Press forming method

Abstract

The press forming method of the present application press forms a press formed piece (1) having a ceiling portion (3), a longitudinal wall portion (7) continuous from the ceiling portion (3) via a punch shoulder portion (5), and a flange portion (11) continuous from the longitudinal wall portion (7) via a die shoulder portion (9), and provided with a bending portion (13) curved in a concave shape in plan view, wherein the bending radius of the die shoulder portion (9) at the bending portion (13) is made larger toward the central portion from the end portion side of the bending.

Description

Technical Field

[0001] The present invention relates to a press forming method, and more particularly to a press forming method for a stamped part, wherein the stamped part has a top plate portion, a side wall portion continuous from the top plate portion via a punch shoulder, and a flange portion continuous from the side wall portion via a die shoulder, and has a curved portion that is recessed when viewed from above. Background Art

[0002] Stamping is a manufacturing method that can produce metal parts at low cost and in a short time, and is used in the manufacture of many automotive parts. In recent years, higher-strength metal sheets have been used for automotive parts to achieve both improved collision safety and lightweighting of automotive bodies. Major issues in stamping high-strength metal sheets include the generation of cracks due to reduced ductility and wrinkles due to increased yield strength.

[0003] For example, Figure 7 As shown in FIG. 1 , in the press forming of the stamped part 101 in which the longitudinal wall portion 107 is bent into a concave shape when viewed from above and formed into a target shape, the flange portion 111 at the bent portion 113 is stretched in the circumferential direction, which makes it easy to generate cracks. In addition, as a reaction force thereof, the top plate portion 103 and the punch shoulder 105 at the bent portion 113 are deformed in the circumferential direction to shrink, which makes it easy to generate wrinkles. This deformation is called stretch flange deformation. Therefore, in the press forming of the stamped part 101 bent into a concave shape, it is important to suppress the generation of cracks and wrinkles in such stretch flange deformation.

[0004] To date, several techniques for suppressing cracks and wrinkles of a press-formed member that is curved in a concave shape when viewed from above have been proposed. For example, Patent Literature 1 discloses a press-forming method of press-forming an L-shaped member having a top plate portion and a vertical wall portion connected to the top plate portion via a bent portion having a portion curved in an arc shape and having a flange portion on a side opposite to the bent portion from a sheet metal blank. Also, according to the press-forming method, in a state where a portion of the sheet metal blank corresponding to the top plate portion is pressed by a pad, and in a state where an end portion of a portion of the sheet metal blank corresponding to an L-shaped lower portion of the L-shaped member is allowed to slide (move in a plane), the portion corresponding to the L-shaped lower portion is introduced to the vertical wall portion side to form the vertical wall portion and the flange portion, whereby generation of a crack at the flange portion and generation of a wrinkle at the top plate portion can be suppressed.

[0005] In addition, Patent Literature 2 discloses a press-forming method of press-forming a member having a hat-shaped or U-shaped cross-sectional shape and having a bent portion curved in a long side direction and straight side portions connected to both ends of the bent portion. Also, according to the press-forming method, by generating material movement that relaxes circumferential tensile deformation generated at a flange portion of the bent portion, generation of a crack caused by tensile flange deformation can be suppressed.

[0006] Prior Art Documents

[0007] Patent Literature

[0008] Patent Literature 1: Japanese Patent No. 5168429

[0009] Patent Literature 2: Japanese Patent No. 6028956 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] In the technique disclosed in Patent Literature 1, as described above, Figure 8As shown in FIG. 1 , the direction of movement of the blank (metal plate) flowing out from the top plate 103 to the flange 111 is inconsistent with the direction in which the material is stretched due to the stretching flange deformation (the circumferential dotted line at the flange 111). Figure 9 If the vectors are decomposed into two directions as shown, the movement from the end of the bend 113 toward the center (the black solid arrow in the figure) is effective in suppressing cracks in the flange portion 111 caused by stretch flange deformation. However, the movement from the top plate 103 toward the vertical wall portion 107 (the black dashed arrow in the figure) does not contribute to suppressing stretch flange deformation. Furthermore, even if the material moves toward the center of the bend 113, the material movement near the center of the bend 113 (the blank arrow in the figure) may induce wrinkles near the top plate 103 and the punch shoulder 105.

[0012] In addition, the technology disclosed in Patent Document 1 suppresses wrinkles on the top plate portion by applying pressure to the portion of the raw material metal sheet corresponding to the top plate portion with a gasket. However, the higher the strength of the steel sheet, the greater the gasket load that needs to be applied to pressurize the wrinkles. Therefore, there is a concern that the pressure generator such as the gas cylinder provided in the pressforming tool may become larger. As a result, there is a problem that sometimes the space for providing the gasket in the mold cannot be ensured, and the cost increases due to the enlargement of the mold. In addition, when applying the technology of Patent Document 1 to Figure 7 In the case of press forming of the stamped part 101 shown, since the punch shoulder 105 cannot be pressurized by a pad, wrinkles on the punch shoulder 105 cannot be suppressed.

[0013] Furthermore, the technique disclosed in Patent Document 2 suppresses wrinkles by deep drawing, which moves the material of the top plate surface of the curved portion away from the flange that causes the deep drawing deformation. However, this technique cannot be applied to component shapes that do not allow such material movement, or to components manufactured by crash forming.

[0014] Furthermore, in Patent Documents 1 and 2, for example, in a press-formed part in which a rib shape needs to be imparted to the top plate portion 103 at the bent portion 113, it is sometimes not possible to use the rib shape. Figure 9 The material of the portion corresponding to the top plate portion 103 at the bent portion 113 shown in the figure moves to the flange portion 111 where the tensile flange deformation occurs, making it difficult to suppress wrinkles, which is a problem.

[0015] The present application has been achieved in order to solve the above-described problems, and has an object to provide a press forming method capable of suppressing a crack at a flange portion where a stretch flange deforms, and suppressing a wrinkle of a top plate portion, a punch shoulder portion on the flange portion side, in a press-formed part having a top plate portion, a vertical wall portion continuous from the top plate portion via a punch shoulder portion, and a flange portion continuous from the vertical wall portion via a die shoulder portion, and curved in a concave shape in plan view.

[0016] Means for solving the problems

[0017] The press forming method of the present application press forms a press-formed part having a top plate portion, a vertical wall portion continuous from the top plate portion via a punch shoulder portion, and a flange portion continuous from the vertical wall portion via a die shoulder portion, and having a curved portion curved in a concave shape in plan view, wherein a bending radius of the die shoulder portion at the curved portion is made larger toward a central portion from an end portion side of the curve.

[0018] Preferably, a minimum bending radius of the die shoulder portion is made smaller than a bending radius of the punch shoulder portion.

[0019] Preferably, the top plate portion at the end portion side of the curve is formed with a portion of shape that restrains rotational motion of a blank in a press forming process.

[0020] Preferably, a flange width of the flange portion at the curved portion is made wider at the central portion than at the end portion side of the curve.

[0021] Preferably, a blank used for press forming of the press-formed part is set to a metal sheet of a tensile strength of 440 MPa grade to 1600 MPa grade.

[0022] The press forming method of the present application press forms a press-formed part by the press forming method as a pre-formed part, and further press forms the pre-formed part into a target shape, wherein a bending radius of the die shoulder portion at a central portion of the curved portion is made larger than the target shape.

[0023] Effects of the Invention

[0024] In the present application, in press forming of a press-formed member having a top plate portion, a longitudinal wall portion continuous from the top plate portion via a punch shoulder portion, and a flange portion continuous from the longitudinal wall portion via a die shoulder portion, and provided with a bending portion bent in a concave shape in plan view, the bending radius of the die shoulder portion at the bending portion is made larger toward the central portion from the end portion side of the bending, so that material is moved from the top plate portion at the end portion side of the bending toward the flange portion at the central portion of the bending, and therefore, cracking at the flange portion of the bending portion can be suppressed, and the top plate portion, the punch shoulder portion at the flange portion side of the bending portion can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a drawing showing an example of a press-formed member as a molding object in the press forming method of the embodiment of the present application ((a) perspective view, (b) plan view).

[0026] Figure 2 is a drawing showing a reason why cracking and wrinkling can be suppressed by the press forming method of the embodiment of the present application ((a) plan view, (b) cross-sectional view at the end portion side of the bending, (c) cross-sectional view at the central portion of the bending).

[0027] Figure 3 is a drawing showing an example of a press-formed member as a molding object in the press forming method of the embodiment of the present application and formed with a bending shape that restricts rotational movement of a blank in a horizontal plane parallel to the top plate portion at the end portion side of the bending portion.

[0028] Figure 4 is a drawing showing an example of a press-formed member as a molding object in the press forming method of the embodiment of the present application and formed with a bead shape that restricts rotational movement of a blank in a horizontal plane parallel to the top plate portion at the end portion side of the bending portion.

[0029] Figure 5 is a drawing showing an example of a press-formed member as a molding object in the press forming method of the embodiment of the present application and formed with a flange width of the flange portion at the central portion of the bending enlarged.

[0030] Figure 6 is a drawing showing a reason why cracking can be suppressed in a press-formed member formed with a flange width of the flange portion at the central portion of the bending enlarged by the press forming method of the embodiment of the present application.

[0031] Figure 7 is a drawing showing cracking and wrinkling generated in press forming of a press-formed member having a portion bent in a concave shape in plan view.

[0032] Figure 8is a diagram illustrating a mechanism of cracks and wrinkles generated in a press forming process of a press-formed member curved in a concave shape in plan view.

[0033] Figure 9 is a diagram illustrating material movement in press forming of a press-formed member curved in a concave shape in plan view. DETAILED DESCRIPTION

[0034] Hereinafter, based on Figures 1 to 6 A press forming method of an embodiment of the present application will be described.

[0035] The press forming method of the present embodiment, as one example Figure 1 As shown in (a), a press-formed member 1 having a top plate portion 3, a longitudinal wall portion 7 continuous from the top plate portion 3 via a punch shoulder portion 5, and a flange portion 11 continuous from the longitudinal wall portion 7 via a die shoulder portion 9, and provided with a curved portion 13 curved in a concave shape in plan view and a straight portion 15 extending in a straight line shape from both ends of the curvature at the curved portion 13 (dotted line in (a)) is press-formed. Figure 1 The curvature radius of the die shoulder portion 9 at the curved portion 13 is made larger from the curved end portion side toward the central portion.

[0036] In the press forming method of the present embodiment, for the reason that both the cracks of the flange portion 11 at the curved portion 13 of the press-formed member 1 and the wrinkles of the top plate portion 3, the punch shoulder portion 5 can be suppressed, based on Figure 2 which schematically represents the movement of the material in the press forming process, will be described. Note that, Figure 2 The dotted line in (a) indicates both ends of the curvature (boundary of the curved portion 13 and the straight portion 15).

[0037] The die shoulder portion 9 is made larger from the curved end portion side toward the central portion with the curvature radius Rd,2( Figure 2 (c)) at the curved central portion (B-B' cross section) being larger than the curvature radius Rd,1( Figure 2 (b)) at the curved end portion side (A-A' cross section). Therefore, at the die shoulder portion 9 at the central portion of the curved portion 13, the material can easily move during the press forming process, and thus, the tensile flange deformation is generated in a wide range, and the strain is dispersed (black dotted arrow in (a)). Figure 2

[0038] ​On the other hand, on the curved end portion side, the bending radius of the die shoulder 9 is smaller than that of the curved central portion, and therefore, in the process of press forming the curved end portion side using a punch and a die, the material deformed in abutment with the die shoulder of the die is difficult to move on the die shoulder, and therefore, the force to stretch the material from the top panel portion 3 toward the flange portion 11 side is increased. At the same time, in the process of press forming the curved central portion, the material is stretched from the curved end portion side toward the central portion. Therefore, the material movement from the top panel portion 3 and the punch shoulder 5 of the curved end portion side toward the flange portion 11 of the curved central portion is increased (indicated by the black solid arrow in (a)). Figure 2

[0039] Thus, on the curved central portion, the stretch flange deformation is generated in a wide range, the strain is dispersed, and the material movement from the curved end portion side toward the flange portion 11 is increased, and therefore, the cracking of the flange portion 11 can be suppressed.

[0040] Further, since the bending radius of the die shoulder 9 of the curved central portion is large, the large material movement toward the curved central portion at the top panel portion 3 in the vicinity of the curved central portion (indicated by the blank arrow in (a)) is small, and the generation of the wrinkles of the top panel portion 3 and the punch shoulder 5 on the flange portion 11 side of the curved central portion can be suppressed. Figure 2

[0041] As described above, in the press forming method of the present embodiment, both the cracking of the flange portion 11 and the wrinkles of the top panel portion 3 and the punch shoulder 5 at the curved portion 13 of the press formed product 1 can be suppressed.

[0042] Note that the press forming method of the present embodiment preferably makes the minimum bending radius of the die shoulder 9 smaller than the bending radius of the punch shoulder 5.

[0043] Here, the minimum bending radius of the die shoulder 9 refers to the smallest bending radius of the die shoulder 9 at the curved portion 13. In the press formed product 1, as shown in (a), since the bending radius of the die shoulder 9 increases from the curved end portion side toward the central portion, the minimum bending radius of the die shoulder 9 is the bending radius Rd,1 of the curved end portion. Figure 2

[0044] Thus, by making the minimum bending radius of the die shoulder 9 (=Rd,1) smaller than the bending radius of the punch shoulder 5 (=Rp), the material movement at the die shoulder 9 during press forming is restricted, and accordingly, the material can be strongly introduced from the top panel portion 3 side to the flange portion 11 side during press forming. As a result, the cracking of the flange portion 11 and the wrinkles of the top panel portion 3 and the punch shoulder 5 at the curved portion can be further suppressed.

[0045] The above description is as shown in (a) to (c). Figure 1 ​​​The bending radius of the die shoulder 9 is changed as shown, but the press forming method of the present application can also be such that, as in the press formed product 21 shown as an example, in addition to the bending radius of the die shoulder 29 being made larger from the curved end side toward the central portion, a rotation movement restraining shape portion 37 is formed at the end side of the curved portion 33 and at the top plate portion 23 at the linear portion 35, which restrains the rotation movement of the blank in the horizontal plane parallel to the top plate portion 23 during press forming. Figure 3 The bending radius of the die shoulder 9 is changed as shown, but the press forming method of the present application can also be such that, as in the press formed product 21 shown as an example, in addition to the bending radius of the die shoulder 29 being made larger from the curved end side toward the central portion, a rotation movement restraining shape portion 37 is formed at the end side of the curved portion 33 and at the top plate portion 23 at the linear portion 35, which restrains the rotation movement of the blank in the horizontal plane parallel to the top plate portion 23 during press forming.

[0046] The rotation movement restraining shape portion 37 is a curved shape formed between the longitudinal wall portion 39 continuous on the side opposite to the longitudinal wall portion 27 of the linear portion 35 and the top plate portion 23.

[0047] Thus, by forming the rotation movement restraining shape portion 37 during press forming, it is possible to restrain the rotation movement of the blank in the horizontal plane parallel to the top plate portion 23 during press forming, and it is possible to make the material move from the top plate portion 23 at the curved end side and at the linear portion 35 to the flange portion 31 at the curved central portion via the die shoulder 29, and it is possible to sufficiently restrain the wrinkling of the top plate portion 23 at the curved portion 33 and the punch shoulder 25.

[0048] Note that the present application is not limited to Figure 3 The rotation movement restraining shape portion 37 shown as an example, for example, as in the rotation movement restraining shape portion 43 of the reinforcing rib shape formed at the top plate portion 23 of the press formed product 41 exemplified, as long as it is a shape that can restrain the rotation movement of the blank in the horizontal plane parallel to the top plate portion 23 during press forming. Also, the reinforcing rib shape formed at the top plate portion 23 is not limited to the concave shape as in the rotation movement restraining shape portion 43, but can be protrusive. Figure 4

[0049] In addition, Figure 3 The rotation movement restraining shape portion 37 shown as an example, Figure 4 The rotation movement restraining shape portion 43 shown as an example is formed from the end of the curved portion 33 to the linear portion 35, but as for the position and range where the rotation movement restraining shape portion is formed, it is not excluded that it is formed at a portion corresponding to only the end of the curved portion 33 or a portion corresponding to only the linear portion 35.

[0050] Also, the press forming method of the present application, in addition to the bending radius of the die shoulder described above, as in the press formed product 51 exemplified, Figure 5 The flange width of the flange portion 61 at the central portion of the curved portion 63 can also be made wider than the curved end side, as in the press formed product 51 exemplified.

[0051] As for Figure 5 ​The punch-formed member 51 shown is formed by punch forming. The effects of the punch forming are described below. For example, as shown in Figure 6 (a), the punch-formed member 1 is obtained by punch forming a blank 71 having a shape such that the punch-formed member 1 is formed when punch forming is performed. In this case, a flange equivalent portion 73 in the blank 71 becomes the flange portion 11 of the punch-formed member 1. Figure 1 ).

[0052] In contrast, as shown in Figure 6 (b), the punch-formed member 51 is formed by punch forming a blank 75 having excess material (hatched area in the drawing) added to a flange equivalent portion 77 corresponding to the flange portion 61. Figure 5

[0053] When the punch-formed member 51 is formed by punch forming using such a blank 75, the material of the flange portion 61 at the bending site 63 is difficult to stretch, and accordingly, the material insufficient to form the flange portion 61 is introduced from the ceiling portion 53 side via the punch shoulder portion 55 and the vertical wall portion 57. As a result, the material toward the central portion of the bend at the bending site 63 is increased, and the cracking of the flange portion 61 can be further suppressed.

[0054] As shown in the punch-formed member 51 shown in Figure 5 , in the case where the flange width of the flange portion 61 at the bending site 63 is wider in the central portion than at the end portion side of the bend, it is preferable that the maximum flange width of the central portion of the bend be 1.1 to 1.5 times the flange width of the end portion side.

[0055] If the flange width of the central portion of the bend is less than 1.1 times, the force to introduce the material from the ceiling portion 53 to the flange portion 61 side during punch forming does not increase much. In addition, if the flange width of the central portion of the bend is wider than 1.5 times, the flange width of the flange portion 61 is too wide and becomes an obstacle when joining with other members, and thus, it is necessary to cut off the flange portion 61 in a subsequent process to narrow the flange width, the number of work processes increases, and the yield rate decreases.

[0056] Note that the punch forming method of the embodiment of the present application is, for example, as shown in Figure 1 , the punch-formed member 1 having the straight portion 15 extending from both ends of the bend of the bending site 13 is the object of forming, but the present application can also punch form a punch-formed member having only a bending site, a punch-formed member having a straight portion extending from only one end of the bend, or the like, with or without a straight portion.

[0057] ​In the above description, the bend radius of the punch shoulder is made larger toward the central portion from the end portion side of either of the two bends, but the bend radius of the punch shoulder can be made larger toward the central portion from the end portion side of either of the two bends.

[0058] The above description illustrates the specific mode of the present application based on the embodiment of the present application. However, the present application also includes, for example, a press forming method in which the press-formed member 1 shown in FIG. 1 is used as an intermediate formed member, and the intermediate formed member is press formed into a target shape. The press-formed member 1 as the intermediate formed member can have a bend radius of the punch shoulder 9 of the central portion of the bend portion 13 larger than that of the target shape. That is, the press forming method includes two processes of press forming by a process of press forming the press-formed member 1 as the intermediate formed member and a process of press forming the press-formed member 1 into a press-formed member of the target shape. Figure 1

[0059] Moreover, if the press-formed member 101 whose bend radius of the punch shoulder 105 is the target shape is press formed by one process, even in a case where cracks of the flange portion 111 at the bend portion 113 of the press-formed member 101 and wrinkles of the top panel portion 103 and the punch shoulder 105 are generated, according to the press forming method of the present application, the cracks of the flange portion 111 at the bend portion 113 and the wrinkles of the top panel portion 103 and the punch shoulder 105 can be suppressed, and the press-formed member 101 of the target shape can be obtained. Figure 7

[0060] The press forming method of the present application is not particularly limited in the kind of the metal plate as a raw material of a blank, but can be preferably applied to a case where a metal plate having low ductility is used. Specifically, a metal plate having a tensile strength of 440 MPa or more and 1600 MPa or less and a thickness of 0.5 mm or more and 3.6 mm or less is preferably used.

[0061] A metal plate having a tensile strength of less than 440 MPa is difficult to generate cracks caused by deformation of a stretched flange due to high ductility, and has less advantages of using the present application. However, if it is a component shape difficult to press form, even a metal plate having a tensile strength of less than 440 MPa is preferably used with the present application. The upper limit of the tensile strength is not particularly limited, and a metal plate exceeding 1600 MPa lacks ductility, and thus cracks are easily generated at a punch shoulder and a die shoulder, and press forming becomes difficult.

[0062] ​​In addition, the press forming method of the present invention can prevent cracks in metal sheets caused by stretching flange deformation in automobile parts having L-shaped, T-shaped, Y-shaped, or S-shaped portions that are curved when viewed from above. As a specific example, the present invention can be preferably applied to situations where the forming targets are A-pillar lowers having L-shaped portions, B-pillars having T-shaped portions, and rear side members having S-shaped portions.

[0063] [Example]

[0064] Specific stamping experiments were conducted to determine the effects of the stamping method of the present invention, and the results will be described below.

[0065] In the stamping experiment, the steel sheets with the mechanical properties of materials shown in Table 1 were used as blanks, and the stamped parts 1 ( Figure 1 )、Stamping parts 21( Figure 3 )、Stamping parts 41( Figure 4 ) and stamped parts 51 ( Figure 5 ) is used as a molding object, and an example of foam molding is used as an invention example.

[0066] It should be noted that the radius of curvature of the curved portion at the center of the height direction of the longitudinal wall portion of each stamped part is 153 mm, the curvature radius of the punch shoulder at the curved portion is 7 mm, the minimum curvature radius of the die shoulder is 6 mm, the flange width of the flange portion is 25 mm, and the longitudinal wall height in the stamping direction of the longitudinal wall portion is 60 mm. In addition, when the flange width of the flange portion 11 of the stamped part 1 is made wider in the central portion than in the end side, the flange width of the flange portion 61 in the curved central portion is 1.5 times the flange width (=25 mm) on the curved end side.

[0067] [Table 1]

[0068] Plate thickness / mm Yield strength / MPa Tensile strength / MPa Elongation / % 1.6 880 1210 13

[0069] In the stamping experiment, the ratio of the bending radius Rd of the die shoulder in the stamped part as the forming object was changed. Here, the ratio of the bending radius Rd of the die shoulder is the ratio of the maximum bending radius to the minimum bending radius (6 mm) in the ridge direction along the bending of the die shoulder.

[0070] In addition, in the press forming experiment, as a comparison object, the method disclosed in Patent Document 1 was used to press the Figure 7 The stamped part 101 shown is a conventional example in which a portion of the stamped part 101 corresponding to the top plate 103 is stamped while allowing the blank to rotate in a horizontal plane parallel to the top plate 103 .

[0071] In the conventional example, the curvature radius of the bend 113, the bend radius of the punch shoulder 105, and the side wall height of the vertical wall 107 are the same as those of the press-formed part of the inventive example. Furthermore, the bend radius of the die shoulder 109 is constant (=6 mm) along the bending direction as the minimum bend radius of the die shoulder.

[0072] Then, the cracks and wrinkles of each stamped part of the invention example and the conventional example were evaluated. The crack evaluation was performed by calculating the thickness of the blank and the flange tip at the deepest bottom portion of the concave portion at the bending part (for example, Figure 2 The thickness reduction ratio (thickness reduction ratio) obtained by dividing the difference in thickness of the plate of the blank (shown in the C part) by the thickness of the blank is calculated. The smaller the value, the better the crack suppression is evaluated. On the other hand, the evaluation of wrinkles is performed by visually inspecting the top plate portion and the punch shoulder at the bending part. The case where there are obvious wrinkles is set as "×", the case where there are tiny wrinkles that can be visually confirmed but are tolerable in terms of component performance is set as "△", and the case where wrinkles cannot be visually confirmed is set as "○". Tables 2 and 3 show the results of evaluating cracks and wrinkles for each stamped part.

[0073] [Table 2]

[0074]

[0075] [Table 3]

[0076]

[0077] In the conventional example, the plate thickness reduction rate was as large as 18%, and minute wrinkles were generated.

[0078] Invention Example 1: stamped part 1 ( Figure 1 ) was used as the forming object, and the bending radius Rd of the die shoulder 9 was increased from the curved end side toward the center at a ratio of 1.1. As shown in Table 2, the plate thickness reduction rate was 17%, which was lower than that of the conventional example, and no wrinkles were observed.

[0079] Inventive Example 2 was conducted using the press-formed product 1 as the formed product, and the ratio of the bend radius Rd of the punch shoulder 9 was made 1.5, which was larger than that of Inventive Example 1. As shown in Table 2, the sheet thickness reduction rate was 14%, which was reduced compared to Inventive Example 1, and in addition, the generation of wrinkles was not observed.

[0080] Inventive Example 3 was conducted using the press-formed product 1 as the formed product, and the ratio of the bend radius Rd of the punch shoulder 9 was made 2.0, which was larger than that of Inventive Example 2. As shown in Table 2, the sheet thickness reduction rate was 12%, which was further reduced compared to Inventive Example 2, and in addition, the generation of wrinkles was not observed.

[0081] Inventive Example 4 was conducted using the press-formed product 21( Figure 3 ) as the formed product, and the ratio of the bend radius Rd of the punch shoulder 29 was made 1.5, and a curved rotation movement constraint shape portion 37 was formed between the ceiling portion 23 and the vertical wall portion 39. As shown in Table 3, the sheet thickness reduction rate was 15%, which was reduced compared to the Conventional Example, and in addition, the generation of wrinkles was not observed.

[0082] Inventive Example 5 was conducted using the press-formed product 41( Figure 4 ) as the formed product, and the ratio of the bend radius of the punch shoulder 29 was made equal to that of Inventive Example 4, and a rotation movement constraint shape portion 43 in the shape of a reinforcing rib was formed from the curved end portion side of the ceiling portion 23 to the straight portion. As shown in Table 3, the sheet thickness reduction rate was 14%, which was reduced compared to the Conventional Example, and in addition, the generation of wrinkles was not observed.

[0083] Inventive Example 6 was conducted using the press-formed product 51( Figure 5 ) as the formed product, and a blank 75 to which a shape imparting excess material to the flange equivalent portion 77 (refer to Figure 6 ) was used, and the ratio of the bend radius Rd of the punch shoulder 59 was made 1.1 as in Inventive Example 1, and the flange width of the flange portion 61 of the central portion of the curved portion 63 was made 1.5 times the flange width (= 25 mm) of the curved end portion side. As shown in Table 3, the sheet thickness reduction rate was 8%, which was reduced compared to Inventive Example 1, and in addition, the generation of wrinkles was not observed.

[0084] Inventive Example 7 was conducted using the press-formed product 51( Figure 5 ) as the formed product, and a blank 75 to which a shape imparting excess material to the flange equivalent portion 77 (refer to Figure 6 ) was used, and the ratio of the bend radius Rd of the punch shoulder 59 was made 1.5 as in Inventive Example 2, and the flange width of the flange portion 61 of the central portion of the curved portion 63 was made 1.5 times the flange width (= 25 mm) of the curved end portion side. As shown in Table 3, the sheet thickness reduction rate was 9%, which was reduced compared to Inventive Example 2, and in addition, the generation of wrinkles was not observed.

[0085] Note that an example of the press-formed product 101 in which the bend radius of the punch shoulder 109 is uniformly increased compared to the prior example is shown in Table 3 as a comparative example. The comparative example sets the bend radius of the ridge of the punch shoulder 109 of the prior example as a whole to 1.5 times, to 9.0 mm. As a result, the sheet thickness reduction rate is 9%, which is good, but there are obvious wrinkles, which is a problem.

[0086] Thus, it is confirmed that, by the press-forming method of the present application, the cracking of the flange portion at the bend site can be suppressed, and the wrinkling of the roof portion, the punch shoulder portion at the bend site can be suppressed.

[0087] Industrial applicability

[0088] According to the present application, it is possible to provide a press-forming method in which, in a press-formed product having a roof portion, a longitudinal wall portion, and a flange portion, and curved into a concave shape in plan view, cracking of the flange portion at the stretch flange deformation occurs can be suppressed, and the wrinkling of the roof portion, the punch shoulder portion on the flange portion side can be suppressed.

[0089] Explanation of reference numerals

[0090] 1 press-formed product

[0091] 3 roof portion

[0092] 5 punch shoulder portion

[0093] 7 longitudinal wall portion

[0094] 9 punch shoulder portion

[0095] 11 flange portion

[0096] 13 bend site

[0097] 15 straight site

[0098] 21 press-formed product

[0099] 23 roof portion

[0100] 25 punch shoulder portion

[0101] 27 longitudinal wall portion

[0102] 29 punch shoulder portion

[0103] 31 flange portion

[0104] 33 bend site

[0105] 35 straight site

[0106] 37 rotation movement restriction shape portion

[0107] 39 longitudinal wall portion

[0108] 41 press-formed member

[0109] 43 rotationally-movement-constraining shape

[0110] 51 press-formed member

[0111] 53 ceiling portion

[0112] 55 punch shoulder portion

[0113] 57 vertical wall portion

[0114] 59 die shoulder portion

[0115] 61 flange portion

[0116] 63 curved portion

[0117] 65 straight portion

[0118] 71 blank

[0119] 73 flange-equivalent portion

[0120] 75 blank

[0121] 77 flange-equivalent portion

[0122] 101 press-formed member

[0123] 103 ceiling portion

[0124] 105 punch shoulder portion

[0125] 107 vertical wall portion

[0126] 109 die shoulder portion

[0127] 111 flange portion

[0128] 113 curved portion

[0129] 115 straight portion

Claims

1. A stamping method for stamping a stamped part, wherein the stamped part comprises a top plate, a longitudinal wall portion continuous from the top plate portion via a punch shoulder portion, and a flange portion continuous from the longitudinal wall portion via a die shoulder portion, the part being L-shaped when viewed from above and having a concavely curved portion, wherein the flange portion at the curved portion is subjected to tensile flange deformation, wherein: In the press forming method, the bending radius of the die shoulder at the bent portion is increased from the bent end portion toward the center portion.

2. The stamping method according to claim 1, wherein: The minimum bending radius of the die shoulder is made smaller than the bending radius of the punch shoulder.

3. The stamping method according to claim 1, wherein: The top plate portion on the bent end side forms a rotational motion restricting shape portion that restricts rotational motion of the blank during the press forming process.

4. The stamping method according to claim 2, wherein: The top plate portion on the bent end side forms a rotational motion restricting shape portion that restricts rotational motion of the blank during the press forming process.

5. The stamping method according to claim 1, wherein: The flange width of the flange portion at the bent portion is made wider in the center portion than on the bent end portions.

6. The stamping method according to claim 2, wherein: The flange width of the flange portion at the bent portion is made wider in the center portion than on the bent end portions.

7. The stamping method according to claim 3, wherein: The flange width of the flange portion at the bent portion is made wider in the center portion than on the bent end portions.

8. The stamping method according to claim 4, wherein: The flange width of the flange portion at the bent portion is made wider in the center portion than on the bent end portions.

9. The stamping method according to claim 1, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

10. The stamping method according to claim 2, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

11. The stamping method according to claim 3, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

12. The stamping method according to claim 4, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

13. The stamping method according to claim 5, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

14. The stamping method according to claim 6, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

15. The stamping method according to claim 7, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

16. The stamping method according to claim 8, wherein: The blank used for press-forming the press-formed product is a metal plate having a tensile strength of 440 MPa to 1600 MPa.

17. A stamping method, comprising: using a stamped part stamped by the stamping method according to any one of claims 1 to 16 as an intermediate part, and further stamping the intermediate part into a target shape, wherein: The intermediate formed member has a bending radius of the die shoulder at the center of the bent portion that is larger than the target shape.

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