Drawing method

Abstract

To provide a drawing method to mold a press product such as a press product with a protrusion having a large draw depth by minimizing inflow of material to be molded with high accuracy and low cost.SOLUTION: A method applying drawing work as press work to a tabular blank material 10 to mold a protrusion 4 of a product in the blank material 10 comprises: a recess molding step S1 which molds a recess 6 at a portion 5 over the protrusion 4 of the product and the excess metal part 3a using a press upper die 21 and a lower side blank holder 24, while sandwiching an excess metal part 3a at the periphery of a product part 2 of the blank material 10 between an upper side blank holder 23 and the lower side blank holder 24; and a lower die molding step S2 which molds the protrusion 4 of the product in the blank material 10 using a press lower die 22 after molding recess 6.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a drawing method, and more particularly to a technique for forming a product convex portion with a large drawing depth in a blank material by drawing. [Background technology]

[0002] For example, when forming the outer body panels of an automobile by press working, drawing is often used from the viewpoint of high flexibility in forming, small number of steps, and therefore low cost.

[0003] A typical device for performing drawing includes an upper mold called a die, a lower mold called a punch, an upper blank holder, and a lower blank holder (see, for example, Patent Document 1). In this type of drawing device, the upper and lower blank holders first hold a plate-like workpiece before forming, called a blank, and then the upper and lower blank holders are brought close to the punch to press the blank against the punch, thereby forming the product shape in the blank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-159918 Summary of the Invention [Problem to be solved by the invention]

[0005] Among the outer panels of an automobile body, the spoiler portion of the outer back door, for example, has a shape that protrudes significantly from the surface side of the product. Therefore, if this is to be formed using the drawing process described in Patent Document 1, an extremely large drawing depth is required. This makes it difficult to form this type of protrusion (convex portion) with high precision. In addition, it becomes necessary to flow a large amount of surrounding blank material toward the convex portion, which reduces yield and ultimately increases costs. Another problem is that the more material is flowed, the more likely molding defects such as wrinkles and cracks are to occur.

[0006] In view of the above circumstances, the technical problem to be solved in this specification is to minimize the inflow of material and enable molding with high precision and low cost, even for press products having convex portions with a large drawing depth. [Means for solving the problem]

[0007] The above-mentioned problems are solved by a drawing method according to the present invention. Specifically, this drawing method involves drawing a plate-shaped blank using an upper press die, a lower press die, an upper blank holder, and a lower blank holder to form a product convex portion in the blank. The drawing method includes a recess forming step in which, while the upper blank holder and the lower blank holder clamp an excess material portion located around a product portion of the blank, the upper press die and the lower blank holder form a recess in a region spanning the product convex portion and the excess material portion. After the recess is formed, the lower press die forms a product convex portion in the blank. In this specification, "protruding" refers to a state in which the blank protrudes toward the surface of the product portion to be formed, and "recessed" refers to a state in which the surface of the product portion to be formed in the blank is recessed. The "product convex portion" as used herein refers to the portion of the blank that protrudes furthest toward the surface of the product.

[0008] As described above, in the drawing method according to the present invention, the upper press die and the lower blank holder form a recess in a region spanning the product protrusion and the excess material surrounding the protrusion, and then the lower press die forms the product protrusion in the blank. First, the upper press die forms the recess, thereby forming the base end of the product protrusion, which forms the inner portion of the recess. In this case, the lower end position of the product protrusion is lower than the position where the blank is pressed by the upper and lower blank holders (i.e., the clamping position of the excess material). Therefore, by forming the product protrusion using the lower press die under the same conditions as conventional methods, the drawing depth of the product protrusion by the lower press die can be reduced. This significantly reduces or even eliminates the inflow of material into the product protrusion. Therefore, even a product protrusion with a large drawing depth can be formed accurately and at low cost.

[0009] In the drawing method according to the present invention, in the recess forming step, the upper press die and the lower blank holder may form a pair of recesses at positions facing each other across the product protrusion.

[0010] By forming a pair of recesses at positions facing each other across the product protrusion in this way, it is possible to apply uniform tension to the portion of the blank that will become the product protrusion in the direction in which the recesses are arranged. This makes it possible to form the recess (the base end side of the product protrusion) with higher precision in the press upper die, and ultimately to form the product protrusion with higher precision in the press lower die. [Effects of the Invention]

[0011] As described above, according to the present invention, it is possible to form a press product having a protrusion with a large drawing depth with high precision and low cost by minimizing the inflow of material. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a plan view of a pressed product obtained by a drawing method according to an embodiment of the present invention. FIG. [Figure 2] 2 is a cross-sectional view taken along line AA of the pressed product shown in FIG. 1. [Figure 3] 2 is a cross-sectional view of the stamping device according to one embodiment of the present invention taken along a line corresponding to the cross section BB in FIG. 1. [Figure 4] FIG. 4 is a diagram showing an example of drawing using the stamping apparatus shown in FIG. 3, and is a cross-sectional view of the stamping apparatus at the time when the blank is clamped between the upper and lower blank holders. [Figure 5] FIG. 4 is a diagram showing an example of drawing using the stamping apparatus shown in FIG. 3, and is a cross-sectional view of the stamping apparatus at the completion of the recess forming step. [Figure 6] FIG. 4 is a cross-sectional view of the press working apparatus at the start of a lower die forming step, showing an example of drawing using the press working apparatus shown in FIG. 3. [Figure 7] FIG. 4 is a diagram showing an example of drawing using the press working apparatus shown in FIG. 3, and is a cross-sectional view of the press working apparatus at the completion of the lower die forming step. DETAILED DESCRIPTION OF THE INVENTION

[0013] A drawing method according to an embodiment of the present invention will be described below with reference to the drawings. In the following description, the vehicle width direction is defined as the X direction, the vehicle body vertical direction is defined as the Y direction, and the vehicle body longitudinal direction is defined as the Z direction.

[0014] FIG. 1 is a plan view of an example of a pressed product 1 obtained by a drawing method according to an embodiment of the present invention. As shown in FIG. 1, this pressed product 1 is an intermediate product for an outer tailgate of an automobile, and integrally includes a product portion 2 and an excess metal portion 3 located around the product portion 2. In this embodiment, the excess metal portion 3 is made up of a first excess metal portion 3a provided on the outer periphery of the product portion 2 and a second excess metal portion 3b provided on the inner periphery of the product portion 2. Of these, the second excess metal portion 3b is a portion that is removed from the product portion 2 to form an opening in the tailgate into which a window glass is to be installed. Both excess metal portions 3a, 3b are removed by trimming or the like after the product portion 2 is formed by drawing.

[0015] The product part 2 has a spoiler part 4 of the back door outer integrally formed on the vertical upper end side as a product protrusion. This spoiler part 4 extends in the vehicle width direction of the product part 2. As shown in FIG. 2, the spoiler part 4 is the part that protrudes most toward the surface 2a of the product part 2.

[0016] The pressed product 1 having the above shape is obtained by drawing a plate-shaped blank material 10 (see FIG. 4, which will be described later) using, for example, a pressing device 20 shown in FIG.

[0017] 3 shows a cross-sectional view of a press working apparatus 20 for performing the drawing process according to the present invention on a blank 10. This cross-sectional view is a cross-sectional view of the press working apparatus 20 at the same position as the BB cross section along the longitudinal direction (vehicle width direction) of the middle part of the spoiler portion 4 of the press-worked product 1 obtained by drawing. The press working apparatus 20 has an upper press die 21, a lower press die 22, an upper blank holder 23, and a lower blank holder 24.

[0018] The upper press die 21 and the lower press die 22 have first press-forming surfaces 25, 26 that are shaped to correspond to each other and are positioned opposite each other in the vertical direction. The upper press die 21 and the lower blank holder 24 have second press-forming surfaces 27, 28 that are shaped to correspond to each other and are positioned opposite each other in the vertical direction. The second press-forming surfaces 27, 28 are configured to form recesses 6 in a portion of the product portion 2 that will become both side portions 4a of the spoiler portion 4 in the vehicle width direction and in a region 5 (the region surrounded by a dashed line in FIG. 1 ) that spans the first excess pad portion 3a adjacent to both side portions 4a in the vehicle width direction. The first press-forming surfaces 25, 26 are configured to form a portion of the product portion 2 excluding the portion that will be formed by the second press-forming surfaces 27, 28 (the both side portions 4a of the spoiler portion 4 in the vehicle width direction).

[0019] Although not shown, for example, a lower die inner pad that can move up and down independently of both the press lower die 22 and the lower blank holder 24 may be provided on the inner periphery of the lower blank holder 24. In this case, the lower die inner pad is configured to be able to support a portion of the blank 10 that corresponds to the second excess pad portion 3b on the inner periphery of the product portion 2 at a stage prior to forming by the press lower die 22 (prior to the lower die forming step S2).

[0020] Next, an example of press working (drawing) using the press working device 20 shown in FIG. 3 will be described with reference to FIGS.

[0021] (S1) Recess forming step First, in the state shown in Fig. 3, a plate-shaped blank 10 (see Fig. 4) is placed on the upper surface 24a of the lower blank holder 24. At this point, the blank 10 is in contact only with the lower blank holder 24, and is separated from the upper press die 21, the lower press die 22, and the upper blank holder 23. The shape of the blank 10 when placed on the upper surface 24a is arbitrary, and the blank 10 may be flat as a whole, or may be curved so as to be convex upward.

[0022] Thereafter, the upper blank holder 23 is moved downward relative to the upper blank holder 21, and the peripheral edge of the blank 10, i.e., the portion that will become the excess metal portion 3 (first excess metal portion 3a), is clamped between the upper blank holder 23 and the lower blank holder 24. Then, with the blank 10 clamped, the upper blank holder 21 is lowered relative to the lower blank holder 24, and a second press-forming surface 27 of the upper blank holder 21, which has a downwardly protruding shape, is pressed into the blank 10. Furthermore, cooperation between the second press-forming surface 27 and the corresponding second press-forming surface 28 of the lower blank holder 24 forms a recess 6 in a region 5 that straddles the portion of the blank 10 that will become the product portion 2 and the portion that will become the excess metal portion 3 (see FIGS. 1 and 5). This forms both side portions 4a in the vehicle width direction that will become part of the base end of the spoiler portion 4 as a product protrusion. At this point, the press lower die 22 is still separated from at least the spoiler portion 4 of the blank 10 .

[0023] (S2) Lower die forming step After a portion of the spoiler portion 4 is formed by the upper press die 21 in this manner, the upper and lower blank holders 23, 24 are lowered together with the upper press die 21 to press the blank 10 against the first press-forming surface 26 of the lower press die 22. This causes the portion of the blank 10 that will become the product portion 2 to be formed into a shape that conforms to the first press-forming surface 26 of the lower press die 22. In this case, the first press-forming surface 26 is first pressed against the highest portion of the product portion 2 of the blank 10, in this case the widthwise center portion of the spoiler portion 4 as the product protrusion, and the drawing continues until it abuts against the first press-forming surface 25 of the upper press die 21 (see FIG. 6). Therefore, if the maximum drawing depth of the spoiler portion 4 is H, then the maximum drawing depth H is equal to the sum of the drawing depth H1 of the spoiler portion 4 by the upper press die 21 and the drawing depth H2 of the spoiler portion 4 by the lower press die 22. As a result, the pressed product 1 shown in FIG. 1 is obtained.

[0024] As described above, in the drawing method according to this embodiment, the upper press die 21 and the lower blank holder 24 form the recess 6 in the region 5 spanning the spoiler portion 4 as a product protrusion and the excess pad portion 3 (first excess pad portion 3a) located around the spoiler portion 4, and then the lower press die 22 forms the spoiler portion 4 as a product protrusion in the blank 10. In this way, by first forming the recess 6 with the upper press die 21, it is possible to form the base end sides (both sides 4a in the vehicle width direction) of the spoiler portion 4 that form the inner portion of the recess 6. In this case, the position of the bottom end of the spoiler portion 4 is lower than the position where the blank 10 is pressed by the upper and lower blank holders 23, 24 (i.e., the position where the first excess pad portion 3a is held) (see FIG. 5, etc.), and therefore the forming position of the spoiler portion 4 can be lowered by this amount compared to conventional methods. Therefore, by forming the spoiler portion 4 using the press lower die 22 under the same conditions as conventionally, the drawing depth H2 of the spoiler portion 4 by the press lower die 22 can be made smaller than the conventional drawing depth H. This makes it possible to significantly reduce or eliminate the inflow of material into the spoiler portion 4. Therefore, even a spoiler portion 4 with a large drawing depth H can be formed accurately and at low cost.

[0025] Furthermore, in this embodiment, in the recess forming step S1, the press upper die 21 and the lower blank holder 24 form a pair of recesses 6 at positions facing each other with the spoiler portion 4 interposed therebetween, so that it is possible to apply uniform tension in the direction in which the recesses 6 are arranged opposite each other to the portion of the blank 10 that will become the spoiler portion 4, i.e., in the longitudinal direction of the spoiler portion 4. Therefore, it is possible to form the recesses 6 (the base end side of the spoiler portion 4) with higher precision with the press upper die 21, and thereby it is possible to form the spoiler portion 4 with higher precision with the press lower die 22.

[0026] Although one embodiment of the present invention has been described above, the drawing method according to the present invention can also adopt configurations other than those described above within the scope of the gist of the method.

[0027] For example, in the above embodiment, a pair (two) of recesses 6 are formed in positions facing each other across the spoiler portion 4 by the press upper die 21 and the lower blank holder 24, but the manner in which the recesses 6 are formed is not limited to this. For example, a pair of recesses 6 may be formed in positions other than those shown in the drawings, or one or three or more recesses 6 may be formed. The key is to set the number and positions of the recesses 6 according to the shape of the product protrusions and the arrangement within the product portion 2.

[0028] Of course, the application of the present invention is not limited to the spoiler portion 4. The part of the product protrusion that is the subject of drawing may be any part, as long as it protrudes toward the surface 2a of the product portion 2 of the plate-shaped blank 10. [Explanation of symbols]

[0029] 1 Pressed products 2 Product Department 2a surface 3a,3b Extra flesh part 4 Spoiler section 4a Both sides in the vehicle width direction 5. Part spanning the product protrusion and excess material 6 recess 10 Blank material 20 Press processing equipment 21 Press upper die 22 Press lower die 23 Upper blank holder 24 Lower blank holder 25,26 First press forming surface 27,28 Second press forming surface S1 Recess forming step S2 Lower die forming step

Claims

[Claim 1] A method for forming a product convex portion on a plate-shaped blank by performing drawing as a press process on the blank using an upper press die, a lower press die, an upper blank holder, and a lower blank holder, the method comprising: a recess forming step in which, with an excess metal portion of the blank sandwiched between the upper blank holder and the lower blank holder, a pair of recesses is formed by the press upper die and the lower blank holder at positions that straddle the product protrusion and the excess metal portion and that face each other across the product protrusion; a lower die forming step of forming the product convex portion in the blank material using the press lower die after forming the concave portion.

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