Patent ID: 12233444

DESCRIPTION OF EMBODIMENTS

Prior to the description of the press forming tool and 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 toFIGS.14and15. If press forming part1illustrated inFIG.14is drawn as a perspective view of a slide door rail which is an automotive part, and includes a top portion3and a flange portion5. The top portion3has a convex part7protruding outward in an in-plane direction and a concave part9adjacent to the convex part7and recessed inward in the in-plane direction. The outer periphery of the top portion3is formed to be a convex and concave outer edge part11including: a convex outer edge part11awhich is an outer peripheral side of the convex part7; a concave outer edge part11bwhich is an outer peripheral side of the concave part9: and a connecting outer edge part11bconnecting the convex of edge part11aand the concave outer edge part11bto each other. The flange portion5is formed on the convex and concave outer edge part11. In the case of an actual slide door rail, a bent portion is formed on an outer edge part of the top portion3facing the convex and concave outer edge part11where the flange portion5is formed. However,FIG.14omits illustration of the bent portion.

When such a press forming part1is formed by a conventional method of press forming, the flange portion5formed in the convex outer edge part11asubjected to shrink flange forming (portion a circled by a broken line in the drawing), and wrinkles are likely to occur due to the excess metal. On the other hand, the flange portion5formed in the concave outer edge part11bis subjected to stretch flange forming (portion b circled by a broken line in the drawing), and is likely to have fractures due to a material shortage.

A mechanism of occurrence of the wrinkles and the fractures will be described with reference toFIG.15.FIG.15is a diagram illustrating a material flow in the forming process in portion EE surrounded by the broken line inFIG.14, illustrating a top view (FIG.15(a)) and a side view of (FIG.15(b)) ofFIG.14. InFIG.15, a broken line is a tip of the blank before forming, and a solid line is an edge of the flange portion5formed into a target shape. Further, points D and B in the drawing are points corresponding to the R-finish (the boundary between a curve and a straight line) of the convex outer edge part11an the blank before forming, and corresponding intersections of 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 D′ and B′. Similarly, points A and E in the drawing are points corresponding to the R-finish of the concave outer edge part11bin the blank before forming, and 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 ofFIG.15(a), since the material flows substantially perpendicularly to the ridge line (bending line), the material flows in a direction in which the material gathers in portion a, and flows in a direction in which the material leaves in portion b. Accordingly, wrinkles are likely to occur in portion a, while fractures are likely to occur in portion b.

In order to solve such a problem, the inventors have considered that interposing a preformed part, which facilitates inflow of a material from a portion where shrink flange forming occurs to a portion where stretch flange forming occurs, in the middle of forming will enable avoidance of concentration of compressive strain and tensile strain in each of the portions, and have devised a press forming tool that can achieve this method of press forming. Specifically, the press forming tool has the following configuration.

As illustrated inFIG.14, for example, a press forming tool13according to the present embodiment forms a press forming part1including: atop portion3having a convex and concave outer edge part11in which a convex outer edge part11aprotruding outward in an in-plane direction and a concave outer edge part11brecessed inward in the in-plane direction are continuous to each other via a connecting outer edge part11c; and a flange portion5continuously formed on the convex and concave outer edge part11of the top portion3. Further, as illustrated inFIGS.1to4, le press forming tool13according to the present embodiment includes: an upper die15and a lower die17for bend-forming the flange portion5along the convex and concave outer edge part11(FIG.5); and a lower pad21and an upper pad23that sandwich a blank19in cooperation with the upper die15and the lower die17. Note that terms of the upper and lower in the upper die and the lower die just indicate a relative relationship, and thus, the positions are not necessarily upper or lower, but simply indicate that they are provided in a pair. With the press forming tool13of the present embodiment, the blank19(FIG.6) is placed on the lower die17and sandwiched by the upper pad23, and the upper die15and the lower pad21are moved to perform bend-forming of the flange portion5at an outer edge of the blank19. The bending edge portions of the upper die15and the lower die17are formed with convex and concave outer surfaces that protrude or recesses in the in-plane direction of the blank19to be placed, similarly to the convex and concave outer parts11of the top portion3.

The upper die15includes: a convex outer edge flange forming portion15athat forms the flange portion5the convex outer edge part11a; a concave outer edge flange forming portion15bthat forms the flange portion5in the concave outer edge part11b; and a connecting outer edge flange forming portion15cthat forms the flange portion5in the connecting outer edge part11c(refer toFIG.4). The convex outer edge flange forming portion15aprotrudes in the press forming direction (downward inFIGS.1to4in the out-of-plane direction of the blank19to be placed) from the concave outer edge flange forming portion15b, while the connecting outer edge flange forming portion15cis inclined from the convex outer edge flange forming portion15atoward the concave outer edge flange forming portion15b(refer toFIGS.2and4).

The lower pad21has a shape corresponding to each of the convex outer edge flange forming portion15a, the concave of edge flange forming portion15b, and the connecting outer edge flange forming portion15cformed in the upper die15. That is, a portion of the lower pad21corresponding to the convex outer edge flange forming portion15aof the upper die15(the portion also referred to as a lower pad convex outer edge flange forming portion21a) is more recessed in the press forming direction compared with a portion corresponding to the concave outer edge flange forming portion15bof the upper die15(the portion also referred to as a lower pad concave outer edge flange forming portion21b). Moreover, a portion corresponding to the connecting outer edge flange forming portion15cof the upper die15(the portion also referred to as a lower pad connecting outer edge flange forming portion21c) is inclined from the lower pad concave outer edge flange forming portion21btoward the lower pad convex outer edge flange forming portion21a(refer toFIGS.1and3).

Next, a method of forming the slide door rail member illustrated inFIG.14using the above-described a press forming tool13of the present embodiment will be described. As illustrated inFIG.5, the method of press forming of the present embodiment includes a forming preparation step S1of setting the blank19in the press forming tool13, an initial forming step S3, and a late forming step S5. Hereinafter, each step will be described in detail with reference toFIGS.5to13. InFIGS.7,8, and11illustrating the movement of the dies, the upper die15and the upper pad23are drawn as transparent perspective views in order to demonstrate the forming state of the blank19.

Forming Preparation Step

In the forming preparation step S1, as illustrated inFIG.6, a blank19made of a metal sheet is placed on the lower die17, and as illustrated inFIG.7, a part of the blank19is sandwiched by using the upper pad23. At this time, the uppermost surface (for example, the lower pad concave outer edge flange forming portion21b) of the lower pad21is flush with the upper surface of lower die17. A portion of the blank19corresponding to the top portion3is disposed on the lower die17, while a portion of the blank19corresponding to the flange portion5is disposed on the lower pad concave outer edge flange forming portion21bof the lower pad21.

Initial Forming Step

In the initial forming step S3, as illustrated inFIG.8, a part of the blank19is supported by the lower pad21in a state where a part of the blank19is sandwiched between the upper pad23and the lower die17, and the upper die15is relatively moved in the press forming direction. With this operation, the flange portion5is formed in the convex outer edge part11aby the convex outer edge flange forming portion15a, and a torsional shape portion25having a shape torsional toward the concave outer edge part11bis formed by the connecting outer edge flange forming portion15ccontinuously from the flange portion5.

In the initial forming step S3, the flange portion5is formed in the convex outer edge part11aof the top portion3, but since the concave outer edge part11bis supported by the lower pad concave outer edge flange forming portion21b, the flange portion5is not formed in the concave outer edge part11bof the top portion3. Therefore, instead of the flange portion5, the torsional shape portion25is formed on the connecting outer edge part11cranging from the convex outer edge part11ato the concave outer edge part11b. As illustrated inFIG.9, the torsional shape portion25is connected, on one end side, to the flange portion5formed on the convex outer edge part11a, while being connected, the other end side, to the top portion3as a flat portion, forming the torsional shape portion25to have a torsional shape. At the time of forming the torsional shape portion25, as indicated by an arrow inFIG.9, a metal inflow occurs in a direction from the flange portion5side to be formed toward the flat portion, leading to alleviation of excess metal in the shrink flange forming and suppression of the occurrence of wrinkles.

A mechanism of occurrence of the material flow will be described with reference toFIG.10.FIG.10is a view illustrating the material flow in the forming process of portion CC surrounded by the broken line inFIG.9, illustrating a top view and a side view ofFIG.9. InFIG.10, a fine broken line is an edge of the blank before forming, a coarse broken line is an edge of the torsional shape portion25, and a solid line is an edge of the target shape. Points A to E and points A′ to E′ in the drawing are the same as those illustrated inFIG.15. That is, point A in the drawing is an R-finish of a curved portion in the blank19, and is a tip position of the torsional shape portion25with little deformation. Point B is a point corresponding to one R-finish of the blank portion having occurrence of shrink flange forming in a conventional case, and point B′ is an intersection of a line extending perpendicularly to the edge of the torsional shape portion25from point B in the top view and the edge of the torsional shape portion25. Point D is an R-finish of the curved portion of the blank19, and point D′ is an 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 shrink flange forming, the distance from point B′ to point D′ is shorter than the distance from point B to point D (B′D′<BD), and thus, wrinkles are likely to occur in the flange portion5formed in the convex outer edge part11cdue to the excess metal. On the other hand, since the distance from point A to point B′ is longer than the distance from point A to point B (AB′>AB) in a three-dimensional view, the material is pulled toward point A and flows while deviating from “substantially perpendicular to the ridge line”. Therefore, the material flow indicated by the arrow inFIG.10is generated, the material flow being closer to point A as compared with the conventional material flow indicated by the arrow in the wrinkle occurrence region inFIG.15. This material flow alleviates the excess metal in shrink flange forming during the initial forming step, leading to suppressing of occurrence of wrinkles.

Late Forming Step

In the late forming step S5, as illustrated inFIG.11, the upper die15and the lower pad21are moved in the press forming direction. With this operation, the torsional shape portion25is formed into the flange portion5by the connecting outer edge flange forming portion15c, while the flange portion5is formed in the concave outer edge part11bby the concave outer edge flange forming portion15b, achieving forming of the target shape. In the forming process of the late forming step S5, as indicated by a thick arrow inFIG.12, the metal inflow occurs from the torsional shape portion25to the stretch flange forming portion, leading to alleviation of material shortage in the stretch flange forming portion and suppression of the occurrence of fractures.

A mechanism of occurrence of the material flow will be described with reference toFIG.13.FIG.13is a view illustrating the material flow in the forming process of portion DD surrounded by the broken line inFIG.12, illustrating a top view and a side view ofFIG.12. InFIG.13, a fine broken line is an edge of the blank before forming, a coarse broken line is an edge of the torsional shape portion25, and a solid line is an edge of the flange portion5in the target shape.

In addition, points A to E and points A′ to E′ in the drawing are the same as those illustrated inFIGS.15and10. That is, point A′ in the drawing is an intersection of a line extending perpendicularly to the ridge line of the target shape in the top view from point A and the target shape. Point E is a point corresponding to one R-finish of the blank portion in which the conventional stretch flange forming occurs, and point E′ is an 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 stretch flange forming, the distance from point A′ to point E′ is longer than the distance from point A to point E (A′E′>AE), and the material shortage is likely to cause an occurrence of fractures in the flange portion5formed in the concave outer edge part11b. 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 toward the A′ side and flows while deviating from “substantially perpendicular to the ridge line”. Therefore, the material flow indicated by the arrow inFIG.13is generated, the material flow being closer to point A′ as compared with the conventional material flow indicated by the arrow in the fracture occurrence region inFIG.15. This material flow alleviates the material shortage in the stretch flange forming during the late forming step S5, leading to suppression of occurrence of fractures.

As described above, with the press forming tool13of the present embodiment, it is possible to form, during the initial stage of forming, the flange portion5in the convex outer edge part11aby the convex outer edge flange forming portion15aand form the torsional shape portion25having a torsional shape toward the concave outer edge part11bcontinuously from the flange portion5by the connecting outer edge flange forming portion15c, and possible to form, during the late stage of forming, the torsional shape portion25into the flange portion5by the connecting outer edge flange forming portion15cand form the flange portion5in the concave outer edge part11bby the concave outer edge flange forming portion15b, achieving formation of the target shape. With this configuration, the torsional shape portion25that promotes the material flow to the portion side occurrence of the stretch flange forming is formed by first forming only the portion of occurrence of the shrink flange forming during the initial stage of forming, and target shape can be formed by suppressing the material shortage due to the stretch flange forming by the material flow from the torsional shape portion25by forming the portion of occurrence of the stretch flange forming during the late stage of forming.

In this manner, by dispersing the strain or a dangerous portion where the stretch flange fracture occurs and a dangerous portion where the shrink flange wrinkles occur, it is possible to suppress the occurrence of wrinkles due to shrink flange forming in the initial forming step S3, suppress occurrence of fractures due to the stretch flange forming in the late forming step S5, and suppress the occurrence of wrinkles and fractures throughout all the steps. In addition, it is possible to press forming using dies by a single action with a movement in a single direction, and leading to achievement of press forming with high efficiency.

EXAMPLE

In order to confirm the effect of the present invention, press forming was performed with an example of a slide door rail member as illustrated inFIG.14as a target shape. The material was a steel sheet having a tensile strength of 1180 MPa class and a thickness of 1.4 mm. First, as Comparative Example, a target shape was formed in one step without forming the torsional shape portion25, and press forming was performed by a method of crash forming by using pad (pad forming), in which the top portion was held with a pad (pressure pad). Next, as Example of the present invention, using the press forming tool13described in the embodiment, press forming is performed, including steps of: an initial forming step S3of forming the flange portion5in the convex outer edge part11aand forming the torsional shape portion25in the connecting outer edge part11c; and a late forming step S5of forming the torsional shape portion25into the flange portion5and forming the flange portion5in the concave outer edge part11b. All the forming steps include a method of crash forming by using pad, in which the top portion was held with a pad.

In the case of Comparative Example, wrinkles occurred in portion a and fractures occurred in portion b illustrated inFIG.14, and the target shape was not successfully obtained. In contrast, in Example of the present invention, the press forming part of high quality was successfully obtained with no fracture or wrinkles in the flange portion5. As described above, the present invention is proven to be effective for suppressing stretch flange fracture and shrink flange wrinkles in formation of a press forming part having convex and concave parts in the in-plane direction on the top portion3.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a press forming tool and a method of press forming applicable to a press forming part having an occurrence of wrinkles and fractures in a flange itself and capable of simultaneously suppressing the wrinkles and fractures occurring in the flange.

REFERENCE SINGS LIST

1PRESS FORMING PART3TOP PORTION5FLANGE PORTION7CONVEX PART9CONCAVE PART11CONVEX AND CONCAVE OUTER EDGE PART11aCONVEX OUTER EDGE PART11bCONCAVE OUTER EDGE PART11cCONNECTING OUTER EDGE PART13TOOLS OF PRESS FORMING15UPPER DIE15aCONVEX OUTER EDGE FLANGE FORMING PORTION15bCONCAVE OUTER EDGE FLANGE FORMING PORTION15cCONNECTING OUTER EDGE FLANGE FORMING PORTION17LOWER DIE19BLANK21LOWER PAD21aLOWER PAD CONVEX OUTER EDGE FLANGE FORMING PORTION21bLOWER PAD CONCAVE OUTER EDGE FLANGE FORMING PORTION21cLOWER PAD CONNECTING OUTER EDGE FLANGE FORMING PORTION23UPPER PAD25TORSIONAL SHAPE PORTION