PRESSURE FORMATION METHOD

Abstract

A pressure forming method according to the present invention forms a pressure forming part, the pressure forming part comprising: an upper portion (3) having a convex and concave outer edge portion (11) wherein a convex outer edge portion (11a) projecting outwards in a plane direction and a concave outer edge portion (11b) recessed inwards in the plane direction are continuous with each other through a connecting outer edge portion (11c); and a flange portion (5) formed continuously in the convex and concave outer edge portion (11) of the upper portion (3).The pressure forming method includes: a first forming step (S1) of forming a preformed part (15) that includes the flange portion (5) formed in the convex outer edge part (11a) and that includes a torsionally shaped portion (17) that has a torsional shape towards the concave outer edge part (11b) to be formed in the connecting outer edge part (11c) continuous from the flange portion (5); and a second forming step (S3) of forming the preformed part (15) formed in the first forming step (S1) into a target shape by forming the torsionally shaped portion (17) in the flange portion (5) and forming the flange portion (5) in the concave outer edge part (11b).

Description

PRESSURE FORMING METHOD FIELD The present invention relates to a pressure forming method applicable to the pressure forming of a part such as an automotive part from a sheet of metal, and particularly relates to a pressure forming method applicable to the forming of a pressure forming part that includes: an upper portion having a convex and concave portion in one direction in the plane; and a flange portion formed continuously from the upper portion. BACKGROUND In recent years, to reduce the weight of car bodies due to environmental concerns, high-strength steel sheets have been frequently used for automotive parts. However, high-strength steel sheets have lower elongation compared to low-strength steel sheets and are therefore prone to fracture during processing. Furthermore, when using high-strength steel sheets, thinning is often performed simultaneously to further reduce weight, leading to a high probability of buckling and wrinkling during press forming. Therefore, the development of a press forming method to suppress fractures and wrinkling is urgently needed. For example, Patent Literature 1 discloses a press forming method that uses a wrinkle suppression pad (workpiece support) driven separately from a punch and press dies (die dies) and that makes it possible to manufacture an automotive part that is likely to cause wrinkles and stretch flange fractures within a product without forming defects. The method disclosed in Patent Literature 1 is deemed to be capable of manufacturing an automotive part that is likely to cause wrinkles and fractures within a product without defects forming. APPOINTMENT LIST PATENT LITERATURE Patent Literature 1: JP 6032374 B2 BRIEF DESCRIPTION Technical Problem However, the pressure forming method disclosed in Patent Literature 1 requires holding the product's interior away from the flange using a wrinkle suppression pad (workpiece support). Therefore, the method has the problem that the technique cannot QPCfr Ln / Zznz / E / YIAI to be applied to a form that has the appearance of wrinkles or fractures in the flange portion itself. The present invention has been made in view of the above problem, and aims to provide a method of pressure forming applicable to a pressure forming part that has an occurrence of wrinkles and fractures in a flange itself and capable of simultaneously suppressing the wrinkle and fracture that occur in the flange. Solution A pressure forming method according to the present invention for forming a pressure forming part, the pressure forming part including: an upper portion having a convex and concave outer edge portion in which a convex outer edge portion projecting outwards in a plane direction and a concave outer edge portion recessed inwards in the plane direction are continuous with each other through a connecting outer edge portion;and a portion of the flange formed continuously on the convex and concave outer edge part of the upper portion, includes: a first step of forming a preformed part, the preformed part including a portion of the flange formed on the convex outer edge part and including a twist-shaped portion having a twist shape towards the concave outer edge part to be formed on the continuous connecting outer edge part from the flange portion; and a second step of forming the preformed part formed in the first forming step into a target shape by forming the twist-shaped portion on the flange portion and forming the flange portion on the concave outer edge part. The first forming step and the second forming step can be performed using different dies. The first and second forming steps can be performed using a die. Favorable Effects of the Invention According to the pressure forming method according to the present invention, the appearance of wrinkles due to the formation of the shrink flange is suppressed in the first forming step, and the appearance of fractures due to the formation of the stretch flange is suppressed in the second forming step, leading to the suppression of the appearance of wrinkles and fractures throughout all steps. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a view illustrating a pressure forming method according to an embodiment of the present invention. Figure 2 is an enlarged view of portion (AA) of a piece made in the first forming step of Figure 1. Figures 3(a) and 3(b) are a view illustrating a mechanism for suppressing the occurrence of QPCfr Ln / Zznz / E / YIAI wrinkles in the first formation step. Figure 4 is an enlarged view of portion (BB) of a target shape in the second formation step of Figure 1. Figures 5(a) and 5(b) are a view illustrating a mechanism for suppressing the occurrence of fractures in the second formation step. Figure 6 is a view that illustrates a target shape and a problem that occurs in a process of forming the target shape according to the modality. Figures 7(a) and 7(b) are a diagram illustrating a mechanism for the appearance of wrinkles and fractures in the process of forming the target shape illustrated in Figure 6. DESCRIPTION OF THE MODALITIES Before describing the method of press forming according to the present embodiment, an example of a press forming part to be formed in the present invention will be described with reference to Figures 6, 7(a), and 7(b). A press forming the part (1) illustrated in Figure 6 is drawn as a perspective view of a sliding door rail, which is an automotive part, and includes an upper portion (3) and a flange portion (5). The upper portion (3) has a convex portion (7) projecting outward in the plane direction and a concave portion (9) adjacent to the convex portion (7) and recessed inward in the plane direction.The outer periphery of the upper portion (3) is a convex and concave outer edge (11) formed by a convex outer edge portion (11a) that is an outer peripheral side of the convex portion (7), a concave outer edge portion (11b) that is an outer peripheral side of the concave portion (9), and a connecting outer edge portion (11c) that connects the convex outer edge portion (11a) and the concave outer edge portion (11b) to each other. The flange portion (5) is formed on the convex and concave outer edge portion (11). In the case of an actual sliding door track, a bent portion is formed on a portion of the outer edge of the upper portion (3) that faces the convex and concave outer edge portion (11) where the flange portion (5) is formed. However, Figure 6 omits the illustration of the bent portion. When the die-formed part (1) is formed by a conventional die-forming method, the portion of the flange (5) formed on the convex outer edge (11a) is subject to shrink flange forming (portion (a) enclosed by a dashed line in the drawing), and wrinkles are likely to occur due to excess metal. On the other hand, the portion of the flange (5) formed on the concave outer edge (11b) is subject to stretch flange forming (portion (b) enclosed by a dashed line in the drawing), and fractures are likely due to insufficient material. A mechanism for the formation of wrinkles and fractures will be described with reference to Figures 7(a) and 7(b). Figure 7(a) is a diagram illustrating a material flow in the forming process. QPCfr ίη / 77Π7 / E / YΙΛΙ in the portion (EE) enclosed by the dashed line in Figure 6, illustrating a top view (Figure 7(a)) and a side view (Figure 7(b)) of Figure 6. In Figure 7(a), a dashed line is a point of the blank before forming, and a solid line is an edge of the flange portion (5) formed into a target shape. Furthermore, points (D) and (B) in the drawing are points corresponding to the finish at R (the boundary between a curve and a straight line) of the convex outer edge portion (11a) on the blank before forming, and the corresponding intersections of the lines perpendicular to the edge of the target shape from points (D) and (B) in the top view and the edge of the target shape are points (D1) and (B1).Similarly, points (A) and (E) on the drawing correspond to the finish R of the concave outer edge portion (11b) on the blank before forming, and the corresponding points of intersection between a line perpendicular to the edge of the target shape from points (E) and (A) in the top view and the edge of the target shape are points (A') and (E'). As illustrated in the top view of Figure 7(a), since the material flows substantially perpendicular to the ridge line (flex line), the material flows in a direction where it accumulates in portion (a) and flows in a direction where it sheds in portion (b). Consequently, wrinkles are likely to occur in portion (a), while cracks are likely to occur in portion (b). To solve this problem, the inventors have devised a pressure forming method in which a preformed part, facilitating the flow of material from a portion where the shrink flange forms to a portion where the stretch flange forms, is interposed in the middle of the forming process. This prevents the concentration of compressive and tensile stresses in each portion. Specifically, the pressure forming method has the following configuration. As illustrated in Figure 1, the pressure forming method according to the present embodiment includes: a first forming step (S1) of forming a blank made of sheet metal (13) into a preformed part (15); and a second forming step (S3) of forming the preformed part (15) formed in the first forming step (S1) into a target shape. Each of the steps is described below. In Figure 1, the portions identical to those in Figure 6 that illustrate the target shape are denoted by the same reference numbers. First step in training The first forming step (S1) is a forming step of the preformed part (15) from the blank. The preformed part (15) includes: a flange portion (5) formed on the convex outer edge part (11a); and a torsionally shaped portion (17) formed on the connecting outer edge part (11c) having the target shape formed continuously from the flange portion (5). In the process of forming the preformed part in the first forming step (S1), the flange portion (5) is formed on the convex outer edge part (11 a) of the upper portion (3), although QPCfr ίη / 77Ω7 / Β / YΙΛΙ The torsionally shaped portion (17) is formed on the concave outer edge part (11b) without forming the flange portion (5). As illustrated in Figure 2, the torsionally shaped portion (17) is connected, on one end side, to the flange portion (5) formed on the convex outer edge part (11a), while it is connected, on the other end side, to the upper portion (3) as a flat portion, forming the torsionally shaped portion (17) to have a torsional shape. At the time of forming the torsionally shaped portion (17), as indicated by an arrow in Figure 2, there is an influx of metal in one direction from the side of the flange portion (5) to be formed towards the flat portion, which leads to reducing the excess metal in the formation of the shrink flange and suppressing the appearance of wrinkles. A material flow mechanism will be described with reference to Figures 3(a) and 3(b). Figure 3(a) is a view illustrating material flow during the forming process in the portion (CC) enclosed by the dashed line in Figure 2, which illustrates a top and side view of Figure 2. In Figure 3(a), a thin dashed line is an edge of the blank before forming, a thick dashed line is an edge of the preformed part (15), and a solid line is an edge of the flange portion (5) in the target shape. Points (A) to (E) and points (A) to (E1) in the drawing are the same as those illustrated in Figures 7(a) and 7(b). That is, point (A) in the drawing is a finish R of a curved portion in the blank, and is a tip position of the torsionally shaped portion (17).Point (B) is a point corresponding to a finish R of the rough portion that has a shrinkage flange formation appearance in a conventional case, and point (B') is the intersection of a line extending perpendicularly to the edge of the torsionally shaped portion (17) from point (B) in the top view and the edge of the torsionally shaped portion (17). Point (D) is a finish R of the curved portion of the rough part, and point (D1) is the intersection of a line perpendicular to the edge of the target shape from point (D) in the top view and the edge of the target shape. Due to the formation of the shrink flange, the distance from point (B') to point (D') is shorter than the distance from point (B) to point (D) ((B')(D') < (B)(D)), and therefore, wrinkles are likely to occur in the portion of the flange (5) formed on the convex outer edge (11a) due to excess metal. Furthermore, since the distance from point (A) to point (B1) is greater than the distance from point (A) to point (B) ((A)(B') > (A)(B)) in a three-dimensional view, the material is pulled toward point (A) and flows while deviating substantially from perpendicularity to the crest line. Therefore, the material flow indicated by the arrow in Figure 5 is generated, being closer to point A' compared to the conventional material flow indicated by the arrow in the fracture region in Figure 7.This material flow relieves excess metal in the formation of the shrink flange in the first forming step (S1), leading to the suppression of wrinkling. Second training step The second forming step (S3) is a forming step of the torsional shaping portion QPCfr Ln / Zznz / E / YIAI (17) of the preformed part (15) formed in the first forming step (S1) in the flange portion (5), and the forming of the flange portion (5) in the concave outer edge part (11b) to achieve the formation of a target shape. In the forming process of the second forming step (S3), as indicated by the arrow in Figure 4, by returning the torsion of the torsionally shaped portion (17) that has absorbed the excess metal in Figure 2, the excess metal causes the entry of metal into the draw flange forming portion, reducing the material shortage of the draw flange forming portion, leading to the suppression of the occurrence of fracture. A material flow mechanism will be described with reference to Figure 5(a). Figure 5(a) is a view illustrating material flow in the forming process of the portion (DD) enclosed by the dashed line in Figure 4, showing a top view and a side view of Figure 4. In Figure 5(a), a thin dashed line is an edge of the blank before forming, a thick dashed line is an edge of the torsionally shaped portion (17), and a solid line is an edge of the flange portion (5) in the target shape. Furthermore, points (A) to (E) and points (A) to (E1) on the drawing are the same as those illustrated in Figures 7(a), 7(b), 3(a), and 3(b). That is, point (A) on the drawing is the intersection of a line extending perpendicularly to the crest line of the target shape in the top view from point (A) and the target shape. Point (E) corresponds to a finish R on the portion of the blank where the conventional draw flange is formed, and point (E') is the intersection of a line perpendicular to the edge of the target shape from point (E) in the top view and the edge of the target shape.Due to the formation of the stretch flange, the distance from point (A1) to point (E1) is longer than the distance from point (A) to point (E) ((A')(E') > (A)(E)), and insufficient material can lead to fractures in the portion of the flange (5) formed on the concave outer edge (11b). On the other hand, since the distance from point (D') to point (E') is shorter than the distance from point (D') to point (E) ((D')(E') < (D')(E)) in a three-dimensional view, the material is pushed towards side (A) and flows while deviating substantially from the perpendicular to the crest line. Therefore, the material flow indicated by the arrow in Figure 5(a) is generated, being the material flow closer to point A' compared to the conventional material flow indicated by the arrow in the fracture occurrence region in Figure 7(a).This material flow reduces the material shortage in the formation of the stretch flange in the second forming step (S3), leading to the suppression of the occurrence of fractures. As described above, in the present embodiment, only the portion of the shrink flange formation that influences the formation of the shrink flange is formed first in the first forming step (S1). Therefore, the torsional shape portion (17) that promotes material flow toward the portion where the stretch flange formation occurs is formed during the forming process. During the second forming step (S3), the portion that becomes the stretch flange is formed, and the target shape is formed as it develops. QPCfr Ln / Zznz / E / YIAI suppresses the material shortage due to the formation of the stretching flange using the material flow from the torsional shape portion (17). In this way, by dispersing the stress from a dangerous portion where the stretching flange fracture occurs and a dangerous portion where the shrinking flange wrinkles occur, it is possible to suppress the occurrence of wrinkles due to the formation of the shrinking flange in the first forming step (S1), suppress the occurrence of fractures due to the formation of the stretching flange in the second forming step (S3), and suppress the occurrence of wrinkles and fractures in all steps. The first and second forming steps of the present invention can be formed with different dies. Alternatively, the first and second forming steps can be formed with one die. Example To confirm the effect of the present invention, pressure forming was performed on a sliding door rail member as illustrated in Figure 6 as a target shape. The material was a steel sheet with a tensile strength of 1180 MPa and a thickness of 1.4 mm. First, as a comparative example, a target shape was formed in one step without forming the preformed part (15), and pressure forming was performed by a shock deformation method using a pad (pad forming), in which the upper portion was held in place by a pressure pad.Next, as an example of the present invention, pressure forming was carried out comprising the first forming step (S1) of forming the preformed piece (15) in which only the shrink flange portion is formed and the second forming step (S3) of forming the preformed piece (15) into a target shape, which are described in the embodiment, with each forming step carried out by a shock forming method using a pad, in which the upper portion was held in place by a pad. In the Comparative Example, wrinkles occurred in portion (a) and fractures in portion (b), as illustrated in Figure 6, and the desired shape was not successfully obtained. In contrast, in the Example of the present invention, the high-quality die-formed part was successfully obtained without fracture or wrinkles in the flange portion (5). As described above, the present invention has proven effective in suppressing stretch flange fracture and shrink flange wrinkles in the forming of a die-formed part having connected, in-plane concave portions in the upper portion (3). INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a pressure forming method applicable to a pressure forming part that has wrinkles and fractures appearing in a flange itself and capable of simultaneously suppressing the wrinkles and fractures that occur in the flange. QPCfr ίη / 77Π7 / E / YΙΛΙ LIST OF REFERENCE SIGNS (1) PRESS FORMING PART (3) UPPER PORTION (5) FLANGE PORTION (7) CONVEX PORTION (8) CONCAVE PORTION (11) CONVEX AND CONCAVE OUTER EDGE PORTION (11a) CONVEX OUTER EDGE PORTION (11b) CONCAVE OUTER EDGE PORTION (11c) CONNECTION OUTER EDGE PORTION (13) METAL SHEET (15) PREFORMED PIECE (17) TORSIONALLY SHAPED PORTION

Claims

1. A pressure forming method for forming a pressure forming part, the pressure forming part including: an upper portion having a convex and concave outer edge portion in which a convex outer edge portion projects outwards in a plane direction and a concave outer edge portion recessed inwards in the plane direction are continuous with each other through a connecting outer edge portion;and a portion of the flange formed continuously in the convex outer edge part and concave part of the upper portion, the pressure forming method comprises: a first step of forming a preformed part, the preformed part includes a portion of the flange formed in the convex outer edge part and includes a torsionally shaped portion having a torsional shape towards the concave outer edge part so that it is formed in the continuous connecting outer edge part from the flange portion; and a second step of forming the preformed part formed in the first forming step into a target shape by forming the torsionally shaped portion in the flange portion and forming the flange portion in the concave outer edge part.

2. The pressure forming method according to claim 1, wherein the first forming step and the second forming step are carried out using different dies.

3. The pressure forming method according to claim 1, wherein the first forming step and the second forming step are performed with a single die.

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