Structural member and method for manufacturing the same

Abstract

The present invention provides a structural member that can reduce tensile residual stress in the welded joint in a curved region. [Solution] The structural member (100, 100A) comprises an inner member (10), an outer member (20), a welded part (32), and a support member (50, 50A). The inner member (10) includes a top plate (11), a first vertical wall (13), and a second vertical wall (12, 14). The vertical wall (13) includes a curved region (15). The curved region (15) curves concavely inward of the structural member (100, 100A) when viewed from the top plate (11) side. The outer member (20) includes a top plate (21), a third vertical wall (23), and a fourth vertical wall (22, 24). The vertical wall (23) is joined to the vertical wall (13) by welding. The support members (50, 50A) are fixed to the vertical wall (13) from within the inner member (10) in the curved region (15), and are also fixed from within the inner member (10) to at least one of the top plate (11) and the vertical walls (12, 14).

Description

[Technical Field]

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

[0002] For example, a plurality of structural members are used in structures such as automobiles. Some structural members have a curved region that curves concavely inward in a plan view.

[0003] For example, Patent Document 1 discloses a structural member having a concave curved portion and a non-concave curved portion in a plan view. The structural member of Patent Document 1 includes a first member and a second member. The first member and the second member each include a main surface portion (top plate) and two wall constituting portions (vertical walls). The wall constituting portion of the first member is arranged inside the wall constituting portion of the second member and is joined to the wall constituting portion of the second member by welding. In Patent Document 1, the height of the wall constituting portion of the first member in the concave curved portion is smaller than the height of the wall constituting portion of the first member in the non-concave curved portion. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2023-122747 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] When a structural member includes a curved region that curves concavely inward in a plan view, as described in Patent Document 1, the tensile residual stress of the welded portion in the curved region tends to be high. In structural members including a curved region, countermeasures are particularly desired to reduce the tensile residual stress of the welded portion in the curved region and improve the fatigue strength of the welded portion.

[0006] An object of the present disclosure is to provide a structural member capable of reducing tensile residual stress in a welded portion in a curved region. [Means for solving the problem]

[0007] The structural member according to this disclosure comprises an inner member, an outer member, a welded portion, and a support member. The inner member includes a first top plate, a first vertical wall, and a second vertical wall. The first vertical wall is continuous with the first top plate. The first vertical wall includes a curved region. The curved region curves concavely inward into the structural member when viewed from the first top plate side. The second vertical wall is continuous with the first top plate on the opposite side of the first vertical wall. The outer member includes a second top plate, a third vertical wall, and a fourth vertical wall. The second top plate faces the first top plate. The third vertical wall is continuous with the second top plate. The third vertical wall is superimposed on the first vertical wall from the outside of the inner member. The third vertical wall is joined to the first vertical wall by welding. The fourth vertical wall is continuous with the second top plate on the opposite side of the third vertical wall. The fourth vertical wall is joined to the second vertical wall. The welded section extends along the end of the third vertical wall. The support member is fixed to the first vertical wall from within the inner member in the curved region, and also fixed to at least one of the first top plate and the second vertical wall from within the inner member. [Effects of the Invention]

[0008] According to the structural member described herein, tensile residual stress in the welded joint can be reduced in the curved region. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a perspective view of a structural member according to the first embodiment. [Figure 2] Figure 2 is another perspective view of the structural member according to the first embodiment. [Figure 3] Figure 3 is a cross-sectional view of the structural member shown in Figure 2 at the location of the curved region. [Figure 4A] Figure 4A is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 4B] Figure 4B is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 4C] Figure 4C is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 4D] Figure 4D is a schematic diagram illustrating the manufacturing method of a structural member according to the first embodiment. [Figure 5A] Figure 5A is a schematic diagram illustrating the behavior of structural members during welding heating. [Figure 5B] Figure 5B is a schematic diagram illustrating the behavior of structural members during cooling. [Figure 6] Figure 6 is a cross-sectional view of the structural member according to the second embodiment at the location of the curved region. [Figure 7] Figure 7 is a cross-sectional view of a structural member at the location of the curved region according to a modified example of the second embodiment. [Figure 8] Figure 8 is a plan view of a structural member relating to a modified example of each of the above embodiments. [Modes for carrying out the invention]

[0010] The structural member according to this embodiment comprises an inner member, an outer member, a welded portion, and a support member. The inner member includes a first top plate, a first vertical wall, and a second vertical wall. The first vertical wall is continuous with the first top plate. The first vertical wall includes a curved region. The curved region curves concavely inward into the structural member when viewed from the first top plate side. The second vertical wall is continuous with the first top plate on the opposite side of the first vertical wall. The outer member includes a second top plate, a third vertical wall, and a fourth vertical wall. The second top plate faces the first top plate. The third vertical wall is continuous with the second top plate. The third vertical wall is superimposed on the first vertical wall from the outside of the inner member. The third vertical wall is joined to the first vertical wall by welding. The fourth vertical wall is continuous with the second top plate on the opposite side of the third vertical wall. The fourth vertical wall is joined to the second vertical wall. The welded section extends along the end of the third vertical wall. The support member is fixed to the first vertical wall from within the inner member in the curved region, and is also fixed from within the inner member to at least one of the first top plate and the second vertical wall (first configuration).

[0011] In a structural member, if the vertical wall (first vertical wall) of the inner member includes a curved region that curves inward in a concave shape when viewed from above, when the vertical wall (third vertical wall) of the outer member is overlapped with the first vertical wall from the outside and welded together, in the curved region, the portion of the first vertical wall near the weld line expands due to welding heat and displaces toward the internal space of the inner member. On the other hand, the portion of the first vertical wall away from the weld line experiences less thermal expansion compared to the portion near the weld line and is constrained by the top plate (first top plate). Therefore, when overlapping and welding the first vertical wall of the inner member and the third vertical wall of the outer member, in the curved region, the first vertical wall tilts so that its free end is located toward the internal space of the inner member relative to the first top plate. After welding the first vertical wall of the inner member and the third vertical wall of the outer member, these vertical walls are naturally cooled to, for example, room temperature. As they cool, the portion of the first vertical wall near the weld contracts, and the first vertical wall attempts to return from its tilted state to its original state. As a result, the weld is pulled in the height direction of the first vertical wall, generating relatively high tensile residual stress in the weld.

[0012] The inventors have found that the tensile residual stress in the welded joint has a high correlation with the out-of-plane deformation of the first vertical wall of the inner member. Directly speaking, the greater the out-of-plane deformation of the first vertical wall during cooling (the amount of recovery from the welding heating state), the higher the tensile residual stress generated in the welded joint. The out-of-plane deformation of the first vertical wall during cooling is the amount of movement of the first vertical wall from the state in which it is maximally tilted towards the internal space during the welding heating process to the state in which it returns to the outside of the internal space after cooling. The greater the out-of-plane deformation (tilting amount) of the first vertical wall during the welding heating process, the greater the out-of-plane deformation of the first vertical wall during cooling tends to be. Based on this finding, in the structural member relating to the first configuration, a support member is fixed to the first vertical wall from inside the inner member in the curved region. The support member is also fixed from inside the inner member to at least one of the first top plate and the other vertical wall (second vertical wall). In this case, when the first vertical wall of the inner member and the third vertical wall of the outer member are overlap-welded, the tilting of the first vertical wall during the welding heating process can be restricted by the support member. Therefore, the amount of out-of-plane deformation of the first vertical wall during the welding heating process can be reduced in the curved region. As a result, the amount of out-of-plane deformation of the first vertical wall during cooling in the curved region is also reduced, and the tensile residual stress of the weld can be reduced.

[0013] In the structural member according to the first configuration, the support member is preferably fixed to at least a portion of the first vertical wall that corresponds to the welded portion (second configuration).

[0014] In the curved region of the first vertical wall of the inner member, the amount of out-of-plane deformation during the welding heating process increases as the distance to the welded portion decreases. On the other hand, in the second configuration, the support member is fixed to at least the portion of the first vertical wall that corresponds to the welded portion. This allows the support member to more effectively suppress out-of-plane deformation of the first vertical wall in the curved region during the welding heating process. Therefore, the tensile residual stress in the welded portion is more easily reduced further.

[0015] In the structural member according to the first or second configuration, the support member may be fixed to the first vertical wall from the inside of the inner member in the curved region, and may also be fixed to the second vertical wall from the inside of the inner member (third configuration).

[0016] In the structural member according to the third configuration, the support member may be disposed spaced apart from the first top plate in a space formed by the inner member and the outer member (fourth configuration).

[0017] In the structural member according to any one of the first to fourth configurations, the support member may be disposed spaced apart from the second top plate in a space formed by the inner member and the outer member (fifth configuration).

[0018] A method for manufacturing a structural member according to an embodiment comprises steps i) and ii). In step i), an inner member, an outer member, and a support member are prepared. The inner member includes a first top plate, a first vertical wall, and a second vertical wall. The first vertical wall is continuous with the first top plate. The first vertical wall includes a curved region. The curved region has a concave shape on the inside of the inner member when viewed from the first top plate side. The second vertical wall is continuous with the first top plate on the opposite side of the first vertical wall. The outer member includes a second top plate, a third vertical wall, and a fourth vertical wall. The third vertical wall is continuous with the second top plate. The fourth vertical wall is continuous with the second top plate on the opposite side of the third vertical wall. In step ii), a portion of the support member is fixed to the first vertical wall from inside the inner member in the curved region, and the other portion of the support member is fixed to at least one of the first top plate and the second vertical wall from inside the inner member. With this state, the third vertical wall is superimposed on the first vertical wall from the outside of the inner member, and the first vertical wall and the third vertical wall are welded together along the end of the third vertical wall (sixth configuration).

[0019] Embodiments of this disclosure will be described below with reference to the drawings. In these drawings, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0020] <First Embodiment> [Structural members] Figures 1 and 2 are perspective views of the structural member 100 according to this embodiment. The structural member 100 is used, for example, in a vehicle such as an automobile. The structural member 100 may be a chassis component of an automobile. The structural member 100 may be a suspension component such as a suspension member, suspension arm, or suspension frame, or it may be a chassis frame, etc. In this embodiment, an example in which the structural member 100 is a lower arm, which is a type of suspension arm, will be described.

[0021] Referring to Figures 1 and 2, the structural member 100 comprises an inner member 10, an outer member 20, and welded portions 31, 32, and 33. In this embodiment, the structural member 100 includes mounting portions 41, 42, and 43.

[0022] The structural member 100 is attached to the vehicle body or wheels at mounting portions 41, 42, and 43. Mounting portion 41 is positioned outward in the vehicle width direction (left-right direction) relative to mounting portions 42 and 43 when the structural member 100 is incorporated into the vehicle. Mounting portion 41 is connected to the wheels, for example, via a ball joint and a steering knuckle (not shown). Mounting portions 42 and 43 are positioned in the vehicle length direction (front-rear direction) when the structural member 100 is incorporated into the vehicle. Mounting portion 42 is positioned in front of mounting portion 43. Mounting portions 42 and 43 are each connected to the vehicle body via bushings (not shown). In Figures 1 and 2, the front-rear direction of the vehicle is indicated by the X direction, the left-right direction by the Y direction, and the up-down direction by the Z direction.

[0023] The inner member 10 includes a top plate 11 and vertical walls 12, 13, and 14. Vertical walls 12 and 13 are continuous with the top plate 11. Vertical wall 12 extends along the top plate 11 from mounting portion 41 to mounting portion 42. Vertical wall 13 extends along the top plate 11 from mounting portion 42 to mounting portion 43. Vertical wall 14 is continuous with the top plate 11 on the opposite side of vertical walls 12 and 13. Vertical wall 14 extends along the top plate 11 from mounting portion 41 to mounting portion 43.

[0024] The outer member 20 is positioned below the inner member 10 when the structural member 100 is installed in the vehicle. Alternatively, the outer member 20 is positioned above the inner member 10 when the structural member 100 is installed in the vehicle.

[0025] The outer member 20 includes a top plate 21 and vertical walls 22, 23, and 24. The top plate 21 is positioned opposite the top plate 11 of the inner member 10, either below or above the top plate 11. The vertical walls 22 and 23 are continuous with the top plate 21. Vertical wall 22 extends along the top plate 21 from mounting portion 41 to mounting portion 42. Vertical wall 23 extends along the top plate 21 from mounting portion 42 to mounting portion 43. Vertical wall 24 is continuous with the top plate 21 on the opposite side of vertical walls 22 and 23. Vertical wall 24 extends along the top plate 21 from mounting portion 41 to mounting portion 43.

[0026] The vertical walls 22, 23, and 24 of the outer member 20 are provided corresponding to the vertical walls 12, 13, and 14 of the inner member 10, respectively. The vertical walls 22, 23, and 24 of the outer member 20 are joined to the vertical walls 12, 13, and 14 of the inner member 10, respectively.

[0027] The vertical wall 22 of the outer member 20 is joined to the vertical wall 12 of the inner member 10. The vertical wall 22 is, for example, overlapped with the vertical wall 12 from the outside of the inner member 10 and joined to the vertical wall 12 by welding. In this case, a welded portion 31 is formed at the end of the vertical wall 22. The welded portion 31 can extend along the end of the vertical wall 22. The welded portion 31 extends, for example, from mounting portion 41 to mounting portion 42. The welded portion 31 is a lap fillet weld that is continuously formed by, for example, arc welding or laser-arc hybrid welding.

[0028] The vertical wall 23 of the outer member 20 is overlapped with the vertical wall 13 from the outside of the inner member 10 and joined to the vertical wall 13 by welding. Therefore, a welded portion 32 is formed at the end of the vertical wall 23. The welded portion 32 extends along the end of the vertical wall 23. The welded portion 32 extends, for example, from mounting portion 42 to mounting portion 43. The welded portion 32 is a lap fillet weld that is continuously formed by, for example, arc welding or laser-arc hybrid welding.

[0029] The vertical wall 24 of the outer member 20 is joined to the vertical wall 14 of the inner member 10. The vertical wall 24 is, for example, overlapped with the vertical wall 14 from the outside of the inner member 10 and joined to the vertical wall 14 by welding. In this case, a welded portion 33 is formed at the end of the vertical wall 24. The welded portion 33 can extend along the end of the vertical wall 24. The welded portion 33 extends, for example, from mounting portion 41 to mounting portion 43. The welded portion 33 is a lap fillet weld that is continuously formed by, for example, arc welding or laser-arc hybrid welding.

[0030] In this embodiment, the vertical wall 13 of the inner member 10 includes a curved region 15. The curved region 15 is the area of ​​the vertical wall 13 that curves inward in a concave shape when viewed from the top plate 11 side of the structural member 100 (inner member 10). The vertical wall 23 of the outer member 20 corresponds to the vertical wall 13 of the inner member 10 and curves along the vertical wall 13 at the location of the curved region 15.

[0031] The curved region 15 can be identified in the same manner as the concave curved portion in Patent Document 1. That is, the shape of the structural member 100 when viewed from the top plate 11 side of the inner member 10 along the height direction of the vertical wall 13 is defined as the plan view shape. First, in the plan view shape of the structural member 100, one evaluation point corresponding to the toe of the welded portion 32 is identified. Next, at the toe of the welded portion 32, two points 4 mm apart on both sides in the extending direction of the welded portion 32 are identified from that evaluation point, and a circle of curvature is identified from these three points. The length of the line segment connecting the evaluation point on the toe of the welded portion 32 and the center of curvature of the identified circle of curvature is defined as the radius of curvature R. If the line segment overlaps with the structural member 100, the radius of curvature R is considered positive, and if the line segment does not overlap with the structural member 100, the radius of curvature R is considered negative. When the radius of curvature R is negative, the evaluation point is located in the portion of the vertical wall 13 that curves inward in a concave shape in plan view. On the other hand, when the radius of curvature R is positive, the evaluation points are located on the portion of the vertical wall 13 that curves outward in a plan view.

[0032] In the plan view of the structural member 100, the region where evaluation points satisfying a radius of curvature R [mm] of -400 ≤ R < 0 are clustered can be defined as the curved region 15. That is, by measuring the radius of curvature R of an evaluation point using the procedure described above, if the radius of curvature R [mm] satisfies -400 ≤ R < 0, it is determined that the evaluation point is included in the curved region 15. On the other hand, at the location of an evaluation point where R < -400, the curvature of the vertical wall 13 in the plan view of the structural member 100 is small, and the vertical wall 13 has a shape close to a straight line, so it is determined that the evaluation point is not included in the curved region 15. The region where evaluation points satisfying a radius of curvature R [mm] of R < -400 or R > 0 are clustered among the vertical wall 13 is a region that is substantially straight when viewed from the top plate 11 side of the inner member 10, or a region that curves convexly outward from the structural member 100.

[0033] In this embodiment, other vertical walls 14 of the inner member 10 may also include curved regions 16. The curved region 16 is a region of the vertical wall 14 that curves inward in a concave shape when viewed from the top plate 11 side of the structural member 100 (inner member 10). The vertical wall 24 of the outer member 20 corresponds to the vertical wall 14 of the inner member 10 and curves along the vertical wall 14 at the location of the curved region 16. The curved region 16 can be identified in the same way as the curved region 15 of the vertical wall 13.

[0034] The inner member 10 and the outer member 20 are formed from, for example, metal plates. The inner member 10 and the outer member 20 may be formed from steel plates or from non-ferrous metal plates. The tensile strength of the inner member 10 and the outer member 20 is, for example, 780 MPa or more, preferably 980 MPa or more. The tensile strength of the inner member 10 and the outer member 20 is, for example, 1470 MPa or less, but may exceed 1470 MPa. The tensile strength of the inner member 10 may be the same as or different from the tensile strength of the outer member 20.

[0035] The thickness of the inner member 10 and the outer member 20 is preferably 4.0 mm or less. The thickness of the inner member 10 and the outer member 20 is, for example, 1.6 mm or more, but may be less than 1.6 mm. The thickness of the inner member 10 may be the same as or different from the thickness of the outer member 20.

[0036] Figure 3 is a cross-sectional view of the structural member 100 at the location of the curved region 15 (section III-III in Figure 2). The cross-sectional view of the structural member 100 refers to the cross-section obtained when the structural member 100 is cut by a plane that runs along the thickness direction of the top plate 11 of the inner member 10. In Figure 3, the cross-section of the structural member 100 is shown when cut by a plane that passes through the vertical wall 13 of the inner member 10 and the vertical wall 23 of the outer member 20, as well as the other vertical wall 14 of the inner member 10 and the other vertical wall 24 of the outer member 20. The configurations of the inner member 10 and the outer member 20 will be described in more detail below with reference to Figure 3.

[0037] Referring to Figure 3, the inner member 10 has a roughly inverted U-shaped cross-section. The inner member 10 opens on the opposite side of the top plate 11 when viewed alone. In the inner member 10, the vertical wall 13 on the curved region 15 side includes a vertical wall body 131 and a ridge portion 132. The vertical wall body 131 is connected to the top plate 11 via the ridge portion 132. That is, the ridge portion 132 is the corner portion between the top plate 11 and the vertical wall body 131. The ridge portion 132 may have an outwardly convex curved shape in a cross-sectional view of the structural member 100. On the other hand, the vertical wall body 131 may have a substantially straight shape in a cross-sectional view of the structural member 100.

[0038] The other vertical walls 14 of the inner member 10 are positioned on the opposite side of the vertical wall 13 from the top plate 11. Each vertical wall 14 includes a vertical wall body 141 and a ridge portion 142. The vertical wall body 141 is connected to the top plate 11 via the ridge portion 142. That is, the ridge portion 142 is the corner portion between the top plate 11 and the vertical wall body 141. The ridge portion 142 may have a curved shape that is convex outward in a cross-sectional view of the structural member 100. For example, in the cross-section of the structural member 100, the direction in which a straight line extends from the R-end of one ridge portion 132 of the inner member 10 on the top plate 11 side to the R-end of the other ridge portion 142 on the top plate 11 side can be defined as the width direction of the inner member 10, and the direction perpendicular to this width direction can be defined as the height direction of the vertical walls 13 and 14.

[0039] The vertical wall body 141 may be substantially straight in a cross-sectional view of the structural member 100. The vertical wall body 141 faces the vertical wall body 131 in a cross-sectional view of the structural member 100. The vertical wall body 141 may be arranged parallel to the vertical wall body 131 in a cross-sectional view of the structural member 100, or it may be arranged non-parallel to the vertical wall body 131.

[0040] The outer member 20 has a generally U-shaped cross-section. The outer member 20 opens on the opposite side of the top plate 21 when viewed alone. However, the outer member 20 is joined to the inner member 10, thereby forming a closed cross-section together with the inner member 10. The top plate 21 of the outer member 20 faces the top plate 11 of the inner member 10. In the outer member 20, the vertical wall 23 on the curved region 15 side includes a vertical wall body 231 and a ridge portion 232. The vertical wall body 231 is connected to the top plate 21 via the ridge portion 232. That is, the ridge portion 232 is the corner portion between the top plate 11 and the vertical wall body 231. The ridge portion 232 may have an outwardly convex curved shape in the cross-sectional view of the structural member 100. On the other hand, the vertical wall body 231 may have a substantially straight shape in the cross-sectional view of the structural member 100.

[0041] The vertical wall body 231 is superimposed on the outer surface of the vertical wall body 131 of the inner member 10 and joined to the vertical wall body 131 by a weld 32. The weld 32 includes weld metal 321. The weld metal 321 is located outside the space formed by the inner member 10 and the outer member 20.

[0042] The other vertical walls 24 of the outer member 20 are positioned on the opposite side of the vertical wall 23 from the top plate 21. The vertical wall 24 includes a vertical wall body 241 and a ridge portion 242. The vertical wall body 241 is connected to the top plate 21 via the ridge portion 242. That is, the ridge portion 242 is the corner portion between the top plate 21 and the vertical wall body 241. The ridge portion 242 may have an outwardly convex curved shape in a cross-sectional view of the structural member 100. On the other hand, the vertical wall body 241 may have a substantially straight shape in a cross-sectional view of the structural member 100. The vertical wall body 241 faces the vertical wall body 231 in a cross-sectional view of the structural member 100. The vertical wall body 241 may be positioned parallel to or non-parallel to the vertical wall body 231 in a cross-sectional view of the structural member 100.

[0043] In the example shown in Figure 3, the vertical wall body 241 is superimposed on the outer surface of the vertical wall body 141 of the inner member 10 and joined to the vertical wall body 141 by a weld 33. The weld 33 includes weld metal 331. The weld metal 331 is located outside the space formed by the inner member 10 and the outer member 20.

[0044] As shown in Figure 3, the structural member 100 further comprises a support member 50. The support member 50 is provided on the structural member 100 to support the vertical wall 13 from within the inner member 10 in the curved region 15. The support member 50 is positioned within the inner member 10.

[0045] In this embodiment, the support member 50 is formed in the shape of a rod. The support member 50 may be a round rod having a circular cross-section, or a square rod having a square cross-section. The support member 50 may have other polygonal cross-sections, or L-shaped, U-shaped, flattened, etc. In the example of Figure 3, in a cross-sectional view of the structural member 100, the support member 50 extends from the vertical wall 13 to the vertical wall 14 of the inner member 10.

[0046] The support member 50 is fixed to the vertical wall 13 from inside the inner member 10 in the curved region 15. In this embodiment, one end of the support member 50 in the longitudinal direction is fixed to the inner surface of the vertical wall 13 in the curved region 15. The support member 50 is fixed to the vertical wall 13 by welding such as arc welding or laser welding, brazing, mechanical joining using a screw mechanism, or adhesive. Alternatively, the support member 50 may be fixed to the vertical wall 13 by friction joining, for example.

[0047] The support member 50 is preferably fixed to at least the portion of the vertical wall 13 corresponding to the welded portion 32. That is, when viewing the structural member 100 along the width direction, it is preferable that the portion of the support member 50 that overlaps with the weld metal 321 of the welded portion 32 is fixed to the vertical wall 13. In the example in Figure 3, the support member 50 supports the vertical wall 13 from the inside at the location of the welded portion 32.

[0048] The support member 50 is fixed from within the inner member 10 to at least one of the vertical walls 13, the top plate 11, and the other vertical walls 14. In this embodiment, the other end of the support member 50 in the longitudinal direction is fixed to the inner surface of the vertical wall 14. The support member 50 is fixed to the vertical wall 14 by welding such as arc welding or laser welding, brazing, mechanical joining using a screw mechanism, or adhesive. Alternatively, the support member 50 may be fixed to the vertical wall 14 by friction joining, for example.

[0049] In this embodiment, the support member 50 is positioned within the space formed by the inner member 10 and the outer member 20, separated from the top plate 11 of the inner member 10. That is, the support member 50 is not joined to the top plate 11. The support member 50 is also positioned within the space formed by the inner member 10 and the outer member 20, separated from the top plate 21 of the outer member 20. In the example of Figure 3, in the cross-section of the structural member 100, the support member 50 is positioned on the top plate 11 side of the inner member 10 relative to the open end faces of the vertical walls 13 and 14. In other words, the entire support member 50 is housed within the inner member 10.

[0050] [Method for manufacturing structural members] Next, the manufacturing method for the structural member 100 will be described with reference to Figures 4A to 4D. The manufacturing method for the structural member 100 according to this embodiment comprises a preparation step and a welding step.

[0051] (preparation process) As shown in Figure 4A, the preparation step involves preparing the inner member 10, the outer member 20, and the support member 50. Figure 4A, and Figures 4B to 4D described later, show the cross-sections of each member at the location of the curved region 15, that is, the cross-sections of each member corresponding to the cross-section of the structural member 100 shown in Figure 3.

[0052] Referring to Figure 4A, the inner member 10 and the outer member 20 can be formed, for example, by press working of metal plates. Referring to Figure 4B, the support member 50 is positioned inside the inner member 10. The support member 50 is provided in the curved region 15 of the inner member 10. Part of the support member 50 is fixed from inside the inner member 10 to the curved region 15 of the vertical wall 13, for example, by the method described above. The other part of the support member 50 is fixed from inside the inner member 10 to at least one of the top plate 11 and the vertical wall 14, for example, by the method described above. The support member 50 only needs to be kept from moving within the inner member 10 and does not necessarily need to be joined to the inner member 10. For example, the support member 50 can be brought into relatively strong contact with the inner surface of the inner member 10 and fixed to the inner member 10 by the static friction force of the contact surface.

[0053] The support member 50 is made of, for example, metal. The support member 50 may be made of steel, or it may be made of a non-ferrous metal such as aluminum alloy or copper. The support member 50 may be made of the same type of metal material as the inner member 10 and the outer member 20, or it may be made of a different type of metal material than the inner member 10 and the outer member 20.

[0054] Referring to Figure 4C, the support member 50 may be made of plastic. Examples of plastics include high-strength plastics such as polyvinyl chloride (PVC), polystyrene (PS), ABS resin, polyethylene terephthalate (PET), polycarbonate, and fiber-reinforced plastic (FRP). However, the heat resistance temperature of plastic is lower than that of metal. Therefore, if the support member 50 is made of plastic, a heat insulating material 60 may be interposed between the support member 50 and the inner member 10 to ensure heat resistance during the welding process.

[0055] (Welding process) Referring to Figure 4D, in the welding process, the vertical wall 13 of the inner member 10 and the vertical wall 23 of the outer member 20 are joined by welding. The vertical walls 13 and 23 are joined, for example, by arc welding. The vertical walls 13 and 23 may also be joined by other welding methods such as laser-arc hybrid welding.

[0056] In the welding process, a portion of the support member 50 is fixed to the vertical wall 13 from inside the inner member 10 in the curved region 15, and the other portion of the support member 50 is fixed to at least one of the top plate 11 and the vertical wall 14 from inside the inner member 10. With this in place, the vertical wall 23 of the outer member 20 is superimposed on the vertical wall 13 from the outside of the inner member 10, and the vertical walls 13 and 23 are welded along the end of the vertical wall 23.

[0057] Although not shown in the diagram, the vertical walls 12 and 14 of the inner member 10 are also joined to the vertical walls 22 and 24 of the outer member 20, respectively. The vertical walls 12 and 14 are typically joined to the vertical walls 22 and 24 by welding. For example, the vertical walls 12 and 14 are joined to the vertical walls 22 and 24 by arc welding. The vertical walls 12 and 14 may also be joined to the vertical walls 22 and 24 by another welding method such as laser-arc hybrid welding. The joining of the vertical walls 12 and 14 of the inner member 10 to the vertical walls 22 and 24 of the outer member 20 may be performed after welding the vertical walls 13 and 23, or before welding the vertical walls 13 and 23.

[0058] This is how the structural member 100 is manufactured. However, the method for manufacturing the structural member 100 according to this embodiment may include one or more other steps in addition to the preparation and welding steps described above, as needed.

[0059] After the vertical wall 13 of the inner member 10 and the vertical wall 23 of the outer member 20 are welded together, the support member 50 may be removed from the inner member 10. For example, if the support member 50 is not firmly fixed to the vertical walls 13 and 14 and can be removed from the vertical walls 13 and 14 relatively easily, the support member 50 may be removed from the structural member 100 through a work hole or the like. However, as shown in Figure 3, the support member 50 may remain inside the inner member 10 even after the structural member 100 is completed. If the support member 50 is attached to the inner member 10 via an insulating material 60 (Figure 4C), the insulating material 60 may be removed from the inner member 10 together with the support member 50, or it may remain inside the inner member 10 together with the support member 50.

[0060] [effect] When the vertical wall 13 of the inner member 10 is overlapped with the vertical wall 23 of the outer member 20 and welded by arc welding or the like, the end (free end) and the surrounding portion of the vertical wall 13 are prone to thermal expansion in the tangential direction of the weld line in the concave curved region 15. When such thermal expansion occurs in the curved region 15, the portion of the vertical wall 13 adjacent to the weld 32 is displaced inward in the width direction of the inner member 10 from the pre-welding state shown by the dashed line in Figure 5A. As a result, the vertical wall 13 tilts inward in the width direction of the inner member 10, causing out-of-plane deformation of the vertical wall 13. The vertical wall 13 of the inner member 10 is welded to the vertical wall 23 of the outer member 20 in this out-of-plane deformed state.

[0061] After welding, the inner member 10 and the outer member 20 are cooled. At this time, as shown in Figure 5B, the portion of the vertical wall 13 adjacent to the weld 32 shrinks due to cooling and is displaced outward in the width direction of the inner member 10. That is, the vertical wall 13 tries to return to its original state, and out-of-plane deformation of the vertical wall 13 occurs. As a result, as shown by the thin arrow in Figure 5B, the weld 32 is pulled in the height direction of the vertical wall 13, and tensile residual stress is generated in the weld 32.

[0062] In this embodiment, when the vertical wall 13 of the inner member 10 is welded to the vertical wall 23 of the outer member 20, the vertical wall 13 is supported from within the inner member 10 by the support member 50 in the curved region 15. More specifically, a part of the support member 50 is fixed to the vertical wall 13 from within the inner member 10 in the curved region 15, and the other part of the support member 50 is fixed to at least one of the top plate 11 and the vertical wall 14 from within the inner member 10, and the welding of the vertical walls 13 and 23 is performed. As a result, when the vertical wall 13 attempts to tilt inward in the width direction in the curved region 15 due to thermal expansion during welding heating, the tilting of the vertical wall 13 is restricted by the support member 50. Therefore, the amount of out-of-plane deformation of the vertical wall 13 during the welding heating process can be reduced in the curved region 15. As a result, the amount of out-of-plane deformation (recovery amount) of the vertical wall 13 during subsequent cooling is also reduced, and the tensile residual stress of the welded part 32 can be reduced.

[0063] In this embodiment, the support member 50 is fixed to at least the portion of the vertical wall 13 corresponding to the welded portion 32. This allows the support member 50 to more effectively suppress out-of-plane deformation of the vertical wall 13 during the welding heating process in the curved region 15. As a result, the tensile residual stress in the welded portion 32 is more easily reduced.

[0064] However, the support member 50 does not have to be fixed to at least the portion of the vertical wall 13 corresponding to the welded portion 32. For example, the support member 50 may be positioned offset in the height direction of the vertical wall 13 from the weld metal 321 of the welded portion 32. However, it is preferable that the support member 50 be positioned away from the top plate 11. For example, when H is the height dimension from the inner surface of the top plate 11 to the open end surface of the vertical wall 13, it is preferable that the support member 50 is fixed to the vertical wall 13 at a position at least H / 3 away from the inner surface of the top plate 11 in the height direction of the vertical wall 13.

[0065] In this embodiment, the support member 50 is formed in the shape of a rod. In this case, the proportion of the volume of the support member 50 to the volume of the structural member 100 is very small. Therefore, the tensile residual stress of the welded joint 32 can be reduced without significantly increasing the weight of the structural member 100.

[0066] In this embodiment, when viewed in cross-section of the structural member 100, one support member 50 is provided within the inner member 10. However, when viewed in cross-section of the structural member 100, multiple support members 50 may be provided within the inner member 10.

[0067] In this embodiment, the support member 50 is fixed to the vertical walls 13 and 14 of the inner member 10. For example, if the vertical wall 14 includes a curved region 16, the support member 50 may be fixed to the vertical wall 13 from inside the inner member 10 in the curved region 15, and also fixed to the vertical wall 14 from inside the inner member 10 in the curved region 16. This allows the support member 50 to restrict the tilting of the vertical wall 14 in the curved region 16, which is separate from the curved region 15, when the vertical wall 14 attempts to tilt inward in the width direction due to thermal expansion during welding heating. Therefore, the amount of out-of-plane deformation of the vertical wall 14 during the welding heating process can be reduced in the curved region 16. Consequently, the amount of out-of-plane deformation (recovery amount) of the vertical wall 14 during cooling is reduced not only in the curved region 15 but also in the curved region 16, and the tensile residual stress of the welded portion 33 can be reduced.

[0068] <Second Embodiment> Figure 6 is a cross-sectional view of the structural member 100A according to this embodiment. In Figure 6, as in Figure 3, a cross-section of the structural member 100A at the location of the curved region 15 is shown. The structural member 100A according to this embodiment differs from the structural member 100 according to the first embodiment in the shape of the support member 50A.

[0069] In the first embodiment, the support member 50 is formed in the shape of a rod. In contrast, in this embodiment, the support member 50A is formed in the shape of a plate. Referring to Figure 6, one end of the support member 50A is fixed to the curved region 15 of the vertical wall 13 in the width direction of the inner member 10. The other end of the support member 50A is fixed to the vertical wall 14 in the width direction of the inner member 10. The support member 50A is fixed to the vertical walls 13 and 14 from inside the inner member 10 by the method illustrated in the first embodiment.

[0070] In the example shown in Figure 6, the support member 50A is also fixed to the top plate 11 from within the inner member 10. The support member 50A is positioned within the inner member 10 with its end faces substantially in contact with the top plate 11 and the vertical walls 13 and 14. However, the support member 50A does not have to be fixed to the top plate 11. As shown in Figure 7, the support member 50A may be positioned within the space formed by the inner member 10 and the outer member 20, separated from the top plate 11 of the inner member 10. In this case, a gap exists between the support member 50A and the top plate 11 in a cross-sectional view of the structural member 100.

[0071] In the examples shown in Figures 6 and 7, the support member 50A is positioned within the space formed by the inner member 10 and the outer member 20, separated from the top plate 21 of the outer member 20. In the cross-section of the structural member 100, the support member 50A is positioned on the top plate 11 side of the inner member 10 with respect to the open end faces of the vertical walls 13 and 14. However, in the cross-section of the structural member 100, the support member 50A may protrude from the open end faces of the vertical walls 13 and 14 towards the top plate 21 side of the outer member 20.

[0072] In this embodiment as well, it is preferable that the support member 50A is fixed to at least the portion of the vertical wall 13 corresponding to the welded portion 32. That is, when viewing the structural member 100A along the width direction, it is preferable that the portion of the plate-shaped support member 50A that overlaps with the weld metal 321 of the welded portion 32 is fixed to the vertical wall 13.

[0073] The structural member 100A according to this embodiment can be manufactured using the same manufacturing method as the structural member 100 according to the first embodiment.

[0074] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0075] In the above embodiment, a single support member 50 or 50A is provided in the concave curved region 15 of the vertical wall 13 of the inner member 10. However, multiple support members 50 or multiple support members 50A may be provided in the curved region 15. Also, different types of support members 50, 50A may be mixed and provided in the curved region 15. In the example of Figure 8, similar to the first embodiment, one support member 50 or 50A is attached to the curved region 15 of the vertical wall 13 of the inner member 10 and to the vertical wall 14 located on the opposite side of the vertical wall 13 from the top plate 11. In addition, another support member 50 or 50A is attached to the curved region 15 of the vertical wall 13 of the inner member 10 and to the vertical wall 12 located on the opposite side of the vertical wall 13 from the top plate 11.

[0076] In the above embodiment, a portion of the support member 50 or 50A is fixed to the vertical wall 13 of the inner member 10 in the curved region 15, while the other portion of the support member 50 or 50A is fixed to the other vertical wall 14 of the inner member 10. However, the other portion of the support member 50 or 50A may be fixed only to the top plate 11 of the inner member 10.

[0077] In the first embodiment, when the support member 50 is rod-shaped, for example, by bending the support member 50, one end of the support member 50 in the longitudinal direction can be fixed to the vertical wall 13, while the other end of the support member 50 in the longitudinal direction can be fixed to the top plate 11. In the second embodiment, when the support member 50A is plate-shaped, the shape of the support member 50A can be adjusted so that a part of the support member 50A is fixed to the vertical wall 13, while the other part of the support member 50A is fixed only to the top plate 11. However, from the viewpoint of ease of manufacturing the structural member 100A, it is preferable that the area to which the support member 50A is fixed to the inner member 10 is small. Therefore, it is preferable that the other part of the support member 50A is fixed to only one of the top plate 11 and the vertical wall 14. Furthermore, in the case of a plate-shaped support member 50A, if the plate-shaped support member 50A is fixed to the vertical walls 13 and 14 but not to the top plate 11, it is preferable because it eliminates the need to match the shape of the support member 50A to the shape of the top plate 11, making the manufacturing of the structural member 100 easier. [Examples]

[0078] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0079] [First Embodiment] To confirm the effects of this disclosure, arc welding analysis of the vertical walls 13 and 23 of the inner member 10 and outer member 20 having the same shape as the above embodiment was performed using general-purpose finite element analysis software (ABAQUS, manufactured by Dassault Systèmes). In Comparative Example 1, arc welding analysis was performed between the vertical wall 13 of the inner member 10 and the vertical wall 23 of the outer member 20 without providing support members 50 and 50A. In Examples 1 to 4, at least one support member 50 or 50A was installed in the curved region 15 of the vertical wall 13 at a location where high tensile residual stress occurred in the welded portion 32 in Comparative Example 1, and the same arc welding analysis as in Comparative Example 1 was performed. In each of Examples 1 to 4 and Comparative Example 1, the plate thickness of the inner member 10 and outer member 20 was 2.6 mm, and the material properties of the inner member 10 and outer member 20 were 980 MPa class steel, respectively.

[0080] For Examples 1 to 4, the installation point of the support member 50 was used as the evaluation point, and the residual stress of the welded joint 32 and the out-of-plane deformation of the vertical wall 13 of the inner member 10 at this evaluation point were evaluated as a reduction rate compared to Comparative Example 1. The reduction rates for residual stress and out-of-plane deformation are expressed as percentages of the reduction in residual stress and out-of-plane deformation from Comparative Example 1, with the tensile residual stress and out-of-plane deformation of Comparative Example 1 set to 100%. The residual stress here is the residual stress at a position approximately 2 mm from the toe of the welded joint 32 toward the top plate 11 of the inner member 10, and is the residual stress component in a direction perpendicular to the extending direction of the welded joint 32 and along the outer surface of the vertical wall 13 of the inner member 10. The out-of-plane deformation (during heating) is the out-of-plane deformation (tilt) of the vertical wall 13 at the evaluation point position during the welding heating process from before welding to welding heating, and the out-of-plane deformation (during cooling) is the out-of-plane deformation (return) of the vertical wall 13 at the evaluation point position during the cooling process from welding heating to cooling. The out-of-plane deformation was defined as the amount of movement in the width direction (maximum movement) of the toe of the weld 32.

[0081] Table 1 shows the analysis conditions and evaluation results for Examples 1-4 and Comparative Example 1.

[0082] [Table 1]

[0083] Referring to Table 1, Example 1 is similar to the second embodiment (Figure 6) above in that a plate-shaped support member 50A is installed in the curved region 15 of the vertical wall 13. In Example 1, it was assumed that the end face of the support member 50A is in full contact and bond with the top plate 11 and vertical walls 13 and 14 of the inner member 10, except for the top plate 21 side of the outer member 20, and the analysis was carried out assuming that 20% of the heat that reaches the contact surface of the support member 50A with respect to the inner member 10 is transferred to the support member 50A. In Example 1, the plate thickness of the support member 50A was set to 2.0 mm, and the material properties of the support member 50A were assumed to be 980 MPa class steel, similar to the inner member 10 and the outer member 20.

[0084] Examples 2 and 3, like the first embodiment described above, involve installing a rod-shaped support member 50 in the curved region 15 of the vertical wall 13. In Example 2, the support member 50 is stretched from the curved region 15 of the vertical wall 13 to the vertical wall 14, and the end face of the support member 50 is brought into contact with and connected to the vertical walls 13 and 14. In Example 3, two rod-shaped support members 50 are installed in the curved region 15 of the vertical wall 13. In Example 3, one support member 50 is stretched from the curved region 15 of the vertical wall 13 to the vertical wall 14, and the end face of this support member 50 is brought into contact with and connected to the vertical walls 13 and 14. In Example 3, the other support member 50 is stretched from the curved region 15 of the vertical wall 13 to the vertical wall 12, and the end face of this support member 50 is brought into contact with and connected to the vertical walls 13 and 12. In Examples 2 and 3, the analysis was performed assuming that 14% of the heat that reached the contact surface of the support member 50 with respect to the inner member 10 was transferred to the support member 50. In Examples 2 and 3, each support member 50 was a cylindrical (round bar) with a diameter of 4.0 mm, and the material properties of the support member 50 were assumed to be 980 MPa class steel, similar to the inner member 10 and the outer member 20.

[0085] Example 4 involves installing a support member 50 with the same shape as in Example 2 in the same position as in Example 2. However, in Example 4, the material properties of the support member 50 were set to polyvinyl chloride (PVC). Since the heat resistance temperature of polyvinyl chloride is lower than that of steel, in Example 4, the presence of an insulating material between the support member 50 and the inner member 10 was simulated, and the analysis was performed assuming that the contact surface between the support member 50 and the inner member 10 was an insulating surface.

[0086] As shown in Table 1, in all of Examples 1 to 4, the out-of-plane deformation of the vertical wall 13 measured during heating at the installation point (evaluation point) of the support member 50 or 50A was reduced compared to Comparative Example 1. As a result, in all of Examples 1 to 4, the out-of-plane deformation of the vertical wall 13 during cooling was also reduced compared to Comparative Example 1. Therefore, in Examples 1 to 4, the residual stress of the welded joint 32 was reduced compared to the tensile residual stress of Comparative Example 1.

[0087] In this analysis, the residual stress reduction effect was greater in Examples 1 to 3, which assumed a steel support member 50 or 50A, than in Example 4, which assumed a polyvinyl chloride support member 50. In Example 1, when a plate-shaped support member 50A was installed in the curved region 15 of the vertical wall 13, the out-of-plane deformation of the vertical wall 13 during cooling at the installation point (evaluation point) of the support member 50A was reduced by 49% compared to Comparative Example 1. In Example 1, the residual stress in the welded joint 32 at the installation point of the support member 50A became compressive residual stress, which was reduced by 140% compared to the tensile residual stress in Comparative Example 1.

[0088] In Example 2, when one rod-shaped support member 50 was installed in the curved region 15 of the vertical wall 13, the amount of out-of-plane deformation of the vertical wall 13 during cooling at the installation point (evaluation point) of the support member 50 was reduced by 31% compared to Comparative Example 1. As a result, in Example 2, the residual stress of the welded joint 32 at the installation point of the support member 50 was reduced by 95% compared to the tensile residual stress in Comparative Example 1.

[0089] In Example 3, when two rod-shaped support members 50 were installed in the curved region 15 of the vertical wall 13, the out-of-plane deformation and residual stress of the vertical wall 13 during cooling at each installation point (evaluation point) of the support members 50 were reduced compared to Comparative Example 1. For the support member 50 installed in the same position as in Example 2, the out-of-plane deformation of the vertical wall 13 during cooling at that installation point was reduced by 29% compared to Comparative Example 1, and the residual stress of the welded joint 32 was reduced by 92% compared to Comparative Example 1. On the other hand, for the other support member 50 installed in a different position than in Example 2, the out-of-plane deformation of the vertical wall 13 during cooling at that installation point was reduced by 33% compared to Comparative Example 1, and the residual stress of the welded joint 32 was reduced by 69% compared to the tensile residual stress of Comparative Example 1.

[0090] [Second Example] A structural member 100 having the same configuration as the first embodiment described above was subjected to a stiffness analysis using the same general-purpose finite element analysis software as in the first embodiment (Example 5). For comparison, a structural member 100 with the support member 50 removed from Example 5 was subjected to the same stiffness analysis (Comparative Example 2). The material properties and dimensions of each member in Example 5, as well as the position of the support member 50, are the same as those of Example 2 described above. The material properties and dimensions of each member in Comparative Example 2 are the same as those of Comparative Example 1 described above.

[0091] In this analysis, the longitudinal direction of the vehicle into which the structural member 100, which is a lower arm, is incorporated is defined as the X direction, the lateral direction as the Y direction, and the vertical direction as the Z direction. Loads in the X direction and Y direction were applied to the mounting portion 41 on the wheel side, respectively. More specifically, a reference point was set on the mounting portion 41 of the structural member 100, and the ball joint was kinematically coupled and constrained at this reference point. The reference point was then fixed in the Z direction, and a load directed backward (load in the X direction) was applied relative to the reference point. Additionally, the reference point was fixed in the Z direction, and a load directed outward in the lateral direction (load in the Y direction) was applied relative to the reference point. The mounting portion 42 on the front side of the vehicle body was fixed in the XYZ directions, and the mounting portion 43 on the rear side of the vehicle body was fixed in the YZ direction.

[0092] The results of the stiffness analysis are shown in Table 2.

[0093] [Table 2]

[0094] Table 2 shows the increase in stiffness in the X and Y directions of Example 5 compared to Comparative Example 2. As shown in Table 2, the stiffness in the X and Y directions of Example 5 were almost the same as those of Comparative Example 2. The stiffness in the X direction of Example 5 increased by only 0.121% compared to Comparative Example 2. The stiffness in the Y direction of Example 5 increased by only 0.015% compared to Comparative Example 2.

[0095] Structural members for vehicles may include bulkheads, for example. Bulkheads are typically installed within structural members to improve rigidity. For example, bulkheads are installed within structural members to suppress or control deformation during collisions by improving rigidity, or to improve the ride comfort of the vehicle. On the other hand, in this disclosure, the support member 50 is placed within the structural member 100 to reduce the tensile residual stress of the welded joint 32, and thus has a different purpose than a typical bulkhead.

[0096] This rigidity analysis and the aforementioned arc welding analysis confirmed that the support member 50 can reduce the out-of-plane deformation of the vertical wall 13 and the tensile residual stress of the welded joint 32 without substantially changing the performance (rigidity) of the structural member 100 during use. [Explanation of Symbols]

[0097] 100, 100A: Structural members 10: Inner component 11: Top plate (first top plate) 13: Vertical wall (First vertical wall) 12,14: Vertical wall (Second vertical wall) 15,16: Curved region 20:Outer member 21: Top plate (second top plate) 23: Vertical wall (Third vertical wall) 22,24: Vertical wall (4th vertical wall) 31, 32, 33: Welded section 50, 50A: Support member

Claims

1. A structural member, An inner member comprising a first top plate, a first vertical wall continuous with the first top plate and including a curved region that curves concavely inward towards the structural member when viewed from the first top plate side, and a second vertical wall continuous with the first top plate on the opposite side of the first vertical wall, An outer member including a second top plate facing the first top plate, a third vertical wall continuous with the second top plate, overlapping the first vertical wall from the outside of the inner member and joined to the first vertical wall by welding, and a fourth vertical wall on the opposite side of the third vertical wall that is continuous with the second top plate and joined to the second vertical wall, A welded portion extending along the end of the third vertical wall, A support member is fixed to the first vertical wall from within the inner member in the curved region, and is also fixed to at least one of the first top plate and the second vertical wall from within the inner member, A structural member equipped with the following features.

2. A structural member according to claim 1, The support member is a structural member that is fixed to at least the portion of the first vertical wall corresponding to the welded portion.

3. A structural member according to claim 1, The support member is a structural member that is fixed to the first vertical wall from within the inner member in the curved region, and also fixed to the second vertical wall from within the inner member.

4. A structural member according to claim 3, The support member is a structural member that is positioned at a distance from the first top plate within the space formed by the inner member and the outer member.

5. A structural member according to claim 1, The support member is a structural member that is positioned at a distance from the second top plate within the space formed by the inner member and the outer member.

6. A method for manufacturing structural members, The process of preparing a first top plate, an inner member including a first vertical wall continuous with the first top plate and including a curved region having a concave shape on the inside when viewed from the first top plate side, and a second vertical wall continuous with the first top plate on the opposite side of the first vertical wall, an outer member including a second top plate, a third vertical wall continuous with the second top plate, and a fourth vertical wall continuous with the second top plate on the opposite side of the third vertical wall, and a support member, The process involves fixing a portion of the support member to the first vertical wall from within the inner member in the curved region, and fixing the other portion of the support member to at least one of the first top plate and the second vertical wall from within the inner member, then overlapping the third vertical wall with the first vertical wall from the outside of the inner member, and welding the first vertical wall and the third vertical wall along the end of the third vertical wall. A manufacturing method that includes the following features.

Images