Press forming method

Abstract

The present invention aims to suppress the occurrence of wrinkles during the bending and forming process. [Solution] A press forming method for forming a flange portion 51 by bending a workpiece 50 using a bending die 10 comprising an upper die 11 that moves in the pressing direction and a lower die 12, wherein the bending die 10 has first compressive stress relief portions 31A, 31C, 31D and a second compressive stress relief portion 32 for relieving the compressive stress generated in the workpiece 50 during the bending process, and the first compressive stress relief portions 31A, 31C, 31D are provided on the molding surface 12a side of the lower die 12 and have first recesses 22A, 22C, 22D that are concave relative to the molding surface 11a side of the upper die 11, and protrusions 21A, 21C, 21D that are provided on the molding surface 11a side of the upper die 11 and fit into the first recesses 22A, 22C, 22D. The second compressive stress relief portion 32 is provided on the molding surface 12a side of the lower mold 12 and has a concave second recess 22B on the molding surface 11a side of the upper mold 11, and the upper mold 11 does not have a convex portion that fits into the second recess 22B.

Description

Technical Field

[0001] The present invention relates to a press forming method.

Background Art

[0002] In hemming forming in press forming, since it is forming in the direction in which the circumference of the workpiece is shortened, the material is gathered during the forming process and wrinkles are formed on its surface, resulting in poor quality.

[0003] On the other hand, for example, in the press forming method of Patent Document 1, a member having a hat-shaped cross section and curved in the longitudinal direction is formed. In this press forming method, in the process of press forming a blank, stepped portions having steps in the press direction are formed at both longitudinal ends of the inner flange portion of the curved shape. Thereby, the inflow of the material toward the central side in the longitudinal direction is restricted, and tension is applied outward in the longitudinal direction at the stepped portion to relieve the compressive stress toward the central side in the longitudinal direction. Thereby, the generation of wrinkles in the flange portion is suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Depending on the workpiece being subjected to joint bending, it may be necessary to form multiple compressive stress relief sections on both the forming die and the forming die used for joint bending in order to increase the actual length after forming. In other words, compressive stress relief sections consisting of a combination of convex and concave parts are formed on the forming surfaces of these dies, and convex parts are formed on the workpiece after joint bending that protrude in the direction of pressing of the die. This increases the actual length of the formed member and suppresses the occurrence of wrinkles. However, if the spacing between the formed convex parts becomes too narrow, the material is constrained between the convex parts, which can actually promote the formation of wrinkles in those areas.

[0006] Given these circumstances, the objective of this invention is to suppress the occurrence of wrinkles during the bending and forming process. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides a press forming method for forming a bent portion of a workpiece by bending it using a press forming die comprising one mold that moves in the pressing direction and the other mold, wherein the press forming die has a first compressive stress relief portion and a second compressive stress relief portion for relieving the compressive stress generated in the workpiece during the press forming process, the first compressive stress relief portion is provided on the molding surface side of the other mold and has a first recess that is concave relative to the molding surface side of the one mold and a convex portion provided on the molding surface side of the one mold and fits into the first recess, the second compressive stress relief portion is provided on the molding surface side of the other mold and has a second recess that is concave relative to the molding surface side of the one mold, and the one mold does not have a convex portion that fits into the second recess.

[0008] In this invention, by combining the first compressive stress relief section and the second compressive stress relief section, multiple recesses (first recess and second recess) can be provided on the other mold side, and parts of one mold side can be combined with parts without protrusions. By providing multiple recesses (first recess and second recess) on the other mold side, the workpiece can be extended toward the recess side, increasing the actual length of the workpiece after molding and suppressing the occurrence of wrinkles in the workpiece. Furthermore, by combining parts of one mold side with and without protrusions, the degree of freedom in their placement can be increased, such as lengthening the section of protrusions formed on one mold side, allowing protrusions to be placed only where necessary. If the spacing between protrusions is narrow, the workpiece material is constrained and compressed in the short section between the protrusions during bending and forming, causing wrinkles. However, in this invention, the occurrence of such wrinkles can be suppressed by combining parts with and without protrusions. [Effects of the Invention]

[0009] According to the present invention, the occurrence of wrinkles in the bending process can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1] This is a rear view of the side outer panel. [Figure 2] This is a cross-sectional view of a collapsible bending mold according to one embodiment of the present invention, corresponding to the shear section A-A in Figure 1, showing the state before collapsible bending. [Figure 3] This is a cross-sectional view of a collapsible bending mold according to one embodiment of the present invention, corresponding to the shear surface A-A in Figure 1, showing the process during collapsible bending. [Figure 4] This is a cross-sectional view of a collapsible bending mold according to one embodiment of the present invention, corresponding to the shear surface A-A in Figure 1, showing the state after collapsible bending. [Figure 5] This is a perspective view showing the molding surface of the lower die of a bending mold according to one embodiment of the present invention. [Figure 6] A perspective view showing the molding surface of the upper die of a bending mold that differs from the embodiment of the present invention. [Figure 7] Figures (a) to (e) show the forming process of the flange surface when bending and forming is performed using the lower mold in Figure 5 and the upper mold in Figure 6. [Figure 8] This is a perspective view showing the molding surface of the upper die of a bending die according to one embodiment of the present invention. [Figure 9] This diagram shows the molding surfaces a of the upper and lower molds, along their respective molding surfaces. [Figure 10] Figures (a) to (e) show the molding process of the flange surface when bending is performed using a bending die according to one embodiment of the present invention. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0012] Figure 1 is a rear view of the side outer panel 1. As shown in Figure 1, the side outer panel 1 is formed through multiple processes, including drawing a plate-shaped material in a direction perpendicular to the plane of the paper in Figure 1, and then forming flange shapes on the roof side and pillar section by bending. The flange portion formed on the roof side of the side outer panel is the part that extends along the upper end of the side outer panel 1.

[0013] Figures 2 to 4 show the process of forming a flange portion on a workpiece 50 by press forming using the press forming method with the press forming die 10 of this embodiment. Figure 2 is a cross-sectional view corresponding to the section along line A-A in Figure 1, forming the portion corresponding to the flange portion on the roof side of the side outer panel. In this embodiment, "press forming" refers to a forming method that reduces the actual length of a workpiece by forming a bent portion through press forming.

[0014] As shown in Figure 2, the bending mold 10 has an upper mold 11 as one of the molds, a lower mold 12 as the other mold, and a pad 13.

[0015] The workpiece 50 is clamped on one side by the lower die 12 and the pad 13. In this state, as shown in FIGS. 3 and 4, the upper die 11 moves in the direction of the lower die 12, and sandwiches the other side of the workpiece 50 between the forming surface 11a of the upper die 11 and the forming surface 12a of the lower die 12 to perform bending and forming. As a result, a flange portion 51 as a bent portion is formed on the workpiece 50. Thus, the upper die 11 is a bending blade that moves in the pressing direction in the bending and forming with respect to the lower die 12 and applies a bending force to the workpiece to form the flange portion 51. The flange portion 51 is formed in a direction that forms a negative angle with respect to the pressing direction in the drawing process (the direction perpendicular to the plane of FIG. 1).

[0016] FIG. 5 is a perspective view of the forming surface side of the lower die 12 as viewed from the direction of arrow B in FIG. 1. As shown in FIG. 5, a plurality of recesses 22A to 22D are formed on the forming surface 12a of the lower die 12 along the longitudinal direction of the flange portion. The recesses 22A to 22D are concave portions with respect to the forming surface of the upper die.

[0017] FIG. 6 is a perspective view showing a forming surface 110a corresponding to FIG. 5 of an upper die 110 having a configuration different from that of the mold of the present embodiment. As shown in FIG. 6, protrusions 111A to 111D corresponding to the recesses 22A to 22D are formed on the forming surface 110a. The protrusions 111A to 111D are portions that protrude toward the forming surface side of the lower die.

[0018] The bending and forming for forming the flange portion on the workpiece 50 is forming in a direction that shortens its actual length. Therefore, when the material is brought closer, the workpiece is compressed, and wrinkles are formed on the surface of the flange portion. On the contrary, as described above, the upper die 110 is provided with protrusions 111A to 111D, and recesses 22A to 22D are provided at positions corresponding to the protrusions 111A to 111D of the lower die 12. As a result, during the bending and forming, the protrusions 111A to 111D enter the recesses 22A to 22D respectively, and the workpiece is protruded toward the recesses 22A to 22D side, and protrusions are formed on the surface of the flange portion. Thereby, the actual length of the flange portion can be increased and the generation of wrinkles can be suppressed. However, providing the protrusions 111A to 111D may conversely cause the generation of wrinkles.

[0019] Figure 7 is a perspective view showing the surface of the flange portion 51 during joint bending molding using the upper die 110 in Figure 6 and the lower die 12 in Figure 5. Figures 7(a) to 7(e) show the joint bending molding process, that is, the process shown in Figures 2 to 4 in which the upper die 110 moves toward the lower die 12 to form the shape, and Figure 7(e) shows the state just before the upper die 110 reaches the bottom dead center.

[0020] As shown in Figures 7(a) to (e), during the molding process, the workpiece is pressed by the protrusions 111A to 111D, and protrusions 52A to 52D are formed on the surface of the flange portion 51, projecting in the direction towards the back of the paper in Figure 7. The protrusions 111A to 111D project toward the center of curvature of the curved flange portion, and as the workpiece 50 is pressed by the protrusions 111A to 111D during the bending process, the workpiece 50 bulges toward the center of curvature. This suppresses the accumulation of material and also increases the actual length of the flange portion, thereby suppressing the occurrence of wrinkles on the surface of the flange portion 51.

[0021] However, in the example shown in Figure 8, wrinkles C are formed, particularly between the protrusions 52B and 52C, during the bending process. In other words, the formation of protrusions 52B and 52C causes the material of the workpiece 50 to be confined to the short section between the protrusions 52B and 52C during bending. As a result, the material of the workpiece 50 is compressed within that section, causing wrinkles C to form. Thus, by forming protrusions on the flange portion using a combination of the convex portion of the upper die and the concave portion of the lower die, it is possible to increase the actual length of the workpiece 50 after molding and suppress the occurrence of wrinkles. However, on the other hand, by trapping the material of the workpiece between the protrusions, it promotes the occurrence of wrinkles in this section, thus creating a cause for wrinkle formation. In this way, the first compressive stress relief section, consisting of the convex portion of the upper die and the concave portion of the lower die, suppresses the occurrence of wrinkles, but it can also change the location of wrinkle formation, causing wrinkles to form in the section between the convex portions.

[0022] Figure 8 is a perspective view showing the molding surface side of the upper mold 11 in this embodiment. As shown in Figure 8, the upper mold 11 in this embodiment has protrusions 21A, 21C, and 21D on the molding surface 11a. The protrusions 21A, 21C, and 21D are portions that project toward the molding surface side of the lower mold. The protrusions 21A, 21C, and 21D in this embodiment have a diameter that narrows toward their tip and have a roughly triangular pyramidal shape with rounded edges. However, the shape is not limited to this, as long as it is a protruding shape toward the lower mold that can increase the actual length of the flange portion. Also, the recesses 22A, 22C, and 22D of the lower mold 12 (see Figure 5) have a concave shape corresponding to the protrusions 21A, 21C, and 21D.

[0023] Figure 9 shows the molding surface 11a of the upper mold 11 shown in Figure 5 and the molding surface 12a of the lower mold 12 shown in Figure 8, along the molding surface. As shown in Figure 9, the protrusion 21A is provided at a position corresponding to the recess 22A of the lower die 12, and similarly, the protrusion 21C is provided at a position corresponding to the recess 22C, and the protrusion 21D is provided at a position corresponding to the recess 22D. In other words, in this embodiment, the protrusion is not provided at a position corresponding to the recess 22B of the lower die 12, which is different from the upper die 110 described in Figure 6. The protrusions 21A, 21C, and 21D protrude toward the center of curvature of the curved flange portion formed on the workpiece, and enter into the recesses 22A, 22C, and 22D, respectively, during the bending process. The protrusions 21A, 21C, and 21D of the upper mold 11 and the recesses 22A to 22D of the lower mold 12 are formed in such a way as to avoid welded areas and other such parts on the side outer panel.

[0024] The combinations of the protrusions 21A, 21C, and 21D of the upper mold 11 and the recesses 22A, 22C, and 22D of the lower mold 12 constitute the first wrinkle-removing sections (first compressive stress-relieving sections) 31A, 31C, and 31D, respectively. Furthermore, the upper mold 11 corresponding to the recess 22B of the lower mold 12 does not have a corresponding convex portion and is flat, and this portion constitutes the second wrinkle-removing section (second compressive stress-relieving section) 32. In other words, the upper mold 11 does not have a portion that fits into the recess 22B at the position corresponding to the recess 22B. However, the portion of the upper mold 11 corresponding to the recess 22B may be concave. Thus, the recesses 22A, 22C, and 22D of the lower mold 12 are the first recesses of this embodiment that constitute the first compressive stress-relieving section. Furthermore, the recess 22B of the lower mold 12 is the second recess of this embodiment that constitutes the second compressive stress-relieving section.

[0025] Figures 10(a) to (e) are perspective views showing the process of forming the flange portion 51 using the upper mold 11 and lower mold 12 of this embodiment.

[0026] As shown in Figures 10(a) to (e), during the bending process, the protrusions 21A, 21C, and 21D of the upper die 11 enter the recesses 22A, 22C, and 22D (see Figure 9) of the lower die 12, pushing the workpiece 50 toward the center of curvature of the flange portion 51. As a result, as shown in Figure 10(e), protrusions 53A, 53C, and 53D are formed that protrude toward the center of curvature of the flange portion 51. In the second compression stress relief portion 32 (see Figure 9), the workpiece 50 is not pressed by the upper die 11, but due to excess material of the workpiece 50 between protrusions 53A and 53C during the bending process, the material flows into the recess 22B (see Figure 9) and protrudes, forming protrusion 53B. Protrusions 53A to 53D protrude toward the interior of the vehicle on the side outer panel.

[0027] In this embodiment, as shown in Figure 9, since the upper mold 11 does not have a portion that fits into the recess 22B, the distance between the protrusions 21A and 21C formed on the upper mold 11 is larger than the distance between the protrusions 111B and 111C of the upper mold 110 shown in Figure 6. Therefore, the occurrence of wrinkles due to material entrapment in this section can be suppressed. Specifically, as can be seen by comparing Figure 7(e) and Figure 10(e), the occurrence of wrinkles is suppressed in the flange portion 51 of this embodiment.

[0028] As described above, in this embodiment, a first wrinkle-removing section (first compressive stress relief section) is provided, which forms a convex portion on the upper die 11 and a first recess on the lower die 12, and a second wrinkle-removing section (second compressive stress relief section) is provided, which forms a second recess on the lower die 12 and does not form a portion on the upper die 11 that fits into the second recess. This makes it possible to suppress the occurrence of wrinkles in the workpiece after bending and forming. In other words, by providing multiple recesses on the lower die 12, a protruding portion is formed on the flange portion that protrudes toward the center of curvature, thereby increasing the actual length of the workpiece and suppressing the occurrence of wrinkles in the workpiece. Furthermore, by providing a convex portion on the upper die 11 with the first compressive stress relief section, the workpiece material can be actively pushed toward the lower die side, and especially toward the center of curvature of the flange portion in this embodiment, thereby actively extending the actual length of the workpiece and effectively suppressing the occurrence of wrinkles. Furthermore, by not forming a protrusion in the upper mold 11 that fits into the second recess due to the second compressive stress relaxation section, the degree of freedom in arranging the protrusions can be increased, such as by widening the spacing between the protrusions formed on one of the molding dies. Consequently, it is possible to suppress the constrainment and compression of the workpiece material in the short sections between the protrusions, which can cause wrinkles. In addition, because the degree of freedom in arranging the protrusions is increased, the location of wrinkles in the flange can be adjusted more freely.

[0029] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention.

[0030] The number of first and second compressive stress relief sections is not limited to the above embodiment; for example, unlike the above embodiment, multiple second compressive stress relief sections can be provided. The arrangement and combination of the first and second compressive stress relief sections can be appropriately selected, taking into consideration the degree of wrinkle formation after bending and the spacing between the protrusions. [Explanation of Symbols]

[0031] 1. Side outer panel 10. Bending and forming mold 11 Upper mold (one of the molding molds) 11a Upper mold molding surface (molding surface of one mold) 12. Lower mold (the other molding mold) 12a. The molding surface of the lower mold (the molding surface of the other mold) 21A, 21C, 21D protrusions 22A, 22C, 22D Recessed parts (first recessed part) 22B Recess (Second recess) 31A, 31C, 31D First wrinkle removal section (first compressive stress relaxation section) 32. Second wrinkle removal section (second compressive stress relaxation section) 50 Work 51 Flange section (bent section)

Claims

[Claim 1] A press forming method for forming a bent portion by bringing a workpiece together and bending it using a bending die comprising one forming die that moves in the pressing direction and the other forming die, The aforementioned bending die has a first compressive stress relief section and a second compressive stress relief section for relieving the compressive stress generated in the workpiece during the bending process. The first compressive stress relief portion is provided on the molding surface side of the other mold and has a first recess that is concave relative to the molding surface side of the one mold and a convex portion that is provided on the molding surface side of the one mold and fits into the first recess. The press molding method is characterized in that the second compressive stress relief portion is provided on the molding surface side of the other mold, has a concave second recess relative to the molding surface side of the one mold, and the one mold does not have a convex portion that fits into the second recess.

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