Structural member, production method for same, and die

Abstract

A production method for a structural member (10, 10A, 10B, 10C, 10D) includes a step for preparing a material (30) that includes a first blank (31) and a second blank (32) and a step for using a first die (21) and a second die (22) to shape the material (30). The shaping step includes a step for sandwiching the material (30) between the second die (22) and a flange surface (212) of the first die (21) such that a protruding part (213) is inserted into a through hole (311) in the first blank (31) and using the protruding part (213) to produce a gap between the first blank (31) and the second blank (32, 32F, 32R) and a step for injecting a fluid into the gap from the protruding part (213) and using the fluid to make the material (30) expand within a hollow space that has been formed by the second die (22) and a shaping surface (211) of the first die (21).

Description

Structural member, its manufacturing method, and mold

[0001] The present disclosure relates to a structural member and a method for manufacturing the same, and more particularly to a mold for manufacturing a structural member.

[0002] In recent years, there has been a demand for reducing greenhouse gas emissions (life cycle GHG) throughout the entire life cycle of vehicle bodies, such as automobiles. In order to reduce life cycle GHG emissions by reducing the number of vehicle body parts and omitting processes during vehicle body manufacturing, the integration of parts has been promoted.

[0003] For example, Patent Document 1 discloses a rear module for a vehicle body. The rear module of Patent Document 1 includes left and right rear rails. Each rear rail includes a front section, a rear section, and a transition region connecting the front and rear sections. Each rear rail is formed, for example, by a tailor welded blank or a tailor rolled blank. Therefore, in Patent Document 1, the front and rear sections of the rear rail are integrated from the blank stage.

[0004] Similarly, Patent Document 2 discloses a technique for integrating the front and rear portions of a rear rail from the blank stage.

[0005] Patent Document 3 also discloses a rear module for a vehicle body. The rear module in Patent Document 3 includes left and right side members and a cross member that connects the side members. This rear module is formed from a single tailor-welded blank. Therefore, in Patent Document 3, the left and right side members and the cross member are integrated from the blank stage.

[0006] International Publication No. 2021 / 044234 International Publication No. 2017 / 098470 International Publication No. 2022 / 097058

[0007] Each patent document discloses a technique for forming multiple components into an integrated part by using a tailored blank including multiple sub-blanks. However, the application of the techniques described in each patent document is limited to integrated parts having an overall open cross section, such as frame components. To achieve further integration of components and improve the efficiency of component manufacturing, a technique for forming integrated parts having hollow cross sections is required. Conventional techniques for forming parts having hollow cross sections include hydroforming of sheet metal and hydraulic or gas blow molding of tubular materials. However, hydroforming requires preforming of flow channels in overlapping sheet metal and full-circumference laser welding of the sheets, resulting in productivity and cost issues. Hydraulic or gas blow molding of tubular materials has a problem in that the parts that can be formed are limited to tubular parts.

[0008] An object of the present disclosure is to provide a method for manufacturing a structural member that can efficiently mold a structural member as an integrated part having a hollow cross section.

[0009] The method for manufacturing a structural member according to the present disclosure includes the steps of preparing a material and molding the material using a first mold and a second mold. The material includes a first blank and a second blank. The first blank has a through hole. The second blank is overlapped and joined to the first blank. The first mold includes a molding surface and a flange surface. The flange surface is arranged around the molding surface. A protrusion is formed on the flange surface. The molding step includes the steps of clamping the material between the flange surface and the second mold with the protrusion inserted into the through hole, creating a gap between the first blank and the second blank by the protrusion, and injecting a fluid into the gap through the protrusion, causing the fluid to expand the material in the hollow space formed by the molding surface and the second mold.

[0010] According to the manufacturing method of a structural member according to the present disclosure, a structural member can be molded with good productivity as an integrated part having a hollow cross section.

[0011] FIG. 1A is a perspective view showing a schematic configuration of a structural member according to the first embodiment. FIG. 1B is an exploded perspective view of the structural member shown in FIG. 1A. FIG. 2 is a perspective view showing a schematic configuration of a mold according to the first embodiment. FIG. 3 is a cross-sectional view of the mold shown in FIG. 2 taken along III-III. FIG. 4 is a view showing an example of a mold different from that shown in FIG. 3. FIG. 5A is a schematic view illustrating a method for manufacturing a structural member according to the first embodiment. FIG. 5B is a schematic view illustrating a method for manufacturing a structural member according to the first embodiment. FIG. 5C is a schematic view illustrating a method for manufacturing a structural member according to the first embodiment. FIG. 5D is a schematic view illustrating a method for manufacturing a structural member according to the first embodiment. FIG. 5E is a schematic view illustrating a method for manufacturing a structural member according to the first embodiment. FIG. 6 is a partial cross-sectional view of the structural member shown in FIG. 1. FIG. 7 is a perspective view showing a schematic configuration of a structural member according to a second embodiment. FIG. 8A is a schematic view illustrating a method for manufacturing a structural member according to the second embodiment. FIG. 8B is a schematic view illustrating a method for manufacturing a structural member according to the second embodiment. FIG. 8C is a schematic view illustrating a method for manufacturing a structural member according to the second embodiment. FIG. 8D is a schematic diagram for explaining a method for manufacturing a structural member according to the second embodiment. FIG. 9 is a perspective view showing a general configuration of a structural member according to the third embodiment. FIG. 10A is a schematic diagram for explaining a method for manufacturing a structural member according to the third embodiment. FIG. 10B is a schematic diagram for explaining a method for manufacturing a structural member according to the third embodiment. FIG. 10C is a schematic diagram for explaining a method for manufacturing a structural member according to the third embodiment. FIG. 10D is a schematic diagram for explaining a method for manufacturing a structural member according to the third embodiment. FIG. 11 is a perspective view showing a general configuration of a structural member according to the fourth embodiment. FIG. 12A is a schematic diagram for explaining a method for manufacturing a structural member according to the fourth embodiment. FIG. 12B is a schematic diagram for explaining a method for manufacturing a structural member according to the fourth embodiment. FIG. 12C is a schematic diagram for explaining a method for manufacturing a structural member according to the fourth embodiment. FIG. 12D is a schematic diagram for explaining a method for manufacturing a structural member according to the fourth embodiment. FIG. 13 is a perspective view showing another example of a structural member.

[0012] A manufacturing method for a structural member according to an embodiment includes a step of preparing a material and a step of molding the material using a first mold and a second mold. The material includes a first blank and a second blank. The first blank has a through hole. The second blank is overlapped and joined to the first blank. The first mold includes a molding surface and a flange surface. The flange surface is arranged around the molding surface. A protrusion is formed on the flange surface. The molding step includes a step of clamping the material between the flange surface and the second mold with the protrusion inserted into the through hole, creating a gap between the first blank and the second blank using the protrusion, and a step of injecting a fluid into the gap through the protrusion, causing the fluid to expand the material in the hollow space formed by the molding surface and the second mold (first configuration).

[0013] In a manufacturing method according to a first aspect, a first mold and a second mold are used to form a material including a first blank and a second blank. A protrusion is formed on the flange surface of the first mold. When the material is clamped between the flange surface of the first mold and the second mold with the protrusion inserted into the through hole of the first blank, the protrusion lifts the second blank toward the second mold, creating a gap between the first blank and the second blank. By injecting a fluid into this gap through the protrusion, the material can be expanded in a hollow space formed by the molding surfaces of the first mold and the second mold, thereby forming the material. At this time, the first blank is pressed against the first mold, and the second blank is pressed against the second mold within the hollow space, forming a hollow cross section in the material. Meanwhile, the material may be simply clamped and molded between the first mold and the second mold in portions of the first and second molds other than the hollow space. A first die forms a first blank into a first member containing one or more components, and a second die forms a second blank into a second member containing one or more components.

[0014] In this way, the manufacturing method according to the first aspect uses a fluid to mold a structural member having a hollow cross section and including multiple integrated components. Furthermore, according to the manufacturing method according to the first aspect, a fluid passage is formed simply by closing the first and second molds, eliminating the need for separate preforming to ensure a fluid flow path. Therefore, a structural member as an integrated component having a hollow cross section can be molded with high productivity.

[0015] The manufacturing method according to the first aspect may further include a step of heating the material before the molding step (second aspect).

[0016] The mold according to this embodiment is a mold for manufacturing a structural member from a material. The material includes a first blank and a second blank. The first blank has a through hole. The second blank is overlapped on the first blank. The mold includes a first mold and a second mold. The first mold includes a first molding surface and a first flange surface. The first flange surface is arranged around the first molding surface. A protrusion is formed on the first flange surface. The second mold includes a second molding surface and a second flange surface. The second molding surface is configured to form a hollow space together with the first molding surface. The second flange surface is arranged around the second molding surface. The second flange surface corresponds to the first flange surface. The first mold further includes a flow path for a fluid. The flow path is formed in the first mold and opens into the protrusion (third configuration).

[0017] A mold according to a third configuration is used to manufacture a structural member from a material including a first blank and a second blank stacked together. This mold includes a first mold and a second mold. The first mold includes a first flange surface on which a protrusion is formed in addition to a first molding surface. Therefore, when the first and second molds are closed with the protrusion inserted into the through hole of the first blank and the material is clamped between the first and second flange surfaces, the protrusion lifts the second blank toward the second mold, creating a gap between the first and second blanks. By injecting a fluid into this gap through a flow path opening into the protrusion in the first mold, the fluid can expand the material in the hollow space formed by the first and second molding surfaces. Within the hollow space, the first blank is pressed against the first mold, and the second blank is pressed against the second mold, forming a hollow cross section in the material. Meanwhile, in the portions of the first and second molds other than the hollow space, the material may be simply clamped and molded between the first and second molds. A first die forms a first blank into a first member containing one or more components, and a second die forms a second blank into a second member containing one or more components.

[0018] Therefore, by using the mold according to the third configuration, when molding a material including the first blank and the second blank with a fluid, there is no need to perform a separate pre-forming step to ensure a fluid flow path, and therefore a structural member as an integrated part having a hollow cross section can be molded with good productivity.

[0019] The mold according to the third configuration may further include a first convex seal portion provided on at least one of the first flange surface and the second flange surface, the first seal portion being disposed so as to surround the hollow space (fourth configuration).

[0020] In a fourth configuration, a first seal portion is provided on at least one of the first flange surface of the first mold and the second flange surface of the second mold. The first seal portion is arranged to surround the hollow space formed by the first molding surface of the first mold and the second molding surface of the second mold. When the first mold and the second mold are closed, the first seal portion can seal the first blank and the second blank outside the hollow space. This makes it less likely for fluid to leak between the first blank and the second blank. This allows for better molding of structural components using fluids.

[0021] The mold according to the fourth configuration may further include a convex second seal portion provided on at least one of the first flange surface and the second flange surface, the second seal portion being disposed so as to surround the first seal portion (fifth configuration).

[0022] In the fifth configuration, a second seal portion is provided on at least one of the first flange surface of the first mold and the second flange surface of the second mold. The second seal portion is provided to surround the first seal portion. In this case, when the first mold and the second mold are closed, the first mold and the second mold can seal around the material. This makes it less likely for the fluid to leak outside the first mold and the second mold, and allows for better molding of a structural member using a fluid.

[0023] A structural member according to an embodiment includes a first member and a second member. One of the first member and the second member includes a member body and a flange. The member body includes a curved portion that is curved in a plan view of the structural member. The flange is provided continuous with the member body. One of the first member and the second member forms a hollow cross section together with the other of the first member and the second member by joining the flange to the other of the first member and the second member. The thickness reduction rate at the curved portion of the member body based on the thickness of the flange is 30% or more (sixth configuration).

[0024] The structural member according to the sixth configuration may be a rear module for a vehicle body. In this case, the member main body includes a pair of side frames and a cross member. The cross member connects the side frames. The curved portion is provided, for example, at a connection between each of the side frames and the cross member (seventh configuration).

[0025] The structural member according to the sixth configuration may be a front module for a vehicle body. In this case, the member main body includes a pair of side frames and a cross member. The cross member connects the side frames. The curved portion is provided, for example, at a connection between each of the side frames and the cross member (eighth configuration).

[0026] The structural member according to the sixth configuration may be a subframe for a vehicle body. In this case, the member main body includes a pair of side frames and a cross member. The cross member connects the side frames. The curved portion is provided, for example, at a connection between each of the side frames and the cross member (ninth configuration).

[0027] The structural member according to the sixth configuration may be a floor module for a vehicle body. In this case, the member body includes a cross member. The curved portion may be provided at an end portion in the longitudinal direction of the cross member (tenth configuration).

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In these drawings, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0029] <First embodiment> [Structural member] Fig. 1A is a perspective view showing a schematic configuration of a structural member 10 according to this embodiment. Fig. 1B is an exploded perspective view of the structural member 10. The structural member 10 is used, for example, in the body of an automobile or the like. In this embodiment, the structural member 10 is a rear module for the 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.

[0030] 1A , the structural member 10 is a member having at least a hollow cross section in at least a portion thereof. The structural member 10 includes a first member 11 and a second member 12. The first member 11 and the second member 12 are each formed of one or more metal plates. For example, the first member 11 and the second member 12 are each formed of one or more steel plates. However, the first member 11 and the second member 12 may also be formed of an aluminum alloy plate or the like.

[0031] The first member 11 and the second member 12 are arranged one above the other 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.

[0032] As shown in Fig. 1B, the member body 111 of the first member 11 has a convex shape on the side opposite to 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 of Fig. 1B, the member body 111 includes one cross member 111b. However, the member body 111 may include multiple cross members 111b.

[0033] The side frames 111a and the cross members 111b each have a hollow shape. In this embodiment, the side frames 111a and the cross members 111b each have a hollow rectangular shape. Each of the side frames 111a extends in the front-to-rear direction of the vehicle body when the structural member 10 is assembled to the vehicle body. The cross members 111b extend in the left-to-right 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.

[0034] The member body 111 has at least one curved portion 111c. The curved portion 111c is a portion 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 is curved concavely toward the inside of the member body 111 or convexly toward the outside of the member body 111. In this embodiment, the curved portion 111c is provided at a connection between each of the side frames 111a and the cross member 111b. That is, the curved portion 111c is a 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, i.e., when viewed from above 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.

[0035] In the first member 11, the flange 112 is provided contiguous 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 contiguous with each of the side frames 111a and the cross member 111b.

[0036] The first member 11 forms a hollow cross section together with the second member 12 by joining the flange 112 to the second member 12. In this embodiment, by joining the flanges 112 and 122, 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.

[0037] The member body 121 of the second member 12 has a convex shape on the opposite side to the first member 11. In this embodiment, the member body 121 includes a pair of side frames 121a and a cross member 121b. In this example of the present embodiment, the member body 121 includes one cross member 121b. However, the member body 121 may include multiple cross members 121b.

[0038] The side frames 121a and the cross members 121b each have a hollow shape. In this embodiment, the side frames 121a and the cross members 121b each have a hollow rectangular shape. Each of the side frames 121a extends in the front-to-rear direction of the vehicle body when the structural member 10 is assembled to the vehicle body. The cross members 121b extend in the left-to-right direction of the vehicle body when the structural member 10 is assembled to the vehicle body. The cross members 121b extend from one side frame 121a to the other side frame 121a, connecting the side frames 121a together.

[0039] The side frame 121a of the second member 12 is disposed to face the side frame 111a of the first member 11. The side frames 111a, 121a have convex shapes on opposite sides. In this embodiment, the cross member 121b of the second member 12 is also disposed to face the cross member 121b of the first member 11. The cross members 111b, 121b have convex shapes on opposite sides.

[0040] 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 concavely inward or convexly outward of the member body 121. In this embodiment, the curved portion 121c is provided at a connection between each side frame 121a and the cross member 121b. That is, the curved portion 121c is a corner portion between each side frame 121a and the cross member 121b. When the structural member 10 is viewed from the second member 12 side, i.e., when viewed from above 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.

[0041] In the second member 12, the flange 122 is provided contiguous with the member body 121. In this 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 contiguous with each of the side frames 121a and the cross member 121b.

[0042] The flange 122 of the second member 12 is joined to the flange 112 of the first member 11. The flanges 112, 122 are typically joined to each other by welding. The flanges 112, 122 are preferably joined intermittently, for example, by spot welding. However, the flanges 112, 122 may also be joined by continuous welding, for example, by laser welding.

[0043] 2 is a perspective view showing a schematic configuration of a mold 20 according to this embodiment. The structural member 10 (FIGS. 1A and 1B) can be manufactured using the mold 20.

[0044] 2, the mold 20 includes 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 attached to a press or the like so that they can approach each other. Hereinafter, the approach direction of the first mold 21 and the second mold 22 will be referred to as the processing direction D. The processing direction D is, for example, a vertical direction.

[0045] The first mold 21 is a mold mainly used to mold the first member 11 (FIGS. 1A and 1B). 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 second mold 22 in the processing direction D.

[0046] The molding surface 211 has a shape corresponding to the member body 111 (FIGS. 1A and 1B) of the first member 11. In this embodiment, the molding surface 211 includes a pair of side frame molding portions 211a and at least one cross member molding portion 211b. The side frame molding portions 211a are portions of the molding surface 211 configured to mold the side frames 111a (FIG. 1B). The cross member molding portion 211b is a portion of the molding surface 211 configured to mold the cross member 111b (FIG. 1B).

[0047] The flange surface 212 is disposed around the periphery of the molding surface 211. The flange surface 212 is provided on the first mold 21 so as to surround the entire periphery of the molding surface 211 when viewed along the processing direction D.

[0048] At least one protrusion 213 is formed on the flange surface 212. The protrusion 213 protrudes from the flange surface 212 toward the second mold 22. In this embodiment, a plurality of protrusions 213 are formed on the flange surface 212. The protrusions 213 are arranged in the vicinity of the side frame molding portion 211 a on the molding surface 211.

[0049] Each of the protrusions 213 has, for example, a circular shape when viewed along the processing direction D. However, the protrusions 213 may also have a polygonal shape such as a triangular shape or a quadrangular shape when viewed along the processing direction D. When the protrusions 213 have a shape other than a circle, the protrusions 213 may be formed so as to be wider on the side closer to the forming surface 211.

[0050] A fluid is used in the manufacture of the structural member 10 ( FIGS. 1A and 1B ). Therefore, the first mold 21 further includes a flow path 214 for the fluid. The flow path 214 is formed within the first mold 21. The flow path 214 opens to each of the protrusions 213. The flow path 214 is connected to a fluid supply source (not shown) provided outside the first mold 21. In the example of FIG. 2 , the first mold 21 is provided with a plurality of flow paths 214 corresponding to the plurality of protrusions 213. Each of the flow paths 214 can open to a side surface of the first mold 21. However, the plurality of flow paths 214 may be integrated into a single system within the first mold 21, and then open to the back surface of the first mold 21, etc.

[0051] The second mold 22 is a mold mainly used to mold the second member 12 (FIGS. 1A and 1B). In this embodiment, the second mold 22 is disposed 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 surfaces of the second mold 22 that face the first mold 21 in the processing direction D.

[0052] The molding surface 221 has a shape corresponding to the member body 121 (FIGS. 1A and 1B) of the second member 12. That is, the molding surface 221 includes a pair of side frame molding portions 221a and at least one cross member molding portion 221b. The side frame molding portion 221a is a portion of the molding surface 221 configured to mold the side frame 121a (FIG. 1B). The cross member molding portion 221b is a portion of the molding surface 221 configured to mold the cross member 121b (FIG. 1B).

[0053] 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, 221 face each other in the processing direction D. Furthermore, one or both of the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22 have a concave shape at least in part. In this embodiment, the molding surfaces 211, 221 have concave shapes on opposite sides to each other. That is, in the first mold 21, the molding surface 211 is formed so as to be concave with respect to the flange surface 212. In the second mold 22, the molding surface 221 is formed so as to be concave with respect to the flange surface 222.

[0054] In the second mold 22, the flange surface 222 is disposed around the molding surface 221. The flange surface 222 is provided on the second mold 22 so as to surround the entire periphery of the molding surface 221 when viewed along the processing direction D.

[0055] In this embodiment, the mold 20 further includes convex seal portions 23 and 24. The seal 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.

[0056] The seal portion 23 is provided on the flange surface 212 of the first mold 21 so as to substantially surround the molding surface 211. In this embodiment, the seal portion 23 also surrounds each of the protrusions 213. It is preferable that the seal portion 23 surrounds the entire molding surface 211 without interruption. However, for example, a portion of the seal portion 23 may be interrupted at a position away from each of the protrusions 213. The seal portion 23 may be interrupted within a range of, for example, 30 mm or less.

[0057] 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 seal portion 23, 24. The seal portion 24 may surround the entire periphery of the seal portion 23 without interruption, but, for example, a portion of the seal portion 24 may be interrupted at a position away from each protrusion 213. The seal portion 24 may be interrupted within a range of, for example, 150 mm or less.

[0058] The seal portion 23 is provided on the flange surface 222 of the second mold 22 so as to substantially surround the molding surface 221. The seal portion 23 of the second mold 22 is provided so as to face the seal portion 23 of the first mold 21 in the processing direction D, and has a shape corresponding to the seal portion 23 of the first mold 21. In the second mold 22, too, it is preferable that the seal portion 23 surrounds the molding surface 221 without interruption over the entire circumference. However, the seal portion 23 may be interrupted within a range of, for example, 30 mm or less.

[0059] 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 seal portion 23, 24. The seal portion 24 of the second mold 22 is provided so as to face the seal portion 24 of the first mold 21 in the processing direction D, 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 over the entire periphery, or may be interrupted within a range of, for example, 150 mm or less.

[0060] Fig. 3 is a cross-sectional view taken along the line III-III of the mold 20 shown in Fig. 2. Fig. 3 shows one of the protrusions 213 provided on the first mold 21 of the mold 20 and its vicinity.

[0061] 3, the protrusion 213 includes a tip surface 213a and a side surface 213b. The tip surface 213a is the surface of the protrusion 213 that is located farthest from the flange surface 212 in the machining direction D. In this embodiment, the tip surface 213a is a flat surface that is substantially perpendicular to the machining direction D.

[0062] The side surface 213b connects the tip surface 213a to the flange surface 212. In this 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 so that the width of the protrusion 213 is large on the base end side and small on the tip end side.

[0063] FIG. 4 is a diagram showing another example of the protrusion 213. In the example of FIG. 3, the side surface 213b of the protrusion 213 is an inclined surface that is inclined overall with respect to the processing direction D, but in the example of FIG. 4, 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, the width of the protrusion 213 is substantially constant at the portion 213c of the side surface 213b adjacent to the flange surface 212. The other portions of the side surface 213b may be inclined with respect to the processing direction D, as in FIG. 3.

[0064] The flow paths 214 preferably open to the side surface 213b of the protrusion 213. The flow paths 214 can open in a portion of the side surface 213b of the protrusion 213 that is closer to the molding surface 211. The flow paths 214 preferably open in the protrusion 213 at a position closer to the tip of the protrusion 213 than to the flange surface 212. In the examples of FIGS. 3 and 4 , the portion of the flow path 214 that passes through the protrusion 213 is substantially parallel to the processing direction D. However, at least the portion of the flow path 214 that passes through the protrusion 213 may be inclined with respect to the processing direction D. When viewed in a cross section including the central axis of the protrusion 213, the flow path 214 can be inclined with respect to the processing direction D so as to intersect with 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 that passes through the protrusion 213 may be inclined, for example, at an angle greater than 0° and less than or equal to 60° with respect to the processing direction D.

[0065] Near the protrusion 213, a recess 222a is formed on the flange surface 222 of the second mold 22. When viewed in a cross section including the central axis of the protrusion 213, the recess 222a extends from a portion of the flange surface 222 facing the tip surface 213a of the protrusion 213 to the molding surface 221. The recess 222a has a concave shape relative to the other portions of the flange surface 222.

[0066] The seal portions 23, 24 of the first mold 21 and the second mold 22 preferably have a shape that allows for surface contact with the mating mold or its seal portions 23, 24. As shown in FIGS. 3 and 4 , each of the seal portions 23, 24 may have, for example, a substantially rectangular cross section. The width W of each of the seal portions 23, 24 may be 1.0 mm or more, preferably 2.0 mm or more. The width W is preferably 5.0 mm or less, more preferably 3.0 mm or less. The height H of each of the seal portions 23, 24 is, for example, 0.2 mm or more. The height H may be 0.5 mm or less. The inner seal portion 23 is made of, for example, metal. The seal portion 23 may be formed integrally with the first mold 21 or the second mold 22. The outer seal portion 24 may be made of metal or an elastic material such as resin. The seal portion 24 may be a resin packing such as an O-ring. In this case, the first mold 21 and the second mold 22 are each formed with a groove for arranging the seal portion 24 .

[0067] [Method for manufacturing a structural member] Next, a method for manufacturing a structural member 10 using a mold 20 will be described with reference to Figures 5A to 5E. The method for manufacturing a structural member 10 according to this embodiment includes a preparation step and a molding step. The manufacturing method may further include a heating step.

[0068] 5A and 5B, in the preparation step, a blank 30 is prepared. The blank 30 includes a first blank 31 and a second blank 32.

[0069] 5A and 5B , the first blank 31 is a blank corresponding to the first member 11 ( FIGS. 1A and 1B ). The first blank 31 has at least one through hole 311. The through hole 311 is provided corresponding to the protrusion 213 ( FIG. 2 ) of the first mold 21. In this embodiment, the first mold 21 is provided with a plurality of protrusions 213, and therefore the first blank 31 is also provided with a plurality of through holes 311 corresponding to the protrusions 213.

[0070] The second blank 32 is a blank corresponding to the second member 12 (FIGS. 1A and 1B). The second blank 32 is overlapped and joined to the first blank 31. The second blank 32 is overlapped on the first blank 31 so as to close each of the through holes 311.

[0071] The first blank 31 and the second blank 32 are joined at portions corresponding to the flanges 112, 122 ( FIGS. 1A and 1B ) of the structural member 10. The first blank 31 and the second blank 32 are typically joined by welding. The first blank 31 and the second blank 32 are preferably joined at their outer peripheries by intermittent welding, such as spot welding. The first blank 31 and the second blank 32 may also be joined at their outer peripheries substantially over their entire peripheries 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 corresponding to the recess 222a ( FIG. 3 ) of the second mold 22. A weld between the first blank 31 and the second blank 32 may not be provided in the portions of the first blank 31 and the second blank 32 corresponding to the protrusion 213 ( FIG. 3 ) of the first mold 21, in other words, around the through hole 311 of the first blank 31. The first blank 31 and the second blank 32 do not have flow paths formed therein before the forming process.

[0072] The first blank 31 and the second blank 32 may each be formed from a single metal plate or may include multiple metal plates (sub-blanks). The metal plate may be, for example, a steel plate. However, the metal plate may also be, for example, an aluminum alloy plate.

[0073] When multiple metal plates are present in the first blank 31 and / or the second blank 32, these metal plates may have different tensile strengths and / or thicknesses. When the first blank 31 includes multiple metal plates, the metal plates are typically joined to each other by welding. Similarly, when the second blank 32 includes multiple metal plates, the metal plates are typically joined to each other by welding. The metal plates are joined to each other by, for example, 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 end faces butted together, or with their end faces overlapping.

[0074] (Heating Step) The heating step is carried out before the forming step. In the heating step, 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 depending on the material of the first blank 31 and the second blank 32. When the first blank 31 and the second blank 32 are made of steel, the material 30 is heated to an austenite transformation finish temperature (A ｃ３ When the first blank 31 and the second blank 32 are made of steel, the blank 30 is heated to, for example, 900° C. or higher. However, the heating step does not necessarily have to be performed.

[0075] (Molding process) In the molding process, the material 30 is molded using the first mold 21 and the second mold 22. If the heating process has been performed, the heated material 30 is molded by the first mold 21 and the second mold 22 in the molding process.

[0076] 5C , in the forming process, first, the first mold 21 and the second mold 22 are spaced apart in the processing direction D, and the raw material 30 is placed between them. At this time, the raw material 30 is placed so that the through holes 311 of the first blank 31 correspond to the protrusions 213 of the first mold 21. In the example of this embodiment, the first mold 21 is placed below the second mold 22, and therefore the raw material 30 is placed on the first mold 21.

[0077] 5D , next, the first mold 21 and the second mold 22 are brought relatively close to each other and closed. Specifically, with the protrusions 213 of the first mold 21 inserted into each through-hole 311 of the first blank 31, the blank 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, and a gap is created between the first blank 31 and the second blank 32 by the protrusions 213. The protrusions 213 are inserted into the through-holes 311 of the first blank 31 and lift the second blank 32 from the inside of the blank 30, creating a gap between the first blank 31 and the second blank 32.

[0078] In this embodiment, the tip surface 213a of the protrusion 213 is substantially flat, so the tip surface 213a of the protrusion 213 can come into surface contact with the second blank 32. When the first mold 21 and the second mold 22 are closed, the raw material 30 is first sandwiched between the tip surface 213a of the protrusion 213 and the relief portion 222a of the flange surface 222 of the second mold 22. This allows the raw material 30 to be positioned.

[0079] When the first mold 21 and the second mold 22 are closed, the material 30 is sandwiched between the seal portion 23 of the first mold 21 and the seal portion 23 of the second mold. Furthermore, when the first mold 21 and the second mold 22 are closed, the seal portion 24 (FIG. 2) of the first mold 21 abuts against the seal portion 24 (FIG. 2) of the second mold. The material 30 is sandwiched more tightly at the position of the seal portion 23 than at other parts of the flange surfaces 212, 222.

[0080] 5E , after the raw material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22, a fluid is injected into the gap between the first blank 31 and the second blank 32 from the protrusion 213. The fluid is supplied to the flow path 214 from a fluid supply source (not shown), passes through the flow path 214, and flows out from the protrusion 213. The fluid expands the raw material 30 in the hollow space formed by the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22.

[0081] Within the hollow space of the mold 20, the first blank 31 of the material 30 is inflated 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 inflated 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 (FIGS. 1A and 1B) having hollow member bodies 111, 121 is molded.

[0082] The fluid used to form the blank 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 high-pressure liquid or gas, for example, at 10 MPa or higher. The temperature of the fluid may be determined appropriately depending on the material of the blank 30, and may be, for example, room temperature. When a heating step is performed, i.e., when forming is performed by hot stamping, the fluid may be heated.

[0083] If a heating process has been carried out before the molding process, the first blank 31 and the second blank 32 are quenched by being brought into contact with the first mold 21 and the second mold 22, respectively, to remove heat.

[0084] Through this molding process, the structural member 10 (FIGS. 1A and 1B) 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 where the through-holes 311 (FIG. 5E) are provided is usually removed after the molding process.

[0085] Figure 6 is a partial cross-sectional view of the structural member 10 after the forming process. Figure 6 shows a cross-section (transverse cross-section) of the structural member 10 cut along the thickness direction of the first member 11 and the second member 12 at the positions of the curved portions 111c, 121c (Figure 1B) of the member bodies 111, 121. The transverse cross-section of the structural member 10 in Figure 6 also includes the welded portion 13 joining the flange 112 of the first member 11 and the flange 122 of the second member 12.

[0086] 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 (FIG. 1B), the vertical wall 114 is curved concavely toward the inside of the member body 111 in a plan view of the structural member 10.

[0087] The member body 121 of the second member 12 also includes a top plate 123 and a vertical wall 124. The top plate 123 is disposed opposite the top plate 113 of the first member 11. The vertical wall 124 connects the top plate 123 and the flange 122. At the position of the curved portion 121c (FIG. 1B), the vertical wall 124 is curved concavely toward the inside of the member body 121 in a plan view of the structural member 10.

[0088] The thickness reduction rate T1 at the curved portion 111c (FIG. 1B) of the member body 111 is 30% or more. The thickness reduction rate T1 depends on the material of the member body 111, the forming height, and the like, but is, for example, 50% or less, preferably less than 45%. The thickness reduction rate T1 is the thickness reduction rate based on the thickness of the flange 112. That is, when the thickness of the flange 112 is t0 and the thickness of the member body 111 at the curved portion 111c is t, the thickness reduction rate T1 [%] can be obtained by (t0 - t) / t0 × 100. The thickness t0 is, for example, the thickness of the flange 112 measured at a position 2.0 mm or more away from the weld 13 toward the free end of the flange 112. The thickness t0 is substantially equal to the thickness of the first blank 31 before forming. The plate thickness t is the minimum value of the plate thickness measured at five or more points at 1 mm intervals, starting from the corner between the flange 112 and the vertical wall 114 and extending to the vertical wall 114, in a cross section of the structural member 10 when cut at the bottom of the curve of the curved portion 111c, for example.

[0089] The thickness reduction rate T2 at the curved portion 121c (FIG. 1B) of the component body 121 is 30% or more. The thickness reduction rate T2 depends on the material and forming height of the component body 121, but is, for example, 50% or less, preferably less than 45%. The thickness reduction rate T2 is based on the thickness of the flange 122. The thickness reduction rate T2 can be obtained using the same measurement and calculation methods as the thickness reduction rate T1. That is, when the thickness of the flange 122 is t0 and the thickness of the component body 121 at the curved portion 121c is t, the thickness reduction rate T2 [%] can be obtained by (t0 - t) / t0 × 100. The thickness t0 is, for example, the thickness of the flange 122 measured at a position 2.0 mm or more away from the weld 13 toward the free end of the flange 122. The thickness t0 is substantially equal to the thickness of the second blank 32 before forming. The thickness t is the minimum value of the thickness measured at five or more points at 1 mm intervals starting from the corner between the flange 122 and the vertical wall 124 along the vertical wall 124 in a cross section of the structural member 10 when cut at the position of the curved bottom of the curved portion 121c, for example.

[0090] When a heating process is performed in the manufacture of the structural member 10, 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 a cross section of the structural member 10 including the weld center of the weld 13, the minimum Vickers hardness of the heat-affected zone of the weld 13 is 70% or more of the Vickers hardness of the non-welded portions of the first member 11 and the second member 12. In this cross section, the minimum Vickers hardness is preferably 80% or more, and more preferably 90% or more, of the Vickers hardness of the first member 11 and the second member 12. In each of the first member 11 and the second member 12, the minimum Vickers hardness of the heat-affected zone is equal to or lower than the Vickers hardness of the non-welded portions.

[0091] The Vickers hardness can be measured by a Vickers hardness test specified in JIS Z 2244-1:2020. Specifically, a test specimen including the first member 11, the second member 12, and the weld 13 is first obtained from the structural member 10 by laser cutting or the like at a position passing through the weld center of the weld 13. The test specimen is then embedded in resin so that a cross section passing through the weld center of the weld 13 is located on the surface, and the cross section is polished. Next, for each of the first member 11 and the second member 12, the Vickers hardness is measured at a position 1 / 4 of the plate thickness from the surface on the weld center side of the weld 13 to a position 12.0 mm outward from the weld center 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. The minimum value of the measured Vickers hardness is 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 at a position 15.0 mm or more away from the weld center of the welded portion 13 and at a position ¼ of the plate thickness from the surface on the weld center side of the welded portion 13, using a test force of, for example, 0.49 N. This Vickers hardness is defined as the Vickers hardness of the non-welded portion of the first member 11 and the second member 12.

[0092] [Effect] In this embodiment, a first mold 21 and a second mold 22 are used to manufacture a structural member 10 from a raw material 30 including a first blank 31 and a second blank 32. At least one protrusion 213 is formed on the flange surface 212 of the first mold 21. In this case, when the protrusion 213 is inserted into the through hole 311 of the first blank 31 and the raw material 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22 in this state, the protrusion 213 lifts the second blank 32 toward the second mold 22. As a result, a gap is formed between the first blank 31 and the second blank 32. By injecting fluid into the gap from the protrusion 213 through the flow path 214 of the first mold 21, the raw material 30 can be inflated and molded into the shape of the molding surfaces 211, 221.

[0093] That is, 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 perform a separate preforming step to ensure a fluid flow path. Therefore, the structural member 10 in which the first member 11 and the second member 12 are integrated can be molded with good productivity using the first blank 31 and the second blank 32 joined together.

[0094] In this embodiment, the fluid used to form the structural member 10 is preferably a gas. That is, in the forming process, the structural member 10 is preferably gas blow molded. For example, if the structural member 10 is formed by hydroforming, liquid remains inside the structural member 10 after forming, and therefore processing is required to drain the liquid from the structural member 10 after the forming process. On the other hand, if the structural member 10 is formed by gas blow molding, post-processing of the fluid is not necessary. Therefore, by using a gas to form the structural member 10, the productivity of the structural member 10 can be improved.

[0095] In this embodiment, the clamping force between the first mold 21 and the second mold 22 can seal the outer peripheries of the overlapping first blank 31 and second blank 32. Therefore, the outer peripheries of the first blank 31 and the second blank 32 do not need to be laser welded all around, as in conventional sheet metal hydroforming techniques. The first blank 31 and the second blank 32 only need to be joined at multiple locations by spot welding, for example. In this case, the number of steps and costs required to manufacture the structural member 10 can be reduced compared to when full-periphery laser welding is performed. Therefore, the structural member 10 having a hollow cross section can be formed with higher productivity.

[0096] In the present embodiment, the raw material 30 may be formed into the structural member 10 using hot stamping. That is, the raw material 30 may be subjected to a heating process before the forming 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 portion 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 a hot-stamped material, HAZ softening occurs due to welding, and the minimum Vickers hardness of the HAZ is approximately 60% of the Vickers hardness of the non-welded portion. However, after the heating process, the minimum Vickers hardness of the HAZ of the welded portion 13 becomes 70% or more of the Vickers hardness of the non-welded portion of the first member 11 and the second member 12. This reduces the number of relatively low-strength portions in the structural member 10, thereby improving the crash resistance of the structural member 10.

[0097] If the structural member 10 is formed using hot stamping, the forming process preferably involves gas blow forming the structural member 10. On the other hand, if the structural member 10 is formed hydroformed during the forming process, typically no heating step is performed and the forming process is a cold forming step.

[0098] In this embodiment, a seal portion 23 is provided on each of the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22. Each seal portion 23 is arranged to surround a hollow space formed by the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22. The seal portion 23 can improve the liquid-tightness or air-tightness of the hollow space. Specifically, when the first mold 21 and the second mold 22 are closed, the seal portion 23 of the first mold 21 and the seal portion 23 of the second mold 22 firmly abut against and sandwich the first blank 31 and the second blank 32, respectively. This makes 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 to leak around the hollow space. This allows for better molding of the structural member 10 using a fluid.

[0099] In this embodiment, a seal portion 24 is further provided on each of the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22. Each seal portion 24 is arranged so as to surround the other seal portion 23. The seal portions 24 can further improve the liquid-tightness or air-tightness of the hollow space. That is, when the first mold 21 and the second mold 22 are closed, the seal portions 24 can seal the periphery of the material 30 in the mold 20. This makes it difficult for fluid to leak outside the mold 20, and allows for even better molding of the structural member 10 using a fluid.

[0100] In this embodiment, the protrusion 213 provided on the first mold 21 may have a step on its side surface 213b. That is, a portion 213c of the side surface 213b of the protrusion 213 adjacent to the flange surface 212 of the first mold 21 may be substantially parallel to the machining direction D in a cross-sectional view. In this case, the size of the portion 213c is preferably equal to or larger than the size of the through hole 311 of the first blank 31. As a result, when the protrusion 213 is inserted into the through hole 311 of the first blank 31, the portion 213c widens the through hole 311. As a result, the periphery of the through hole 311 strongly contacts the side surface 213b of the protrusion 213 along its entire circumference, making it difficult for a gap to form between the periphery of the through hole 311 and the protrusion 213. This makes it difficult for fluid from the protrusion 213 to enter between the first blank 31 and the first mold 21. Therefore, the fluid is more reliably supplied between the first blank 31 and the second blank 32, and the material 30 can be formed more effectively.

[0101] In this embodiment, the flow path 214 formed in the first mold 21 preferably opens at a position near the tip of the protrusion 213. Furthermore, at least the portion of the flow path 214 that passes through the protrusion 213 is preferably inclined with respect to the processing direction D so as to intersect with the side surface 213b of the protrusion 213. This makes it difficult for the fluid from the protrusion 213 to enter between the first blank 31 and the first mold 21, and makes it easier for the fluid to be supplied between the first blank 31 and the second blank 32. Therefore, the material 30 can be molded more effectively using the fluid.

[0102] In this embodiment, a structural member 10 having a hollow cross section is formed by inflating the blank 30 with a fluid. In this case, a greater reduction in thickness can be tolerated than in conventional press molding. Specifically, in conventional press molding, cracks, necking, and the like occur in the blank 30 when the thickness reduction rate reaches 30, resulting in poor molding. In contrast, in the manufacturing method according to this embodiment, cracks, necking, and the like are less likely to occur in the portion of the blank 30 that is formed by the fluid, even when the thickness reduction rate is large. In the structural member 10 according to this embodiment, the thickness reduction rate T1 at the curved portion 111c of the first member 11, where thickness reduction is most likely to occur, is 30% or more. Similarly, the thickness reduction rate T2 at the curved portion 121c of the second member 12, where thickness reduction is most likely to occur, is 30% or more. Even when the thickness reduction rates T1 and T2 are 30% or more, the member bodies 111 and 121 can be successfully formed without cracks, necking, and the like.

[0103] Second Embodiment Fig. 7 is a perspective view showing the schematic configuration of a structural member 10A according to this embodiment. The structural member 10A is a front module for a vehicle body. In this case, the structural member 10A is provided at the front and bottom of a vehicle body such as an automobile. However, the structural member 10A may also be a subframe for a vehicle body. In this case, the structural member 10A is provided at the front or rear and bottom of a vehicle body such as an automobile. The subframe can have a configuration generally similar to that of the front module.

[0104] As shown in FIG. 1B , in the structural member 10 according to the first embodiment, the side frames 111a of the first member 11 are connected at their longitudinal centers by the cross member 111b. Similarly, in the structural member 10 according to the first embodiment, the side frames 121a of the second member 12 are connected at their longitudinal centers by the cross member 121b. On the other hand, as shown in FIG. 7 , in the structural member 10A according to the present embodiment, the side frames 111a of the first member 11 are connected at one longitudinal end by the cross member 111b. Similarly, in the structural member 10A, the side frames 121a of the second member 12 are connected at one longitudinal end by the cross member 121b. When the structural member 10A is assembled to the vehicle body, the cross members 111b, 121b are positioned, for example, at the rear ends of the side frames 111a, 121a.

[0105] The structural member 10A according to this embodiment can also be manufactured by the same manufacturing method as the manufacturing method according to Embodiment 1. Figures 8A to 8D are schematic diagrams for explaining the manufacturing method of the structural member 10A.

[0106] 8A and 8B , in this embodiment, a blank 30 including a first blank 31 and a second blank 32 is also prepared. The basic configurations of the first blank 31 and the second blank 32 are the same as those described in the first embodiment. However, because the shape of the structural member 10A ( FIG. 7 ) is different from that in the first embodiment, the first blank 31 and the second blank 32 have shapes different from the first blank 31 and the second blank 32 ( FIGS. 5A and 5B ) used in the manufacturing method according to the first embodiment.

[0107] The blank 30 is subjected to the same molding process as in the first embodiment. The blank 30 may be subjected to the molding process after the heating process described above. Referring to FIG. 8C , in this embodiment, the protrusions 213 of the first mold 21 are inserted into the through holes 311 of the first blank 31, and the blank 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22. A gap is formed between the first blank 31 and the second blank 32 by the protrusions 213. A fluid is then injected into the gap from the protrusions 213, and the fluid expands the blank 30 between the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22.

[0108] In this embodiment, protrusions 213 are provided in the first mold 21 and the second mold 22 near the cross member molding portions 211b, 221b of the molding surfaces 211, 221. In the cross member molding portions 211b, 221b, the material 30 is expanded by 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 Fig. 8D, in the side frame molding portions 211a, 221a, the material 30 is expanded by the fluid flowing from the cross member molding portions 211b, 221b side (Fig. 8C), and the first blank 31 and the second blank 32 are pressed against the first mold 21 and the second mold 22, respectively.

[0109] After the molding process, the outer periphery of the structural member 10A (FIG. 7) may be removed by laser cutting, etc. At least the portion of the structural member 10A where the through-holes 311 (FIG. 8C) are provided is typically removed after the molding process.

[0110] In this embodiment, immediately after the molding process using the fluid, the flanges 112, 122 are provided so as to surround the entire periphery of the member bodies 111, 121. For example, both end portions of the cross members 111b, 121b, including the through holes 311, may be removed after the molding process, thereby opening both longitudinal ends of the cross members 111b, 121b. Alternatively, for example, one longitudinal end of the side frames 111a, 121a may be opened by removing the end portions of the side frames 111a, 121a opposite to the cross members 111b, 121b after the molding process.

[0111] 9 is a perspective view showing a schematic configuration of a 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 portion of the floor of a vehicle body such as an automobile.

[0112] 9 , in the structural member 10B, similar to the 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 at one longitudinal end thereof by the cross member 121b. The member body 121 forms a hollow cross section together with the first member 11 by joining a flange 122 to the first member 11.

[0113] In this embodiment, the first member 11 includes a floor panel 115 and a floor tunnel 116. As in other embodiments, the first member 11 may include at least one cross member 111b (FIGS. 1B and 7). 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 convex shape toward the second member 12 relative to the floor panel 115. If the first member 11 includes a cross member 111b, the cross member 111b may be positioned to face the cross member 121b of the second member. Portions of the flanges 122 of the second member 12 that are continuous with the side frames 121a are joined to the floor panel 115. Portions of the flanges 122 of the second member 12 that are continuous with the cross member 121b are joined to the floor panel 115 and the floor tunnel 116.

[0114] The structural member 10B according to this embodiment can be manufactured by the same manufacturing method as the manufacturing methods according to the other embodiments. Figures 10A to 10D are schematic diagrams for explaining the manufacturing method of the structural member 10B.

[0115] 10A and 10B , in this embodiment, a blank 30 including a first blank 31 and a second blank 32 is prepared. As in the other embodiments, the first blank 31 and the second blank 32 are overlapped and joined. However, in this embodiment, since the shape of the first member 11 and the shape of the second member 12 are significantly different as shown in FIG. 9 , the first blank 31 and the second blank 32 also have different shapes.

[0116] The blank 30 is subjected to the same molding process as in the other embodiments. The blank 30 may be subjected to the molding process after the heating process described above. Referring to FIG. 10C , in this embodiment, the protrusions 213 of the first mold 21 are inserted into the through holes 311 of the first blank 31, and the blank 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22. A gap is formed between the first blank 31 and the second blank 32 by the protrusions 213. A fluid is then injected into the gap from the protrusions 213, and the fluid expands the blank 30 between the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22.

[0117] In this embodiment, the first mold 21 and the second mold 22 have protrusions 213 provided near the cross member molding portions 211b, 221b of the molding surfaces 211, 221. In the cross member molding portions 211b, 221b, the material 30 is expanded by 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 FIG. 10D , in this embodiment, since the first member 11 ( FIG. 9 ) does not include side frames, the side frame molding portion 221a is present only in the second mold 22. At the position of the side frame molding portion 221a, the material 30 is expanded by fluid flowing from the cross member molding portions 211b, 221b side ( FIG. 10C ), 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 portion 221a, the material 30 bulges mainly toward the second mold 22 and does not substantially bulge toward the first mold 21. The portion of the first blank 31 that does not overlap with the second blank 32 is clamped between the first mold 21 and the second mold 22 as in normal press molding, and is molded into a shape that conforms to the molding surfaces 211, 221.

[0118] After the molding process, the outer periphery of the structural member 10B (FIG. 9) may be removed by laser cutting or the like. At least the portion of the structural member 10B where the through-hole 311 (FIG. 10C) is provided is typically removed after the molding process. For example, both ends of the cross member 121b may be removed to open both longitudinal ends of the cross member 121b. At this time, the left and right ends of the floor panel 115, including the through-hole 311, may also be removed.

[0119] 11 is a perspective view showing a schematic configuration of a 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 10C is provided in the center or rear part of the floor of a vehicle body such as an automobile.

[0120] As shown in FIG. 11 , the structural member 10C includes multiple second members 12F and 12R. When the structural member 10C is assembled to the vehicle body, the second member 12F is disposed 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 a member body 121. A curved portion 121c is provided at one or both longitudinal ends of the cross member 121b. In this embodiment, the cross member 121b has wide portions at both longitudinal ends. The corners between these wide portions and other portions form the curved portions 121c. Flanges 122 are provided on both sides of the cross member 121b.

[0121] The flanges 122 of the second members 12F, 12R are joined to the first member 11, so that the member bodies 121 of the second members 12F, 12R form a hollow cross section together with the first member 11. As in the third embodiment, the first member 11 includes a floor panel 115 and a floor tunnel 116. As in the other embodiments, the first member 11 may include at least one cross member 111b (FIGS. 1B and 7). The first member 11 may also include multiple cross members 111b corresponding to the second members 12F, 12R.

[0122] 12A and 12B , in this embodiment, a raw 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 that correspond to the second members 12F, 12R ( FIG. 11 ), respectively. The first blank 31 has through holes 311 formed at positions that correspond to the second members 12F, 12R.

[0123] The blank 30 is subjected to the same molding process as in the other embodiments. The blank 30 may be subjected to the molding process after the heating process described above. Referring to FIGS. 12C and 12D , in this embodiment, the protrusions 213 of the first mold 21 are inserted into the through holes 311 of the first blank 31, and the blank 30 is sandwiched between the flange surface 212 of the first mold 21 and the flange surface 222 of the second mold 22. A gap is then formed between the first blank 31 and the second blank 32F by the protrusions 213. A fluid is then injected into the gap through the protrusions 213, and the fluid expands the blank 30 between the molding surface 211 of the first mold 21 and the molding surface 221 of the second mold 22. As a result, the first blank 31 and the second blank 32F are pressed against the first mold 21 and the second mold 22, respectively, as shown in FIG. 12C . Furthermore, as shown in FIG. 12D, the first blank 31 and the second blank 32R are pressed against the first mold 21 and the second mold 22, respectively.

[0124] After the molding process, the outer periphery of the structural member 10C (FIG. 11) may be removed by laser cutting or the like. At least the portion of the structural member 10C where the through-holes 311 (FIGS. 12C and 12D) are provided is typically removed after the molding process. For example, both ends of the second members 12F and 12R may be removed to open both longitudinal ends of each cross member 121b. At this time, the left and right ends of the floor panel 115, including the through-holes 311, may also be removed.

[0125] In the structural members 10A to 10C according to the second, third, and fourth embodiments, the thickness reduction rate T1 of the curved portion 111c and / or the thickness reduction rate T2 of the curved portion 121c have the same characteristics as those in the first embodiment. Furthermore, in these embodiments, when a heating step is performed before the forming step, the minimum Vickers hardness of the heat-affected zone of the weld 13 also has the same characteristics as those in the first embodiment.

[0126] In the structural members 10A to 10C according to the second, third, and fourth embodiments, the first blank 31 is formed of one or more metal plates (sub-blanks) as in the first embodiment. The second blanks 32, 32F, and 32R are also formed of one or more metal plates (sub-blanks) as in the first embodiment.

[0127] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0128] In the above embodiments, the structural member 10 is a rear module of the vehicle body, the structural member 10A is a front module, and the structural members 10B and 10C are floor modules. However, the structural members manufactured by the manufacturing method according to the present disclosure are not limited to the structural members 10, 10A to 10C illustrated in the above embodiments. The manufacturing method according to the present disclosure 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 continuing from the member body may be provided on both the first member and the second member as in the first and second embodiments, or may be provided on only one of the first member and the second member as in the third and fourth embodiments.

[0129] For example, as shown in Fig. 13 , the manufacturing method according to the present disclosure can also be applied to a structural member 10D including a first member 11, which is a lid for a battery case, and multiple second members 12. In the structural member 10D, the member body 121 of each of the second members 12 is a cross member. In the example of Fig. 13 , the first member 11 also serves as a floor panel for the vehicle body. The second members 12 are disposed on the first member 11 and each extend in the left-right direction of the vehicle body.

[0130] The through holes 311 in the first blank 31 may be arranged according to the shape of the structural member to be formed, etc. The through holes 311 are preferably provided in locations of the first blank 31 where a relatively small amount of material flows into the hollow space of the mold 20 during the forming process. For example, if the raw material 30 is rectangular and the first blank 31 and the second blank 32 are overlapped at the corners of the raw material 30, the through holes 311 are preferably arranged in the corners of the raw material 30. This allows the structural member to be formed while suppressing deformation of the through holes 311.

[0131] In the above embodiment, an example has been described in which the first mold 21 including one or more protrusions 213 is disposed below the 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 disposed above the second mold 22, for example. In this case, the protrusions 213 are located 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. Therefore, there is no need to provide the protrusions 213 with flat tip surfaces 213a to position the material 30.

[0132] In the above embodiment, the seal portions 23, 24 are provided on both the first mold 21 and the second mold 22. However, the seal portion 23 and / or the seal portion 24 may not be provided on one of the first mold 21 and the second mold 22, or neither the first mold 21 nor the second mold 22 may be provided with either the seal portion 23, 24. However, from the viewpoint of preventing leakage of fluid, it is preferable that at least the seal portion 23 is provided on both the first mold 21 and the second mold 22. More preferably, the seal portions 23, 24 are provided in duplicate on both the first mold 21 and the second mold 22.

[0133] 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 may be attached to a portion of the structural member 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 molding at a position corresponding to the ridge of the floor tunnel 116. The reinforcing plate may be joined to the first blank 31 from the side opposite the surface where the first blank 31 and the second blank 32 are joined. Alternatively, the reinforcing plate may be joined to the second blank 32 from the side opposite the surface where the first blank 31 and the second blank 32 are joined. 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.

[0134] In the above embodiment, an example has been described in which the die 20 is used to form the structural member 10, 10A to 10C from the material 30 including the first blank 31 and the second blank 32 or 32F, 32R joined to the first blank 31. However, the die 20 can also be used for forming using a material 30 in which the second blank 32 is superimposed on the first blank 31 but is not joined to the first blank 31.

[0135] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0136] To confirm the differences between a structural member manufactured using the manufacturing method according to the present disclosure and a structural member manufactured using a conventional manufacturing method, a forming test was conducted on the structural member 10 according to the first embodiment. In this test, the structural member 10 was formed using the manufacturing method described in the above embodiment (hydraulic blowing or gas blowing), and the thickness reduction rate T2 at the curved portion 121c of the member body 121 of the upper member (second member) 12 was measured. For the hydraulic blowing, industrial water mixed with a rust inhibitor was used as the forming fluid, and for the gas blowing, compressed air was used as the forming fluid. A heating process for the material was not performed during the hydraulic blowing, but a heating process for the material was performed before the forming process during the gas blowing. Furthermore, the second member 12 was formed using cold press forming and hot stamping, which are conventional manufacturing methods, and the thickness reduction rate T2 at the curved portion 121c of the member body 121 was measured. The test conditions and results are shown in Table 1.

[0137]

[0138] Table 1 shows the forming method, material and strength (tensile strength), forming height, thickness reduction rate T2, and forming evaluation for each example and comparative example. The thickness reduction rate T2 was calculated by obtaining the thickness t of the curved portion 121c of the member body 121 using the measurement method described in the above embodiment, and setting the 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. Regarding the forming evaluation, a case in which no forming defects occurred in the curved portion 121c, where the thickness is reduced the most during forming, was evaluated as A, a case in which necking occurred was evaluated as B, and a case in which cracking occurred was evaluated as C. In this test, a crack of 0.1 mm or more in the curved portion 121c was evaluated as cracking, and a case in which no cracking occurred but the thickness of only one of the measurement points used to obtain the curved portion 121c's thickness t was reduced by 0.05 mm or more compared to the surrounding area was evaluated as necking.

[0139] As shown in Table 1, in Comparative Examples 1 and 2 in which the second member 12 was formed by cold press forming only, the plate thickness reduction rate T2 at the curved portion 121c of the member main body 121 was 34%, and cracks occurred at the curved portion 121c.

[0140] In Comparative Examples 3 and 4, a 1.5 GPa-class hot stamp material was used as the raw material, and the second member 12 was formed solely by hot stamping. In Comparative Example 3, the forming height was relatively small, so the sheet thickness reduction rate T2 at the curved portion 121c of the member main body 121 was less than 30%, and no forming defects occurred at the curved portion 121c. However, in Comparative Example 4, the forming height was relatively large, so the sheet thickness reduction rate T2 was 30%, and necking occurred at the curved portion 121c.

[0141] In Comparative Examples 5 and 6, a 2.0 GPa-class hot stamp material was used as the raw material, and the second member 12 was formed solely by hot stamping. In Comparative Example 5, the forming height was relatively small, so no forming defects occurred at the curved portion 121c of the member main body 121. However, in Comparative Example 6, the forming height was relatively large, so necking occurred at the curved portion 121c. In Comparative Example 5, the sheet thickness reduction rate T2 at the curved portion 121c was 26%, and in Comparative Example 6, the sheet thickness reduction rate T2 was 28%.

[0142] Thus, among Comparative Examples 1 to 6, there was no example in which the curved portion 121c of the component body 121 was formed without forming defects even when the plate thickness reduction rate T2 was 30% or more. However, in Examples 1 to 8, regardless of whether hydraulic blowing or gas blowing was used, no forming defects occurred in the curved portion 121c, even though the plate thickness reduction rate T2 was 30% or more. In Examples 1 to 8, it is presumed that the use of hydraulic blowing or gas blowing promoted the inflow and outflow of material, thereby promoting biaxial tensile deformation even in corner portions, and therefore enabled the curved portion 121c to be formed well even when the plate thickness reduction rate T2 was 30% or more.

[0143] In order to confirm the upper limit of the thickness reduction rate T2 for Examples 1 to 8, a separate test was conducted. In Examples 1, 3, 5, and 7, in which the forming height was 30 mm, no forming defects occurred in the curved portion 121c even when the thickness reduction rate T2 exceeded 50%, regardless of the forming method (hydraulic blowing or gas blowing) and material. On the other hand, in Examples 2, 4, 6, and 8, in which the forming height was 40 mm, forming defects occurred in the curved portion 121c as the thickness reduction rate T2 increased. When the forming method was hydraulic blowing, in Example 2, which used a steel plate with a tensile strength of 270 MPa, cracks occurred in the curved portion 121c when the 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 thickness reduction rate T2 was 45%. When the forming method was gas blowing, necking occurred in the curved portion 121c when the thickness reduction rate T2 was 55% in both Example 6, which used a 1.5 GPa-class hot-stamped material, and Example 8, which used a 2.0 GPa-class hot-stamped material. Therefore, with regard to the forming method, material, and forming height of this test, it was confirmed that forming defects were generally suppressed when the thickness reduction rate T2 was 50% or less, and no forming defects occurred when the thickness reduction rate T2 was less than 45%.

[0144] 10, 10A, 10B, 10C, 10D: structural member 11: first member 111: member body 111a: side frame 111b: cross member 111c: curved portion 112: flange 12, 12F, 12R: second member 121: member body 121a: side frame 121b: cross member 121c: curved portion 122: flange 20: mold 21: first mold 211: (first) molding surface 212: (first) flange surface 213: protrusion 214: flow path 22: second mold 221: (second) molding surface 222: (second) flange surface 23: (first) seal portion 24: (second) seal portion 30: material 31: first blank 311: through hole 32, 32F, 32R: Second blank

Claims

1. A method for manufacturing a structural member, comprising the steps of: preparing a material including a first blank having a through hole and a second blank superimposed and joined to the first blank; and molding the material using a first mold and a second mold, wherein the first mold includes a molding surface and a flange surface disposed around the molding surface and having protrusions formed thereon; and the molding step includes the steps of: clamping the material between the flange surface and the second mold with the protrusions inserted into the through holes, and creating a gap between the first blank and the second blank by the protrusions; and injecting a fluid into the gap through the protrusions, and using the fluid to expand the material in the hollow space formed by the molding surface and the second mold.

2. The manufacturing method according to claim 1, further comprising the step of heating the material before the molding step.

3. A mold for manufacturing a structural member from a material including a first blank having a through hole and a second blank superimposed on the first blank, comprising: a first mold including a first molding surface and a first flange surface arranged around the first molding surface and having a protrusion formed thereon; and a second mold including a second molding surface configured to form a hollow space together with the first molding surface and a second flange surface arranged around the second molding surface and corresponding to the first flange surface, wherein the first mold further includes a flow path for a fluid formed within the first mold and opening into the protrusion.

4. A mold according to claim 3, further comprising a first convex seal portion provided on at least one of the first flange surface and the second flange surface and arranged to surround the hollow space.

5. A mold according to claim 4, further comprising a convex second seal portion provided on at least one of the first flange surface and the second flange surface and arranged to surround the first seal portion.

6. A structural member comprising: a first member; and a second member; one of the first member and the second member includes a member body including a curved portion that is curved in a plan view of the structural member, and a flange provided continuous with the member body, the flange being 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 thickness at the curved portion of the member body based on the thickness of the flange is 30% or more.

7. A structural member according to claim 6, wherein the structural member is a rear module for a vehicle body, the member body includes a pair of side frames and a cross member connecting the side frames, and the curved portion is provided at the connection between each of the side frames and the cross member.

8. A structural member according to claim 6, wherein the structural member is a front module for a vehicle body, the member body includes a pair of side frames and a cross member connecting the side frames, and the curved portion is provided at the connection between each of the side frames and the cross member.

9. A structural member as claimed in claim 6, wherein the structural member is a subframe for a vehicle body, the member body includes a pair of side frames and a cross member connecting the side frames, and the curved portion is provided at the connection between each of the side frames and the cross member.

10. A structural member according to claim 6, wherein the structural member is a floor module for a vehicle body, the member body includes a cross member, and the curved portion is provided at a longitudinal end of the cross member.

Images