Vehicle side frame component and method for producing same

Abstract

The purpose of the present invention is to provide a vehicle side frame component (for example, a door ring for an automobile) that is further improved by addressing production of the vehicle side frame component not only from the viewpoint of production technology but also from the viewpoints of safety and weight reduction.　The present invention is a vehicle side frame component configured from a plurality of steel plates, wherein a side frame component includes a side sill and pillars connected to the side sill, at least one of the pillars has a joint section in which a blank corresponding to the pillar and a blank corresponding to the side sill are joined at an overlapping section where the blanks overlap, the overlapping section is disposed in the pillar and is located outside a lower connection section which is a part where the side sill and the pillar are connected in a region surrounded by virtual lines indicating the width of the side sill and the width of the pillar, and the overlapping section is formed integrally by cold-pressing the integrated blanks, which are configured so as to be separated from the lower connection section by 50-250 mm.

Description

Vehicle Side Frame Parts and Manufacturing Method Thereof

[0001] The present invention relates to vehicle side frame parts and a manufacturing method thereof.

[0002] In particular, in the automotive industry, there is a demand to reduce the life cycle GHG (total greenhouse gas emissions over the entire life cycle), and there is an increasing requirement for component-module integration aimed at improving the efficiency of the manufacturing line by reducing the number of parts and omitting processes. In particular, if it becomes possible to integrally mold large parts such as vehicle side frame parts, for example, automotive door rings, which are combinations of a large number of members and parts, the effect will be extremely great. Therefore, there is an increasing demand for integral press molding of side frame parts using a blank in which different types of steel sheets are combined and integrated, so-called tailored welded blank (TWB).

[0003] Several proposals have been made regarding the application of TWB to vehicle side frame parts, particularly door rings. In Patent Document 1, a manufacturing method using an integrated blank for the inner reinforcement parts of the door ring is proposed. A flat integrated blank (TWB) is manufactured using blanks corresponding to the inner front pillar, inner center pillar, and inner side rail (roof rail) that connect them in the inner reinforcement parts, and this is hot forged to integrally press mold the inner reinforcement parts. In Patent Document 2, a manufacturing method using an integrated blank for the door ring is proposed. A method of manufacturing an automotive side structure frame (door ring) by integrally press molding a TWB created by partially overlapping and joining blanks corresponding to each part of the door ring is proposed.

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

[0005] In the trend of improving the efficiency and reducing the cost of component manufacturing, when manufacturing a vehicle side frame such as an automotive door ring, which is a large part, manufacturing by integrally press molding an integrated blank using TWB is attracting increasing attention.

[0006] On the other hand, vehicles such as automobiles are constantly required to be lightweight, not only in terms of ensuring safety but also from the perspective of energy efficiency. For this reason, it is necessary to balance the inherent requirements of safety and lightweight design of the vehicle itself, as well as the demands from production technology perspectives such as efficiency and cost reduction in parts manufacturing. Therefore, the present invention aims to provide a vehicle side frame component that incorporates not only production technology perspectives but also the perspectives of safety and lightweight design when manufacturing vehicle side frame components, and to provide a further improved vehicle side frame component.

[0007] To achieve the above objectives, the inventors diligently developed a vehicle side frame based on the door rings of automobiles, particularly the door ring inners, incorporating the perspectives of safety and weight reduction. (Hereafter, unless otherwise specified, "door ring" refers to the door ring inner, and the various parts of the door ring, such as the pillar and side sill, refer to the various parts of the door ring inner.) In this process, since the target of the vehicle side frame component was a vehicle side frame component, development proceeded from the perspective of safety during side collisions (side collision safety). As an indicator of the side collision safety of the vehicle side frame component (door ring), the inventors based the development on the side collision test of the US IIHS (Insurance Institute for Highway Safety), aiming to reduce the amount of deformation of the side frame, specifically the amount of displacement (maximum penetration) of the pillar pushed inward into the vehicle body. The IIHS side collision test simulates a side collision in an actual automobile and evaluates collision safety mainly at the lower side of the vehicle. Specifically, since the impact load from a collision is applied to the area around the connection point between the side sill and the pillar, which is located at the bottom of the door ring, we focused on the structure of the connection point between the side sill and the pillar. As a result, we obtained the following findings.

[0008] (a) When manufacturing an integrated blank for door rings using TWB, from the standpoint of weight reduction, it is preferable to simply butt-join blanks made of steel plates that will form each component to create a TWB. However, due to differences in the thickness of each steel plate, the workability of butt welding is poor and it takes a long time. Furthermore, as the size of the component increases, welding-induced distortion accumulates, making it difficult to improve the shape accuracy of the integrated blank, which may worsen productivity and lead to increased costs.

[0009] Therefore, the connection between the pillar and the side sill, which is crucial for side-impact safety, was designed with the assumption that the blanks corresponding to the pillar and the side sill would overlap, and the overlapping portion of the blanks would be joined by spot welding or similar methods. While the overlapping portion of the blanks has a strength advantage due to its increased thickness, it is disadvantageous in terms of weight. Therefore, a detailed analysis was conducted to determine how the position and size of the overlapping portion of the blanks corresponding to the pillar and the side sill affect side-impact safety.

[0010] 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.

[0011] (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.

[0012] (c) The width of the overlapping portion (length in the axis direction of the pillar center) is preferable to be as short as possible as it affects the weight increase. On the other hand, since it is necessary to secure a weldable area for joining, it is preferable to secure a length that allows for at least one row of spot welds (15 mm or more), and more preferably a length that allows for two rows (25 mm or more).

[0013] (e) When press forming an integrated blank using high-strength steel plate, the press forming method used will differ depending on the desired shape. When the amount of deformation due to press forming is small, cold press forming (press forming performed at room temperature to about 500°C) is mainly used. On the other hand, when the shape is complex or the amount of deformation is large, hot press forming, such as hot stamping forming (press forming in which the material is heated to the austenite region of about 900°C or higher, pressed, and then rapidly cooled in the mold), is used. On the other hand, for example, door ring inners often have a shallow forming height and the amount of deformation due to press forming is small, so it is desirable to use cold press forming whenever possible. Also, for forming processes of the same magnitude, cold press forming is more cost-effective than hot stamping forming, so there is a demand for expanding the application of cold working.

[0014] In the case of cold-press-formed parts, the material flow due to press forming is constrained at the joints (e.g., welds such as spot welds), resulting in work hardening around the joints. While the work-hardened areas have increased strength, excessive work hardening can worsen toughness and make them prone to crack initiation. Excessive work hardening refers to excessive strain when the material flow is constrained in areas where the material flow is relatively large during press forming, exceeding the fracture limit and making cracks more likely. Therefore, we have found that it is effective to perform joining (such as welding) before press forming in areas where the material flow is not constrained or where the material flow is small (e.g., the top surface of a part with a hat-shaped cross-section) (by positioning the joints). Unjoined parts that are not joined before press forming should be joined after press forming. Naturally, work hardening due to press forming does not occur around joints joined after press forming. In other words, in side frame parts manufactured by cold press forming of an integrated blank, the joints in the overlapping sections of the blank that were joined before press forming will be work-hardened. Since the unjoined sections are joined after press forming, the manufactured part will have both work-hardened and non-work-hardened joints.

[0015] This invention is based on the above findings, and its purpose is as follows.

[0016] [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 that is 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 50 mm to 250 mm away from the lower connection portion along the longitudinal central axis of the pillar, and has a work-hardened portion which is a work-hardened portion around at least one of the joints. The separation distance between the overlapping portion and the lower connecting portion is preferably 60 mm or more, 70 mm or more, 80 mm or more, 90 mm or more, or 100 mm or more, and also preferably 240 mm or less, 220 mm or less, 200 mm or less, or 150 mm or less. [2] The vehicle side frame part according to [1], wherein the joint portion is a joint portion having the work-hardened portion and a joint portion without the work-hardened portion that coexist. [3] The vehicle side frame part 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 having the work-hardened portion is present 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 having the work-hardened 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 1 / 4 of the plate thickness from the surface of the outermost blank, when the Vickers hardness at a position 15 mm or more away from the center of the joint and not joined is Hvm, the difference between the maximum Vickers hardness in a range within 5 mm toward the base material from the end of the weld metal portion of the joint and Hvm is 0.07 Hvm or more (preferably △Hv is 0.09 Hvm or more) (i.e., it has a work-hardened 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 preferably 50 mm or less. [6] The vehicle side frame component according to any one of [1] to [5], wherein the side frame component is further positioned on the upper part of the side frame component and has a roof rail 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 the portion 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 vehicle side frame component according to any one of [1] to [6], wherein the side frame component is an automotive door ring inner. [8] The vehicle side frame component according to any one of [1] to [7], 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 any one of [1] to [8], wherein the side frame component is cold press formed.

[10] 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 [9] 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 cold press forming process for cold press forming the integrated blank; and a post-press component joining process for joining portions of the integrated blank press formed in the cold press forming process as necessary, 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 50 mm to 250 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 60 mm or more, 70 mm or more, 80 mm or more, 90 mm or more, or 100 mm or more, and also preferably 240 mm or less, 220 mm or less, 200 mm or less, or 150 mm or less.

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

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

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

[10] or

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

[13] The method for manufacturing a vehicle side frame part according to any one of

[10] to

[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.

[0017] 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.

[0018] 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, Figure 1(b) shows an example of the blank configuration of the double door ring inner, and Figure 1(c) shows an example of the blank configuration of the double door ring outer. This is a diagram showing an example of the blank configuration of a single door ring for an automobile. Figure 2(a) shows an example of the blank configuration of the single door ring inner, and Figure 2(b) shows an example of the blank configuration of the single door ring outer. 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 inner. This is a diagram showing an example of an integrated blank for manufacturing the double door ring inner 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 inner in Figure 4. This is a diagram to explain the overlapping portion in the integrated blank of the door ring inner in Figure 4. This is a diagram to explain the manufacturing process of a typical TWB by press forming. 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.

[0019] 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.

[0020] Figure 1(a) shows an external view of a double door ring 110 as an example of an automotive door ring. An automotive 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 110, 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.

[0021] 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. Therefore, the door ring inner and door ring outer are structurally in a front-and-back relationship, and the component configurations such as pillars and side sills are basically the same. For example, Figure 1(b) is an example of the door ring inner 100 of the double door ring 110 in Figure 1(a), and Figure 1(c) is an example of the door ring outer 101 of the double door ring 110. 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, where the material flow due to press molding is relatively small. 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 be described as referring 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 each part of the door ring outer.

[0022] An 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 divided into its constituent 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.

[0023] 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.

[0024] Figure 2 shows an example of a single door ring, with Figure 2(a) showing an example of a single door ring inner 200 and Figure 2(b) showing an example of a single door ring outer 201. 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 single door ring in Figure 2(a) may be a structure in which the center pillar 112 is omitted from the double door ring 100 in Figure 1(b).

[0025] Figure 2(a) 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 inner 200. Similar to the example in Figure 1(b), the blanks often have different plate thicknesses and steel types, such as the front pillar equivalent blank 213 and the rear pillar upper equivalent blank 217 from the viewpoint of securing interior space during a collision, and the rear pillar lower equivalent blank 218, which is joined to the side sill equivalent blank 215, from the viewpoint of ensuring workability and toughness. These blanks can be joined to manufacture an integrated blank (TWB), and this integrated blank can be press-formed to manufacture a single door ring.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] <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.

[0031] 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.

[0032] 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.

[0033] 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).

[0034] 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.

[0035] 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.

[0036] 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).

[0037] 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).

[0038] <Overlapping portion of pillar and side sill blanks> Figure 9 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.

[0039] 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.

[0040] 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.

[0041] 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 50 mm or more. More preferably, it should be 60 mm or more, 70 mm or more, 80 mm or more, 90 mm or more, or 100 mm or more. If the separation distance between the overlapping portion 330 and the lower connecting portion 301 is too long, the penetration reduction effect will not be obtained, so it is desirable that the separation distance be 250 mm or less. More preferably, it should be 240 mm or less, 220 mm or less, 200 mm or less, or 150 mm or less.

[0042] <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, reference numeral 332 in Figure 6) is not particularly limited. A wider overlapping portion 332 is preferable from the viewpoint of collision safety as it increases the strength of the pillar 112. However, if the width of the overlapping portion 332 is large, the weight increase is significant and is undesirable from the viewpoint of weight reduction. From the viewpoint of weight reduction, it is preferable to make it as short as possible. On the other hand, if the width of the overlapping portion 332 is made small, 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 about 6 to 10 mm, so at least about 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 increased. Therefore, the width of the overlapping portion 332 is good to be 25 mm or more, and preferably 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, preferably 50 mm or less. Alternatively, it can be derived from the number of spot welds required for structural design.

[0043] <Pillar and Roof Rail (Upper Connection Part)> The structure of the connection part (upper connection part) between the pillar and the roof rail is not particularly limited. In the relationship between the pillar and the side sill described above, the side sill may be replaced with the roof rail for interpretation. That is, when the roof rail has a function of ensuring side collision safety, the overlapping part of the roof rail equivalent blank and the pillar equivalent blank may be arranged inside the pillar outside the upper connection part.

[0044] When the roof rail has a function of ensuring safety against impacts from the upper part of the vehicle, such as vehicle rollover, rather than impacts from side collisions, the overlapping part of the roof rail equivalent blank and the pillar equivalent blank may be arranged inside the upper connection part. Usually, in the case of a door ring for an automobile, the area of the upper connection part is smaller than the area of the lower connection part. Therefore, even if the upper overlapping part is arranged outside the upper connection part, it is not much different from the case where the upper overlapping part is arranged inside the upper connection part. Therefore, the structural design may be carried out according to the functions required for the vehicle.

[0045] <Steel Grade Applied to the Blank> As described above, the type of steel plate for each blank is not particularly limited. It may be selected according to the structural design. Because it is for vehicle use, it is preferable to use high-tensile steel plates (high-tensile steel). High-tensile steel plates (high-tensile steel) often refer to steel plates having a tensile strength of 340 MPa or more, but for vehicle use, it is preferable to apply high-tensile steel plates exceeding 590 MPa, exceeding 780 MPa, or exceeding 980 MPa. On the other hand, from the perspective of side collision safety, for example, when it is desirable to absorb impacts at the side sill, the tensile strength of the steel plate forming the side sill (side sill equivalent blank) may be set to 1400 MPa or less.

[0046] <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.

[0047] <Partial blank processing step> This is a step of manufacturing a partial blank that becomes a part of the integrated blank. A blank is cut out (blanking) from a predetermined steel sheet and refined such as by laser trimming to manufacture the partial blank.

[0048] <Integrated blank processing step> This is a step of manufacturing a press-forming blank (integrated blank) by joining the obtained plurality of partial blanks. At this time, 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 portion where they overlap each other is outside the connection portion (lower connection portion) between the side sill and the pillar and is disposed within the pillar after pressing. The joining method of the overlapping portion is not particularly limited, but it can be efficiently joined by spot welding (resistance spot welding or laser spot welding). The joining method of the other blanks is not particularly limited. For example, when butt-welding the blanks, it can be performed by laser welding or arc welding. Also, when the blanks are overlapped and joined, the joining of the overlapping portion can be performed, for example, by 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 to integrate them.

[0049] In manufacturing the integrated blank, as described above, at least the blank corresponding to at least one pillar and the blank corresponding to the side sill are joined so as to have at least one joint portion joined by an overlapping portion where they overlap each other. The overlapping portion 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 portion where the side sill and the pillar are connected, and is disposed within the pillar. The overlapping portion is separated from the lower connection portion along the longitudinal central axis of the pillar by 50 mm or more and 250 mm or less to manufacture the integrated blank.

[0050] 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 constrained by the joints, introducing localized deformation. This not only worsens formability but can also lead to the accumulation of plastic strain and cracking. Therefore, it is effective to perform joining (welding, etc.) in areas where the material flow during press forming is not constrained or where the material flow is minimal (i.e., to position the joints).

[0051] 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, and this point (position) can be used for joining (spot welding) 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.

[0052] We actually overlapped 980 MPa class steel plates (1.2 mm thick) and spot-welded them to form a joint. After cold-pressing the joint at room temperature, 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 of the steel plates at room temperature was about 0 to 0.75 mm, the TSS of the joint at room temperature was greater than when the slip amount was 0 mm (i.e., no deformation) due to work hardening around the spot-welded area. On the other hand, when the slip amount exceeded 0.75 mm, a localized reduction in plate thickness occurred around the spot-welded area, causing the TSS to tend to decrease. In other words, we have found for the first time that even in cold press forming, it is possible to ensure a tensile shear strength (TSS) equivalent to that of the case without deformation, even if a difference in material flow rate of 0.0 mm to 0.75 mm or less (corresponding to the slip amount mentioned above) occurs at the spot-welding point. Based on this finding, in the case of cold pressing, it is preferable to pre-set the limit value for the difference in material flow rate to 0.75 mm and join 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 (0.75 mm) as determined by simulation. Preferably, the limit value for the material inflow rate should be pre-set to 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, or 0.2 mm, and the points or regions to be joined before press forming should be determined by simulation.

[0053] 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.

[0054] <Regions separated by bends> In particular, areas where the material flow is not restricted or where the material flow is small during press forming are often the parts of the blank that are sandwiched by pads during press forming, and these areas 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 boundary between the top surface and the vertical wall corresponds to a bend, and the top surface is one of the regions separated by bends, which is likely to be the part that is sandwiched by pads during press forming, and corresponds to an area where the material flow is not restricted during press forming, that is, an area where the material flow is small.

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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.

[0059] 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.

[0060] <Press forming process (cold press forming process)> This is the process of 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 press process is called a press-formed product). The press forming method is not particularly limited, but a conventional press forming method can be applied. Generally, even when high-strength steel sheets (for example, steel sheets with a tensile strength of more than 590 MPa) are used, cold press forming is preferable if the amount of deformation is small. Cold press forming is the process of press forming a blank (steel sheet) at room temperature to about 500°C.

[0061] <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 that have taken on 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 (laser trimming) to remove burrs and other debris that have formed on the edges of the press-formed products using a laser to shape them to a predetermined shape. 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.

[0062] <Post-Press Parts Joining Process> This process involves joining unjoined portions of overlapping sections or other parts after press forming. In the press-formed integrated blank processing process, parts that were not joined to restrict material flow during press forming may be joined (welded, etc.) in this process. 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, the parts joined at this stage are not affected by material flow due to cold pressing, and the joints will be work-hardened. In other words, in the side frame parts manufactured by integrated press forming of the integrated blank according to this embodiment, at least one joint (joined before press forming) among the joints of the overlapping sections of the blank will have a work-hardened area (work-hardened portion) around that joint. Since the remaining parts are joined after press forming, the side frame parts according to this embodiment will have both joints with work-hardened areas and joints without work-hardened areas. Furthermore, if it is necessary to join other parts to the obtained press-formed product, those parts may also be joined.

[0063] 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.

[0064] By going through these processes, the desired vehicle side frame parts (such as door rings) can finally be obtained. It should be noted that the manufacturing process for parts by press forming of an integrated blank is not limited to the processes described above, and other necessary processes can be added.

[0065] <Presence or Absence of Work-Hardened Areas> In the case of automotive parts, high-tensile steel sheets (high-strength steel sheets with a tensile strength of 590 MPa or more) are sometimes used for the blanks. For example, in the case of 1470 MPa class high-tensile steel sheets, it has been confirmed that they can be formed without cracking if the plastic strain is approximately 4%. In the side frame parts obtained by the press forming method according to this embodiment, a portion of the overlapping part of the blank is joined before press forming, and the remaining unjoined part is joined after press forming. Therefore, naturally, there is no strain due to press forming (bending) in the part joined after press forming. In addition, the part joined before press forming is also a part that is less affected by bending during press forming, and even if bending is performed, it is a region where the plastic strain will be 4% or less. Therefore, even if the side frame parts according to this embodiment are processed with bending, the maximum strain of the blank around the joint (the part where the blanks are joined) is kept to 4% or less. Here, the perimeter of the joint refers to the area within 5 mm outward (on the opposite side of the joint center, towards the base metal) from the edge of the weld metal (the outer edge of the weld metal in the case of welding, the outer edge of the adhesive application area in the case of adhesives, and the outer edge of the agitated area in the case of friction stir welding, etc.). In the case of spot welding, since no nugget appears on the blank surface, the perimeter of the joint may be defined as the area within 12 mm from the joint point on the blank surface (the center of the spot weld).

[0066] On the other hand, work-hardened areas exist around parts joined (such as spot welds) before press forming, which improves the member's shear deformation strength. In particular, in the case of high-tensile steel, it has been confirmed that areas near parts joined (such as spot welds) before press forming are work-hardened to a degree of 7% or more of the base material hardness in Vickers hardness (Hv). In other words, if the base material hardness is Hvm, the difference between the maximum hardness around the joint (maximum hardness of the work-hardened area) Hvmax and the base material hardness Hvm, ΔHv, is 7% or more of the base material hardness Hvm (see the formula below). Preferably, ΔHv is 8% or more, 9% or more, or 10% or more of Hvm. ΔHv = Hvmax - Hvm ≥ 0.07 × Hvm

[0067] The Vickers hardness around the joint is measured in a cross-section perpendicular to the surface of the blank (thickness direction cross-section) that includes the center of the joint (center of the spot weld) of the outermost blank. At a position 1 / 4 of the plate thickness from the surface of the outermost blank, along a line parallel to the blank surface (hardness measurement line), the hardness is measured at a range of no more than 5.0 mm outward (opposite the center of the joint and towards the base material) from the outer edge of the weld metal (nugget) (the outer edge of the weld metal in the case of arc welding, the outer edge of the adhesive application area in the case of adhesive, and the outer edge of the stirred area in the case of friction stir welding, etc.) with a measurement interval (pitch) of 0.1 to 0.2 mm. The maximum value of the measured hardness is taken as the maximum hardness Hvmax of the work-hardened area around the joint. Alternatively, in the case of spot welding, the hardness may be measured in a range from the center of the joint (spot weld point) up to 12 mm, or in a range from 1.0 mm inside the outer edge of the spot weld (spot weld point) to 5.0 mm outside the outer edge, with a measurement interval (pitch) of 0.1 to 0.2 mm. The outer edge of the weld metal (such as the outer edge of the weld metal) can be identified by the contrast with the base material obtained by etching the Vickers hardness test sample.

[0068] The hardness of the base material is the hardness (Vickers hardness) of the part that is not affected by joining such as spot welding or bending. Of course, the hardness of the base material may be measured before press forming or spot welding. For example, as the hardness of the base material (hardness of the base material in a part that is not affected by spot welding, etc.), the hardness can be measured at a location that is 15 mm or more away from the center of the spot weld and where no spot welding has been performed, and this hardness can be 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. Note that 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 material by the contrast created by etching the Vickers hardness measurement sample.

[0069] 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.

[0070] In other words, the side frame component according to this embodiment is a press-formed component in which blanks corresponding to pillars and side sills are joined at an overlapping portion where the blanks are superimposed, and the overlapping portion has a bent portion. The work-hardened portion, in which the difference ΔHv between the maximum hardness Hvmax in a range within 5 mm from the end (outer edge) of the weld metal portion on the outer surface of the blank in the overlapping portion (in the case of spot welding, it may be within a range within 12 mm from the center of the joining point (center of the welding point)) and the hardness Hvm of the base material of the base blank is 7% or more of the hardness Hvm of the base material of the base blank, exists only in one of the regions of the overlapping portion with respect to the bent portion if there is one bent portion, and only in the region between two adjacent bent portions if there are two or more bent portions.

[0071] Furthermore, since work hardening does not occur around the joint after press forming, the side frame component according to this embodiment includes a configuration in which a joint having a work-hardened portion and a joint without a work-hardened portion coexist.

[0072] The above explanation of hardness measurement for softened areas during processing was based on the example of resistance spot welding. For other joining methods, the same considerations apply. For example, arc welding is similar to resistance spot welding. In the case of laser welding, the "weld metal area" should be replaced with the molten metal portion; in the case of FSW and friction welding, it should be replaced with the agitated area. In the case of brazing, the "weld metal area" should be replaced with the portion directly above the blank surface perpendicular to the brazed area.

[0073] This section describes the simulation results performed using the double door ring inner shown in Figure 6 as an example of a vehicle side frame component. This door ring inner 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 inner 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. The blanks corresponding to the roof rails and the blanks corresponding to the pillars were joined (resistance spot welded) at the overlapping upper section where they were superimposed on each other. This upper overlapping section is where the roof rail and the center pillar connect, and is located inside the upper connection section, which is the area enclosed by the imaginary lines indicating the width of the roof rail and the imaginary lines indicating the width of the center pillar. The other blanks were joined by butt welding. In this way, an integrated blank was prepared.

[0074] Next, the integrated blank was cold-press-formed, and 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 inner) 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 specimens for work hardening evaluation were cut out. The test specimens for work hardening evaluation were 40 mm square with the center of the joint at the center. For each test specimen, Vickers hardness was measured at a cross section perpendicular to the surface of the outermost blank including the center of the joint (cross section in the thickness direction), at a position 1 / 4 of the 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. The maximum value among the measured values ​​was defined as the maximum hardness Hvmax. In addition, Vickers hardness was measured at a position 15 mm or more away from the center of the spot weld point and not joined, and this was defined as the base material hardness Hvm. The evaluation was based on how many times greater the difference between Hvmax and the base material hardness Hvm (ΔHv) was compared to Hvm.

[0076] 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.

[0077] As a result, in Example 1, for example, the joints joined before press forming had ΔHv values ​​of 0.08 Hvm and 0.10 Hvm, both of which were greater than 0.07 Hvm, and the distribution of Vickers hardness confirmed the presence of work-hardened areas. On the other hand, the joints joined after press forming (spot welding) had ΔHv values ​​of 0.03 Hvm and 0.02 Hvm, both of which were less than 0.07 Hvm, and the distribution of Vickers hardness confirmed the absence of work-hardened areas. Similar measurements and confirmations were performed for other examples. That is, it was confirmed that the joints joined before press forming (joints on the top surface of the overlapping parts) had work-hardened areas, while the joints joined after press forming (joints on the vertical walls of the overlapping parts) did not. These results are shown in Table 4. If work-hardened areas are confirmed and ΔHvm ≥ 0.07 Hvm, it is indicated as "○", and otherwise as "×".

[0078] The main dimensions of the door ring inner 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). <Dimensions of Door Ring Inner> 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. Next, Table 2 shows the steel materials and plate thicknesses used for each blank of the door ring outer during the simulation. Furthermore, Table 3 shows the steel materials and plate thicknesses used for each blank of the door ring inner applied to the example and comparative example.

[0080]

[0081]

[0082]

[0083] 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 4.

[0084] The negative separation distance indicates that, as in the conventional design, the overlapping portion exists within the lower connection portion. Figure 9 is a conceptual diagram showing a conventional example (Comparative Example 3). In the conventional example, as shown in Figure 9, 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.

[0085] Comparative Example 3 is an example in which a pillar-equivalent blank and a side sill-equivalent blank overlap and are joined at the lower connection section (these correspond to the example in Patent Document 2). Comparative Example 3 is an example in which the joining of the overlapping section at the lower connection section is performed before pressing all of them. Therefore, all joined sections have a processing effect section.

[0086] Comparative Example 4 is an example where the separation distance 331 between the overlapping portion 330 and the lower connecting portion 301 is too long.

[0087] Reference Example 1 is an example where a door ring was manufactured by individually press-molding each section blank, rather than using a single integrated blank, and then joining these sections together. Since this door ring, manufactured by joining these separate sections, is not a single-piece molding using an integrated blank, it is presented as a reference example rather than a comparative example.

[0088] Furthermore, an IIHS test simulation was performed using an integrated part with the same specifications as Example 2, but with only the overlap width of 330 mm reduced to 20 mm. In this case, since there is only one row of spot welds, the maximum penetration depth of the center pillar was 50.5 mm, which was larger than that of Example 2, but it was confirmed to be smaller than that of Comparative Example 3, which is a conventional example.

[0089] As can be seen from the results in Table 4, 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.

[0090]

[0091] 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.).

[0092] 100 Double door ring inner 101 Double door ring outer 110 Automotive double door ring 111 Front pillar 112 Center pillar 113 Side sill 114 Rear pillar 115 Roof rail 200 Single door ring inner 201 Single door ring outer 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 300 Integrated blank for double door ring inner 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 section (upper connection section of the center pillar) 305 Imaginary line indicating the width of the roof rail 311 Lower connection section of the front pillar 312 Lower connection section of the rear pillar 313 Upper connection section of the front pillar 314 Upper connection section of the rear pillar 330 Overlap section 331 Distance between the overlap section and the lower connection section 332 Width of the overlap section 400 Double door ring inner 500 Integrated blank for the double door ring inner

Claims

1. A vehicle side frame component comprising the side of a vehicle and configured as a joint structure in which blanks made of multiple 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 at 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 50 mm to 250 mm away from the lower connection portion along the longitudinal central axis of the pillar, and has a work-hardened portion around at least one of the joints.

2. The vehicle side frame component according to claim 1, wherein the joint portion comprises a joint portion having a work-hardened portion and a joint portion without a work-hardened 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 having the work-hardened portion is present only on the top surface portion.

4. The side frame part for a vehicle according to claim 1 or 2, wherein the joint having the work-hardened 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 1 / 4 of the plate thickness from the surface of the outermost blank, when the Vickers hardness at a position 15 mm or more away from the center of the joint and not joined is Hvm, the difference between the maximum Vickers hardness in a range within 2 mm toward the base material from the end of the weld metal portion of the joint and Hvm is 0.07 Hvm or more.

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 automotive door ring inner.

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 side frame component is cold press-formed.

10. A method for manufacturing a vehicle side frame component that constitutes the side surface of a vehicle according to claim 1 or 2, 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 cold press forming process for cold press forming the integrated blank; and a post-press component joining process for joining portions of the integrated blank formed in the cold press forming process that were not joined in the integrated blanking process, as necessary, 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 a region 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, and the overlapping portion is spaced 50 mm to 250 mm away from the lower connection portion along the longitudinal central axis of the pillar.

11. The method for manufacturing a vehicle side frame component according to claim 10, wherein the overlapping portion has a length of 25 mm or more along the longitudinal central axis of the pillar.

12. The method for manufacturing a vehicle side frame part according to claim 10 or 11, wherein the joint is located in one of the regions separated by the portion that is bent by press forming in the overlapping portion.

13. A method for manufacturing a vehicle side frame component according to any one of claims 10 to 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.

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