Method for manufacturing press-molded article and method for designing mold

Abstract

Even if a high-strength material or the like is used, dimensional accuracy variation can be reduced by a simple mold structure when twisting, bending return, wall opening and material strength variation occur. A method for manufacturing a press-molded article forms a metal plate (3) into a target member shape (1) having a curved section (2) curved in the longitudinal direction in a cross-section having a top plate section (1A) and a vertical wall section (1B). The angle between the top plate part (1A) and the vertical wall part (1B) is set as a vertical wall angle. The present invention is provided with: a first step (10A) for press-forming an intermediate member (4) using a mold having a forming surface having a first vertical wall angle smaller than the vertical wall angle of a target member shape (1); and a second step (10B) for press-forming the intermediate member (4) using a die having a forming surface having a second vertical wall angle equal to or greater than the vertical wall angle of the target member shape (1). The longitudinal wall angle of the intermediate member (4) after mold release is set to a first longitudinal wall angle that is smaller than the longitudinal wall angle of the target member shape (1).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a stamped part and a method for designing a mold used therefor. The present invention relates to a technique for manufacturing a component having a top plate portion and a vertical wall portion, and having a cross-sectional shape of a target component such as a U-shape, an L-shape, or a cap-shape, by stamping. Furthermore, the target component shape has one or more curved portions that curve along a direction intersecting the cross-sectional shape, i.e., the longitudinal direction.

[0002] In this specification, the above-mentioned curved portion is bent into a desired component shape that is concave or convex toward the vertical wall portion when viewed from above, and is also referred to as a "left-right curved shape." Furthermore, the above-mentioned curved portion is bent into a desired component shape that is concave or convex toward the top plate portion, and is also referred to as a "top-down curved shape."

[0003] Furthermore, if the target component shape is a "left-right curved shape" and has a cross-sectional shape with vertical walls on both sides of the top plate in the width direction, the target component shape is as follows. Specifically, in the curved portion, if the vertical wall side of one of the left and right vertical walls is concave in a plan view, the vertical wall side of the other vertical wall is convex in a plan view. However, the vertical wall angles of the left and right vertical walls do not need to be the same.

[0004] Here, the angle between the top plate and the vertical wall in the cross-sectional shape is referred to as the vertical wall angle. Furthermore, in the mold, the angle (shoulder angle) between the top plate forming surface (molding shape) that forms the top plate and the vertical wall forming surface (molding shape) that forms the vertical wall is referred to as the vertical wall angle. Furthermore, the vertical wall angle is the angle on the inside of the bend that is less than 180 degrees. Background Art

[0005] In recent years, the use of high-strength materials with strengths exceeding 590 MPa in vehicle body components has been promoted to balance improved collision safety and lightweighting. Furthermore, the use of ultra-high-strength materials with strengths exceeding 980 MPa in vehicle body components has been promoted. High-strength and ultra-high-strength materials have high yield and tensile strengths. Therefore, when using these materials in vehicle body components, forming defects such as springback become a problem during stamping.

[0006] As one of the stamped products used for vehicle body structural parts, there is a part of the following shape. This part has a cross-sectional shape in which the top plate portion and the longitudinal wall portion are continuous in the cross-sectional direction, and a portion of the longitudinal direction is bent in the width direction of the top plate portion when viewed from above. The inventors have obtained the following insight: when such a part is stamped, at the bottom dead point of forming, compressive stress is generated on the curved outer side (convex side) of the longitudinal wall portion, and tensile stress is generated on the curved inner side (concave side) of the longitudinal wall portion. Furthermore, the inventors have obtained the following insight: due to these stresses, rebound including torsion occurs in the part after demolding. In particular, when ultra-high strength materials are used as the material of the part, the stress at the bottom dead point of forming becomes larger, resulting in the problem of increased rebound.

[0007] The inventors also discovered that even in vertically curved parts, tensile stress is generated in the top plate and compressive stress is generated in the flange at the bottom dead center of forming. These stresses cause springback, including camber back, in the part after demolding. Therefore, similar findings were obtained for vertically curved parts. Furthermore, vertically curved parts also present similar challenges.

[0008] Furthermore, ultra-high-strength materials experience relatively large strength variations during mass production. Specifically, ultra-high-strength materials are susceptible to strength variations between coils (or batches). Consequently, the use of ultra-high-strength materials also presents the issue of varying springback, leading to significant variations in component dimensional accuracy.

[0009] As conventional press forming methods, there are technologies described in Patent Documents 1 to 4, for example.

[0010] In the press forming method described in Patent Document 1, a blank sheet is bent along a bend line extending along its longitudinal direction. During this bending process, the sheet is bent beyond the desired angle and then returned to the desired angle. Patent Document 1 describes how this method reduces the stress that contributes to torsion to zero, thereby suppressing torsion.

[0011] The stamping forming method described in Patent Document 2 is a method for forming a component that is curved in the longitudinal direction. At this time, in Patent Document 2, the portion subjected to shrinkage flange deformation is formed so that the length of the line in the longitudinal direction is shorter than the length of the line in the target component shape. In addition, in Patent Document 2, the portion subjected to tension flange deformation is formed so that the length of the line in the longitudinal direction is longer than the length of the line in the target component shape. After this forming, in Patent Document 2, the target component shape is formed. Through this method, Patent Document 2 records that the stress, which is the main factor of torsion, is reduced, and torsion is reduced.

[0012] The press forming method described in Patent Document 3 targets a molded product having a top plate portion curved in the longitudinal direction and two longitudinal walls extending from both ends of the top plate portion toward the inner side of the curve. Furthermore, Patent Document 3 discloses changing the curvature of the top plate portion and the angle between the top plate portion and the longitudinal walls in the previous step. This method reduces stress generated in subsequent steps and suppresses springback, as described in Patent Document 3.

[0013] Furthermore, Patent Document 4 targets a product shape in which the top plate and flange are continuous in the width direction via a longitudinal wall, and the top plate and flange have a hat-shaped cross-section that curves vertically along the longitudinal direction when viewed from the side. Furthermore, Patent Document 4 employs a method for forming the product to a smaller radius of curvature than the product shape in a preceding process and a larger radius of curvature in a subsequent process. Thus, Patent Document 4 describes reducing stress generated in the subsequent process and suppressing springback.

[0014] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-195535

[0015] Patent Document 2: Japanese Patent No. 5664810

[0016] Patent Document 3: Japanese Patent Application Laid-Open No. 2011-206789

[0017] Patent Document 4: Japanese Patent Application Publication No. 2019-25533

[0018] The goal of the stamping forming method described in Patent Document 1 is to reduce the stress, the main factor of torsion, to zero after bending recovery. However, in the case of a significant change in the material strength of an ultra-high-strength material, the amount of torsion changes due to the change in material strength. Therefore, there is a possibility that the product size cannot be within the allowable tolerance. In addition, in the method described in Patent Document 1, the mold structure becomes very complicated. Therefore, when forming ultra-high-strength materials, there is a concern that the mold will become insufficiently rigid. Therefore, when the method of Patent Document 1 is adopted, there is a possibility that the cost of repairing and repairing the equipment will increase.

[0019] Furthermore, there is a concern that the target component having curved portions on both sides when viewed from above may be twisted and have its vertical wall angle changed simultaneously due to press forming. However, Patent Document 1 does not provide a method for considering the vertical wall angle of the target product.

[0020] Furthermore, the stamping method described in Patent Document 2 cannot be applied to parts without a flange portion continuous with one end of a vertical wall portion. Furthermore, the method in Patent Document 2 is implemented in a single step. Therefore, the method in Patent Document 2 results in a complex mold structure and poor productivity.

[0021] Furthermore, the press forming method described in Patent Document 3 results in a loosened vertical wall portion during subsequent forming steps. Consequently, the behavior of the sheet metal during forming becomes unstable. For these reasons, the method of Patent Document 3 raises concerns about difficulty in achieving stable dimensional accuracy in mass production.

[0022] Furthermore, the stamping method described in Patent Document 4 changes the curvature radius of the top plate and flange in the previous process. Therefore, it cannot be applied to components with a U-shaped cross-section without a flange. Furthermore, when the target is a component with a cap-shaped cross-section and a flange, the curved shape of the component being stamped in the previous process differs from the curved shape of the mold in the subsequent process. Therefore, there is a concern that the product formed in the previous process cannot be accurately placed in the mold of the subsequent process. Summary of the Invention

[0023] The present invention has been completed with an eye on the above-mentioned points. One of the purposes of the present invention is to reduce the change in torsion, bend return or longitudinal wall angle by a simple die structure even when using high-strength materials or ultra-high-strength materials. Another purpose is to significantly reduce the change in dimensional accuracy when the material strength changes. Another purpose is to provide a stamping method that is capable of obtaining a high-precision component shape close to a target component shape (target component shape) and has excellent shape freezing and material strength sensitivity.

[0024] To solve the problem, one embodiment of the present invention is a method for manufacturing a stamped product, comprising forming a metal sheet into a target component shape, the target component shape having a cross section including a top plate portion and a longitudinal wall portion connected to a widthwise end portion of the top plate portion and extending in a direction different from the top plate portion, the target component shape having one or more bent portions bent in a direction intersecting the cross section, i.e., a longitudinal direction, wherein the method comprises: a first step of stamping the metal sheet into an intermediate component having the top plate portion and the longitudinal wall portion using a forming surface having a first longitudinal wall angle smaller than the longitudinal wall angle of the target component shape at a position forming the bent portion, when an angle between the top plate portion and the longitudinal wall portion in the cross section is defined as a longitudinal wall angle; and a second step of stamping the intermediate component using a forming surface having a second longitudinal wall angle greater than the longitudinal wall angle of the target component shape at a position forming the bent portion, wherein, at the position forming the bent portion, the first longitudinal wall angle is set so as to have a smaller angle than the longitudinal wall angle of the target component shape with respect to the longitudinal wall angle in the intermediate component after demolding in the first step.

[0025] In the embodiment of the present invention, for at least the portion to be curved, an intermediate component having a smaller vertical wall angle than that of the stamped product of the target component shape is manufactured in the first step. Furthermore, for at least the portion to be curved, the intermediate component is stamped in the second step using a die having a vertical wall angle greater than that of the stamped product.

[0026] Therefore, according to the embodiment of the present invention, when manufacturing a press-formed product having a target component shape of a "laterally curved shape", for example, the stress generated in the vertical wall of the curved portion in the second step can be reversed and reduced.

[0027] Furthermore, according to the embodiment of the present invention, even when manufacturing a press-formed product whose target component shape is a "vertically curved shape", springback during press forming can be reduced, thereby improving the dimensional accuracy of the press-formed product.

[0028] Furthermore, according to the aspect of the present invention, since the problem is solved by adjusting the vertical wall angle of the mold, it can be implemented with a simple mold structure.

[0029] In summary, the present invention achieves the following advantages even when using high-strength materials of 590 MPa or more or ultra-high-strength materials of 980 MPa or more. Specifically, in the manufacture of press-formed products with "left-right curved shapes," it is possible to appropriately reduce torsion or bend return relative to the target part shape and changes in vertical wall angles.

[0030] Furthermore, according to the method of the present invention, when manufacturing both a "left-right curved shape" stamped part and a "vertically curved shape" stamped part, even when the material strength varies, a component with high dimensional accuracy can be obtained. Therefore, according to the method of the present invention, the yield rate during mass production can also be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a diagram showing the shape of a press-formed product according to the first embodiment of the present invention. Figure 1 (a) is a top view. Figure 1 (b) is a bird's-eye view. Figure 1 (c) is Figure 1 (a) Diagram of the XX section.

[0032] Figure 2 It is a diagram showing a stamping process according to the first embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram for explaining the punching process using a die in the first step in the first embodiment.

[0034] Figure 4This is a schematic cross-sectional view illustrating the mold in the first step.

[0035] Figure 5 This is a schematic diagram for explaining the punching process using a die in the second step in the first embodiment. Figure 5 (a) is a diagram showing the relationship between the punch (lower die), the gasket, and the intermediate member during stamping. Figure 5 (b) is a diagram showing the relationship between the punch (lower die) and the die (upper die).

[0036] Figure 6 This is a schematic cross-sectional view illustrating the relationship between the mold and the intermediate member in the second step.

[0037] Figure 7 This is a schematic diagram illustrating comparative forming methods.

[0038] Figure 8 This is a diagram illustrating the problems of comparative forming methods. Figure 8 (a) represents the stamped product produced. Figure 8 (b) shows its AA′ cross-sectional view.

[0039] Figure 9 Graphs showing the distribution of longitudinal stress at the bottom dead point of punching in comparative forming methods. Figure 9 (a) is a view from the convex side of the longitudinal wall. Figure 9 (b) is a view viewed from the concave side of the longitudinal wall.

[0040] Figure 10 This is a diagram showing the stress-strain relationship in press forming for explaining variations in dimensional accuracy in comparative forming methods.

[0041] Figure 11 This is a diagram showing an example of stress distribution after the first step. Figure 11 (a) is a view from the convex side of the longitudinal wall. Figure 11 (b) is a view viewed from the concave side of the longitudinal wall.

[0042] Figure 12 This is a diagram showing an example of stress distribution after the second step. Figure 12 (a) is a view from the convex side of the longitudinal wall. Figure 12 (b) is a view viewed from the concave side of the longitudinal wall.

[0043] Figure 13 This is a diagram showing a stress-strain relationship in press forming for explaining a change in dimensional accuracy according to the first embodiment of the present invention.

[0044] Figure 14 This is a diagram showing an example of strain distribution after the first step. Figure 14 (a) is a view from the convex side of the longitudinal wall. Figure 14 (b) is a view viewed from the concave side of the longitudinal wall.

[0045] Figure 15 This is a diagram showing an example of strain distribution after the second step. Figure 15 (a) is a view from the convex side of the longitudinal wall. Figure 15 (b) is a view viewed from the concave side of the longitudinal wall.

[0046] Figure 16 This is a diagram showing the relationship between the twist amount and (θ1 / θ2).

[0047] Figure 17 This is a diagram showing the relationship between the twist amount and (θ1 / θ0).

[0048] Figure 18 This is a diagram showing the relationship between the twist amount and (θ1′ / θ2).

[0049] Figure 19 This is a graph showing the relationship between the twist amount and |ε2 / ε1|.

[0050] Figure 20 This is a graph showing the relationship between the twist amount and |ε2′ / ε1′|.

[0051] Figure 21 It is a diagram showing the shape of a press-formed product according to a second embodiment of the present invention. Figure 21 (a) is a bird's-eye view, Figure 21 (b) is a side view, Figure 21 (c) is a cross-sectional view in the width direction.

[0052] Figure 22 This is a schematic diagram for explaining the punching process using a die in the first step in the second embodiment.

[0053] Figure 23 This is a schematic diagram for explaining the punching by the die in the second step in the second embodiment. Figure 23 (a) is a diagram showing the relationship between the punch (lower die), the gasket, and the intermediate member during stamping. Figure 23 (b) is a diagram showing the relationship between the punch (lower die) and the die (upper die).

[0054] Figure 24 This is a side view illustrating the occurrence of a bend return.

[0055] Figure 25 Graphs showing the distribution of longitudinal stress at the bottom dead point of punching in comparative forming methods.

[0056] Figure 26This is a diagram showing the stress-strain relationship in press forming for explaining variations in dimensional accuracy in comparative forming methods.

[0057] Figure 27 It is a diagram showing the cross-sectional shape after the first step and the second step in the second embodiment. Figure 27 (a) shows the cross-sectional shape after the first step, Figure 27 (b) shows the cross-sectional shape after the second step.

[0058] Figure 28 This is a diagram showing an example of stress distribution after the first step.

[0059] Figure 29 This is a diagram showing an example of stress distribution after the second step.

[0060] Figure 30 This is a diagram showing a stress-strain relationship in press forming for explaining a change in dimensional accuracy according to the second embodiment of the present invention.

[0061] Figure 31 This is a diagram showing an example of strain distribution after the first step.

[0062] Figure 32 This is a diagram showing an example of strain distribution after the second step.

[0063] Figure 33 This is a diagram showing the relationship between the height deviation amount and εt2 / εt1.

[0064] Figure 34 This is a diagram showing the relationship between the height deviation amount and εb2 / εb1. DETAILED DESCRIPTION

[0065] Hereinafter, examples of a press forming method and the like according to an embodiment of the present invention will be described with reference to the drawings.

[0066] "First Implementation Method"

[0067] (Target part shape)

[0068] This embodiment exemplifies a case where the target component shape is a "left-right curved shape."

[0069] In this embodiment, if Figure 1As shown, the target part shape 1 of the part to be manufactured (stamped product) becomes a cross-section having a top plate portion 1A and longitudinal wall portions 1B on the left and right sides. The longitudinal wall portions 1B on the left and right sides are respectively connected to the two end portions in the width direction of the top plate portion 1A and extend in a direction different from the top plate portion 1A. That is, in this embodiment, the shape of the cross section is illustrated as a case where the cross section is a U-shaped cross section. Of course, even if the cross section of the target part shape 1 is a hat-shaped cross section or an L-shaped cross section, the present invention can be applied. The hat shape is a shape having a flange portion. The L-shape is a shape in which the longitudinal wall portion 1B exists only on one side in the width direction of the top plate portion 1A.

[0070] Furthermore, the present invention can be applied even if the target component shape has both a "left-right curved shape" and a "top-bottom curved shape."

[0071] also, Figure 1 The dimensions used in the embodiments are also marked in the figure (unit: [mm]). However, the present invention is not limited to these dimensions. The same applies to the other drawings.

[0072] Moreover, if Figure 1 (a) Figure 1 As shown in (b), the target component shape 1 of this embodiment illustrates a shape having a curved portion 2 that curves toward the longitudinal wall portion 1B on one side along the longitudinal direction when viewed from above. The longitudinal direction refers to a direction intersecting the above-mentioned cross section. The target component shape 1 illustrated in this embodiment is composed of two straight portions of the top plate portion 1A that are flat when viewed from above along the longitudinal direction, and the curved portion 2 between the two straight portions. Here, reference numeral 2A represents the top plate portion of the curved portion 2, and reference numeral 2B represents the longitudinal wall portion (concave side) of the curved portion 2.

[0073] Furthermore, the present invention also targets the manufacture of a target component shape 1 having a plurality of curved portions 2 along the longitudinal direction. In this case, there may not be a straight portion between adjacent curved portions 2.

[0074] like Figure 1 As shown, when the top plate portion 1A has longitudinal wall portions 1B on both the left and right sides, the structure becomes as follows. That is, when viewed from above, the left and right longitudinal wall portions 1B in one curved portion 2 protrude toward the longitudinal wall portion 1B side on one side and are recessed toward the longitudinal wall portion 1B side on the other side. In addition, in this specification, the protruding longitudinal wall portion 1B side is also described as the outer side of the curved portion 2 when viewed from above or the longitudinal wall convex portion. In addition, the recessed longitudinal wall portion 1B side is also described as the inner side of the curved portion 2 when viewed from above or the longitudinal wall concave portion. However, the longitudinal wall angle on the longitudinal wall portion 1B side on one side and the longitudinal wall angle on the longitudinal wall portion 1B side on the other side can be the same angle or different from each other.

[0075] (Manufacturing Method)

[0076] The method for manufacturing a stamped product of this embodiment is a method for manufacturing a metal plate 3 (blank) into the target component shape 1 described above by stamping. The present invention is suitable for cases where the material of the metal plate 3 is a high-strength material or an ultra-high-strength material. The high-strength material is a steel plate with a tensile strength of 590 MPa or more. In addition, the present invention can also be applied to metal plates 3 such as mild steel plates and aluminum plates.

[0077] One of the purposes of this embodiment is to reduce the springback caused by torsion and vertical wall angle variation and the variation in dimensional accuracy of the part due to the variation in material strength (difference in strength) when manufacturing a press-formed product of the target part shape 1 .

[0078] like Figure 2 As shown, the method for manufacturing a press-formed product according to the present embodiment includes a first step 10A and a second step 10B.

[0079] As described above, the angle between the top plate portion 1A and the vertical wall portion 1B in cross section is referred to as the vertical wall angle. The angle (shoulder angle) between the top plate forming surface for forming the top plate portion 1A and the vertical wall forming surface for forming the vertical wall portion 1B on the mold forming surface is referred to as the vertical wall angle.

[0080] (First step 10A)

[0081] In the first step 10A, as shown in the schematic diagram Figure 4 As shown, an upper die 11 and a lower die 12 are used. The forming surfaces of the upper die 11 and the lower die 12 have a first vertical wall angle θ1 that is smaller than the vertical wall angle θ0 of the target part shape 1. Furthermore, the first step 10A is a step of press-forming the intermediate part 4 using these dies 11 and 12 to form the intermediate part 4 having a top plate portion and vertical walls with a width consistent with the target part shape 1. Furthermore, the intermediate part 4 may include portions that are cut in a subsequent trimming step.

[0082] like Figure 3 and Figure 4 As shown, the mold used in the first step 10A includes a die 11 (upper die) and a punch 12 (lower die). The forming surfaces 11A and 12A of the die 11 and punch 12 used in the first step 10A have forming surfaces with at least a vertical wall angle different from the target part shape 1. In addition, the mold used in the first step 10A includes a gasket 13. The gasket 13 is a component of the mold that suppresses the portion of the metal plate 3 that becomes the top plate portion 1A on the top plate forming surface 12Aa of the punch 12. Reference numerals 12Aa and 11Aa indicate top plate forming surfaces, and reference numerals 12Ab and 11Ab indicate vertical wall forming surfaces.

[0083] That is, in the first step 10A, if Figure 3 and Figure 4As shown, punching is performed by the die 11 and the punch 12 in a state where the metal plate 3 is pressed by the top plate forming surface 12Aa of the punch 12 and the pad 13 .

[0084] However, as described above, the first vertical wall angle θ1 on the molding surfaces 11A and 12A of the molds 11 and 12 used in the first step 10A is set to an angle smaller than the vertical wall angle θ0 in the target component shape 1 .

[0085] Furthermore, the first vertical wall angle θ1 is set based on the vertical wall angle θ1′ of the intermediate component 4. Furthermore, the vertical wall angle θ1′ is the vertical wall angle of the intermediate component 4 after the metal sheet 3 is press-formed and released from the mold in the first step 10A. Specifically, the first vertical wall angle θ1 is set to be smaller than the vertical wall angle θ0 in the target component shape 1. Consequently, the intermediate component 4 assumes the shape after release from the mold, i.e., the shape of the intermediate component 4 after springback.

[0086] The first vertical wall angle θ1 may be set by, for example, CAE analysis or actual stamping evaluation.

[0087] Furthermore, the first vertical wall angle θ1 is set as described above for each of the vertical wall angles on the left and right vertical wall portions 1B side.

[0088] Alternatively, only the vertical wall angle on one of the left and right vertical wall portions, on the vertical wall portion 1B side, may be set to the first vertical wall angle θ1 as described above. In this case, the vertical wall angle on the other vertical wall portion 1B side may be set to an angle equal to the vertical wall angle θ0 in the target component shape 1. Even if only the first vertical wall angle is set on one vertical wall portion 1B side based on the present disclosure, an effect is achieved. However, it is preferred that the vertical wall angles on both the left and right vertical wall portions 1B sides be set to the first vertical wall angle θ1 as described above.

[0089] (Second step 10B)

[0090] The second step 10B is a step of press-forming the intermediate component 4 manufactured in the first step 10A to manufacture a press-formed product having the target component shape 1 .

[0091] The molding surface of the mold used in the second step 10B has a second vertical wall angle θ2 that is greater than the vertical wall angle θ0 of the target part shape 1. Figure 5 and as a schematic diagram Figure 6 As shown, the forming surfaces of the dies 14 and 15 used in the second step 10B have forming surfaces 14A and 15A that follow the target part shape 1 except for the vertical wall angle. The dies 14 and 15 are a die 14 as an upper die and a punch 15 as a lower die.

[0092] The second vertical wall angle θ2 is preferably greater than the vertical wall angle θ0 of the target part shape 1. That is, in the second step 10B, the vertical wall portion 1B is bent and restored. Therefore, the molding surface shape of the mold in the second step 10B is preferably designed so that the second vertical wall angle θ2 is greater than the vertical wall angle θ0 of the target part shape 1.

[0093] Furthermore, the mold used in the second step 10B includes a spacer 16 for pressing the top plate portion of the intermediate member 4 .

[0094] Here, the second vertical wall angle θ2 is set to an angle greater than the vertical wall angle θ0. Therefore, the second vertical wall angle θ2 is greater than the vertical wall angle θ1′ of the intermediate component 4. Therefore, during the forming process in the second step 10B, a problem arises if the following forming method is used. Specifically, consider a case where a spacer 16 is extended from the die 14 side, and the top plate portion of the intermediate component 4 is sandwiched between the spacer 16 and the punch 15 for forming. In this case, when the intermediate component 4 is placed on the punch 16, there is a high possibility that the intermediate component 4 will not be placed in the specified position on the punch 16, resulting in an unstable forming state.

[0095] Therefore, in the second step 10B of the present embodiment, the intermediate component 4 is placed on the pad 16 in a state where the pad 16 protrudes from the top plate forming surface of the punch 15 before forming. Thereafter, the top plate portion of the intermediate component 4 is pressed against the top plate forming surface of the die 14 by the pad 16 (see FIG. Figure 6 (a)). In this state, the intermediate member 4 is press-formed by the spacer 16 and the die 14. The above-described operation is the structure of the second step 10B of this embodiment.

[0096] (Regarding the relationship between the vertical wall angles)

[0097] Here, the vertical wall angle in the target component shape 1 is recorded as θ0. The first vertical wall angle on the forming surfaces 11A and 12A of the molds 11 and 12 in the first step 10A is recorded as θ1. The vertical wall angle in the intermediate component 4 is recorded as θ1′. For the intermediate component 4, the angle after forming in the first step 10A, demolding, and rebounding is the first vertical wall angle θ1′. The second vertical wall angle on the forming surfaces 14A and 15A of the molds 14 and 15 in the second step 10B is recorded as θ2. In addition, in this embodiment, the vertical wall portion 1B exists on the left and right, but it is preferable that each left and right separately meet the following conditions.

[0098] The first vertical wall angle θ1 and the second vertical wall angle θ2 are preferably set to satisfy the following formula (1). That is, the second vertical wall angle θ2 of the mold in the second step 10B is preferably set larger than the vertical wall angle θ0 in the target component shape 1 .

[0099] θ1<θ1′<θ0<θ2…(1)

[0100] Furthermore, it is preferable that the second vertical wall angle θ2 is smaller than 1.05 times the vertical wall angle θ0.

[0101] Next, suitable conditions related to setting the first vertical wall angle θ1 and the second vertical wall angle θ2 will be described.

[0102] Figure 16 Yes Figure 1 The results of the stamping investigation of the relationship between (θ1 / θ2) and the amount of torsion after stamping are shown in the stamping of the stamped product. Here, "○" is the result when using a steel plate with a tensile strength of 980MPa. "△" is the result when using a steel plate with a tensile strength of 1180MPa.

[0103] In addition, if Figure 8 As shown, Figure 16 The twist amount of the vertical axis in is the value that represents the difference between the target part shape 1 and the shape after demolding. Specifically, the angle is aligned at the center of the length so that the slope of the top plate of the target part shape 1 is consistent with the slope of the top plate of the shape after demolding. Then, Figure 8 The inclination angle of the top plate portion in the AA′ cross section at the longitudinal end portion shown in (a) is taken as the twist amount.

[0104] In this embodiment, the target range of the twist amount that will produce a good shape is set to within ±2°. Figure 16 It is understood that it is preferable to set the relationship between the first vertical wall angle θ1 and the second vertical wall angle θ2 so as to satisfy the following formula (2).

[0105] 0.7≤(θ1 / θ2)…(2)

[0106] If (θ1 / θ2) is less than 0.7, there is a concern that excessive bending recovery may occur in the second step (second step 10B). Excessive bending recovery can increase dimensional accuracy fluctuations due to springback (opening and twisting) and material strength variations. To achieve better results, (θ1 / θ2) is preferably 0.75 or greater and less than 0.95.

[0107] Next, suitable conditions related to setting the first vertical wall angle θ1 and the vertical wall angle θ0 in the target component shape 1 will be described.

[0108] Figure 17 Yes Figure 1 The results of the stamping investigation of the relationship between (θ1 / θ0) and the amount of torsion after stamping are shown.

[0109] In this embodiment, the target range of the twist amount that will produce a good shape is set to within ±2°. Figure 17 It is understood that it is preferable to set the first vertical wall angle θ1 so as to have a value that satisfies the following formula (3).

[0110] 0.75≤(θ1 / θ0)…(3)

[0111] If (θ1 / θ0) is less than 0.75, θ1 is too small relative to θ0, which may lead to excessive bending recovery in the second step (second step 10B). Excessive bending recovery may increase the springback (opening and twisting) and dimensional accuracy fluctuations caused by fluctuations in material strength.

[0112] In the present invention, since θ1<θ0 is satisfied, θ1 / θ0 is less than 1. In order to obtain a better effect, (θ1 / θ0) is preferably equal to or greater than 0.8 and less than 0.97.

[0113] Next, suitable conditions related to the setting of the vertical wall angle θ1 ′ and the second vertical wall angle θ2 during mold release and springback in the first step will be described.

[0114] Figure 18 Yes Figure 1 The results of the stamping investigation of the relationship between (θ1′ / θ2) and the amount of torsion after stamping are shown.

[0115] In this embodiment, the target range of the twist amount that will produce a good shape is set to within ±2°. Figure 18 It is understood that it is preferable to set the second vertical wall angle θ2 so as to have a value that satisfies the following formula (4).

[0116] 0.8≤(θ1′ / θ2)…(4)

[0117] If (θ1′ / θ2) is less than 0.8, θ1′ is too small relative to θ2. Therefore, there is a risk of excessive bend recovery in the second step (second step 10B). Excessive bend recovery can increase dimensional accuracy fluctuations due to springback (opening and twisting) and material strength variations.

[0118] In the present invention, since θ1′<θ2, θ1′ / θ2 is less than 1. In order to obtain a better effect, (θ1′ / θ2) is preferably 0.85 or more and less than 0.99.

[0119] Next, the second vertical wall angle θ2 is preferably set to a value that satisfies the following formula (5).

[0120] 1.0<(θ2 / θ0)<1.05…(5)

[0121] When (θ2 / θ0) exceeds 1.05, there is a high possibility that the target component shape 1 cannot be formed to the vertical wall angle θ0 after the springback in the second step (second step 10B).

[0122] Here, the above-mentioned appropriate ranges (values) may vary depending on the shape of the component and the strength of the material. Therefore, it is preferable to examine the conditions of the above-mentioned vertical wall angles for each component.

[0123] Furthermore, regarding the conditions of the above-mentioned formulas (1) to (5), the ranges of the vertical wall angles θ1 and θ2 may be set so as to satisfy the conditions of one or more formulas selected from the formulas (1) to (5). These formulas were set mainly based on the embodiments and other studies conducted by the inventors.

[0124] (Action and other)

[0125] Comparative Forming Methods

[0126] Here, as a comparative forming method, consider Figure 7 The method shown. That is, the entire surface of the top plate portion 1A of the metal plate 3 is clamped by the punch 20 and the pad 22. In this state, the metal plate 3 is stamped by the punch 20 (lower die) and the die 21 (upper die). In addition, in the comparative forming method, the forming surface (die shape) of the punch 20 and the die 21 is formed to imitate the shape of the target component 1. The comparative forming method is a conventional stamping forming method in which collision forming with a pad is applied. At this time, the target component shape 1 and the shape after demolding of the die are aligned so that the slope of the top plate of the longitudinal central section is consistent.

[0127] Figure 8 (b) shows the cross-sectional shape 6 of the part after stamping based on the comparative forming method. Reference numeral 6C indicates a bent portion. Figure 8 (b)) is Figure 8 The shape of the AA' cross section at the length end when viewed from above as shown in (a) is shown in FIG. Figure 8 As shown in (b), top plate portion 6A tilts before and after springback (before and after demolding). This indicates that the component twists due to springback when using the comparative molding method. Furthermore, the vertical wall angle at the cross-section of the molded component is larger than that of the mold due to springback.

[0128] Figure 9 The stress distribution in the longitudinal direction of the plate thickness center at the bottom dead point of the punching in the comparative forming methods is shown.

[0129] according to Figure 9 As can be seen from (a), a compressive stress is generated in a large area on the vertical wall portion 1B side of the convex side when viewed from above. Figure 9 As can be seen from (b), tensile stress is generated in a large area in the longitudinal wall portion 1B on the concave side when viewed from above. Based on this state, it is believed that the torsion of the cross section of the component after demolding is caused by the release of these stresses when the mold is demolded. Moreover, as the material strength increases, the residual stress increases and the amount of springback increases. Moreover, if the material strength increases, the material strength fluctuation during mass production also becomes relatively large. Therefore, if the material strength increases, the material strength between the coils used as the material fluctuates relatively greatly. As a result, there is also the issue of fluctuation in dimensional accuracy due to changes in the amount of springback.

[0130] This dimensional accuracy change is explained using a stress-strain relationship diagram.

[0131] Figure 10 The relationship between stress and strain of the concave side vertical wall when forming based on the comparative forming method is shown. Figure 10 In the figure, a schematic diagram of two metal plates 3, one for the strength-enhancing material and one for the strength-reducing material, is shown, assuming fluctuations in material strength. In the comparative forming method, when stamping is used to form the target component shape 1, the material on the concave side of the curved portion 2, when viewed from above, is stretched. This generates tensile stress.

[0132] In addition, if Figure 10 As shown, there is a difference in the stress value at the bottom dead point of forming between the strength-reinforcing material and the strength-reducing material. If the molds 20 and 21 are demolded from this state, springback occurs, resulting in twisting of the stamped part. In addition, since the amount of springback is different between the strength-reinforcing material and the strength-reducing material, dimensional accuracy varies. Moreover, the higher the material strength, the greater the dimensional accuracy variation, deviating from the dimensional tolerance of the product. This is listed as an important issue in stamping.

[0133] Furthermore, changes in the vertical wall angle due to springback are primarily caused by the stress difference between the front and back of the sheet at the punch shoulder. Furthermore, as material strength increases, the amount of springback increases. Furthermore, changes in the vertical wall angle due to springback also contribute to fluctuations in dimensional accuracy.

[0134] <Molding method of this embodiment>

[0135] On the other hand, in this embodiment, the mold shapes for the first step 10A and the second step 10B are designed as described above. This reverses the stress that is the primary factor contributing to torsion in the second step 10B. As a result, in this embodiment, both the amount of torsion and the variation in torsion dimensional accuracy are reduced.

[0136] Furthermore, stress, a major factor in changes in the vertical wall angle, is suppressed by the following phenomenon. Specifically, the bending recovery in the second step 10B reverses the stress on the punch shoulder, or applies stress in the opposite direction around the punch shoulder. As a result, changes in the vertical wall angle and variations in dimensional accuracy can be simultaneously reduced.

[0137] Here, for example, stretch forming or collision forming may be applied in the first step 10A, and the target component shape 1 may be formed in the second step 10B.

[0138] In this embodiment, as described above, in the second step 10B, the stamping is performed while the intermediate member 4 is pressed toward the die 14 by the spacer 16. This stabilizes the stamping in the second step 10B. Figure 5 、 Figure 6 As shown, in the second step 10B, the intermediate component 4 is placed on the spacer 16 while the spacer 16 protrudes from the top plate forming surface of the punch 15 before forming. Subsequently, forming is performed while the top plate portion of the intermediate component 4 is sandwiched between the die 14 and the spacer 16. This enables stable forming.

[0139] Here, in the second step 10B, consider the case where, as in conventional forming (a comparative forming method), a spacer 16 extends from the die 14 side, and the intermediate component 4 is formed between the spacer 16 and the punch 15. In this case, when the intermediate component 4 is placed on the lower die (spacer 16), the vertical wall angle θ1′ of the intermediate component 4 becomes smaller than the vertical wall angle θ2 of the die. Consequently, the intermediate component 4 is supported and formed in an unstable state, with only partial contact with the punch 15. As a result, the component may experience positional deviation, and the desired shape cannot be achieved.

[0140] Figure 11 、 Figure 12 An example of stress distribution at the center of the longitudinal plate thickness at the bottom dead point of a stamped product formed by the method of this embodiment is shown. The forming process is performed under the same conditions as the comparative forming method, except for the two-step forming and the adjustment of the vertical wall angle.

[0141] like Figure 11 As shown, at the bottom dead center of the forming in the first step 10A, a large compressive stress is generated on the vertical wall portion 1B side on the convex side in plan view, and a large tensile stress is generated on the vertical wall portion 1B side on the concave side in plan view.

[0142] On the other hand, Figure 12As shown, at the bottom dead center of forming in the second step 10B, tensile stress is generated in the vertical wall portion 1B on the convex side 2A when viewed from above. Furthermore, compressive stress is generated in the vertical wall portion 1B on the concave side 2B when viewed from above. As can be seen, in this embodiment, stress is reversed compared to conventional methods (conventional forming), and the stress value and stress-generating region are reduced.

[0143] In this embodiment, the second step 10B forms the longitudinal wall portion 1B so that it expands. As a result, the longitudinal wall portion 1B on the convex side 2A, when viewed from above, is formed in a direction in which its linear length increases, thereby exerting tensile stress. On the other hand, the longitudinal wall portion 1B on the concave side 2B, when viewed from above, is formed in a direction in which its linear length decreases, thereby exerting compressive stress.

[0144] The variation in dimensional accuracy due to variation in material strength when forming is performed by the method of this embodiment will be described with reference to a schematic diagram of stress-strain relationship.

[0145] Figure 13 This is a diagram showing the relationship between stress and strain of the concave side vertical wall in a plan view in this embodiment. Here, a schematic diagram of a strength-enhancing material and a strength-reducing material is shown, assuming a change in material strength.

[0146] In the present embodiment, when the intermediate component 4 is formed into a shape having a smaller vertical wall angle than the target component shape 1 in the first step 10A, a larger strain and tensile stress are applied than in a conventional method.

[0147] After that, if the vertical wall angle of the target part shape 1 is formed in the second step 10B, the material on the concave side is formed in the direction of contraction when viewed from above. Therefore, the tensile stress is reversed to compressive stress. Here, if the stress is reversed, the history curves (respective stress-strain curves) of the strength-enhancing material and the strength-reducing material of the material intersect in the low stress area. This intersection point is Figure 13 The middle position represents the bottom dead center in the second step. Aiming for this, the vertical wall angle in the first step 10A is reduced during forming. This reduces the stress and stress difference between the strength-reinforcing and strength-reducing materials at the bottom dead center of forming. Consequently, both torsion and torsional dimensional accuracy variation are reduced. The zero stress position corresponds to the state after demolding.

[0148] Furthermore, the change in the vertical wall angle in the first step 10A can be applied only to the convex side of the curve in plan view, or only to the concave side. Therefore, it can be applied even when a flange portion is provided on one or both sides of the curved portion 2.

[0149] In the second step 10B, the longitudinal wall portion of the intermediate component 4 formed in the first step 10A is formed in a manner that allows it to bend and recover. In other words, stress is applied in the opposite direction to that in the first step 10A. Specifically, the stress in the cross-sectional direction of the punch shoulder is reversed, or stress is applied in the opposite direction around the punch shoulder. Consequently, variations in the longitudinal wall angle and dimensional accuracy are reduced. In this case, forming is performed under conditions that reduce the aforementioned torsion and dimensional accuracy variations. In this case, the stress in or around the punch shoulder is excessively reversed. Consequently, springback occurs in a direction smaller than the longitudinal wall angle of the die in the second step 10B.

[0150] Thus, the first vertical wall angle θ1 and the second vertical wall angle θ2 are set so that the vertical wall angle after rebound in the second step 10B becomes the vertical wall angle θ0 in the target component shape 1. For example, the vertical wall angles of the mold in the first step 10A and the second step 10B can be designed to satisfy the above-mentioned equations (1) to (5). The vertical wall angles of the mold in the first step 10A and the second step 10B are the first vertical wall angle θ1 and the second vertical wall angle θ2.

[0151] here, Figure 14 、 Figure 15 The figure shows the distribution of the longitudinal strain in the center portion of the plate thickness at the bottom dead point of forming when a component is formed by the forming method of the present embodiment.

[0152] like Figure 14 As shown in FIG. 1 , after the first step 10A, a large compressive strain is generated on the convex side of the longitudinal wall, and a large tensile strain is generated on the concave side of the longitudinal wall. On the other hand, after the second step 10B, as shown in FIG. Figure 15 As shown, the compressive strain on the convex side decreases, and the tensile strain on the concave side also decreases.

[0153] From the above, it can be seen that it is preferred to become Figure 13 The vertical wall angles θ1 and θ2 of the dies in the first step 10A and the second step 10B are set in a manner that corresponds to the strain behavior shown. Furthermore, the second vertical wall angle θ2 is preferably set so that the stress applied to the bottom dead center of the punch in the second step 10B is consistent or similar within the strength range of the material used.

[0154] Based on such considerations, it is preferable to set the vertical wall angles θ1 and θ2 as follows.

[0155] [Looking down at the convex side 2A]

[0156] Regarding the longitudinal strain distribution at the bottom dead center during the press forming in the second step 10B, the average value of the strain in the lower half of the vertical wall portion 1B, which is convex in plan view, is defined as ε2. This is defined at least at the position of the bent portion 2.

[0157] Regarding the longitudinal strain distribution at the bottom dead center during the press forming process 10A, the average value of the strain in the lower half of the vertical wall portion 1B, which is convex in plan view, is defined as ε1. This is defined at least at the position of the bent portion 2.

[0158] Figure 19 Yes Figure 1 The results of the stamping investigation of the relationship between |ε2 / ε1| and the amount of torsion after stamping are shown for the stamped products.

[0159] In this embodiment, the target range of the twist amount that will produce a good shape is set to within ±2°. Figure 19 It can be seen that |ε2 / ε1| is preferably in the range of 0.4 to 0.85.

[0160] Therefore, it is preferable to set the first vertical wall angle θ1 and the second vertical wall angle θ2 so as to satisfy the following formula (6).

[0161] 0.4×|ε1|≤|ε2|<0.85×|ε1|…(6)

[0162] Here, ε2 is the above-mentioned average value at the bottom dead point of the press in the second step 10B, where the strain in the longitudinal direction before the first step 10A (before forming) is set to a reference value of 0. That is, ε2 is the sum of the strain in the longitudinal direction applied by the first step 10A and the strain in the longitudinal direction applied by the second step 10B.

[0163] In addition, if |ε2| is less than 0.4×|ε1|, then there exists Figure 13 The amount of recovery from the strain shown may become too large. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be absorbed below the desired value. Therefore, |ε2| is preferably greater than 0.4×|ε1|, and more preferably greater than 0.6×|ε1|.

[0164] On the other hand, if |ε2| exceeds 0.85×|ε1|, there is a concern that the amount of strain recovery after the second step 10B may become insufficient. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be reduced to below the desired value. Therefore, |ε2| is preferably less than 0.85×|ε1|, and more preferably not more than 0.8×|ε1|.

[0165] [Looking down at the concave side 2B]

[0166] Regarding the longitudinal strain distribution at the bottom dead center during the press forming in the second step 10B, the average strain value of the lower half of the vertical wall portion 1B, which is concave when viewed from above, is defined as ε2′. This is defined at least at the position that becomes the bent portion 2.

[0167] Regarding the longitudinal strain distribution at the bottom dead center during the press forming process 10A, the average value of the strain in the lower half of the vertical wall portion 1B, which is concave when viewed from above, is defined as ε1′. This is defined at least at the position that becomes the bent portion 2.

[0168] Figure 20 Yes Figure 1 The results of the investigation of the relationship between |ε2' / ε1'| and the amount of torsion after stamping are shown in the stamping of the stamped product. In addition, as the shape and size of the stamped product, it is assumed that Figure 1 The dimensions are given in [mm].

[0169] In this embodiment, the target range of the twist amount that will produce a good shape is set to within ±2°. Figure 20 It can be seen that |ε2′ / ε1′| is preferably in the range of 0.4 to 0.85.

[0170] Therefore, it is preferable to set the first vertical wall angle θ1 and the second vertical wall angle θ2 so as to satisfy the following formula (7).

[0171] 0.4×|ε1′|≤|ε2′|<0.85×|ε1′|…(7)

[0172] Here, ε2′ is the above-mentioned average value at the bottom dead point of the press in the second step 10B, where the strain in the longitudinal direction before the first step 10A (before forming) is set to a reference value of 0. That is, ε2′ is the sum of the strain in the longitudinal direction applied by the first step 10A and the strain in the longitudinal direction applied by the second step 10B.

[0173] In addition, if |ε2′| is less than 0.4×|ε1′|, then there exists Figure 13 The amount of recovery from the strain shown may become too large. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be absorbed below the desired value. Therefore, |ε2′| is preferably at least 0.4×|ε1′|, and more preferably at least 0.45×|ε1′|.

[0174] On the other hand, if |ε2′| exceeds 0.85×|ε1′|, there is a concern that the amount of strain recovery after the second step 10B may become insufficient. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be reduced to below the desired value. Therefore, |ε2′| is preferably less than 0.85×|ε1′|, and more preferably 0.7×|ε1′| or less.

[0175] In the above description, the molds of the first step 10A and the second step 10B are set so that the first vertical wall angle θ1 and the second vertical wall angle θ2 satisfy the formula (1) over the entire longitudinal length of the top plate 1A. However, the present invention is not limited to this.

[0176] For example, only the region to be the bent portion 2 in plan view may be set so that the first vertical wall angle θ1 and the second vertical wall angle θ2 satisfy equation (1). Furthermore, the vertical wall angles of the dies in the first step 10A and the second step 10B in the straight portion other than the bent portion 2 may be set to, for example, the vertical wall angles of the target part shape 1.

[0177] (About mold design)

[0178] When designing the mold shapes (molding surface shapes) for the first step 10A and the second step 10B, consider starting the design process without considering the vertical wall angles of the target part shape 1. Alternatively, consider starting the design process from the mold for the second step 10B. In these cases, finding an appropriate mold shape may be impossible or require an extremely long time.

[0179] On the other hand, in the present embodiment, the vertical wall angles of the molds in the first step 10A and the second step 10B are designed as follows.

[0180] First, CAE analysis or actual stamping is performed on the vertical wall angle θ1 of the die in the first step 10A, with the angle being smaller than the vertical wall angle θ0 of the target part shape 1. Based on this evaluation, conditions are identified under which the vertical wall angle θ1′ of the intermediate part 4 after springback in the first step 10A is smaller than the vertical wall angle θ0 of the target part shape 1.

[0181] Then, in the second step 10B, CAE analysis or actual stamping is performed using a die shape having a vertical wall angle greater than or equal to the target part shape 1's vertical wall angle θ0. Based on the evaluation of this execution, conditions are identified under which the vertical wall angle after springback in the second step 10B reaches the target part shape 1's vertical wall angle θ0 and twisting is suppressed.

[0182] According to such a mold design, the mold shape can be designed in a short time.

[0183] As described above, in this embodiment based on the present disclosure, even when using high-strength materials with a tensile strength of 590 MPa or greater, or ultra-high-strength materials with a tensile strength of 980 MPa or greater, variations in dimensional accuracy resulting from variations in material strength can be significantly reduced through a simple mold structure. Consequently, a high-precision component with a shape close to the target can be obtained.

[0184] "Second Implementation Method"

[0185] Next, a second embodiment of the present invention will be described.

[0186] The basic structure of this embodiment is the same as that of the first embodiment. The same components as those of the first embodiment are denoted by the same reference numerals and described below.

[0187] (Target part shape)

[0188] Similar to the first embodiment, this embodiment is applicable to cases where the cross section is U-shaped, a hat-shaped with a flange, or an L-shaped. The L-shaped cross section is a shape where the vertical wall 1B exists only on one side of the top plate 1A in the width direction.

[0189] In addition, similarly to the first embodiment, this embodiment targets a target component shape having one or more curved portions that curve along the longitudinal direction in a direction intersecting the longitudinal direction. Figure 21 As shown, the target component shape 1 of the present embodiment is an example of a case where the curved portion 2 is curved toward the top plate portion 1A side and has a “vertical curved shape”.

[0190] also, Figure 21 The example is an example in which the curved portion 2 is curved in a manner convex toward the top plate portion 1A. Figure 21 The dimensions used in the examples are also noted. However, the present invention is not limited to these dimensions. In addition, the unit of the dimensions is [mm].

[0191] Figure 21 The example is a hat-shaped cross-section with a single curved portion 2 formed along its entire length. However, any desired component shape may be any shape that has a curved portion along a portion of its length. For example, the desired component shape may be a shape where a flat portion (straight portion) of the top plate 1A is connected to at least one of the left and right sides of the curved portion along its length when viewed from the side.

[0192] However, the present invention also targets the manufacture of a target component shape 1 having a plurality of curved portions 2 along the longitudinal direction. In this case, there may not be a straight portion between adjacent curved portions 2.

[0193] (Manufacturing Method)

[0194] The method for manufacturing a stamped product according to this embodiment is a method for manufacturing a metal plate 3 (blank) into the target component shape 1 described above by stamping. The present invention is suitable for cases where the material of the metal plate 3 is a high-strength material or an ultra-high-strength material. The high-strength material is a steel plate having a tensile strength of 590 MPa or more. The present invention is also applicable to metal plates 3 such as mild steel plates and aluminum plates.

[0195] Similar to the first embodiment, the method for manufacturing a press-formed product of this embodiment includes a first step 10A and a second step 10B (see Figure 2 ).

[0196] (First step 10A)

[0197] In the first step 10A, Figure 4 Similarly, an upper die 11 and a lower die 12 are used, each having a first vertical wall angle θ1 smaller than the vertical wall angle θ0 of the target component shape 1. Furthermore, a first step 10A is a step in which the metal sheet is press-formed into an intermediate component 4 using these dies 11 and 12. This intermediate component 4 has a top plate portion and vertical wall portions that conform to the width of the target component shape 1, for example, and that follow the width of the target component shape 1. Furthermore, the intermediate component 4 may include portions that are cut in a subsequent trimming step.

[0198] like Figure 22 As shown, the mold used in the first step 10A includes a die 11 (upper die) and a punch 12 (lower die). The forming surfaces of the die 11 and punch 12 used in the first step 10A have at least a vertical wall angle that differs from the target component shape 1. Furthermore, the mold used in the first step 10A includes a spacer 13 that suppresses the portion of the top plate forming surface of the punch 12 from becoming the top plate portion 1A of the metal plate 3.

[0199] That is, in the first step 10A, if Figure 22 As shown, punching is performed by the die 11 and the punch 12 in a state where the metal plate 3 is pressed by the top plate forming surface of the punch 12 and the pad 13 .

[0200] However, as described above, the first vertical wall angle θ1 on the molding surfaces of the dies 11 and 12 used in the first step 10A is set to an angle smaller than the vertical wall angle θ0 in the target component shape 1 .

[0201] However, the first vertical wall angle θ1 is set based on the vertical wall angle θ1′ of the intermediate component 4. Furthermore, the vertical wall angle θ1′ is the vertical wall angle of the intermediate component 4 after the metal sheet 3 is press-formed and released from the mold in the first step 10A. Specifically, the first vertical wall angle θ1 is set to be smaller than the vertical wall angle θ0 in the target component shape 1. Furthermore, the intermediate component 4 assumes the shape after release from the mold, that is, the shape of the intermediate component 4 after springback.

[0202] The first vertical wall angle θ1 may be set by, for example, CAE analysis or actual stamping evaluation.

[0203] Furthermore, the first vertical wall angle θ1 is set as described above for each of the vertical wall angles on the left and right vertical wall portions 1B side.

[0204] Alternatively, only the vertical wall angle on one of the left and right vertical wall portions, on the vertical wall portion 1B side, may be set to the first vertical wall angle θ1 as described above. In this case, the vertical wall angle on the other vertical wall portion 1B side may be set to an angle equal to the vertical wall angle θ0 in the target component shape 1. Even if only the first vertical wall angle is set on one vertical wall portion 1B side based on the present disclosure, an effect is achieved. However, it is preferred that the vertical wall angles on both the left and right vertical wall portions 1B sides be set to the first vertical wall angle θ1 as described above.

[0205] (Second step 10B)

[0206] The second step 10B is a step of press-forming the intermediate component 4 manufactured in the first step 10A to manufacture a press-formed product having the target component shape 1 .

[0207] The molding surface of the mold used in the second step 10B has a second vertical wall angle θ2 that is greater than the vertical wall angle θ0 of the target component shape 1. In addition, the molding surfaces of the molds 14 and 15 used in the second step 10B are Figure 23 (a) and as a schematic diagram Figure 6 Similarly, the molds 14A and 15A have molding surfaces 14A and 15A that follow the target part shape 1 except for the vertical wall angle. The molds 14 and 15 are a die 14 as an upper mold and a punch 15 as a lower mold.

[0208] The second vertical wall angle θ2 is preferably greater than the vertical wall angle θ0 of the target part shape 1. That is, in the second step 10B, the vertical wall portion 1B is bent and restored. Therefore, the molding surface shape of the mold in the second step 10B is preferably designed so that the second vertical wall angle θ2 is greater than the vertical wall angle θ0 of the target part shape 1.

[0209] Furthermore, the mold used in the second step 10B includes a spacer 16 for pressing the top plate portion of the intermediate member 4 .

[0210] Here, the second vertical wall angle θ2 is set to an angle greater than the vertical wall angle θ0. Therefore, the second vertical wall angle θ2 is greater than the vertical wall angle θ1′ of the intermediate component 4. Therefore, during the forming process in the second step 10B, a problem arises if the following forming method is used. Specifically, consider a case where a spacer 16 is extended from the die 14 side, and the top plate portion of the intermediate component 4 is sandwiched between the spacer 16 and the punch 15 for forming. In this case, when the intermediate component 4 is placed on the punch 16, there is a high possibility that the intermediate component 4 will not be placed in the specified position on the punch 16, resulting in an unstable forming state.

[0211] Therefore, in the second step 10B of the present embodiment, the intermediate component 4 is placed on the pad 16 in a state where the pad 16 protrudes from the top plate forming surface of the punch 16 before forming. Thereafter, the top plate portion of the intermediate component 4 is pressed against the top plate forming surface of the die 14 by the pad 16 (see FIG. Figure 6 (a)). In this state, the intermediate member 4 is press-formed by the spacer 16 and the die 14. In this embodiment, the second step 10B is a structure that performs the above-mentioned operations.

[0212] (Regarding the mutual relationship between the vertical wall angles)

[0213] Here, the vertical wall angle in the target component shape 1 is denoted as θ0. The first vertical wall angle on the molding surfaces of dies 11 and 12 in the first step 10A is denoted as θ1. The vertical wall angle in the intermediate component 4 is denoted as θ1′. The vertical wall angle θ1′ is the angle after release from the mold and springback. The second vertical wall angle on the molding surfaces of dies 14 and 15 in the second step 10B is denoted as θ2.

[0214] In addition, in this embodiment, the vertical wall portion 1B exists on the left and right, but it is preferable that each of the left and right independently satisfies the following conditions.

[0215] The first vertical wall angle θ1 and the second vertical wall angle θ2 are preferably set to satisfy the following formula (1). That is, the second vertical wall angle θ2 of the mold in the second step 10B is preferably set larger than the vertical wall angle θ0 in the target component shape 1 .

[0216] θ1<θ1′<θ0<θ2…(1)

[0217] Furthermore, it is preferable that the second vertical wall angle θ2 is smaller than 1.05 times the vertical wall angle θ0.

[0218] Furthermore, it is preferable to set the first vertical wall angle θ1 and the second vertical wall angle θ2 so as to satisfy the following formula (8).

[0219] 0.4×εt1≤εt2<0.9×εt1…(8)

[0220] Here, regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the second step 10B, the absolute value of the average strain of the top plate portion at least at the position forming the bent portion is defined as εt2. In addition, regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the first step, the absolute value of the average strain of the top plate portion at least at the position forming the above-mentioned bent portion is defined as εt1.

[0221] When the cross-sectional shape is a hat shape having a flange portion, it is preferable to set the first vertical wall angle θ1 and the second vertical wall angle θ2 so as to satisfy the following formula (9).

[0222] 0.4×εb1≤εb2<0.9×εb1…(9)

[0223] Here, regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the second step, the absolute value of the average value of the strain of the flange portion at least at the position that becomes the bent portion is defined as εb2. In addition, regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the first step, the absolute value of the average value of the strain of the flange portion at least at the position that becomes the bent portion is defined as εb1.

[0224] When the cross-sectional shape is a U-shape without a flange portion, the absolute value of the average value of the strain of the lower half of the vertical wall portion may be used as εb1 and εb2 instead of the absolute value of the average value of the strain of the flange portion.

[0225] Here, the reasons for the conditions of formulas (8) and (9) will be described later.

[0226] In addition, the above-mentioned appropriate ranges (values) may vary depending on the shape of the component and the strength of the material. Therefore, it is preferable to examine the conditions for each component.

[0227] (Action and other)

[0228] Comparative Forming Methods

[0229] Here, as a comparative forming method, a pad that presses the entire surface of the top plate portion is used, and collision forming with a pad is applied. Figure 24 Indicates the shape before and after mold release (before and after springback). Here, the target part shape is set to Figure 21 The shape shown is formed into the target component shape through a single press forming operation. Specifically, the entire surface of the metal plate 3, which will become the top plate portion 1A, is clamped between the punch and the spacer. In this state, press forming is performed using the punch (lower die) and the die (upper die). Furthermore, the forming surfaces (die shape) of the punch and die are formed to mimic the target component shape 1.

[0230] In this case, according to Figure 24 It can be seen that the curvature when viewed from the side changes before and after the springback. Specifically, it can be seen that the curvature radius when viewed from the side increases along the longitudinal direction due to the springback.

[0231] Figure 25 The stress distribution in the longitudinal direction of the plate thickness center at the bottom dead point of the punching of the component 6 when the comparative forming method is adopted is shown.

[0232] like Figure 25 As shown, tensile stress is generated on a large scale in the top plate portion. In addition, compressive stress is generated on a large scale in the flange portion. It is believed that the above-mentioned springback in the length direction is caused by the release of these stresses when the mold is demolded. In addition, the springback in the length direction is also called bending return. Moreover, the higher the material strength, the more the residual stress increases, and the rebound amount tends to increase. Moreover, if the material strength becomes higher, the material strength variation during mass production also becomes relatively larger. Therefore, the material strength varies between the above-mentioned coils (between manufacturing batches of the plate), and the dimensional accuracy variation issue of the change in the rebound amount also arises.

[0233] This dimensional accuracy change is explained using a stress-strain relationship diagram. Figure 26 The relationship between the stress and strain of the flange portion during normal forming using a comparative forming method is shown. Here, the stress of the flange portion is the stress in the longitudinal direction. Figure 26 In the figure, the variation of material strength is assumed, and a schematic diagram of two materials, a strength-enhancing material and a strength-reducing material, is shown. In this example, when the material is formed into the product shape, the material of the flange portion is formed in a shrinking manner. Therefore, although compressive stress is generated in the flange portion, in the strength-enhancing material and the strength-reducing material, as shown in FIG. Figure 26 As shown in the figure, there are differences in the stress values ​​at the bottom dead point of forming. Figure 26 The position that becomes the product shape is called the bottom dead point of forming.

[0234] If the mold is released from the state of the lower dead point of the forming process, a bend return (springback) occurs. Furthermore, this bend return causes a change in the curvature in the longitudinal direction. Furthermore, the amount of bend return varies between strength-enhancing materials and strength-reducing materials. In other words, dimensional accuracy varies between materials. As the material strength increases, this dimensional accuracy variation increases, deviating from the product's dimensional tolerance. Therefore, dimensional accuracy variation is a significant issue for materials with high strength.

[0235] In order to reduce the bending return and dimensional accuracy variation, in this embodiment, it is set to Figure 27 That is, in the stamping method of this embodiment, in the first step 10A, the vertical wall angle θ1 between the top plate portion and the vertical wall portion is formed to be smaller than the vertical wall angle of the target part shape (refer to Figure 27 (a)). In addition, in the second step 10B, the vertical wall angle θ2 is larger than the vertical wall angle after rebound in the first step 10A (see Figure 27 (b)). In addition, in this embodiment, as Figure 27As shown, in the first step 10A, the vertical wall portion is preferably temporarily formed so that its line length L1 is equal to or greater than the line length of the vertical wall portion of the target component shape. The line length of the vertical wall portion of the target component shape corresponds to the line length L2. Subsequently, in the second step 10B, the vertical wall portion is preferably formed so that its line length L2 is equal to the line length of the vertical wall portion of the target component shape.

[0236] Here, consider the intermediate component 4 after being released from the mold in the first step 10A. Due to springback, the vertical wall angle θ1′ of this intermediate component 4 becomes slightly larger than the vertical wall angle θ1 of the mold in the first step. The mold in the first step 10A is preferably designed so that the vertical wall angle θ1′ after springback in the first step is smaller than the vertical wall angle θ0 of the target component shape. In this embodiment, the metal plate 3 is primarily made of a high-strength material. However, the present invention is not limited to high-strength materials; mild steel plates, aluminum plates, and the like may also be used.

[0237] In the second step 10B, the vertical wall portion needs to be bent back. Therefore, it is preferable to design the mold for the second step 10B so that the vertical wall angle θ2 in the second step 10B is equal to or greater than the vertical wall angle θ0 of the target component shape.

[0238] In this embodiment, the target component shape 1 has a hat-shaped cross section with a pair of left and right vertical wall portions 1B and a flange portion 1C on either side of the top plate portion 1A in the width direction. Alternatively, the first step 10A and the second step 10B may be performed using a mold in which at least one of the left and right vertical wall portions has a first vertical wall angle θ1 and a second vertical wall angle θ2.

[0239] In this embodiment, the mold shapes for the first step 10A and the second step 10B are designed as described above. This reverses the stress that primarily contributes to the return bend in the second step 10B. As a result, the return bend amount and the dimensional accuracy variation of the return bend are reduced. Furthermore, the stress that primarily contributes to the change in vertical wall angle is also restored by bending in the second step 10B. This reverses the stress on the punch shoulder, or applies stress in the opposite direction around the punch shoulder. As a result, in this embodiment, both vertical wall angle variation and dimensional accuracy variation are reduced.

[0240] Here, stretch forming or collision forming can be applied in the first process 10A. In addition, in the second process 10B, it can be formed into the target part shape. However, in the second process 10B, as in normal forming, when the liner is extended from the die side and the intermediate part is clamped by the liner and the punch for forming, there is a possibility of the following problem. That is, when the intermediate part is placed on the lower die, the vertical wall angle θ1′ of the intermediate part 4 is smaller than the vertical wall angle θ2 of the die (product) of the second process. Therefore, the intermediate part is formed in an unstable state supported by the lower die (punch). As a result, there is a concern that positional deviation will occur and the target shape cannot be obtained.

[0241] In order to avoid this situation, in this embodiment, Figure 23 As shown, in the second step 10B, before forming, the intermediate component 4 is placed on the spacer 16, with the spacer 16 extending from the top plate forming surface of the punch 15. Then, forming is performed with the top plate portion of the intermediate component 4 sandwiched between the die 14 and the spacer 16. This forming method prevents the intermediate component 4 from being in an unstable state supported by the punch 15 in the second step, allowing for stable forming.

[0242] Figure 28 、 Figure 29 The stress distribution at the center of the plate thickness in the longitudinal direction at the bottom dead point of forming when a stamped product is formed by the method of this embodiment is shown. Here, θ1 = 95° and θ2 = 130° are set. Figure 28 shows the stress distribution after the first step 10A, Figure 29 It represents the stress distribution after the second process 10B. Figure 28 As shown in FIG. 1 , at the bottom dead center of the first step 10A, compressive stress is generated in a wide range in the flange portion. In addition, tensile stress is generated in a wide range in the top plate portion. Figure 29 As shown, at the bottom dead center of the second step 10B, the flange portion is reversed to tensile stress, and the tensile stress of the top plate portion is reduced. Therefore, by adopting the method of this embodiment, stress is reversed or reduced compared to the conventional method.

[0243] This is for the following reason. Specifically, in the second step 10B, the flange portion is formed so as to be stretched in the longitudinal direction. This causes the flange portion to be formed in the direction of linear extension, thus generating tensile stress. Furthermore, influenced by this, the top plate portion is formed in the direction of linear contraction, resulting in a reduction in tensile stress. Furthermore, in the absence of a flange portion with a U-shaped cross-section, the lower side of the vertical wall portion performs the same function as the flange portion described above.

[0244] Thus, the variation in dimensional accuracy when forming is performed by the method of this embodiment will be described with reference to the stress-strain relationship diagram. Figure 30 This is a diagram showing the relationship between stress and strain in the flange portion according to the method of this embodiment. Figure 30 In the figure, a schematic diagram of two materials, a strength-enhancing material and a strength-reducing material, is shown, assuming a change in material strength.

[0245] In this embodiment, in the first process 10A, the longitudinal wall angle θ1 is formed to be smaller than the longitudinal wall angle θ0 of the target part shape 1. As a result, a strain and stress greater than those in the conventional method (comparative forming method) are imparted. Thereafter, in this embodiment, in the second process 10B, the longitudinal wall angle θ2 is formed to be greater than the longitudinal wall angle θ0 of the target part shape 1. As a result, the material of the flange portion is formed in the direction in which it is stretched. As a result, the compressive stress is reversed to the tensile stress. Here, as Figure 30 As shown, if stress is reversed, the history curves of the strength-enhancing and strength-reducing materials intersect in the low-stress region. By targeting this intersection point and setting the bottom dead center, the vertical wall angle in the first step 10A can be reduced. In this case, the stress and stress difference between the strength-enhancing and strength-reducing materials at the bottom dead center are further reduced, further minimizing warpage and dimensional accuracy variations.

[0246] Furthermore, if the curvature of a single bent portion in the longitudinal direction is not constant, it is sufficient to reduce the vertical wall angle of only a portion of the bent portion in the first step 10A. For component shapes composed of multiple bent portions, it is sufficient to reduce the vertical wall angle of at least one of the bent portions in the first step 10A.

[0247] Furthermore, in the second step 10B, the longitudinal wall portion of the intermediate component 4 formed in the first step 10A is formed in a manner that allows for bending recovery. Consequently, the stress in the cross-sectional direction of the punch shoulder is reversed, or stress in the opposite direction is applied to the area surrounding the punch shoulder. Consequently, variations in the longitudinal wall angle and dimensional accuracy are reduced. However, when forming is performed under conditions that minimize the amount of bending recovery and variations in dimensional accuracy associated with the aforementioned bending recovery, the following phenomenon may occur: The stress in or around the punch shoulder is excessively reversed. Consequently, springback may occur in a direction smaller than the longitudinal wall angle of the die used in the second step.

[0248] Therefore, it is preferable to design the vertical wall angle after springback in the second step 10B so as to achieve the target part shape. In other words, it is preferable to design the vertical wall angle θ2 of the mold in the second step 10B to be greater than the vertical wall angle θ0 of the product.

[0249] Here, in this embodiment, the strain of the top plate portion is described as t, as represented by εt1 and εt2, and the strain of the flange portion is described as b, as represented by εb1 and εb2.

[0250] in addition, Figure 31 、 Figure 32 The figure shows the strain distribution at the center of the plate thickness in the longitudinal direction at the bottom dead point of forming when a pressed product is formed by the manufacturing method of the present embodiment. Figure 31 It shows the strain distribution in the first step. Figure 32 represents the strain distribution in the second process. Figure 31 As shown in FIG. 1 , a large compressive strain is generated particularly in the flange portion in the first step 10A. Figure 32 As shown, in the second step 10B, the compressive strain of the flange portion generated in the first step 10A is reduced.

[0251] As such, the method of this embodiment becomes Figure 30 The strain behavior shown here is shown. Here, regarding the strain distribution in the longitudinal direction generated at the bottom dead point of the press in the second step 10B, the absolute value of the average strain of the top plate portion is defined as εt2. Furthermore, regarding the strain distribution in the longitudinal direction generated at the bottom dead point of the press in the first step 10A, the absolute value of the average strain of the top plate portion is defined as εt1.

[0252] Figure 33 Yes Figure 21 The results of the stamping investigation of the relationship between εt2 / εt1 and the height deviation of the product after stamping are shown. Figure 33 In the table, “□” indicates the result when a steel plate with a tensile strength of 590 MPa is used. “○” indicates the result when a steel plate with a tensile strength of 980 MPa is used. “△” indicates the result when a steel plate with a tensile strength of 1180 MPa is used.

[0253] In addition, if Figure 24 As shown, Figure 33 The height deviation of the vertical axis in the figure is the value indicating the height difference between the target part shape and the part shape after demolding. The height deviation is calculated as follows. First, at the center of the length, the top plate of the target part shape 1 is aligned with the top plate of the shape after demolding. In this state, Figure 24 The height difference between the longitudinal end portions shown is regarded as the height deviation from the product in this embodiment.

[0254] In this embodiment, the target range of the height deviation amount that will become a good shape is set to within ±2mm. Figure 33 It can be seen that εt2 / εt1 is preferably in the range of 0.4 to 0.9.

[0255] That is, it is preferable to set the values ​​of the vertical wall angles θ1 and θ2 of the mold in the first step 10A and the second step 10B so as to satisfy the following formula (11).

[0256] 0.4×εt1≤εt2<0.9×εt1…(11)

[0257] Figure 34 Yes Figure 21 The results of the stamping investigation of the relationship between εb2 / εb1 and the height deviation of the product after stamping are shown. Figure 34 In the table, “□” indicates the result when a steel plate with a tensile strength of 590 MPa is used. “○” indicates the result when a steel plate with a tensile strength of 980 MPa is used. “△” indicates the result when a steel plate with a tensile strength of 1180 MPa is used.

[0258] Here, regarding the strain distribution in the longitudinal direction generated at the bottom dead point of the stamping in the second step, the absolute value of the average strain of the flange portion is defined as εb2. Furthermore, regarding the strain distribution in the longitudinal direction generated at the bottom dead point of the stamping in the first step, the absolute value of the average strain of the flange portion is defined as εb1.

[0259] In this embodiment, the target range of the height deviation amount that will become a good shape is set to within ±2mm. Figure 34 It can be seen that εb2 / εb1 is preferably in the range of 0.4 to 0.9.

[0260] That is, it is preferable to set the values ​​of the vertical wall angles of the dies in the first and second steps so as to satisfy the following formula (12).

[0261] 0.4×εb1≤εb2<0.9×εb1…(12)

[0262] Here, in this embodiment, the case where the cross section of the target component shape is a hat shape is described. In the case where the cross section of the target component shape is a U-shape, the phenomenon generated in the flange portion in the first process 10A and the second process 10B occurs in the lower side portion of the vertical wall portion. Therefore, in the case of a U-shaped cross section without a flange portion, the stamped product can be set as follows. That is, it is preferred that the absolute value of the average value of the strain of the portion forming the lower half of the vertical wall portion be set to εb2 relative to the second process 10B and to εb1 relative to the first process 10A. Furthermore, it is preferred to set the values ​​of the vertical wall angles θ1 and θ2 of the molds of the first process 10A and the second process 10B in a manner that satisfies formula (11) or formula (12).

[0263] Here, if εt2 is less than 0.4×εt1, then there exists Figure 30There is a concern that the strain recovery in the second step 10B shown may become excessive. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be reduced to below the desired value. Therefore, εt2 is preferably at least 0.4×εt1. εt2 is more preferably at least 0.5×εt1.

[0264] On the other hand, if εt2 exceeds 0.9 × εt1, there is a concern that the strain recovery in the second step 10B may become insufficient. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be reduced to below the desired value. Therefore, εt2 is preferably less than 0.9 × εt1. More preferably, εt2 is 0.8 × εt1 or less.

[0265] In addition, if εb2 is less than 0.4×εb1, then there exists Figure 30 There is a concern that the strain recovery in the second step 10B shown may become excessive. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be reduced to below the desired value. Therefore, εb2 is preferably 0.4×εb1 or greater. εb2 is more preferably 0.6×εb1 or greater.

[0266] On the other hand, if εb2 exceeds 0.9 × εb1, there is a concern that the strain recovery in the second step 10B may be insufficient. In this case, there is a possibility that the difference in springback caused by the difference in material strength cannot be reduced to below the desired value. Therefore, εb2 is preferably less than 0.9 × εb1. More preferably, εb2 is 0.8 × εb1 or less.

[0267] Furthermore, when designing the mold shapes for the first step 10A and the second step 10B, if the design is started without taking into account the vertical wall angle θ0 of the product, or if the design is started from the mold of the second step 10B, the following problems may occur: Specifically, it may be impossible to find an appropriate mold shape, or it may take an extremely long time to find it.

[0268] Therefore, in this embodiment, when designing the mold shape of the first process 10A and the second process 10B, it can be done as follows. First, the vertical wall angle θ1 of the mold of the first process 10A is set to a value smaller than the vertical wall angle θ0 of the product, and CAE analysis or actual stamping is performed. Then, the condition is found that the vertical wall angle θ1′ after the rebound of the first process 10A is smaller than the vertical wall angle θ0 of the product. Thereafter, in the second process 10B, CAE analysis or actual stamping is performed with the mold shape of the forming surface having a vertical wall angle greater than the vertical wall angle θ0 of the target part shape. Then, the condition is found that the vertical wall angle after the rebound of the second process 10B becomes the target part shape and the dimensional accuracy variation is suppressed. Through such a design, the mold shape can be designed in a short time.

[0269] Based on the above, the method of this embodiment can be appropriately applied even when using high-strength materials with a tensile strength of 590 MPa or greater, or ultra-high-strength materials with a tensile strength of 980 MPa or greater. Specifically, according to this disclosure, variations in dimensional accuracy resulting from variations in material strength can be significantly reduced through a simple mold structure. Consequently, according to this disclosure, high-precision components with shapes close to the target can be obtained.

[0270] (other)

[0271] The present disclosure may also adopt the following structures.

[0272] (1) Disclosure 1 is a method for manufacturing a stamped product, wherein a metal sheet is formed into a target component shape, wherein the target component shape has a cross section including a top plate portion and a longitudinal wall portion connected to a widthwise end portion of the top plate portion and extending in a direction different from the top plate portion, and has one or more curved portions curved in a direction intersecting the cross section, i.e., in a longitudinal direction, wherein:

[0273] When the angle between the top plate portion and the vertical wall portion in the above cross section is defined as the vertical wall angle,

[0274] A first step of press-forming a metal plate into an intermediate member having the top plate portion and the vertical wall portion using a die having a forming surface having a first vertical wall angle smaller than the vertical wall angle of the target member shape at a position forming the bent portion; and

[0275] a second step of press-forming the intermediate component using a die having a forming surface having a second vertical wall angle greater than the vertical wall angle of the target component shape at a position forming the bent portion;

[0276] At the position forming the bent portion, the first vertical wall angle is set so as to be smaller than the vertical wall angle of the target component shape regarding the vertical wall angle of the intermediate component after demolding in the first step.

[0277] (2) Disclosure 2 is that the bent portion has a curve that is concave or convex toward the vertical wall portion.

[0278] (3) Disclosure 3 is that, when the vertical wall angle in the target component shape is defined as θ0, the first vertical wall angle is defined as θ1, the vertical wall angle in the intermediate component formed and demolded in the first step is defined as θ1′, and the second vertical wall angle is defined as θ2,

[0279] The first vertical wall angle θ1 and the second vertical wall angle θ2 are press-formed using a die having a forming surface that satisfies the following formula (1).

[0280] θ1<θ1′<θ0<θ2…(1)

[0281] (4) Disclosure 4 is that, when the first vertical wall angle is defined as θ1 and the second vertical wall angle is defined as θ2,

[0282] The first vertical wall angle θ1 and the second vertical wall angle θ2 are set so as to satisfy the following formula (2).

[0283] 0.7≤(θ1 / θ2)…(2)

[0284] (5) Disclosure 5 is that, when the vertical wall angle in the target component shape is defined as θ0 and the first vertical wall angle is defined as θ1,

[0285] The first vertical wall angle θ1 is set to a value that satisfies the following formula (3).

[0286] 0.75≤(θ1 / θ0)…(3)

[0287] (6) Disclosure 6 is that, when the second vertical wall angle is defined as θ2 and the vertical wall angle of the intermediate member formed and demolded in the first step is defined as θ1′,

[0288] The second vertical wall angle θ2 is set to a value that satisfies the following formula (4).

[0289] 0.8≤(θ1′ / θ2)…((4)

[0290] (7) Disclosure 7 is that, when the vertical wall angle in the target component shape is defined as θ0 and the second vertical wall angle is defined as θ2,

[0291] The value of the second vertical wall angle θ2 is set so as to satisfy the following formula (5).

[0292] (θ2 / θ0)<1.05…(5)

[0293] (8) Disclosure 8 is to bend the bent portion into a target component shape that is convex toward the vertical wall portion.

[0294] Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the second step, the average value of the strain of the lower half of the vertical wall portion of the vertical wall portion that protrudes when viewed from above at the position forming the curved portion is defined as ε2.

[0295] Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the stamping process of the first step, when the average value of the strain of the lower half of the vertical wall portion of the vertical wall portion protruding when viewed from above at the position of the bent portion is defined as ε1,

[0296] The first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (6).

[0297] 0.4×|ε1|≤|ε2|<0.85×|ε1|…(6)

[0298] (9) Disclosure 9 is to bend the bent portion into a target component shape that is concave toward the vertical wall portion.

[0299] Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the second step, the average value of the strain of the lower half of the vertical wall portion of the vertical wall portion that is concave when viewed from above at the position of the bent portion is defined as ε2′.

[0300] Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the stamping process of the first step, when the average value of the strain of the lower half of the vertical wall portion of the vertical wall portion that is concave when viewed from above is defined as ε1′,

[0301] The first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (7).

[0302] 0.4×|ε1′|≤|ε2′|<0.85×|ε1′|…(7)

[0303] (10) Disclosure 10 is that the curved portion has a curve that is concave or convex toward the top plate portion.

[0304] (11) Disclosure 11 is that, when the vertical wall angle in the target component shape is defined as θ0, the first vertical wall angle is defined as θ1, the vertical wall angle in the intermediate component formed and demolded in the first step is defined as θ1′, and the second vertical wall angle is defined as θ2,

[0305] The first vertical wall angle θ1 and the second vertical wall angle θ2 are press-formed using a die having a forming surface that satisfies the following formula (1).

[0306] θ1<θ1′<θ0<θ2…(1)

[0307] (12) Disclosure 12 is that regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the stamping forming of the second step, the absolute value of the average value of the strain of the top plate portion at the position of the bent portion is defined as εt2,

[0308] Regarding the strain distribution in the longitudinal direction at the bottom dead point of the press in the first step, when the absolute value of the average value of the strain of the top plate portion at the position of the bent portion is defined as εt1,

[0309] The first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (8).

[0310] 0.4×εt1≤εt2<0.9×εt1…(8)

[0311] (13) Disclosure 13 is that the cross section is a U-shaped or a cap-shaped having a flange portion,

[0312] Regarding the strain distribution in the longitudinal direction at the stamping bottom dead point in the stamping forming of the second step, at the position of the bent portion, when the cross section is a U-shaped portion, the absolute value of the average value of the strain in the lower half of the longitudinal wall portion is defined as εb2, and when the cross section is a hat shape having a flange portion, the absolute value of the average value of the strain in the flange portion is defined as εb2.

[0313] Regarding the strain distribution in the longitudinal direction at the stamping bottom dead point in the stamping forming of the above-mentioned first process, at the position of the above-mentioned bent portion, when the above-mentioned cross-section is a U-shaped, the absolute value of the average value of the strain in the lower half of the vertical wall portion is defined as εb1, and when the above-mentioned cross-section is a hat shape with a flange portion, the absolute value of the average value of the strain in the above-mentioned flange portion is defined as εb1.

[0314] The first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (9).

[0315] 0.4×εb1≤εb2<0.9×εb1…(9)

[0316] (14) Disclosure 14 is that the mold used in the second step comprises: a die constituting one of the upper mold and the lower mold, and a punch constituting the other of the upper mold and the lower mold,

[0317] In the second step, press forming is performed in a state where the top plate portion of the intermediate member is sandwiched between the top plate forming surface of the die and the spacer extending from the top plate forming surface of the punch.

[0318] (15) Disclosure 15 is a method for designing a mold used in the method for manufacturing a stamped product described in any one of Disclosures 1 to 9, wherein:

[0319] When designing the vertical wall angles of each mold in the first and second steps,

[0320] First, perform CAE analysis or actual stamping on the vertical wall angle of the die in the first process with a value smaller than the vertical wall angle of the product. Find the condition where the vertical wall angle after springback in the first process is smaller than the vertical wall angle of the product, and then set the first vertical wall angle.

[0321] Afterwards, for the second process, CAE analysis or actual stamping is performed with a mold shape having a forming surface with a longitudinal wall angle greater than the longitudinal wall angle of the target part shape, and the condition that the part shape after rebound in the second process satisfies the allowable range of the longitudinal wall angle and torsion in the above-mentioned target part shape is found to set the above-mentioned second longitudinal wall angle.

[0322] (16) Disclosure 16 is a method for designing a mold used in the method for manufacturing a stamped product described in any one of Disclosures 10 to 13, wherein:

[0323] When designing the vertical wall angles of each mold in the first and second steps,

[0324] First, perform CAE analysis or actual stamping on the vertical wall angle of the die in the first process with a value smaller than the vertical wall angle of the product. Find the condition where the vertical wall angle after springback in the first process is smaller than the vertical wall angle of the product, and then set the first vertical wall angle.

[0325] Afterwards, for the second process, CAE analysis or actual stamping is performed on the mold shape having a forming surface with a longitudinal wall angle greater than the longitudinal wall angle of the target part shape, and the condition that the part shape after rebound in the second process meets the allowable range of the longitudinal wall angle in the above-mentioned target part shape is found to set the above-mentioned second longitudinal wall angle.

[0326] Example

[0327] The torsional springback reduction effect of the stamping method of the present invention was confirmed. To conduct this confirmation, stamping analysis and springback analysis based on the finite element method (FEM) were performed. The results are described below.

[0328] "Examples relative to the first embodiment"

[0329] (Example 1)

[0330] In this embodiment, the target part shape 1 is set to Figure 1 The shape shown is a left-right curve in the center of the longitudinal direction, curving toward the width of the top plate. The metal sheets 3 (blanks) used in the stamping process were steel sheets with tensile strengths of 980 MPa and 1180 MPa, respectively. This was done to evaluate the strength of the two materials in order to compare dimensional accuracy variations. Furthermore, the thickness t of both steel sheets was 1.4 mm.

[0331] The case of stamping a blank 3 (metal plate) was used as the subject. Furthermore, the first vertical wall angle θ1 of the die in the first step 10A was reduced. Then, stamping analysis and springback analysis were performed on this case, and the torsion of the component before and after springback was measured.

[0332] Here, the vertical wall angle θ2 of the mold in the second step 10B was selected from 105°, 110°, and 115°. Then, the vertical wall angle θ1 of the mold in the first step 10A was changed between 90° and 115°, and FEM analysis was performed for evaluation.

[0333] The twist amount is calculated as follows. First, the target part shape 1 and the shape after demolding are aligned so that the slope of the top plate of the longitudinal center section is consistent. Then, Figure 8 The inclination angle of the top plate portion of the AA′ cross section at the longitudinal end portion shown was evaluated. Furthermore, a counterclockwise twist was indicated as positive, and a clockwise twist was indicated as negative.

[0334] In this example, a twist amount within ±2.0° was considered acceptable. Also, a twist amount difference between the 980 MPa material and the 1180 MPa material within ±1.0° was considered acceptable.

[0335] (first example)

[0336] In the first example, the vertical wall angle θ2 of the mold in the second step 10B was fixed at 115°. The evaluations in Table 1 are the results when the vertical wall angle θ1 of the mold in the first step 10A was set to 90°, 95°, and 115°.

[0337] In the first example, the vertical wall angle θ0 of the target component shape 1 is set to 110°.

[0338] Table 1 shows the evaluation results of the first example.

[0339] [Table 1]

[0340]

[0341] <No.1-5、No.1-6>

[0342] No. 1-5 and No. 1-6 in Table 1 are evaluations of the torsion amounts of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 115°.

[0343] As can be seen from No. 1-6, in the 1180 MPa material, the vertical wall angle after springback after the first step 10A, i.e., the vertical wall angle θ1′ of the intermediate component 4, is greater than 120°. This vertical wall angle θ1′ significantly exceeds the vertical wall angle θ0 of the target component shape 1, which is 110°, and the vertical wall angle θ2 of the mold in the second step 10B, which is 115°. Furthermore, the amount of twist after springback in both the first step 10A and the second step 10B is relatively large, at 3.6°.

[0344] Furthermore, as can be seen from No. 1-5, the vertical wall angle after springback after the first step 10A, i.e., the vertical wall angle θ1′ of the intermediate component 4, also exceeded 120°. This vertical wall angle θ1′ significantly exceeded the vertical wall angle θ0 of the target component shape 1, which was 110°, and the vertical wall angle θ2 of the mold in the second step 10B, which was 115°. Furthermore, the amount of twist after springback in both the first step 10A and the second step 10B was 2.0°.

[0345] Furthermore, according to No. 1-5 and No. 1-6, the variation in dimensional accuracy between material strengths was 1.6°.

[0346] Furthermore, while the vertical wall angle θ2 of the die in the second step 10B was 115°, the vertical wall angle after springback in the second step 10B of the 1180 MPa material of No. 1-6 was approximately 123°. In other words, a large springback occurred.

[0347] In addition, in the 980 MPa material of No. 1-5, the vertical wall angle after the springback in the second step 10B was 122°. This shows that there was a dimensional accuracy variation of 1° or more between No. 1-5 and No. 1-6.

[0348] <No.1-3、No.1-4>

[0349] No. 1-3 and No. 1-4 are the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 95°.

[0350] As shown in No. 1-4, the vertical wall angle θ1′ after springback in the 1180 MPa material after the first step 10A is approximately 105°. This vertical wall angle θ1′ is smaller than the vertical wall angle θ0 of 110° for the target part shape 1 and the vertical wall angle θ2 of 115° for the mold in the second step 10B. Furthermore, the twist after springback in the second step 10B is significantly reduced to 0.0°.

[0351] Furthermore, as can be seen from No. 1-3, in the 980 MPa material, the amount of twist after springback in the second step 10B was also significantly reduced to -0.1°. Furthermore, the dimensional accuracy variation between material strengths was also reduced to 0.1°.

[0352] Furthermore, the vertical wall angle, relative to the vertical wall angle θ2 of 115° in the mold of the second step 10B, was as follows. Specifically, after the springback in the second step 10B, the vertical wall angle remained approximately 110° for both the 1180 MPa and 980 MPa materials, indicating a reduced springback. Furthermore, the difference between the 1180 MPa material of No. 1-4 and the 980 MPa material of No. 1-3 was reduced to approximately 0.5°.

[0353] <No.1-1、No.1-2>

[0354] No. 1-1 and No. 1-2 show the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 90°.

[0355] According to No. 1-2, in the 1180 MPa material, the vertical wall angle θ1′ after springback in the first step 10A is approximately 100°. This vertical wall angle θ1′ is smaller than the vertical wall angle θ0 of the target part shape 1 (110°) and the vertical wall angle θ2 of the mold in the second step 10B (115°).

[0356] In addition, the twist amount after the springback in the second step 10B was -1.0° in the opposite direction.

[0357] Furthermore, according to No. 1-1, the twist after springback in the second step 10B also produced a twist of -0.7° in the opposite direction in the 980 MPa material. However, this twist was lower than that in the conventional method, and the dimensional accuracy variation between material strengths was also reduced to 0.3°. This suggests that excessively reducing the vertical wall angle θ1 in the first step 10A leads to excessive stress reversal, resulting in twist in the opposite direction.

[0358] Based on the above, by performing forming with a vertical wall angle θ1 of 95° in the mold in the first step 10A and a vertical wall angle θ2 of 115° in the mold in the second step 10B, as in No. 1-3 and No. 1-4, the amount of twisting, the amount of change in the vertical wall angle, and the resulting dimensional accuracy variations were significantly reduced. Furthermore, under these conditions, the vertical wall angle after springback in the second step 10B was approximately 110°, which was lower than the vertical wall angle θ2 of the mold in the second step 10B.

[0359] This shows that, when the vertical wall angle after springback in the second step 10B is set as the target part shape 1, the vertical wall angle θ1 of the mold in the first step 10A needs to be designed to be smaller than the target part shape 1. Furthermore, it can be seen that the vertical wall angle θ2 of the mold in the second step 10B needs to be designed to be greater than the vertical wall angle θ0 of the target part shape 1.

[0360] (Second example)

[0361] In the second example, the vertical wall angle θ2 of the mold in the second step 10B is fixed at 110°. Furthermore, the vertical wall angle θ1 of the mold in the first step 10A is selected and set from 90°, 92°, 95°, and 110°.

[0362] Furthermore, in the second example, the vertical wall angle θ0 of the target component shape 1 is set to 106°.

[0363] Table 2 shows the evaluation results of the second example.

[0364] [Table 2]

[0365]

[0366] <No.2-7、No.2-8>

[0367] No. 2-7 and No. 2-8 are the results of the torsion amounts of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 110°.

[0368] As shown in No. 2-8, the vertical wall angle θ1′ after springback in the first step 10A of the 1180 MPa material is approximately 120°. This vertical wall angle θ1′ significantly exceeds the vertical wall angle θ0 of the target part shape 1, which is 106°, and the vertical wall angle θ2 of the mold in the second step 10B, which is 110°. Furthermore, the amount of twist after springback in the first step 10A and the second step 10B is relatively large, at 4.0° and 3.9°, respectively.

[0369] Furthermore, according to No. 2-7, the 980 MPa material experienced 2.3° and 2.4° of twist after springback in the first step 10A and the second step 10B, respectively. Therefore, the dimensional accuracy variation between material strengths was 1.5° after the second step 10B.

[0370] Furthermore, while the vertical wall angle θ2 of the die in the second step 10B was 110°, the vertical wall angle after springback in the second step 10B of the 1180 MPa material of No. 2-8 was approximately 118°. Therefore, a large springback occurred.

[0371] In addition, in the 980 MPa material of No. 2-7, the vertical wall angle after springback in the second step 10B was approximately 117°, resulting in a dimensional accuracy variation of 1° or more.

[0372] <No.2-5、No.2-6>

[0373] No. 2-5 and No. 2-6 show the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 95°.

[0374] As shown in No. 2-6, for the 1180 MPa material, the vertical wall angle θ1′ after springback in the first step 10A is approximately 105°. This angle is smaller than the 110° angle in the die of the second step 10B. Furthermore, the twist after springback in the second step 10B is reduced to 1.0°.

[0375] Furthermore, according to No. 2-5, in the 980 MPa material, the twist amount after springback in the second step 10B was reduced to 0.2°, and the dimensional accuracy variation between material strengths was also reduced to 0.8°.

[0376] The vertical wall angle was also configured such that the vertical wall angle θ2 of the die in the second step 10B was 110°, and the vertical wall angle after springback in the second step 10B of the 1180 MPa material was approximately 107°, and the springback amount was reduced.

[0377] In addition, the difference between the 1180 MPa material of No. 2-6 and the 980 MPa material of No. 2-5 is reduced to about 0.5°.

[0378] <No.2-3、No.2-4>

[0379] No. 2-3 and No. 2-4 show the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 92°.

[0380] As shown in No. 2-4, for the 1180 MPa material, the vertical wall angle θ1′ after springback in the first step 10A is approximately 102°. This vertical wall angle θ1′ is smaller than the vertical wall angle θ0 of 106° for the target part shape 1 and the vertical wall angle θ2 of 110° for the mold in the second step 10B. Furthermore, the twist after springback in the second step 10B is significantly reduced to 0.1°.

[0381] As can be seen from No. 2-3, in the 980 MPa material, the twist amount after springback in the second step 10B is also significantly reduced to 0.0°.

[0382] Therefore, the dimensional accuracy variation between material strengths is also reduced to 0.1°.

[0383] The vertical wall angle was also configured such that the vertical wall angle θ2 of the die in the second step 10B was 110°, and the vertical wall angle after springback in the second step 10B of the 1180 MPa material was approximately 106°, and the springback amount was reduced.

[0384] In addition, the difference between the 1180 MPa material of No. 2-4 and the 980 MPa material of No. 2-3 is reduced to about 0.7°.

[0385] <No.2-1、No.2-2>

[0386] No. 2-1 and No. 2-2 show the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 90°.

[0387] According to No. 2-2, in the 1180 MPa material, the vertical wall angle θ1′ after springback in the first step 10A is approximately 100°. This vertical wall angle θ1′ is smaller than the vertical wall angle θ0 of 106° in the target part shape 1 and the vertical wall angle θ2 of 110° in the mold in the second step 10B. Furthermore, the twist after springback in the second step 10B is -0.9° in the opposite direction.

[0388] Furthermore, according to No. 2-1, the twist after springback in the second step 10B also produced a twist of -0.4° in the opposite direction in the 980 MPa material. However, this was lower than the twist in the conventional method, and the dimensional accuracy variation between material strengths was also reduced to 0.5°.

[0389] This shows that if the vertical wall angle θ1 in the first step 10A is excessively reduced, the stress is excessively reversed and twisted in the opposite direction.

[0390] As described above, by setting the vertical wall angle θ1 of the mold in the first step 10A to 92° and the vertical wall angle θ2 of the mold in the second step 10B to 110°, the amount of twisting, the amount of angular change in the vertical wall portion, and the resulting dimensional accuracy fluctuations were significantly reduced. Furthermore, under these conditions, the vertical wall angle after springback in the second step 10B was approximately 106°, which was lower than the vertical wall angle θ2 of the mold in the second step 10B.

[0391] As can be seen from this, when the vertical wall angle after springback in the second step 10B is used as the target part shape 1, the following design is necessary. That is, the vertical wall angle θ1 of the mold in the first step 10A must be designed to be smaller than the target part shape 1, and the vertical wall angle θ2 of the mold in the second step 10B must be designed to be greater than the vertical wall angle of the product.

[0392] (Third example)

[0393] In the third example, the vertical wall angle θ2 of the mold in the second step 10B is fixed at 105°. Furthermore, the vertical wall angle θ1 of the mold in the first step 10A is selected and set from 90°, 95°, 100°, and 105°.

[0394] Furthermore, in the third example, the vertical wall angle θ0 of the target component shape 1 is set to 103°.

[0395] Table 3 shows the evaluation results of the third example.

[0396] [Table 3]

[0397]

[0398] <No.3-7、No.3-8>

[0399] No. 3-7 and No. 3-8 are the results of the torsion amounts of the 980 MPa material and the 1180 MPa material when the vertical wall angle in the first step 10A was set to 105 degrees.

[0400] As shown in No. 3-8, the vertical wall angle θ1′ after springback in the first step 10A of the 1180 MPa material is approximately 115°. This vertical wall angle θ1′ significantly exceeds the vertical wall angle θ0 of the target part shape 1, which is 103°, and the vertical wall angle θ2 of the mold in the second step 10B, which is 105°. Furthermore, the amount of twist after springback in the first step 10A and the second step 10B is relatively large, at 4.1° and 3.7°, respectively.

[0401] Furthermore, according to No. 3-7, in the 980 MPa material, the amounts of torsion after springback in the first step 10A and the second step 10B were 2.5° and 2.3°, respectively.

[0402] Therefore, the variation in dimensional accuracy between material strengths becomes 1.4° after the second step 10B.

[0403] Furthermore, while the vertical wall angle θ2 of the mold in the second step 10B was 105°, the vertical wall angle after springback in the second step 10B for the 1180 MPa material of No. 3-8 was approximately 113°. Furthermore, significant springback occurred. Furthermore, the vertical wall angle for the 980 MPa material of No. 3-7 was approximately 112°. Consequently, there was a dimensional accuracy variation of more than 1° between the 1180 MPa material of No. 3-8 and the 980 MPa material of No. 3-7.

[0404] <No.3-5, No.3-6 and No.3-3, No.3-4>

[0405] No. 3-5 and No. 3-6 show the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 100 degrees.

[0406] No. 3-3 and No. 3-4 show the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 95 degrees.

[0407] Under all conditions, the vertical wall angle θ1′ after springback in the first step 10A was larger than the vertical wall angle θ0 of 103° in the target component shape 1. Furthermore, no significant decrease in dimensional accuracy variation of the twist amount after springback in the second step 10B was observed.

[0408] <No.3-1、No.3-2>

[0409] No. 3-1 and No. 3-2 show the results of the 980 MPa material and the 1180 MPa material when the vertical wall angle θ1 in the first step 10A was set to 90°.

[0410] As shown in No. 3-2, for the 1180 MPa material, the vertical wall angle θ′ after springback in the first step 10A is approximately 101°. This vertical wall angle θ′ is smaller than the vertical wall angle θ0 of 103° for the target part shape 1 and the vertical wall angle θ2 of 105° for the mold in the second step 10B. Furthermore, the twist after springback in the second step 10B is significantly reduced to -0.1°.

[0411] Furthermore, it can be seen from No. 3-1 that in the 980 MPa material, the twist amount after springback in the second step 10B is also significantly reduced to 0.0°.

[0412] Therefore, the dimensional accuracy variation between the material strengths of No. 3-1 (980 MPa) and No. 3-2 (1180 MPa) was reduced to 0.1°.

[0413] Furthermore, the vertical wall angle is also about 103° after the springback of the second step 10B of the 1180 MPa material, which is smaller than the vertical wall angle θ2 of the mold in the second step 10B: 105°.

[0414] In addition, the difference between the 1180 MPa material of No. 3-2 and the 980 MPa material of No. 3-1 is reduced to about 0.3°.

[0415] Based on the above, it can be seen that forming can be performed with a vertical wall angle θ1 of 90° for the mold in the first step 10A and a vertical wall angle θ2 of 105° for the mold in the second step 10B. In this case, the amount of twisting, the amount of angular change in the vertical wall portion, and the resulting dimensional accuracy fluctuations are significantly reduced. Furthermore, under these conditions, the vertical wall angle after springback in the second step 10B is approximately 103°, which is lower than the vertical wall angle θ2 of the mold in the second step 10B.

[0416] As can be seen from this, when the vertical wall angle after springback in the second step 10B is used as the target part shape 1, the following design is necessary. That is, the vertical wall angle θ1 of the mold in the first step 10A must be designed to be smaller than the vertical wall angle θ0 of the target part shape 1, and the vertical wall angle θ2 of the mold in the second step 10B must be designed to be greater than the vertical wall angle θ0 of the target part shape 1.

[0417] Similarly, for the 590 MPa and 780 MPa materials, based on the present invention, the following was confirmed, using the vertical wall angle after springback in the second step 10B as the target part shape 1. Specifically, the vertical wall angle θ1 of the mold in the first step 10A was designed to be smaller than the vertical wall angle θ0 of the target part shape 1, while the vertical wall angle θ2 of the mold in the second step 10B was designed to be greater than the vertical wall angle θ0 of the target part shape 1. This confirmed that the vertical wall angle θ0 of the target part shape 1 was achieved, and torsion was suppressed. Furthermore, dimensional accuracy variation was significantly reduced for both the 590 MPa and 780 MPa materials.

[0418] The relationship between the above-described springback and the amount of change in the vertical wall angle after the first step 10A is considered to vary depending on the steel type and shape, and therefore it is necessary to design a shape suitable for each.

[0419] <Examples relative to Embodiment 2>

[0420] In this embodiment, the target part shape 1 is set to Figure 21 The shape shown is curved vertically along the longitudinal direction toward the top plate. The metal sheets 3 (blanks) used for the stamping process were three types of steel sheets with tensile strengths of 590 MPa, 980 MPa, and 1180 MPa. This was done to evaluate the material strengths at various levels in order to compare variations in dimensional accuracy.

[0421] The thickness t of the metal sheet used in stamping is 1.4 mm. The dimensions of the base product shape are: a top plate width of 60 mm, a vertical wall height of 30 mm, a 130° vertical wall angle between the top plate and the vertical wall, a maximum spacing of 150 mm between the left and right flanges, a 400 mm longitudinal length, and a 1600 mm radius of curvature of the top plate at the bend. These 130° angle between the top plate and the vertical wall and the 1600 mm radius of curvature of the top plate at the bend are reference values ​​and are not necessarily the target values ​​after stamping.

[0422] Furthermore, press forming analysis and springback analysis were performed when the vertical wall angle in the first step was reduced, and the curvature radius and the vertical wall angle before and after springback were measured.

[0423] In this example, the side-view curvature radius of each mold in the first step 10A and the second step 10B was R1600 [mm]. Furthermore, FEM analysis was conducted by varying the vertical wall angle θ1 of the mold in the first step 10A within a range of 90° to 130°, while standardizing the vertical wall angle θ2 of the mold in the second step 10B to 130°. Table 4 shows the evaluation results. Furthermore, the bending return after springback in the second step 10B was considered acceptable if the value was within ±2.0 mm. Furthermore, the height difference between the three steel grades was considered acceptable if it was 1.0 mm or less.

[0424] In addition, the "mold vertical wall angle" in Table 4 means the "mold vertical wall angle".

[0425] [Table 4]

[0426]

[0427] <No.4-1~4-3>

[0428] Examples No. 4-1 to 4-3 show the case where the longitudinal wall angle θ1 of the mold in the first step was set to 130°. Furthermore, 590 MPa, 980 MPa, and 1180 MPa steel plates were used. Furthermore, examples No. 4-1 to 4-3 show the relationship between the average strain of the top plate and flange at the bottom dead center of forming, the longitudinal radius of curvature of the top plate after springback, and the longitudinal wall angle for each material. Here, the "longitudinal radius of curvature of the top plate" is also referred to as "top plate R."

[0429] In samples No. 4-1 to 4-3, the vertical wall angle θ1 after springback in the first step 10A of each material was greater than the vertical wall angle θ2 of the die in the second step 10B, which was 130°. For the 1180 MPa material, the vertical wall angle θ1′ after springback in the first step 10A was 138.3°. Furthermore, the top plate R after springback in the second step 10B of the 1180 MPa material was R1964 [mm]. Furthermore, the maximum variation ΔR between the 590 MPa and 1180 MPa materials was R221 mm. Thus, the height difference between the steel grades was as large as 1.22 mm, failing to meet the target height difference of 1 mm or less.

[0430] <No.4-4~4-6>

[0431] In contrast, Nos. 4-4 to 4-6 represent the case where the vertical wall angle θ1 of the mold in the first step 10A was set to 100°. Furthermore, Nos. 4-4 to 4-6 show the results of determining the relationship between the average strain of the top plate portion and the flange portion at the bottom dead point of forming for each material, and the top plate R after springback, and the vertical wall angle.

[0432] The vertical wall angle θ1′ after rebound in the first step 10A of each material becomes an angle smaller than the vertical wall angle θ2 of the mold in the second step 10B, which is 130°. For example, if we look at the 1180MPa material, the vertical wall angle θ1′ after rebound in the first step 10A becomes 111.7°. In addition, the top plate R after rebound in the second step 10B of the 1180MPa material becomes R1611 [mm]. Moreover, the maximum variation ΔR of the 590MPa material to the 1180MPa material is R102mm. The height difference between the steel grades is 0.93mm, which meets the target condition of less than 1mm. In addition, the vertical wall angle after rebound in the second step 10B is 127.6° in the 1180MPa material. In addition, the springback amount of the die in the second step 10B from the vertical wall angle θ2 of 130° and the variation amount between the 590 MPa material and the 1180 MPa material were reduced compared to the comparative examples No. 4-1 to No. 4-3.

[0433] <No.4-7~4-9>

[0434] Next, Nos. 4-7 to 4-9 are cases where the vertical wall angle θ1 of the mold in the first step 10A is set to 95°. Nos. 4-7 to 4-9 show the results of determining the relationship between the average strain of the top plate portion and the flange portion at the bottom dead point of forming for each material, and the top plate R after springback and the vertical wall angle.

[0435] The vertical wall angle θ1′ after rebound in the first step 10A of each material becomes an angle smaller than the vertical wall angle θ2 of the mold in the second step 10B, which is 130°. For example, if we look at the 1180MPa material, the vertical wall angle θ′ after rebound in the first step 10A becomes 105.8°. In addition, the top plate R after rebound in the second step 10B in the 1180MPa material becomes R1506 [mm]. Moreover, the maximum variation ΔR of the 590MPa material to the 1180MPa material is R52mm. The height difference between the steel grades is 0.46mm, which meets the target condition of less than 1mm. In addition, the vertical wall angle after rebound in the second step 10B is 127° in the 1180MPa material. Furthermore, in No. 4-7 to No. 4-9, the springback amount of the die in the second step 10B from the vertical wall angle θ2 of 130° and the variation between the 590 MPa material and the 1180 MPa material were reduced compared to the comparative examples of No. 4-1 to No. 4-3.

[0436] <No.4-10~4-12>

[0437] Next, Nos. 4-10 to 4-12 are cases where the vertical wall angle θ1 of the mold in the first step 10A is set to 90°. Nos. 4-10 to 4-12 show the results of determining the relationship between the average strain of the top plate portion and the flange portion at the bottom dead point of forming for each material, and the top plate R after springback and the vertical wall angle.

[0438] The vertical wall angle θ1′ after rebound in the first step 10A of each material becomes an angle smaller than the vertical wall angle θ2 of the mold in the second step 10B, which is 130°. Moreover, for example, if we look at the 1180MPa material, the vertical wall angle θ1′ after rebound in the first step 10A becomes 102.1°. In addition, the top plate R after rebound in the second step 10B in the 1180MPa material becomes R1402 [mm]. Moreover, the maximum variation ΔR of the 590MPa material to the 1180MPa material is R74mm. The height difference between the steel grades is 0.76mm, which meets the target condition of less than 1mm. In addition, the vertical wall angle after rebound in the second step 10B is 125.8° in the 1180MPa material. Furthermore, the springback amount from the vertical wall angle θ2 of 130° and the variation between the 590 MPa material and the 1180 MPa material of the mold in the second step 10B of Nos. 4-10 to 4-12 were reduced compared with the comparative examples of Nos. 4-1 to 4-3.

[0439] Description of Reference Numerals

[0440] 1…target component shape; 1A…top plate portion; 1B…vertical wall portion; 1C…flange portion; 2…bent portion; 3…metal plate (blank); 4…intermediate component; 10A…first process; 10B…second process; 11…die of first process; 12…punch of first process; 13…gasket of first process; 14…die of second process; 15…punch of second process; 16…gasket of second process; θ0…vertical wall angle of target component shape; θ1…first longitudinal wall angle (vertical wall angle of die of first process); θ1′…vertical wall angle of intermediate component; θ2…second longitudinal wall angle (vertical wall angle of die of second process).

Claims

1. A method for manufacturing a stamped product, comprising forming a metal sheet into a target component shape, wherein the target component shape has a cross section having a top plate portion and a longitudinal wall portion connected to a widthwise end portion of the top plate portion and extending in a direction different from the top plate portion, wherein the target component shape has one or more curved portions curved in a direction intersecting the cross section, i.e., in a longitudinal direction. The method for manufacturing a stamped product is characterized by comprising: When the angle between the top plate portion and the vertical wall portion in the cross section is defined as the vertical wall angle, A first step of press-forming a metal plate into an intermediate member having the top plate portion and the vertical wall portion using a die having a forming surface having a first vertical wall angle smaller than a vertical wall angle of the target member shape at a position forming the bent portion; and a second step of press-forming the intermediate component using a die having a forming surface having a second vertical wall angle greater than the vertical wall angle of the target component shape at a position forming the bent portion; At the position forming the bent portion, the first vertical wall angle of the intermediate component after demolding in the first step is set to be smaller than the vertical wall angle of the target component shape.

2. The method for manufacturing a stamped product according to claim 1, wherein: The curved portion has a curve that is concave or convex toward the vertical wall portion.

3. The method for manufacturing a stamped product according to claim 2, wherein: When the vertical wall angle in the target component shape is defined as θ0, the first vertical wall angle is defined as θ1, the vertical wall angle in the intermediate component formed and demolded in the first step is defined as θ1′, and the second vertical wall angle is defined as θ2, Regarding the first vertical wall angle θ1 and the second vertical wall angle θ2, press forming is performed using a die having a forming surface that satisfies the following formula (1): θ1<θ1′<θ0<θ2…(1).

4. The method for manufacturing a stamped product according to claim 2 or 3, wherein: When the first vertical wall angle is defined as θ1 and the second vertical wall angle is defined as θ2, The first vertical wall angle θ1 and the second vertical wall angle θ2 are set to satisfy the following formula (2): 0.7≤(θ1 / θ2)…(2).

5. The method for producing a press-formed product according to any one of claims 2 to 4, wherein: When the vertical wall angle in the target component shape is defined as θ0 and the first vertical wall angle is defined as θ1, The first vertical wall angle θ1 is set to a value satisfying the following formula (3): 0.75≤(θ1 / θ0)…(3).

6. The method for producing a press-formed product according to any one of claims 2 to 5, wherein: When the second vertical wall angle is defined as θ2 and the vertical wall angle of the intermediate component formed and demolded in the first step is defined as θ1′, The second vertical wall angle θ2 is set to a value that satisfies the following formula (4): 0.8≤(θ1′ / θ2)…(4).

7. The method for producing a press-formed product according to any one of claims 2 to 6, wherein: When the vertical wall angle in the target component shape is defined as θ0 and the second vertical wall angle is defined as θ2, The value of the second vertical wall angle θ2 is set so as to satisfy the following formula (5): (θ2 / θ0)<1.05 (5).

8. The method for producing a press-formed product according to any one of claims 2 to 7, wherein: The target component shape is a shape in which the bent portion is bent into a shape that is convex toward the vertical wall portion. Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the second step, the average value of the strain of the lower half of the vertical wall portion that protrudes when viewed from above at the position of the bent portion is defined as ε2. Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the first step, the average value of the strain of the lower half of the vertical wall portion that protrudes when viewed from above at the position of the bent portion is defined as ε1. In the above case, the first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (6): 0.4×|ε1|≤|ε2|<0.85×|ε1|…(6).

9. The method for producing a press-formed product according to any one of claims 2 to 8, wherein: The target component shape is one in which the bent portion is bent so as to be concave toward the vertical wall portion. Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the second step, the average value of the strain of the lower half of the vertical wall portion, which is concave when viewed from above, at the position of the bent portion is defined as ε2′. Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the first step, the average value of the strain of the lower half of the vertical wall portion, which is concave when viewed from above, at the position of the bent portion is defined as ε1′. In the above case, the first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (7): 0.4×|ε1′|≤|ε2′|<0.85×|ε1′|…(7).

10. The method for manufacturing a stamped product according to claim 1, wherein: The curved portion has a curve that is concave or convex toward the top plate portion.

11. The method for manufacturing a press-formed product according to claim 10, wherein: When the vertical wall angle in the target component shape is defined as θ0, the first vertical wall angle is defined as θ1, the vertical wall angle in the intermediate component formed and demolded in the first step is defined as θ1′, and the second vertical wall angle is defined as θ2, Regarding the first vertical wall angle θ1 and the second vertical wall angle θ2, press forming is performed using a die having a forming surface that satisfies the following formula (1): θ1<θ1′<θ0<θ2…(1).

12. The method for manufacturing a press-formed product according to claim 10 or 11, wherein: Regarding the strain distribution in the longitudinal direction at the bottom dead point of the press in the second step, the absolute value of the average value of the strain of the top plate portion at the position of the bent portion is defined as εt2. Regarding the strain distribution in the longitudinal direction at the bottom dead point of the press in the first step, the absolute value of the average value of the strain of the top plate portion at the position of the bent portion is defined as εt1. In the above case, the first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (8): 0.4×εt1≤εt2<0.9×εt1…(8).

13. The method for producing a press-formed product according to any one of claims 10 to 12, wherein: The cross section is in the shape of a letter "コ" or a cap shape with a flange portion. Regarding the strain distribution in the longitudinal direction at the stamping bottom dead point in the stamping forming of the second process, at the position of the bent portion, when the cross section is in a "コ" shape, the absolute value of the average value of the strain in the lower half of the vertical wall portion is defined as εb2, and when the cross section is in a hat shape with a flange portion, the absolute value of the average value of the strain in the flange portion is defined as εb2. Regarding the strain distribution in the longitudinal direction at the bottom dead point of the stamping in the stamping forming of the first process, at the position of the bent portion, when the cross section is in a "コ" shape, the absolute value of the average value of the strain in the lower half of the vertical wall portion is defined as εb1, and when the cross section is in a hat shape with a flange portion, the absolute value of the average value of the strain in the flange portion is defined as εb1. In the above case, the first vertical wall angle and the second vertical wall angle are set so as to satisfy the following formula (9): 0.4×εb1≤εb2<0.9×εb1…(9).

14. The method for producing a press-formed product according to any one of claims 1 to 13, wherein: The mold used in the second step includes: a die constituting one of the upper mold and the lower mold, and a punch constituting the other of the upper mold and the lower mold. In the second step, press forming is performed in a state where the top plate portion of the intermediate member is sandwiched between the top plate forming surface of the die and the spacer extending from the top plate forming surface of the punch.

15. A method for designing a mold used in the method for manufacturing a stamped product according to any one of claims 1 to 9, characterized in that: When designing the vertical wall angles of the molds in the first and second steps, First, perform CAE analysis or actual stamping on the longitudinal wall angle of the die in the first process with a value smaller than the longitudinal wall angle of the product, and find the condition where the longitudinal wall angle after rebound in the first process is smaller than the longitudinal wall angle of the product, and then set the first longitudinal wall angle. Afterwards, for the second process, CAE analysis or actual stamping is performed with a mold shape having a forming surface with a longitudinal wall angle greater than the longitudinal wall angle of the target part shape, and the second longitudinal wall angle is set by finding the condition that the part shape after rebound in the second process satisfies the allowable range of the longitudinal wall angle and torsion in the target part shape.

16. A method for designing a mold used in the method for manufacturing a press-formed product according to any one of claims 10 to 13, characterized in that: When designing the vertical wall angles of the molds in the first and second steps, First, perform CAE analysis or actual stamping on the longitudinal wall angle of the die in the first process with a value smaller than the longitudinal wall angle of the product, and find the condition where the longitudinal wall angle after rebound in the first process is smaller than the longitudinal wall angle of the product, and then set the first longitudinal wall angle. Afterwards, for the second process, CAE analysis or actual stamping is performed on the mold shape having a forming surface with a longitudinal wall angle greater than the longitudinal wall angle of the target part shape, and the second longitudinal wall angle is set by finding the condition that the part shape after rebound in the second process meets the allowable range of the longitudinal wall angle in the target part shape.

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