Structural member, method for manufacturing structural member, and mold

Abstract

A structural member (S, S2) comprises a wheel house (20) and side frames (31). The wheel house (20) includes a wheel house body (21) and a flange (22). The wheel house body (21) forms a space for accommodating a wheel. The flange (22) protrudes outward from the distal end of the wheel house body (21). The side frames (31) are formed integrally with the wheel house (20). The side frames (31) are joined to the wheel house (20) by welding. In each side frame (31), the minimum value of the Vickers hardness of the heat affected zone of a welded portion (50) is 70% or more of the Vickers hardness of the non-welded portions.

Description

Structural member, manufacturing method of structural member, and mold

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

[0002] A structure such as an automobile body is composed of multiple structural members. Each structural member is fabricated, for example, by processing a blank using a mold. The structure is then formed by joining the formed structural members together using techniques such as spot welding.

[0003] In recent years, particularly in the automotive field, there has been an accelerating trend toward integrating structural components for vehicle bodies at the blank stage. Forming a module consisting of multiple structural components from a single blank reduces the number of vehicle body parts compared to joining multiple structural components after molding. This eliminates processes during the manufacturing of the vehicle body, enabling a reduction in greenhouse gas (GHG) emissions throughout the vehicle's life cycle.

[0004] However, when a module that was previously composed of multiple structural members is molded into a single structural member, the structural member may have a portion that forms a negative angle with respect to the processing direction of the mold. If a portion that forms a negative angle with respect to the processing direction exists, molding the structural member becomes difficult.

[0005] Patent Document 1 discloses a technique for forming negative angle portions (groove-shaped bead portions) on the left and right vertical walls of a structural member having a hat-shaped cross section. Patent Document 1 uses a mold including an upper mold, a lower mold, and a pair of slide molds attached to both sides of the upper mold via a cam mechanism. The lower mold includes a central mold and a pair of split molds attached to both sides of the central mold via a cam mechanism. In Patent Document 1, as the mold is clamped, the pair of split molds move apart in the width direction of the mold. Also, as the mold is clamped, the pair of slide molds move closer to each other in the width direction of the mold. Then, each vertical wall is sandwiched between the split molds and the slide mold, and a bead portion is formed on the vertical wall.

[0006] JP 2011-83807 A

[0007] As described above, when multiple structural members are integrated at the blank stage and molded into a single structural member, this structural member may have a portion that forms a negative angle with respect to the processing direction of the mold. Furthermore, when multiple structural members are integrally molded into a single structural member, it may be necessary to mold a flange that is parallel to the processing direction. For example, when a wheel house and a side frame are integrated into a single structural member in a vehicle body, the wheel house may have a portion that forms a negative angle with respect to the processing direction of the mold, and may also have a flange that is parallel to the processing direction. However, from the perspective of reducing the number of parts on a larger scale, it is preferable that these structural members be integrally molded into a single member.

[0008] An object of the present disclosure is to provide a structural member for a vehicle body that integrates at least a wheel house and a side frame. Another object of the present disclosure is to provide a manufacturing method for a structural member that is capable of integrally molding multiple structural members into a single structural member, thereby enabling molding of a portion that forms a negative angle with respect to the processing direction and molding a flange that is parallel to the processing direction.

[0009] A vehicle body structural member according to the present disclosure includes a wheel house and a side frame. The wheel house includes a wheel house main body and a first flange. The wheel house main body forms a space for accommodating wheels. The first flange protrudes outward from a leading end of the wheel house main body. The side frame is formed integrally with the wheel house. The side frame is joined to the wheel house by welding. In the side frame, the minimum Vickers hardness value of the heat-affected zone of the weld is 70% or more of the Vickers hardness of the non-welded portion.

[0010] A method for manufacturing a structural member according to the present disclosure includes the steps of preparing a blank and forming the blank into a structural member using a mold. The mold has at least a first direction and a second direction perpendicular to the first direction as processing directions. The structural member includes a bottom plate portion, a vertical wall portion, and a flange. The bottom plate portion intersects with the first direction. The vertical wall portion rises from the bottom plate portion in the first direction. The flange is continuous with the vertical wall portion on the opposite side of the bottom plate portion. The flange protrudes from the vertical wall portion in the first direction when viewed in a cross section along the first and second directions. The forming step includes a first step and a second step. In the first step, an end of the blank is formed into a flange from the second direction by a first forming portion of the mold. In the second step, while the flange is constrained by the first forming portion and the bottom plate portion is constrained by another portion of the mold, another portion of the blank is formed into the vertical wall portion from the second direction by a second forming portion of the mold.

[0011] According to the present disclosure, a structural member for a vehicle body can be provided that integrates at least a wheel house and a side frame. Furthermore, according to the manufacturing method of the structural member according to the present disclosure, it is possible to form a portion that forms a negative angle with respect to the processing direction, and to form a flange that is substantially parallel to the processing direction. Therefore, multiple structural members can be integrally molded into a single structural member.

[0012] FIG. 1 is a perspective view schematically illustrating a structural member according to the first embodiment. FIG. 2 is another perspective view schematically illustrating the structural member according to the first embodiment. FIG. 3 is a view showing an example of a cross section of the structural member according to the first embodiment. FIG. 4 is a view showing another example of a cross section of the structural member according to the first embodiment. FIG. 5A is a schematic view for explaining a method for manufacturing a structural member according to the first embodiment. FIG. 5B is a schematic view for explaining a method for manufacturing a structural member according to the first embodiment. FIG. 5C is a schematic view for explaining a method for manufacturing a structural member according to the first embodiment. FIG. 5D is a schematic view for explaining a method for manufacturing a structural member according to the first embodiment. FIG. 5E is a schematic view for explaining a method for manufacturing a structural member according to the first embodiment. FIG. 5F is a schematic view for explaining a method for manufacturing a structural member according to the first embodiment. FIG. 5G is a schematic view for explaining a method for manufacturing a structural member according to the first embodiment. FIG. 6 is a perspective view schematically illustrating a structural member according to a second embodiment. FIG. 7 is a cross-sectional view of the structural member shown in FIG. 7. FIG. 8 is a view showing the distribution of Vickers hardness at spot-welded cross sections of side frames for examples and comparative examples.

[0013] A vehicle body structural member according to an embodiment includes a wheel house and a side frame. The wheel house includes a wheel house main body and a first flange. The wheel house main body forms a space for accommodating wheels. The first flange protrudes outward from a leading end of the wheel house main body. The side frame is formed integrally with the wheel house. The side frame is joined to the wheel house by welding. In the side frame, the minimum Vickers hardness value of the heat-affected zone of the weld is 70% or more of the Vickers hardness of the non-welded portion (first configuration).

[0014] In the first configuration, the wheel house and the side frame are integrated as a single structural member. Specifically, the wheel house and the side frame are simultaneously formed as a single member by hot working, such as hot stamping. Therefore, in the side frame, the minimum Vickers hardness of the heat-affected zone of the weld is 70% or more of the Vickers hardness of the non-welded portion. In other words, because the wheel house and the side frame are integrated at the blank stage and simultaneously formed as a single structural member, even if softening of the heat-affected zone (HAZ softening) occurs in the side frame during welding before forming, the HAZ softening is reduced by the heat treatment during forming, and the hardness difference between the non-welded portion and the heat-affected zone is reduced.

[0015] In this way, in the first configuration, at least the wheel house and the side frame are integrated as a single structural member. This reduces the number of parts in the vehicle body compared to when the wheel house and the side frame are separate members. As a result, a process can be omitted during the manufacturing of the vehicle body, thereby reducing lifecycle GHG emissions.

[0016] In the structural member according to the first configuration, the side frame may include a top plate, a vertical wall, and a second flange. The top plate is adjacent to the wheel house main body. The vertical wall is continuous with the top plate on the opposite side of the wheel house main body. The second flange is continuous with the vertical wall on the opposite side of the top plate. The second flange protrudes outward from the vertical wall (second configuration).

[0017] The structural member according to the first or second configuration may further include a floor panel. In this case, the wheel house and the side frame may be provided on both sides of the floor panel in the width direction (third configuration).

[0018] The structural member according to the first or second configuration may further include a cross member. In this case, the wheel house and the side frame may be provided on both sides of the cross member in the longitudinal direction (fourth configuration).

[0019] The structural member according to the fourth configuration may further include a floor panel. In this case, the floor panel is integrally formed with the side frame and the cross member. Each of the side frame and the cross member is provided on the wheel house side or the opposite side of the wheel house with respect to the floor panel (fifth configuration).

[0020] The structural member according to the first or second configuration may further include a dash cross member connected to the side frame, and the dash cross member may extend in a direction intersecting the longitudinal direction of the side frame (sixth configuration).

[0021] The structural member according to the sixth configuration may further include a cross member. The cross member may be connected to the side frame. The cross member may extend in a direction intersecting with the longitudinal direction of the side frame (seventh configuration).

[0022] A manufacturing method for a structural member according to an embodiment includes a step of preparing a blank and a step of forming the blank into a structural member using a mold. The mold has at least a first direction and a second direction perpendicular to the first direction as processing directions. The structural member includes a bottom plate portion, a vertical wall portion, and a flange. The bottom plate portion intersects the first direction. The vertical wall portion rises from the bottom plate portion in the first direction. The flange is continuous with the vertical wall portion on the opposite side of the bottom plate portion. The flange protrudes from the vertical wall portion in the first direction when viewed in a cross section along the first and second directions. The forming step includes a first step and a second step. In the first step, an end of the blank is formed into a flange from the second direction by a first forming portion of the mold. In the second step, while the flange is constrained by the first forming portion and the bottom plate portion is constrained by another portion of the mold, another portion of the blank is formed into the vertical wall portion from the second direction by a second forming portion of the mold (eighth configuration).

[0023] In a method for manufacturing a structural member according to an eighth aspect, a structural member including a bottom plate portion, a vertical wall portion, and a flange protruding from the vertical wall portion in a first direction in a cross-sectional view is formed from a blank. In a first forming step, an end portion of the blank is first formed into a flange by a first forming section of a mold. The first forming section forms the end portion of the blank into a flange in a second direction perpendicular to the first direction, i.e., from a side relative to the first direction, so that the flange can be formed even if the flange is parallel to the first direction. Subsequently, in a second forming step, while the flange is constrained by the first forming section of the mold and the bottom plate portion is constrained by another portion of the mold, a second forming section of the mold constrains the other portion of the blank to form the vertical wall portion. The second forming section forms the other portion of the blank into the vertical wall portion in the second direction perpendicular to the first direction, i.e., from a side relative to the first direction, so that even if a portion of the vertical wall portion forms a negative angle with respect to the first direction, that portion can be formed.

[0024] In this way, the manufacturing method of a structural member according to the eighth aspect makes it possible to form a portion that forms a negative angle with respect to the first direction, which is one of the processing directions of the mold, and also to form a flange that is parallel to the first direction. Therefore, even if a portion that forms a negative angle with respect to the first direction, which is one of the processing directions, or a flange that is parallel to the first direction is generated, it is possible to integrally mold multiple structural members into a single structural member.

[0025] In the method for manufacturing a structural member according to the eighth configuration, the first molding section may include a first movable mold that moves in the second direction. The second molding section may include a second movable mold that moves in the second direction. In this case, the molding surfaces of the first movable mold and the second movable mold are arranged side by side in the first direction when viewed in a cross section along the first and second directions (ninth configuration).

[0026] In the method for manufacturing a structural member according to the ninth configuration, the mold may include an upper mold and a lower mold. The lower mold may include a first movable mold and a second movable mold. In this case, in the first step, after placing a blank between the upper mold and the lower mold, the upper mold and the lower mold may be moved relatively close to each other in a first direction, and with the upper mold pressing the blank toward the lower mold, the first movable mold may be moved in a second direction to clamp an end of the blank between the first movable mold and the upper mold and form it into a flange. In the second step, with the flange restrained between the first movable mold and the upper mold, the second movable mold may be moved in the second direction to clamp another portion of the blank between the second movable mold and the upper mold and form it into a vertical wall portion (tenth configuration).

[0027] In the tenth configuration of the method for manufacturing a structural member, the upper mold may include an upper mold body, a first pad, and a second pad. In the first step, after the first pad presses the blank into the lower mold, the second pad, together with the first movable mold, can clamp the end of the blank to form a flange. In the second step, with the second pad and the first movable mold restraining the flange and the first pad and other parts of the lower mold restraining the bottom plate portion, the upper mold body can clamp the portion of the blank between the first pad and the second pad together with the second movable mold to form a vertical wall portion (eleventh configuration).

[0028] In the manufacturing method for a structural member according to the eleventh aspect, the upper mold includes an upper mold body, a first pad, and a second pad. In the second molding step, the upper mold body clamps the portion of the blank between the first and second pads together with the second movable mold of the lower mold, while the first and second pads press the blank. In other words, the blank can be molded by the upper mold body while the blank is fixed by the first and second pads on both sides of the upper mold body. This makes it possible to suppress the occurrence of wrinkles in the blank.

[0029] The mold according to the embodiment includes an upper mold and a lower mold. The lower mold is configured to be able to move relatively close to and away from the upper mold in a first direction. The lower mold includes a first movable mold and a second movable mold. The first movable mold and the second movable mold are each configured to move in a second direction perpendicular to the first direction. The molding surfaces of the first movable mold and the second movable mold are arranged side by side in the first direction when viewed in cross section along the first and second directions (twelfth configuration).

[0030] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0031] <First embodiment> [Structural member] Figures 1 and 2 are perspective views schematically showing a structural member S according to this embodiment. The structural member S is used in the body of an automobile or the like. The structural member S is, for example, a rear under module of the vehicle body. As shown in Figures 1 and 2, the structural member S includes a floor panel 10 and a pair of wheel houses 20L, 20R. In this embodiment, the structural member S further includes frame units 30, 40.

[0032] Referring to FIG. 1 , wheel houses 20L, 20R are disposed on both widthwise sides of floor panel 10. The widthwise direction of floor panel 10 corresponds to the left-right direction of the vehicle body when structural member S is assembled to the vehicle body. Wheel houses 20L, 20R are formed integrally with floor panel 10. Floor panel 10 and wheel houses 20L, 20R are formed from metal plate material. For example, floor panel 10 and wheel houses 20L, 20R are formed from one or more steel plates.

[0033] Each of the wheel houses 20L, 20R includes a wheel house main body 21 and a flange 22. In the example of FIG. 1 , the wheel house main body 21 is adjacent to the floor panel 10 in the width direction. The wheel house main body 21 is provided on one side of the floor panel 10 in the thickness direction of the floor panel 10. The thickness direction of the floor panel 10 corresponds to the up-down direction of the vehicle body when the structural member S is assembled to the vehicle body. The wheel house main body 21 rises upward from the floor panel 10.

[0034] The wheel house main body 21 forms a space for accommodating wheels. Specifically, the wheel house main body 21 includes a side wall 211 and a peripheral wall 212. The side wall 211 has, for example, an upwardly convex arch shape when viewed along the left-right direction of the vehicle body. The peripheral wall 212 is provided continuous with the side wall 211. The peripheral wall 212 protrudes outward from the edge of the side wall 211 in the left-right direction of the vehicle body. Wheels of an automobile or the like are arranged in the space formed by the side wall 211 and the peripheral wall 212.

[0035] The flange 22 protrudes outward from the tip of the wheel house main body 21. More specifically, the flange 22 is continuous with the peripheral wall 212 of the wheel house main body 21 on the side opposite to the side wall 211, and protrudes outward from the peripheral wall 212. The flange 22 extends along the edge of the peripheral wall 212.

[0036] In the example of FIG. 1 , the frame unit 30 is disposed on the floor panel 10. The frame unit 30 is disposed, for example, on the upper surface of the floor panel 10 with the structural member S assembled to the vehicle body. The frame unit 30 is formed from a metal plate. For example, the frame unit 30 is formed from one or more steel plates. The frame unit 30 includes a pair of side frames 31L, 31R and a cross member 32. In this embodiment, the frame unit 30 includes one cross member 32. However, the frame unit 30 may include multiple cross members 32.

[0037] The side frames 31L, 31R and the cross member 32 each have an elongated shape. The side frames 31L, 31R are disposed on both widthwise sides of the floor panel 10. The side frames 31L, 31R and the wheel houses 20L, 20R are disposed on both longitudinal sides of the cross member 32. The side frames 31L, 31R are disposed on the wheel houses 20L, 20R sides of the floor panel 10. The side frames 31L, 31R are disposed on the left and right sides when the structural member S is assembled to the vehicle body. The side frames 31L, 31R also extend in the fore-and-aft direction of the vehicle body when the structural member S is assembled to the vehicle body. Each of the side frames 31L, 31R includes a front portion 311 and a rear portion 312. The rear portion 312 is disposed rearward of the front portion 311 when the structural member S is assembled to the vehicle body. The rear portion 312 extends rearward from the front portion 311 .

[0038] Like the side frames 31L, 31R, the cross member 32 is provided on the wheel housing 20L, 20R side of the floor panel 10. That is, the cross member 32 is provided on the side frame 31L, 31R side of the floor panel 10 in the thickness direction. The cross member 32 extends in the left-right direction of the vehicle body when the structural member S is assembled to the vehicle body. The cross member 32 extends from the side frame 31L to the side frame 31R. The cross member 32 connects the side frames 31L, 31R. The cross member 32 is connected to the side frames 31L, 31R. More specifically, one longitudinal end of the cross member 32 is connected to one side frame 31L. The other longitudinal end of the cross member 32 is connected to the other side frame 31R.

[0039] Each of the side frames 31L, 31R and the cross member 32 is joined to the floor panel 10. In the example shown in Fig. 1, the side frames 31L, 31R and the cross member 32 are joined to the upper surface of the floor panel 10. The side frames 31L, 31R and the cross member 32 may be joined to the upper surface of the floor panel 10 by spot welding or laser welding.

[0040] Referring to FIG. 2 , the frame unit 40 is disposed on the opposite side of the floor panel 10 from the frame unit 30. The frame unit 40 is disposed, for example, on the underside of the floor panel 10 with the structural member S assembled to the vehicle body. That is, the frame unit 40 is the lower frame unit, and the frame unit 30 is the upper frame unit. The frame unit 40 is formed from a metal plate. For example, the frame unit 40 is formed from one or more steel plates. The frame unit 40 includes a pair of side frames 41L, 41R and a cross member 42. In this embodiment, the frame unit 40 includes multiple cross members 42. However, it is sufficient that the frame unit 40 includes at least one cross member 42.

[0041] The side frames 41L, 41R and the cross member 42 each have an elongated shape. The side frames 41L, 41R are disposed on both widthwise sides of the floor panel 10. The side frames 41L, 41R and the wheel houses 20L, 20R are disposed on both longitudinal sides of the cross member 42. The side frames 41L, 41R are disposed on the opposite side of the floor panel 10 from the wheel houses 20L, 20R. The side frames 41L, 41R are disposed on the left and right sides when the structural member S is assembled to the vehicle body. The side frames 41L, 41R also extend in the fore-and-aft direction of the vehicle body when the structural member S is assembled to the vehicle body. Each of the side frames 41L, 41R includes a front portion 411 and a rear portion 412. The rear portion 412 is disposed rearward of the front portion 411 when the structural member S is assembled to the vehicle body. The rear portion 412 extends rearward from the front portion 411 .

[0042] Like the side frames 41L, 41R, the cross members 42 are provided on the opposite side of the floor panel 10 from the wheel houses 20L, 20R. That is, each of the cross members 42 is provided on the side frame 41L, 41R side of the floor panel 10 in the thickness direction. The cross members 42 extend in the left-right direction of the vehicle body when the structural member S is assembled to the vehicle body. The cross members 42 extend from the side frame 41L to the side frame 41R. The cross members 42 connect the side frames 41L, 41R. The cross members 42 are connected to the side frames 41L, 41R. More specifically, one longitudinal end of the cross member 42 is connected to one side frame 41L. The other longitudinal end of the cross member 42 is connected to the other side frame 41R.

[0043] Each of the side frames 41L, 41R and the cross member 42 is joined to the floor panel 10. In the example shown in Fig. 2, the side frames 41L, 41R and the cross member 42 are joined to the underside of the floor panel 10. The side frames 41L, 41R and the cross member 42 may be joined to the underside of the floor panel 10 by spot welding or laser welding.

[0044] Figure 3 is a cross-sectional view taken along line III-III of the structural member S shown in Figure 1. Figure 3 shows the cross sections of the floor panel 10 and the wheel houses 20L, 20R of the structural member S, i.e., the cross sections of the floor panel 10 and the wheel houses 20L, 20R when cut along the thickness direction and width direction of the floor panel 10 (the vertical and horizontal directions of the vehicle body).

[0045] As shown in FIG. 3 , the floor panel 10 and the wheel houses 20L, 20R may be formed, for example, from separate metal plates. In this case, the wheel houses 20L, 20R are typically joined to the floor panel 10 by welding. That is, a weld 50 exists at the boundary between each of the wheel houses 20L, 20R and the floor panel 10. The weld 50 is, for example, a spot weld. The weld 50 may also be a laser weld. That is, the weld 50 may be formed by spot welding or laser welding. Each of the wheel houses 20L, 20R may be joined to the floor panel 10 by spot welding with their ends overlapping, or may be butt-joined by laser welding.

[0046] FIG. 4 is a cross-sectional view of the floor panel 10 and wheel houses 20L, 20R, but shows a different aspect from FIG. 3 . As shown in FIG. 4 , the structural member S according to this embodiment may be integrated with at least a portion of the upper frame unit 30 ( FIG. 1 ) in addition to the floor panel 10 and wheel houses 20L, 20R. The structural member S may further include, for example, side frames 31L, 31R as integrated members. Hereinafter, unless a distinction is required, the left and right side frames 31L, 31R will be collectively referred to as side frames 31. Similarly, unless a distinction is required, the left and right wheel houses 20L, 20R will be collectively referred to as wheel houses 20.

[0047] Referring to Figure 4, the side frame 31 is disposed between the floor panel 10 and the wheel house 20. The side frame 31 is formed integrally with the floor panel 10 and the wheel house 20. In the structural member S shown in Figure 4, the side frame 31 is formed in a stepped shape with respect to the side wall 211 of the wheel house main body 21. The side frame 31 includes a top plate 313, a vertical wall 314, and a flange 315.

[0048] The top plate 313 is adjacent to the wheel house main body 21 and is disposed spaced apart from the floor panel 10 in the thickness direction. In the example of FIG. 4 , the top plate 313 is positioned higher than the floor panel 10 in a cross-sectional view of the structural member S. The vertical wall 314 is continuous with the top plate 313 on the side opposite to the wheel house main body 21. In a cross-sectional view of the structural member S, the vertical wall 314 extends from the top plate 313 toward the floor panel 10. The flange 315 is continuous with the vertical wall 314 on the side opposite to the top plate 313. The flange 315 protrudes from the vertical wall 314 to the outside of the side frame 31. More specifically, the flange 315 protrudes from the vertical wall 314 toward the floor panel 10 in the width direction of the floor panel 10.

[0049] In a cross section of the structural member S, the flange 315 of the side frame 31 extends in the left-right direction of the vehicle body when the structural member S is assembled to the vehicle body. The flange 315 may be inclined with respect to the left-right direction of the vehicle body in a cross-sectional view of the structural member S, or may be substantially parallel to the left-right direction of the vehicle body. On the other hand, in a cross section of the structural member S, the flange 22 of the wheel house 20 extends in the up-down direction of the vehicle body when the structural member S is assembled to the vehicle body. The flange 22 protrudes in the thickness direction from the tip of the wheel house main body 21 when viewed in a cross section along the thickness and width directions of the floor panel 10. The flange 22 may be inclined with respect to the up-down direction of the vehicle body in a cross-sectional view of the structural member S, or may be substantially parallel to the up-down direction of the vehicle body. In a cross section of the structural member S, the angle θ formed between the flange 315 of the side frame 31 and the flange 22 of the wheel house 20 is, for example, 85° to 90°, and preferably 88° to 90°.

[0050] The side frame 31 is formed of a metal plate different from that of at least the wheel house 20. The side frame 31 is joined to the wheel house 20 by welding. That is, a weld 50 exists at the boundary between the side frame 31 and the wheel house 20. In the example of FIG. 4 , the weld 50 is located between a top plate 313 of the side frame 31 and the wheel house 20. The side frame 31 may also be formed of a metal plate different from that of the floor panel 10. In this case, the side frame 31 is typically joined to the floor panel 10 by welding. That is, a weld 50 exists at the boundary between the side frame 31 and the floor panel 10. In the example of FIG. 4 , the weld 50 is located between a flange 315 of the side frame 31 and the floor panel 10. The weld 50 is, for example, a spot weld. The weld 50 may also be a laser weld. That is, the weld 50 may be formed by spot welding or laser welding. The side frame 31 may be joined to the floor panel 10 or the wheel house 20 by spot welding with the ends overlapping, or may be butt-joined by laser welding.

[0051] Although not shown, the structural member S may further include a cross member 32 ( FIG. 1 ) as an integrated member. The structural member S may also include at least a portion of the lower frame unit 40 ( FIG. 2 ) as an integrated member, in addition to the floor panel 10 and the wheel houses 20L, 20R. That is, the structural member S may include side frames 41L, 41R as integrated members. The structural member S may also include at least one cross member 42 ( FIG. 2 ) as an integrated member.

[0052] [Method for Manufacturing Structural Member] A method for manufacturing a structural member S according to this embodiment will be described below with reference to Figures 5A to 5G. In this embodiment, a case will be described in which a structural member S having a cross section shown in Figure 4, i.e., a structural member S in which a floor panel 10, a wheel house 20, and a side frame 31 are integrated, is molded. However, a structural member S having a cross section shown in Figure 3, i.e., a structural member S in which a floor panel 10 and a wheel house 20 are integrated and which does not include a side frame 31, can also be manufactured by the manufacturing method according to this embodiment. The method for manufacturing a structural member S according to this embodiment includes a preparation step and a molding step.

[0053] 5A, in the preparation step, a blank 60 is prepared. In this embodiment, the blank 60 has a shape obtained by unfolding the floor panel 10, the wheel houses 20L, 20R, and the side frames 31L, 31R (FIG. 4). The blank 60 includes a floor panel equivalent portion 61, wheel house equivalent portions 62L, 62R, and side frame equivalent portions 63L, 63R.

[0054] The floor panel equivalent portion 61 is a portion of the structural member S that corresponds to the floor panel 10 (FIG. 4). The floor panel equivalent portion 61 may be formed from a single metal plate, or may be formed from multiple metal plates (sub-blanks). When the floor panel equivalent portion 61 is formed from multiple metal plates, these metal plates may be butt-joined by laser welding, or may be joined by spot welding with their ends overlapping. The multiple metal plates may differ from each other in at least one of the plate thickness and tensile strength.

[0055] The wheel house equivalent portions 62L, 62R are portions corresponding to the wheel houses 20L, 20R (FIG. 4) of the structural member S. The wheel house equivalent portions 62L, 62R may each be formed from a single metal plate or from multiple metal plates (sub-blanks). When each of the wheel house equivalent portions 62L, 62R is formed from multiple metal plates, these metal plates may be butt-joined by laser welding or may be joined by spot welding with their ends overlapping. The multiple metal plates may differ from each other in at least one of their plate thickness and tensile strength.

[0056] The side frame equivalents 63L, 63R correspond to the side frames 31L, 31R ( FIG. 4 ) of the structural member S. The side frame equivalents 63L, 63R may each be formed from a single metal plate or from multiple metal plates (sub-blanks). When the side frame equivalents 63L, 63R are each formed from multiple metal plates, the metal plates may be butt-joined by laser welding or may be joined by spot welding with their ends overlapping. The multiple metal plates may differ from each other in at least one of their thickness and tensile strength. For example, the portion of the side frame equivalents 63L, 63R corresponding to the front portion 311 ( FIG. 1 ) may be formed from a metal plate having a greater thickness and / or tensile strength than the portion corresponding to the rear portion 312 ( FIG. 1 ).

[0057] In this embodiment, the blank 60 is a tailored blank, and at least the floor panel equivalent portion 61, the wheel house equivalent portions 62L, 62R, and the side frame equivalent portions 63L, 63R are formed from different metal plates (sub-blanks). The blank 60 is a tailor welded blank in which multiple metal plates are joined by welding. The metal plates included in the blank 60 are typically steel plates. However, the metal plates may also be, for example, aluminum alloy plates.

[0058] 5B to 5G, in the forming process, a die 70 is used to form the blank 60 into the structural member S. In this embodiment, the blank 60 is press-formed into the structural member S by the die 70.

[0059] First, the configuration of the mold 70 will be described with reference to FIG. 5B . The mold 70 has at least a first direction and a second direction perpendicular to the first direction as processing directions. In this embodiment, the mold 70 includes an upper mold 71 and a lower mold 72. The lower mold 72 is capable of moving relatively close to and away from the upper mold 71 in the first direction. In this embodiment, the first direction is a pressing direction P of the upper mold 71 and the lower mold 72. The pressing direction P is, for example, a vertical direction. When performing the molding process, the upper mold 71 and the lower mold 72 may be attached to a pressing device.

[0060] The upper mold 71 includes an upper mold body 711, a first pad 712, and a second pad 713. The first pad 712 is disposed on one side of the upper mold body 711 in the width direction of the mold 70. The second pad 713 is disposed on the other side of the upper mold body 711 in the width direction of the mold 70. The width direction of the mold 70 is perpendicular to the pressing direction P and corresponds to, for example, the width direction of the floor panel 10 ( FIG. 4 ). In this embodiment, the width direction of the mold 70 is the second direction. However, the second direction (the width direction of the mold 70) may be inclined with respect to the width direction of the floor panel 10 in a top view of the structural member S ( FIGS. 1 and 2 ). That is, when viewed from above, the structural member S when applied to a vehicle body may be inclined with respect to the left-right direction (vehicle width direction) within a range of, for example, ±30°. The second direction can be adjusted as appropriate, taking into account the formability of the structural member S.

[0061] The upper mold body 711 has a molding surface 711a. The molding surface 711a is provided on one side surface of the upper mold body 711 in the width direction of the mold 70. In this embodiment, the molding surface 711a is provided on the outer side surface of the upper mold body 711 in the width direction of the mold 70.

[0062] The molding surface 711a is a surface for molding at least a part of the wheel house main body 21 (FIG. 4). In the present embodiment, the molding surface 711a also molds the side frame 31 (FIG. 4). Therefore, the molding surface 711a includes a step 711s that is recessed toward the inside of the upper mold main body 711 in correspondence with the side frame 31 that is integral with the wheel house main body 21.

[0063] In this embodiment, the upper mold body 711 further has a molding surface 711b. The molding surface 711b is a surface for molding at least a portion of the floor panel 10 (FIG. 4). The molding surface 711b is provided on the lower surface of the upper mold body 711, for example.

[0064] The first pad 712 is disposed on the side of the upper mold body 711. The first pad 712 is disposed, for example, inside the upper mold body 711 in the width direction of the mold 70. The first pad 712 is movable relative to the upper mold body 711 in the pressing direction P.

[0065] The first pad 712 has a pressing surface 712a. The pressing surface 712a is provided, for example, on the lower surface of the first pad 712. The pressing surface 712a is a surface for forming at least a portion of the floor panel 10 (FIG. 4).

[0066] The second pad 713 is disposed on the side of the upper mold body 711 opposite to the first pad 712. The second pad 713 is disposed, for example, on the outer side of the upper mold body 711 in the width direction of the mold 70. The second pad 713 is movable relative to the upper mold body 711 and the first pad 712 in the pressing direction P.

[0067] The second pad 713 has a pressing surface 713a. The pressing surface 713a is a surface for forming the flange 22 (FIG. 4) of the wheel house 20. The pressing surface 713a is provided on the side surface of the second pad 713 opposite the upper mold body 711. In this embodiment, the pressing surface 713a is provided on the side surface of the second pad 713 that is outer in the width direction of the mold 70. The pressing surface 713a extends in the press direction P in a cross-sectional view of the mold 70. The pressing surface 713a may be substantially parallel to the press direction P in a cross-sectional view of the mold 70, or may be slightly inclined with respect to the press direction P. The cross-section of the mold 70 is a cross section along the first direction and the second direction as processing directions.

[0068] The second pad 713 may further have a molding surface 713b. The molding surface 713b is a surface for molding the remaining portion of the wheel house main body 21 (FIG. 4). The molding surface 713b is arranged on the upper mold main body 711 side with respect to the pressing surface 713a. In this embodiment, the molding surface 713b is arranged more inward than the pressing surface 713a in the width direction of the mold 70. The molding surface 713b may be provided adjacent to the pressing surface 713a.

[0069] The lower mold 72 includes a fixed mold 721, a first movable mold 722, and a second movable mold 723. In this embodiment, the first movable mold 722 and the second movable mold 723 are arranged on the fixed mold 721. In addition, the first movable mold 722 and the second movable mold 723 are arranged so as to be shifted in position in the width direction of the mold 70 with respect to the upper mold 71.

[0070] The fixed mold 721 has a molding surface 721a. The molding surface 721a faces the molding surface 711b of the upper mold body 711 and the pressing surface 712a of the first pad 712 in the pressing direction P. The molding surface 721a, together with the molding surface 711b of the upper mold body 711 and the pressing surface 712a of the first pad 712, is a surface for molding the floor panel 10 (FIG. 4).

[0071] In a cross-sectional view of the mold 70, the first movable die 722 and the second movable die 723 are arranged in the pressing direction P. In this embodiment, the first movable die 722 is arranged on the second movable die 723. The first movable die 722 has a molding surface 722a. The molding surface 722a is provided on a side surface of the first movable die 722 on one side in the width direction of the mold 70. In this embodiment, the molding surface 722a is provided on a side surface of the first movable die 722 on the inner side in the width direction of the mold 70.

[0072] The molding surface 722a is a surface for molding the flange 22 ( FIG. 4 ) of the wheel house 20 together with the pressing surface 713a of the second pad 713. Therefore, the molding surface 722a has a shape corresponding to the pressing surface 713a of the second pad 713. That is, like the pressing surface 713a of the second pad 713, the molding surface 722a extends in the press direction P in a cross-sectional view of the mold 70. The molding surface 722a may be substantially parallel to the press direction P in a cross-sectional view of the mold 70, or may be slightly inclined with respect to the press direction P.

[0073] The second movable die 723 is disposed between the first movable die 722 and the fixed die 721. The second movable die 723 has a molding surface 723a. The molding surface 723a is provided on a side surface of the second movable die 723 on one side in the width direction of the die 70. In this embodiment, the molding surface 723a is provided on a side surface of the second movable die 723 on the inner side in the width direction of the die 70. The molding surface 723a is disposed, for example, adjacent to the molding surface 722a of the first movable die 722. In this example embodiment, the molding surface 722a of the first movable die 722 is disposed so as to surround the molding surface 723a of the second movable die 723. The molding surface 722a of the first movable die 722 and the molding surface 723a of the second movable die 723 are disposed side by side in the pressing direction P when viewed in a cross section along the pressing direction P, which is the first direction, and the width direction of the die 70, which is the second direction.

[0074] The molding surface 723a is a surface for mainly molding the wheel house main body 21 (FIG. 4) together with the molding surface 711a of the upper mold main body 711 and the molding surface 713b of the second pad 713. Therefore, the molding surface 723a has a shape corresponding to the molding surface 711a of the upper mold main body 711 and the molding surface 713b of the second pad 713. In the present embodiment, the molding surface 723a has a step 723s that protrudes toward the outside of the second movable mold 723 in correspondence with the side frame 31 (FIG. 4) that is integral with the wheel house main body 21.

[0075] The first movable die 722 and the second movable die 723 are movable in the width direction of the die 70. The first movable die 722 and the second movable die 723 can be moved in the width direction of the die 70 by, for example, a cam mechanism. In this case, the die 70 can include a cam driver 73. The cam driver 73 is capable of moving relatively close to and away from the first movable die 722 and the second movable die 723 in the pressing direction P. The first movable die 722 and the second movable die 723 can function as slide cams operated by the cam driver 73.

[0076] In this embodiment, the first movable die 722 has a sliding surface 722b on the side opposite the molding surface 722a. Similarly, the second movable die 723 has a sliding surface 723b on the side opposite the molding surface 723a. The sliding surfaces 722b, 723b are, for example, inclined surfaces that are inclined with respect to the pressing direction P in a cross-sectional view of the die 70. The sliding surfaces 722b, 723b are inclined with respect to the pressing direction P so that, for example, the sliding surfaces 722b, 723b approach the fixed die 721 in the pressing direction P as they move away from the upper die 71 in the width direction of the die 70. The cam driver 73 has a sliding surface 731 that corresponds to the sliding surface 722b of the first movable die 722 and the sliding surface 723b of the second movable die 723.

[0077] In this embodiment, the mold 70 has a configuration that is symmetrical with respect to the center line in the width direction. Therefore, only one side of the mold 70 with respect to the center line in the width direction is shown in Fig. 5B and Figs. 5C to 5G described below. However, the mold 70 does not necessarily have to have a shape that is completely symmetrical with respect to the center line in the width direction.

[0078] In the forming step, the blank 60 is subjected to, for example, press working by the die 70. The forming step includes a first step and a second step.

[0079] As shown in FIG. 5B , before the start of the forming process, the upper mold 71 and the lower mold 72 are spaced apart in the press direction P (first direction). In the first forming step, the first forming section of the mold 70 forms the end of the blank 60 into the flange 22 ( FIG. 4 ) from the width direction (second direction) of the mold 70. The first forming section of the mold 70 can form the flange 22, for example, by clamping the end of the blank 60 from the width direction of the mold 70. In this embodiment, the first forming section includes a first movable mold 722 of the lower mold 72. In the first step, the blank 60 is first placed between the upper mold 71 and the lower mold 72. When the lower mold 72 is positioned below the upper mold 71, the blank 60 may be placed on the first movable mold 722.

[0080] 5C , in the first step, the upper die 71 and the lower die 72 are then brought closer to each other in the pressing direction P, and the first pad 712 of the upper die 71 presses the blank 60 toward the lower die 72. More specifically, the first pad 712 presses the central portion of the blank 60 toward the fixed die 721 of the lower die 72, causing the blank 60 to bend in the pressing direction P.

[0081] 5D , in the first step, the first movable die 722 is moved in the width direction of the die 70 while the upper die 71 presses the blank 60 toward the lower die 72. That is, after the first pad 712 presses the blank 60 in the press direction P, the first movable die 722 moves in the width direction of the die 70. The movement of the first movable die 722 starts, for example, before the blank 60 is clamped between the first pad 712 and the fixed die 721 of the lower die 72.

[0082] In this embodiment, as the cam driver 73 approaches the first movable die 722 relatively in the press direction P, the sliding surface 731 of the cam driver 73 contacts the sliding surface 722b of the first movable die 722 and slides on the sliding surface 722b. As a result, the first movable die 722 is pushed out in the width direction of the mold 70 toward the upper die 71. Then, as shown in FIG. 5E , the end of the blank 60 is clamped between the first movable die 722 and the upper die 71 to form the flange 22. More specifically, the second pad 713 of the upper die 71 clamps the end of the blank 60 together with the first movable die 722 to form the flange 22. The flange 22 is formed by the molding surface 722a of the first movable die 722 and the pressing surface 713a of the second pad 713. In this embodiment, the first movable die 722 and the second pad 713 of the mold 70 function as a first molding unit for molding the flange 22.

[0083] In the first step, the end portion of the blank 60 may be clamped between the first movable die 722 and the second pad 713, and at the same time, the center portion of the blank 60 may be clamped between the first pad 712 and the fixed die 721. The first pad 712 presses the center portion of the blank 60 with the pressing surface 712a. When the end portion of the blank 60 is clamped between the first movable die 722 and the second pad 713, the first movable die 722 stops. Furthermore, when the center portion of the blank 60 is clamped between the first pad 712 and the fixed die 721, the relative movement of the first pad 712 with respect to the lower die 72 in the pressing direction P ends.

[0084] 5F , in the second forming step, with the flange 22 restrained by the first forming portion of the mold 70 and the bottom plate portion restrained by the other portions of the mold 70, the other portions of the blank 60 are formed into vertical wall portions by the second forming portion of the mold 70 from the width direction (second direction) of the mold 70. The second forming portion of the mold 70 can form the vertical wall portions, for example, by clamping the other portions of the blank 60 from the width direction of the mold 70. In this embodiment, the second forming portion includes a second movable mold 723 of the lower mold 72. In the second step, with the end portion of the blank 60, i.e., the flange 22, clamped between the first movable mold 722 and the upper mold 71, the second movable mold 723 is moved in the width direction of the mold 70. In this embodiment, as the cam driver 73 approaches the second movable die 723 relatively in the press direction P, the sliding surface 731 of the cam driver 73 contacts the sliding surface 723b of the second movable die 723 and slides on the sliding surface 723b. As a result, the second movable die 723 is pushed out in the width direction of the mold 70 toward the upper die 71. Then, as shown in FIG. 5G , the second movable die 723 and the upper die 71 clamp another portion of the blank 60 to form a vertical wall portion. The bottom plate portion is a portion of the structural member S that intersects with the press direction P, which serves as the first direction. In this embodiment, the floor panel 10 corresponds to the bottom plate portion of the structural member S. The vertical wall portion is a portion of the structural member S that rises from the bottom plate portion in the press direction P. In this embodiment, the wheel house main body 21 mainly corresponds to the vertical wall portion of the structural member S. When the blank 60 is clamped between the second movable die 723 and the upper die 71, the second movable die 723 stops.

[0085] In the second step, with the second pad 713 and the first movable die 722 restraining the flange 22 and the first pad 712 and other parts of the lower die 72 (e.g., the fixed die 721) restraining the bottom plate portion, the upper die body 711, together with the second movable die 723, clamps the portion of the blank 60 between the first pad 712 and the second pad 713 and forms it into a vertical wall portion. This forms the structural member S. The vertical wall portion and bottom plate portion of the structural member S are formed mainly by the forming surfaces 711a and 711b of the upper die body 711, the forming surface 713b of the second pad 713, and the forming surface 723a of the second movable die 723. In this embodiment, the second movable die 723, the upper die body 711, and the second pad 713 of the mold 70 function as a second forming portion for forming the vertical wall portion.

[0086] By returning mold 70 to its initial state ( FIG. 5B ), structural member S, which is an integrated unit of floor panel 10, wheel house 20, and side frame 31, can be removed from mold 70. After the above-described molding process, lower frame unit 40 ( FIG. 2 ) may be joined to structural member S by, for example, welding.

[0087] Each of the side frames 41L, 41R (FIG. 2) of the frame unit 40 can form a closed cross section with the stepped side frame 31. The cross member 42 (FIG. 2) of the frame unit 40 can form a closed cross section with the floor panel 10. The portion of the floor panel 10 corresponding to the cross member 42 of the frame unit 40 may have an upper cross member 32 (FIG. 1) formed integrally with the other portions.

[0088] If the side frame 31 is not integral with the wheel house 20, after the above-described molding process, both of the frame units 30, 40 (FIGS. 1 and 2) may be joined to the floor panel 10 by, for example, welding. In this case, the side frames 31L, 31R and the cross member 32 (FIG. 1) of the frame unit 30 can each form a closed cross section with the floor panel 10. Similarly, the side frames 41L, 41R and the cross member 42 (FIG. 2) of the frame unit 40 can each form a closed cross section with the floor panel 10.

[0089] The frame units 30, 40 (FIGS. 1 and 2) can be produced, for example, by press forming separately from the floor panel 10 and the wheel house 20. In this case, in the frame unit 30, the side frames 31L, 31R and the cross member 32 may be press-formed integrally from a single blank, or may be press-formed separately (FIG. 1). Similarly, in the frame unit 40, the side frames 41L, 41R and the cross member 42 may be press-formed integrally from a single blank, or may be press-formed separately (FIG. 2).

[0090] [Effect] In this embodiment, a structural member S is manufactured by press-forming a blank 60. The structural member S includes, for example, a floor panel 10 as a bottom plate portion, a wheel house main body 21 as a vertical wall portion, and a flange 22 protruding from the wheel house main body 21 in the press direction P in a cross-sectional view. In a first forming step, a first forming section of the die 70 first forms an end of the blank 60 into the flange 22. The first forming section forms the end of the blank 60 from the side with respect to the width direction of the die 70, i.e., the press direction P. This allows the flange 22 to be formed even if the flange 22 is parallel to the press direction P. In a second forming step, a second forming section of the die 70 forms the other portion of the blank 60 into the vertical wall portion. The second forming section forms the blank 60 from the side with respect to the width direction of the die 70, i.e., the press direction P. This allows the formation of even a portion of the vertical wall portion that forms a negative angle with respect to the press direction P.

[0091] More specifically, in the press-molding mold 70, the lower mold 72 includes a first movable mold 722 and a second movable mold 723 arranged in the press direction P. In the first molding step, the first movable mold 722 included in the first molding section moves in the width direction of the mold 70, and the end of the blank 60 is clamped by the first movable mold 722 and the upper mold 71 and molded into the flange 22. In this case, the end of the blank 60 is clamped by the first movable mold 722 and the upper mold 71 from the side with respect to the press direction P. Therefore, even if the flange 22 is parallel to the press direction P, the flange 22 can be molded.

[0092] In the second forming step, while the end of the blank 60 remains clamped between the first movable die 722 and the upper die 71, the second movable die 723 included in the second forming unit moves in the width direction of the die 70 and, together with the upper die 71, clamps another portion of the blank 60 to form it into a vertical wall portion. The other portion of the blank 60 is also clamped by the second movable die 723 and the upper die 71 from the side with respect to the press direction P. Therefore, even if a portion forming a negative angle with respect to the press direction P exists in the vertical wall portion, the second movable die 723 and the upper die 71 can form that portion. In other words, even if the wheel house main body 21 or the side frame 31 integrated with the wheel house main body 21, as a vertical wall portion, has a recessed portion on the inside of the structural member S with respect to the press direction P, in other words, a portion having an unevenness in the horizontal direction, the second movable die 723 and the upper die 71 can form that portion. For example, even if a bead exists in the wheel house main body 21 , this bead can be formed by the second movable die 723 and the upper die 71 .

[0093] In this way, the manufacturing method of the structural member S according to this embodiment makes it possible to form a portion that forms a negative angle with respect to the press direction P, and also to form a flange 22 that is parallel to the press direction P. Therefore, even in cases where a portion that forms a negative angle with respect to the press direction P or a flange 22 that is parallel to the press direction P occurs when the blanks 60 are integrated and press-formed, such as in the case of the floor panel 10 and the wheel house 20, they can be formed as a single structural member S in the same forming process.

[0094] In this embodiment, the upper mold 71 includes an upper mold body 711, a first pad 712, and a second pad 713. The upper mold body 711, the first pad 712, and the second pad 713 are separate bodies and can independently move relative to the lower mold 72 in the press direction P. In this case, in the second molding step, while the blank 60 is held down by the first pad 712 and the second pad 713, the upper mold body 711 can clamp the portion of the blank 60 between the first pad 712 and the second pad 713 together with the second movable mold 723. In other words, the blank 60 can be molded by the upper mold body 711 while the blank 60 is fixed by the first pad 712 and the second pad 713 on both sides of the upper mold body 711. This makes it possible to suppress the occurrence of wrinkles in the portion of the blank 60 to be molded by the upper mold body 711 during the molding step.

[0095] In the structural member S according to this embodiment, at least the floor panel 10, the pair of wheel houses 20L, 20R, and the side frames 31L, 31R are integrated as a single member from the stage of the blank 60. This reduces the number of parts in the vehicle body in which the structural member S is used. This allows for omission of a process during the manufacture of the vehicle body, resulting in a reduction in lifecycle GHG emissions.

[0096] For example, by using aluminum casting, it is possible to integrate multiple structural members into a single member. For example, it is conceivable to produce a rear under module such as the structural member S according to the present embodiment by using aluminum casting. However, when a cast member is produced from aluminum, the plate thickness of the flange portion and the like is relatively large, which may increase the difficulty of joining the cast member when assembling it to the vehicle body.

[0097] In contrast, in this embodiment, the structural member S, which integrates at least the floor panel 10 and the wheel houses 20L, 20R, is manufactured by, for example, press forming. The structural member S can be manufactured, for example, by press forming a blank 60 made of one or more steel plates. In this case, for example, the plate thickness of each flange 22 of the wheel houses 20L, 20R can be reduced. Therefore, compared to aluminum cast members, the structural member S can be easily attached to the vehicle body.

[0098] For example, when the wheel house 20 is manufactured as a single unit by press molding, the direction corresponding to the left-right direction of the vehicle body is usually the press direction P. In this case, when the side frame 31 is integrated with the wheel house 20, the flange 315 of the side frame 31 becomes substantially parallel to the press direction P. Therefore, the flange 315 cannot be formed by normal press molding, and it is difficult to manufacture the wheel house 20 with the side frame 31 integrated therewith.

[0099] In contrast, in the manufacturing method according to this embodiment, by using the first movable die 722, the flange 315 can be formed even if the flange 315 is parallel to the pressing direction P. Therefore, the manufacturing method according to this embodiment can also be suitably used for the integrated member of the wheel house 20 and the side frame 31. In other words, the application of the manufacturing method according to this embodiment is not limited to the integral molding of the floor panel 10 and the wheel house 20. Structural members other than the structural member S described in this embodiment can also be manufactured using the manufacturing method according to this embodiment. The manufacturing method according to this embodiment can be applied not only to the manufacture of structural members for vehicle bodies, but also to the manufacture of structural members for uses other than vehicle bodies.

[0100] In the case where the structural member S is a rear under module of a vehicle body as in this embodiment, the structural member S may be manufactured by cold forming, but is preferably manufactured by hot forming, for example, hot stamping. In the case of hot forming, the manufacturing method according to this embodiment further includes a step of heating the blank 60. The blank 60 includes at least one steel plate and is heated, for example, in a heating furnace. The blank 60 is heated to an austenite transformation finish temperature (A ｃ３ The blank 60 is preferably heated to a temperature of 900°C or higher. The blank 60 is heated to, for example, 900°C or higher. In the forming process, the heated blank 60 is formed into the structural member S using a mold 70. In the forming process, the blank 60 (structural member S) is rapidly cooled (heat is removed) by contact with the mold 70.

[0101] When the structural member S is manufactured by hot forming, such as hot stamping, the side frame 31 integral with the floor panel 10 and the wheel house 20 is preferably formed from hot-stamped material. Hot-stamped material generally refers to a steel plate that can achieve a desired strength by hot-forming a blank made of high-strength steel (e.g., a steel plate having a high tensile strength of over 440 MPa) and then pressing it into a die and quenching it. By using hot-stamped material, it is possible to produce a strength ranging from 590 MPa to 2000 MPa. For hot-stamped material, a forming method is used in which a blank (steel plate) is heated to an austenite temperature range of, for example, approximately 900°C, and then hot-formed while simultaneously pressing it into a die and quenching it to induce martensitic transformation. Hot forming reduces the forming load because the blank is formed at a high temperature, and martensitic transformation occurs in the blank, resulting in high strength and excellent shape fixability after forming.

[0102] When a structural member S, in which the floor panel 10, wheel house 20, and side frame 31 are integrated, is manufactured by hot forming, such as hot stamping, the heating process prior to forming reduces HAZ softening at the welded joints 50 between the side frame 31 and other parts. In other words, the side frame 31 experiences a relatively small decrease in hardness in the heat-affected zones of the welded joints 50 compared to non-welded joints. Specifically, in the side frame 31, the minimum Vickers hardness of the heat-affected zones of the welded joints 50 is 70% or more of the Vickers hardness of the non-welded joints. In the side frame 31, the minimum Vickers hardness of the heat-affected zones of the welded joints 50 is preferably 80% or more, and more preferably 90% or more, of the Vickers hardness of the non-welded joints. In the side frame 31, the minimum Vickers hardness of the heat-affected zones is equal to or less than the Vickers hardness of the non-welded joints. That is, in the side frame 31, the minimum value of the Vickers hardness of the heat-affected zone of the welded portion 50 is 100% or less of the Vickers hardness of the non-welded portion.

[0103] The Vickers hardness of the side frame 31 can be measured by a Vickers hardness test specified in JIS Z 2244-1:2020. Specifically, a test piece including the side frame 31 and the welded portion 50 is first obtained from the structural member S at a position passing through the weld center of the welded portion 50 by laser cutting or the like. The test piece is then embedded in resin so that a cross section passing through the weld center of the side frame 31 and the welded portion 50 is located on the surface, and the cross section is polished. Next, Vickers hardness is measured at a position 1 / 4 of the plate thickness from the surface closest to the weld center on both surfaces of the side frame 31, to a position 12.0 mm outward from the weld center, in accordance with JIS Z 2244-1:2020, using a test force of 0.49 N and a measurement interval (pitch) of 0.1 to 0.2 mm. The minimum value of the measured Vickers hardness is defined as the minimum Vickers hardness of the heat-affected zone of the side frame 31. Furthermore, the Vickers hardness is measured at a position 15.0 mm or more away from the weld center of the welded portion 50 and at a position ¼ of the plate thickness from the surface of the side frame 31 in accordance with JIS Z 2244-1:2020, using a test force of, for example, 0.49 N. This Vickers hardness is defined as the Vickers hardness of the non-welded portion of the side frame 31.

[0104] The structural member S may be formed by integrating the lower side frames 41L, 41R with the floor panel 10 and the wheel house 20, instead of the upper side frame 31. Even when the structural member S, in which the floor panel 10, the wheel house 20, and the side frames 41L, 41R are integrated, is manufactured by hot forming, such as hot stamping, the heating process before forming reduces HAZ softening at the welds between the side frames 41L, 41R and other parts. In this case, too, in the formed structural member S, the minimum Vickers hardness of the heat-affected zones of the welds in the side frames 41L, 41R is 70% or more of the Vickers hardness of the non-welded portions. In the side frames 41L, 41R, the minimum Vickers hardness of the heat-affected zones of the welds is preferably 80% or more, and more preferably 90% or more, of the Vickers hardness of the non-welded portions. In the side frames 41L, 41R, the minimum Vickers hardness of the heat-affected zone is equal to or less than the Vickers hardness of the non-welded zone. That is, in the side frames 41L, 41R, the minimum Vickers hardness of the heat-affected zone of the welded zone 50 is equal to or less than 100% of the Vickers hardness of the non-welded zone. The Vickers hardness of the side frames 41L, 41R can be measured in the same manner as the Vickers hardness of the side frame 31.

[0105] Second Embodiment Fig. 6 is a perspective view showing a structural member S2 according to this embodiment, which is, for example, a front under module of a vehicle body.

[0106] Like the structural member S according to the first embodiment, the structural member S2 includes a wheel house 20 and a side frame 31. The structural member S2 may further include a cross member 32 and a dash cross member 33.

[0107] The dash cross 33 is a member that is joined to a dash panel (not shown) when the structural member S2 is assembled to the vehicle body. In the structural member S2, the dash cross 33 is connected to the side frame 31. The dash cross 33 is connected, for example, to one longitudinal end of the side frame 31. The dash cross 33 may be joined to the side frame 31 by welding. The cross member 32 is disposed in front of the dash cross 33 when the structural member S2 is assembled to the vehicle body. As in the first embodiment, the cross member 32 is connected to the side frame 31. In the example of FIG. 6 , one longitudinal end of the cross member 32 is connected to the side frame 31. The cross member 32 may be joined to the side frame 31 by welding. The cross member 32 and the dash cross 33 each extend in a direction that intersects with the longitudinal direction of the side frame 31. When the structural member S2 is attached to the vehicle body, the cross member 32 and the dash cross member 33 extend inward from the side frame 31 in the left-right direction of the vehicle body.

[0108] FIG. 7 is a cross-sectional view (VII-VII cross-sectional view of FIG. 6 ) of the structural member S2. In the structural member S2 according to this embodiment, the side frame 31 is also joined to the wheel house 20 by welding. The side frame 31 is integrally formed with the wheel house 20. The wheel house 20 and the side frame 31 are joined by welding at the blank (not shown) stage and integrally formed by hot forming such as hot stamping. Therefore, as in the first embodiment, in the side frame 31, the minimum Vickers hardness of the heat-affected zone of the welded portion 50 is 70% or more of the Vickers hardness of the non-welded portion. In the side frame 31, the minimum Vickers hardness of the heat-affected zone of the welded portion 50 is preferably 80% or more, more preferably 90% or more, of the Vickers hardness of the non-welded portion. In the side frame 31, the minimum Vickers hardness of the heat-affected zone is equal to or less than the Vickers hardness of the non-welded portion. That is, in the side frame 31, the minimum value of the Vickers hardness of the heat-affected zone of the welded portion 50 is 100% or less of the Vickers hardness of the non-welded portion. The Vickers hardness of the side frame 31 can be measured by the method described in the first embodiment.

[0109] In the structural member S2, at least the wheel house 20 and the side frame 31 are integrally formed. Such a structural member S2 can be manufactured by the same manufacturing method as in the first embodiment. That is, the structural member S2 can be manufactured by the same manufacturing method as in the first embodiment, with the flange 315 of the side frame 31 serving as a bottom plate portion, the top plate 313 and vertical wall 314 of the side frame 31 and the wheel house main body 21 serving as a vertical wall portion, and the flange 22 of the wheel house 20 serving as a flange protruding from the vertical wall portion.

[0110] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0111] In the above embodiment, the first movable die 722 and the second movable die 723 of the lower die 72 are moved in the width direction of the die 70 by a cam mechanism. The first movable die 722 and the second movable die 723 are moved in the width direction of the die 70 by a common cam driver 73. However, separate cam drivers can be provided for the first movable die 722 and the second movable die 723. For example, if the position of the sliding surface 722b of the first movable die 722 and the position of the sliding surface 723b of the second movable die 723 are different in the depth direction of the die 70, a cam driver can be provided for each of the movable dies 722 and 723. However, it is sufficient that the first movable die 722 and the second movable die 723 are configured to be movable in the width direction of the die 70. A cam mechanism does not necessarily have to be used as a means for operating the first movable die 722 and the second movable die 723. For example, the first movable die 722 and the second movable die 723 may be moved in the width direction (second direction) of the die 70 by an actuator such as a hydraulic cylinder. When the first movable die 722 and the second movable die 723 are operated by means other than a cam mechanism, the die 70 does not need to be provided with a cam driver 73 .

[0112] In the above embodiment, the first movable die 722 and the second movable die 723 are arranged in the press direction P in a cross-sectional view of the mold 70. That is, the first movable die 722 is arranged on the second movable die 723. However, the arrangement of the first movable die 722 and the second movable die 723 is not limited to this. For example, the first movable die 722 may be configured to be housed within the second movable die 723 and protrude from the second movable die 723. In this case as well, in the cross-section of the mold 70, the molding surface 722a of the first movable die 722 for molding the flange 22 and the molding surface 723a of the second movable die 723 for molding the vertical wall portion are arranged side by side in the press direction P, which is the first direction. The molding surface 722a of the first movable die 722 and the molding surface 723a of the second movable die 723 being aligned in the first direction means that, in the first direction, the molding surface 722a of the first movable die 722 is disposed on one side of the molding surface 723a of the second movable die 723. In the cross section of the mold 70, it is sufficient that the molding surfaces 722a, 723a are at different positions in the first direction, and they do not necessarily have to be aligned in a straight line in the first direction.

[0113] In the above embodiment, the first movable die 722 and the second movable die 723 are arranged on the fixed die 721. However, the first movable die 722 and the second movable die 723 do not necessarily have to be arranged on the fixed die 721. For example, the fixed die 721 may be arranged to the side of the first movable die 722 and the second movable die 723 in the width direction of the mold 70. Alternatively, the fixed die 721 may not be provided on the lower die 72. The configuration of the lower die 72 can be changed as appropriate depending on the shapes of the structural members S, S2 to be molded.

[0114] In the above embodiment, the lower mold 72 includes two movable molds 722 and 723. However, the lower mold 72 may include three or more movable molds. For example, the second movable mold 723 may be divided in the first direction, so that the lower mold 72 includes three or more movable molds.

[0115] In the above embodiment, the mold 70 is provided with a first movable die 722 as at least a part of the first molding section, and a second movable die 723 as at least a part of the second molding section. However, the mold 70 does not necessarily have to have the configuration described in the above embodiment. The first molding section of the mold 70 only needs to be configured so that it can restrain the end of the blank 60 from the width direction of the mold 70 and mold it into the flange 22. The second molding section of the mold 70 only needs to be configured so that it can restrain the other part of the blank 60 from the width direction of the mold 70 and mold the vertical wall section.

[0116] In the above embodiment, the upper mold 71 includes a separate upper mold body 711, a first pad 712, and a second pad 713. However, the configuration of the upper mold 71 is not limited to this. For example, the upper mold body 711 and the first pad 712 may be integrated, or the upper mold body 711 and the second pad 713 may be integrated. Alternatively, the upper mold body 711, the first pad 712, and the second pad 713 may all be integrated. The configuration of the upper mold 71 can be changed as appropriate depending on the shape of the structural members S, S2 to be molded.

[0117] In the above embodiment, the upper mold 71 is disposed above the lower mold 72 in the drawing. However, the positional relationship between the upper mold 71 and the lower mold 72 is not limited to this. For example, the lower mold 72 may be disposed above the upper mold 71. Alternatively, the upper mold 71 and the lower mold 72 do not have to be disposed one above the other. That is, in the mold 70, the first direction, which is one of the processing directions, does not necessarily have to be the vertical direction (up-down direction).

[0118] In the above embodiment, an example has been described in which the die 70 performs press forming on the blank 60. However, the die 70 does not necessarily have to be for press forming. The die 70 may be any die that has at least a first direction and a second direction perpendicular to the first direction as processing directions.

[0119] In the first embodiment, the structural member S shown in FIG. 4 is an integrated member of the floor panel 10, the pair of wheel houses 20L, 20R, and the pair of side frames 31L, 31R. However, the structural member S may be an integrated member of at least one of the wheel houses 20L, 20R and one of the side frames 31L, 31R. Alternatively, the structural member S may be an integrated member of one of the wheel houses 20L, 20R and one of the side frames 41L, 41R. In other words, the structural member S includes at least the wheel house 20L or 20R and the upper or lower side frame corresponding to the wheel house. The structural member S may also include the pair of wheel houses 20L, 20R and the pair of side frames 31L, 31R or the pair of side frames 41L, 41R as an integrated member. In this case, the structural member S may further include an integrated floor panel 10, or may include an integrated cross member 32 or 42 instead of or in addition to the floor panel 10.

[0120] In the first embodiment, the structural member S is formed using a blank 60 including multiple metal plates (sub-blanks). However, the structural member S may be formed from a single metal plate. The number, arrangement, thickness, and tensile strength of the metal plates forming the structural member S can be determined appropriately depending on, for example, the specifications of the structural member S. Similarly, the number, arrangement, thickness, and tensile strength of the metal plates forming the structural member S2 according to the second embodiment can also be determined appropriately depending on, for example, the specifications of the structural member S2.

[0121] In the first embodiment, the blank 60 before the forming process may be provided with a metal plate as a patch material. The patch material is overlapped on a portion of the blank 60 and joined to the blank 60 by spot welding, laser welding, or the like. The blank 60 may be formed into the structural member S with the patch material joined thereto. The patch material can be placed in areas of the structural member S that require reinforcement. Similarly, in the structural member S2 according to the second embodiment, the patch material can be placed in areas that require reinforcement.

[0122] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0123] As an example, a structural member having a configuration similar to that of the structural member S shown in Fig. 4 was integrally formed by the manufacturing method (hot stamping) according to the above embodiment. Also, as a comparative example, a structural member having a configuration similar to that of the structural member S shown in Fig. 4 was produced by forming the floor panel, wheel house, and side frame individually by press molding and then joining them together.

[0124] In both the example and the comparative example, the side frame was joined to the wheel house by spot welding with their ends overlapping. For the example in which the floor panel, wheel house, and side frame were integrally molded, the Vickers hardness was measured at the spot weld cross section on the wheel house side of the side frame. Similarly, for the comparative example in which the floor panel, wheel house, and side frame were press-formed separately and then joined by spot welding after molding, the Vickers hardness was measured at the spot weld cross section on the wheel house side of the side frame.

[0125] For the spot-welded cross sections of the side frames of the example and comparative example, Vickers hardness was measured at 0.2 mm intervals along a straight line located 1 / 4 of the way through the plate thickness from the surface closest to the weld center in accordance with JIS Z 2244-1:2020 (test force: 0.49 N). Figure 8 shows the distribution of Vickers hardness at the spot-welded cross sections of the side frames for the example and comparative example. As shown in Figure 8, a heat-affected zone 52 exists around the weld metal portion (nugget portion) 51 of the weld 50. At a point approximately 1.0 mm away from the outer edge of the weld metal portion 51, a decrease in Vickers hardness (softening) due to heat influence occurs. However, at a point further away from the outer edge of the weld metal portion 51, the Vickers hardness converges to the base metal hardness of 500 Hv.

[0126] 8, when the Vickers hardness was measured at 0.2 mm intervals from the weld center toward both outer sides of the weld metal zone 51 to positions spaced apart by, for example, 7.0 mm or more, and the minimum measured Vickers hardness was taken as the minimum Vickers hardness of the heat-affected zone 52, the minimum Vickers hardness of the heat-affected zone 52 of the side frame in the comparative example was approximately 300 Hv. In the side frame of the comparative example, the minimum Vickers hardness of the heat-affected zone 52 was approximately 60% of the Vickers hardness (base metal hardness) of the non-welded zone: 500 Hv.

[0127] On the other hand, in the example, the minimum Vickers hardness of the heat-affected zone 52 of the side frame was 420 Hv, which was higher than the minimum Vickers hardness of the heat-affected zone 52 in the comparative example. In the side frame of the example, the minimum Vickers hardness of the heat-affected zone 52 was 84% ​​of the Vickers hardness (base material hardness) of the non-welded portion: 500 Hv. Note that even when the side frame is butt-welded to the wheel house, the relationship between the minimum Vickers hardness of the heat-affected zone 52 in the side frame and the Vickers hardness of the non-welded portion is the same as in the example.

[0128] In this way, when the side frame is integrated with at least the wheel house from the blank stage and formed by hot stamping, softening of the heat-affected zone 52 of the side frame is reduced. It has been confirmed that in a structural member in which the side frame is integrated with the wheel house, the minimum Vickers hardness of the heat-affected zone 52 of the side frame welded to the wheel house is ensured to be 70% or more of the Vickers hardness of the non-welded portion.

[0129] S, S2: Structural member 10: Floor panel 20, 20L, 20R: Wheel house 21: Wheel house main body 22: Flange 31, 31L, 31R: Side frame 313: Top plate 314: Vertical wall 315: Flange 32: Cross member 33: Dash cross 41L, 41R: Side frame 42: Cross member 50: Welded part 60: Blank 70: Mold 71: Upper mold 711: Upper mold main body 712: First pad 713: Second pad 72: Lower mold 722: First movable mold 722a: Forming surface 723: Second movable mold 723a: Forming surface

Claims

1. A structural member for a vehicle body, comprising: a wheel house including a wheel house main body forming a space for accommodating wheels, and a first flange protruding outward from a tip of the wheel house main body; and a side frame formed integrally with the wheel house, wherein the side frame is joined to the wheel house by welding, and the minimum Vickers hardness of the heat-affected zone of the weld in the side frame is 70% or more of the Vickers hardness of a non-welded portion.

2. A structural member as claimed in claim 1, wherein the side frame includes: a top plate adjacent to the wheel house main body; a vertical wall continuing with the top plate on the opposite side of the wheel house main body; and a second flange continuing with the vertical wall on the opposite side of the top plate and protruding outward from the vertical wall.

3. A structural member as claimed in claim 1, further comprising a floor panel, the wheel house and the side frame being provided on either side of the floor panel in the width direction.

4. A structural member according to claim 1, further comprising a cross member, said wheel house and said side frame being provided on either side of said cross member in the longitudinal direction.

5. A structural member as claimed in claim 4, further comprising a floor panel formed integrally with said side frame and said cross member, each of said side frame and said cross member being provided on the wheel house side or on the opposite side of said wheel house with respect to said floor panel.

6. A structural member according to claim 1, further comprising a dash cross connected to said side frame and extending in a direction intersecting with the longitudinal direction of said side frame.

7. A structural member according to claim 6, further comprising a cross member connected to said side frame and extending in a direction intersecting with the longitudinal direction of said side frame.

8. A method for manufacturing a structural member, comprising: a step of preparing a blank; and a step of molding, using a mold having at least a first direction and a second direction perpendicular to the first direction, the blank into a structural member including a bottom plate portion intersecting the first direction, a vertical wall portion rising from the bottom plate portion in the first direction, and a flange continuing to the vertical wall portion on the opposite side of the bottom plate portion and protruding from the vertical wall portion in the first direction when viewed in a cross section along the first and second directions, wherein the molding step includes a first step of molding an end portion of the blank into the flange from the second direction by a first molding portion of the mold, and a second step of molding the other portion of the blank into the vertical wall portion from the second direction by a second molding portion of the mold, with the flange being constrained by the first molding portion and the bottom plate portion being constrained by the other portion of the mold.

9. A manufacturing method as described in claim 8, wherein the first molding section includes a first movable mold that moves in the second direction, the second molding section includes a second movable mold that moves in the second direction, and the molding surfaces of the first movable mold and the molding surfaces of the second movable mold are arranged side by side in the first direction when viewed in a cross section along the first direction and the second direction.

10. A manufacturing method as described in claim 9, wherein the mold includes an upper mold and a lower mold including the first movable mold and the second movable mold, and in the first step, after the blank is placed between the upper mold and the lower mold, the upper mold and the lower mold are brought closer together in the first direction, and while the upper mold is pressing the blank into the lower mold, the first movable mold is moved in the second direction, and the end portion of the blank is clamped between the first movable mold and the upper mold to form the flange, and in the second step, while the flange is restrained between the first movable mold and the upper mold, the second movable mold is moved in the second direction, and the other portion of the blank is clamped between the second movable mold and the upper mold to form the vertical wall portion.

11. The manufacturing method as recited in claim 10, wherein the upper mold includes an upper mold body, a first pad, and a second pad; in the first step, after the first pad presses the blank into the lower mold, the second pad, together with the first movable mold, clamps the end of the blank to form the flange; and in the second step, while the second pad and the first movable mold restrain the flange and the first pad and other parts of the lower mold restrain the bottom plate portion, the upper mold body clamps the portion of the blank between the first pad and the second pad together with the second movable mold to form it into the vertical wall portion.

12. A mold comprising: an upper mold; and a lower mold configured to be able to approach and move away from the upper mold in a first direction, wherein the lower mold includes a first movable mold and a second movable mold each configured to move in a second direction perpendicular to the first direction, and the molding surfaces of the first movable mold and the molding surfaces of the second movable mold are arranged side by side in the first direction when viewed in a cross section along the first direction and the second direction.

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