Vehicle side frame component and integrated blank for side frame component

Abstract

An objective of the present invention is to provide a vehicle side frame component (for example, an automobile door ring) that is further improved by taking into account not only aspects relating to production technology but also aspects relating to safety and weight reduction when manufacturing the vehicle side frame component.　The vehicle side frame component comprises a plurality of steel plates, and includes a side sill and pillars connected to the side sill, wherein: in at least one of the pillars, a blank corresponding to the pillar and a blank corresponding to the side sill have a joint portion that is joined at an overlapping portion where the blanks overlap each other; the overlapping portion is located outside a lower connecting portion, which is a part where the side sill and the pillar are connected and which is a region surrounded by an imaginary line indicating the width of the side sill and an imaginary line indicating the width of the pillar, and the overlapping portion is disposed within the pillar; the overlapping portion is spaced apart from the lower connecting portion by 10 mm to 200 mm; and an integrated blank formed by joining parts of the overlapping portion that do not hinder material flow due to press forming (parts with little material flow) is formed integrally by hot stamping.

Description

Vehicle side frame components and integrated blanks for side frame components

[0001] The present invention relates to a vehicle side frame component and a blank for the same side frame component.

[0002] In the automotive and other sectors, there is a growing demand for reducing lifecycle GHGs (total greenhouse gas emissions over the entire lifecycle), leading to increased demand for the integration of parts and modules to improve the efficiency of manufacturing lines by reducing the number of parts and streamlining processes. The benefits are particularly significant if large parts, such as side frame components for vehicles, or automotive door rings, which combine numerous components, can be molded as a single unit. Therefore, there is a growing demand for the integrated press molding of side frame components using tailored welded blanks (TWB), which are blanks made by combining different types of steel sheets.

[0003] Several proposals have been made for the application of TWBs to vehicle side frame components, particularly door rings. Patent Document 1 proposes a manufacturing method for the inner reinforcing components of a door ring using an integrated blank. This method involves manufacturing a flat integrated blank (TWB) using blanks corresponding to the inner front pillar, inner center pillar, and the inner side rails (roof rails) that connect them, and then hot-forging this to integrally press-form the inner reinforcing components. Patent Document 2 proposes a manufacturing method for door rings using an integrated blank. This method involves creating a TWB by partially overlapping and joining blanks corresponding to each component of the door ring, and then manufacturing the side structure frame (door ring) of an automobile by integral press-forming. Patent Document 3 proposes a side structure (door ring) of an automobile in which the inner and outer frames of the door ring (double door ring) are manufactured by hot-stamping an integrated blank created by butt-welding partial blanks, and then assembling the resulting inner and outer frames to form a hollow volume.

[0004] International Publication No. 2016 / 046590, International Publication No. 2020 / 002335, International Publication No. 2022 / 064331

[0005] In the trend of improving the efficiency and reducing the cost of component manufacturing, when manufacturing a vehicle side frame such as an automobile door ring, which is a large component, mass-producing and manufacturing an integrated blank by TWB through press forming has been attracting increasing attention.

[0006] On the other hand, vehicles such as automobiles are constantly required to be lightweight from the perspective of energy efficiency, in addition to ensuring safety. Therefore, it is necessary to balance not only the requirements from the perspective of production technology such as improving the efficiency and reducing the cost of component manufacturing, but also the requirements of the inherent safety and lightweight of the vehicle itself. Therefore, an object of the present invention is to provide a vehicle side frame component with further improvement by adding perspectives not only from the aspect of production technology but also from the aspects of safety and lightweight when manufacturing a vehicle side frame component.

[0007] In order to achieve the above problems, the inventors have intensively developed based on an automobile door ring as a vehicle side frame, adding perspectives of safety and lightweight. At that time, regarding safety, development was advanced from the perspective of safety during side collisions (side collision safety) because the target was vehicle side frame components. As an index of the side collision safety of vehicle side frame components (door rings), based on the side collision test of the US IIHS (Insurance Institute For Highway Safety), development was advanced with the goal of reducing the amount of deformation of the side frame, specifically, the displacement amount (maximum penetration amount) pushed into the vehicle interior direction of the pillar. The IIHS side collision test simulates a side collision in an actual automobile and evaluates the collision safety mainly around the lower part of the vehicle side. That is, since an impact load due to a collision is applied around the connection part of the side sill and the pillar arranged at the lower part of the door ring, attention was paid to the structure of the connection part of the side sill and the pillar. As a result, the following findings were obtained.

[0008] (a) When manufacturing an integrated door ring blank using TWB, from the standpoint of weight reduction, it is preferable to simply butt-join blanks made of steel plates that will become each component to create a TWB. However, due to differences in the thickness of each steel plate, butt welding is difficult to perform and time-consuming, and as the size of the part increases, welding strain accumulates, making it difficult to improve the shape accuracy of the integrated blank, which may worsen productivity and lead to increased costs. Therefore, for the connection between the pillar and the side sill, which is important for side impact safety, it was assumed that the blanks corresponding to the pillar and the side sill would overlap, and the overlapping part of the blanks (overlap portion) would be joined by spot welding or the like. The overlapping part of the blank has a thicker plate, which is advantageous in terms of strength, but it is disadvantageous in terms of weight due to the increased plate thickness. Therefore, the position and width of the overlapping part of the blanks corresponding to the pillar and the side sill were analyzed in detail to see how it affects side impact safety.

[0009] As a result, we found that to reduce the maximum penetration amount of the pillar (the maximum displacement of the pillar surface from its original position), it is better to place the overlapping section of the blank corresponding to the pillar and side sill not at the connection point between the pillar and the side sill, but in the pillar near the connection point. From the standpoint of weight reduction, we confirmed that overlapping within the pillar rather than at the connection point between the pillar and the side sill reduces the overlapping area, thereby reducing weight.

[0010] (i) As a result of the simulation analysis, it was found that it is effective to position the overlapping portion of the blank corresponding to the pillar and the blank corresponding to the side sill separately from the connection point between the side sill and the pillar.

[0011] (c) The width of the overlapping section (length in the axis direction of the pillar center) is preferable to be as short as possible as it affects the weight increase. However, since it is necessary to secure a weldable area for joining, it has also been found that it is desirable to secure a length that allows for at least two rows of spot welds (30 mm or more).

[0012] (e) When press forming an integrated blank using high-strength steel plate, hot stamping is preferable. In the case of hot-stamped parts, the heat treatment during hot stamping eliminates the HAZ softened area at the joint (especially the welded joint). This also contributes to improving the strength of the joint. In particular, it is effective to perform joining (welding, etc.) (place the joint) in areas that do not hinder material flow during press forming or in areas with little material flow (for example, the area corresponding to the top surface of a part with a hat-shaped cross section). Unjoined parts that were not joined before press forming can be joined after press forming, and these joints will have HAZ softened areas. That is, in a side frame part manufactured by integral press forming of an integrated blank using hot stamping, at least one joint (a joint joined before hot stamping) among the joints of the overlapping parts of the blank will be a joint without HAZ softened areas. Furthermore, since the unjoined parts are joined after press molding, the joint will have both areas without HAZ softening and areas with HAZ softening.

[0013] This invention is based on the above findings, and its purpose is as follows.

[0014] [1] A vehicle side frame component comprising the side of a vehicle and configured as a joint structure in which blanks made of a plurality of steel plates are joined together, wherein the side frame component comprises a side sill located at the lower part of the side frame component and extending in the direction of vehicle travel, and one or more pillars extending perpendicular to the direction of vehicle travel and connected to the side sill, wherein in at least one of the pillars, the blank corresponding to the pillar and the blank corresponding to the side sill are joined by an overlapping portion where they are superimposed on each other, the overlapping portion is located outside the lower connection portion which is the area enclosed by a virtual line indicating the width of the side sill and a virtual line indicating the width of the pillar, and is located inside the pillar, the overlapping portion is spaced 10 mm to 200 mm away from the lower connection portion along the longitudinal central axis of the pillar, and at least one of the joints does not have a HAZ softening portion. The separation distance between the overlapping portion and the lower connecting portion is preferably 20 mm or more, 30 mm or more, 40 mm or more, or 50 mm or more, and also preferably 180 mm or less, 160 mm or less, 150 mm or less, 140 mm or less, 130 mm or less, 120 mm or less, 110 mm or less, or 100 mm or less. [2] The vehicle side frame component according to [1], wherein the joint portion has both a joint portion without the HAZ softening portion and a joint portion with the HAZ softening portion. [3] The vehicle side frame component according to [1] or [2], wherein the pillar has a top surface portion and a vertical wall portion adjacent to the top surface portion, the cross-section of the pillar is C-shaped or hat-shaped, and the joint portion without the HAZ softening portion exists only on the top surface portion.[4] The side frame part for a vehicle according to any one of the above [1] to [3], wherein the joint without a HAZ softened portion is such that, in a cross section perpendicular to the surface of the outermost blank including the center of the joint, at a position 3 / 4 of the plate thickness from the surface of the outermost blank, when the Vickers hardness at a position that is not joined and is 15 mm or more away from the center of the joint is Hvm, the difference between the maximum and minimum Vickers hardness in a range within 5 mm toward the base material from the end of the weld metal portion of the joint is 0.2 Hvm or less (preferably △Hv is 0.1 Hvm or less) (i.e., there is no HAZ softened portion). [5] The side frame part for a vehicle according to any one of the above [1] to [4], wherein the overlapping portion has a length of 25 mm or more along the longitudinal central axis of the pillar. The length of the overlapping portion along the longitudinal central axis of the pillar is preferably 30 mm or more, and more preferably 100 mm or less, 80 mm or less, 60 mm or less, or 50 mm or less. [6] The side frame component further has a roof rail positioned on the upper part of the side frame component and extending in the direction of vehicle travel, wherein the blank corresponding to the roof rail and the blank corresponding to the pillar are joined at an upper overlapping portion that overlaps each other, and the upper overlapping portion is the part where the roof rail and the pillar connect, and is positioned inside an upper connection portion which is an area enclosed by a virtual line indicating the width of the roof rail and a virtual line indicating the width of the pillar. [7] The side frame component of a vehicle according to any one of the above [1] to [6], wherein the side frame component is an automobile door ring. [8] A vehicle side frame component according to any one of items [1] to [7], wherein the pillar is one or more selected from a front pillar, a center pillar, and a rear pillar. [9] A vehicle side frame component according to any one of items [1] to [9], wherein the steel plate corresponding to the side sill is a surface-softened steel plate (high-bend material).

[10] A vehicle side frame component according to any one of items [1] to [9], wherein the side frame component is hot-stamped.

[11] A press-formed integrated blank configured as a joint structure of multiple steel plates for a vehicle side frame component that constitutes the side of a vehicle, wherein the side frame component has a side sill located at the lower part of the side frame component and extending in the direction of vehicle travel, and one or more pillars extending perpendicular to the direction of vehicle travel and connected to the side sill, and at least one blank corresponding to one of the pillars and the blank corresponding to the side sill have at least one joint where they are joined by overlapping portions, the joint is located in one of the regions divided by a bent portion that is bent by press forming in the overlapping portion, the overlapping portion is located outside the lower connection portion which is the portion where the side sill and the pillar are connected and is located inside the pillar, and the overlapping portion is spaced 10 mm to 200 mm away from the lower connection portion along the longitudinal central axis of the pillar. The separation distance between the overlapping portion and the lower connecting portion is preferably 20 mm or more, 30 mm or more, 40 mm or more, or 50 mm or more, and also preferably 180 mm or less, 160 mm or less, 150 mm or less, 140 mm or less, 130 mm or less, 120 mm or less, 110 mm or less, or 100 mm or less.

[12] The integrated blank for a vehicle side frame part according to

[11] , wherein the overlapping portion has a length of 25 mm or more along the longitudinal central axis of the pillar.

[13] The integrated blank for a vehicle side frame part according to

[11] or

[12] , wherein the pillar has a top surface portion and a vertical wall portion adjacent to the top surface portion, the cross section of the pillar is C-shaped or hat-shaped, and the overlapping portion is joined only at the portion corresponding to the top surface portion.

[14] A method for manufacturing a vehicle side frame component that constitutes the side surface of a vehicle as described in any one of the items [1] to

[10] above, comprising: an integrated blanking process for preparing an integrated blank for press forming configured as a joining structure of a plurality of steel plates for the side frame component; a hot press forming process for hot press forming the integrated blank; and a post-press component joining process for joining portions of the integrated blank press-formed in the hot press forming process that were not joined in the integrated blanking process, wherein in the integrated blanking process, at least one blank corresponding to the pillar and the blank corresponding to the side sill are joined such that they have at least one joint portion joined by an overlapping portion that is superimposed on each other, the overlapping portion is located outside the lower connection portion which is the portion where the side sill and the pillar are connected and is surrounded by a virtual line indicating the width of the side sill and a virtual line indicating the width of the pillar, and is located inside the pillar, and the overlapping portion is spaced 10 mm to 200 mm away from the lower connection portion along the longitudinal central axis of the pillar. The separation distance between the overlapping portion and the lower connecting portion is preferably 20 mm or more, 30 mm or more, 40 mm or more, or 50 mm or more, and also preferably 180 mm or less, 160 mm or less, 150 mm or less, 140 mm or less, 130 mm or less, 120 mm or less, 110 mm or less, or 100 mm or less.

[15] The method for manufacturing a vehicle side frame part according to

[14] , wherein the overlapping portion has a length of 25 mm or more along the longitudinal central axis of the pillar.

[16] The method for manufacturing a vehicle side frame part according to

[14] or

[15] , wherein the joint portion is located in one of the regions separated by the portion that is bent by the hot press forming in the overlapping portion.

[17] A method for manufacturing a vehicle side frame part according to any one of the above

[14] to

[16] , wherein the pillar has a top surface portion and a vertical wall portion adjacent to the top surface portion, the cross section of the pillar is C-shaped or hat-shaped, and in the integrated blanking process, the overlapping portion is joined only at the portion corresponding to the top surface portion.

[0015] According to the present invention, a vehicle side frame component can be obtained by integrally molding an integrated blank (TWB) formed by joining multiple partial blanks, while maintaining advantages in production technology, ensuring safety (side collision safety), and further reducing weight.

[0016] This is a schematic diagram showing an example of a double door ring for an automobile. Figure 1(a) shows the external appearance of an example of a double door ring, and Figure 1(b) shows an example of the blank configuration of that door ring. This is a diagram showing an example of the blank configuration of a single door ring for an automobile. This is a diagram showing an example of an integrated blank used when manufacturing the door ring in Figure 1(b). This is a diagram showing an example of the blank configuration of a double door ring. This is a diagram showing an example of an integrated blank for manufacturing the double door ring in Figure 4. This is a diagram to explain the overlapping portion between the side sill equivalent blank and the center pillar equivalent blank in the double door ring diagram in Figure 4. This is a diagram to explain the overlapping portion in the integrated blank of the door ring in Figure 4. This is a diagram to explain the manufacturing process of a part by press forming of a typical TWB. This is a diagram to explain the HAZ softening portion by spot welding. This is a diagram to explain the overlapping portion between the side sill equivalent blank and the center pillar equivalent blank in a conventional double door ring.

[0017] The present invention will be described using an automobile door ring, which is one embodiment of a vehicle side frame component according to the present invention (hereinafter simply referred to as "this embodiment"), as an example.

[0018] Figure 1(a) shows an external view of a double door ring 100 as an example of an automotive door ring. The door ring is a side frame component that forms the side of an automobile vehicle, and in Figure 1(a), the direction from right to left in the drawing is the direction of vehicle travel (direction of the arrow in Figure 1(a). Hereafter, unless otherwise specified, the direction of vehicle travel in the door ring diagram will be from right to left in the drawing, as in Figure 1(a).) In the example of Figure 1(a), a side sill 113 extending in the direction of vehicle travel is located at the bottom of the door ring 100, and three pillars extending vertically upward with respect to the direction of vehicle travel are connected to the side sill 113. The three pillars are the front pillar (A pillar) 111, the center pillar (B pillar) 112, and the rear pillar (C pillar) 114. Furthermore, a roof rail 115 extending in the direction of vehicle travel and to which each pillar is connected is located at the top of the door ring.

[0019] Automotive door rings 110 typically consist of a door ring inner, which is located on the inside of the vehicle, and a door ring outer, which is located on the outside of the vehicle. The door ring inner and door ring outer are manufactured separately and then bonded together. Structurally, the door ring inner and door ring outer are in a front-and-back relationship, and the component configurations of pillars, side sills, etc., are basically the same. In the following description, this embodiment will be explained using the door ring inner (the part of the door ring on the inside of the vehicle) as an example. Unless otherwise specified, "door ring" refers to the door ring inner, and each part of the door ring, such as "pillar" and "side sill," will refer to each part of the door ring inner. Needless to say, the "door ring" described below can also be applied to the door ring outer and its various components.

[0020] The integrated blank for vehicle side frame components is constructed as a joint structure in which multiple types of steel plates (blanks) are joined together. The door ring 100 according to this embodiment is manufactured by press forming the integrated blank. Figure 1(b) shows an example of the door ring 100 in Figure 1(a) divided into its respective blanks. In the example shown in Figure 1(b), the door ring 100 is composed of a blank corresponding to the side sill 113 (side sill equivalent blank) 215, a blank corresponding to the front pillar 111 (front pillar equivalent blank) 213, a lower blank (center pillar lower equivalent blank) 212 and an upper blank (center pillar upper equivalent blank) 211 corresponding to the center pillar 112 (these lower and upper blanks of the center pillar are collectively called the center pillar equivalent blank), a lower blank (rear pillar lower equivalent blank) 218 ​​and an upper blank (rear pillar upper equivalent blank) 217 ​​corresponding to the rear pillar 114 (these lower and upper blanks of the rear pillar are collectively called the rear pillar equivalent blank), and a blank corresponding to the roof rail (roof rail equivalent blank) 214. The term "equivalent blank" means that the area of ​​the door ring and the blank do not necessarily coincide, but rather that the blank primarily constitutes that area. For example, in Figure 1, it can be seen that a portion of the front pillar equivalent blank 213 that constitutes the front pillar 111 also constitutes the roof rail 115.

[0021] These blanks utilize steel plates of varying strengths and thicknesses as needed. For example, the front pillar 213, center pillar upper 211, and rear pillar upper 217 blanks use 2.0 GPa class high-strength steel plates to ensure interior space during collisions, while the center pillar lower 212 and rear pillar lower 218, which join to the side sill 215, may use 1.3 GPa class high-strength steel plates to ensure workability and toughness. In this case, the side sill 215 and roof rail 214 may be made of 1.2 GPa class high-strength steel plates. Furthermore, the thickness of each blank is determined by the vehicle body structure design, and therefore often differs from blank to blank. These blanks are joined together to manufacture a tangible blank (TWB: tailored blank), and this tangible blank is press-formed to manufacture side frame components (door rings). Therefore, compared to the method of press-forming each blank and joining them to assemble the door ring, this not only achieves a significant reduction in process time and costs, but also improves the reliability of the joints, leading to improved safety. In other words, the vehicle side frame component according to this embodiment constitutes the side of the vehicle and is configured as a joining structure of blanks made of multiple steel plates.

[0022] Figure 2 shows an example of a single door ring 200. The single door ring consists of two pillars, a front pillar and a rear pillar, each connected to the side sill and roof rail. In the example in Figure 2, the shape of the rear pillar is similar to the center pillar 112 of the double door ring in Figure 1, but the structure is not particularly limited. For example, the structure could be the same as the double door ring 100 in Figure 1 but without the center pillar 112.

[0023] Figure 2 is a diagram showing an example of the blank configuration, similar to Figure 1(b), and is a diagram divided by the blanks that make up the single door ring 200. Similar to the example in Figure 1(b), the front pillar equivalent blank 213 and the rear pillar upper equivalent blank 217 are made of 2.0 GPa class high-strength steel plate from the viewpoint of securing interior space during a collision, while the rear pillar lower equivalent blank 218, which is joined to the side sill equivalent blank 215, may be made of 1.3 GPa class high-strength steel plate to ensure workability and toughness. In this case, the side sill equivalent blank 215 and the front roof rail equivalent blank 214 may be made of 1.2 GPa class high-strength steel plate, and the plate thickness often differs for each component. These blanks can be joined to manufacture an integrated blank (TWB), and this integrated blank can be press-formed to manufacture the single door ring.

[0024] Figure 3 shows an example of an integrated blank 300 used when manufacturing the door ring 100 shown in Figure 1(b). It is made by combining various blanks (side sill equivalent blank 215, front pillar equivalent blank 213, center pillar lower equivalent blank 212 and center pillar upper equivalent blank 211, rear pillar lower equivalent blank 218 and rear pillar upper equivalent blank 217, and roof rail equivalent blank 214), and joining the blanks together (for example, spot welding, overlap welding, etc.) to form an integrated blank. Since the blanks before press forming are flat steel plates, the integrated blank 300 is also flat, unlike the door ring 100 shown in Figure 1(b) after press forming.

[0025] As mentioned above, the IIHS side impact test simulates a side impact on an actual vehicle and evaluates impact safety mainly in the lower side of the vehicle. In other words, since the impact load from the collision is applied to the area around the connection between the side sill and the pillar located at the bottom of the door ring, we focused on the structure of the connection between the side sill and the pillar. In the case of a double door ring, three pillars—the front pillar, the center pillar, and the rear pillar—are connected to one side sill. In the case of a single door ring, two pillars—the front pillar and the rear pillar—are connected. Regarding side impact safety, all pillars are required to perform similar functions, but the center pillar is particularly easy to evaluate in terms of response during a side impact. For these reasons, the vehicle side frame component according to this embodiment will be explained using the double door ring shown in Figure 1 as an example, and the center pillar as an example of a pillar. Hereafter, unless otherwise specified, the center pillar may be simply referred to as the pillar in the explanation, and for the sake of convenience in the explanation, the term "equivalent blank" may be omitted for each blank.

[0026] For the sake of clarity, it should be noted that this embodiment is not limited to the center pillar, but can be applied to any pillar that is positioned to connect to the side sill. Therefore, although the center pillar is used as an example in the explanation, the term "pillar" in the explanation may be interpreted as a general term for the front pillar (A pillar), center pillar (B pillar), and rear pillar (C pillar), and can be reinterpreted as referring to one or more pillars selected from the front pillar (A pillar), center pillar (B pillar), and rear pillar (C pillar).

[0027] Furthermore, the vehicle side frame component according to this embodiment is not limited to the structure shown in Figures 1 and 2. This embodiment can be applied to any vehicle side frame component having a side sill located at the bottom of the side frame component and extending in the direction of vehicle travel, and at least one pillar connected to the side sill and extending vertically upward with respect to the direction of vehicle travel. For example, it may be a side frame component with a structure in which there are multiple center pillars in addition to the front pillar and rear pillar. It may also be a side frame component with a structure without roof rails. Moreover, the vehicle is not limited to automobiles, but can be broadly applied to vehicles such as industrial vehicles such as heavy machinery, railway vehicles, and commercial vehicles such as transport vehicles.

[0028] <Connection between side sill and pillar> When joining blanks together, overlapping the blanks increases the weight by the amount of overlap. If one tries to reduce the weight increase by reducing the area of ​​the overlapping part of the blanks, the area where the overlapping steel plates are joined together becomes smaller, leading to a decrease in the strength of the joint. Therefore, in order to ensure the strength of the door ring and guarantee safety while suppressing the increase in weight, it is necessary to optimize the position and overlapping area of ​​the overlapping part.

[0029] In considering a door ring structure that can minimize weight increase while ensuring safety in the IIHS side-impact test, the inventors focused on the connection point between the side sill and the pillar (connection point) from the perspective of side-impact safety. Since the pillar has connection points to the side sill at the bottom and to the roof rail at the top, for convenience, the connection point between the side sill and the pillar is called the lower connection point, and the connection point between the pillar and the roof rail is called the upper connection point.

[0030] Figure 4 shows an example of the blank configuration of the double door ring 400 after press forming. For the sake of explanation, the lines separating the blanks have been omitted. The center pillar upper equivalent blank and the center pillar lower equivalent blank are combined to form the center pillar equivalent blank 221, and the rear pillar upper equivalent blank and the rear pillar lower equivalent blank are combined to form the rear pillar equivalent blank 222. There are three pillars: the front pillar, the center pillar, and the rear pillar, but as mentioned above, the center pillar will be used as an example. Therefore, for the sake of explanation, unless otherwise specified, the center pillar will simply be referred to as the pillar.

[0031] The connection portion (lower connection portion) 301 between the side sill 113 and the pillar 112 is the region enclosed by a virtual line 302 representing the width of the side sill 113 and a virtual line 303 representing the width of the pillar 112. The virtual line 302 representing the width of the side sill is a line that represents the end face (i.e., outer edge) of the side sill 113 in a direction perpendicular to the longitudinal direction. For example, if the side sill 113 has a hat-shaped cross section when viewed in a cross section perpendicular to the longitudinal direction (a shape with a top surface in the center, vertical walls on both sides of it, and flanges on both sides of the vertical walls), the lines corresponding to the outer edges of both flanges become the virtual line 302 representing the width of the side sill. For example, if the side sill 113 has a U-shaped cross section (a shape with a top surface in the center, and vertical walls on both sides of it), the lines corresponding to the outer edges of both vertical walls become the virtual line 302 representing the width. The imaginary line 303 indicating the width of the pillar is defined as a line drawn perpendicular to the longitudinal direction of the side sill 113 from the intersection point of the end face (outer edge) of the pillar 112 in the direction perpendicular to the longitudinal direction (width direction) and the imaginary line 302 indicating the width of the side sill (i.e., the intersection point of the width direction end face (outer edge) of the pillar 112 after pressing and the width direction end face (outer edge) of the side sill 113).

[0032] In the case of the front pillar 111 and the rear pillar 114, when the pillars intersect at the end of the side sill 113, the imaginary lines indicating the width of each pillar passing through that intersection will be lines that follow the shape of the end of the side sill. The lower connection portion 311 of the front pillar, the lower connection portion 301 of the center pillar, and the lower connection portion 312 of the rear pillar shown in Figure 4 are regions obtained in this way.

[0033] Similarly, the connection portion (upper connection portion) 304 between the roof rail 115 and the pillar 112 is the area enclosed by the imaginary line 305 indicating the width of the roof rail and the imaginary line 303 indicating the width of the pillar. Figure 4 shows the upper connection portion 313 of the front pillar, the upper connection portion 304 of the center pillar, and the upper connection portion 314 of the rear pillar, respectively.

[0034] Figure 5 shows a schematic diagram of the integrated blank 500 of the double door ring 400 shown in Figure 4. As with Figure 4, the dividing lines of the blank are omitted for the sake of explanation. When manufacturing the integrated blank, the lower connection part 301 and the upper connection part 304 are determined in the same way as the door ring after pressing as explained in Figure 4. That is, in the blank as well, the connection part (lower connection part) 301 between the side sill 215 and the pillar 221 is the area enclosed by a virtual line 302 indicating the width of the side sill 215 and a virtual line 303 indicating the width of the pillar 221. The virtual line 302 indicating the width of the side sill is a line indicating the end face (i.e., outer edge) of the side sill 215 in a direction perpendicular to the longitudinal direction. The imaginary line 303 indicating the width of the pillar is a line drawn perpendicular to the longitudinal direction of the side sill 215 from the intersection point of the end face (outer edge) of the pillar 221 in the direction perpendicular to the longitudinal direction (width direction) and the imaginary line 302 indicating the width of the side sill 215 (more precisely, the point corresponding to the intersection point of the width direction end face (outer edge) of the pillar 112 after pressing and the side sill 113).

[0035] The lower connection portion 311 of the front pillar 213 and the lower connection portion 312 of the rear pillar also conform to the shape of the end face of the side sill, just as they do after press forming. The upper connection portion 304 of the center pillar, the upper connection portion 313 of the front pillar, and the upper connection portion 314 of the rear pillar are also the same as they are after press forming (as explained in Figure 4 above).

[0036] <Overlapping portion of pillar and side sill blanks> Figure 10 shows an example of a conventional integrated blank (for example, Patent Document 2). The overlapping portion 330 of the pillar-equivalent blank 221 and the side sill-equivalent blank 215 is located inside the lower connection portion 301, and since the two blanks overlap over a considerable area, a considerable increase in weight was unavoidable. Therefore, the inventors of this embodiment conceived of the idea that weight could be reduced by placing the overlapping portion of the pillar-equivalent blank 221 and the side sill-equivalent blank 215 outside the lower connection portion 301, and proceeded with development.

[0037] First, through repeated simulations from the perspective of suppressing the amount of pillar penetration during a side impact in the IIHS side impact test, it was found that it is desirable for the overlapping portion 330 of the pillar-equivalent blank 221 and the side sill-equivalent blank 215 to be located outside the lower connection portion 301 and inside the pillar 112 (i.e., on the pillar 112 side). In other words, it is desirable to join the pillar-equivalent blank 221 with the side sill-equivalent blank 215 so that a part of it constitutes a part of the lower part of the pillar.

[0038] Figure 6 shows the arrangement of the overlapping portion 330 between the side sill equivalent blank 215 and the center pillar equivalent blank 221 in the blank configuration of the double door ring 400 shown in Figure 4. Similarly, Figure 7 shows the overlapping portion 330 between the side sill equivalent blank 215 and the pillar equivalent blank 221 in the blank configuration of the integrated door ring blank 500 shown in Figure 4. As shown in Figures 6 and 7, the overlapping portion 330 between the pillar equivalent blank 221 and the side sill equivalent blank 215 should be located within the pillar 112 and spaced away from the lower connection portion 301 (in this case, the boundary line of the lower connection portion 301 (a virtual line 302 indicating the width of the side sill)). This is because the area near the lower connection portion 301, including the press-formed pillar 112, is the first to receive the impact force during a side collision, so the plate thickness can be increased even partially near the collision point of the pillar to increase strength. For this reason, it is presumed that deformation due to a side collision can be suppressed.

[0039] The separation distance (reference numeral 331 in Figure 6) between the overlapping portion 330 and the lower connecting portion 301 should be greater than 0 mm. On the other hand, since the lower connecting portion 301 of the side sill 113 and pillar 112 after pressing will be T-shaped or L-shaped, overlapping the two blanks at the corner will cause complex material flow during press forming. To avoid this complex material flow at the corner, it is desirable that the separation distance 331 between the overlapping portion 330 and the lower connecting portion 301 be 10 mm or more. More preferably, it should be 20 mm or more, 30 mm or more, 40 mm or more, or 50 mm or more. If the separation distance between the overlapping portion 330 and the lower connecting portion 301 is too long, the effect of reducing penetration amount will not be obtained, so it is preferable that the separation distance be 200 mm or less, 180 mm or less, 160 mm or less, 150 mm or less, 140 mm or less, 130 mm or less, 120 mm or less, 110 mm or less, or 100 mm or less.

[0040] <Width of the overlapping portion> Next, the width of the overlapping portion 330 of the pillar-equivalent blank 221 and the side sill-equivalent blank 215 (length along the longitudinal central axis of the pillar, indicated by reference numeral 332 in Figure 6) was investigated. A wider overlapping portion 332 is preferable from the viewpoint of collision safety, as it increases the strength of the pillar 112. However, a large overlapping portion width 332 leads to a significant increase in weight, which is undesirable from the viewpoint of weight reduction. On the other hand, if the overlapping portion width 332 is made smaller, it becomes impossible to secure the joining area of ​​the two blank portions. For example, in the case of resistance spot welding, the spot diameter is usually around 6 to 10 mm, so at least 15 mm is needed to secure the spot welding allowance. Furthermore, by applying at least two rows of spot welds in the direction of the pillar's central axis, the bending rigidity is increased and the effect of reducing penetration is greatly enhanced. Therefore, it is preferable for the overlapping portion width 332 to be 25 mm or more, or 30 mm or more. There is no particular upper limit to the width of the overlapping section (332 mm), but as mentioned above, the weight of the door ring increases with increasing width, so it is preferable to keep it to the minimum necessary, and it is advisable to set it to 200 mm or less, 150 mm or less, 100 mm or less, 80 mm or less, 60 mm or less, or 50 mm or less. Alternatively, it may be derived from the number of spot welds required for the structural design.

[0041] <Pillar and Roof Rail (Upper Connection)> The structure of the connection between the pillar and the roof rail (upper connection) is not particularly limited. In the relationship between the pillar and the side sill described above, the side sill may be interpreted as being replaced by the roof rail. That is, if the roof rail has the function of ensuring side collision safety, it is preferable that the overlapping portion of the roof rail equivalent blank and the pillar equivalent blank be located outside the upper connection and inside the pillar.

[0042] If the roof rails have the function of ensuring safety from impacts from above, such as vehicle rollovers, rather than from impacts from side collisions, the overlapping portion of the roof rail-equivalent blank and the pillar-equivalent blank may be placed within the upper connection portion. Typically, in the case of automotive door rings, the area of ​​the upper connection portion is smaller than the area of ​​the lower connection portion. Therefore, even if the upper overlap portion is placed outside the upper connection portion, it does not make much difference compared to if it is placed inside the upper connection portion. For this reason, the structural design should be done according to the functions required of the vehicle.

[0043] <Steel types to be used for blanks> As mentioned above, there are no particular limitations on the type of steel plate used for each blank. It is best to select according to the structural design. Since it is for vehicle use, it is preferable to use high-tensile steel. High-tensile steel often refers to steel plates with a tensile strength of 340 MPa or more, but for vehicle use, it is preferable to use high-tensile steel plates with a tensile strength of over 590 MPa, over 780 MPa, or over 980 MPa. On the other hand, from the viewpoint of side collision safety, if it is desirable to absorb the impact with the side sill, for example, the tensile strength of the steel plate that will become the side sill member (side sill equivalent blank) may be set to 1400 MPa or less.

[0044] Furthermore, it is preferable to use a steel sheet with a softened surface (surface-softened steel sheet (high bending material)) because breakage during collision deformation can be suppressed and the impact energy absorption capacity can be improved. In particular, by using a surface-softened steel sheet (high bending material) as a member of the side sill (side sill equivalent blank), the impact energy absorption capacity is increased and the effect of suppressing the maximum penetration amount of the pillar is enhanced. Here, the surface-softened steel sheet (high bending material) is a steel sheet in which the Vickers hardness of the surface layer portion of the steel sheet (region within 10 μm from the steel sheet surface) is smaller than the Vickers hardness of the central portion of the steel sheet cross-section (the 1 / 2 portion of the plate thickness), and the hardness difference is 20 Hv or more. The hardness difference between the surface layer portion and the central portion of the steel sheet is preferably 25 Hv or more, 30 Hv or more, 35 Hv or more, 40 Hv or more, 45 Hv or more, 50 Hv or more, 55 Hv or more, 60 Hv or more, 65 Hv or more, or 70 Hv or more.

[0045] <Manufacturing method of side frame parts> The manufacturing method of the side frame parts according to this embodiment is not particularly limited. It can be manufactured according to a conventional method. For example, FIG. 8 shows an outline of the manufacturing process of parts (press-formed parts) by general TWB press forming.

[0046] Partial blank processing step: This is a step of manufacturing partial blanks that are parts of the integrated blank. A blank is cut out (blanking) from a predetermined steel sheet and refined by laser trimming or the like to manufacture a partial blank.

[0047] Integrated blank processing step: This is a step of manufacturing a blank for press forming (integrated blank) by joining a plurality of obtained partial blanks. Here, among the plurality of blanks, the blank corresponding to the pillar and the blank corresponding to the side sill are joined such that the overlapping parts that overlap each other are outside the connection part (lower connection part) between the side sill and the pillar and are arranged inside the pillar after pressing, and the overlapping parts are joined. The joining method of the overlapping parts is not particularly limited, but spot welding (resistance spot welding or laser spot welding) can be used for efficient joining. The joining methods of the other blanks are not particularly limited. For example, when butting and welding the blanks, laser welding or arc welding can be used. Also, when the blanks are overlapped, the joining of the overlapping parts can be performed by, for example, spot welding (resistance spot welding, laser spot welding, etc.), overlap welding (arc welding, laser welding), fillet welding (arc welding, laser welding), brazing, friction stir welding (FSW), friction pressure welding, etc. An integrated blank for press forming can be obtained by combining and joining predetermined blanks into one body.

[0048] In manufacturing the integrated blank, as described above, at least one blank corresponding to at least one pillar and a blank corresponding to the side sill are joined so as to have at least one joint part joined by overlapping parts that overlap each other. The overlapping part is an area surrounded by a virtual line indicating the width of the side sill and a virtual line indicating the width of the pillar, is outside the lower connection part which is the part where the side sill and the pillar are connected, and is arranged inside the pillar. The overlapping part is separated from the lower connection part along the longitudinal central axis of the pillar by 10 mm or more and 200 mm or less to manufacture the integrated blank.

[0049] Furthermore, when manufacturing integrated blanks for side frame components, if all blank joints are joined (welded, etc.) before forming, the material flow during press forming is obstructed by the joints, introducing localized deformation. This not only worsens formability but can also cause cracking. Therefore, it is effective to perform joining (welding, etc.) in areas that do not obstruct material flow during press forming or in areas where material flow is minimal (positioning the joints accordingly).

[0050] As a concrete example, we will explain using spot welding. Other joining methods can be applied in a similar manner. For example, when press forming the overlapping portion of a center pillar blank and a side sill blank, we assume that the blanks corresponding to the center pillar and the side sill are fixed (meaning they are joined by spot welding, etc.) at at least one point within the area pressed by the pad or die (for example, the center of gravity of the overlapping portion). Then, we perform a press forming analysis of the integrated blank (simulation analysis using FEM, etc.). In this process, we determine the movement vector of each point from the positions of the corresponding points in the blanks corresponding to the center pillar and the side sill, respectively, that correspond to any point in the overlapping portion, before and after their movement. The absolute value of the difference between the obtained movement vectors of each point (i.e., the distance between each point) is obtained as the material flow rate at that point. If the obtained material flow rate is smaller than a predetermined limit value, the material flow is small, so it can be designated as a point (position) to be joined (spot welded) before press forming. On the other hand, if the calculated material flow rate is greater than a predetermined limit, it means that the material flow is large, so joining (spot welding) should not be done before press forming, but rather after press forming.

[0051] We actually overlapped 980 MPa class steel plates (1.2 mm thick) and spot-welded them to form a joint. After hot-press forming (hot stamping), we pulled the steel plates at 1 mm / s at room temperature and observed the calculated material flow rate (slip amount) of the two steel plates and the tensile shear strength (TSS) of the joint (spot-welded area) at room temperature. As a result, when the slip amount exceeded 1.0 mm, a localized reduction in plate thickness occurred around the spot-welding point, causing a tendency for the TSS to decrease. In other words, we discovered for the first time that even in hot-press forming, it is possible to guarantee a tensile shear strength (TSS) equivalent to that of a case without deformation, even if a material flow rate difference (slip amount) of less than 1.0 mm occurs at the spot-welding point. From this finding, in the case of hot pressing, it is best to pre-set the limit value of the material flow rate difference as 1.0 mm and join the plates at points (or regions including these points) where the material flow rate at each point is less than or equal to this pre-set limit value (1.0 mm) through simulation. Preferably, the limit value for the material inflow can be set in advance as 0.9 mm, 0.8 mm, 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, or 0.2 mm, and the points or areas to be joined before press forming can be determined by simulation.

[0052] There is no particular limitation on the point (location) where the material flow rate is to be determined. For example, the material flow rate may be analyzed at the point (location) that is ultimately set as the spot welding location. Alternatively, for example, the analysis mesh may be made finer to find the region where the material flow rate is below a limit value. In this case, it is advisable to set the location of the joint (spot welding point, etc.) before press forming within the region where the material flow rate is analyzed to be small.

[0053] <Regions separated by bends> In particular, areas that do not hinder material flow during press forming or areas with little material flow are often the parts of the blank that are sandwiched by pads during press forming, and these are one of the regions separated by bends that are bent during press forming in the overlapping area. Therefore, it is desirable for the joint to be located in one of the regions separated by bends that are bent during press forming in the overlapping area. For example, in the case of a member with a hat-shaped cross section (a member having a top surface, an adjacent vertical wall, and a flange adjacent to the vertical wall) or a member with a C-shaped cross section (a member having a top surface and an adjacent vertical wall), the top surface is one of the regions separated by bends, and it is likely to be the part that is sandwiched by pads during press forming, and corresponds to an area that does not hinder material flow during press forming, that is, an area with little material flow.

[0054] Therefore, when joining blanks at an overlapping section, it is best to avoid the bend and join only one of the areas of the bend using spot welding or similar methods. If there is only one bend in the overlapping section (for example, in the case of bending that results in an L-shaped cross-section), it is best to join the blanks only on one of the surfaces of the overlapping section, with the bend as the boundary.

[0055] If there are two bends on the overlapping section, that is, if the cross-section is groove-shaped (C-shaped) or stepped (Step Shape, Z-shaped), it is best to join the blanks in the area between the bends (corresponding to the top surface).

[0056] When there are two or more bends on an overlapping section (for example, in the case of a hat-shaped cross section part), it is best to join the blank only in the area between two adjacent bends on the surface of the overlapping section. Therefore, when manufacturing an integrated blank for a hat-shaped cross section part or a groove-shaped (C-shaped) cross section part, it is best to join only the portion of the overlapping section corresponding to the top surface.

[0057] Generally, part shapes are complex and diverse, so there are often three or more bends on overlapping sections. In the case of press-formed parts with three or more bends, the material flow behavior becomes complex, and cracking due to bending is particularly likely to occur. In these embodiments, even when there are three or more bends, it is preferable to create an integrated blank by joining the blanks in only one of the regions sandwiched between adjacent bends (since there are three or more bends, there will be two or more regions sandwiched between bends). After press-forming the integrated blank thus created, the unjoined regions are joined to obtain a part with a complex shape without cracking.

[0058] When the number of bends is odd, it is preferable to join the blanks in the central region from the standpoint of symmetry. For example, when the cross-section of the overlapping portion after press forming is groove-shaped or hat-shaped, it is preferable to join only in the region corresponding to the top surface. Also, for example, when the bends are arranged asymmetrically, it is preferable to join only in the region close to the center of the overlapping portion (e.g., the centroid of the surface). In any case, it is preferable to join only in one of the regions between two adjacent bends.

[0059] Hot press forming process: This process involves 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 generally, when press forming a blank made of high-strength steel sheet (for example, a steel sheet with a tensile strength of more than 590 MPa), hot press forming is preferable. Hot press forming is also called hot stamping (hot stamping method), and it is a press forming method in which the blank (steel sheet) is heated to the austenite temperature range of approximately 900°C, and then press-formed while simultaneously rapidly cooling 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 martensitic transformation occurs during cooling, it has high strength after forming while having excellent shape retention. For this reason, it is widely used for press forming of high-strength steel sheet.

[0060] Trimming process: There are no particular limitations on the ancillary processes after press forming. For example, there is a trimming process. This is a process of refining press-formed products (including those with a part shape and near-net-shape parts) that have been hot-press-formed. There are no particular limitations on the method of refining the press-formed products. For example, it includes processing to remove burrs and other debris from the edges of the press-formed products using a laser and to shape them to a predetermined shape (laser trimming). In the case of near-net-shape press-formed products, it also includes processing to create the final part shape. If a press-formed product with the final shape can be obtained by hot-press forming, this trimming process can be omitted.

[0061] Post-pressing parts joining process: This is a process to join unjoined parts of overlapping sections or other parts after press forming. Parts that were not joined in the press-forming integrated blank processing process because they would hinder material flow during press forming may be joined (welded, etc.) at this stage. Since joining is done after press forming, material flow has already occurred, so there is no introduction of deformation or cracking due to joining. Therefore, since the parts joined at this stage have not undergone heat treatment by hot pressing, the joined parts will have HAZ softening areas. In other words, in the side frame parts manufactured by integrated press forming of the integrated blank according to this embodiment, at least one of the joining parts of the overlapping section of the blank (the joining part joined before hot stamping) will be a joint without HAZ softening. Then, since the remaining parts are joined after press forming, the side frame parts according to this embodiment will have both joints without HAZ softening and joints with HAZ softening. Furthermore, if it is necessary to join other parts to the obtained press-formed product, those parts may also be joined.

[0062] The joining method here is not particularly limited. For example, joining may be done by spot welding, arc welding, laser welding, brazing, etc. Also, it may be used to attach partial reinforcing materials to press-formed products 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.

[0063] By going through these processes, the desired vehicle side frame parts (such as door rings) can ultimately be obtained. However, the manufacturing process for parts by press forming of integrated blanks is not limited to the processes described above. Other necessary processes can be added.

[0064] <Presence or Absence of HAZ Softening Area> Since the side frame parts obtained from the integrated blank are hot press-formed, the HAZ softening area that occurred before hot press-forming is eliminated by the heat treatment during hot press-forming at the joints formed by welding such as spot welding and lap welding, friction stir welding, and friction pressure welding. In other words, in the parts according to this embodiment, the joints of the overlapping parts of the blank that were joined (welded, etc.) before hot press-forming do not have a HAZ softening area. A HAZ softening area is a phenomenon in which the heat-affected zone (HAZ) in the base material just outside the outer edge of the weld metal in spot welding nuggets and arc welding is tempered and becomes softer than the base material. Similarly, in friction stir welding, friction pressure welding, and brazing, the softened area that occurs in the heat-affected zone (HAZ) of the base material just outside the outer edge of the joint is the HAZ softening area. The elimination of the HAZ (Heat-Absorbing Zone) softening increases the strength of the joint, contributing to improved collision resistance of the finished part.

[0065] In other words, the side frame component according to this embodiment has stronger joints than conventional side frame components, which are completed by joining all parts together after molding, and is expected to improve the impact resistance of the component. In the side frame component according to this embodiment, at least one joint is joined (welded) before hot press forming only in the integrated blanking process, in a portion that does not obstruct the material flow during press forming (for example, the blank portion corresponding to the top surface of the component). As a result, the HAZ softening portion of those joints is eliminated (i.e., at least one joint does not have a HAZ softening portion), and thus the joint is stronger than that of conventional components, and is expected to improve the impact resistance of the component. The following explanation will use resistance spot welding as an example.

[0066] Figure 9 shows a schematic cross-sectional view of a spot weld test piece 900 and an example of the correspondence between the hardness distribution of the spot weld 901 (near the spot weld point) and the base material 902 (corresponding to the blank). Unless otherwise specified, hardness refers to Vickers hardness. As can be seen in Figure 9, the spot weld, including the weld metal (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 can be used as a representative value). 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 edge (outer edge) of the spot weld weld metal (nugget) 903 (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 edge (outer edge) of the weld metal (nugget or weld metal).

[0067] Further away from the joint (nugget 903), the hardness converges to the hardness of the base material 902 (Figure 9 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 901 is, for example, 50 Hv or more less when the base material 902 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 902, that is, the hardness of the base material 902 in the area unaffected by spot welding, and the maximum value among the hardness measured within 5 mm outward (towards the base material) from the end of the weld metal part (nugget) (or within a radius of 12 mm from the center of the spot weld part 901) is defined as the maximum hardness, and the minimum value as the minimum hardness, and the difference between the maximum hardness and the minimum hardness is defined as ΔHv, then if the HAZ is not softened, ΔHv should be 0.2 Hvm or less, preferably 0.1 Hvm or less. Conversely, if the HAZ is softened, ΔHv will be greater than 0.2 Hvm.

[0068] The hardness distribution of the HAZ softened area can be determined by measuring the hardness (Vickers hardness) along a line parallel to the blank surface (hardness measurement line) at a position 3 / 4 of the way from the blank's surface (i.e., 1 / 4 of the way from the surface of the blank that is in contact with other blanks), in a cross section perpendicular to the surface (thickness direction cross section) that includes the center of the weld metal part (center of the spot weld) of the outermost blank among the blanks, moving outwards from the center of the spot weld point. For example, it is preferable to measure the hardness distribution in the thickness direction cross section of the outermost blank among the blanks that make up the overlapping part. First, as the base material hardness (hardness of the part of the base material not affected by the spot weld), the hardness is measured at a position 15 mm or more away from the center of the spot weld and where no spot weld has been made, and this hardness is defined as Hvm. Note that the outermost blank here refers to the blank on the top surface when the press-formed part is placed with the convex shape facing upwards.

[0069] Next, measure the hardness along the hardness measurement line, in a range of 5.0 mm from the outer edge (end) of the weld metal (nugget) outward (towards the base metal) at measurement intervals (pitch) of 0.1 to 0.2 mm. The maximum value of the measured hardness is taken as the maximum hardness, and the minimum value as the minimum hardness, and the difference between the maximum and minimum hardness, ΔHv, can be determined. Alternatively, in the case of spot welding, the range from the center of the spot weld to 12.0 mm, or from 1.0 mm inside the outer edge of the spot weld (spot welding point) to 5.0 mm outside the outer edge, can be measured at measurement intervals (pitch) of 0.1 to 0.2 mm. Within these ranges, the minimum hardness of the HAZ softened area due to spot welding can be captured. The outer edge of the weld metal (such as the outer edge of the spot weld) can be identified as the boundary between the spot weld and the base metal by the contrast created by etching the Vickers hardness measurement sample.

[0070] Vickers hardness is measured on a sample with a thickness-direction cross-section including the center of the weld metal (center of the spot weld) as the measurement surface, in accordance with JIS Z 2244:2024, with an indentation load of 300 gf (2.942 N) and an indentation load holding time of 10 to 15 seconds.

[0071] Joints that do not have a HAZ softened area (spot-welded joints in the above description) are formed before hot press forming. That is, in the side frame component according to this embodiment, at least one joint (spot-welded in the above description) in the overlapping portion of the blank corresponding to the pillar and the blank corresponding to the side sill is a joint that does not have a HAZ softened area, meaning that the difference between the maximum hardness and minimum hardness ΔHv near the end of the joint is 0.2 times or less the hardness of the base material (0.2 Hvm or less).

[0072] The above explanation of hardness measurement of the HAZ softened area was given using resistance spot welding as an example. For other joining methods, the same considerations apply as to resistance spot welding. For example, the same applies to arc welding. In the case of laser welding, the "weld metal area" should be interpreted as the molten metal portion, and in the case of FSW and friction welding, it should be interpreted as the agitated area. In the case of brazing, the "weld metal area" should be interpreted as the portion directly above the blank surface perpendicular to the brazed portion.

[0073] This section describes the simulation results obtained using a double door ring as an example of a vehicle side frame component, as shown in Figure 6. This door ring 400 has a front pillar 111, a center pillar 112, a rear pillar 114, a side sill 113, and a roof rail 115. Each of these components is a member having a hat-shaped cross-section (a member having a top surface, vertical wall sections adjacent to both sides thereof, and a flange section adjacent to the vertical wall sections). The blanks constituting this door ring 400 are as shown in Figure 7. The center pillar equivalent blank 221 is constructed with a center pillar lower equivalent blank at the part that joins with the lower side sill equivalent blank, and a center pillar upper equivalent blank at the top (the boundary line between the two blanks is not shown). The center pillar lower equivalent blank and the side sill equivalent blank 215 are overlapped at the overlapping portion 330, and the portions corresponding to the top surfaces of both blanks are joined by resistance spot welding. At this time, if the overlap width is 20 mm, one row of spot welding is used, and if the overlap width is 30 mm or more, two rows of spot welding are used. In this way, an integrated blank was prepared.

[0074] Next, the integrated blank was heated to 900°C and hot-stamped (press-formed). After cooling, the unjoined parts of the overlapping sections were spot-welded. Again, if the overlap width was 20 mm, one row of spot welds was used; if the overlap width was 30 mm or more, two rows of spot welds were used. In this way, the specified side frame component (double door ring) was obtained.

[0075] Visual inspection of the joints (welded areas) of the obtained door rings, including the connection and overlapping sections, revealed no cracks or defects. Furthermore, two joints joined before press forming and two joints welded after press forming were arbitrarily selected from the obtained door ring joints, and test pieces for HAZ softening evaluation were cut out. The HAZ softening evaluation test pieces were 40 mm square with the center of the joint at the center. For each test piece, Vickers hardness was measured at a cross section perpendicular to the surface of the outermost blank including the center of the joint, at a position 3 / 4 of the plate thickness from the surface of the outermost blank, from 1 mm inside the outer edge of the spot weld point to 5 mm outside the outer edge (base material side) with a measurement interval (pitch) of 0.1 mm. In addition, Vickers hardness was measured at an unjointed location more than 15 mm away from the center of the spot weld point. Vickers hardness was measured in accordance with JIS Z 2244:2024, using a Vickers hardness tester (fully automatic micro-Vickers hardness tester HV-100 series, manufactured by Mitutoyo Corporation). The indentation load was 300 gf (2.942 N), and the indentation load holding time was 15 seconds.

[0076] When the Vickers hardness at an unjointed location 15 mm or more away from the center of the joint (spot weld point) is defined as Hvm, the evaluation was based on how many times greater ΔHv is than the difference between the maximum and minimum Vickers hardness in the range within 5 mm toward the base material from the edge of the joint (outer edge of the spot weld point).

[0077] As a result, the joints joined before press forming (hot stamping) had ΔHv values ​​of 0.12 Hvm and 0.16 Hvm, both below 0.2 Hvm, and the distribution of Vickers hardness confirmed the absence of HAZ softening. On the other hand, the joints joined after press forming (spot welding) had ΔHv values ​​of 0.42 Hvm and 0.49 Hvm, both exceeding 0.2 Hvm, and the distribution of Vickers hardness confirmed the presence of HAZ softening. In other words, it was confirmed that there was no HAZ softening in the joints joined before press forming (joints on the top surface of the overlapping section), while there was HAZ softening in the joints joined after press forming (joints on the vertical wall section of the overlapping section).

[0078] The main dimensions of the door ring 400 are as follows. Note that the door ring outer and door ring inner have the same structure (including the position and dimensions of overlapping parts), and the same steel material is used. <Door Ring Dimensions> Overall length in the direction of vehicle travel: 2000 mm Length in the direction of vehicle height: 1500 mm Side sill width: 200 mm Center pillar width lower connection boundary: 400 mm Upper connection boundary: 300 mm

[0079] <Components (Blanks)> Table 1 shows a list of the steel materials used, and Table 2 shows the steel materials and plate thickness used for each blank.

[0080]

[0081]

[0082] During the simulation, the separation distance 331 between the overlapping section 330 of the center pillar lower blank and the side sill equivalent blank and the lower connection section 301, and the width 332 of the overlapping section were varied for evaluation. For the side impact safety of the door ring, an IIHS side impact test simulating an SUV (barrier weight: 4200 pounds (approx. 1.9 t), side impact speed 37 mph (miles per hour) (approx. 60 km / h)) was simulated, and the maximum penetration amount of the center pillar obtained at that time was used for evaluation. A smaller penetration amount indicates less deformation and better side impact safety. For weight reduction, the total weight of the door ring was used for evaluation. The separation distance, overlapping section width, and their evaluation results are shown in Table 3.

[0083] The negative separation distance indicates that, as in the conventional design, the overlapping portion exists within the lower connection portion. Figure 10 is a conceptual diagram showing conventional examples (Comparative Examples 1, 2, 4, and 5). In the conventional example, as shown in Figure 10, the overlapping portion 301 of the center pillar equivalent blank 221 and the side sill equivalent blank 215 is located within the lower connection portion 301 of the center pillar 112 and the side sill 113. Since the overlapping portions of both blanks overlap and are joined at the top surfaces of both blanks, the end of the overlapping portion 330 does not coincide with the imaginary side sill line 302 and is located inside the lower connection portion 301. That is, the overlapping portion 330 is separated from the end of the lower connection portion 301 (corresponding to the imaginary side sill line 302) in the inward direction of the lower connection portion. The inward direction of the lower connection portion 301 is indicated as the negative direction. The width 332 of the overlapping portion is expressed as an absolute value regardless of direction.

[0084] Comparative Examples 1, 2, 4, and 5 are examples in which the pillar-equivalent blank and the side sill-equivalent blank overlap and are joined at the lower connection portion (these correspond to the examples in Patent Document 2). Comparative Example 3 is an example in which the separation distance 331 between the overlapping portion 330 and the lower connection portion 301 is too long. Reference Example 1 is an example in which, instead of an integrated blank, each partial blank is individually press-molded to produce separate parts, and these are joined together to produce a door ring. This door ring, manufactured by joining these separate parts, is not integrally molded using an integrated blank, so it is listed as a reference example and not a comparative example.

[0085] As can be seen from the results in Table 3, it was confirmed that, in the embodiment of this design, compared to the comparative and reference examples which are conventional examples, weight reduction is ensured, and the maximum pillar penetration amount is also reduced, thereby improving side collision safety.

[0086]

[0087] This invention can be widely used in industries dealing with vehicles and vehicle structures, such as the transportation machinery industry (automobiles, etc.) and the industrial machinery industry (heavy machinery, etc.).

[0088] 100 Double door ring 111 Front pillar 112 Center pillar 113 Side sill 114 Rear pillar 115 Roof rail 211 Blank equivalent to upper center pillar 212 Blank equivalent to lower center pillar 213 Blank equivalent to front pillar 214 Blank equivalent to roof rail 215 Blank equivalent to side sill 217 Blank equivalent to upper rear pillar 218 Blank equivalent to lower rear pillar 221 Blank equivalent to center pillar 222 Blank equivalent to rear pillar 301 Lower connection part (lower connection part of center pillar) 302 Imaginary line indicating the width of the side sill 303 Imaginary line indicating the width of the pillar 304 Upper connection part (upper connection part of center pillar) 305 Imaginary line indicating the width of the roof rail 311 Lower connection part of front pillar 312 Lower connection part of rear pillar 313 Upper connection part of front pillar 314 Rear pillar upper connection part 330 Overlap part 331 Distance between overlap part and lower connection part 332 Width of overlap part 400 Double door ring 500 Integrated blank of double door ring 900 Spot weld test piece 901 Spot weld part 902 Base material (blank) 903 Nugget

Claims

1. A vehicle side frame component comprising the side of a vehicle and configured as a joint structure of blanks made of multiple steel plates, wherein the side frame component comprises a side sill located at the lower part of the side frame component and extending in the direction of vehicle travel, and one or more pillars extending perpendicular to the direction of vehicle travel and connected to the side sill, wherein at least one of the pillars has a joint where a blank corresponding to the pillar and a blank corresponding to the side sill are joined at an overlapping portion, wherein the overlapping portion is located outside the lower connection portion which is the area enclosed by a virtual line indicating the width of the side sill and a virtual line indicating the width of the pillar, and is located inside the pillar, wherein the overlapping portion is spaced 10 mm to 200 mm away from the lower connection portion along the longitudinal central axis of the pillar, and at least one of the joints does not have a HAZ softening portion.

2. The vehicle side frame component according to claim 1, wherein the joint portion comprises both a joint portion without the HAZ softening portion and a joint portion with the HAZ softening portion.

3. The vehicle side frame component according to claim 1 or 2, wherein the pillar has a top surface portion and a vertical wall portion adjacent to the top surface portion, the cross-section of the pillar is C-shaped or hat-shaped, and the joint portion without the HAZ softening portion exists only on the top surface portion.

4. The side frame part for a vehicle according to claim 1 or 2, wherein, in a joint without a HAZ softened portion, in a cross section perpendicular to the surface of the outermost blank including the center of the joint, at a position 3 / 4 of the plate thickness from the surface of the outermost blank, when the Vickers hardness at a position that is not joined and is 15 mm or more away from the center of the joint is Hvm, the difference between the maximum and minimum Vickers hardness in a range within 5 mm toward the base material from the end of the weld metal portion of the joint is 0.2 Hvm or less.

5. The vehicle side frame component according to claim 1 or 2, wherein the overlapping portion has a length of 25 mm or more along the longitudinal central axis of the pillar.

6. The vehicle side frame component according to claim 1 or 2, wherein the side frame component further has a roof rail positioned on the upper part of the side frame component and extending in the direction of vehicle travel, and the blank corresponding to the roof rail and the blank corresponding to the pillar are joined at an upper overlapping portion that overlaps each other, and the upper overlapping portion is located inside an upper connection portion which is the portion where the roof rail and the pillar connect, and is an area enclosed by a virtual line indicating the width of the roof rail and a virtual line indicating the width of the pillar.

7. The vehicle side frame component according to claim 1 or 2, wherein the side frame component is an automobile door ring.

8. The vehicle side frame component according to claim 5, wherein the pillar is one or more selected from a front pillar, a center pillar, and a rear pillar.

9. The vehicle side frame component according to claim 1 or 2, wherein the steel plate corresponding to the side sill is a surface-softened steel plate.

10. The vehicle side frame component according to claim 1 or 2, wherein the side frame component is hot stamped.

11. An integrated blank for press forming, configured as a joint structure of multiple steel plates for a vehicle side frame component that constitutes the side of a vehicle, wherein the side frame component has a side sill located at the lower part of the side frame component and extending in the direction of vehicle travel, and one or more pillars extending perpendicular to the direction of vehicle travel and connected to the side sill, and at least one blank corresponding to one of the pillars and the blank corresponding to the side sill have at least one joint where they are joined by overlapping portions, the joint is located in one of the regions divided by a bent portion that is bent by press forming in the overlapping portion, the overlapping portion is located outside the lower connection portion which is the portion where the side sill and the pillar are connected and is located inside the pillar, and the overlapping portion is spaced 10 mm to 200 mm away from the lower connection portion along the longitudinal central axis of the pillar.

12. The integrated blank for a vehicle side frame component according to claim 11, wherein the overlapping portion has a length of 25 mm or more along the longitudinal central axis of the pillar.

13. The integrated blank for a vehicle side frame component according to claim 11 or 12, wherein the pillar has a top surface portion and a vertical wall portion adjacent to the top surface portion, the cross-section of the pillar is C-shaped or hat-shaped, and the overlapping portion is joined only at the portion corresponding to the top surface portion.

14. A method for manufacturing a vehicle side frame component that constitutes the side surface of a vehicle according to any one of claims 1 to 10, comprising: an integrated blanking process for preparing an integrated blank for press forming configured as a joining structure of a plurality of steel plates for the side frame component; a hot press forming process for hot press forming the integrated blank; and a post-press component joining process for joining portions of the integrated blank press-formed in the hot press forming process that were not joined in the integrated blanking process, wherein in the integrated blanking process, at least one blank corresponding to the pillar and the blank corresponding to the side sill are joined such that they have at least one joint portion joined by an overlapping portion that is superimposed on each other, the overlapping portion is located outside the lower connection portion which is the portion where the side sill and the pillar are connected and is surrounded by a virtual line indicating the width of the side sill and a virtual line indicating the width of the pillar, and is located inside the pillar, and the overlapping portion is spaced 10 mm to 200 mm away from the lower connection portion along the longitudinal central axis of the pillar.

15. The method for manufacturing a vehicle side frame part according to claim 14, characterized in that the joint portion is located in one of the regions that are divided in the overlapping portion by the portion that is bent by hot press forming.

16. The method for manufacturing a vehicle side frame component according to claim 14 or 15, wherein the overlapping portion has a length of 25 mm or more along the longitudinal central axis of the pillar.

17. A method for manufacturing a vehicle side frame part according to any one of claims 14 to 16, wherein the pillar has a top surface portion and a vertical wall portion adjacent to the top surface portion, the cross section of the pillar is C-shaped or hat-shaped, and in the integrated blanking process, the joint is made only at the portion of the overlapping portion corresponding to the top surface portion.

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