JP7795849B2 - Drawing method - Google Patents

Description

The present invention relates to a drawing method, and in particular to a technique for forming a product convex portion with a large drawing depth in a blank material by drawing.

For example, when forming the outer panels of an automobile body using press working, drawing is often used due to its high degree of freedom in forming, minimal labor required, and therefore low cost.

Apparatus for performing drawing typically 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 apparatus, the upper and lower blank holders first hold a plate-shaped workpiece before forming, called a blank, and then the upper and lower blank holders are brought close to the punch, pressing the blank against the punch, thereby forming the product shape into the blank.

Japanese Patent Application Laid-Open No. 2021-159918

Among the exterior panels of an automobile body, the spoiler on the outer back door, for example, has a shape that protrudes significantly from the surface of the product. Therefore, if these are 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 precision. Furthermore, it becomes necessary to flow a large amount of the surrounding blank material toward the convex portion, resulting in a decrease in yield and ultimately an increase in costs. Another problem is that the more material is flowed, the more likely molding defects such as wrinkles and cracks are to occur.

In light of the above, the technical problem to be solved in this specification is to minimize the inflow of material and enable high-precision, low-cost molding, even for pressed products with protrusions that have a large drawing depth.

The above-mentioned problems are solved by the drawing method of the present invention. Specifically, this drawing method uses an upper press die, a lower press die, an upper blank holder, and a lower blank holder to perform drawing as a press process on a plate-shaped blank to form a product convex portion in the blank. It is characterized by including: a recess forming step in which, with the upper blank holder and the lower blank holder clamping the excess material located around the 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; and a lower die forming step in which, after forming the recess, the lower press die forms a product convex portion in the blank. Note that, in this specification, "protruding" refers to a state in which the surface of the product portion formed in the blank protrudes toward the surface of the product, and "concave" refers to a state in which the surface of the product portion formed in the blank is recessed. Furthermore, the "product convex portion" as used herein refers to the portion of the product portion formed in the blank that protrudes furthest toward the surface of the product.

In this way, in the drawing method of the present invention, the upper press die and lower blank holder form a recess in the area 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 bottom end 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), so the forming position of the product protrusion can be lowered by this amount compared to conventional methods. 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 using the lower press die can be reduced. This makes it possible to significantly reduce or even eliminate the inflow of material into the product protrusion. Therefore, even product protrusions with large drawing depths can be formed accurately and at low cost.

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

By forming a pair of recesses in opposing positions across the product convexity in this way, it is possible to apply uniform tension to the part of the blank that will become the product convexity in the direction in which the recesses are arranged. This allows the recesses (the base end side of the product convexity) to be formed with greater precision in the press upper die, which in turn allows the product convexity to be formed with greater precision in the press lower die.

As described above, according to the present invention, it is possible to form press products with convex portions with a large drawing depth with high precision and low cost by minimizing the inflow of material.

1 is a plan view of a pressed product obtained by a drawing method according to an embodiment of the present invention. 2 is a cross-sectional view of the pressed product shown in FIG. 1 taken along line AA. 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. FIG. 4 is a cross-sectional view of the press working apparatus at a point in time when a blank is clamped between upper and lower blank holders, showing an example of drawing using the press working apparatus shown in FIG. 3 . FIG. 4 is a cross-sectional view of the press working apparatus at the completion of a recess forming step, showing an example of drawing using the press working apparatus shown in FIG. 3 . 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 . FIG. 4 is a cross-sectional view of the press working apparatus at the completion of a lower die forming step, showing an example of drawing using the press working apparatus shown in FIG. 3 .

The following describes the details of a drawing method according to one embodiment of the present invention, with reference to the drawings. In the following description, the vehicle width direction is defined as the X direction, the vehicle body vertical direction as the Y direction, and the vehicle body longitudinal direction as the Z direction.

Figure 1 is a plan view of an example of a pressed product 1 obtained by a drawing method according to one embodiment of the present invention. As shown in Figure 1, this pressed product 1 is an intermediate product for an outer tailgate of an automobile, and integrally comprises a product portion 2 and an excess metal portion 3 located around the periphery of the product portion 2. In this embodiment, the excess metal portion 3 consists 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 installed. Both excess metal portions 3a, 3b are removed by trimming or the like after the product portion 2 has been formed by drawing.

The product portion 2 has a spoiler portion 4 of the tailgate outer integrally formed on the vertical upper end as a product protrusion. This spoiler portion 4 extends in the vehicle width direction of the product portion 2. As shown in Figure 2, the spoiler portion 4 is the portion that protrudes most from the surface 2a of the product portion 2.

The pressed product 1 having the above shape is obtained by drawing a plate-shaped blank 10 (see Figure 4, described below) using, for example, the press working device 20 shown in Figure 3.

Figure 3 shows a cross-sectional view of a press working device 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 device 20 at the same position as the B-B cross section along the longitudinal direction (vehicle width direction) of the middle of the spoiler section 4 of the pressed product 1 obtained by drawing. This press working device 20 has an upper press die 21, a lower press die 22, an upper blank holder 23, and a lower blank holder 24.

The upper press die 21 and the lower press die 22 have first press-forming surfaces 25, 26 of corresponding shapes, 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 of corresponding shapes, positioned opposite each other in the vertical direction. In this case, the second press-forming surfaces 27, 28 are configured to form a recess 6 in the portion of the product portion 2 that will become both side edges 4a of the spoiler portion 4 in the vehicle width direction and in a region 5 (the area surrounded by a dashed line in FIG. 1 ) that spans both side edges 4a in the vehicle width direction and the first excess pad portion 3a adjacent to each of these side edges 4a. The first press-forming surfaces 25, 26 are configured to form the entire portion of the product portion 2 excluding the portion formed by the second press-forming surfaces 27, 28 (both side edges 4a in the vehicle width direction of the spoiler portion 4).

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 support the portion of the blank 10 that corresponds to the second excess pad portion 3b on the inner periphery of the product portion 2, primarily at the stage prior to forming by the press lower die 22 (prior to the lower die forming step S2).

Next, an example of press working (drawing) using the press working device 20 shown in Figure 3 will be described with reference to Figures 3 to 7.

(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.

The upper blank holder 23 is then moved downward relative to the upper blank holder 21, clamping the peripheral edge of the blank 10, i.e., the portion that will become the excess pad 3 (first excess pad 3a), between the upper blank holder 23 and the lower blank holder 24. With the blank 10 clamped, the upper blank holder 21 is then lowered relative to the lower blank holder 24, pressing the downwardly protruding second press-forming surface 27 of the upper blank holder 21 into the blank 10. Furthermore, the second press-forming surface 27 cooperates with the corresponding second press-forming surface 28 of the lower blank holder 24 to form a recess 6 in the region 5 that straddles the portion of the blank 10 that will become the product portion 2 and the excess pad 3 (see Figures 1 and 5). This forms both vehicle width direction side portions 4a that form 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.

(S2) Lower Die Forming Step After a portion of the spoiler portion 4 has been 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 convex portion, and the drawing process 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 of the above, the pressed product 1 shown in FIG. 1 is obtained.

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 3 (first excess pad 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, the base end side (both sides 4a in the vehicle width direction) of the spoiler portion 4, which forms the inner portion of the recess 6, can be formed. In this case, the lower end position 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 holding position of the first excess pad 3a) (see Figure 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 spoiler portions 4 with a large drawing depth H can be formed accurately and at low cost.

In addition, 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 across the spoiler portion 4. This allows uniform tension to be applied to the portion of the blank 10 that will become the spoiler portion 4 in the direction in which the recesses 6 are arranged, i.e., in the longitudinal direction of the spoiler portion 4. Therefore, the press upper die 21 can form the recesses 6 (the base end side of the spoiler portion 4) with greater precision, which in turn allows the press lower die 22 to form the spoiler portion 4 with greater precision.

The above describes one embodiment of the present invention, but the drawing method according to the present invention can also be configured in other ways without departing from the spirit of the method.

For example, in the above embodiment, a pair of recesses 6 are formed between the press upper die 21 and the lower blank holder 24 at positions facing each other across the spoiler portion 4, 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 at a position other than that shown in the figure, or one or three or more recesses 6 may be formed. The key is to determine the number and positions of the recesses 6 according to the shape of the product protrusions and their arrangement within the product portion 2.

Of course, the application of the present invention is not limited to the spoiler portion 4. The portion of the product protrusion that can be subjected to drawing can be any portion, as long as it protrudes toward the surface 2a of the product portion 2 of the plate-shaped blank 10.

1 Press-formed product 2 Product portion 2a Surface 3a, 3b Excess material portion 4 Spoiler portion 4a Both sides in the vehicle width direction 5 Portion spanning the product convex portion and excess material portion 6 Recess 10 Blank material 20 Press processing device 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 (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.