Structural member and method for manufacturing same

Abstract

This method for manufacturing a structural member (10) is provided with: a step for preparing a raw material (M); and a molding step for performing cold press working on the raw material (M) using a mold (20). The die (20) comprises a pressing pad (23), an upper die (22) and a lower die (21). The lower die (21) includes first and second lower dies (211, 212). The molding step includes a first step and a second step. In the first step, the raw material (M) is pressed by the swaging pad (23) and the first lower die (211) in a state where the side surface (212c) of the second lower die (212) is retracted with respect to the side surface (211c) of the first lower die (211) as viewed from the pressing direction. In the second step, the material (M) is sandwiched between the upper die (22) and the first lower die (211), and the material (M) is sandwiched between the upper die (22) and the second lower die (212) by moving the second lower die (212) so that the side surfaces (212c) and the side surfaces (211c) are aligned.

Description

Technical Field

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

[0002] A structure such as an automobile body is composed of many structural members. Examples of structural members for automobiles include pillars, longitudinal beams, side sills (lower side sills), cross beams, floors, body roofs, and the like. Such structural members are generally manufactured by stamping a metal plate.

[0003] For example, Patent Document 1 discloses a method for manufacturing a structural member having an L-shaped configuration in a plan view. The structural member includes a top plate, a ridge line portion, and a longitudinal wall connected to the top plate via the ridge line portion. The ridge line portion includes a corner portion bent along the length direction of the ridge line portion. In the manufacturing method of Patent Document 1, a metal plate is stamped using a die including an upper die, a lower die, and a blank holder to form the structural member.

[0004] For example, Patent Document 2 discloses a method for manufacturing a structural member having a hat-shaped configuration in a cross-sectional view. A ridge portion is formed in the longitudinal wall of the structural member. In the manufacturing method of Patent Document 2, an intermediate formed body formed from a metal plate is prepared, and the intermediate formed body is formed into the structural member using a die including an upper die, a lower die, and a sliding die mounted on the upper die via a cam mechanism. The lower die includes a central die and a split die mounted on the central die via a cam mechanism. In Patent Document 2, as the die is closed, the sliding die and the split die press a corresponding portion of the longitudinal wall of the intermediate formed body to form the ridge portion of the longitudinal wall.

[0005] For example, Patent Document 3 discloses a method for manufacturing a structural member having a T-shaped configuration in a plan view. The manufacturing method of Patent Document 3 includes the following steps: a first forming step of forming a metal plate into an intermediate shaped member by drawing; a trimming step of trimming the intermediate shaped member; a second forming step of forming the trimmed intermediate shaped member into the structural member by foam molding. In the second forming step, the structural member having the target shape is stamped using a die including an upper die and a lower die.

[0006] Prior art documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2022-072562

[0009] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-083807

[0010] Patent Document 3: Japanese Patent No. 6690605 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] However, there are structural members in which the member body and the flange are arranged with a corner therebetween. Both the member body and the flange include a top plate, a ridge line portion, and a longitudinal wall. The ridge line portion and the longitudinal wall of the flange are connected to the ridge line portion and the longitudinal wall of the member body by means of the corner.

[0013] In the case of manufacturing such a structural member by stamping, cracks sometimes occur in the flange (continuous flange) continuously provided with the member body by means of the corner. Especially when the radius of curvature of the corner is small, cracks are likely to occur in the continuous flange during stamping. If the structural member is formed from a high-strength metal plate, cracks in the continuous flange during stamping are more likely to occur.

[0014] An object of the present disclosure is to provide a method for manufacturing a structural member capable of suppressing the occurrence of cracks in a continuous flange.

[0015] Solutions to the Problems

[0016] The method for manufacturing a structural member according to the present disclosure includes the following steps: a preparation step of preparing a raw material made of a metal plate; and a forming step of performing cold pressing on the raw material using a die to form the same. The die includes a blank holder, an upper die, and a lower die. The lower die includes a first lower die, a second lower die, and a corner portion. The first lower die includes a first top surface, a first shoulder portion, and a first side surface. The first top surface intersects the stamping direction. The first shoulder portion extends along the edge of the first top surface. The first side surface is connected to the first top surface by means of the first shoulder portion. The second lower die includes a second top surface, a second shoulder portion, and a second side surface. The second top surface intersects the stamping direction. The second shoulder portion extends along the edge of the second top surface. The second side surface is connected to the second top surface by means of the second shoulder portion. The second lower die is independent of the first lower die. The corner portion is provided between the first shoulder portion and the first side surface and the second shoulder portion and the second side surface. The corner portion has a shape recessed inwardly of the lower die when viewed from the stamping direction. The forming step includes a first step and a second step. In the first step, with the first lower die and the second lower die arranged such that the second side surface is in a position retracted relative to the first side surface when viewed from the stamping direction, the blank holder and the upper die are relatively approximated to the lower die in the stamping direction, and the raw material is clamped and pressed by the blank holder and the first lower die. In the second step, with the raw material pressed by the blank holder and the first lower die, the upper die is further relatively approximated to the lower die in the stamping direction, and the raw material is clamped by the upper die and the first lower die. Further, the second lower die is moved so that the second side surface is aligned with the first side surface when viewed from the stamping direction, and the raw material is clamped by the upper die and the second lower die.

[0017] Effects of the Invention

[0018] According to the manufacturing method of the structural member of the present disclosure, the generation of cracks in the continuous flange can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a perspective view of the structural member of the first embodiment.

[0020] Figure 2 is Figure 1 a top view of the structural member shown.

[0021] Figure 3 is Figure 1 a side view of the structural member shown.

[0022] Figure 4A is a schematic diagram for explaining the manufacturing method of the structural member of the first embodiment.

[0023] Figure 4B is a schematic diagram for explaining the manufacturing method of the structural member of the first embodiment.

[0024] Figure 4C is a schematic diagram for explaining the manufacturing method of the structural member of the first embodiment.

[0025] Figure 4D is a schematic diagram for explaining the manufacturing method of the structural member of the first embodiment.

[0026] Figure 4E is a schematic diagram for explaining the manufacturing method of the structural member of the first embodiment.

[0027] Figure 4F is a schematic diagram for explaining the manufacturing method of the structural member of the first embodiment.

[0028] Figure 4G is a schematic diagram for explaining the manufacturing method of the structural member of the first embodiment.

[0029] Figure 5 is Figure 1 a partial enlarged view of the structural member shown.

[0030] Figure 6 is a perspective view of the structural member of the second embodiment.

[0031] Figure 7 is Figure 6 a side view of the structural member shown.

[0032] Figure 8 is a schematic diagram of the structural member for explaining the analysis conditions.

[0033] Figure 9 is a schematic diagram of the structural member for explaining the analysis conditions.

[0034] Figure 10 It is a schematic diagram of a structural member for explaining the conditions of analysis.

[0035] Figure 11 It is a graph showing the relationship between the distance from the edge of the continuous flange and the Vickers hardness for a structural member with a tensile strength of 1180 MPa. Detailed implementation mode

[0036] The manufacturing method of the structural member of the implementation mode includes the following processes: a preparation process of preparing a raw material composed of a metal plate; and a forming process of performing cold pressing on the raw material using a die to form it. The die includes a blank holder, an upper die, and a lower die. The lower die includes a first lower die, a second lower die, and a corner. The first lower die includes a first top surface, a first shoulder, and a first side surface. The first top surface intersects the stamping direction. The first shoulder extends along the edge of the first top surface. The first side surface is connected to the first top surface by the first shoulder. The second lower die includes a second top surface, a second shoulder, and a second side surface. The second top surface intersects the stamping direction. The second shoulder extends along the edge of the second top surface. The second side surface is connected to the second top surface by the second shoulder. The second lower die is independent of the first lower die. The corner is provided between the first shoulder and the first side surface and the second shoulder and the second side surface. The corner has a shape that is recessed inwardly of the lower die when viewed from the stamping direction. The forming process includes a first process and a second process. In the first process, in a state where the first lower die and the second lower die are arranged such that the second side surface is in a position retracted with respect to the first side surface when viewed from the stamping direction, the blank holder and the upper die are relatively approximated with respect to the lower die in the stamping direction, and the raw material is clamped and pressed by the blank holder and the first lower die. In the second process, in a state where the raw material is pressed by the blank holder and the first lower die, the upper die is further relatively approximated with respect to the lower die in the stamping direction to clamp the raw material by the upper die and the first lower die, and the second lower die is moved so that the second side surface is aligned with the first side surface when viewed from the stamping direction to clamp the raw material by the upper die and the second lower die (the first configuration).

[0037] In the manufacturing method of the first configuration, a die including a blank holder, an upper die, and a lower die is used to form a structural member from a raw material by cold pressing. The lower die includes a second lower die disposed across a corner portion from the first lower die. At the start of the forming process, the second lower die is disposed at a position retracted from the first lower die when viewed in the stamping direction. Therefore, until the middle of the forming process, the portion of the raw material that is finally formed by the second lower die, that is, the flange (continuous flange) continuously provided with the member body via the corner portion in the structural member, is not constrained by the second lower die. In a state where the second lower die does not constrain the continuous flange, the upper die relatively approaches the lower die including the second lower die in the stamping direction to apply tension to the raw material. Therefore, the inflow of the material from the top surface side to the side surface side of the second lower die is promoted at the position of the continuous flange. As a result, the strain generated in the continuous flange can be dispersed. Thus, even when, for example, the radius of curvature of the corner portion is small or the strength of the raw material is large, the generation of cracks in the continuous flange can be suppressed.

[0038] For example, in the case where cracks are expected to occur in the continuous flange, especially at the edge of the continuous flange, during the forming process, in order to prevent the generation of cracks, the forming process is sometimes carried out in a state where a surplus portion is provided in advance on a metal plate (blank), and a trimming process is sometimes carried out after the forming process to remove the unnecessary surplus portion. In contrast, in the manufacturing method of the first configuration, the cracks at the continuous flange can be suppressed by not constraining the continuous flange at the initial stage of the forming process. Therefore, there is no need for a surplus portion, and the trimming process of the surplus portion after the forming process can be omitted. In the case of omitting the trimming process of the surplus portion, compared with the case of performing the trimming process, the amount of the raw material input into the forming process can be reduced. As a result, the yield rate of manufacturing the structural member can be increased. In addition, by reducing the input amount of the raw material and not performing the trimming process, the conveyance amount, electric energy, etc. during the manufacturing process of the structural member are reduced. Therefore, the emission amount of greenhouse gases can also be reduced.

[0039] According to the manufacturing method of the first configuration, preferably, the moving distance of the second lower die in the second process is 9.0 times or less the plate thickness of the raw material (second configuration).

[0040] The second lower die is disposed at a position retracted from the first lower die in the first process of forming, and is moved in the second process of forming to align its position with the position of the first lower die. In the second configuration, the moving distance of the second lower die is 9.0 times or less the plate thickness of the raw material. In this case, wrinkles can be suppressed from being generated in the structural member during the forming process.

[0041] According to the manufacturing method of the first or second configuration, it may also be that the second lower die further includes at least a part of the corner portion. In this case, the second shoulder portion and the second side surface are continuous with the corner portion (third configuration).

[0042] In the third configuration, at least a part of the corner portion of the lower die is included in the second lower die that is disposed at a position retracted from the first lower die at the start of the forming process. In this case, in addition to the continuous flange, at least a part of the corner portion adjacent to the continuous flange is not constrained in the middle of the forming process. As a result, compared with a case where, for example, the entire corner portion is included in the first lower die and the entire corner portion is constrained by the first lower die from the early stage of the forming process, the bending of the continuous flange in the middle stage of the forming process becomes gentle, and the strain of the continuous flange is reduced. Since the second lower die moves in the later stage of the forming process, the continuous flange and the corner portion are formed by bending upward while following the flow of the material using the second lower die. As a result, it is more difficult to generate cracks in the continuous flange.

[0043] According to the manufacturing method of any one of the first to third configurations, it is possible to arrange that the blank holder also presses a portion of the raw material that is adjacent to the outside of the bend of the corner portion (fourth configuration).

[0044] In the fourth configuration, the blank holder presses the raw material together with the first lower die in the forming process, and also presses the raw material near the corner portion between the first lower die and the second lower die. In this case, it is possible to prevent wrinkles from occurring in the raw material at the position of the corner portion.

[0045] According to the manufacturing method of any one of the first to fourth configurations, it may also be that the second top surface is inclined with respect to a plane perpendicular to the stamping direction such that the distance from the second shoulder and the second side surface in the stamping direction increases as it goes from the edge on the second shoulder side toward the edge on the side opposite to the second shoulder (fifth configuration).

[0046] In the fifth configuration, the top surface of the second lower die is inclined with respect to a plane perpendicular to the stamping direction. The top surface of the second lower die is inclined with respect to a plane perpendicular to the stamping direction such that it is lower on the shoulder side and higher on the side opposite to the shoulder. In this case, in the forming process, the material more easily flows from the top surface side of the second lower die through the shoulder to the side surface side. Therefore, in the continuous flange formed using the second lower die, it is possible to further suppress the generation of local strain and cracks.

[0047] The structural component of the embodiment includes a component body and a flange. The component body includes a first top plate, a first ridge portion, and a first longitudinal wall. The first ridge portion extends along the end edge of the first top plate. The first longitudinal wall is connected to the first top plate via the first ridge portion. The flange includes a second top plate, a second ridge portion, and a second longitudinal wall. The second ridge portion extends along the end edge of the second top plate. The second longitudinal wall is connected to the second top plate via the second ridge portion. The second ridge portion and the second longitudinal wall are connected to the first ridge portion and the first longitudinal wall via a corner portion. The second top plate is continuous with the first top plate at the outer side of the bend of the corner portion. In a cross section obtained by cutting the flange along the plate thickness direction of the second top plate at the junction between the second top plate and the second ridge portion, the difference between the Vickers hardness measured at the end on the opposite side of the corner portion and the Vickers hardness measured at the end on the corner side is 30Hv or less (sixth configuration).

[0048] In the structural member of the sixth configuration, the hardness of the flange (continuous flange) provided continuously with the member body by means of the corner is made uniform. In more detail, in the cross section at the junction between the top plate and the ridge portion of the continuous flange, the difference between the Vickers hardness measured at the end on the opposite side of the corner and the Vickers hardness measured at the end on the corner side is 30Hv or less. This means that in the continuous flange, the strain generated when the structural member is formed is dispersed along the ridge portion. In this case, when a load is input to the structural member and additional strain is generated at the edge of the continuous flange where the strain is relatively concentrated, it is possible to suppress cracks from occurring in the continuous flange starting from the edge. Therefore, when the structural member is used in the body of an automobile, the structural member can exhibit excellent collision resistance.

[0049] The structural member of the sixth configuration may be formed of a steel plate having a tensile strength of 590 MPa or more (seventh configuration).

[0050] In the structural member according to the sixth or seventh configuration, the corner portion may have a curvature radius of 100 mm or less when viewed from the first top plate side (eighth configuration).

[0051] According to any one of the sixth to eighth configurations, the first top plate may include a flat surface on its surface. Alternatively, the second top plate may be inclined relative to the flat surface so that the distance from the second ridge portion and the second vertical wall in a direction perpendicular to the flat surface increases from the end edge on the second ridge portion toward the end edge on the side opposite to the second ridge portion (ninth configuration).

[0052] Below, with reference to the attached Figure 1 The embodiments of the present disclosure will be described. In the drawings, the same or corresponding structures are denoted by the same reference numerals, and the same description will not be repeated.

[0053] <First embodiment>

[0054] [Structure of Structural Member]

[0055] Figure 1 is a perspective view of the structural member 10 of the first embodiment. Figure 2 is a top view of the structural member 10. The structural member 10 is typically used for an automobile body. There is no particular limitation, and the structural member 10 may also be, for example, an inner panel of the rear part of a side sill.

[0056] Refer to Figure 1 , the structural member 10 is formed of a metal plate. The structural member 10 is formed of, for example, a steel plate. The steel plate preferably has a tensile strength of 590 MPa or more. The steel plate more preferably has a tensile strength of 980 MPa or more, and still more preferably has a tensile strength of 1180 MPa or more. The plate thickness of the structural member 10 is, for example, 0.8 mm or more, preferably 1.0 mm or more. The plate thickness of the structural member 10 is, for example, 4.0 mm or less, preferably 3.0 mm or less.

[0057] The structural member 10 includes a member body 11, a flange 12, and a corner portion 13. The member body 11, the flange 12, and the corner portion 13 are integrally formed. The corner portion 13 is disposed between the member body 11 and the flange 12. That is, the flange 12 is continuously provided with the member body 11 via the corner portion 13. Hereinafter, the flange 12 will be referred to as the continuous flange 12.

[0058] Refer to Figure 1 and Figure 2 , the member body 11 has, for example, a substantially hat-shaped cross section. The member body 11 includes a top plate 111, ridge line portions 112, 113, and longitudinal walls 114, 115. The member body 11 further includes flange portions 116, 117.

[0059] The surface of the top plate 111 includes a flat surface 111a. The flat surface 111a is a part of the top plate 111 that becomes a reference surface for operations when the structural member 10 is mounted or assembled to, for example, an automobile body. The flat surface 111a has a flat shape and substantially does not include a curved surface. In the example of the present embodiment, the periphery of a through hole 111b that penetrates the top plate 111 in the plate thickness direction becomes the flat surface 111a.

[0060] The ridge line portions 112, 113 are provided on both sides of the top plate 111. The ridge line portion 112 extends along the edge of the top plate 111. In the example of the present embodiment, when the structural member 10 is viewed from above, that is, when the structural member 10 is observed from the side of the top plate 111, the ridge line portion 112 includes a bent portion. The ridge line portion 113 extends along the edge of the top plate 111 on the opposite side of the ridge line portion 112. In Figure 1 and Figure 2In the example shown, the distance between the ridge portions 112 and 113 when looking down at the structural member 10, that is, the width of the top plate 111, is smaller on one side in the length direction of the member main body 11 and larger on the other side. The ridge portions 112 and 113 can each be seen to substantially have an arc shape in a cross-section (transverse section) perpendicular to their extending directions.

[0061] The longitudinal wall 114 is connected to the top plate 111 by means of the ridge portion 112. The longitudinal wall 115 is connected to the top plate 111 on the opposite side of the longitudinal wall 114 by means of the ridge portion 113. The longitudinal walls 114 and 115 can either stand upright perpendicular to the flat surface 111a of the top plate 111 or be inclined with respect to the direction perpendicular to the flat surface 111a. The longitudinal walls 114 and 115 can also, for example, separate from each other as they are farther away from the top plate 111.

[0062] The flange portion 116 is connected to one longitudinal wall 114 on the opposite side of the top plate 111. The flange portion 117 is connected to the other longitudinal wall 115 on the opposite side of the top plate 111. The flange portions 116 and 117 respectively project from the longitudinal walls 114 and 115 toward the outside of the structural member 10. The flange portions 116 and 117 respectively extend along the longitudinal walls 114 and 115.

[0063] Continue to refer to Figure 1 and Figure 2 The continuous flange 12 is connected to the member main body 11 by means of the corner portion 13. The corner portion 13 has a curved shape that is recessed inward when looking down at the structural member 10. The corner portion 13 can also have an arc shape when looking down at the structural member 10. The radius of curvature of the corner portion 13 is, for example, 100 mm or less. The radius of curvature of the corner portion 13 is preferably 50 mm or less, and more preferably 30 mm or less. There is no particular regulation for the lower limit value, but the radius of curvature of the corner portion 13 is preferably 1 mm or more.

[0064] The continuous flange 12 includes a top plate 121, a ridge portion 122, and a longitudinal wall 123. The continuous flange 12 also includes a flange portion 124.

[0065] The top plate 121 is continuous with the top plate 111 of the member main body 11 on the outside of the bend of the corner portion 13. The ridge portion 122 extends along one end edge of the top plate 121. The ridge portion 122 can be seen to substantially have an arc shape when observed in a cross-section (transverse section) perpendicular to its extending direction. The ridge portion 122 is connected to one ridge portion 112 of the member main body 11 by means of the corner portion 13. When looking down at the structural member 10, the ridge portion 122 of the continuous flange 12 is bent with respect to the ridge portion 112 of the member main body 11.

[0066] At least a portion of the ridge line portion 112 of the member main body 11 that is adjacent to the corner portion 13 is substantially linear when looking down at the structural member 10. Similarly, at least a portion of the ridge line portion 122 of the continuous flange 12 that is adjacent to the corner portion 13 is substantially linear when looking down at the structural member 10. In the present embodiment, "substantially linear" includes not only a complete straight line but also a curve that is regarded as a straight line due to a large radius of curvature. For example, a curve extending with a radius of curvature of 200 mm or more is regarded as a straight line. Although not particularly limited, the extension length of the ridge line portion 122 when looking down at the structural member 10 may be, for example, 15 mm or more.

[0067] The longitudinal wall 123 is connected to the top plate 121 by means of the ridge line portion 122. The longitudinal wall 123 is connected to one longitudinal wall 114 of the member main body 11 by means of the corner portion 13. When looking down at the structural member 10, the longitudinal wall 123 of the continuous flange 12 is bent with respect to the longitudinal wall 114 of the member main body 11.

[0068] The flange portion 124 is connected to the longitudinal wall 123 on the opposite side of the top plate 121. The flange portion 124 protrudes from the longitudinal wall 123 toward the outside of the structural member 10. The flange portion 124 is continuous with one flange portion 116 of the member main body 11.

[0069] Figure 3 is a side view of the structural member 10. In Figure 3 shows a view of the structural member 10 observed from the side of the continuous flange 12. As Figure 3 shown, when looking at the structural member 10 from the side, the top plate 121 of the continuous flange 12 is inclined with respect to the horizontal plane. The horizontal plane refers to a plane that is the same plane as the flat surface 111a of the top plate 111 of the member main body 11 or a plane parallel to the flat surface 111a. In addition, the direction perpendicular to such a plane is called the vertical direction.

[0070] In the example of the present embodiment, the top plate 121 of the continuous flange 12 is inclined with respect to the horizontal plane in such a manner that the distance in the vertical direction from the ridge line portion 122 and the longitudinal wall 123 increases as it goes from the edge on the side of the ridge line portion 122 toward the opposite edge (free edge). When looking at the structural member 10 from the side, the surface of the top plate 121 is an inclined surface that rises as it approaches the free edge. However, the top plate 121 may also be substantially horizontal when looking at the structural member 10 from the side.

[0071] At least a part of the top plate 111 of the member main body 11 that is continuous with the top plate 121 of the continuous flange 12 can be inclined with respect to the horizontal plane in the same manner as the top plate 121 of the continuous flange 12. In the example of the present embodiment, the top plate 111 of the member main body 11 is inclined with respect to the horizontal plane so as to rise as it approaches the continuous flange 12 side from the vicinity of the middle in its longitudinal direction. However, when the top plate 121 of the continuous flange 12 is substantially horizontal, the part of the top plate 111 of the member main body 11 that is continuous with the top plate 121 of the continuous flange 12 can also be made substantially horizontal.

[0072] [Manufacturing method of structural member]

[0073] Hereinafter, while referring to Figures 4A to 4G the manufacturing method of the structural member 10 will be described. Figures 4A to 4G is a schematic diagram for explaining the manufacturing method of the structural member 10. The manufacturing method of the structural member 10 includes a preparation process and a forming process. The structural member 10 is manufactured by cold press forming.

[0074] (Preparation process)

[0075] The preparation process is a process of preparing a raw material made of a metal plate. The raw material can be a steel plate having a tensile strength of, for example, 590 MPa or more, preferably 980 MPa or more, and more preferably 1,180 MPa or more. The raw material can also be, for example, a blank in the shape obtained by unfolding the structural member 10 ( Figures 1 to 3 ). Such a blank can be formed by performing blanking on a metal strip (coil) using a die of the target shape. Alternatively, the blank can also be formed by performing laser blanking on the coil. The raw material can also be, for example, a preformed body formed by performing preforming on the blank.

[0076] In addition, as long as a flat tensile test piece of the entire thickness is collected from the top plate 111 ( Figures 1 to 3 ) of the structural member 10 and a tensile test is performed, it is possible to confirm that a steel plate having a tensile strength of 590 MPa or more, preferably 980 MPa or more, and more preferably 1,180 MPa or more is used as the raw material. This is because the influence of plastic working can be ignored in the top plate 111 of the structural member 10, and it is in the state of the raw material immediately before the manufacturing process of the structural member 10.

[0077] (Forming process)

[0078] In the forming process, cold pressing is performed on the raw material using the die 20 shown in Figures 4A to 4C to perform forming. First, the structure of the die 20 will be described.

[0079] In the present embodiment, a part on one side (continuous flange 12 side) in the width direction of the forming structure member 10 in the mold 20 will be mainly described. For a part on the other side (opposite side of the continuous flange 12) in the width direction of the forming structure member 10 in the mold 20, since it is not particularly different from a general mold for stamping and forming a structure member having a cap shape in cross-sectional view, the description thereof is omitted in the present embodiment.

[0080] Figure 4A is a perspective view of the mold 20. As Figure 4A shown, the mold 20 includes a lower die 21, an upper die 22, and a blank holder 23. The lower die 21 is a punch, and the upper die 22 is a die corresponding to the lower die 21. At the start of the forming process, the lower die 21 is disposed opposite to the upper die 22 and the blank holder 23. The lower die 21 is disposed, for example, below the upper die 22 and the blank holder 23. The lower die 21, the upper die 22, and the blank holder 23 are mounted on a known press (not shown), for example. The upper die 22 and the blank holder 23 can approach the lower die 21 relatively. Hereinafter, the direction in which the lower die 21 approaches the upper die 22 and the blank holder 23 relatively will be referred to as the stamping direction.

[0081] The lower die 21 includes a first lower die 211 and a second lower die 212. The first lower die 211 is a part of the lower die 21 that is mainly used for forming the member main body 11 ( Figures 1 to 3 ) of the forming structure member 10. The second lower die 212 is a part of the lower die 21 that is mainly used for forming the continuous flange 12 ( Figures 1 to 3 ) of the forming structure member 10. The second lower die 212 is separated from the first lower die 211.

[0082] The first lower die 211 includes a top surface 211a, a shoulder 211b, and a side surface 211c. The first lower die 211 further includes a flange surface 211d.

[0083] The top surface 211a is a surface that intersects the stamping direction. The top surface 211a is a surface that is mainly used for forming the top plate 111 ( Figures 1 to 3 ) of the member main body 11. Therefore, the top surface 211a has a shape corresponding to the top plate 111.

[0084] The shoulder 211b extends along the edge of the top surface 211a. The shoulder 211b is a surface that is mainly used for forming the ridge line portion 112 ( Figures 1 to 3 ) of the member main body 11. Therefore, the shoulder 211b has a shape corresponding to the ridge line portion 112.

[0085] The side surface 211c is connected to the top surface 211a via the shoulder 211b. The side surface 211c is a surface that is mainly used for forming the longitudinal wall 114 ( Figures 1 to 3)'s surface. Therefore, the side surface 211c has a shape corresponding to the longitudinal wall 114.

[0086] The flange surface 211d is connected to the side surface 211c on the opposite side of the top surface 211a. The flange surface 211d is mainly the surface for forming the flange portion 116 ( Figures 1 to 3 ) of the forming member main body 11 and the flange portion 124 ( Figures 1 to 3 ) of the continuous flange 12. Therefore, the flange surface 211d has a shape corresponding to the flange portions 116 and 124.

[0087] The second lower die 212 includes a top surface 212a, a shoulder 212b, and a side surface 212c.

[0088] The top surface 212a is a surface intersecting the stamping direction. The top surface 212a is mainly the surface for forming the top plate 121 ( Figures 1 to 3 ) of the continuous flange 12 of the forming structural member 10. Therefore, the top surface 212a has a shape corresponding to the top plate 121.

[0089] The shoulder 212b extends along the edge of the top surface 212a. The shoulder 212b is mainly the surface for forming the ridge line portion 122 ( Figures 1 to 3 ) of the continuous flange 12. Therefore, the shoulder 212b has a shape corresponding to the ridge line portion 122.

[0090] The side surface 212c is connected to the top surface 212a by means of the shoulder 212b. The side surface 212c is mainly the surface for forming the longitudinal wall 123 ( Figures 1 to 3 ) of the continuous flange 12. Therefore, the side surface 212c has a shape corresponding to the longitudinal wall 123.

[0091] The lower die 21 further includes a corner portion 213. The corner portion 213 has a shape that is recessed inward of the lower die 21 when viewed from the stamping direction. The corner portion 213 is disposed between the shoulder 211b and the side surface 211c of the first lower die 211 and the shoulder 212b and the side surface 212c of the second lower die 212. The shoulder 211b and the side surface 211c of the first lower die 211 are adjacent to the corner portion 213. The shoulder 212b and the side surface 212c of the second lower die 212 are adjacent to the corner portion 213 on the opposite side of the shoulder 211b and the side surface 211c of the first lower die 211. When viewed from the stamping direction, the shoulder 212b and the side surface 212c of the second lower die 212 are disposed in a manner that is bent with respect to the shoulder 211b and the side surface 211c of the first lower die 211.

[0092] When viewed from the stamping direction, the corner portion 213 has a radius of curvature of, for example, 100 mm or less. When viewed from the stamping direction, the radius of curvature of the corner portion 213 is preferably 50 mm or less, more preferably 30 mm or less. There is no particular limitation on the lower limit value, but the radius of curvature of the corner portion 213 is preferably 1 mm or more. At least a portion of the shoulder 211b of the first lower die 211 that is adjacent to the corner portion 213 is substantially linear when viewed from the stamping direction. Similarly, at least a portion of the shoulder 212b of the second lower die 212 that is adjacent to the corner portion 213 is substantially linear when viewed from the stamping direction.

[0093] Figure 4B FIG. is a view of the lower die 21 when viewed along the stamping direction from the top surface 211a, 212a side. Refer to Figure 4B , at least a part of the corner portion 213 preferably is included in the second lower die 212 corresponding to the continuous flange 12 ( Figures 1 to 3 ). In other words, when the lower die 21 is viewed along the stamping direction, the dividing line 214 between the first lower die 211 and the second lower die 212 is preferably positioned within the range from the end (rounding R end) on the second lower die 212 side of the corner portion 213 to the end (rounding R end) on the first lower die 211 side. When viewed from the stamping direction, the dividing line 214 may, for example, cross the corner portion 213 within the range from the center in the extending direction of the corner portion 213 to the end (rounding R end) on the first lower die 211 side. However, the dividing line 214 may also cross the corner portion 213 at a position closer to the second lower die 212 side than the center in the extending direction of the corner portion 213 when viewed from the stamping direction. When viewed from the stamping direction, the dividing line 214 may, for example, extend substantially parallel to the edge of the continuous flange 12 ( Figures 1 to 3 ).

[0094] The lower die 21 is divided into a first lower die 211 and a second lower die 212 at the position of the dividing line 214. Before the forming process starts, the second lower die 212 retracts relative to the first lower die 211. More specifically, when viewed from the stamping direction, the first lower die 211 and the second lower die 212 are arranged such that the shoulder 212b and the side surface 212c of the second lower die 212 are in a position retracted relative to the shoulder 211b and the side surface 211c of the first lower die 211.

[0095] Return [[ID=, the upper die 22 and the blank holder 23 are arranged in a manner opposite to the lower die 21 in the stamping direction. The upper die 22 is, for example, mounted on a slide block (not shown) that can be lifted and lowered in a press. The blank holder 23 is connected to the slide block by, for example, a telescopic elastic member (not shown). The blank holder 23 mainly faces the top surface 211a of the first lower die 211. For the top surface 212a of the second lower die 212, it is mainly the forming surface 221 of the upper die 22 that faces it. The forming surface 221 of the upper die 22 has a shape corresponding to the shoulder 211b, side surface 211c, and flange surface 211d of the first lower die 211, the top surface 212a, shoulder 212b, and side surface 212c of the second lower die 212, and the corner 213.

[0096] ​ is a view of the upper die 22 and the blank holder 23 as observed along the stamping direction. Refer to ​ , when observed from the stamping direction, the dividing line 24 between the upper die 22 and the blank holder 23 is preferably arranged at the position of the corner 213 ( ​ ) or near the corner 213. The dividing line 24 between the upper die 22 and the blank holder 23 may also be located at the same position as the dividing line 214 ( ​ ) between the first lower die 211 and the second lower die 212 when viewed from the stamping direction, or may be arranged deviating from the dividing line 214 toward the first lower die 211 side or the second lower die 212 side. Similar to the dividing line 214 of the lower die 21, the dividing line 24 is, for example, positioned within the range from the end (rounding R terminal) on the second lower die 212 side of the corner 213 to the end (rounding R terminal) on the first lower die 211 side. However, the dividing line 24 may also be arranged slightly beyond the corner 213 on the second lower die 212 side. The dividing line 24 may also extend substantially in the normal direction of the corner 213 or the shoulder 212b of the second lower die 212 when viewed from the stamping direction.

[0097] In the forming process, cold pressing is performed on the raw material using the mold 20 configured as described above to carry out forming. The forming process includes a first process and a second process.

[0098] Refer to ​ , at the start of the forming process, the upper die 22 and the blank holder 23 mounted on the slide block (not shown) of the press are at the top dead center. At this time, the second lower die 212 is arranged in a position retracted relative to the first lower die 211 when viewed from the stamping direction.

[0099] ​ is a view schematically showing the ​ IVD-IVD cross-section. As shown in ​As shown, before starting the forming process, the second lower die 212 is arranged in a manner that separates from the flange surface 211d of the first lower die 211 in the lateral direction. When the mold 20 is in a sectional view, the second lower die 212 is arranged at a gap G from the first lower die 211. The second lower die 212 is mounted on a press (not shown) by means of a cam mechanism 25. The cam mechanism 25 includes a cam driver 251 for moving the second lower die 212.

[0100] Referring to ​ , in the first forming process, in the arranged state of the second lower die 212 as described above, the upper die 22 and the blank holder 23 are relatively approximated in the stamping direction with respect to the lower die 21, and the raw material M arranged between the upper die 22, the blank holder 23 and the lower die 21 is clamped by the blank holder 23 and the first lower die 211 and the raw material M is pressed. The blank holder 23 presses the raw material M prior to the upper die 22. The blank holder 23 and the top surface 211a of the first lower die 211 press the raw material M together. On the other hand, the raw material M is not substantially pressed between the blank holder 23 and the top surface 212a of the second lower die 212. That is, in the raw material M, the portion mainly located on the top surface 211a of the first lower die 211 is pressed by the blank holder 23, while the portion of the raw material M located on the top surface 212a of the second lower die 212 is not pressed or hardly pressed by the blank holder 23 at all.

[0101] In the second forming process, in the state where the raw material M is pressed by the blank holder 23 and the first lower die 211, the upper die 22 is relatively approximated in the stamping direction with respect to the lower die 21, and the raw material M is clamped by the upper die 22 and the first lower die 211. Further, the second lower die 212 is moved so that the side surface 212c of the second lower die 212 is aligned with the side surface 211c of the first lower die 211 when viewed from the stamping direction, and the raw material M is clamped by the upper die 22 and the second lower die 212. The state where the side surface 212c of the second lower die 212 is aligned with the side surface 211c of the first lower die 211 means that the height difference (height difference) between the adjacent side surfaces 211c and 212c becomes, for example, 0.5 mm or less.

[0102] More specifically, while maintaining the state where the raw material M on the top surface 211a of the first lower die 211 is pressed by the blank holder 23 unchanged, the upper die 22 is further relatively approximated in the stamping direction with respect to the first lower die 211 and the second lower die 212. Thus, as ​ shown, the raw material M is pressed down by the upper die 22. At the initial stage of the second process, the raw material M is not clamped by the upper die 22, the blank holder 23 and the second lower die 212. Therefore, at the position of the second lower die 212, the raw material M is pressed down by the upper die 22 and is stretched toward the flange surface 211d side, thereby promoting the flow of the material from the top surface 212a side to the side surface 212c side.

[0103] As ​As shown, the cam driver 251 of the cam mechanism 25 operates at the end of the second process. For example, as the cam driver 251 descends in the stamping direction, the second lower die 212 is moved in a direction perpendicular to the stamping direction. For example, the second lower die 212 starts to move due to the cam mechanism 25 just before the upper die 22 reaches the bottom dead center. As ​ shown, for example, when the upper die 22 reaches the bottom dead center, the second lower die 212 reaches the position of the first lower die 211 and stops, and the second lower die 212 and the upper die 22 clamp the raw material M together. At the bottom dead center, the gap between the flange surface 211d of the first lower die 211 and the second lower die 212 substantially disappears. Also, at the bottom dead center, the gap between the upper die 22 and the raw material M and the gap between the raw material M and the first lower die 211 and the second lower die 212 substantially disappear, and the raw material M is stamped by the upper die 22 and the lower die. Thereby, the formed structural member 10 ( ​ ).

[0104] The moving distance (cam stroke) of the second lower die 212 in the second forming process is preferably 9.0 times or less the thickness of the raw material M. The moving distance of the second lower die 212 can also be, for example, 2.0 times or more the thickness of the raw material M. The thickness of the raw material M is, for example, 0.8 mm or more and 4.0 mm or less, preferably 1.0 mm or more and 3.0 mm or less. The moving distance of the second lower die 212 is equal to the gap G between the second lower die 212 and the first lower die 211 at the start of forming ( ​ ).

[0105] The forming process described in this embodiment may be included in the manufacturing process until the structural member 10 obtains the shape of the final product. In the case where the manufacturing process includes a plurality of forming processes, the forming process described in this embodiment may be the first forming process, the intermediate forming process, or the final forming process.

[0106] [Effect]

[0107] In the manufacturing method of the structural member 10 according to the present embodiment, at the start of the forming process, the first lower die 211 and the second lower die 212 are arranged such that the position of the side surface 212c of the second lower die 212 retreats relative to the position of the side surface 211c of the first lower die 211 when viewed from the stamping direction. Therefore, when the upper die 22 and the blank holder 23 are relatively approximated to the first lower die 211 and the second lower die 212, the raw material M is not restricted at the position of the second lower die 212. The second lower die 212 starts clamping the raw material M together with the upper die 22 from the latter stage of the forming process to form the continuous flange 12. By not restricting the continuous flange 12 until the latter stage of the forming process in this way, the flow of the material is promoted in the continuous flange 12. More specifically, in the state where the second lower die 212 does not restrict the continuous flange 12, the upper die 22 presses down the continuous flange 12 to apply tension, so that the material can be promoted to flow from the top plate 121 of the continuous flange 12 into the longitudinal wall 123. Therefore, the strain generated in the continuous flange 12 can be dispersed, and the generation of cracks in the continuous flange 12 can be suppressed.

[0108] In the present embodiment, in the second forming process, the second lower die 212 moves from the position where the side surface 212c of the second lower die 212 retreats relative to the side surface 211c of the first lower die 211 when viewed from the stamping direction to the position aligned with the side surface 211c. The moving distance of the second lower die 212 is preferably 9.0 times or less the plate thickness of the raw material M. Thereby, the generation of wrinkles in the structural member 10 in the second forming process can be suppressed.

[0109] In the present embodiment, the second lower die 212 for forming the continuous flange 12 preferably includes at least a part of the corner portion 213. That is, the dividing line 214 between the first lower die 211 and the second lower die 212 is preferably arranged on the first lower die 211 side relative to the end (rounding R end) on the second lower die 212 side of the corner portion 213. Since at least a part of the corner portion 213 is included in the second lower die 212, the restriction of the raw material M at the position of the corner portion 213 can be reduced. That is, the part of the corner portion 213 that becomes a part of the second lower die 212 does not restrict the raw material M until the latter stage of the forming process. Therefore, the bending of the continuous flange 12 in the middle of the forming process becomes gentle, and the strain of the continuous flange 12 can be reduced. As a result, it is more difficult to generate cracks in the continuous flange 12.

[0110] In the present embodiment, the blank holder 23 is preferably configured to press the raw material M on the outer side of the bend of the corner portion 213 of the lower die 21. In this case, the generation of wrinkles in the raw material M at the position of the corner portion 213 can be prevented.

[0111] In the structural member 10 of the present embodiment, the top plate 121 of the continuous flange 12 is inclined with respect to the flat surface 111a in the top plate 111 of the member body 11. In the die 20 for forming the structural member 10, the top surface 212a of the second lower die 212 corresponding to the top plate 121 of the continuous flange 12 is also inclined with respect to the surface perpendicular to the stamping direction. The top surface 212a of the second lower die 212 is inclined with respect to the surface perpendicular to the stamping direction so as to be lower on the shoulder 212b side and higher on the side opposite to the shoulder 212b. In this case, in the forming process, the material more easily flows from the top surface 212a side of the second lower die 212 toward the shoulder 212b and the side surface 212c side, and generation of local strain and cracks in the continuous flange 12 can be further suppressed.

[0112] In the structural member 10 of the present embodiment, the continuous flange 12 is continuously provided with respect to the member body 11. By providing the continuous flange 12, the impact absorption performance of the structural member 10 can be improved. Further, in the present embodiment, the continuous flange 12 is connected to the member body 11 by a corner portion 13 having a relatively small radius of curvature of, for example, 100 mm or less. Thereby, a relatively large flat surface portion is ensured in the continuous flange 12, and thus, it is easy to form, for example, a spot weld in the continuous flange 12, which is advantageous when joining the continuous flange 12 to other members. However, when the radius of curvature of the corner portion 13 is small, cracks are likely to occur in the continuous flange 12 when forming the structural member 10. In contrast, in the manufacturing method of the present embodiment, as described above, the continuous flange 12 is not restricted until the later stage of the forming process, and the strain of the continuous flange 12 can be dispersed. Therefore, even when the radius of curvature of the corner portion 13 is small, generation of cracks in the continuous flange 12 can be suppressed.

[0113] ​ is an enlarged view of the continuous flange 12 of the structural member 10. Refer to ​, the structural member 10 manufactured by the manufacturing method of the present embodiment is characterized in the hardness distribution of the continuous flange 12. More specifically, in the cross-section obtained by cutting along the plate thickness direction of the top plate 121 at the boundary 125 between the top plate 121 and the ridge line portion 122 of the continuous flange 12, when the Vickers hardness measured at the end E1 on the opposite side of the corner 13 is set as HV1 [Hv] and the Vickers hardness measured at the end E2 on the corner 13 side is set as HV2 [Hv], the difference between the two: HV1 - HV2 becomes 30 Hv or less (however, HV1 ≥ HV2). This means that the strain of the continuous flange 12 generated when forming the structural member 10 is dispersed along the ridge line portion 122. In this case, when a load is input to the structural member 10 and further strain is generated in the continuous flange 12, it is possible to prevent, for example, cracks from occurring starting from the edge of the continuous flange 12. Therefore, when the structural member 10 is used for an automobile body, the structural member 10 can exhibit excellent collision resistance performance. HV1 - HV2 is preferably 20 Hv or less.

[0114] The Vickers hardness HV1 and HV2 of the cross-section of the continuous flange 12 can be measured as follows. That is, first, the structural member 10 is cut by laser along the boundary 125 between the top plate 121 and the ridge line portion 122, and a part of the structural member 10 is collected. Next, the collected part is cut with an underwater cutter, and resin filling and polishing are performed in such a way that the cross-section of the continuous flange 12 (the cross-section along the boundary 125 between the top plate 121 and the ridge line portion 122) is disposed on the surface to produce a test piece for hardness measurement. And, using this test piece and a commercially available measuring instrument (fully automatic Vickers hardness tester HV-100, manufactured by Mitutoyo Corporation), a Vickers hardness test is performed in accordance with JIS Z 2244. For example, the test force is set as 294.2 N (the value of HV30), and the holding time of the test force is set as 15 s to measure the Vickers hardness. In the cross-section included in the test piece, the Vickers hardness is measured at a position that is 1 / 4 of the plate thickness from the surface of the top plate 121. In the cross-section of the continuous flange 12, the Vickers hardness measured at the end E2 on the corner 13 side is HV2 [Hv], and the Vickers hardness measured at the end E1 on the opposite side of the corner 13 (the edge side of the continuous flange 12) is HV1 [Hv].

[0115] <Second Embodiment>

[0116] ​ is a perspective view of the structural member 10A of the second embodiment. Refer to ​ , the structural member 10A of the present embodiment has the same as the structural member 10 of the first embodiment ( ​) has the same structure. However, the structural member 10A is different from the structural member 10 of the first embodiment in that the member body 11 does not include the ridge line portion 113, the longitudinal wall 115, and the flange portion 117. In the structural member 10A, the member body 11 includes the ridge line portion 112, the longitudinal wall 114, and the flange portion 116 on the side of the continuous flange 12.

[0117] The member body 11, like that of the first embodiment, includes a flat surface 111a and a through hole 111b in its top plate 111. However, the flat surface 111a is different from that of the first embodiment in that it is concave with respect to the other parts of the top plate 111. The flat surface 111a, like that of the first embodiment, is the part that becomes the reference surface for operations when the structural member 10A is mounted or assembled to, for example, an automobile body. The flat surface 111a is a surface perpendicular to the stamping direction.

[0118] ​ is a side view of the structural member 10A. In ​ shows a view of the structural member 10A observed from the side of the continuous flange 12. As ​ shown, when the structural member 10A is viewed from the side, the top plate 121 of the continuous flange 12 is inclined with respect to the horizontal plane. The definition of the horizontal plane is as described in the first embodiment.

[0119] The structural member 10A of the present embodiment can also be manufactured by the manufacturing method described in the first embodiment.

[0120] The embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above embodiments, and various changes can be made without departing from its gist.

[0121] For example, the structural members 10 and 10A of the above embodiments each include a single continuous flange 12. However, both the structural members 10 and 10A can include a plurality of continuous flanges 12. In the case of manufacturing the structural member 10 or 10A including a plurality of continuous flanges 12, the second lower die 212 that can be moved by the cam mechanism 25 can be provided in the die 20 according to each continuous flange 12.

[0122] In the case where the structural member 10 or 10A including a plurality of continuous flanges 12 is formed using the die 20, the structural member 10 or 10A can also be divided after forming. Thus, a plurality of structural members 10 or 10A each including one or more continuous flanges 12 can be manufactured by one forming process.

[0123] In the above-described embodiment, the following example was described: with the die 20 installed on the press, the upper die 22 and the blank holder 23 are disposed above the lower die 21, and the upper die 22 and the blank holder 23 move toward the lower die 21. However, conversely to the above-described embodiment, the upper die 22 and the blank holder 23 may be disposed below the lower die 21. Additionally, it may be that the upper die 22 and the blank holder 23 approach the lower die 21 relatively in the stamping direction by moving the lower die 21 toward the upper die 22 and the blank holder 23.

[0124] In the above-described embodiment, an example in which the second lower die 212 moves in a direction perpendicular to the stamping direction in the second forming step was described. However, the moving direction of the second lower die 212 is not limited thereto. The moving direction of the second lower die 212 may also be inclined with respect to the direction perpendicular to the stamping direction. The moving direction of the second lower die 212 can be set, for example, within a range of ±30° with respect to a plane perpendicular to the stamping direction.

[0125] In the above-described embodiment, the second lower die 212 is moved by the cam mechanism 25. However, the second lower die 212 may be moved by a component other than the cam mechanism 25. It is sufficient that the second lower die 212 is configured to be movable from a position retracted with respect to the first lower die 211 to a position aligned with the first lower die 211.

[0126] Example

[0127] Hereinafter, the present disclosure will be described in more detail using examples. However, the present disclosure is not limited to the following examples.

[0128] In order to confirm the effects of the present disclosure, CAE analysis was performed using commercially available software (AutoForm Forming R8, manufactured by AutoForm) for cold press forming using the die 20 described in the above embodiment. The analysis conditions and results are shown in Table 1.

[0129] [Table 1]

[0130] Table 1

[0131] ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 1.2 1180 - - - ​ - 12.4 - ​ 1.2 1180 ​ 3 2.5 ​ ​ 10.9 0.025 ​ 1.2 1180 ​ 5 4.2 ​ ​ 10.4 0.053 ​ 1.2 1180 ​ 8 6.7 ​ ​ 10.1 0.136 ​ 1.2 1180 ​ 10 8.3 ​ ​ 10.5 0.176 ​ 1.2 1180 ​ 12 10.0 ​ ​ 11.5 0.216 ​ 1.2 1180 ​ 3 2.5 ​ ​ 11.4 0.026 ​ 1.2 1180 ​ 5 4.2 ​ ​ 11.9 0.030 ​ 1.2 1180 ​ 3 2.5 ​ ​ 8.9 0.157 ​ 1.2 1180 ​ 5 4.2 ​ ​ 9.2 0.145 ​ 1.2 1180 ​ 10 8.3 ​ ​ 10.3 0.054 ​ 1.5 1180 - - - ​ - 13.7 - ​ 1.5 1180 ​ 5 3.3 ​ ​ 10.8 0.029 ​ 2.0 1180 - - - ​ - 16.5 - ​ 2.0 1180 ​ 6 3.0 ​ ​ 11.7 0.042 ​ 1.2 590 - - - ​ - 15.2 - ​ 1.2 590 ​ 10 8.3 ​ ​ 13.4 0.120

[0132] In Table 1, the "split position" indicates the position of the split line 214 between the first lower die 211 and the second lower die 212. When the split position is the "center of fillet R", as ​ shown, it means that the split line 214 extends from the midpoint between the two ends in the extending direction of the corner 213 (the two fillet R terminals when viewed from the stamping direction). When the split position is the "start of fillet R", as ​As shown, it means that the dividing line 214 extends from the end on the side of the second lower die 212 (round corner R terminal) among the two ends in the extending direction from the corner 213. When the dividing position is "the end of the round corner R", as ​ shown, it means that the dividing line 214 extends from the end on the side of the first lower die 211 (round corner R terminal) among the two ends in the extending direction from the corner 213.

[0133] The "cam stroke" in Table 1 is the distance that the second lower die 212 has moved in the latter stage of the forming process.

[0134] Regarding the "cracks" in Table 1, the evaluation was carried out using the maximum plate thickness reduction rate of the edge of the continuous flange 12. For the examples and comparative examples with a tensile strength of 1180 MPa, when the maximum plate thickness reduction rate is 11.0% or less, it is rated as good (no cracks); when it is greater than 11.0% and less than 12.0%, it is rated as acceptable (few cracks); when it is 12.0% or more, it is rated as unacceptable (cracks present). On the other hand, for the examples and comparative examples with a tensile strength of 590 MPa, when the maximum plate thickness reduction rate is 14.0% or less, it is rated as good (no cracks); when it is greater than 14.0% and less than 15.0%, it is rated as acceptable (few cracks); when it is 15.0% or more, it is rated as unacceptable (cracks present).

[0135] Regarding the "wrinkles" in Table 1, the evaluation was carried out based on the value of the wrinkles in the analysis software. When the value of the wrinkles is 0.150 or less, it is rated as good (no wrinkles); when it is greater than 0.150 and less than 0.200, it is rated as acceptable (few wrinkles); when it is 0.200 or more, it is rated as unacceptable (many wrinkles).

[0136] As shown in Table 1, in each of the examples where the first lower die 211 and the second lower die 212 are divided and the second lower die 212 does not restrain the continuous flange 12 until the latter stage of the forming process, compared with the comparative example where the first lower die 211 is not divided from the second lower die 212 and restrains the continuous flange 12 from an earlier stage of the forming process, cracks in the continuous flange 12 are suppressed.

[0137] As shown in Table 1, in Examples 1 to 4 and 6 to 13, the moving distance (cam stroke) of the second lower die 212 is 9.0 times or less the plate thickness of the raw material. On the other hand, in Example 5, the cam stroke is greater than 9.0 times the plate thickness of the raw material. In Example 5, compared with Examples 1 to 4 and 6 to 13, many wrinkles are generated in the structural member. That is, in this analysis, it can be confirmed that when the cam stroke is 9.0 times or less the plate thickness of the raw material, the generation of wrinkles is suppressed.

[0138] The evaluation of cracks in the embodiment where the dividing position between the first lower die 211 and the second lower die 212 is "rounding R start" is acceptable. In contrast, in the embodiments of "rounding R center" and "rounding R end", the evaluation of cracks in most embodiments is good, and the cracks in the continuous flange 12 are improved. Therefore, it can be said that in order to further suppress the generation of cracks in the continuous flange 12, the dividing line 214 between the first lower die 211 and the second lower die 212 is preferably located in the middle in the extending direction of the corner 213 or at a position closer to the first lower die 211 than the middle.

[0139] For the test pieces that had undergone strain, the Vickers hardness test was actually carried out in the order described in the above embodiment, and the correlation between the Vickers hardness measured in the Vickers hardness test and the strain calculated from the plate thickness reduction rate of the test pieces was obtained. And based on this correlation, the conversion from the equivalent plastic strain obtained by this analysis to the Vickers hardness was carried out for Comparative Example 1, Example 1, Example 2, and Example 8 shown in Table 1. ​ It is a chart showing the relationship between the Vickers hardness in the cross section of the junction 125 between the top plate 121 and the ridge line portion 122 and the distance from the edge of the continuous flange ( ​ the shown end E1) for Comparative Example 1, Example 1, Example 2, and Example 8. Comparative Example 1, Example 1, Example 2, and Example 8 are all structural members formed of a steel plate with a tensile strength of 1180 MPa. As ​ shown, in Comparative Example 1, the farther away from the edge E1 of the continuous flange, the smaller the Vickers hardness. On the other hand, in Example 1, Example 2, and Example 8, if the distance from the edge E1 of the continuous flange is increased, the Vickers hardness becomes smaller, but the degree of change in the Vickers hardness of these embodiments is intentionally made smaller than the degree of change in the Vickers hardness of Comparative Example 1.

[0140] In Comparative Example 1, the Vickers hardness at the rounding R start ( ​ the shown end E2) of the corner 13 is significantly smaller than the Vickers hardness at the edge E1 of the continuous flange. In Comparative Example 1, the difference between the Vickers hardness at the edge E1 of the continuous flange and the Vickers hardness at the rounding R start E2 of the corner 13 is 49 Hv.

[0141] On the other hand, in Example 1, Example 2, and Example 8, the Vickers hardness at the rounding R start E2 of the corner 13 is not reduced as much as the Vickers hardness at the edge E1 of the continuous flange. The difference between the Vickers hardness at the edge E1 of the continuous flange and the Vickers hardness at the rounding R start E2 of the corner 13 is 9 Hv in Example 1, 13 Hv in Example 2, and 25 Hv in Example 8.

[0142] Thus, it was confirmed that the difference in Vickers hardness between the edge E1 of the continuous flange and the starting point E2 of the rounded corner R of the corner 13 was significantly greater than 30 Hv in Comparative Example 1. In contrast, this difference in Vickers hardness was 30 Hv or less in each of the Examples, and the strain during forming was dispersed. In particular, in Example 1 and Example 2, the difference in Vickers hardness between the edge E1 of the continuous flange and the starting point E2 of the rounded corner R of the corner 13 was 20 Hv or less, and the strain during forming was well dispersed.

[0143] The Vickers hardness is roughly proportional to the material strength. For example, if the Vickers hardness increases by 30 Hv, the material strength increases by about 100 MPa. In Example 1, Example 2, and Example 8, the Vickers hardness did not decrease so much from the edge E1 of the continuous flange toward the starting point E2 of the rounded corner R of the corner 13, and the Vickers hardness at the starting point E2 of the rounded corner R of the corner 13 was greater than that in Comparative Example 1. Therefore, it can be said that in each of the Examples, the material strength is higher than that in Comparative Example 1, and good component performance (strength) can be exhibited as compared with Comparative Example 1.

[0144] Explanation of reference numerals

[0145] 10, 10A, structural member; 11, member body; 111, top plate; 111a, flat surface; 112, 113, ridge line portion; 114, 115, longitudinal wall; 12, flange; 121, top plate; 122, ridge line portion; 123, longitudinal wall; 13, corner; 20, die; 21, lower die; 211, first lower die; 211a, top surface; 211b, shoulder; 211c, side surface; 212, second lower die; 212a, top surface; 212b, shoulder; 212c, side surface; 22, upper die; 23, blank holder.

Claims

1. A manufacturing method, which is a manufacturing method of a structural member, wherein, this manufacturing method includes the following steps: a preparation step of preparing a raw material made of a metal plate; and a forming step of performing cold pressing on the raw material using a die including a blank holder, an upper die, and a lower die to form it, the lower die includes: a first lower die, which includes: a first top surface that intersects the stamping direction; a first shoulder that extends along the edge of the first top surface; and a first side surface that is connected to the first top surface by means of the first shoulder; a second lower die, which includes: a second top surface that intersects the stamping direction; a second shoulder that extends along the edge of the second top surface; and a second side surface that is connected to the second top surface by means of the second shoulder, and the second lower die is independent of the first lower die; and a corner portion, which is provided between the first shoulder and the first side surface and the second shoulder and the second side surface, and has a shape that is recessed inward of the lower die when viewed from the stamping direction, the forming step includes: a first step, in a state where the first lower die and the second lower die are arranged such that the second side surface is in a position retracted relative to the first side surface when viewed from the stamping direction, the blank holder and the upper die are relatively approximated in the stamping direction relative to the lower die, and the raw material is clamped and pressed by the blank holder and the first lower die; and a second step, in a state where the raw material is pressed by the blank holder and the first lower die, the upper die is further relatively approximated in the stamping direction relative to the lower die to clamp the raw material by the upper die and the first lower die, and the second lower die is moved so that the second side surface is aligned with the first side surface when viewed from the stamping direction, and the raw material is clamped by the upper die and the second lower die.

2. The manufacturing method according to claim 1, wherein, the moving distance of the second lower die in the second step is 9.0 times or less of the plate thickness of the raw material.

3. The manufacturing method according to claim 1, wherein, the second lower die further includes at least a part of the corner portion, the second shoulder and the second side surface are continuous with the corner portion.

4. The manufacturing method according to claim 1, wherein, the blank holder also presses a portion of the raw material that is adjacent to the outside of the bend of the corner portion.

5. The manufacturing method according to claim 1, wherein, the second top surface is inclined with respect to a plane perpendicular to the stamping direction such that the distance in the stamping direction from the edge on the side of the second shoulder toward the edge opposite to the second shoulder increases.

6. A structural member, wherein, this structural member includes: a member main body, which includes: a first top plate; a first ridge line portion that extends along the edge of the first top plate; and a first longitudinal wall that is connected to the first top plate by means of the first ridge line portion; and A flange, comprising: a second top plate; a second ridge portion extending along an edge of the second top plate; and a second longitudinal wall connected to the second top plate by means of the second ridge portion, The second ridge portion and the second longitudinal wall are connected to the first ridge portion and the first longitudinal wall by means of a corner portion, The second top plate is continuous with the first top plate on the outer side of the bend of the corner portion, In a cross section obtained by cutting along the plate thickness direction of the second top plate at the junction between the second top plate and the second ridge portion of the flange, the difference between the Vickers hardness measured at the end on the opposite side of the corner portion and the Vickers hardness measured at the end on the corner portion side is 30 Hv or less.

7. The structural member according to claim 6, wherein, The structural member is formed of a steel plate having a tensile strength of 590 MPa or more.

8. The structural member according to claim 6, wherein, Viewed from the side of the first top plate, the corner portion has a radius of curvature of 100 mm or less.

9. The structural member according to claim 6, wherein, The surface of the first top plate includes a flat surface, The second top plate is inclined with respect to the flat surface such that the distance from the second ridge portion and the second longitudinal wall in a direction perpendicular to the flat surface increases as it goes from the edge on the side of the second ridge portion toward the edge opposite to the second ridge portion.

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