Manufacturing methods for automotive parts

Abstract

This invention provides a method for manufacturing automotive parts that suppresses the occurrence of wrinkles, cracks, and delayed fracture in overlapping areas during press forming, thereby enabling the production of automotive parts with stable quality. [Solution] The method for manufacturing automotive parts involves temporarily joining multiple blank materials 10 together so that overlap portions 11 are formed where at least a portion of the blank materials 10 overlap, then press-forming the overlap portions 11 while the surfaces of the temporarily joined blank materials 10 slide against each other in the overlap portions 11, and finally permanently joining the press-formed overlap portions 11.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing automotive parts.

Background Art

[0002] In recent years, there has been an increasing demand for reducing the number of automotive parts and improving the efficiency of manufacturing lines through process integration. As a technology to meet such demands, the technology of Tailored Welded Blank (TWB) is known. Tailored Welded Blank is a technology for press-forming a blank material obtained by combining and integrating steel sheets of different varieties, and can optimize the manufacturing process.

[0003] Patent Document 1 discloses a method for manufacturing an integral vehicle body side structure frame. The method includes a step of supplying a plurality of blank materials and a step of joining the blank materials to each other to form a composite blank material. The step of joining the blank materials includes forming one or more overlapping ranges (overlap portions) by partially overlapping two blank materials. The method includes a step of deforming the composite blank material to form an integral vehicle body side structure frame. The step of joining the blank materials to each other includes spot-welding the blank materials to each other in one or more overlapping ranges.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In conventional methods, blank materials are spot-welded together in overlapping sections where they partially overlap. However, when the spot-welded overlapping section is press-formed, wrinkles and cracks are likely to occur in the automotive part due to the difference in material flow rate between the two blank materials, and this method may not be suitable for automotive parts, especially those with overlapping sections on curved surfaces or vertical walls. Furthermore, in such cases, residual stress is generated mainly at the joint after press forming, and if ultra-high-tensile steel sheets are used, there is a risk of delayed fracture.

[0006] This invention has been made in view of the problems of the prior art. The object of this invention is to provide a method for manufacturing automotive parts that can suppress the occurrence of wrinkles, cracks, and delayed fracture in the overlap portion during press forming, and that can produce automotive parts of stable quality. [Means for solving the problem]

[0007] A method for manufacturing an automobile part according to one aspect of the present invention involves temporarily joining multiple blank materials together so that overlap portions are formed where at least a portion of the blank materials overlap; press-forming the overlap portion while the surfaces of the temporarily joined blank materials slide against each other in the overlap portion; and permanently joining the press-formed overlap portion. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for manufacturing automotive parts that can suppress the occurrence of wrinkles, cracks, and delayed fracture in the overlap portion during press forming, and produce automotive parts of stable quality. [Brief explanation of the drawing]

[0009] [Figure 1] This is a plan view showing an example of an integrated blank material after the temporary bonding process according to the first embodiment. [Figure 2]This is a perspective view showing the process of welding a base metal with a laser. [Figure 3] This is a side view showing the relationship between the fusion zone and the HAZ (heat-affected zone). [Figure 4] This graph shows the Vickers hardness near the fusion joint in various types of steel materials. [Figure 5] This is a plan view showing an example of an integrated blank material after the temporary bonding process according to the second embodiment. [Figure 6] This is a plan view showing an example of an integrated blank material after the temporary bonding process according to the third embodiment. [Modes for carrying out the invention]

[0010] The manufacturing method for automotive parts according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] [First Embodiment] First, a method for manufacturing an automotive part according to the first embodiment will be described. The method for manufacturing an automotive part according to this embodiment includes a temporary bonding step, a press forming step, and a final bonding step. The method for manufacturing an automotive part may also include a trimming step. Figure 1 is a plan view showing an example of an integrated blank material 12 after the temporary bonding step according to the first embodiment. The automotive part is not particularly limited and may be, for example, a pillar such as a center pillar, or a rear floor.

[0012] (temporary bonding process) In the tack joining process, the blank materials 10 are tack-joined together such that overlapping portions 11 are formed where parts of the multiple blank materials 10 overlap. Tack joining is a positioning joining process performed before the main joining to fix the blank materials 10 in predetermined positions. Specifically, tack joining may be tack welding. Tack welding is also called tack welding or assembly welding. By tack joining multiple blank materials 10, an integrated blank material 12 can be obtained in which multiple blank materials 10 are joined together, as shown in Figure 1. Therefore, the blank materials 10 do not separate from each other, and the transport of the multiple blank materials 10 and the positioning of the blank materials 10 in the press forming process can be easily facilitated.

[0013] The blank material 10 may be made of steel. The blank material 10 may be, for example, an ultra-high-strength steel plate which is a metallic material with a tensile stress of 980 MPa or more.

[0014] In this embodiment, the plurality of blank materials 10 includes two blank materials 10, a first blank material 10a and a second blank material 10b, and an example of temporarily joining the first blank material 10a and the second blank material 10b will be described. However, the plurality of blank materials 10 may include three or more blank materials 10. The composition and thickness of the blank materials 10 may be the same or different.

[0015] The blank material 10 is also called a partial blank material. Multiple blank materials 10 may be manufactured by a method that includes a division process and a blank material processing process.

[0016] In the splitting process, the target part is conceptually divided into multiple blank materials 10 along predetermined splitting lines. Specifically, in the splitting process, assuming an automotive part as the final product, the target part is conceptually divided into multiple blank materials 10 along predetermined splitting lines, for example, on a drawing. The splitting lines may be provided in areas where elongation forces are applied to the blank material 10 during press forming. The positions where the splitting lines are provided may be determined by empirical rules or forming simulations.

[0017] In the blank material processing step, a planar blank shape may be determined based on the developed shape of each blank material 10 divided in the dividing step. In the blank material processing step, a metal plate material may be processed into blank materials 10 along the determined blank shape to obtain a plurality of blank materials 10. In the blank material processing step, for example, a blank material 10 may be obtained by punching a coil material with a blanking press.

[0018] In the temporary joining step, the blank materials 10 may be temporarily joined with a temporary joining member 20. Further, by temporarily joining the blank materials 10 with the temporary joining member 20, the temporary joining member 20 serves as a handle, so that the conveyance of the blank materials 10 can be made easier. Further, by performing temporary joining using the temporary joining member 20, temporary joining can be performed even in a location where a spot electrode for performing spot welding does not enter.

[0019] In the temporary joining step, the temporary joining member 20 may be temporarily joined to each of the blank materials 10 by butt welding. In butt welding, the welding strength is stronger compared to spot welding etc., and the management of welding conditions is easy. Therefore, by temporarily joining the temporary joining member 20 by butt welding, the variation in welding quality can be reduced. Further, as will be described later, when the manufacturing method of automotive parts removes the temporary joining member 20 by trimming from a plurality of blank materials 10 formed by press molding, welding marks are less likely to remain. Therefore, it is only necessary for the blank material 10 and the temporary joining member 20 to be joined, and the importance of welding strength is low. Thus, the management of welding conditions can be made easier. The butt welding may be butt laser welding using a laser. By using laser welding, welding can be performed faster compared to the case of using arc welding, and the influence of the HAZ (heat affected zone) can also be reduced.

[0020] As shown in FIGS. 2 to 4, the HAZ is a portion where the hardness and strength around the fusion zone are locally reduced due to the influence of welding heat when two base metals are welded with a laser or the like, and is also called a HAZ softened portion. Specifically, as shown in FIG. 4, when various steels are welded, the Vickers hardness of the HAZ softened portion is lower than that of the fusion zone, and it has been confirmed that cracks occur in such a HAZ softened portion. The HAZ is caused by the annealing phenomenon in which a hard structure obtained by severe plastic deformation or heat treatment (quenching and tempering) is coarsened or changed to soft ferrite or the like due to welding heat and is annealed.

[0021] The larger the heat input during welding, the slower the cooling rate of the HAZ, the larger the softened area, and the easier the hardness and strength are to decrease. However, as described above, in this embodiment, since the purpose of the welding of the temporary fixing member 20 is temporary fixing welding, it is easy to manage the welding conditions, and there is no need to manage the joint strength. Therefore, the welding method is not particularly limited, such as laser welding, spot welding, and arc welding, and there are few restrictions on the welding method. Further, for example, when laser welding is used, it is easy to set conditions such as laser output, welding speed, focal position (defocus amount), and pulse conditions (frequency and pulse width). When spot welding is used, it is easy to set conditions such as welding current, energization time, electrode pressing force, and electrode management. In particular, when the blank material 10 has a plating layer, variations in welding strength are likely to occur, and it is difficult to manage stable welding strength. However, by using the temporary fixing member 20, the management of welding conditions can be facilitated.

[0022] The temporary fixing member 20 may be butt-welded to the end face of the edge portion of the blank material 10. By temporarily joining by butt welding, the heat influence on the blank material 10 due to welding can be suppressed. Therefore, it is possible to suppress the remaining softened HAZ in automotive parts.

[0023] The temporary attachment member 20 may be L-shaped. For example, the temporary attachment member 20 may include a first extending portion 21 extending in a first direction and a second extending portion 22 extending from the first extending portion 21 in a second direction intersecting the first direction. With such a configuration, the temporary attachment member 20 is easily deformed in the planar direction including the first and second directions and in the height direction perpendicular to the planar direction. Therefore, even if the positional relationship of the blank material 10 changes during the press forming process, the temporary attachment member 20 can absorb the deformation. Consequently, it is possible to suppress the occurrence of wrinkles and cracks in the blank material 10 during the press forming process.

[0024] In this embodiment, the first extension portion 21 is linear. The second extension portion 22 is also linear. The acute angle formed by the first extension portion 21 and the second extension portion 22 may be 30° or more and 90° or less. When the acute angle is within the above range, changes in the positional relationship of the blank material 10 can be efficiently absorbed. The connection portion between the first extension portion 21 and the second extension portion 22 may be fixed so that the acute angle is a constant value, or it may be configured to be rotatable so that the acute angle can be varied. The temporary attachment member 20 may be formed from a plate-shaped member. With such a configuration, the temporary attachment member 20 becomes even more easily deformable in the height direction perpendicular to the plane direction.

[0025] The temporary bonding member 20 may be temporarily bonded to the non-overlapping portion 13 where the blank material 10 does not overlap. In the non-overlapping portion 13, the difference in material flow during the press forming process tends to be smaller. Therefore, it is possible to suppress the occurrence of wrinkles and cracks in the joint portion 14 during press forming.

[0026] (Press forming process) In the press forming process, the overlapping portion 11 is press-formed while the surfaces of the temporarily joined blank materials 10 slide against each other in the overlapping portion 11. This process ensures that even if the relative positions of the blank materials 10 change during the press forming process, the surfaces of the blank materials 10 slide against each other in the overlapping portion 11. Therefore, deformation caused by press forming can be absorbed in the overlapping portion 11, suppressing wrinkles, cracks, and delayed fracture in the blank material 10. Furthermore, in the press forming process, by press-forming the integrated blank material 12, which has been integrated by the temporary joining process, a press-formed product with high precision and a minimal number of steps can be obtained.

[0027] In the press forming process, the integrated blank material 12 may be press-formed into the shape of an automotive part using a press device. The press device may include, for example, a forming die that includes a lower die with a convex die having a shape that conforms to the outer shape of the automotive part, and an upper die with a punch positioned above the lower die so as to be vertically movable. In this embodiment, there is no joint 14 within the overlap portion 11. Therefore, sliding occurs between the blank materials 10 during press forming in the overlap portion 11 of the blank material 10. This sliding can suppress the occurrence of wrinkles, cracks, and delayed fracture in the automotive part.

[0028] Press forming is not particularly limited and may be cold press forming, but hot press forming is preferred. Hot press forming is also called hot stamping, hot pressing, or hot forming. Hot press forming is a press forming method in which an integrated blank material 12 is heated to a predetermined temperature range, such as 900°C, in a heating furnace, and the heated integrated blank material 12 is press-formed and rapidly cooled at the same time. By press-forming the heated integrated blank material 12, the integrated blank material 12 can be processed while it is still soft. Furthermore, since the press-formed integrated blank material 12 can be rapidly cooled and hardened in a mold cooled by a refrigerant, the strength of the press-formed automotive part can be improved.

[0029] In hot press forming, the integrated blank material 12 may be heated in a heating furnace. In this embodiment, the blank materials 10 are tack-joined together. Therefore, the blank materials 10 are integrated together, and separation of the blank materials 10 in the conveying path of the heating furnace can be suppressed. As a result, the blank materials 10 can be stably conveyed by rollers. Furthermore, since the blank materials 10 are tack-joined together, the integrated blank material 12 can be easily installed in a predetermined position in the molding die.

[0030] Furthermore, because the blank material 10 overlaps in the overlapping section 11, the total thickness is greater than that of the non-overlapping section 13, and it may take time for the contact surface between the blank material 10, which is the center of the thickness direction of the integrated blank material 12, to heat up. On the other hand, in this embodiment, the blank material 10 is temporarily joined together with a temporary bonding member 20. Therefore, heat is transferred to the blank material 10 via the temporary bonding member 20, allowing the entire blank material 10 to heat up quickly. Also, for the same reason, even when the blank material 10 is cooled by the molding die after press molding, the blank material can be cooled via the temporary bonding member 20, allowing the entire blank material 10 to cool down quickly. In addition, by installing the temporary bonding member 20, the overlapping section 11 can be heated and cooled as quickly as the non-overlapping section 13, thus allowing a wider process window to be secured.

[0031] Furthermore, in this embodiment, the blank materials 10 are temporarily joined together with temporary joining members 20. Therefore, the temporary joining members 20 can be held down by the blank holder during press forming, and the area for fixing the temporarily joined blank materials 10 during press forming is increased. As a result, the amount of material flowing in during press forming can be adjusted, and the occurrence of wrinkles, cracks, and delayed fracture in the blank materials 10 can be further suppressed.

[0032] (Main joining process) In this joining process, the press-formed overlap portion 11 is joined. This joining process completes the joining of the overlap portion 11, resulting in an automotive part.

[0033] The method of joining in this joining process is not particularly limited. In this joining process, the overlapping portion 11 can be joined by welding and fastening, or at least one of the two. For example, in this joining process, the joining can be performed by at least one method selected from the group consisting of spot welding, laser welding, and riveting.

[0034] (Trimming process) In the trimming process, temporary bonding members 20 are removed from multiple press-formed blank materials 10 by trimming. By trimming the temporary bonding members 20, it is possible to suppress the remaining temporary bonding members 20 in the final product and maintain the design of the product. Temporary bonding is removed after press forming. Specifically, the trimming process may be performed before the final bonding, after the final bonding, or simultaneously with the final bonding. The method of trimming the temporary bonding members 20 is not particularly limited, and known methods can be used. Residual stress may occur within the temporary bonding members 20 and around the joint 14, but this will be outside the automotive part. Therefore, by trimming the temporary bonding members 20 and the area around the joint 14 after press forming, it is possible to suppress the generation of residual stress due to molding within the final automotive part.

[0035] [Second Embodiment] Next, a method for manufacturing automotive parts according to the second embodiment will be described. The method for manufacturing automotive parts according to this embodiment includes a temporary bonding step, a press forming step, and a final bonding step. Figure 5 is a plan view showing an example of an integrated blank material 12 after the temporary bonding step according to the second embodiment.

[0036] (Temporary bonding process) In the temporary joining process, the blank materials 10 are temporarily joined together such that overlapping portions 11 are formed where parts of the multiple blank materials 10 overlap. By temporarily joining multiple blank materials 10, an integrated blank material 12 can be obtained, in which multiple blank materials 10 are integrated into one, as shown in Figure 5. Therefore, the blank materials 10 do not fall apart, and the transport of the multiple blank materials 10 and the positioning of the blank materials 10 in the press forming process can be easily facilitated. In addition, by temporarily joining the blank materials 10 together, even if the positional relationship of the blank materials 10 changes during the press forming process, the deformation can be absorbed by the overlapping portion 11. Therefore, it is possible to suppress the occurrence of wrinkles and cracks in the blank material 10 during the press forming process.

[0037] In this embodiment, the blank materials 10 are tack-joined by spot welding the overlap portion 11. The joint 14 tack-joined by spot welding is joined in such a way that it can be detached by press forming. Therefore, the blank materials 10 only need to be tack-joined, and there is little need to maintain high weld strength. Consequently, it is easier to manage the joint strength compared to normal spot welding. In addition, spot welding for tack joining requires less welding current compared to spot welding for main joining, reducing the amount of heat generated and resulting in less softened heat-affected zone (HAZ). Because the HAZ is small, quenching (reheating) is not required. Furthermore, when hot press forming is performed in the press forming process, the softened HAZ hardens during quenching. Therefore, the need to strictly control the welding quality of the blank material 10 can be reduced. Moreover, because the HAZ is small, it is not necessary to perform CAE (Computer-Aided Engineering) analysis or FLD (Forming Limit Diagram) acquisition tests in accordance with ISO 12004-2. Furthermore, spot welding for temporary joining requires a lower welding current and produces fewer weld marks compared to spot welding for permanent joining. Therefore, it can improve the aesthetic appearance of automotive parts.

[0038] Furthermore, the areas with low material flow in the press forming process are limited. Because the areas with low material flow are limited, the area where permanent joining can be performed to prevent wrinkles and cracks from occurring in automotive parts during press forming is not wide. On the other hand, in this embodiment, the overlapping portion 11, which has a relatively large material flow, can be tack-joined. Therefore, there are fewer constraints on the locations where spot welding is performed, and there is a high degree of freedom in the welding machine and welding position.

[0039] Spot welding may be performed only at locations corresponding to at least one of the curved surfaces and edges of the automotive parts. Spot welding is difficult on curved surfaces and edges. Therefore, by performing spot welding only at locations corresponding to at least one of the curved surfaces and edges of the automotive parts, it is possible to avoid spot welding at the same location for both tack joining and permanent joining, thereby improving the joint strength between the blank materials 10.

[0040] The blank material 10 used in the temporary joining process can be manufactured by the same method as in the first embodiment, and the same blank material 10 as in the first embodiment can be used.

[0041] (Press forming process) In the press forming process, the overlapping portion 11 is press-formed while the surfaces of the temporarily joined blank materials 10 slide against each other in the overlapping portion 11. In the press forming process, similar to the first embodiment, the temporarily joined integrated blank material 12 is press-formed into the shape of an automobile part using a press device. In the overlapping portion 11 of the blank material 10, sliding occurs between the blank materials 10 during press forming. This sliding can suppress the occurrence of wrinkles, cracks, and delayed fracture in the automobile part.

[0042] Furthermore, in this embodiment, the blank materials 10 are temporarily joined together. As a result, the blank materials 10 are integrated, which prevents them from separating in the transport path of a heating furnace or the like. Therefore, the blank materials 10 can be transported stably by rollers.

[0043] In this embodiment, during the press forming process, the tack-jointed overlap portion 11 is press-formed, and at the same time, the tack-jointed portion, which was tack-jointed by spot welding, is removed. In the overlap portion 11, the difference in the amount of material flowing between the blank materials 10 is relatively large during press forming, causing shear deformation at the tack-joint. Since the tack-joint can be removed by this shear deformation, it is possible to suppress the concentration of large deformation around the tack-joint. Therefore, it is possible to suppress the occurrence of wrinkles, cracks, and delayed fracture in the automotive part due to the sliding of the surfaces of the blank materials 10 that occurs during press forming in the overlap portion 11, and to suppress the occurrence of crack fracture in the blank material 10 at the tack-joint. In addition, since the tack-joint is removed during press forming, it is possible to suppress a localized decrease in the plate thickness of the blank material 10 at the tack-joint.

[0044] Furthermore, the sliding of the surfaces of the blank material 10 in the overlap portion 11 can suppress the generation of residual stress around the tack joint of the blank material 10. Therefore, delayed fracture can be suppressed in automotive parts. Delayed fracture is also called delayed cracking, cold cracking (cold working cracking), or hydrogen embrittlement cracking. Delayed fracture is thought to occur when three factors coincide: high tensile stress, material sensitivity, and hydrogen embrittlement. High tensile stress is caused by residual tensile stress inside the material, such as that generated by tightening bolts, and the presence of stress concentration points such as notches on the material surface. Regarding material sensitivity, generally, the risk of delayed fracture increases with higher strength steels, such as those with a tensile strength of 1000 MPa or more. Hydrogen embrittlement is a phenomenon in which hydrogen atoms penetrate into the material, causing the material to lose its ductility and malleability and become brittle. The timing of hydrogen penetration into the material can be broadly divided into two categories: penetration from the outside during the manufacturing process and penetration from the outside under the usage environment. Delayed fracture is a phenomenon in which high-strength steel components, such as those with a tensile strength of 1000-1200 MPa or more and a Rockwell hardness of HRC40 or more, suddenly fracture brittle after a certain period of time under static conditions where tensile stress is generated due to the presence of residual stress, with little to no apparent plastic deformation.

[0045] Three representative theories regarding the hydrogen embrittlement mechanism have been proposed: the lattice embrittlement theory, the hydrogen local deformation enhancement theory, and the hydrogen strain-induced vacancy theory. The lattice embrittlement theory posits that hydrogen dissolved between lattices reduces the bonding force between matrix atoms. The hydrogen local deformation enhancement theory posits that hydrogen promotes the movement and occurrence of transitions within the material, leading to localized plastic deformation. The hydrogen strain-induced vacancy theory posits that hydrogen promotes the generation and aggregation of atomic vacancies associated with plastic deformation, facilitating the progression of ductile fracture.

[0046] In conventional methods, welding within the overlap portion hinders the sliding of the blank material surfaces. However, if the welded portion of the blank material remains welded, residual stress can be generated in the weld during press forming, potentially leading to delayed fracture. Therefore, even if cracks do not occur in the automotive part immediately after forming, hydrogen may penetrate the automotive part over time, corroding it and potentially causing cracks. On the other hand, in the manufacturing method of the automotive part according to this embodiment, the temporarily joined blank material 10 peels off, and the surfaces of the blank material 10 slide against each other throughout the overlap portion 11, thereby reducing the residual stress in the joint 14. If the tensile tension (residual stress), one of the three elements of delayed fracture, can be reduced, delayed fracture can be suppressed even if hydrogen penetrates the automotive part.

[0047] Furthermore, the overlapping portion 11 exhibits a relatively large difference in material flow between the blank materials 10 during press forming. As a result, the blank materials 10 gradually separate and detach during press forming. Consequently, the joint between the blank materials 10 peels off before the sliding surface of the blank materials 10 during press forming is inhibited, making it difficult for large residual stresses to occur. This significantly reduces the risk of delayed fracture. In addition, the fluttering of the blank materials 10 during press forming is suppressed, and the material flow into the blank materials 10 can be made uniform. Therefore, it is possible to suppress the occurrence of wrinkles, cracks, and delayed fracture in automotive parts.

[0048] (Main joining process) In this joining process, the press-formed overlap portion 11 is joined. This joining process completes the joining of the overlap portion 11, resulting in an automotive part. This joining process can be carried out in the same manner as in the first embodiment.

[0049] [Third Embodiment] Next, a method for manufacturing automotive parts according to the third embodiment will be described. The method for manufacturing automotive parts according to this embodiment is a patchwork method. The patchwork method is mainly applied to automotive parts such as center pillars and front pillars, and by applying "patches" to the minimum necessary locations, it is possible to achieve high impact absorption strength, such as 1.5 GPa class, while keeping weight down. Therefore, it is possible to locally increase the strength of the necessary areas and contribute to the weight reduction of the vehicle. The patchwork method can accommodate structural parts with complex shapes by combining steel plates of different thicknesses and materials, and compared to conventional hot stamping (hot pressing) technology, the production process is simplified and a reduction in manufacturing costs can be expected. The method for manufacturing automotive parts according to this embodiment includes a temporary bonding process, a press forming process, and a final bonding process. Figure 6 is a plan view showing an example of an integrated blank material 12 after the temporary bonding process according to the third embodiment.

[0050] (temporary bonding process) In the temporary joining process, the blank materials 10 are temporarily joined together so that an overlap portion 11 is formed where all of the blank materials 10 overlap. Similar to the above embodiment, by temporarily joining multiple blank materials 10, an integrated blank material 12 can be obtained in which multiple blank materials 10 are combined, as shown in Figure 6.

[0051] In this embodiment, similar to the second embodiment, the blank materials 10 are temporarily joined together by spot welding the overlapping portion 11.

[0052] In the overlap portion 11, the entirety of at least one first blank material 10a among the multiple blank materials 10 overlaps with at least one second blank material 10b among the multiple blank materials 10 that are different from the first blank material 10a. With this configuration, the second blank material 10b is reinforced by the first blank material 10a. As a result, high-strength automotive parts can be manufactured. The joint portion 14, which is tack-welded by spot welding, is joined in such a way that it can be detached by press forming, similar to the second embodiment. As a result, during press forming, shear stress caused by the difference in wire length between the inside and outside of the blank material 10 can be suppressed, preventing wrinkles, cracks, delayed fracture, and reduction in plate thickness of the blank material 10.

[0053] The blank material 10 used in the tack joining process can be manufactured by the same method as in the first and second embodiments, and the same blank material 10 as in the first and second embodiments can be used. Similar to the second embodiment, spot welding may be performed only at locations corresponding to at least one of the curved surface and edge portions of the automotive part.

[0054] (Press forming process) In the press forming process, the overlapping portion 11 is press-formed while the surfaces of the temporarily joined blank materials 10 slide against each other in the overlapping portion 11. A press-formed product is obtained through the press forming process. In the press forming process, the integrated blank material 12 formed by the temporary joining process is press-formed into the shape of an automotive part using a press device, similar to the first and second embodiments. In the overlapping portion 11 of the blank material 10, sliding occurs between the blank materials 10 during press forming. This sliding can suppress the occurrence of wrinkles, cracks, and delayed fracture in the automotive part.

[0055] In this embodiment, as in the second embodiment, the tack-jointed overlap portion 11 is press-formed during the press forming process, while the spot-welded tack-joint portion is removed at the same time. This suppresses the occurrence of wrinkles, cracks, and delayed fracture in the automotive part due to the sliding of the surfaces of the blank material 10 during press forming, and also suppresses the occurrence of crack fracture in the blank material 10 at the tack-joint portion. Furthermore, since the tack-joint portion is removed during press forming, it is possible to suppress a localized reduction in the thickness of the blank material 10 at the tack-joint portion.

[0056] (Main joining process) In this joining process, the press-formed overlap portion 11 is joined. This joining process joins the overlap portion 11, resulting in an automotive part. This joining process is the same as in the first and second embodiments, so a detailed explanation is omitted. From the viewpoint of high productivity and low cost, it is preferable that the overlap portion 11 is joined by spot welding.

[0057] Next, the operation and effects of the manufacturing methods for automotive parts according to the first to third embodiments will be described.

[0058] As described above, the method for manufacturing automotive parts involves temporarily joining multiple blank materials 10 together such that overlapping portions 11 are formed where at least a portion of each blank material 10 overlap. The method for manufacturing automotive parts involves press-forming the overlapping portions 11 while the temporarily joined blank materials 10 slide against each other in the overlapping portions 11. The method for manufacturing automotive parts involves permanently joining the press-formed overlapping portions 11.

[0059] According to the manufacturing method for automotive parts of this embodiment, the blank materials 10 are tack-joined together before press forming, and the tack-joined blank materials 10 slide against each other in the overlap portion 11 while the overlap portion 11 is press-formed. Therefore, wrinkles, cracks, and delayed fractures in the overlap portion 11 are suppressed during press forming, and automotive parts of stable quality can be manufactured.

[0060] The temporary joints may be removed after press forming. This method facilitates sliding between the blank materials 10 in the overlapping portion 11.

[0061] In the method for manufacturing automotive parts, the blank materials 10 may be temporarily joined together with temporary joining members 20. In the method for manufacturing automotive parts, the temporary joining members 20 may be removed from the press-formed blank materials 10 by trimming. With this method, the blank materials 10 are not directly joined together at the overlap portion 11. Therefore, during press forming, the blank materials 10 can easily slide against each other at the overlap portion 11.

[0062] The manufacturing method for automotive parts may involve tack-welding the tack-fitting members 20 to each of the blank materials 10 by butt welding. Compared to spot welding and other methods, butt welding offers stronger weld strength and easier control of welding conditions. Therefore, by tack-welding the tack-fitting members 20 by butt welding, variations in welding quality can be reduced.

[0063] The temporary attachment member 20 may be L-shaped. With this configuration, the temporary attachment member 20 is easily deformed in the planar direction and in the height direction perpendicular to the planar direction. Therefore, even if the positional relationship of the blank material 10 changes during the press forming process, the temporary attachment member 20 can absorb the deformation.

[0064] The temporary bonding member 20 may be temporarily bonded to the non-overlapping portion 13 where the blank material 10 does not overlap. In the non-overlapping portion 13, the difference in material flow during the press forming process tends to be smaller. Therefore, it is possible to suppress the occurrence of wrinkles, cracks, and delayed fracture at the joint portion 14 during press forming.

[0065] In the manufacturing method of automotive parts, the blank materials 10 may be temporarily joined together by spot welding the overlap portion 11. In the manufacturing method of automotive parts, the temporarily joined overlap portion 11 may be press-formed at the same time as the temporarily joined portion is removed by spot welding. In the overlap portion 11, the difference in the amount of material flowing between the blank materials 10 is relatively large during press forming, causing shear deformation at the temporarily joined portion. Since the temporarily joined portion can be removed by this shear deformation, it is possible to suppress the concentration of large deformation around the temporarily joined portion.

[0066] Spot welding may be performed only at locations corresponding to at least one of the curved surfaces and edges of the automotive part. Spot welding is difficult on curved surfaces and edges. Therefore, by performing spot welding only at locations corresponding to at least one of the curved surfaces and edges of the automotive part, it is possible to avoid spot welding at the same location for both tack welding and permanent welding, thereby improving the joint strength between the blank materials 10. In addition, since a tack welding member 20 is used in this embodiment, welding can be performed anywhere in the overlap portion 11, and there are no restrictions on the welding position. Because of the high degree of freedom in welding position, it is not necessary to verify, analyze, and test the effects of welding position in advance. Also, because of the high degree of freedom in welding position, verification is not required when design changes are made, resulting in high versatility.

[0067] In the overlap portion 11, the entirety of at least one first blank material 10a among the plurality of blank materials 10 may overlap with at least one second blank material 10b among the plurality of blank materials 10 that are different from the first blank material 10a. With this configuration, the second blank material 10b is reinforced by the first blank material 10a. Therefore, it is possible to manufacture automotive parts with high strength.

[0068] Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment. [Explanation of Symbols]

[0069] 10 Blank materials 10a First blank material 10b Second blank material 11 Overlap section 12. Integrated blank material 13 Non-overlapping section 14 Joint 20 Temporary attachment components 21 1st extension part 22 Second extension part

Claims

1. Multiple blank materials are temporarily joined together with a temporary joining member so that at least a portion of each blank material overlaps to form an overlapping section. The surfaces of the temporarily joined blank materials slide against each other in the overlapping portion, and the overlapping portion is press-formed. The press-formed overlapping portions are then joined together. In the aforementioned tack joining, the tack joining members are tack-joined to each of the blank materials by butt welding. A method for manufacturing automotive parts.

2. The blank materials are temporarily joined together with a temporary joining member separate from the blank materials so that an overlap portion is formed in which at least a part of the blank materials overlap, The surfaces of the temporarily joined blank materials slide against each other in the overlapping portion, and the overlapping portion is press-formed. The press-formed overlapping portions are then joined together. The temporary attachment member is temporarily attached to the non-overlapping portion where the blank material does not overlap. A method for manufacturing automotive parts.

3. The method for manufacturing an automobile part according to claim 1 or 2, wherein the temporary joint is removed after the press forming.

4. The temporary attachment member is removed from the press-formed plurality of blank materials by trimming. A method for manufacturing an automobile part according to claim 1 or 2.

5. The aforementioned temporary attachment member is L-shaped. A method for manufacturing an automobile part according to claim 1 or 2.

6. The blank materials are temporarily joined together with a temporary joining member such that at least a portion of the blank materials overlap to form an overlapping portion, The surfaces of the temporarily joined blank materials slide against each other in the overlapping portion, and the overlapping portion is press-formed. The press-formed overlapping portions are then joined together. In the aforementioned temporary joining, the blank materials are temporarily joined together by spot welding the overlapping portion. In the aforementioned press forming process, the overlapping portion that has been temporarily joined is press-formed, and at the same time, the temporarily joined portion that has been temporarily joined by spot welding is removed. A method for manufacturing automotive parts.

7. The method for manufacturing an automobile part according to claim 6, wherein the spot welding is performed only at locations corresponding to at least one of the curved surface portion and the ridge portion of the automobile part.

8. The method for manufacturing an automobile part according to claim 6 or 7, wherein in the overlap portion, the entirety of at least one first blank material among the plurality of blank materials overlaps with at least one second blank material among the plurality of blank materials which is different from the first blank material.

9. The method for manufacturing the automotive part according to claim 6 or 7, wherein the method for manufacturing the automotive part is a patchwork method.

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