Stamping forming method

Abstract

The stamping forming method according to the present invention is a method for forming a stamped forming part (1), which has: a top plate part (3); a longitudinal wall part (5), which is continuous from the top plate part (3) and has a concave part (7) that is recessed from the edge part on the side opposite to the top plate part in side view, that is, the lower edge (11), toward the top plate part (3); and a flange part (9) formed outwardly at the lower edge of the longitudinal wall part (5), the flange part (9) being subjected to stretch flange deformation and shrink flange deformation. The stamping forming method includes: a first forming step (S1) of forming an intermediate formed part (23), which has a longitudinal wall part (5), a flange part (9) formed at the lower edge (11) at a portion with a deep wall depth, and a torsion shape part (25) formed continuously with the flange part (9); and a second forming step S3 of forming the torsion shape part (25) into a flange part (9) and forming a flange part (9) at a second bending part (19) continuous with an inclined edge part (13) and a concave edge part (15) with a shallow wall depth to form the intermediate formed part (23) into a target shape.

Description

Technical Field

[0001] The present invention relates to a press forming method for press forming automotive parts and other members from a metal sheet, and particularly relates to a press forming method for a press formed part having a top portion, a side wall portion having a portion where the wall height changes when viewed from the side, and a flange portion formed at a side portion, i.e., a bottom edge, on the side opposite to the top portion of the side wall portion. Background Art

[0002] In recent years, due to the weight reduction of automotive bodies caused by environmental problems, high-strength steel sheets are often used for automotive parts. However, compared with steel sheets having low strength, high-strength steel sheets lack elongation and are prone to fracture during processing. In addition, in the case of using high-strength steel sheets, in order to further reduce the weight, sheet metal thinning is also carried out at the same time. Therefore, there is also a problem that buckling of the steel sheet is likely to occur and wrinkles are likely to occur during press forming. Therefore, there is a strong demand for developing a press forming method for suppressing fracture and press wrinkles.

[0003] For example, Patent Document 1 discloses a press forming method for manufacturing automotive parts that are prone to wrinkles and stretch flange fractures inside the product without forming defects by using a wrinkle suppression pad that is driven separately from the punch and the die. According to the method disclosed in Patent Document 1, automotive parts that are prone to wrinkles and cracks inside the product can be manufactured without forming defects.

[0004] Patent Document 1: Japanese Patent Publication No. 6032374

[0005] However, the press forming method disclosed in Patent Document 1 is a method that requires the use of a wrinkle suppression pad to restrain the inside of the product away from the flange. Therefore, there is a problem that it cannot be applied to a shape in which wrinkles and cracks occur in the flange portion itself. Summary of the Invention

[0006] The present invention has been completed in view of the above problems, and an object thereof is to provide a stamping method that can also be applied to a stamped part in which wrinkles and cracks occur in the flange itself and can suppress wrinkles and cracks generated in the flange at the same time.

[0007] The stamping method according to the present invention is a stamping method for forming a stamped part, and the stamped part has: a top plate portion; a vertical wall portion that is continuous from the top plate portion and has a recessed portion that is recessed toward the top plate portion side from the edge portion on the opposite side of the top plate portion in a side view, that is, the lower end edge; and a flange portion that is formed outward at the lower end edge of the vertical wall portion. The recessed portion sequentially has, from the lower end edge of the portion with a deep wall depth: a first curved portion that is continuous with the lower end edge; an inclined side portion that is continuous with the first curved portion; a second curved portion that is continuous with the inclined side portion; and a concave edge portion with a shallow wall depth. The flange portion formed at the first curved portion is a shrink flange, and the flange portion formed at the second curved portion is an extension flange. Among them, the stamping method includes: a first forming process in which a preformed part is formed. The preformed part has the above vertical wall portion, a flange portion formed at the lower end edge of the portion with a deep wall depth, and a torsional shape portion formed at the inclined side portion that is continuous with the flange portion and reaches the second curved portion; and a second forming process in which the torsional shape portion is formed into a flange portion and a flange portion is formed at the second curved portion continuous with the inclined side portion and the concave edge portion with a shallow wall depth to form the preformed part formed in the first forming process into a target shape.

[0008] The above first forming process and the above second forming process can be formed by different tools of press forming.

[0009] The above first forming process and the above second forming process can be performed by one tool.

[0010] According to the present invention, in the first forming process, the generation of wrinkles caused by the shrink flange deformation is suppressed, and in the second forming process, the generation of cracks caused by the extension flange deformation is suppressed, and the generation of wrinkles and cracks can be suppressed throughout the process. Description of the Drawings

[0011] Figure 1 It is an explanatory diagram of the stamping method according to an embodiment of the present invention.

[0012] Figure 2 is Figure 1An enlarged view of the AA part of the intermediate formed part in the first forming process.

[0013] Figure 3 It is an explanatory diagram for explaining the mechanism of suppressing the generation of wrinkles in the first forming process.

[0014] Figure 4 It is Figure 1 An enlarged view of the BB part of the target shape in the second forming process.

[0015] Figure 5 It is an explanatory diagram for explaining the mechanism of suppressing the generation of cracks in the second forming process.

[0016] Figure 6 It is an explanatory diagram for explaining the target shape in the embodiment and the problems generated in the forming process of the target shape.

[0017] Figure 7 It is for Figure 6 An explanatory diagram for explaining the mechanism of generating wrinkles and cracks in the forming process of the target shape described above.

[0018] Figure 8 It shows Figure 1 A diagram showing other examples of the intermediate formed part. Detailed implementation mode

[0019] Before explaining the stamping forming method according to the present embodiment, regarding an example of the stamping formed part to be formed by the present invention, based on Figure 6 , Figure 7 the shape and problems thereof will be described. Figure 6 The stamping formed part 1 shown is a floor front cross member as an automotive part. The stamping formed part 1 has: a top plate part 3; a longitudinal wall part 5 that is continuous from the top plate part 3 and has a concave part 7 that is recessed from the edge part on the opposite side of the top plate part 3 in a side view, that is, the lower end edge 11, toward the top plate part 3; and a flange part 9 that is formed outward at the lower end edge 11 of the longitudinal wall part 5.

[0020] Moreover, the concave part 7 has: a pair of inclined edge parts 13 that are continuous from the lower end edge 11 of the part with a deep wall depth; and a concave edge part 15 with a shallow wall depth that connects the ends of the inclined edge parts 13. A pair of first bending parts 17 that bend from the lower end edge 11 of the part with a deep wall depth to the inclined edge parts 13 and a pair of second bending parts 19 that bend from the inclined edge parts 13 to the part with a shallow wall depth are formed. The flange part 9 formed at the first bending part 17 is a shrink flange deformation, and the flange part 9 formed at the second bending part 19 is an extended flange deformation.

[0021] In the case where such a stamped part 1 is formed by an existing stamping method, in the portion that becomes the shrink flange deformation (part a enclosed by a circular dashed line in the figure), wrinkles are likely to occur due to excess metal, and in the portion that becomes the stretch flange deformation (part b enclosed by a circular dashed line in the figure), cracks are likely to occur due to insufficient material.

[0022] Based on Figure 7 to explain the mechanism of generation of such wrinkles and cracks. Figure 7 Is a diagram for explaining the material flow during the forming process in the EE portion enclosed by a quadrilateral dashed line of Figure 6 , showing a top view observation ( Figure 7 of (a)) and a side view observation ( Figure 7 of (b)) Figure 6 of the state. In addition, in Figure 7 , the dashed line is the front end of the blank before forming, and the solid line is the edge of the flange portion 9 formed into the target shape. In addition, points D and B in the figure are points corresponding to the R-finish of the first bending portion 17 in the blank before forming, and correspondingly, in the side view, the intersection points of the lines perpendicular to the edge of the target shape from points D and B with the edge of the target shape are points D' and B'. Similarly, points A and E in the figure are points corresponding to the R-finish of the second bending portion 19 in the blank before forming, and correspondingly, in the side view, the intersection points of the lines perpendicular to the edge of the target shape from points E and A with the edge of the target shape are points A' and E'. As shown in Figure 7 of the side view of (b), the material flows substantially perpendicular to the ridgeline (curved line), so in part a, it flows in the direction approaching the material, and in part b, it flows in the direction away from the material. Therefore, wrinkles are likely to occur in part a, and cracks are likely to occur in part b.

[0023] To solve such problems, the inventor came up with a stamping method that can avoid the concentration of compressive strain and tensile strain in each part by interposing an intermediate forming part that easily allows the material to flow from the portion where the shrink flange deformation occurs to the portion where the stretch flange deformation occurs during the forming process. Specifically, the stamping method is composed of the following structure.

[0024] As Figure 1 shown, the stamping method according to the present embodiment includes: a first forming step S1 of forming a blank, that is, a metal plate 21, into an intermediate forming part 23; and a second forming step S3 of forming the intermediate forming part 23 formed in the first forming step S1 into a target shape. Hereinafter, each step will be described. In addition, inFigure 1 In the example, the target shape is shown. Figure 6 The same parts and corresponding parts are marked with the same reference numerals.

[0025] <First Forming Process>

[0026] The first forming step S1 is a step of forming an intermediate formed part 23. The intermediate formed part 23 includes: a longitudinal wall portion 5; a flange portion 9 formed at the lower end side 11 and the first bent portion 17 at a portion where the wall depth is deep; and a twisted shape portion 25, which is continuous with the flange portion 9 and is formed at the inclined side 13 of the second bent portion 19 to reach the target shape.

[0027] During the intermediate molded product forming process of the first forming step S1, the flange portion 9 is formed on the lower end side 11 and the first curved portion 17 of the deep wall portion, but the twisted shape portion 25 is formed on the inclined side portion 13 instead of the flange portion 9. Figure 2 As shown, one end of the twisted shape portion 25 is connected to the flange portion 9 formed on the first bent portion 17, and the other end is connected to the blank end portion 15a before forming, thereby forming a twisted shape. Figure 2 As shown by the arrow, material flows from the flange portion 9 of the first bent portion 17 to the twisted shape portion 25, and the excess material in the shrinkage flange deformation is alleviated, which can suppress the generation of wrinkles.

[0028] based on Figure 3 The mechanism of the material flow is explained below. Figure 3 Yes Figure 2 The figure illustrates the material flow during the forming process of the CC portion surrounded by the dotted line, showing the top view and the side view. Figure 2 The state of the intermediate molded part 23. Figure 3 In the figure, the thin dotted line is the end edge of the blank before forming, the thick dotted line is the end edge of the intermediate formed part 23, and the solid line is the end edge of the flange portion 9 in the target shape. Points A to E and A' to E' in the figure are Figure 7 That is, point A is the R end point of the second bend 19 in the blank, which is the front end position of the twisted shape portion 25. Point B is the R end point of one side of the blank portion where the shrinkage flange deformation occurs (refer to Figure 7 ), and point B' is the intersection of a straight line perpendicular to the end side of the twisted shape portion 25 from point B in the side view and the end side of the twisted shape portion 25. Point D is the R end point of the first bent portion 17 in the blank, and point D' is the intersection of a line perpendicular to the end side of the target shape from point D in the side view and the end side of the target shape.

[0029] Due to the shrinkage flange deformation, the distance from point B' to point D' is shorter than the distance from point B to point D (B'D' < BD), and wrinkles are likely to occur in the first bending portion 17 due to the remaining material based on the forming of the flange portion 9. On the other hand, when observed three-dimensionally, the distance from point A to point B' is longer than the distance from point A to point B (AB' > AB), so the material is stretched toward point A and flows deviating from " Figure 7 substantially perpendicular to the ridge line" as shown in the a portion of Figure 7 . Therefore, compared with the material flow of the arrow in the wrinkle generation region of the existing Figure 3 , a material flow indicated by an arrow closer to point A is generated. Through this material flow, the remaining material in the shrinkage flange deformation formed in the first forming process S1 is alleviated, and the generation of wrinkles can be prevented.

[0030] In addition, in the first forming process S1, as shown in Figure 8 , a bending portion 27 can also be formed at the middle portion in the height direction of the vertical wall portion 5, and the bending portion 27 has an angle such that the opening side of the vertical wall portion 5 opens outward. The reason for this is as follows. When applying the present invention, if the vertical wall portion 5 is formed with the flange portion 9 while keeping it vertical, the bending angle between the vertical wall portion 5 and the flange portion 9 becomes larger due to springback, and warping (curl) is likely to occur in the vertical wall portion 5. By forming the bending portion 27, the flange portion 9 can be formed using a die with a downward V-shaped front end, so that the bending angle between the vertical wall portion 5 and the flange portion 9 can be made sharp, and the height of the vertical wall portion 5 adjacent to the flange portion 9 can be reduced to suppress warping. As a result, it is easy to form only a part of the flange portion 9, that is, the shrinkage flange deformation portion.

[0031] <Second Forming Process>

[0032] The second forming process S3 is a process of forming the torsion shape portion 25 of the intermediate formed part 23 formed in the first forming process S1 into the flange portion 9 and forming the second bending portion 19 continuous with the inclined edge portion 13 and the flange portion 9 of the concave edge portion 15 with a shallow wall depth into the target shape. During the forming process of the second forming process S3, as shown by the arrow in Figure 4 , by retracting the torsion from the torsion shape portion 25 that has absorbed the Figure 2 material allowance, material inflow is generated toward the extended flange deformation portion using the remaining material, so the material shortage in the extended flange deformation portion is alleviated, and the generation of cracks can be suppressed.

[0033] Based on Figure 5 to explain the mechanism of this material flow. Figure 5 is for Figure 4A diagram for explaining the material flow during the forming process of the DD part enclosed by a dashed line, showing a top view and a side view Figure 4 of the state. In addition, in Figure 5 , the thin dashed line is the edge of the blank before forming, the thick dashed line is the edge of the torsion-shaped part 25, and the solid line is the edge of the flange part 9 in the target shape. In addition, points A to E and points A' to E' in the figure are the same points as those Figure 7 shown.

[0034] Due to the stretch flange deformation, the distance from point A' to point E' is longer than the distance from point A to point E (A'E' > AE). Due to the material shortage caused by the forming of the flange part 9, cracks are likely to occur in the second bending part 19. On the other hand, when observing three-dimensionally, the distance from point D' to point E' is shorter than the distance from point D' to point E (D'E' < D'E). Therefore, the material is pressed toward the A' side and flows deviating from Figure 7 the "substantially perpendicular to the ridge line" shown in the b part of. Therefore, compared with the material flow of the arrow in the crack generation area of the existing Figure 7 , the material flow shown by the arrow near point A' is generated. Through this material flow, the material shortage in the stretch flange deformation formed in the second forming process S3 is alleviated, and the generation of cracks can be prevented. Figure 5 As described above, in the present embodiment, in the first forming process S1, only the part that becomes the shrink flange deformation is formed first, and the torsion-shaped part 25 that promotes the material to flow toward the part that becomes the stretch flange deformation is formed during this forming. Then, in the second forming process S3, the torsion-shaped part 25 is formed in the second bending part 19, and the part that becomes the stretch flange deformation is formed. Thus, it is possible to suppress the insufficient forming of the target shape due to the material shortage of the stretch flange deformation by the material flow from the torsion-shaped part 25.

[0035] As described above, by intervening the forming of the torsion-shaped part 25 during the forming, the strain of the dangerous part where shrink flange wrinkles are generated and the dangerous part where stretch flange cracks are generated is dispersed. Thus, in the first forming process S1, the generation of wrinkles caused by the shrink flange deformation is suppressed, and in the second forming process S3, the generation of cracks caused by the stretch flange deformation is suppressed, and the generation of wrinkles and cracks can be suppressed throughout the process.

[0036] In this way, by intervening the forming of the torsion-shaped part 25 during the forming, the strain of the dangerous part where shrink flange wrinkles are generated and the dangerous part where stretch flange cracks are generated is dispersed. Thus, in the first forming process S1, the generation of wrinkles caused by the shrink flange deformation is suppressed, and in the second forming process S3, the generation of cracks caused by the stretch flange deformation is suppressed, and the generation of wrinkles and cracks can be suppressed throughout the process.

[0037] In addition, the first forming process and the second forming process of the present invention can also be formed by different molds. Alternatively, the first forming process and the second forming process can also be performed by one mold.

[0038] Examples

[0039] To confirm the effects of the present invention,Figure 6 The front floor cross member component shown was stamped and formed as a target shape. The material is a steel sheet with a tensile strength of 1180 MPa-class and a thickness of 1.4 mm. First, as a comparative example, without forming the intermediate formed part 23, the target shape was formed in one process, and a stamping forming by using a pad that presses the top plate part was performed. Next, as an embodiment of the present invention, a stamping forming including a first forming process S1 of forming only the shrink flange deformation part of the intermediate formed part 23 described in the embodiment and a second forming process S3 of forming the intermediate formed part 23 into the target shape was performed, and any of the forming processes was a stamping forming by using a pad that presses the top plate part.

[0040] In the case of the comparative example, wrinkles were generated at the a part shown in Figure 6 and cracks were generated at the b part, and the target shape could not be obtained. On the other hand, in the embodiment of the present invention, neither cracks nor wrinkles were generated in the flange part 9, and a high-quality stamped formed part 1 could be obtained. From the above, it was shown that the present invention is effective for suppressing stretch flange cracks and shrink flange wrinkles when forming a stamped forming part having a flange part and a large change in the depth of the longitudinal wall.

[0041] Industrial availability

[0042] According to the present invention, a stamping forming method that can also be applied to a stamped formed part in which wrinkles and cracks are generated in the flange itself and can simultaneously suppress wrinkles and cracks generated in the flange can be provided.

[0043] Explanation of reference numerals

[0044] 1... Stamped formed part; 3... Top plate part; 5... Longitudinal wall part; 7... Concave part; 9... Flange part; 11... Lower end edge of the deeper part; 13... Inclined edge part; 15... Concave edge part; 15a... Blank end; 17... First bending part; 19... Second bending part; 21... Metal plate; 23... Intermediate formed part; 25... Twisted shape part; 27... Bending part.

Claims

1. A stamping forming method for forming a stamped forming part, the stamped forming part having: a top plate portion; a longitudinal wall portion that is continuous from the top plate portion and has a concave portion that is recessed from the end portion on the opposite side of the top plate portion in side view, i.e., the lower end edge, toward the top plate portion side; and a flange portion that is formed outwardly at the lower end edge of the longitudinal wall portion. The concave portion successively has, starting from the lower end edge of the portion with a deep wall depth: a first bending portion that is continuous with the lower end edge; an inclined edge portion that is continuous with the first bending portion; a second bending portion that is continuous with the inclined edge portion; and a concave edge portion with a shallow wall depth. The flange portion formed at the first bending portion is a shrinking flange, and the flange portion formed at the second bending portion is an expanding flange. The stamping forming method is characterized by including: a first forming process in which an intermediate forming part is formed. The intermediate forming part has the longitudinal wall portion, a flange portion formed at the lower end edge of the portion with a deep wall depth, and a twisted shape portion formed at the inclined edge portion that is continuous with the flange portion and reaches the second bending portion; and a second forming process in which the twisted shape portion is formed into a flange portion and flange portions are formed at the second bending portion that is continuous with the inclined edge portion and the concave edge portion with a shallow wall depth to form the intermediate forming part formed in the first forming process into the target shape.

2. The stamping forming method according to claim 1, characterized in that: The first forming process and the second forming process are formed by different dies.

3. The stamping forming method according to claim 1, characterized in that: The first forming process and the second forming process are carried out by one die.

Images