body may be provided on both the first member and the second member as in the first and second embodiments, or on only one of the first member and the second member as in the third and fourth embodiments.

[0223] In the above embodiment, an example was described in which a first mold 21 including one or more protrusions 213 is positioned below a second mold 22. However, the positional relationship between the first mold 21 and the second mold 22 is not limited to this. When manufacturing a structural member, the first mold 21 may be positioned above the second mold 22, for example. In this case, the protrusions 213 are positioned above the material 30, and the material 30 is placed on the flange surface 222 of the second mold 22. Therefore, the material 30 can be stably positioned before the mold 20 is closed. Thus, it is not necessary to provide a flat tip surface 213a on the protrusions 213 for positioning the material 30.

[0224] In the above embodiment, sealing portions 23 and 24 are provided in both the first mold 21 and the second mold 22. However, the sealing portion 23 and / or sealing portion 24 may not be provided in either the first mold 21 or the second mold 22, or neither the sealing portion 23 nor 24 may be provided in either the first mold 21 or the second mold 22. However, from the viewpoint of preventing fluid leakage, it is preferable that at least the sealing portion 23 is provided in both the first mold 21 and the second mold 22. More preferably, the sealing portions 23 and 24 are provided in a double configuration in both the first mold 21 and the second mold 22.

[0225] In the above embodiment, each of the structural members 10, 10A to 10C is formed using a material 30 including a first blank 31 and a second blank 32. A reinforcing plate may be attached to at least one of the first blank 31 and the second blank 32. The reinforcing plate can be attached to parts of the structural members 10, 10A to 10C where rigidity is required. For example, in the structural member 10B according to the third embodiment, a reinforcing plate may be attached to the second blank 32 before forming, at a position corresponding to the ridge of the floor tunnel 116. The reinforcing plate is joined to the first blank 31 from the opposite side of the overlapping surface with the second blank 32, for example. Alternatively, the reinforcing plate may be joined to the second blank 32 from the opposite side of the overlapping surface with the first blank 31. The reinforcing plate is joined to at least one of the first blank 31 and the second blank 32 by welding, for example, spot welding or laser welding.

[0226] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0227] To confirm the difference between a structural member manufactured by the manufacturing method described herein and a structural member manufactured by a conventional manufacturing method, a molding test was conducted on the structural member 10 according to the first embodiment. In this test, the structural member 10 was molded by the manufacturing method (hydraulic blow or gas blow) described in the above embodiment, and the rate of plate thickness reduction T2 at the curved portion 121c of the member body 121 of the upper member (second member) 12 was measured. For hydraulic blow, industrial water mixed with a rust inhibitor was used as the molding fluid, and for gas blow, compressed air was used as the molding fluid. In the case of hydraulic blow, the material heating process was not performed, but in the case of gas blow, the material heating process was performed before the molding process. In addition, the second member 12 was molded by cold press forming and hot stamping, respectively, as conventional manufacturing methods, and the rate of plate thickness reduction T2 at the curved portion 121c of the member body 121 was measured. The test conditions and results are shown in Table 6.

[0228] [Table 6]

[0229] Table 6 shows the forming method, material and strength (tensile strength), forming height, plate thickness reduction rate T2, and forming evaluation for each of the examples and comparative examples. The plate thickness reduction rate T2 was calculated by obtaining the plate thickness t of the curved portion 121c of the member body 121 using the measurement method described in the above embodiment, and setting the plate thickness of the blank (steel plate) before forming: 1.2 mm as t0. The forming height is the length along the processing direction D from the flange 122 to the top plate 123 of the second member 12. For the forming evaluation, A was defined as no forming defects occurring in the curved portion 121c where the plate thickness is reduced the most during forming, B as necking occurred, and C as cracking occurred. In this test, a crack of 0.1 mm or more occurred in the curved portion 121c, and necking was determined as the plate thickness at only one of the measurement points when obtaining the plate thickness t of the curved portion 121c being reduced by 0.05 mm or more compared to the surrounding area, even if no cracking occurred.

[0230] As shown in Table 6, in Comparative Examples 1 and 2, in which the second member 12 was formed by cold press forming alone, the plate thickness reduction rate T2 at the curved portion 121c of the member body 121 was 34%, and cracks occurred at the curved portion 121c.

[0231] In Comparative Examples 3 and 4, a 1.5 GPa class hot-stamping material was used as the base material, and the second member 12 was formed solely by hot stamping. In Comparative Example 3, because the forming height was relatively small, the plate thickness reduction rate T2 at the curved portion 121c of the member body 121 was less than 30%, and no forming defects occurred at the curved portion 121c. However, in Comparative Example 4, because the forming height was relatively large, the plate thickness reduction rate T2 was 30%, and necking occurred at the curved portion 121c.

[0232] In Comparative Examples 5 and 6, a 2.0 GPa class hot-stamping material was used as the base material, and the second member 12 was formed solely by hot stamping. In Comparative Example 5, because the forming height was relatively small, no forming defects occurred in the curved portion 121c of the member body 121. However, in Comparative Example 6, due to the relatively large forming height, necking occurred in the curved portion 121c. In Comparative Example 5, the plate thickness reduction rate T2 in the curved portion 121c was 26%, and in Comparative Example 6, the plate thickness reduction rate T2 was 28%.

[0233] Thus, among Comparative Examples 1 to 6, there were no cases where the thickness reduction rate T2 was 30% or more and the curved portion 121c of the member body 121 could be formed without causing molding defects. However, in Examples 1 to 8, no molding defects occurred in the curved portion 121c, even though the thickness reduction rate T2 was 30% or more in both hydraulic blowing and gas blowing. It is presumed that in Examples 1 to 8, the inflow and outflow of material were promoted by using hydraulic blowing or gas blowing, and biaxial tensile deformation was promoted even in the corner portion, so that the curved portion 121c could be formed well even when the thickness reduction rate T2 was 30% or more.

[0234] In order to confirm the upper limit of the plate thickness reduction rate T2 for Examples 1 to 8, separate tests were conducted. In Examples 1, 3, 5, and 7, where the forming height was 30 mm, no forming defects occurred in the curved portion 121c even when the plate thickness reduction rate T2 exceeded 50%, regardless of the forming method (hydraulic blow or gas blow) and material. On the other hand, in Examples 2, 4, 6, and 8, where the forming height was 40 mm, forming defects occurred in the curved portion 121c as the plate thickness reduction rate T2 increased. When the forming method was hydraulic blow, in Example 2, which used a steel plate with a tensile strength of 270 MPa, cracks occurred in the curved portion 121c when the plate thickness reduction rate T2 exceeded 50%, and in Example 4, which used a steel plate with a tensile strength of 590 MPa, cracks occurred in the curved portion 121c when the plate thickness reduction rate T2 was 45%. In the case of gas blow molding, necking occurred at the curved portion 121c when the plate thickness reduction rate T2 was 55% in both Example 6, which used 1.5 GPa class hot stamping material, and Example 8, which used 2.0 GPa class hot stamping material. Therefore, regarding the molding method, material, and molding height in this test, it was confirmed that molding defects were generally suppressed if the plate thickness reduction rate T2 was 50% or less, and that no molding defects occurred if the plate thickness reduction rate T2 was less than 45%.

[0235] (Elemental Technology C2) Element technology C2 is a material comprising a first blank and a second blank superimposed on the first blank, wherein the first blank and the second blank are not joined in the regions of the material that will become the first structural member and the second structural member; and a first structural member manufactured by a manufacturing method comprising holding the material with a first mold and a second mold and supplying fluid between the first blank and the second blank to deform the material in the hollow space formed by the first mold and the second mold to form a first molded product including the first structural member from the first blank and a second molded product including the second structural member from the second blank, and a second structural member separate from the first structural member.

[0236] According to elemental technology C2, it is possible to provide multiple structural members that can be manufactured with fewer processes.

[0237] Embodiments of this disclosure will be described below with reference to the drawings. In these drawings, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0238] <First Embodiment> [Structural members] Figure 29 is a perspective view showing the schematic configuration of the first structural member 10 and the second structural member 20 in this embodiment. The structural members 10 and 20 are rear frames for a vehicle body. In this case, the structural members 10 and 20 are provided at the rear and lower part of a vehicle body such as an automobile. The first structural member 10 is positioned above the second structural member 20 when incorporated into the vehicle body. The first structural member 10 is the rear frame upper, and the second structural member 20 is the rear frame lower.

[0239] The first structural member 10 includes a pair of side frames 11 and at least one cross member 12. The first structural member 10 may include a plurality of cross members 12. When the first structural member 10 is incorporated into the vehicle body, each side frame 11 extends in the longitudinal direction (vehicle length direction) of the vehicle body. The side frames 11 are connected by the cross members 12. The side frames 11 are connected by the cross members 12, for example, at their longitudinal intermediate portions. The cross members 12 extend from one side frame 11 to the other side frame 11. When the first structural member 10 is incorporated into the vehicle body, the cross members 12 extend in the lateral direction (vehicle width direction) of the vehicle body.

[0240] The second structural member 20 includes a pair of side frames 21 and at least one cross member 22. The second structural member 20 may include a plurality of cross members 22. The side frames 21 each extend in the vehicle length direction when the second structural member 20 is incorporated into the vehicle body. The side frames 21 are connected by the cross members 22. The side frames 21 are connected by the cross members 22, for example, at their longitudinal intermediate portions. The cross members 22 extend from one side frame 21 to the other side frame 21. The cross members 22 extend in the vehicle width direction when the second structural member 20 is incorporated into the vehicle body.

[0241] With the structural members 10 and 20 assembled into the vehicle body, the side frame 11 of the first structural member 10 is joined to the side frame 21 of the second structural member 20. Figure 30 is a cross-sectional view (sectional plane) of the side frames 11 and 21 perpendicular to the longitudinal direction.

[0242] Referring to Figure 30, the side frame 11 may have a substantially hat shape in cross-sectional view. In this embodiment, the side frame 11 includes a top plate 111, two vertical walls 112, and two flanges 113. In cross-sectional view of the side frame 11, the vertical walls 112 are located on both sides of the top plate 111. Each vertical wall 112 is connected to the top plate 111 via a ridge 114. The flanges 113 are on the opposite side of the top plate 111 and are connected to the vertical walls 112 via a ridge 115. The flanges 113 project outward from the vertical walls 112 toward the side frame 11.

[0243] In this embodiment, the side frame 21 forms a closed section together with the side frame 11 when the structural members 10 and 20 are incorporated into the vehicle body. The side frame 21 may have a substantially hat shape in cross-sectional view. The side frame 21 includes a top plate 211, two vertical walls 212, and two flanges 213. The top plate 211 faces the top plate 111 of the side frame 11. In a cross-sectional view of the side frame 21, the vertical walls 212 are located on both sides of the top plate 211. The vertical walls 212 are each connected to the top plate 211 via ridges 214. The flanges 213 are on the opposite side of the top plate 211 and are each connected to the vertical walls 212 via ridges 215. The flanges 213 project outward from the vertical walls 212 toward the side frame 21. The flanges 213 are joined to the flanges 113 of the side frame 11. The flanges 113 and 213 are joined, for example, by spot welding. Flanges 113 and 213 may be joined by laser welding or the like.

[0244] With the structural members 10 and 20 assembled into the vehicle body, the cross member 12 of the first structural member 10 is also joined to the cross member 22 of the second structural member 20. Figure 31 is a cross-sectional view (sectional plane view) of the cross members 12 and 22 perpendicular to the longitudinal direction.

[0245] Referring to Figure 31, the cross member 12 may have a substantially hat shape in cross view. In this embodiment, the cross member 12 includes a top plate 121, two vertical walls 122, and two flanges 123. In a cross view of the cross member 12, the vertical walls 122 are located on both sides of the top plate 121. Each vertical wall 122 is connected to the top plate 121 via a ridge 124. The flanges 123 are on the opposite side of the top plate 121 and are connected to the vertical walls 122 via a ridge 125. The flanges 123 project outward from the vertical walls 122.

[0246] In this embodiment, the cross member 22 forms a closed section together with the cross member 12 when the structural members 10 and 20 are incorporated into the vehicle body. The cross member 22 may have a substantially hat shape in cross view. The cross member 22 includes a top plate 221, two vertical walls 222, and two flanges 223. The top plate 221 faces the top plate 121 of the cross member 12. In a cross view of the cross member 22, the vertical walls 222 are located on both sides of the top plate 221. The vertical walls 222 are each connected to the top plate 221 via ridges 224. The flanges 223 are on the opposite side of the top plate 221 and are each connected to the vertical walls 222 via ridges 225. The flanges 223 project outward from the vertical walls 222 toward the cross member 22. The flanges 223 are joined to the flanges 123 of the cross member 12. The flanges 123 and 223 are joined by, for example, spot welding. Alternatively, the flanges 123 and 223 may be joined by laser welding or the like.

[0247] [Mold] Figure 32 is a perspective view showing the schematic configuration of the mold 30 in this embodiment. The structural members 10 and 20 (Figure 29) can be manufactured using the mold 30.

[0248] Referring to Figure 31, the mold 30 comprises a first mold 31 and a second mold 32. The first mold 31 and the second mold 32 are a pair of molds. When the mold 30 is in use, the first mold 31 and the second mold 32 are mounted on a press device or the like so that they can approach each other relatively. Hereinafter, the direction in which the first mold 31 and the second mold 32 approach each other will be referred to as the processing direction D. The processing direction D is, for example, the vertical direction.

[0249] The first mold 31 is a mold primarily for molding the first structural member 10 (Figure 29). The first mold 31 includes a molding surface 311 and a flange surface 312. The molding surface 311 and the flange surface 312 are provided on the surface of the first mold 31 that faces the processing direction D relative to the second mold 32.

[0250] The molded surface 311 is formed to correspond to the portion of the first structural member 10 that is convex upward relative to the flanges 113 and 123 (Figures 29 to 31). In this embodiment, the molded surface 311 has a shape that corresponds to the top plate 111, vertical wall 112, and ridge portions 114 and 115 (Figure 30) of the side frame 11 of the first structural member 10, and the top plate 121, vertical wall 122, and ridge portions 124 and 125 (Figure 31) of the cross member 12. When viewed along the processing direction D, the flange surface 312 is arranged around the molded surface 311.

[0251] In this embodiment, the second mold 32 is located below the first mold 31. The second mold 32 is a mold primarily for molding the second structural member 20 (Figure 29). The second mold 32 includes a molding surface 321 and a flange surface 322. The molding surface 321 and the flange surface 322 are provided on the surface of the second mold 32 that faces the processing direction D relative to the first mold 31.

[0252] The molded surface 321 is formed to correspond to the portion of the second structural member 20 that is concave downward relative to the flanges 213 and 223 (Figures 29 to 31). In this embodiment, the molded surface 321 has a shape that corresponds to the top plate 211, vertical wall 212, and ridge portions 214 and 215 (Figure 30) of the side frame 21 of the second structural member 20, and the top plate 121, vertical wall 122, and ridge portions 124 and 125 (Figure 31) of the cross member 22. When viewed along the processing direction D, the flange surface 322 is arranged around the molded surface 321.

[0253] The molding surface 321 of the second mold 32, together with the molding surface 311 of the first mold 31, forms a hollow space. Therefore, when the mold 30 is in use, the molding surfaces 311 and 321 face the processing direction D. One or both of the molding surfaces 311 and 321 have a concave shape in at least a part of them. In this embodiment, each of the molding surfaces 311 and 321 has an overall concave shape. More specifically, in the first mold 31, the molding surface 311 is formed to be concave with respect to the flange surface 312. In the second mold 32, the molding surface 321 is formed to be concave with respect to the flange surface 322.

[0254] One of the first mold 31 and the second mold 32 may include convex sealing portions 33 and 34. In this embodiment, the other of the first mold 31 and the second mold 32 also includes convex sealing portions 33 and 34. That is, each of the first mold 31 and the second mold 32 includes sealing portions 33 and 34. The sealing portion 33 is made of, for example, metal. The sealing portion 33 may be formed integrally with the first mold 31 or the second mold 32. The outer peripheral sealing portion 34 may be made of metal, but may also be made of an elastic material such as resin. When the sealing portion 34 is provided in the first mold 31 and / or the second mold 32, the sealing portion 34 may be a resin packing such as an O-ring. In this case, the mold having the sealing portion 34 among the first mold 31 and the second mold 32 has a groove for arranging the sealing portion 34.

[0255] In the first mold 31, the sealing portions 33 and 34 are provided on the surface facing the second mold 32. The sealing portions 33 and 34 are provided, for example, on the flange surface 312. The sealing portion 33 substantially surrounds the molding surface 311 when viewed along the machining direction D. The sealing portion 33 may surround the molding surface 311 without interruption around its entire circumference, but may be interrupted in part at positions relatively far from the fluid supply port, for example, described later. The sealing portion 33 may be interrupted at positions far from each fluid supply port, for example, in a range of 150 mm or less.

[0256] In the first mold 31, the seal portion 34 substantially surrounds the seal portion 33 when viewed along the machining direction D. That is, the first mold 31 is provided with a double layer of seal portions 33 and 34. The seal portion 34 may surround the seal portion 33 without interruption around its entire circumference, but it may be interrupted in part, for example, at a position relatively far from the fluid supply port. The seal portion 34 may be interrupted at a position far from the fluid supply port, for example, in a range of 150 mm or less.

[0257] In the second mold 32, the sealing portions 33 and 34 are provided on the surface facing the first mold 31. The sealing portions 33 and 34 are provided, for example, on the flange surface 322. The sealing portion 33 substantially surrounds the molding surface 321 when viewed along the machining direction D. The sealing portion 33 of the second mold 32 is provided so as to face the sealing portion 33 of the first mold 31 in the machining direction D, and has a shape corresponding to the sealing portion 33 of the first mold 31. In the second mold 32 as well, the sealing portion 33 may surround the molding surface 321 without interruption around its entire circumference, or it may be interrupted in a range of, for example, 150 mm or less.

[0258] In the second mold 32, the seal portion 34 substantially surrounds the seal portion 33 when viewed along the machining direction D. That is, the second mold 32 is provided with a double set of seal portions 33 and 34. The seal portion 34 of the second mold 32 is provided so as to face the seal portion 34 of the first mold 31 in the machining direction D, and has a shape corresponding to the seal portion 34 of the first mold 31. In the second mold 32 as well, the seal portion 34 may surround the seal portion 33 without interruption around its entire circumference, or it may be interrupted in a range of, for example, 150 mm or less.

[0259] The second mold 32 may have at least one projection 35. The projection 35 is formed, for example, on the flange surface 322 of the second mold 32. In this embodiment, multiple projections 35 are formed on the flange surface 322. The projections 35 are arranged, for example, on both sides of the portion of the molding surface 321 corresponding to the cross member 22 (Figure 29).

[0260] Each of the projections 35 has, for example, a circular shape when viewed along the machining direction D. However, the projections 35 may have a polygonal shape such as a triangular or quadrilateral shape when viewed along the machining direction D. If the projections 35 have a shape other than a circle, they may be formed to be wider on the side facing the molded surface 321.

[0261] Figures 33A and 33B are cross-sectional views of the mold 30 shown in Figure 32. Figures 33A and 33B show the longitudinal section of the mold 30 at the position of the projection 35. The longitudinal section of the mold 30 is the section along the machining direction D.

[0262] First, referring to Figure 33A, one of the first mold 31 and the second mold 32 includes at least one fluid supply port 36. The fluid supply port 36 is formed on the surface of one of the first mold 31 and the second mold 32 that faces the other. In this embodiment, the second mold 32 has the fluid supply port 36. More specifically, the second mold 32 has a fluid channel 37 inside, the end of which opens to the surface of the second mold 32 as the fluid supply port 36. The channel 37 is connected to a fluid supply source (not shown) provided outside the second mold 32.

[0263] In the flow path 37, the end opposite to the fluid supply port 36 can open, for example, to the side of the second mold 32. However, if multiple flow paths 37 are provided in the second mold 32, these flow paths 37 may be consolidated into a single system within the second mold 32 and then open to the back of the second mold 32 or the like.

[0264] The fluid supply port 36 may be located on the projection 35. The projection 35 having the fluid supply port 36 includes a tip surface 351 and a side surface 352. The tip surface 351 is the surface of the projection 35 that is located furthest from the flange surface 322. In this embodiment, the tip surface 351 is a flat surface substantially perpendicular to the machining direction D.

[0265] The side surface 352 connects the tip surface 351 to the flange surface 322. In this embodiment, when viewed in a longitudinal cross-section of the mold 30, the side surface 352 is inclined with respect to the machining direction D such that the width of the projection 35 is larger at the base end and smaller at the tip end.

[0266] Figure 33B shows another example of the projection 35. In the example in Figure 33A, the side surface 352 of the projection 35 is an inclined surface that is inclined overall with respect to the machining direction D, but in the example in Figure 33B, a step is provided on the side surface 352 at the base end of the projection 35. That is, when viewed in a longitudinal cross-section of the mold 30, the portion 353 of the side surface 352 adjacent to the flange surface 322 is substantially parallel to the machining direction D. Therefore, the width of the projection 35 is substantially constant in the portion 353 of the side surface 352 adjacent to the flange surface 322. Other portions of the side surface 352 may be inclined with respect to the machining direction D, as in Figure 5A.

[0267] The fluid supply port 36 is located, for example, on the side surface 352 of the projection 35. The fluid supply port 36 is located on the side surface 352 of the projection 35 that is on the molding surface 321 side. Preferably, the fluid supply port 36 is located on the tip side of the projection 35. In the examples in Figures 33A and 33B, the portion of the flow path 37 having the fluid supply port 36 at its end that passes through the projection 35 is substantially parallel to the machining direction D. However, at least the portion of the flow path 37 that passes through the projection 35 may be inclined with respect to the machining direction D. The flow path 37 can be inclined with respect to the machining direction D so as to intersect the side surface 352 of the projection 35 when viewed in the longitudinal section of the mold 30. At least the portion of the flow path 37 that passes through the projection 35 may be inclined with respect to the machining direction D at an angle greater than 0° and less than or equal to 60° when viewed in the longitudinal section of the mold 30.

[0268] Near the projection 35, a relief portion 312a is formed on the flange surface 312 of the first mold 31. Viewed in a longitudinal section of the mold 30, the relief portion 312a extends from the portion of the flange surface 312 facing the tip surface 351 of the projection 35 to the molding surface 311. The relief portion 312a has a concave shape relative to the rest of the flange surface 312.

[0269] The sealing portions 33 and 34 of the first mold 31 and the second mold 32 preferably have a shape that allows surface contact with the mating mold or its sealing portions 33 and 34. Each of the sealing portions 33 and 34 may, for example, have a substantially rectangular cross-section. The width of each sealing portion 33 and 34 may be 1.0 mm or more, and preferably 2.0 mm or more. The width of each sealing portion 33 and 34 is preferably 5.0 mm or less, and more preferably 3.0 mm or less. The height of each sealing portion 33 and 34 is, for example, 0.2 mm or more. The height of each sealing portion 33 and 34 may be 0.5 mm or less.

[0270] [Method for manufacturing structural members] Next, the manufacturing method for the structural members 10 and 20 will be described with reference to Figures 34A to 34G. The manufacturing method according to this embodiment comprises a preparation step and a molding step. The manufacturing method may further include a heating step.

[0271] (preparation process) As shown in Figures 34A and 34B, the preparation step involves preparing the material 40. The material 40 includes a first blank 41 and a second blank 42.

[0272] The first blank 41 is a blank corresponding to the first structural member 10 (Figure 29). The first blank 41 includes regions 411 and 412. Region 411 is the region of the first blank 41 that will be molded into the first structural member 10 by a molding process described later. Region 412 is the region of the first blank 41 other than region 411. In this embodiment, region 412 is provided around region 411.

[0273] The second blank 42 is a blank corresponding to the second structural member 20 (Figure 29). The second blank 42 includes regions 421 and 422. Region 421 is the region of the second blank 42 that will be molded into the second structural member 20 by a molding process described later. Region 422 is the region of the second blank 42 other than region 421. In this embodiment, region 422 is provided around region 421.

[0274] Through holes 43 are formed in the second blank 42. In this embodiment, multiple through holes 43 are formed in the second blank 42. The through holes 43 are located, for example, in the region 422 of the second blank 42 outside the second structural member 20 (Figure 29).

[0275] The second blank 42 is superimposed on the first blank 41. The second blank 42 may or may not be joined to the first blank 41. However, in the regions 411 and 421 of the material 40 that will become the first structural member 10 and the second structural member 20 (Figure 29), the first blank 41 and the second blank 42 are not joined. In the regions 412 and 422 of the material 40 outside the structural members 10 and 20, the first blank 41 and the second blank 42 may be joined (temporarily fixed) by, for example, spot welding.

[0276] The first blank 41 and the second blank 42 may each be formed from a single metal sheet, or they may each include multiple metal sheets (subblanks). The metal sheets may be, for example, iron sheets (steel sheets) or non-ferrous metal sheets such as aluminum alloy sheets. The first blank 41 and the second blank 42 may be formed from different types of metal sheets. For example, one of the first blank 41 and the second blank 42 may be formed from one or more iron sheets (steel sheets), and the other of the first blank 41 and the second blank 42 may be formed from one or more non-ferrous metal sheets.

[0277] If the first blank 41 includes multiple metal plates, these metal plates may differ in at least one of their tensile strength and thickness. If the first blank 41 includes multiple metal plates, the metal plates are joined together, for example, by welding. Similarly, if the second blank 42 includes multiple metal plates, these metal plates may differ in at least one of their tensile strength and thickness. If the second blank 42 includes multiple metal plates, the metal plates are joined together, for example, by welding. The metal plates are joined together, for example, by spot welding or laser welding. In each of the first blank 41 and the second blank 42, adjacent metal plates may be joined with their end faces butted together, or with their ends overlapping together.

[0278] (Heating process) The heating process is carried out before the forming process. In the heating process, the prepared material 40 is heated. The material 40 is heated, for example, in a heating furnace. The heating temperature of the material 40 is determined according to the material of the first blank 41 and the second blank 42. If the first blank 41 and the second blank 42 are formed from steel sheets, the material 40 is heated to the austenite transformation completion temperature (A) of the first blank 41 and the second blank 42. c3 It is preferable that the material be heated to a temperature of 900°C or higher. If the first blank 41 and the second blank 42 are made of steel plates, the material 40 is heated to, for example, 900°C or higher. However, the heating step is not necessarily required.

[0279] (molding process) In the molding process, structural members 10 and 20 (Figure 29) are formed from the material 40 using the first mold 31 and the second mold 32. The molding process may be a cold forming process or a hot forming process (hot stamping). If the molding process is a hot forming process, a heating process is performed before the molding process, and in the molding process, the heated material 40 is formed into structural members 10 and 20.

[0280] Referring to Figure 34C, in the molding process, first, with the first mold 31 and the second mold 32 separated in the processing direction D, the material 40 is placed between the first mold 31 and the second mold 32. At this time, the material 40 is placed between the first mold 31 and the second mold 32 such that the first blank 41 is located on the first mold 31 side and the second blank 42 is located on the second mold 32 side. If the second mold 32 is located below the first mold 31, the material 40 may be placed on the second mold 32. In this embodiment, the material 40 is placed such that each through hole 43 of the second blank 42 corresponds to the projection 35 of the second mold 32.

[0281] Referring to Figure 34D, the first mold 31 and the second mold 32 are then brought relatively close together and closed, holding the material 40 between the first mold 31 and the second mold 32. The first mold 31 and the second mold 32 clamp the area of ​​the material 40 that is at least the region where the first blank 41 and the second blank 42 overlap, and is outside the structural members 10,20 (Figure 29), specifically the areas 412,422 (Figures 34A and 34B). The first mold 31 and the second mold 32 can further clamp the areas 411,421 (Figures 34A and 34B) that will become the structural members 10,20, specifically the portions that will be formed into the flanges 113,213 (Figure 30) of the side frames 11,21 and the flanges 123,223 (Figure 31) of the cross members 12,22.

[0282] In this embodiment, with the projections 35 of the second mold 32 inserted into each through hole 43 of the second blank 42, the material 40 can be clamped between the flange surface 312 and the flange surface 322 of the second mold 32. The projections 35 create a gap between the first blank 41 and the second blank 42. The projections 35 are inserted into the through holes 43 of the second blank 42 and lift the first blank 41 from the inside of the material 40. As a result, a gap is created between the first blank 41 and the second blank 42.

[0283] As described above, the tip surface 351 of the projection 35 may be substantially flat. In this case, the projection 35 can make surface contact with the first blank 41 at its tip surface 351. When the first mold 31 and the second mold 32 are closed, the material 40 is first sandwiched between the tip surface 351 of the projection 35 and the relief portion 312a of the flange surface 312 of the first mold 31. This allows the material 40 to be positioned.

[0284] When the first mold 31 and the second mold 32 are closed, the material 40 is held between the sealing portion 33 of the first mold 31 and the sealing portion 33 of the second mold 32. Also, when the first mold 31 and the second mold 32 are closed, the sealing portion 34 (Figure 32) of the first mold 31 abuts against the sealing portion 34 (Figure 32) of the second mold 32. At the location of the sealing portion 33, the material 40 is held more strongly than at other parts of the first mold 31 and the second mold 32.

[0285] Referring to Figures 34E and 34F, in the molding process, the material 40 is held by the first mold 31 and the second mold 32, and fluid is supplied between the first blank 41 and the second blank 42, thereby deforming the material 40 in the hollow space formed by the first mold 31 and the second mold 32. As a result, the first molded product 51 is formed from the first blank 41, and the second molded product 52 is formed from the second blank 42. In this embodiment, after the material 40 is sandwiched between the flange surface 312 of the first mold 31 and the flange surface 322 of the second mold 32, fluid is supplied from the fluid supply port 36 located in the projection 35 into the gap between the first blank 41 and the second blank 42. The fluid is supplied from a fluid supply source (not shown) to the flow path 37, passes through the flow path 37, and flows out from the fluid supply port 36. This fluid causes the material 40 to expand within the hollow space defined by the molding surface 311 of the first mold 31 and the molding surface 321 of the second mold 32.

[0286] The fluid used in the molding process is not particularly limited. The fluid may be a liquid such as water, or a gas such as nitrogen gas or compressed air. The fluid may be a liquid or gas under high pressure, for example, 10 MPa or higher. The temperature of the fluid may be appropriately determined according to the material of the material 40, and may be, for example, room temperature. If a heating process is performed, i.e., when molding is performed by hot stamping, the fluid may be heated.

[0287] Within the hollow space of the mold 30, the first blank 41 of the material 40 is expanded by the fluid and then pressed against the molding surface 311 of the first mold 31. The second blank 42 of the material 40 is expanded by the fluid and then pressed against the molding surface 321 of the second mold 32. As a result, regions 411 and 412 of the material 40 (Figures 34A and 34B) are molded into the shapes of the structural members 10 and 20, respectively. Thus, a first molded product 51 including the first structural member 10 and a second molded product 52 including the second structural member 20 can be obtained.

[0288] If a heating process was performed before the molding process, the first molded product 51 and the second molded product 52 are deheated and hardened by the first mold 31 and the second mold 32, respectively.

[0289] In the molding process, the molding height H1 of the first structural member 10 may be equal to or different from the molding height H2 of the second structural member 20. The molding height H1 is the maximum depth of the molding surface 311 relative to the flange surface 312 in the first mold 31, and is the maximum distance in the processing direction D from the flange surface 312 to the bottom surface of the molding surface 311. The molding height H2 is the maximum depth of the molding surface 321 relative to the flange surface 322 in the second mold 32, and is the maximum distance in the processing direction D from the flange surface 322 to the bottom surface of the molding surface 321. When the molding height H1 of the first structural member 10 and the molding height H2 of the second structural member 20 are different, the difference between the molding heights H1 and H2 is, for example, 1 mm or more. The difference between the molding heights H1 and H2 may be 5 mm or more. The difference between the molding heights H1 and H2 is, for example, 150 mm or less.

[0290] (Trimming process) The manufacturing method according to this embodiment may further include a trimming step. Referring to Figure 34G, in the trimming step, after the molding step, the first molded product 51 and the second molded product 52 are trimmed to obtain separate first structural member 10 and second structural member 20.

[0291] The trimming process may be performed while the first molded product 51 and the second molded product 52 are still inside the mold 30, or it may be performed after the first molded product 51 and the second molded product 52 have been removed from the mold 30. In the trimming process, for example, the outer periphery of the first molded product 51 is removed. More specifically, the portion of the first molded product 51 that was outside the first structural member 10 in the first blank 41 (Figure 34A) is removed. This allows the first structural member 10 to be obtained.

[0292] Similarly, in the trimming process, for example, the outer periphery of the second molded product 52 is removed. More specifically, the portion of the second molded product 52 that was outside the second structural member 20 region 422 in the second blank 42 (Figure 34B) is removed. The portion of the second molded product 52 in which the through hole 43 is provided is usually removed in the trimming process. If the first blank 41 and the second blank 42 were joined (temporarily fixed) in the material 40, there is a joint between the first molded product 51 and the second molded product 52, but this joint is removed in the trimming process. This makes it possible to obtain a second structural member 20 that is separate from the first structural member 10. The trimming of the first molded product 51 and the second molded product 52 can be carried out by, for example, laser cutting.

[0293] After the trimming process, the first structural member 10 and the second structural member 20 may each be subjected to a painting process. The first structural member 10 and the second structural member 20 are joined together after undergoing necessary processes such as painting. This allows for the creation of a rear frame for the vehicle body.

[0294] [effect] In the manufacturing method according to this embodiment, a mold 30 is used to mold a material 40 including a first blank 41 and a second blank 42 that are stacked on top of each other. More specifically, the material 40 is held in the first mold 31 and the second mold 32, and a fluid is supplied between the first blank 41 and the second blank 42 to deform the material 40 within the hollow space of the mold 30. As a result, a first molded product 51 including the first structural member 10 is molded from the first blank 41, and a second molded product 52 including the second structural member 20 is molded from the second blank 42. In other words, the first structural member 10 and the second structural member 20 can be molded simultaneously in a single process. Therefore, the number of molding processes can be reduced compared to when the structural members 10 and 20 are molded in separate molding processes, and multiple structural members 10 and 20 can be manufactured productively with fewer processes. In addition, since the number of molds can be reduced compared to when the structural members 10 and 20 are molded in separate molding processes, the cost required for the molds can also be reduced.

[0295] In this embodiment, the clamping force between the first mold 31 and the second mold 32 can seal the periphery of the hollow space of the mold 30. Therefore, even if the first blank 41 and the second blank 42 are not joined in the regions 411 and 412 that will become structural members 10 and 20, the structural members 10 and 20 can be molded using fluid.

[0296] In the manufacturing method according to this embodiment, the first blank 41 and the second blank 42 are not joined in the regions 411 and 421 of the material 40 that will become structural members 10 and 20. That is, in the regions 411 and 421 of the material 40 that will become structural members 10 and 20, the first blank 41 and the second blank 42 are not constrained by a joint. Therefore, when the structural members 10 and 20 are formed by fluid during the molding process, material is more likely to flow into the hollow space of the mold 30, and the structural members 10 and 20 can be formed well. Consequently, even when the molding height H1 of the first structural member 10 and / or the molding height H2 of the second structural member 20 are large, the structural members 10 and 20 can be formed while suppressing the occurrence of molding defects such as cracks and wrinkles. Furthermore, even if the molding height H1 of the first structural member 10 and the molding height H2 of the second structural member 20 are different, it is possible to allow a difference in material inflow corresponding to the difference in molding heights H1 and H2, and the structural members 10 and 20 can be molded while suppressing the occurrence of molding defects.

[0297] In the manufacturing method according to this embodiment, the structural members 10 and 20 are formed in a manner in which no joints exist in at least the regions 411 and 421 of the material 40 that will become the structural members 10 and 20. The structural members 10 and 20 are joined together after the forming process, for example by spot welding. Therefore, no plastic deformation occurs at the joint between the first structural member 10 and the second structural member 20 during the forming process, and the tensile shear strength (TSS) of the joint can be ensured in the structural members 10 and 20 as a rear frame.

[0298] The structural members 10 and 20 manufactured by the manufacturing method according to this embodiment can have various strengths. Depending on the strength of the structural members 10 and 20, cold forming or hot forming (hot stamping) can be selected. Material inflow into the hollow space of the mold 30 is more likely to occur with cold forming than with hot forming, and the formability is better; therefore, when the tensile strength of the structural members 10 and 20 is less than 590 MPa, the forming process is preferably a cold forming process. On the other hand, when the tensile strength of the structural members 10 and 20 is 590 MPa or more, the forming process is preferably a hot forming process because the material 40 is formed while being stretched.

[0299] In the manufacturing method according to this embodiment, the first blank 41 and the second blank 42 are not joined in at least the regions 411 and 421 of the material 40 that will become the first structural member 10 and the second structural member 20. Joining dissimilar metals is generally difficult, but since forming is carried out with the first structural member 10 and the second structural member 20 not joined, structural members 10 and 20 can be formed simultaneously even if they are made of different types of metals. For example, even if one of the structural members 10 and 20 is made of iron plate (steel plate) and the other is made of a non-ferrous metal plate such as an aluminum alloy plate, structural members 10 and 20 can be formed simultaneously.

[0300] In this embodiment, each of the first mold 31 and the second mold 32 is provided with a sealing portion 33. The sealing portion 33 of the first mold 31 and the sealing portion 33 of the second mold 32 are arranged to surround the molding surfaces 311 and 321, respectively. The sealing portion 33 can improve the liquid-tightness or airtightness of the hollow space formed between the molding surfaces 311 and 321. Specifically, when the first mold 31 and the second mold 32 are closed, the sealing portion 33 of the first mold 31 and the sealing portion 33 of the second mold 32 strongly abut and clamp the first blank 41 and the second blank 42, making it difficult for fluid to leak from between the first blank 41 and the second blank 42. Therefore, the molding of structural members 10 and 20 using fluid can be performed more effectively.

[0301] In this embodiment, a sealing portion 34 is further provided in each of the first mold 31 and the second mold 32. This sealing portion 34 allows the mold 30 to seal around the material 40 when the first mold 31 and the second mold 32 are closed. As a result, fluid leakage to the outside of the mold 30 is reduced, and the molding of the structural members 10 and 20 using fluid can be performed even more effectively.

[0302] <Second Embodiment> Figure 35 is a perspective view showing the schematic configuration of structural members 10A and 20A according to this embodiment. Structural members 10A and 20A are front frames for a vehicle body. In this case, structural members 10A and 20A are provided at the front and lower part of a vehicle body such as an automobile. The first structural member 10A is positioned above the second structural member 20A when incorporated into the vehicle body. The first structural member 10A is the front frame upper, and the second structural member 20A is the front frame lower. However, structural members 10A and 20A may also be subframes for a vehicle body. In this case, structural members 10A and 20A are provided at the front or rear and lower part of the vehicle body. The subframe can have a configuration that is generally similar to that of the front frame.

[0303] In this embodiment, the first structural member 10A includes a pair of side frames 11 and at least one cross member 12, similar to the first structural member 10 in the first embodiment. The first structural member 10A may include a plurality of cross members 12. In the example of Figure 35, the side frames 11 are connected by a cross member 12 at one end in their longitudinal direction. The cross member 12 is positioned, for example, at the rear end of the side frame 11 when the first structural member 10A is assembled to the vehicle body.

[0304] The second structural member 20A, like the second structural member 20 of the first embodiment, includes a pair of side frames 21 and at least one cross member 22. The second structural member 20A may include a plurality of cross members 22. In the example of Figure 35, the side frames 21 are connected by a cross member 22 at one end in their longitudinal direction. The cross member 22 is positioned, for example, at the rear end of the side frame 21 when the second structural member 20A is incorporated into the vehicle body.

[0305] Similar to the first embodiment, with the structural members 10A and 20A assembled to the vehicle body, the first structural member 10A is joined to the second structural member 20A. For example, the side frame 11 of the first structural member 10A is joined to the side frame 21 of the second structural member 20A. Also, for example, the cross member 12 of the first structural member 10A is joined to the cross member 22 of the second structural member 20A.

[0306] The manufacturing method described in the first embodiment can also be applied to the manufacturing of structural members 10A and 20A.

[0307] Referring to Figures 36A and 36B, in this embodiment, a material 40A including a first blank 41A and a second blank 42A is prepared. The basic configuration of the first blank 41A and the second blank 42A is the same as that of the first blank 41 and the second blank 42 (Figures 34A and 34B) used in the manufacturing method according to the first embodiment. However, since the shape of the first structural member 10A (Figure 35) is different from that of the first structural member 10 in the first embodiment, the first blank 41A has a different shape from the first blank 41. Similarly, since the shape of the second structural member 20A (Figure 35) is different from that of the second structural member 20 in the first embodiment, the second blank 42A has a different shape from the second blank 42.

[0308] The first blank 41A includes a region 411A that will become the first structural member 10A (Figure 35) and a region 412A outside the first structural member 10A. The second blank 42A includes a region 421A that will become the second structural member 20A (Figure 35) and a region 422A outside the second structural member 20A. In at least the regions 411A and 421A of the material 40A that will become the first structural member 10A and the second structural member 20A, the first blank 41A and the second blank 42A are not joined. In the regions 412A and 422A of the material 40A outside the structural members 10A and 20A, the first blank 41A and the second blank 42A may be joined (temporarily fixed) by, for example, spot welding.

[0309] Material 40A is subjected to a molding process similar to that of the first embodiment. Material 40A may also be subjected to the molding process after the heating process described above. In the molding process, material 40A is held in the first mold 31 and the second mold 32 (Figures 34C to 34F), and a fluid is supplied between the first blank 41A and the second blank 42A to deform the material 40A in the hollow space formed by the first mold 31 and the second mold 32. As a result, a first molded product is formed from the first blank 41A, and a second molded product is formed from the second blank 42A. The first molded product includes a first structural member 10A (Figure 35). The second molded product includes a second structural member 20A (Figure 35).

[0310] Specifically, as shown in Figures 34C to 34F, similar to the first embodiment, the projection 35 of the second mold 32 is inserted into the through hole 43 of the second blank 42A, and the material 40A (Figures 36A and 36B) is sandwiched between the first mold 31 and the second mold 32, creating a gap between the first blank 41A and the second blank 42A by the projection 35. The first mold 31 and the second mold 32 sandwich the areas 412A and 422A (Figures 36A and 36B) of the material 40A that are outside the structural members 10A and 20A. Then, fluid is injected from the projection 35 into the gap between the first blank 41A and the second blank 42A, and the fluid expands the material 40A within the hollow space of the mold 30. As a result, a first molded product including the first structural member 10A and a second molded product including the second structural member 20A can be obtained.

[0311] Referring to Figure 36C, the first and second molded products may be subjected to a trimming process similar to that of the first embodiment after the molding process. The trimming process may be carried out while the first and second molded products remain in the mold 30 (Figures 34C to 34F), or it may be carried out after the first and second molded products have been removed from the mold 30.

[0312] In the trimming process, the portion of the first blank 41A of the first molded product that was outside the first structural member 10A (region 412A) is removed. Similarly, the portion of the second blank 42A of the second molded product that was outside the second structural member 20A (region 422A) is removed. If the first blank 41A and the second blank 42A were joined (temporarily fixed), a joint would exist in the first and second molded products immediately after the molding process, but this joint is removed in the trimming process. This allows for the production of the first structural member 10A and the second structural member 20A, which is separate from the first structural member 10A.

[0313] After the trimming process, the first structural member 10A and the second structural member 20A may each be subjected to a painting process. The first structural member 10A and the second structural member 20A are joined together after undergoing necessary processes such as painting. This allows for the creation of a front frame for the vehicle body.

[0314] The same effects as in the first embodiment can be achieved when the manufacturing method described in the first embodiment is applied to the manufacturing of structural members 10A and 20A.

[0315] <Third Embodiment> Figure 37 is a perspective view showing the schematic configuration of structural members 10B and 20 according to this embodiment. The first structural member 10B is a member in which the floor panel for the vehicle body and the rear frame upper are integrated. The second structural member 20 is the rear frame lower.

[0316] In this embodiment, the first structural member 10B includes a pair of side frames 11 and at least one cross member 12, similar to the first structural member 10 in the first embodiment. The first structural member 10B may include a plurality of cross members 12. The first structural member 10B further includes a floor panel 13. The floor panel 13 is integrated with the side frames 11 and the cross members 12. The side frames 11 and the cross members 12 have a shape that protrudes from the floor panel 13 on the opposite side of the second structural member 20. The second structural member 20 has the same configuration as the second structural member 20 described in the first embodiment. Similar to the first embodiment, the first structural member 10B is joined to the second structural member 20 when the structural members 10B and 20 are assembled into the vehicle body.

[0317] The manufacturing method described in the first embodiment can also be applied to combinations of structural members 10B and 20.

[0318] Referring to Figures 38A and 38B, in this embodiment, a material 40B including a first blank 41B and a second blank 42 is prepared. The basic configuration of material 40B is the same as that of material 40 (Figures 34A and 34B) used in the manufacturing method according to the first embodiment. However, since the shape of the first structural member 10B (Figure 37) is different from that of the first structural member 10 in the first embodiment, the first blank 41B has a different shape from the first blank 41. The second blank 42 is substantially the same as the second blank 42 in the first embodiment.

[0319] The first blank 41B includes a region 411B that will become the first structural member 10B and a region 412B outside the first structural member 10B. Region 411B includes the portion of the first blank 41B that will be formed into the side frame 11 and the cross member 12 (Figure 37), as well as the portion that will be formed into the floor panel 13 (Figure 37). In the regions 411B and 421 of the material 40B that will become the first structural member 10B and the second structural member 20 (Figure 37), the first blank 41B and the second blank 42 are not joined. In the regions 412B and 422 of the material 40B outside the structural members 10B and 20, the first blank 41B and the second blank 42 may be joined (temporarily fixed) by, for example, spot welding.

[0320] The second blank 42 has a plurality of through holes 43, similar to the first embodiment. In the first embodiment, each through hole 43 is located in the middle of the second blank 42 in the longitudinal direction and at the end in the width direction. In contrast, in this embodiment, each through hole 43 is located at the ends of the second blank 42 in both the longitudinal and width directions. In this embodiment, the through holes 43 are located at the corners (four corners) of the second blank 42. The longitudinal direction of the second blank 42 corresponds to the vehicle length direction of the vehicle body on which the second structural member 20 is provided, and the width direction of the second blank 42 corresponds to the vehicle width direction of the vehicle body on which the second structural member 20 is provided.

[0321] Material 40B is subjected to a molding process similar to that of the first embodiment. Material 40B may also be subjected to the molding process after the heating process described above. In the molding process, material 40B is held in the first mold 31 and the second mold 32 (Figures 34C to 34F), and a fluid is supplied between the first blank 41B and the second blank 42 to deform the material 40B in the hollow space formed by the first mold 31 and the second mold 32. As a result, a first molded product is formed from the first blank 41B, and a second molded product is formed from the second blank 42. The first molded product includes a first structural member 10B (Figure 37). The second molded product includes a second structural member 20 (Figure 37).

[0322] Specifically, as shown in Figures 34C to 34F, similar to the first embodiment, the projection 35 of the second mold 32 is inserted into the through hole 43 of the second blank 42, and the material 40B (Figures 38A and 38B) is sandwiched between the first mold 31 and the second mold 32, creating a gap between the first blank 41B and the second blank 42 by the projection 35. The first mold 31 and the second mold 32 sandwich the areas 412B and 422 (Figures 38A and 38B) of the material 40B that are outside the structural members 10B and 20. Then, fluid is injected from the projection 35 into the gap between the first blank 41B and the second blank 42, and the fluid expands the material 40B in the hollow space of the mold 30. As a result, a first molded product including the first structural member 10B and a second molded product 52 including the second structural member 20 can be obtained.

[0323] Although not shown in the figures, the first and second molded products may be subjected to a trimming process similar to that of the first embodiment after the molding process. The trimming process may be performed while the first and second molded products remain inside the mold 30 (Figures 34C to 34F), or it may be performed after the first and second molded products have been removed from the mold 30.

[0324] In the trimming process, the portion of the first molded product, material 40B that was outside the first structural member 10B (region 412B), is removed. Similarly, the portion of the second molded product, material 40B that was outside the second structural member 20 (region 422), is removed. If the first blank 41B and the second blank 42 were joined (temporarily fixed) in material 40B, a joint will exist in the first and second molded products immediately after the molding process, but this joint is removed in the trimming process. This allows for the production of the first structural member 10B and the second structural member 20, which is separate from the first structural member 10B.

[0325] After the trimming process, the first structural member 10B and the second structural member 20 may each be subjected to a painting process. The first structural member 10B and the second structural member 20 are joined together after undergoing necessary processes such as the painting process.

[0326] The same effects as in the first embodiment can be achieved when the manufacturing method described in the first embodiment is applied to the manufacturing of structural members 10B and 20.

[0327] <Fourth Embodiment> Figure 39 is a perspective view showing the schematic configuration of structural members 10C and 20C according to this embodiment. Structural members 10C and 20C are door rings for a vehicle body. The first structural member 10C is positioned outside the second structural member 20C in the vehicle width direction when assembled into the vehicle body. The first structural member 10C is the door ring outer, and the second structural member 20C is the door ring inner.

[0328] The first structural member 10C may include an A-pillar 14, a B-pillar 15, and a rocker 16. The B-pillar 15 is positioned behind the A-pillar 14 when the first structural member 10C is incorporated into the vehicle body. The A-pillar 14 and B-pillar 15 are connected by the rocker 16. The A-pillar 14, B-pillar 15, and rocker 16 form an annular structure. The first structural member 10C may further include a C-pillar 17. The C-pillar 17 is positioned behind the B-pillar 15 when the first structural member 10C is incorporated into the vehicle body.

[0329] The second structural member 20C may include an A-pillar 24, a B-pillar 25, and a rocker 26. The B-pillar 25 is positioned behind the A-pillar 24 when the second structural member 20C is incorporated into the vehicle body. The A-pillar 24 and B-pillar 25 are connected by the rocker 26. The A-pillar 24, B-pillar 25, and rocker 26 form an annular structure. The second structural member 20C may further include a C-pillar 27. The C-pillar 27 is positioned behind the B-pillar 25 when the second structural member 20C is incorporated into the vehicle body.

[0330] Similar to the first embodiment, with the structural members 10C and 20C incorporated into the vehicle body, the first structural member 10C is joined to the second structural member 20C. For example, the A-pillar 14 of the first structural member 10C is joined to the A-pillar 24 of the second structural member 20C. Also, for example, the B-pillar 15 of the first structural member 10C is joined to the B-pillar 25 of the second structural member 20C. The rocker 16 of the first structural member 10C may be joined to the rocker 26 of the second structural member 20C. If the structural members 10C and 20C each include C-pillars 17 and 27, the C-pillars 17 and 27 may be joined to each other.

[0331] Although not shown in the illustration, the A-pillar 14, B-pillar 15, and rocker 16 of the first structural member 10C may each have a substantially hat-shaped cross-section in at least a portion of it. Similarly, the A-pillar 24, B-pillar 25, and rocker 26 of the second structural member 20C may each have a substantially hat-shaped cross-section in at least a portion of it. The C-pillars 17 and 27 may also have a substantially hat-shaped cross-section in at least a portion of it.

[0332] The manufacturing method described in the first embodiment can also be applied to the manufacturing of structural members 10C and 20C.

[0333] Referring to Figures 40A and 40B, in this embodiment, a material 40C including a first blank 41C and a second blank 42C is prepared. The basic configuration of the first blank 41C and the second blank 42C is the same as that of the first blank 41 and the second blank 42 (Figures 34C and 34B) used in the manufacturing method according to the first embodiment. However, since the shape of the first structural member 10C (Figure 39) is different from that of the first structural member 10 in the first embodiment, the first blank 41C has a different shape from the first blank 41. Similarly, since the shape of the second structural member 20C (Figure 39) is different from that of the second structural member 20 in the first embodiment, the second blank 42C has a different shape from the second blank 42.

[0334] The first blank 41C includes a region 411C that will become the first structural member 10C (Figure 39) and a region 412C outside the first structural member 10C. The second blank 42C includes a region 421C that will become the second structural member 20C (Figure 39) and a region 422C outside the second structural member 20C. In the regions 411C and 421C of the material 40C that will become the first structural member 10C and the second structural member 20C, the first blank 41C and the second blank 42C are not joined. In the regions 412C and 422C of the material 40C outside the structural members 10C and 20C, the first blank 41C and the second blank 42C may be joined (temporarily fixed) by, for example, spot welding.

[0335] Material 40C is subjected to a molding process similar to that of the first embodiment. Material 40C may be subjected to the molding process after the heating process described above. In the molding process, material 40C is held in the first mold 31 and the second mold 32 (Figures 34C to 34F), and a fluid is supplied between the first blank 41C and the second blank 42C to deform the material 40C in the hollow space formed by the first mold 31 and the second mold 32. As a result, a first molded product is formed from the first blank 41C, and a second molded product is formed from the second blank 42C. The first molded product includes a first structural member 10C (Figure 39). The second molded product includes a second structural member 20C (Figure 39).

[0336] Specifically, as shown in Figures 34C to 34F, similar to the first embodiment, the projection 35 of the second mold 32 is inserted into the through hole 43 of the second blank 42C, and the material 40C (Figures 40A and 40B) is sandwiched between the first mold 31 and the second mold 32, creating a gap between the first blank 41C and the second blank 42C by the projection 35. The first mold 31 and the second mold 32 sandwich the regions 412C and 422C (Figures 38A and 38B) of the material 40C that are outside the structural members 10C and 20C. Then, fluid is injected from the projection 35 into the gap between the first blank 41C and the second blank 42C, and the fluid expands the material 40C within the hollow space of the mold 30. As a result, a first molded product including the first structural member 10C and a second molded product including the second structural member 20C can be obtained.

[0337] Although not shown in the figures, the first and second molded products may be subjected to a trimming process similar to that of the first embodiment after the molding process. The trimming process may be performed while the first and second molded products remain inside the mold 30 (Figures 34C to 34F), or it may be performed after the first and second molded products have been removed from the mold 30.

[0338] In the trimming process, the portion of the first molded product that was outside the first structural member 10C (region 412C) in the material 40C is removed. Similarly, the portion of the second molded product that was outside the second structural member 20C (region 422C) in the material 40C is removed. If the first blank 41C and the second blank 42C were joined (temporarily fixed) in the material 40C, a joint will exist in the first and second molded products immediately after the molding process, but this joint is removed in the trimming process. This allows for the production of the first structural member 10C and the second structural member 20C, which is separate from the first structural member 10C.

[0339] After the trimming process, the first structural member 10C and the second structural member 20C may each be subjected to a painting process. The first structural member 10C and the second structural member 20C are joined together after undergoing necessary processes such as painting. This makes it possible to obtain a door ring for a vehicle body.

[0340] Even when the manufacturing method described in the first embodiment is applied to the manufacturing of structural members 10C and 20C, the same effects as in the first embodiment can be achieved.

[0341] <Fifth Embodiment> Figure 41 is a perspective view showing the schematic configuration of structural members 10D and 20D according to this embodiment. The first structural member 10D is a cross member. The second structural member 20D is a lid for a battery case used in a battery unit in the vehicle body. The second structural member 20D may also serve as a floor panel. In this embodiment, a plurality of first structural members 10D are provided on the second structural member 20D.

[0342] Each of the first structural members 10D extends in the vehicle width direction when incorporated into the vehicle body. Each of the first structural members 10D can have the same configuration as the cross member 12 of the first structural member 10 in the first embodiment (Figure 31). Each of the first structural members 10D is positioned on the second structural member 20D and joined to the second structural member 20D.

[0343] The manufacturing method described in the first embodiment can also be applied to the manufacturing of structural members 10D and 20D.

[0344] Referring to Figures 42A and 42B, in this embodiment, a material 40D is prepared that includes a plurality of first blanks 41D and second blanks 42D. The basic configuration of the first blanks 41D and second blanks 42D is the same as that of the first blanks 41 and 2 blanks 42 (Figures 34A and 34B) used in the manufacturing method according to the first embodiment. However, since the shape of the first structural member 10D (Figure 41) is different from that of the first structural member 10 in the first embodiment, the first blank 41D has a different shape from the first blank 41. Similarly, since the shape of the second structural member 20D (Figure 41) is different from that of the second structural member 20 in the first embodiment, the second blank 42D has a different shape from the second blank 42.

[0345] Each of the first blanks 41D includes a region 411D that will become the first structural member 10D and a region 412D outside the first structural member 10D. The second blank 42D includes a region 421D that will become the second structural member 20D and a region 422D outside the second structural member 20D. In at least the regions 411D and 421D of the material 40D that will become the first structural member 10D and the second structural member 20D, the first blank 41D and the second blank 42D are not joined. In the regions 412D and 422D of the material 40D outside the structural members 10D and 20D, the first blank 41D and the second blank 42D may be joined (temporarily fixed) by, for example, spot welding.

[0346] The material 40D is subjected to a molding process similar to that of the first embodiment. The material 40D may also be subjected to the molding process after the heating process described above. As shown in Figure 42C, in the molding process, the material 40D is held in the first mold 31 and the second mold 32, and a fluid is supplied between the first blank 41D and the second blank 42D to deform the material 40D in the hollow space formed by the first mold 31 and the second mold 32. As a result, a first molded product 51D is formed from each first blank 41D, and a second molded product 52D is formed from the second blank 42D. The first molded product 51D includes a first structural member 10D. The second molded product 52D includes a second structural member 20D.

[0347] Specifically, as shown in Figures 34C to 34F, similar to the first embodiment, the projection 35 of the second mold 32 is inserted into the through hole 43 of the second blank 42D, and the material 40D (Figure 42C) is sandwiched between the first mold 31 and the second mold 32, with the projection 35 creating a gap between each of the first blank 41D and the second blank 42D. The first mold 31 and the second mold 32 sandwich the areas 412D and 422D (Figures 42A and 42B) of the material 40D that are outside the structural members 10D and 20D. Then, fluid is injected from the projection 35 into the gap between each of the first blank 41D and the second blank 42D, and the fluid expands the material 40D within the hollow space of the mold 30. This makes it possible to obtain a first molded product 51D (Figure 42C) including a first structural member 10D and a second molded product 52D (Figure 42C) including a second structural member 20D.

[0348] Although not shown in the illustration, the first molded product 51D and the second molded product 52D may be subjected to a trimming process similar to that of the first embodiment after the molding process. The trimming process may be carried out while the first molded product 51D and the second molded product 52D are still inside the mold 30, or it may be carried out after the first molded product 51D and the second molded product 52D have been removed from the mold 30.

[0349] In the trimming process, the portion of the first molded product 51D that was outside the first structural member 10D in the material 40D (region 412D) is removed. Similarly, the portion of the second molded product 52D that was outside the second structural member 20D in the material 40D (region 422D) is removed. If the first blank 41D and the second blank 42D were joined (temporarily fixed) in the material 40D, a joint exists between the first molded product 51D and the second molded product 52D, but this joint is removed in the trimming process. This allows for the production of the first structural member 10D and the second structural member 20D, which is separate from the first structural member 10D.

[0350] After the trimming process, the first structural member 10D and the second structural member 20D may each be subjected to a painting process. The first structural member 10D and the second structural member 20D are joined together after undergoing necessary processes such as the painting process.

[0351] The same effects as in the first embodiment can be achieved when the manufacturing method described in the first embodiment is applied to the manufacturing of structural members 10D and 20D.

[0352] <Sixth Embodiment> Figure 43 is a cross-sectional view showing the schematic configuration of structural members 10E and 20E according to this embodiment. Structural members 10E and 20E are battery cases used for the battery unit in the vehicle body. The first structural member 10E is the lid of the battery case. The second structural member 20E may also serve as a floor panel. The second structural member 20E is the main body of the battery case.

[0353] The second structural member 20E has, for example, a tray-like shape with a recess at the bottom. The second structural member 20E has an opening on its upper surface. The first structural member 10E seals the opening of the second structural member 20E. The first structural member 10E is joined to the second structural member 20E.

[0354] The manufacturing method described in the first embodiment can also be applied to the manufacturing of structural members 10E and 20E.

[0355] Referring to Figures 44A and 44B, in this embodiment, a material 40E is prepared, including a first blank 41E and a second blank 42E. The basic configuration of the first blank 41E and the second blank 42E is the same as that of the first blank 41 and the second blank 42 (Figures 34A and 34B) used in the manufacturing method according to the first embodiment. However, since the shape of the first structural member 10E (Figure 43) is different from that of the first structural member 10 in the first embodiment, the first blank 41E has a different shape from the first blank 41. Similarly, since the shape of the second structural member 20E (Figure 43) is different from that of the second structural member 20 in the first embodiment, the second blank 42E has a different shape from the second blank 42.

[0356] The first blank 41E includes a region 411E that will become the first structural member 10E (Figure 43) and a region 412E outside the first structural member 10E. The second blank 42E includes a region 421E that will become the second structural member 20E (Figure 43) and a region 422E outside the second structural member 20E. In the regions 411E and 421E of the material 40E that will become the first structural member 10E and the second structural member 20E, the first blank 41E and the second blank 42E are not joined. In the regions 412E and 422E of the material 40E outside the structural members 10E and 20E, the first blank 41E and the second blank 42E may be joined (temporarily fixed) by, for example, spot welding.

[0357] Similar to the third embodiment, in this embodiment, each through-hole 43 is located at the longitudinal and widthwise ends of the second blank 42E. The through-holes 43 are located at the corners (four corners) of the second blank 42E. The longitudinal direction of the second blank 42E corresponds to the vehicle length direction of the vehicle body on which the second structural member 20E is provided, and the width direction of the second blank 42E corresponds to the vehicle width direction of the vehicle body on which the second structural member 20E is provided.

[0358] The material 40E is subjected to a molding process similar to that of the first embodiment. The material 40E may be subjected to the molding process after the heating process described above. As shown in Figure 44C, in the molding process, the material 40E is held in the first mold 31 and the second mold 32, and a fluid is supplied between the first blank 41E and the second blank 42E, thereby inflating the material 40E in the hollow space formed by the first mold 31 and the second mold 32. This forms the first molded product 51E from the first blank 41E and the second molded product 52E from the second blank 42E. The first molded product 51E includes the first structural member 10E. The second molded product 52E includes the second structural member 20E.

[0359] Specifically, as shown in Figures 34C to 34F, similar to the first embodiment, the projection 35 of the second mold 32 is inserted into the through hole 43 of the second blank 42E, and the material 40E (Figures 44A and 44B) is sandwiched between the first mold 31 and the second mold 32, creating a gap between the first blank 41E and the second blank 42E by the projection 35. The first mold 31 and the second mold 32 sandwich the areas 412E and 422E (Figures 44A and 44B) of the material 40E that are outside the structural members 10E and 20E. Then, fluid is injected from the projection 35 into the gap between the first blank 41E and the second blank 42E, and the fluid expands the material 40E within the hollow space of the mold 30. This makes it possible to obtain a first molded product 51E (Figure 44C) including a first structural member 10E and a second molded product 52E including a second structural member 20E (Figure 44C).

[0360] Although not shown in the illustration, the first molded product 51E and the second molded product 52E may be subjected to a trimming process similar to that of the first embodiment after the molding process. The trimming process may be carried out while the first molded product 51E and the second molded product 52E are still inside the mold 30, or it may be carried out after the first molded product 51E and the second molded product 52E have been removed from the mold 30.

[0361] In the trimming process, the portion of the first molded product 51E that was outside the first structural member 10E in the raw material 40E (region 412E) is removed. Similarly, the portion of the second molded product 52E that was outside the second structural member 20E in the raw material 40E (region 422E) is removed. If the first blank 41E and the second blank 42E were joined (temporarily fixed) in the raw material 40E, a joint exists between the first molded product 51E and the second molded product 52E, but this joint is removed in the trimming process. This allows for the production of the first structural member 10E and the second structural member 20E, which is separate from the first structural member 10E.

[0362] After the trimming process, the first structural member 10E and the second structural member 20E may each be subjected to a painting process. The first structural member 10E and the second structural member 20E are joined together after undergoing necessary processes such as the painting process.

[0363] The same effects as in the first embodiment can be achieved when the manufacturing method described in the first embodiment is applied to the manufacturing of structural members 10E and 20E.

[0364] <Seventh Embodiment> Figure 45 is a cross-sectional view showing an example of structural members 10F and 20F in this embodiment. Figure 46 is a cross-sectional view showing another example of structural members 10F and 20F in this embodiment. Structural members 10F and 20F are members used in the vehicle body, for example, as patch materials or bracket parts.

[0365] Referring to Figure 45, the first structural member 10F has, for example, a substantially L-shape in cross-sectional view. The first structural member 10F may include flat plate portions 18 and 19. Flat plate portion 18 is connected to flat plate portion 19 via a bent portion. Similarly, the second structural member 20F has, for example, a substantially L-shape in cross-sectional view. The second structural member 20F may include flat plate portions 28 and 29. Flat plate portion 28 is connected to flat plate portion 29 via a bent portion.

[0366] Referring to Figure 46, the first structural member 10F may also include two flat plate sections 19. In this case, the flat plate sections 19 are connected by a flat plate section 18. Similarly, the second structural member 20F may also include two flat plate sections 29. In this case, the flat plate sections 29 are connected by a flat plate section 28.

[0367] The manufacturing method described in the first embodiment can also be applied to the production of such structural members 10F and 20F. That is, by the manufacturing method described in the first embodiment, multiple first structural members 10F and multiple second structural members 20F can be molded simultaneously.

[0368] Referring to Figures 47A and 47B, in this embodiment, a material 40F is prepared that includes a plurality of first blanks 41F and second blanks 42F. In this embodiment, the material 40F includes the first blank 41F. The basic configuration of the first blank 41F and the second blank 42F is the same as that of the first blank 41 and the second blank 42 (Figures 34A and 34B) used in the manufacturing method according to the first embodiment. However, since the shape of the first structural member 10F (Figures 45 and 46) is different from that of the first structural member 10 in the first embodiment, the first blank 41F has a different shape from the first blank 41. Similarly, since the shape of the second structural member 20F (Figures 45 and 46) is different from that of the second structural member 20 in the first embodiment, the second blank 42F has a different shape from the second blank 42.

[0369] Each of the first blanks 41F includes a region 411F that will become the first structural member 10F (Figures 45 and 46) and a region 412F outside the first structural member 10F. The second blank 42F includes a region 421F that will become the second structural member 20F (Figures 45 and 46) and a region 422F outside the second structural member 20F. The second blank 42F has multiple regions 421F corresponding to multiple second structural members 20F. In this embodiment, a first blank 41F is prepared for each first structural member 10F, while a common second blank 42F is prepared for multiple second structural members 20F.

[0370] In the regions 411F and 421F of the material 40F that will become at least the first structural member 10F and the second structural member 20F, the first blank 41F and the second blank 42F are not joined. In the regions 412F and 422F of the material 40F that are outside the structural members 10F and 20F, the first blank 41F and the second blank 42F may be joined (temporarily fixed) by, for example, spot welding.

[0371] The material 40F is subjected to a molding process similar to that of the first embodiment. The material 40F may be subjected to the molding process after the heating process described above. As shown in Figure 47C, in the molding process, the material 40F is held in the first mold 31 and the second mold 32, and a fluid is supplied between the first blank 41F and the second blank 42F to deform the material 40F in the hollow space formed by the first mold 31 and the second mold 32. As a result, a first molded product 51F is formed from each of the first blanks 41F, and a second molded product 52F is formed from the second blank 42F. Each of the first molded products 51F contains a first structural member 10F. The second molded product 52F contains a plurality of second structural members 20F.

[0372] Specifically, as shown in Figures 34C to 34F, similar to the first embodiment, the projection 35 of the second mold 32 is inserted into the through hole 43 of the second blank 42F, and the material 40F (Figures 47A and 47B) is sandwiched between the first mold 31 and the second mold 32, with the projection 35 creating a gap between each of the first blank 41F and the second blank 42F. The first mold 31 and the second mold 32 sandwich the regions 412F and 422F (Figures 47A and 47B) of the material 40F that are outside the structural members 10F and 20F. Then, fluid is injected from the projection 35 into the gap between each of the first blank 41F and the second blank 42F, and the fluid expands the material 40F within the hollow space of the mold 30. This makes it possible to obtain a first molded product 51F (Figure 47C) including a first structural member 10F and a second molded product 52F (Figure 47C) including a second structural member 20F.

[0373] Multiple first molded products 51F and second molded products 52F may be subjected to a trimming process similar to that in the first embodiment after the molding process. The trimming process may be carried out while the first molded products 51F and second molded products 52F remain inside the mold 30, or it may be carried out after the first molded products 51F and second molded products 52F have been removed from the mold 30.

[0374] In the trimming process, the portion of each first molded product 51F that was outside the first structural member 10F in the material 40F is removed. From each first molded product 51F, the first structural member 10F with the shape shown in Figure 45 or Figure 46 is obtained. In addition, the portion of the second molded product 52F that was outside the second structural member 20F in the material 40F is removed. From the second molded product 52F, multiple second structural members 20F with the shape shown in Figure 45 or Figure 46 are obtained.

[0375] If the first blank 41F and the second blank 42F are joined (temporarily fixed) in material 40F, a joint exists in the first molded product 51F and the second molded product 52F, but this joint is removed in the trimming process. As a result, multiple first structural members 10F and multiple second structural members 20F, which are separate from the first structural member 10F, can be obtained.

[0376] After the trimming process, the first structural member 10F and the second structural member 20F may each be subjected to a painting process. After undergoing necessary processes such as the painting process, the first structural member 10F and the second structural member 20F are joined to a predetermined member.

[0377] The same effects as in the first embodiment can be achieved when the manufacturing method described in the first embodiment is applied to the manufacturing of structural members 10F and 20F.

[0378] In this embodiment, a first blank 41F is prepared for each first structural member 10F, while a common second blank 42F is prepared for multiple second structural members 20F. When multiple second structural members 20F are formed from a common second blank 42F, the material flow is restricted compared to when each first structural member 10F is formed from a separate first blank 41F. Therefore, it is preferable that the molding height H2 of the second structural member 20F is smaller than the molding height H1 of the first structural member 10F.

[0379] <Eighth Embodiment> The manufacturing method according to each embodiment may also use the mold 30A shown in Figure 48. Figure 48 is a cross-sectional view of the mold 30A. In this embodiment, an example of the mold 30A for manufacturing the structural members 10 and 20 of the first embodiment is described. However, the mold 30A can also be applied to the manufacturing of structural members of other embodiments.

[0380] Referring to Figure 48, mold 30A differs from mold 30 of other embodiments (Figure 32) in that it is provided with a positioning pin 38. In mold 30A, one of the first mold 31A and the second mold 32A includes the positioning pin 38. The other of the first mold 31A and the second mold 32A includes a recess 39.

[0381] In this embodiment, the second mold 32A includes a positioning pin 38. The positioning pin 38 is provided on the surface of the second mold 32A facing the first mold 31A. The positioning pin 38 protrudes from this surface toward the first mold 31A. The positioning pin 38 may also be provided on the flange surface 322.

[0382] On the other hand, the first mold 31A includes a recess 39. The recess 39 is located on the surface of the first mold 31A facing the second mold 32A, at a position corresponding to the positioning pin 38. The recess 39 may also be provided on the flange surface 312.

[0383] Figure 48 partially shows the longitudinal section of the mold 30A passing through the center of gravity of the molding surface 321 of the second mold 32A and the fluid supply port 36. The center of gravity of the molding surface 321 refers to the center of gravity of the shape when the molding surface 321 is projected in the processing direction D. Looking at the longitudinal section of the mold 30A passing through the center of gravity of the molding surface 321 and the fluid supply port 36, the positioning pin 38 is positioned outside the molding surface 321 beyond the fluid supply port 36. The seal portion 33 of the second mold 32A includes the portion passing between the fluid supply port 36 and the positioning pin 38.

[0384] Referring to Figures 49A and 49B, it is preferable to use the mold 30A when the first blank 41 and the second blank 42 are not joined at all in the material 40. In this case, a notch 44 is provided at the edge of the part of the material 40 where the first blank 41 and the second blank 42 overlap. During the molding process, a positioning pin 38 is placed in the notch 44 of the material 40. This makes it less likely for the first blank 41 and the second blank 42 to be misaligned, even when they are not joined (temporarily fixed) and are independent. The positioning pin 38 is housed in the recess 39 when the first mold 31A and the second mold 32A are closed.

[0385] After the molding process, the first molded product 51 formed from the first blank 41 and the second molded product 52 formed from the second blank 42 are discharged from the mold 30A. The first molded product 51 and the second molded product 52 may be discharged individually from the mold 30A, or they may be discharged simultaneously. When the first molded product 51 and the second molded product 52 are discharged simultaneously from the mold 30A, the lower mold of the first mold 31A and the second mold 32A may be provided with a recess for inserting, for example, an arm of a transport mechanism.

[0386] For example, by providing a recess in the flange surface 322 of the second mold 32, the arm of the transport mechanism can be inserted below the second molded product 52 and the arm can grip the second molded product 52. The first molded product 51 may be removed from the mold 30A together with the second molded product 52 while it is placed on top of the second molded product 52, or it may be removed from the mold 30A while being gripped together with the second molded product 52. If a trimming process is performed in the mold 30A, both structural members 10 and 20 (Figure 34F) after the trimming process may be gripped by the arm of the transport mechanism, etc., and removed from the mold 30A at the same time, or the structural members 10 and 20 may be removed from the mold 30A separately.

[0387] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0388] In the embodiments described above, examples were given in which a projection 35 having a fluid supply port 36 is provided on the second mold 32, 32A. However, the projection 35 may also be provided on the first mold 31, 31A. The projection 35 only needs to be provided in the first mold 31, 31A or the second mold 32, 32A at a position that can supply fluid to the hollow space of the mold 30, 30A. When the projection 35 is provided on the first mold 31, 31A, the through holes 43 are formed in the first blanks 41, 41A, 41F, respectively, in the materials 40, 40A to 40F.

[0389] In the embodiments described above, examples were given in which the second molds 32, 32A are positioned below the first molds 31, 31A. However, the positional relationship between the first molds 31, 31A and the second molds 32, 32A is not limited thereto. When manufacturing structural members 10, 10A~10F, 20, 20A, 20C~20F, the second molds 32, 32A may be positioned above the first molds 31, 31A, for example. The projection 35 may be provided on the mold positioned below the first molds 31, 31A and the second molds 32, 32A, or on the mold positioned above. When the upper of the first molds 31, 31A and the second molds 32, 32A is provided with a projection 35, the materials 40, 40A to 40F are not placed on the projection 35 during the molding process, so the materials 40, 40A to 40F can be stably positioned before the molds 31, 31A and the second molds 32, 32A are closed. Therefore, it is not necessary to provide a flat tip surface 351 on the projection 35 for positioning the materials 40, 40A to 40F.

[0390] In each of the above embodiments, sealing portions 33 and 34 are provided in both the first mold 31, 31A and the second mold 32, 32A. However, the sealing portions 33 and / or 34 may not be provided in either the first mold 31, 31A or the second mold 32, 32A, and the sealing portions 33 and 34 may not be provided in either the first mold 31, 31A or the second mold 32, 32A. However, from the viewpoint of preventing fluid leakage, it is preferable that at least the sealing portions 33 are provided in both the first mold 31, 31A and the second mold 32, 32A. More preferably, the sealing portions 33 and 34 are provided in a double configuration in both the first mold 31, 31A and the second mold 32, 32A.

[0391] In each of the above embodiments, a gap is created between the first blank 41 and each of the second blanks 42 by projections 35 provided on the molds 30 and 30A, thereby securing a fluid passage. However, the molds 30 and 30A do not necessarily have projections 35. In the molding process, with the material 40, 40A to 40F held between the first blanks 41, 41A to 41F and the second blanks 42, 42A, 42C to 42F, fluid is supplied, and the material 40, 40A to 40F is deformed within the hollow space of the molds 30 and 30A by this fluid, thereby forming the first and second molded products. For example, fluid can also be supplied into the hollow space at positions within the material 40, 40A to 40F that will become the first structural members 10, 10A to 10F or the second structural members 20, 20A, 20C to 20F.

[0392] In the embodiments described above, examples were given in which a trimming process is performed after the molding process. However, the manufacturing methods according to each embodiment do not necessarily include a trimming process. For example, if the first molded product formed in the molding process becomes the first structural members 10, 10A to 10F as is, trimming of the first molded product is unnecessary. Similarly, if the second molded product formed in the molding process becomes the second structural members 20, 20A, 20C to 20F as is, trimming of the second molded product is unnecessary.

[0393] The manufacturing method described herein is not limited to the application of the first structural members 10, 10A to 10F and the second structural members 20, 20A, 20C to 20F described in each embodiment. The manufacturing method can be applied to the manufacture of various structural members.

[0394] (Elemental Technology D1) Element technology D1 is a structural member comprising a lid for a battery case, a top plate facing the lid at a distance from it, two vertical walls connected to the top plate via their edges, and two flanges connected to the vertical walls on the opposite side of the top plate and joined to the lid, and a cross member extending in the width direction of the lid, wherein the rate of reduction in plate thickness at the center of the top plate, based on the plate thickness of the flanges, is 2.0% or more and 30.0% or less.

[0395] According to elemental technology D1, it is possible to provide a structural member for a vehicle body that can reduce the number of parts in the battery unit and its surrounding structure.

[0396] Embodiments of this disclosure will be described below with reference to the drawings. In these drawings, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0397] [Structural members] Figure 50 is a perspective view showing the schematic configuration of the structural member 10 according to this embodiment. Referring to Figure 50, the structural member 10 is used in the body of a vehicle such as an electric vehicle or a hybrid vehicle. The structural member 10 comprises a lid 111 for the battery case 11 and at least one cross member 12.

[0398] The lid 111 constitutes part of the battery case 11. The lid 111 is attached to the main body 112 of the battery case 11. The case body 112 may, for example, have a tray shape. The case body 112 has a concave shape on the bottom when the battery case 11 is mounted on the vehicle body. Multiple battery cells (not shown) are arranged inside the case body 112. The lid 111 is attached to the case body 112 so as to seal the opening of the case body 112. The lid 111 may have a flat shape or an uneven shape.

[0399] In this embodiment, the structural member 10 comprises a plurality of cross members 12. Each of the cross members 12 is positioned on the lid 111. Each of the cross members 12 is positioned on the upper surface 111a of the lid 111.

[0400] The cross members 12 are arranged in parallel with space between them. Each cross member 12 extends substantially in the width direction of the cover 111. The width direction of the cover 111 substantially coincides with the left-right direction (vehicle width direction) of the vehicle body to which the structural member 10 is applied. That is, each of the cross members 12 extends in the vehicle width direction when the structural member 10 is attached to the vehicle body. Each of the cross members 12 may extend in the width direction of the cover 111 such that at least one end in its longitudinal direction protrudes outward from the cover 111. In this embodiment, both longitudinal ends of each cross member 12 protrude outward from the cover 111.

[0401] The cover 111 and the cross member 12 are each formed from a metal plate. Preferably, the cover 111 and the cross member 12 are each formed from a steel plate. The material of the cross member 12 may be the same as or different from the material of the cover 111.

[0402] The cover 111 is made of, for example, a plated steel sheet. Preferably, the cover 111 is made of an aluminum-based plated steel sheet. Each of the cross members 12 may be made of a steel sheet without a plating layer (bare material), or it may be made of a plated steel sheet such as an aluminum-based plated steel sheet. Known aluminum-based plated steel sheets can be used. When both the cover 111 and the cross members 12 are made of aluminum-based plated steel sheets, the amount of aluminum-based plating on the cover 111 may be greater than the amount of aluminum-based plating on the cross members 12.

[0403] Figure 51 is a cross-sectional view of structural member 10 shown in Figure 50, taken along line II-II. In Figure 51, a cross-section (transverse plane) of structural member 10 perpendicular to the longitudinal direction of the cross member 12 (the width direction of the cover 111) is shown.

[0404] Referring to Figure 51, each cross member 12 is separate from the other cross members 12. Each cross member 12 has a substantially hat shape in cross view. Each cross member 12 includes a top plate 121, two vertical walls 122a, 122b, and two flanges 123a, 123b. Each cross member 12 further includes ridge sections 124a, 124b, 125a, 125b.

[0405] The top plate 121 faces the cover 111 with a gap between them. When the structural member 10 is attached to the vehicle body, the top plate 121 faces the upper surface 111a of the cover 111 in the vertical direction (vehicle height direction) of the vehicle body. In a cross-sectional view of the structural member 10, the top plate 121 extends substantially in the longitudinal direction (vehicle length direction) of the vehicle body. The top plate 121 may be flat overall, or it may have recesses or protrusions. Ridge portions 124a and 124b are continuously provided on both sides of the top plate 121.

[0406] The vertical walls 122a and 122b are connected to the top plate 121 via ridge sections 124a and 124b, respectively. That is, ridge section 124a is the corner between the top plate 121 and the vertical wall 122a. Ridge section 124b is the corner between the top plate 121 and the vertical wall 122b. The ridge sections 124a and 124b may have an arc shape in a cross-sectional view of the structural member 10. In a cross-sectional view of the structural member 10, the vertical walls 122a and 122b extend from the top plate 121 toward the lid 111. The vertical walls 122a and 122b may be parallel to each other or non-parallel to each other.

[0407] The flanges 123a and 123b are connected to the vertical walls 122a and 122b, respectively, on the opposite side of the top plate 121. In this embodiment, one flange 123a is connected to the vertical wall 122a via a ridge portion 125a. The other flange 123b is connected to the vertical wall 122b via a ridge portion 125b. That is, the ridge portion 125a is the corner portion between the vertical wall 122a and the flange 123a. The ridge portion 125b is the corner portion between the vertical wall 122b and the flange 123b. The ridge portions 125a and 125b can have an arc shape in a cross-sectional view of the structural member 10.

[0408] The flanges 123a and 123b protrude outward from the vertical walls 122a and 122b. The flanges 123a and 123b are joined to the cover 111. The flanges 123a and 123b are joined to the cover 111, for example, by welding. The flanges 123a and 123b may be joined to the cover 111 by spot welding or the like, or by laser welding or the like.

[0409] The flanges 123a and 123b have a width W. The width W is the length of the surface of the flanges 123a and 123b that is in contact with the cover 111 in a cross-sectional view of the structural member 10. The width W is, for example, 20.0 mm or more and 40.0 mm or less. In each cross member 12, the width W of flange 123a may be the same as or different from the width W of flange 123b. The width W of flanges 123a and 123b in each cross member 12 may be the same as or different from the width W of flanges 123a and 123b in other cross members 12.

[0410] Each of the cross members 12 has a height H. The height H is the maximum distance in the thickness direction of the flanges 123a and 123b from the contact surface of the flanges 123a and 123b with respect to the cover 111 to the outer surface of the top plate 121. The height H is, for example, 20.0 mm or more, preferably 40.0 mm or more, and more preferably 60.0 mm or more. The height H may also be 100.0 mm or less. The height H of each cross member 12 is preferably the same as the height H of the other cross members 12, but they may be different.

[0411] [Method for manufacturing structural members] Figures 52A to 52E are schematic diagrams illustrating an example of a manufacturing method for the structural member 10. The manufacturing method for the structural member 10 includes, for example, a preparation step, a heating step, and a molding step.

[0412] (preparation process) As shown in Figures 52A and 52B, the preparation step involves preparing the material 20. The material 20 includes a first blank 21 and at least one second blank 22. In this embodiment, the material 20 includes a plurality of second blanks 22.

[0413] The first blank 21 is a blank corresponding to the lid 111 for the battery case 11 (Figures 50 and 51). The second blank 22 is a blank corresponding to the cross member 12 (Figures 50 and 51). The second blank 22 is superimposed on the first blank 21.

[0414] Each of the second blanks 22 is joined to the first blank 21. More specifically, the outer periphery of each second blank 22 is joined to the first blank 21, for example, by welding. The outer periphery of each second blank 22 may be joined to the first blank 21 by spot welding or by laser welding.

[0415] The first blank 21 or each of the second blanks 22 may have through holes 23. In this embodiment, the first blank 21 has a plurality of through holes 23. The through holes 23 are formed in the first blank 21 at positions corresponding to both ends in the longitudinal direction of each of the second blanks 22. The through holes 23 may be formed in the first blank 21 at positions corresponding to one end in the longitudinal direction of each of the second blanks 22. Instead of the first blank 21, through holes 23 can also be formed in each of the second blanks 22.

[0416] Each second blank 22 is joined to the first blank 21 at least near the through hole 23, in a portion of the cross member 12 where the height H (Figure 51) is relatively small. In order to ensure the amount of material flow in the molding process described later, each second blank 22 does not need to be joined to the first blank 21 in a portion of the cross member 12 where the height H is relatively large. The first blank 21 and the second blank 22 may each be formed from a single metal plate, or they may include multiple metal plates (subblanks). The metal plate is preferably a steel plate. The steel plate is, for example, a plated steel plate such as an aluminum-plated steel plate. The material of the first blank 21 may be the same as or different from the material of the second blank 22.

[0417] (Heating process) In the heating process, the material 20, including the first blank 21 and the second blank 22, is heated using, for example, a heating furnace. If the first blank 21 and the second blank 22 are each formed from one or more steel plates, the first blank 21 and the second blank 22 are heated to the austenite transformation completion temperature (A c3 It is heated to a temperature of 1.5°C or higher.

[0418] (molding process) As shown in Figures 52C to 52E, in the molding process, the heated material 20 is molded into a structural member 10. In the molding process, hot stamping and blow molding or hydraulic molding are used in combination to mold the material 20 into a structural member 10.

[0419] In the molding process, for example, a mold 30 including a first mold 31 and a second mold 32 can be used. The mold 30 is used, for example, by being mounted on a known press device. Figures 52C to 52E show cross-sections (transverse views) of the material 20 and the mold 30 perpendicular to the longitudinal direction of the second blank 22.

[0420] Referring to Figure 52C, in the molding process, first, the first mold 31 and the second mold 32 are separated, and the material 20 is placed between the first mold 31 and the second mold 32. If the first mold 31 is positioned below the second mold 32, the material 20 may be placed on top of the first mold 31. Then, the first mold 31 and the second mold 32 are brought relatively close together, and a portion of the material 20 is held between the first mold 31 and the second mold 32.

[0421] Referring to Figure 52D, when the first mold 31 and the second mold 32 are closed, the area of ​​the material 20 other than the area that will become the main body of the cross member 12 (Figures 50 and 51) is sandwiched between the first mold 31 and the second mold 32. The main body of the cross member 12 is the part of the cross member 12 that has a shape that protrudes from the lid 111 (Figures 50 and 51), and is composed of, for example, the top plate 121, the vertical walls 122a, 122b, and the ridge portions 124a, 124b, 125a, 125b (Figures 50 and 51). At the location of the area of ​​the material 20 that will become the main body of the cross member 12 (Figures 50 and 51), the first mold 31 and the second mold 32 form a hollow space.

[0422] Referring to Figure 52E, fluid is then supplied between the first blank 21 and each of the second blanks 22, causing the second blanks 22 to expand within the hollow space. The fluid is supplied between the first blank 21 and each of the second blanks 22, for example, through a through hole 23 (Figure 52B). After each of the second blanks 22 has expanded within the hollow space by the fluid, it is pressed against the molding surface 321 of the second mold 32. This forms each second blank 22 into a cross member 12. The first blank 21 is formed into a lid 111 by the molding surface 311 of the first mold 31. The lid 111 and each of the cross members 12 are cooled and hardened by contact with the first mold 31 and the second mold 32.

[0423] The fluid used in the molding process is not particularly limited. The fluid may be a liquid such as water, or a gas such as nitrogen gas or compressed air. The fluid may be a liquid or gas under high pressure, for example, 10 MPa or higher. The temperature of the fluid may be appropriately determined according to the material of the material 20, and may be, for example, room temperature. If a heating process is performed, i.e., when molding is performed by hot stamping, the fluid may be heated.

[0424] The structural member 10 can be obtained through the process described above. After the molding process, the outer periphery of the structural member 10 may be removed by laser cutting or the like. For example, at least the portion of the structural member 10 in which through holes 23 (Figure 52B) are provided may be removed after the molding process. In this embodiment, through holes 23 (Figure 52B) for fluid supply are provided in the first blank 21 at positions corresponding to both ends in the longitudinal direction of the second blank 22. Therefore, a portion of the structural member 10 can be removed at these positions after the molding process.

[0425] Figure 53 is a partial cross-sectional view of the structural member 10 after the molding process, for example, after the removal of the outer periphery, which has resulted in its final shape.

[0426] In this embodiment, each of the cross members 12 is formed by fluid-assisted deep drawing (hydraulic or blow molding). By performing hot hydraulic or blow molding, each cross member 12 has a different thickness distribution than when each cross member 12 is formed by general press molding or the like. Specifically, in each cross member 12, the thickness reduction rate at the center of the top plate 121 is 2.0% or more and 30.0% or less. The thickness reduction rate at the center of the top plate 121 may be 3.5% or more. The center of the top plate 121 is the part of the top plate 121 located at the center in the vehicle length direction when viewed in cross-section of the cross member 12.

[0427] The rate of thickness reduction at the center of the top plate 121 is the rate of thickness reduction based on the thickness of flanges 123a and 123b. Flanges 123a and 123b are parts of the cross member 12 where thickness reduction is less likely to occur during the molding process. In other words, the rate of thickness reduction based on the thickness of flanges 123a and 123b corresponds to the rate of thickness reduction from the raw material 20 before the molding process (Figures 52A and 52B).

[0428] When the thickness of flange 123a is t0 and the thickness of the center of top plate 121 is t1, the percentage reduction in thickness at the center of top plate 121 can be calculated as {(t0-t1) / t0}×100. The thicknesses t0 of flanges 123a and 123b, and the thickness t1 at the center of top plate 121 can be measured by cutting the cross member 12, which has been removed from the vehicle body, perpendicular to its longitudinal direction, and measuring the cross section of this cross member 12 using, for example, a micrometer. The thicknesses t0 and t1 are measured at the part of the cross member 12 with the maximum height H, and at the outermost position in the longitudinal direction (vehicle width direction). The thickness t0 of flanges 123a and 123b is measured at the flat portion of flanges 123a and 123b. Specifically, the plate thickness t0 of flanges 123a and 123b is measured at a position 2 mm away from the free end of flanges 123a and 123b.

[0429] The plate thickness t0 of flanges 123a and 123b is, for example, 1.4 mm or more. A plate thickness t0 of 1.6 mm or more is more preferable. The plate thickness t0 may be 2.3 mm or less.

[0430] The plate thickness t2 of the lid 111 is preferably smaller than the plate thickness t0 of the cross member 12. t0-t2 is, for example, 0.4 mm or more, preferably 0.6 mm or more, and more preferably 0.8 mm or more. The plate thickness t2 of the lid 111 may be 0.4 mm or more. The plate thickness t2 of the lid 111 may be 1.4 mm or less. The plate thickness t2 of the lid 111 can be measured, for example, by a micrometer or the like in a flat area of ​​the lid 111, sufficiently far from the outer edge.

[0431] Each of the cross members 12 can have a Vickers hardness of 300 HV or more. The Vickers hardness of the cross members 12 is preferably 400 HV or more, and more preferably 500 HV or more.

[0432] The Vickers hardness of the cross member 12 can be measured by the Vickers hardness test specified in JIS Z 2244-1:2024. Specifically, after removing the cross member 12 from the vehicle body, a test piece is obtained by cutting the cross member 12 perpendicular to its longitudinal direction using laser cutting or the like. The cross member 12 is cut at the point where its height H is maximum and at the outermost position in the longitudinal direction (vehicle width direction). The test piece is then embedded in resin so that the cross section of the cross member 12 is positioned on the surface, and this cross section is polished. Subsequently, the Vickers hardness of the center of the top plate 121 is measured with a test force of 0.49 N at a position 1 / 4 of the plate thickness from the surface of the cross member 12. The measured Vickers hardness can be taken as the Vickers hardness HV1 of the center of the top plate 121. In addition, the Vickers hardness of the flanges 123a and 123b is measured at a position 1 / 4 of the plate thickness from the surface of the cross member 12. The Vickers hardness may be measured at a predetermined distance (e.g., 2 mm) away from the free ends of the flanges 123a and 123b. The measured Vickers hardness can be taken as the Vickers hardness HV2 of the flanges 123a and 123b. Both Vickers hardness HV1 and HV2 may be 300 HV or greater. However, because the cross member 12 is formed by fluid-assisted deep drawing (hydraulic or blow molding), the Vickers hardness HV1 at the center of the top plate 121 is greater than the Vickers hardness HV2 of the flanges 123a and 123b.

[0433] The lid 111 may have a Vickers hardness of 80 HV or higher. Preferably, the Vickers hardness of the lid 111 is 120 HV or higher, and more preferably 400 HV or higher. The Vickers hardness of the lid 111 can be measured in the same manner as the Vickers hardness of the cross member 12. However, when measuring the Vickers hardness of the lid 111, the test specimen for the Vickers hardness test can be obtained at any position on the lid 111.

[0434] Figure 54 is a partial cross-sectional view of the structural member 10 after the molding process, for example, after the removal of the outer periphery, which has resulted in its final shape. Figure 54 shows an example of a structural member 10 different from that shown in Figure 53.

[0435] Referring to Figure 54, each of the flanges 123a and 123b of the cross member 12 is joined to the cover 111, for example, by spot welding. In this case, multiple spot welds 13 are formed on the flanges 123a and 123b. One or more of the spot welds 13 may be formed after the structural member 10 has been formed.

[0436] Flange 123a may have a recess 126a on the surface opposite to the cover 111. The recess 126a is the portion of the surface of flange 123a where at least one spot weld 13 is located, viewed in a cross-section perpendicular to the width direction of the cover 111, and has a concave shape relative to the rest of the surface. Similarly, the surface of flange 123b may have a recess 126b on the surface opposite to the cover 111. The recess 126b is the portion of the surface of flange 123b where at least one spot weld 13 is located, viewed in a cross-section, and has a concave shape relative to the rest of the surface. On the surfaces of flanges 123a and 123b, the recesses 126a and 126b may be recessed by 0.1 mm or more relative to the rest of the surface.

[0437] The cover 111 may have recesses 112a and 112b on the surface opposite to the flanges 123a and 123b. The recesses 112a and 112b are located on the surface of the cover 111 at positions corresponding to the recesses 126a and 126b of the flanges 123a and 123b, respectively. Recess 126a, when viewed in cross-section, is the portion of the surface of the cover 111 where the spot welds 13 are located, and has a concave shape relative to the rest of the surface. Similarly, recess 126b, when viewed in cross-section, is the portion of the surface of the cover 111 where the spot welds 13 are located, and has a concave shape relative to the rest of the surface. On the surface of the cover 111, the recesses 112a and 112b may be recessed by 0.1 mm or more relative to the rest of the surface.

[0438] The recesses 126a, 126b in the flanges 123a, 123b and the recesses 112a, 112b in the cover 111 are formed during the molding process when the first blank 21 and the second blank 22 are sandwiched between the first mold 31 and the second mold 32 (Figures 52D and 52E). That is, if the first mold 31 and the second mold 32 are provided with convex sealing portions (not shown), the pressure from these sealing portions forms minute recesses 126a, 126b, 112a, 112b in the flanges 123a, 123b and the cover 111 of the cross member 12. During the molding process, high-pressure sliding occurs between the sealing portion of the second mold 32 and the flanges 123a, 123b, causing the bottom surfaces of the recesses 126a, 126b to be smoothed. Similarly, during the molding process, high-pressure sliding occurs between the seal portion of the first mold 31 and the lid 111, causing the bottom surfaces of the recesses 112a and 112b to be smoothed. Therefore, when spot welding the lid 111 to the flange 123a of the cross member 12 after the molding process, the lid 111 and the flange 123a of the cross member 12 can be stably joined by positioning the spot welding points 13 within the recesses 126a and 112a. Furthermore, when spot welding the lid 111 to the flange 123b of the cross member 12 after the molding process, the lid 111 and the flange 123b of the cross member 12 can be stably joined by positioning the spot welding points 13 within the recesses 126b and 112b.

[0439] [effect] In this embodiment, the cross member 12 is joined to the lid 111 for the battery case 11. Therefore, the lid 111 can also serve as the floor panel of the vehicle body. In this case, the number of parts of the vehicle body can be reduced compared to the case where the lid 111 is provided separately from the floor panel. Furthermore, in this embodiment, the lid 111 for the battery case 11 and the cross member 12 are integrally molded using a combination of hydraulic and blow molding. By integrally molding the lid 111, which also serves as the floor panel, and the cross member 12, the number of parts of the vehicle body can be further reduced.

[0440] Therefore, according to the structural member 10 of this embodiment, the number of parts in the battery unit and its surrounding structure can be reduced. As a result, the manufacturing process of the vehicle body can be streamlined, and the life cycle GHG emissions can be reduced. Furthermore, the vehicle body can be made lighter by reducing the number of parts.

[0441] In this embodiment, the lid 111 for the battery case 11 and the cross member 12 are integrally molded using hydraulic or blow molding, resulting in a unique plate thickness distribution in each cross member 12. Specifically, in the cross member 12, the plate thickness reduction rate of the top plate 121, based on the plate thickness t0 of the flanges 123a and 123b, is between 2.0% and 30.0%, indicating that a plate thickness reduction also occurs in the top plate 121. This suppresses the increase in the plate thickness reduction rate at the boundary between the vertical wall 122a and the ridge portion 124a, and at the boundary between the vertical wall 122b and the ridge portion 124b. In other words, the plate thickness reduction is distributed not only to the ridge portions 124a and 124b but also to the top plate 121. As a result, the overall plate thickness reduction in the structural member 10 can be suppressed compared to general press molding. Therefore, the collision resistance performance of the structural member 10 can be improved.

[0442] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0443] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0444] To confirm the effects of this disclosure, a commercially available analysis software (LS-DYNA, manufactured by Livermore Software Technology Corporation) was used to perform an analysis on forming the structural member 10 described in the above embodiment. In this analysis, one of the materials (steel plates) shown in Table 7 was used for the cover 111 and the cross member 12.

[0445] [Table 7]

[0446] The analysis conditions and results are shown in Table 8.

[0447] [Table 8]

[0448] Examples 1 to 9 and Reference Example 1 in Table 8 are in which the lid 111 and cross member 12 are blow-molded as a single unit, as described in the above embodiments. Reference Example 2 and Comparative Example 1 are in which the lid 111 and cross member 12 are molded separately by conventional press molding without the use of fluid. Reference Example 2 assumes hot stamping with deep drawing (draw HS molding), and Comparative Example 1 assumes hot stamping with deep bending (draw bend HS molding).

[0449] In this analysis, a crack was determined to have occurred in the cross member 12 if the maximum thickness reduction rate of the cross member 12, based on the material, was 39.0% or more, and no crack was determined to have occurred in the cross member 12 if the maximum thickness reduction rate was less than 39.0%. The maximum thickness reduction rate is the thickness reduction rate at the boundary between the vertical wall 122a and the edge portion 124a, or at the boundary between the vertical wall 122b and the edge portion 124b.

[0450] As shown in Table 8, in each embodiment utilizing blow molding, it was confirmed that the lid 111 and the cross member 12 could be molded as a single integrated part. As can be seen from the results of Examples 1 to 9 and Reference Example 1, with the shape of this analysis, the lid 111 and the cross member 12 can be blow molded as a single integrated part until the height H of the cross member 12 reaches 100 mm. On the other hand, in Reference Example 2, which assumed draw HS molding, the cross member 12 was molded separately from the lid 111, but cracks occurred in the cross member 12. In Comparative Example 1, which assumed draw bend HS molding, no cracks occurred during the individual molding of the cross member 12.

[0451] For each of Examples 1 to 9 and Comparative Example 1, the rate of thickness reduction at the center of the top plate 121 was measured at the outermost position in the longitudinal direction (vehicle width direction) of the cross member 12, where the height H is the maximum, based on the thickness of the material. Since there is virtually no reduction in thickness at the flanges 123a and 123b of the cross member 12 during molding, the thickness of the material corresponds to the thickness of the flanges 123a and 123b. As shown in Table 8, in Examples 1 to 9, the rate of thickness reduction at the center of the top plate 121 was 2.0% or more. On the other hand, in Comparative Example 1, the rate of thickness reduction at the center of the top plate 121 was 0.1%. Therefore, it can be seen that when the lid 111 and the cross member 12 are integrally molded using fluid, the thickness of the top plate 121 is reduced during molding compared to when the lid 111 and the cross member 12 are separated and molded individually.

[0452] Comparing Example 3 and Comparative Example 1, both of which have the same height H and material for the cross member 12, the maximum thickness reduction rate of the cross member 12 in Example 3 is smaller than that of Comparative Example 1. This is because in Example 3, the thickness reduction is distributed to the top plate 121, and the thickness reduction at the ridges 124a and 124b is suppressed. Thus, when the lid 111 and the cross member 12 are integrally molded using fluid, the maximum thickness reduction rate of the cross member 12 can be suppressed.

[0453] (Element technology D2) Element technology D2 is a cooling member comprising a plate-shaped first member, a plurality of second members each including a flange portion disposed on one surface of the first member and a main body portion having a shape convex to the flange portion, and which together form a refrigerant flow path with the first member, wherein the total area of ​​the region on the surface of the first member in which the refrigerant flow path is provided is 50% or more and less than 90% of the area of ​​the smallest rectangle circumscribing the second member within the range of the surface, at least one of the second members protrudes outward from the first member at each side edge in the width direction of the first member, and in each of the second members, the rate of reduction in plate thickness at the center of the main body portion relative to the plate thickness of the flange portion is ...

Claims

1. An understructure for an electric vehicle having a battery housing, a floor module, a side sill, and brackets joined to these components as its constituent parts, When viewed from a direction perpendicular to the reference plane, the projected area of ​​the battery housing and the battery housing adjacent portion of the side sill, which is the part adjacent to the battery housing, is S (m²). ２ ), The height of the aforementioned side sill is H (m), The total weight of the components of the aforementioned lower structure for electric vehicles is W ＴＯＴＡＬ (kg) The total weight of the steel components of the aforementioned electric vehicle substructure, which have a plate thickness of 1.5 mm or less and a minimum Vickers hardness of HV230 or higher, is W. Ａ , When defined as, W ＴＯＴＡＬ / SH is 180 or less, W Ａ / W ＴＯＴＡＬ is 0.10 or higher A lower structure for electric vehicles characterized by the following features.

2. The weight of the steel material of the component of the lower structure for the electric vehicle is W ＳＴＥＥＬ (kg) When defined as such, W ＳＴＥＥＬ / W ＴＯＴＡＬ is 0.56 or more The lower structure for an electric vehicle according to claim 1, characterized in that

3. Battery The battery housing includes a tray, a bottom plate, a frame, a cross member, a cooler, and a top cover. The floor module includes a floor cross member, a floor cross member extension, a floor panel, and components that constitute the floor section. The side sill includes a side sill outer, a side sill inner, and an internal side sill shock absorbing member. The lower structure for an electric vehicle according to claim 1, characterized in that

4. At least one of element technology A1 and element technology A2, At least one of elemental technology B1, elemental technology C1, elemental technology C2, elemental technology D1, and elemental technology D2, Equipped with, The aforementioned element technology A1 has a chemical composition in mass percent of: C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.1 It contains 5%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder being Fe and impurities, and by area percentage, a total of 10-30% ferrite and granular bainite, and martensite. A hot-stamped molded body having a metallic structure consisting of the remainder being one or more of bainite and tempered martensite, wherein in the texture from the surface to a position 1 / 4 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10> to {001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 1.8, and in the texture from a position 1 / 4 of the plate thickness from the surface to a position 1 / 2 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10> to {001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 2.

3. The aforementioned element technology A2 has a chemical composition in mass percent of C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, Ca: 0-0.010%, and REM: 0-0.30%, with the remainder being Fe and impurities, and containing a total area percentage of 90% or more of martensite and bainard. A hot-stamped molded body having a metallic structure including thread and tempered martensite, wherein in the texture from the surface to a position 1 / 4 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10> to {001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 1.8, and in the texture from a position 1 / 4 of the plate thickness from the surface to a position 1 / 2 of the plate thickness from the surface, the ratio of the polar density of the orientation group consisting of {001}<1-10> to {001}<-1-10> to the polar density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 2.

3. The element technology B1 is a press-formed part in which a plurality of partial blanks made of steel plates are joined together, and at least two of the partial blanks are joined at a plurality of joining portions in an overlapping portion formed by partially overlapping, and in a cross section perpendicular to the surface of the partial blank including the center of the joining portion of the outermost partial blank, at a position 1 / 4 of the plate thickness from the surface of the partial blank that is in contact with other partial blanks, when the Vickers hardness at a position that is 15 mm or more away from the center of the joining portion and is not joined is Hvm, a portion of the plurality of joining portions has a Vickers hardness of ΔHv, which is the difference between the maximum hardness and the minimum hardness in a range of 5 mm toward the base material from the end of the joining portion, less than 0.2 Hvm, preferably 0.1 Hvm or less, and the other joining portions of the plurality of joining portions have a ΔHv of 0.2 Hvm or more. The element technology C1 is a structural member comprising a first member and a second member, wherein one of the first member and the second member includes a member body including a curved portion that curves in a plan view of the structural member, and a flange provided continuously with the member body, wherein the flange is joined to the other of the first member and the second member to form a hollow cross section together with the other of the first member and the second member, and the rate of reduction in plate thickness in the curved portion of the member body, based on the plate thickness of the flange, is 30% or more. The element technology C2 is a material comprising a first blank and a second blank superimposed on the first blank, wherein the first blank and the second blank are not joined in the regions of the material that will become the first structural member and the second structural member; and a first structural member manufactured by a manufacturing method comprising: holding the material with a first mold and a second mold and supplying fluid between the first blank and the second blank to deform the material in the hollow space formed by the first mold and the second mold to form a first molded product including the first structural member from the first blank and a second molded product including the second structural member from the second blank; and a second structural member which is separate from the first structural member. The element technology D1 is a structural member comprising a lid for a battery case, a top plate facing the lid at a distance from it, two vertical walls connected to the top plate via their respective edges, and two flanges connected to the vertical walls on the opposite side of the top plate and joined to the lid, and a cross member extending in the width direction of the lid, wherein the rate of reduction in plate thickness at the center of the top plate, based on the plate thickness of the flanges, is 2.0% or more and 30.0% or less. The element technology D2 includes a plate-shaped first member, a flange portion disposed on one surface of the first member, and a main body portion having a convex shape relative to the flange portion, and a plurality of second members that together with the first member form a refrigerant flow path. A cooling member comprising the following: the total area of ​​the region on the surface of the first member in which the refrigerant flow path is provided is 50% or more and less than 90% of the area of ​​the smallest rectangle that circumscribes the second member within the range of the surface; at each side edge in the width direction of the first member, at least one of the second member protrudes outward from the first member; and in each of the second member, the rate of reduction in plate thickness at the center of the main body portion, based on the plate thickness of the flange portion, is 5.0% or more. The lower structure for an electric vehicle according to any one of claims 1 to 3.

5. At least one of the aforementioned element technology A1 and element technology A2, The aforementioned element technology B1, The lower structure for an electric vehicle according to claim 4, characterized by comprising the above.

6. At least one of the aforementioned element technology A1 and element technology A2, At least one of the aforementioned element technology C1 and element technology C2, The lower structure for an electric vehicle according to claim 4, characterized by comprising the above.

7. At least one of the aforementioned element technology A1 and element technology A2, At least one of the element technology D1 and the element technology D2, The lower structure for an electric vehicle according to claim 4, characterized by comprising the above.

8. At least one of the aforementioned element technology A1 and element technology A2, The aforementioned element technology B1, At least one of the aforementioned element technology C1 and element technology C2, At least one of the element technology D1 and the element technology D2, The lower structure for an electric vehicle according to claim 4, characterized by comprising the above.

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