METAL MEMBER MANUFACTURING METHOD AND METAL MEMBER

Abstract

To improve fatigue strength of a weld zone in a metal member including a first component and a second component joined by welding.SOLUTION: A manufacturing method of a metal member (100) includes the steps of: preparing a first component (41) and a second component (42); and welding vertical walls (415, 425) of the components (41, 42). Slits (417, 427) extending from edge portions (415a, 425a) of the vertical walls (415, 425) to top plates (411, 421) sides are provided at least in one of the first component (41) and the second component (42). The slits (417, 427) are arranged in recessed curved regions (416, 426). In the welding step, the vertical walls (415, 425) are welded along the edge portion (415a) of the vertical wall (415) of the first component (41) or the edge portion (425a) of the vertical wall (425) of the second component (42) in a state that the slits (417, 427) are arranged in an overlapping part of the vertical walls (415, 425).SELECTED DRAWING: Figure 4E

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a metal member, and a metal member. [Background technology]

[0002] For example, metal members are widely used as structural members that constitute the body of an automobile. Some metal members include two parts joined together. For example, Patent Document 1 discloses a structure in which an upper part and a lower part, each having an opening on one side of a cross section, are joined together.

[0003] In the joining structure of Patent Document 1, each of the upper and lower components includes a top plate and vertical walls continuous with both side edges of the top plate. A step is formed in the vertical wall of the lower component. A portion of the vertical wall of the lower component that is further toward the tip end than the step is fitted into an opening in the upper component. The step of the lower component is line-joined (lap fillet welded) to the tip end of the vertical wall of the upper component by arc welding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-147593 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 exemplifies an automobile lower arm as a component having the above-described joining structure. The lower arm includes a concavely curved region that has a concavely curved shape on the inside of the component in a plan view. Fatigue cracks are likely to occur in the concavely curved region at the welded joint. For example, when the components to be welded are made of high-strength metal, such as ultra-high tensile steel of 980 MPa class or higher, fatigue cracks are particularly likely to occur in the concavely curved region at the welded joint.

[0006] An object of the present disclosure is to improve the fatigue strength of a welded portion in a metal member including a first component and a second component joined by welding. [Means for solving the problem]

[0007] A method for manufacturing a metal member according to the present disclosure includes the steps of preparing a first component and a second component made of metal, each component including a top plate, a ridge portion continuous with the top plate, and a vertical wall connected to the top plate via the ridge portion, and welding the vertical wall of the first component to the vertical wall of the second component. At least one of the first component and the second component has a slit extending from an edge of the vertical wall toward the top plate. The slit is located in a concavely curved region. The concavely curved region is a region of the first component or the second component that is concavely curved inward when viewed from the top plate. In the welding step, the top plate of the first component and the top plate of the second component are opposed to each other, and the vertical wall of the second component is overlapped from the inside onto the vertical wall of the first component. With the slit located at the overlapping portion of the vertical walls, the vertical walls are welded along the edge of the vertical wall of the first component or the edge of the vertical wall of the second component. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to improve the fatigue strength of the welded portion in a metal member including a first component and a second component joined by welding. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a metal member according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the metal member shown in FIG. [Figure 3] 3 is a view of a first component and a second component included in the metal member as viewed from the inside in the concavely curved region of the metal member shown in FIG. [Figure 4A] FIG. 4A is a schematic view illustrating a method for manufacturing a metal member according to an embodiment. [Figure 4B] FIG. 4B is a schematic view for explaining the method for manufacturing the metal member according to the embodiment. [Figure 4C] FIG. 4C is a schematic view for explaining the method for manufacturing the metal member according to the embodiment. [Figure 4D] FIG. 4D is a schematic view illustrating the method for manufacturing the metal member according to the embodiment. [Figure 4E] FIG. 4E is a schematic view illustrating the method for manufacturing the metal member according to the embodiment. [Figure 4F] FIG. 4F is a schematic view for explaining the method for manufacturing the metal member according to the embodiment. [Figure 5A] FIG. 5A is a schematic diagram for explaining the mechanism by which high tensile residual stress occurs in a welded portion of a typical metal member. [Figure 5B] FIG. 5B is a schematic diagram for explaining the mechanism by which high tensile residual stress occurs in a welded portion of a typical metal member. [Figure 6] FIG. 6 is a perspective view showing a concavely curved region of a metal member according to a modified example of the above embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A manufacturing method for a metal component according to an embodiment includes the steps of preparing a first component and a second component made of metal, each of which includes a top plate, a ridge portion continuous with the top plate, and a vertical wall connected to the top plate via the ridge portion, and welding the vertical wall of the first component to the vertical wall of the second component. At least one of the first component and the second component has a slit extending from an edge of the vertical wall toward the top plate. The slit is located in a concavely curved region. The concavely curved region is a region of the first component or the second component that is concavely curved inward when viewed from the top plate. In the welding step, the top plate of the first component and the top plate of the second component are opposed to each other, and the vertical wall of the second component is overlapped from the inside onto the vertical wall of the first component. With the slit located at the overlapping portion of the vertical walls, the vertical walls are welded together along the edge of the vertical wall of the first component or the edge of the vertical wall of the second component (first configuration).

[0011] According to the modified Goodman diagram, the higher the tensile residual stress, the lower the fatigue strength of the material. In the concavely curved region of a metal component, the tensile residual stress in the weld tends to be higher than in other regions. The mechanism by which high tensile residual stress occurs in the weld in the concavely curved region of a metal component is explained below.

[0012] Generally, when the vertical walls of a first part and the vertical walls of a second part are overlapped and welded, the portions of the vertical walls near the weld line thermally expand in the tangential direction of the weld line. For example, in regions of the first and second parts that are linear in plan view, the tangential direction of the weld line coincides with the direction along each vertical wall (in-plane direction), so the portions of the vertical walls near the weld line essentially expand in the in-plane direction. In contrast, in concavely curved regions, the vertical walls of the first and second parts are concavely curved inward in plan view, so the tangential direction of the weld line intersects with the vertical walls of each part (out-of-plane direction). Therefore, the portions of the overlapping vertical walls of the first and second parts near the weld line expand in the out-of-plane direction of the vertical walls. On the other hand, the portions of the vertical walls away from the weld line experience less thermal expansion than the portions near the weld line and are constrained by the top plate. Therefore, when the portions near the weld line expand in the out-of-plane direction of the vertical walls and displace inward, the vertical walls tilt inward. Therefore, the overlapping vertical walls are welded together in a state in which the vertical walls are tilted toward the inside of the component (in an out-of-plane deformed state).

[0013] After welding, the first and second parts are naturally cooled, for example, to room temperature. The welded portions of the vertical walls of the first and second parts shrink due to the cooling. As a result, the vertical walls, which had been deformed out of plane, attempt to return to their original state, and the vertical walls pull the weld in the height direction of the metal member, generating tensile residual stress in the weld. This tensile residual stress reduces the fatigue strength of the weld in the concavely curved region of the metal member.

[0014] In contrast, in the manufacturing method according to the first configuration, a slit is provided in the vertical wall of the concavely curved region of at least one of the first and second components. When the vertical wall of the first component and the vertical wall of the second component are overlapped and welded, the slit is disposed at the overlapping portion of the vertical walls. This suppresses out-of-plane deformation of the vertical wall during welding. More specifically, because the vertical wall of at least one of the first and second components is divided by the slit, thermal expansion of the vertical wall on one side of the slit is less likely to affect thermal expansion of the vertical wall on the other side. Therefore, thermal expansion of the vertical wall that deviates from the tangent direction of the weld line is reduced throughout the concavely curved region, and out-of-plane deformation of the vertical wall due to this thermal expansion is less likely to occur. Therefore, the return amount of each vertical wall during the cooling process of the metal members after welding is also reduced. As a result, tensile residual stress in the weld is reduced, improving the fatigue strength of the weld.

[0015] The slits are preferably arranged in a range including a portion where stress concentration is expected to occur when a load is input to the metal member during use (second configuration).

[0016] According to the second configuration, the slit is arranged in a location where stress concentration is expected to occur when a load is applied to the metal member, or in the vicinity thereof. For example, if the metal member is a structural member that constitutes the body of an automobile, the slit is provided in a location where stress concentration is expected to occur when a load is applied to the metal member from the road surface on which the automobile travels after the metal member is assembled to the body, or in the vicinity thereof. This reduces the tensile residual stress, particularly in the weld, in the location where stress concentration is expected to occur, thereby efficiently improving the fatigue strength of the weld.

[0017] The slit may be provided in the second component (third configuration).

[0018] Of the vertical walls of the first and second components that are stacked together, out-of-plane deformation of the inner vertical wall is likely to increase tensile residual stress in the weld. Therefore, in the third configuration, a slit is provided in the vertical wall of the second component that is positioned inner than the vertical wall of the first component. This makes it easier to suppress out-of-plane deformation of the vertical wall of the second component during the welding process. Therefore, tensile residual stress in the weld is more likely to be reduced.

[0019] The depth of the slit may be greater than the length of the overlapping portion between the vertical walls in the depth direction of the slit (fourth configuration).

[0020] In at least one of the first and second components, a plurality of slits may be provided in the concavely curved region, the plurality of slits being aligned along the edge of the vertical wall (fifth configuration).

[0021] A metal member according to an embodiment includes a first metal part, a second metal part, and a weld. The first part includes a first top plate, a first ridge portion, and a first vertical wall. The first ridge portion is continuous with the first top plate. The first vertical wall is connected to the first top plate via the first ridge portion. The second part includes a second top plate, a second ridge portion, and a second vertical wall. The second top plate faces the first top plate. The second ridge portion is continuous with the second top plate. The second vertical wall is connected to the second top plate via the second ridge portion. The second vertical wall is overlapped with the first vertical wall from the inside. The weld portion welds the first vertical wall and the second vertical wall. The metal member includes a concavely curved region. The concavely curved region is curved concavely toward the inside of the metal member in a plan view of the metal member. In the concavely curved region, a slit is provided in at least one of the first vertical wall and the second vertical wall. The slit is disposed in the overlapping portion of the first vertical wall and the second vertical wall (sixth configuration).

[0022] 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.

[0023] [Metal component composition] FIG. 1 is a perspective view of a metal member 100 according to this embodiment. The metal member 100 is used, for example, as a structural member that constitutes the body of an automobile. The metal member 100 may be, for example, a suspension member, a suspension arm, or a frame of an automobile. In this embodiment, an example will be described in which the metal member 100 is a lower arm, which is a type of suspension arm.

[0024] In the example shown in FIG. 1 , the metal member 100 is curved overall in a plan view. The metal member 100 includes arms 11 and 12. The arms 11 and 12 extend in different directions in a plan view of the metal member 100. When the metal member 100, which is a lower arm, is attached to a vehicle, one arm 11 extends generally in the vehicle width direction (left-right direction), and the other arm 12 extends generally in the vehicle length direction (front-rear direction). The tip of the arm 11 is attached to a wheel of the vehicle via, for example, a ball joint and a steering knuckle (not shown). The tip of the arm 12 is attached to the body of the vehicle via a bushing (not shown). The boundary between the arms 11 and 12 is also attached to the body of the vehicle via a bushing (not shown). A tubular portion 20 for inserting a bushing is fixed to the boundary between the arms 11 and 12.

[0025] 1, the metal member 100 includes a concavely curved region 30. The concavely curved region 30 is a region of the metal member 100 that is concavely curved toward the inside of the member in a plan view. The concavely curved region 30 is located, for example, in the arm 11 near the tubular portion 20 at the boundary between the arms 11 and 12.

[0026] 2 is a cross-sectional view (II-II cross-sectional view) of the metal member 100. As shown in FIG.

[0027] The first component 41 includes a top plate 411, ridge portions 412 and 413, and vertical walls 414 and 415. The ridge portions 412 and 413 are continuous with both side edges of the top plate 411 in a cross-sectional view of the metal member 100. The ridge portions 412 and 413 have a substantially arc shape in a cross-sectional view of the metal member 100. The vertical walls 414 and 415 are arranged to face each other with the top plate 411 in between. One vertical wall 414 is connected to the top plate 411 via the ridge portion 412. The other vertical wall 415 is connected to the top plate 411 via the ridge portion 413.

[0028] The second component 42 and the first component 41 form a closed cross section. When the metal member 100 is attached to the automobile, the second component 42 may be located below or above the first component 41. The second component 42 includes a top plate 421, ridge portions 422 and 423, and vertical walls 424 and 425. The top plate 421 faces the top plate 411 of the first component 41. The ridge portions 422 and 423 have a substantially arc shape in a cross-sectional view of the metal member 100. The vertical walls 424 and 425 are disposed to face each other with the top plate 421 sandwiched between them. One vertical wall 424 is connected to the top plate 421 via the ridge portion 422. The other vertical wall 425 is connected to the top plate 421 via the ridge portion 423. In a cross-sectional view of the metal member 100, the vertical walls 424 and 425 extend from the ridge portions 422 and 423 toward the top plate 411 of the first component 41.

[0029] The vertical walls 424, 425 of the second component 42 are disposed inside the vertical walls 414, 415 of the first component 41. One vertical wall 424 of the second component 42 is overlapped with one vertical wall 414 of the first component 41 from the inside. The other vertical wall 425 of the second component 42 is overlapped with the other vertical wall 415 of the first component 41 from the inside. More specifically, portions of the vertical walls 424, 425 of the second component 42 are overlapped with portions of the vertical walls 414, 415 of the first component 41. Therefore, the edge portions 424a, 425a of the vertical walls 424, 425 of the second component 42 are located closer to the top panel 411 of the first component 41 than the edge portions 414a, 415a of the vertical walls 414, 415 of the first component 41.

[0030] The welds 51 and 52 are portions where the vertical walls 414 and 415 of the first component 41 are welded to the vertical walls 424 and 425 of the second component 42. The weld 51 is provided linearly along an edge 414a of one vertical wall 414 of the first component 41. The weld 52 is provided linearly along an edge 415a of the other vertical wall 415 of the first component 41.

[0031] FIG. 3 is a view of the first component 41 and the second component 42 seen from the inside of the metal member 100 in the concavely curved region 30 shown in FIG.

[0032] 3, the concavely curved region 30 includes a concavely curved region 416 of the first component 41 and a concavely curved region 426 of the second component 42. The concavely curved region 416 of the first component 41 is a region that curves concavely inward of the first component 41 when viewed from the top panel 411 side (in a plan view). The concavely curved region 426 of the second component 42 is also a region that curves concavely inward of the second component 42 when viewed from the top panel 421 side (in a plan view). The concavely curved region 426 of the second component 42 is provided in the second component 42 to correspond to the concavely curved region 416 of the first component 41.

[0033] The concavely curved region 416 of the first part 41 and the concavely curved region 426 of the second part 42 can be defined as follows: When the first part 41 is observed from the top panel 411 side, the radius of curvature of the edge 415a of the vertical wall 415 is calculated from three points: the evaluation node and two adjacent nodes on either side, each about 4 mm apart; and the concavely curved region 416 is defined as the range in which the center of curvature is located outside the first part 41. Similarly, when the second part 42 is observed from the top panel 421 side, the radius of curvature of the edge 425a of the vertical wall 425 is calculated from three points: the evaluation node and two adjacent nodes on either side, each about 4 mm apart; and the concavely curved region 426 is defined as the range in which the center of curvature is located outside the second part 42. The extent of the concavely curved region 30 of the metal member 100 coincides with the extent of the concavely curved region 416 of the first component 41 and the concavely curved region 426 of the second component 42 .

[0034] One or more slits 427 are provided in the vertical wall 425 of the second component 42. In this embodiment, a plurality of slits 427 are provided in the vertical wall 425. The plurality of slits 427 are provided in the vertical wall 425 of the second component 42 so as to be positioned in the overlapping portion between the vertical wall 425 of the second component 42 and the vertical wall 415 of the first component 41. The plurality of slits 427 are provided in at least the concavely curved region 426 of the second component 42.

[0035] [Metal component manufacturing method] Next, a method for manufacturing the metal member 100 will be described with reference to Figures 4A to 4F. The manufacturing method according to this embodiment includes a preparation step and a welding step.

[0036] (preparation process) In the preparation step, a first part 41 and a second part 42 are prepared. Fig. 4A is a partial perspective view of the first part 41 and the second part 42. Fig. 4B is a partial side view of the first part 41 and the second part 42. Figs. 4A and 4B show at least a portion of the concavely curved region 416 of the first part 41 and the concavely curved region 426 of the second part 42, respectively.

[0037] 4A and 4B, the prepared first part 41 has a ridge portion 413 and a vertical wall 415 on the side of a concave curved region 416. The prepared second part 42 has a ridge portion 423 and a vertical wall 425 on the side of a concave curved region 426. In the concave curved region 426 of the second part 42, the vertical wall 425 includes a plurality of slits 427.

[0038] Each of the slits 427 extends from an edge 425a of the vertical wall 425 toward the top panel 421. One depthwise end (base end) of each slit 427 opens at the edge 425a of the vertical wall 425. The other end (tip) of each slit 427 does not reach the end (only R) of the ridge portion 423 on the vertical wall 425 side. That is, as shown in FIG. 4B , if the distance from the end of the ridge portion 423 on the vertical wall 425 side to the edge 425a of the vertical wall 425 is defined as the vertical wall height H and the depth of each slit 427 is defined as the slit depth D, then the slit depth D is smaller than the vertical wall height H. In the example shown in FIG. 4B , the tip shape of each slit 427 is generally arc-shaped. However, the tip shape of each slit 427 is not limited to this.

[0039] 4B, the plurality of slits 427 are arranged along the edge 425a of the vertical wall 425. The plurality of slits 427 are arranged at intervals A. Each of the slits 427 has a slit width W. The slit width W is the maximum length of the slit 427 in the direction in which the edge 425a of the vertical wall 425 extends. The interval A between the slits 427 can be, for example, not less than 0.5 mm and not more than 5.0 mm.

[0040] The length of the concavely curved region 426 in the direction in which the edge portion 425a of the vertical wall 425 extends is L, and the total of the slit widths W of all the slits 427 provided in the concavely curved region 426 is S. W Then, S W When the range in which the slit 427 is introduced in the concave curved region 426 is R, S W / R can be, for example, 0.25 or more.

[0041] The first component 41 and the second component 42 are made of metal. The first component 41 and the second component 42 can each be produced by press-forming a metal plate. The first component 41 and the second component 42 may also be produced by press-forming a steel plate. The steel plate used as the material for the first component 41 and the second component 42 can have a tensile strength of, for example, 980 MPa or more.

[0042] The slits 427 of the second component 42 may be formed in the metal plate before press forming. The slits 427 may also be formed in the vertical wall 425 after the metal plate has been formed into the second component 42. The slits 427 can be formed, for example, by laser cutting. The slit width W is 0.2 mm or more, taking into account the processability of laser cutting. If the slit width W is large, the slits 427 can also be formed in the second component 42 by punching or other processes.

[0043] The slits 427 are preferably provided in a range that includes the stress concentration portion. The stress concentration portion is a portion where stress is expected to occur when a load is input to the metal member 100 during use. If the metal member 100 is a structural member that constitutes the body of an automobile, the stress concentration portion is a portion where stress is expected to occur when the metal member 100 is assembled to the body and a load is input from the road surface while the automobile is traveling. For example, the slits 427 can be provided within 10 mm on both sides of the stress concentration portion, centered on the stress concentration portion, along the direction in which the edges 415a, 425a of the vertical walls 415, 425 extend. The stress concentration portion can be identified using general-purpose analysis software (e.g., Abaqus by Dassault Systèmes or Nastran by MSC). Specifically, the software is used to identify stress concentration locations by performing linear elastic analysis under the conditions shown in the reference (J.-L. Fayard and A. Bignonnet, "Fatigue Design of Welded Thin Sheet Structures," European Structural Integrity Society 22, 145-152 (1997)), i.e., by fixing the tip of arm 12 and tubular portion 20 and applying a load to the portion of the tip of arm 11 that is connected to the ball joint in a direction of 45 degrees from the X-axis on the XY plane or in the opposite direction, 225 degrees. In this case, the positive direction of the X-axis is the direction from the center of tubular portion 20 toward the center of the width of the tip of arm 12, and the positive direction of the Y-axis is the direction from the center of tubular portion 20 toward the tip of arm 11, which is at a 90-degree angle from the X-axis.

[0044] (welding process) In the welding process, the first component 41 and the second component 42 are joined by welding. Referring to FIGS. 4C and 4D , in the welding process, first, the top plate 411 of the first component 41 and the top plate 421 of the second component 42 are placed opposite each other, and the vertical wall 425 of the second component 42 is overlapped from the inside onto the vertical wall 415 of the first component 41. At this time, a slit 427 is formed in the overlapping portion between the vertical walls 415 and 425. In this embodiment, a portion of the slit 427 formed in the vertical wall 425 of the second component 42 is exposed from the overlapping portion between the vertical walls 415 and 425. In other words, if the length of the overlapping portion between the vertical walls 415 and 425 in the depth direction of the slit 427 is defined as overlap C, the slit depth D is greater than overlap C. However, the slit depth D may be equal to or less than overlap C.

[0045] In the welding process, with a slit 427 disposed in the overlapping portion of the vertical walls 415, 425, the vertical walls 415, 425 are welded together along the edge portion 415a of the vertical wall 415 of the first component 41. That is, the vertical wall 415 of the first component 41 and the vertical wall 425 of the second component 42 are lap-fillet welded. As a result, a linear weld 52 is formed on the edge portion 415a of the vertical wall 415 of the first component 41, as shown in FIGS. 4E and 4F .

[0046] Even after the welding process, the slit 427 remains at least in the overlapping portion of the vertical walls 415, 425. Part of the slit 427 may remain in the portion of the vertical wall 425 of the second component 42 that was exposed from the vertical wall 415 of the first component 41. After the welding process, it is preferable that the slit 427 be covered by the vertical wall 415 of the first component 41 and the welded portion 52 so that the slit 427 is not visible from outside the metal member 100. Even after the welding process, the entire slit 427 usually remains on the surface of the vertical wall 425 of the second component 42 that is seen from the inside of the metal member 100.

[0047] The vertical wall 415 of the first component 41 and the vertical wall 425 of the second component 42 are joined by, for example, arc welding. The vertical wall 415 of the first component 41 and the vertical wall 425 of the second component 42 may also be joined by laser-arc hybrid welding. There is no particular limitation on the welding material used in the welding process.

[0048] Although detailed description will be omitted, the other vertical wall 414 (FIG. 2) of the first component 41 and the other vertical wall 424 (FIG. 2) of the second component 42 are also joined by lap fillet welding, similar to the vertical walls 415, 425. Therefore, a linear weld 51 (FIG. 2) is formed on the edge 414a (FIG. 2) of the vertical wall 414 of the first component 41.

[0049] [effect] Generally, in the concavely curved regions 416, 426 of the first component 41 and the second component 42, when the vertical wall 415 of the first component 41 is overlapped with the vertical wall 425 of the second component and fillet welded, the edge 415a of the vertical wall 415 and its surrounding area thermally expand in the tangential direction of the weld line. When such thermal expansion occurs in the concavely curved regions 416, 426, the portions of the vertical walls 415, 425 adjacent to the welded portion 52 are displaced toward the inside of the components 41, 42 from the state before welding shown by the two-dot chain line in FIG. 5A . This causes the vertical walls 415, 425 to tilt toward the inside of the components 41, 42, resulting in out-of-plane deformation. The vertical walls 415, 425 are joined by the welded portion 52 in an out-of-plane deformed state.

[0050] After welding, the first component 41 and the second component 42 are naturally cooled. At this time, as shown in FIG. 5B , the portions of the vertical walls 415, 425 of the first component 41 and the second component 42 adjacent to the welded portion 52 shrink due to cooling and are displaced outward from the components 41, 42. As a result, the vertical walls 415, 425, which have been deformed out of plane, attempt to return to their original state, and the welded portion 52 is pulled in the height direction of the components 41, 42 by the vertical walls 415, 425, as indicated by the thin arrows in FIG. 5B . As a result, high tensile residual stress is generated in the welded portion 52.

[0051] However, in this embodiment, a slit 427 is provided in the vertical wall 425 in the concavely curved region 426 of the second component 42. When the vertical wall 415 of the first component 41 and the vertical wall 425 of the second component 42 are overlapped and welded, the slit 427 is disposed in the overlapping portion of the vertical walls 415, 425. This makes it possible to mitigate out-of-plane deformation of the vertical walls 415, 425 during the welding process. More specifically, because the vertical wall 425 is divided by the slit 427, thermal expansion of adjacent portions of the vertical wall 425 across the slit 427 is less likely to affect each other. Therefore, thermal expansion that would cause out-of-plane deformation of the vertical wall 425 is reduced across the concavely curved region 426 of the second component 42 as a whole, and the return amount of the vertical wall 425 when the metal member 100 is cooled after welding is also reduced. Furthermore, as the out-of-plane deformation of the vertical wall 425 of the second component 42 is alleviated, the out-of-plane deformation of the vertical wall 415 of the first component 41, which is welded to the vertical wall 425 of the second component 42, is also alleviated. As a result, the tensile residual stress in the welded portion 52 is reduced, and the fatigue strength of the welded portion 52 is improved.

[0052] In this embodiment, the slits 427 are preferably provided in a range including a portion where stress concentration is expected to occur during use of the metal member 100. For example, after the metal member 100 is assembled to the body of a vehicle as a component of the vehicle, the slits 427 are provided in a range including a portion where stress concentration is expected to occur due to input of load from the road surface while the vehicle is traveling. This reduces the tensile residual stress, particularly in the welded portion 52, in the portion where stress concentration is expected to occur, and therefore the fatigue strength of the welded portion 52 can be efficiently improved.

[0053] Of the overlapping vertical walls 415, 425, out-of-plane deformation of the inner vertical wall 425 is likely to affect an increase in tensile residual stress in the welded portion 52. For this reason, in this embodiment, a slit 427 is provided in the vertical wall 425 of the second component 42 that is arranged inside the vertical wall 415 of the first component 41. This makes it easier to suppress out-of-plane deformation of the vertical wall 425 of the second component 42 during the welding process. Therefore, the tensile residual stress in the welded portion 52 is more likely to be reduced.

[0054] In the concavely curved region 30 of the metal member 100, if a slit is present in the vertical wall 415 of the first component 41 that is located outside the vertical wall 425 of the second component 42, the slit may become a fracture starting point when a vehicle using the metal member 100 collides. However, in this embodiment, no slit is provided in the vertical wall 415 of the first component 41. Furthermore, the slit 427 provided in the vertical wall 425 of the second component 42 is not exposed from the vertical wall 415 of the first component 41 and the welded portion 52. This ensures the strength of the metal member 100.

[0055] In this embodiment, the depth D of the slit 427 is greater than the overlap C between the vertical wall 415 of the first component 41 and the vertical wall 425 of the second component 42. This makes it easier to reduce the tensile residual stress in the welded portion 52.

[0056] 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.

[0057] In the above embodiment, one or more slits 427 are provided in the vertical wall 425 of the second component 42. However, as shown in FIG. 6, one or more slits 417 may be provided in the vertical wall 415 of the first component 41. In the example shown in FIG. 6, a plurality of slits 417 are provided in the vertical wall 415. These slits 417 are provided in at least the concavely curved region 416 of the first component 41. Each of the slits 417 extends from an edge 415a of the vertical wall 415 toward the top plate 411. During the welding process, when the vertical wall 415 of the first component 41 is overlapped on the vertical wall 425 of the second component 42 from the outside, the slit 417 is positioned at the overlapping portion of the vertical walls 415, 425. The interval A of the slits 417, the slit width W, and the total slit width S are W 6, the out-of-plane deformation of the vertical walls 415, 425 can be reduced in the concave curved regions 416, 426, as in the above embodiment.

[0058] Alternatively, one or more slits 427 may be provided in the vertical wall 425 of the second component 42, and one or more slits 417 may be provided in the vertical wall 415 of the first component 41. In this case, it is preferable that the positions of the slits 417 of the first component 41 coincide with the positions of the slits 427 of the second component 42.

[0059] In the above embodiment, the slits 427 are provided in the vertical wall 425 only in the concavely curved region 426 of the second component 42. However, the slits 427 may also be provided in the vertical wall 425 in regions of the second component 42 other than the concavely curved region 426. For example, the slits 427 may be arranged along the entire length of the vertical wall 425.

[0060] Similarly, when the slits 417 are provided in the vertical wall 415 of the first component 41, the slits 417 may be arranged in the concavely curved region 416 of the first component 41, as well as in a region other than the concavely curved region 416. For example, the slits 417 may be arranged over the entire length of the vertical wall 415.

[0061] In the above embodiment, the slit 427 is provided in the vertical wall 425 of the second component 42 in the concavely curved region 30 of the metal component 100 near the boundary between the arms 11 and 12. However, for example, if the metal component has multiple concavely curved regions, the slit 417 and / or the slit 427 may be provided in two or more of the concavely curved regions.

[0062] In the above embodiment, the weld 52 is formed linearly along the edge 415a of the vertical wall 415 of the first component 41. However, the weld 52 may be formed linearly along the edge 425a of the vertical wall 425 of the second component 42. [Example]

[0063] 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.

[0064] To confirm the effects of the present disclosure, a CAE analysis of arc welding was performed using general-purpose software (Abaqus, manufactured by Dassault Systèmes) on a metal component having a shape similar to that of the metal component 100 according to the above embodiment. In this analysis, the conditions for the slits provided in the concavely curved region were varied, and the tensile residual stress (component in the direction perpendicular to the weld line when viewed from the vertical wall side (component height direction)) was evaluated at multiple evaluation points on the weld toe. For comparison, a similar analysis was also performed on a metal component without a slit provided in the concavely curved region. The analysis conditions and evaluation results are shown in Table 1.

[0065] [Table 1]

[0066] As shown in Table 1, in Examples 1 to 5, in which welding was performed by arranging slits in the overlapping portion of the vertical walls of the first and second parts, there was a range in which the tensile residual stress was reduced compared to the comparative example. The range in which the tensile residual stress was reduced was determined by the ratio of the total slit width in the concave curved region: S W The increase in the concentration of α- and β-blockers increased with increasing / L.

[0067] This analysis confirmed that the tensile residual stress in the weld can be reduced by placing a slit in the overlapping area between the vertical walls in the concave curved region and welding it. Reducing the tensile residual stress in the weld can suppress fatigue cracking in the weld, improving the fatigue strength of the weld. [Explanation of symbols]

[0068] 100: Metallic parts 30: Concave curve area 41: First part 411: Top plate 412, 413: Ridge 414,415: Vertical wall 414a, 415a: Edge 416: Concave curve area 417: Slit 42: Second part 421: Top plate 422, 423: Ridge 424, 425: Vertical wall 424a, 425a: Edge 426: Concave curve area 427: Slit 51, 52: Welded parts

Claims

1. A method for manufacturing a metal member, comprising: a step of preparing a first part and a second part made of metal, each of the first part and the second part including a top plate, a ridge portion continuous with the top plate, and a vertical wall connected to the top plate via the ridge portion, wherein at least one of the first part and the second part is provided with a slit that is disposed in a concavely curved region that is concavely curved toward the inside of the part when viewed from the top plate side, and that extends from an edge of the vertical wall toward the top plate; a step of placing the top plate of the first component and the top plate of the second component opposite each other, overlapping the vertical wall of the second component with the vertical wall of the first component from the inside, and welding the vertical walls together along an edge of the vertical wall of the first component or an edge of the vertical wall of the second component with the slit disposed at the overlapping portion of the vertical walls; A manufacturing method comprising:

2. The method for manufacturing a metal member according to claim 1, A manufacturing method in which the slits are arranged in a range including a portion where stress concentration is expected to occur when a load is input to the metal member during use of the metal member.

3. The method for manufacturing a metal member according to claim 1, The manufacturing method, wherein the slit is provided in the second component.

4. The method for manufacturing a metal member according to claim 1, The manufacturing method, wherein the depth of the slit is greater than the length of the overlapping portion between the vertical walls in the depth direction of the slit.

5. The method according to any one of claims 1 to 4, In at least one of the first part and the second part, the concavely curved region is provided with a plurality of the slits aligned along the edge portion of the vertical wall.

6. A metal member, a first component made of metal including a first top plate, a first ridge portion continuous with the first top plate, and a first vertical wall connected to the first top plate via the first ridge portion; a second metal component including a second top plate facing the first top plate, a second ridge portion continuing to the second top plate, and a second vertical wall connected to the second top plate via the second ridge portion and overlapping the first vertical wall from the inside; a weld portion that welds the first vertical wall and the second vertical wall along an edge portion of the first vertical wall or an edge portion of the second vertical wall; Equipped with the metal member includes a concavely curved region that is concavely curved toward the inside of the metal member in a plan view, In the concavely curved region, at least one of the first vertical wall and the second vertical wall is provided with a slit that is positioned at an overlapping portion between the first vertical wall and the second vertical wall.

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