JP7744730B2 - Drawing method for plate-shaped workpieces - Google Patents

Description

The present invention relates to a method for drawing a plate-shaped workpiece, and in particular to a technique for forming a protrusion on a plate-shaped workpiece 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.

On the other hand, when attempting to form a pressed product 1 having a sharp, three-dimensional protrusion 3 (shown in Figure 1 as an example of a corner 7 between three flat surfaces 4-6) from a flat blank material by drawing, for example, as shown in Figure 1, cracks can occur in the protrusion 3.

To solve this type of problem, for example, Patent Document 1 discloses a method for manufacturing a drawn product, which includes a first drawing (also called overdraw) process in which a convex portion is formed by drawing a metal sheet blank into a preformed product whose convex portion is larger than the shape of the final product, and a second drawing process in which a portion of the convex portion is deformed when the preformed product obtained in the first drawing process is formed into a shape closer to the shape of the final product than the preformed product.

Japanese Patent Application Laid-Open No. 2021-37356

As described in Patent Document 1, by forming the convex portion larger than the final product shape during the first press forming (first drawing process), it is possible to minimize the risk of cracks occurring due to force concentrating on, for example, the apex of the convex portion. However, this method results in the convex portion being formed by expanding it more than necessary, resulting in a significant difference in the actual cross-sectional length of the convex portion between the end of the first press forming and the end of the second press forming (for example, the difference between the actual cross-sectional length L31 of the convex portion 30a at the end of the first press forming and the actual cross-sectional length L41 of the convex portion 30b at the end of the second press forming, as shown in Figure 8). Therefore, when the convex portion is reshaped to the final product shape during the second press forming, excess material is generated relative to the final product shape by the difference in actual cross-sectional length (for example, L41 - L31 in Figure 8), and this excess material is a cause of wrinkles. The greater the difference in actual cross-sectional length, the more likely wrinkles are to occur.

In light of the above, the technical problem to be solved in this specification is to enable the formation of protrusions on plate-shaped workpieces by drawing while preventing the occurrence of cracks and wrinkles.

The above-mentioned problems are solved by the method for drawing a plate-shaped workpiece according to the present invention. Specifically, this drawing method is a method for forming a protrusion on a plate-shaped workpiece by applying drawing as a press process to the plate-shaped workpiece. It includes a first press process in which a bulge that bulges out more than the protrusion is formed on the plate-shaped workpiece by drawing, and a second press process in which the plate-shaped workpiece with the formed bulge is pressed to reshape the bulge into a protrusion. In this method, the first press process forms an inclined surface on part of the bulge, which serves as a chamfer for the bulge.

Note that the chamfering of the bulge here refers to replacing the convex curved surface, including the apex of the bulge, with an inclined surface, in the bulge that would be expected without the chamfered portion (the bulge before chamfering), excluding the inclined surface portion of the bulge.

In this way, in the drawing method of the present invention, when forming a protrusion on a plate-shaped workpiece by drawing, a bulge that bulges out more than the protrusion is formed on the plate-shaped workpiece, and an inclined surface that chamfers the bulge is formed on a portion of the bulge. By providing an inclined surface that chamfers the bulge on the bulge in this way, the actual length of the cross section passing through the inclined surface of the bulge on the plate-shaped workpiece after the first press process can be made shorter than the actual length of the corresponding cross section of a conventional bulge. This makes it possible to reduce the difference with the actual cross section of the plate-shaped workpiece after the second press process compared to conventional methods, thereby preventing wrinkles from occurring during the second press process. Furthermore, because the inclined surface is part of the bulge, the inclined surface still provides the effect of preventing cracks from occurring due to the bulge. As described above, the drawing method of the present invention makes it possible to form a protrusion on a plate-shaped workpiece by drawing while preventing not only cracks but also wrinkles.

In the drawing method according to the present invention, the protrusion may be an edge formed between two flat surfaces, or a corner formed between three flat surfaces. In this case, an inclined surface may be formed in the first press step so as to form part of the edge or corner.

The drawing method of the present invention enables the formation of protrusions on plate-shaped workpieces by drawing without the occurrence of cracks or wrinkles, making it suitable for forming edge portions formed between two flat surfaces or corner portions formed between three flat surfaces by drawing. Furthermore, when forming these types of edge portions or corner portions, by forming an inclined surface portion that forms part of the edge portion or corner in the first press process, the inclined surface portion can be positioned close to at least one of the flat surfaces that form the corner or the side portion formed between two flat surfaces. This makes it possible to minimize the amount of deformation of the plate-shaped workpiece during the second press process while preventing the occurrence of cracks and wrinkles, thereby improving not only yield (improving the stability of the press process) but also press quality.

Furthermore, when the inclined surface portion is formed to form part of an edge or corner as described above, in the drawing method according to the present invention, the inclined surface portion may be formed in the first press step so that the difference in inclination angle between the inclined surface portion and the flat surface portion or the side portion formed between two flat surfaces is 10° or more and 30° or less.

In this way, by keeping the difference in inclination angle between the inclined surface portion and the flat surface portion or edge portion within an appropriate range (10° or more and 30° or less), the plate-shaped workpiece being deformed by the drawing process during the first press step can be more easily supported by the press die on its surface (the forming surface of the inclined surface portion provided on the press die). This makes it possible to more effectively prevent cracks from occurring. Of course, by keeping the upper limit of the inclination angle difference below an appropriate value (30° or less), the difference in actual cross-sectional length between the bulge portion (at the end of the first press step) and the protrusion portion (at the end of the second press step) can be kept within an allowable range, making it possible to effectively prevent wrinkles from occurring.

Furthermore, when the inclined surface portion is formed to form part of an edge portion or corner portion as described above, in the drawing method of the present invention, the inclined surface portion may be formed in the first press step so that the difference in actual cross-sectional length, which is the actual cross-sectional length of the inclined surface portion minus the actual cross-sectional length of the flat portion or the side portion formed between two flat portions, is 20% or less of the actual cross-sectional length of the flat portion or the side portion.

In this way, by keeping the difference in actual cross-sectional length between the inclined surface portion and the flat surface portion or side portion to 20% or less, it becomes possible to stably form the protruding portion that will become the final product shape without wrinkles when re-forming during the second press process. This makes it possible to further improve the yield rate in press processing.

As described above, according to the present invention, it is possible to form protrusions on plate-shaped workpieces by drawing while preventing the occurrence of cracks and wrinkles.

1 is an enlarged perspective view of a main part of a pressed product obtained by a drawing method according to an embodiment of the present invention. FIG. FIG. 1 is an enlarged perspective view of a main portion of a plate-shaped workpiece (an intermediate press-formed product) obtained by drawing in the first press step. FIG. 10 is an enlarged perspective view of a main part for conceptually explaining a procedure for creating an inclined surface portion. 2 is a cross-sectional view of a main part of a press molding device used in a first press process, taken along line AA. FIG. FIG. 5 is a cross-sectional view of a main part taken along line AA, showing an example of drawing using the press forming apparatus shown in FIG. 4, in which a plate-shaped workpiece is undergoing drawing. 1A-1A cross-sectional view of a main part of the plate-shaped workpiece at the end of the first press process (solid line: bulging portion with inclined surface portion, two-dot chain line: bulging portion when there is no inclined surface portion), and FIG. 1B-1A cross-sectional view of a main part of the plate-shaped workpiece at the end of the second press process (two-dot chain line). This is a BB cross-sectional view (solid line) of a main part of the plate-shaped workpiece at the end of the first press process, and a BB cross-sectional view (dashed two-dot line) of a main part of the plate-shaped workpiece at the end of the second press process. This is a cross-sectional view (solid line) of a main part of a convex-shaped portion at the end of the first press working in a conventional drawing method, and a cross-sectional view (dashed line) of a main part of a convex-shaped portion at the end of the second press working.

The following describes a method for drawing a plate-shaped workpiece according to one embodiment of the present invention, with reference to the drawings.

Figure 1 shows an enlarged perspective view of a main portion 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 integrally comprises a base 2 and a protruding portion 3 that protrudes from the base 2 to one side in the plate thickness direction. In this embodiment, three flat portions 4 to 6 are erected adjacent to each other from the base 2. Furthermore, a corner 7 is provided between the three flat portions 4 to 6. This corner portion 7 corresponds to the protruding portion 3.

In this case, a first side 8a extending from the vertex 7a of the corner 7 is formed between the first flat surface 4 and the second flat surface 5. A second side 8b extending from the vertex 7a of the corner 7 is formed between the second flat surface 5 and the third flat surface 6, and a third side 8c extending from the vertex 7a of the corner 7 is formed between the third flat surface 6 and the first flat surface 4 (see Figure 1 for both).

In this case, the vertex 7a of the corner 7 and the first vertex 9a between the base 2, the first flat surface 4, and the second flat surface 5 are interconnected via the first side 8a. The vertex 7a of the corner 7 and the second vertex 9b between the base 2, the second flat surface 5, and the third flat surface 6 are interconnected via the second side 8b. The vertex 7a of the corner 7 and the third vertex 9c between the base 2, the third flat surface 6, and the first flat surface 4 are interconnected via the third side 8c (see Figure 1 for all).

The flat surfaces 4-6 do not need to be completely flat, and may have a curved surface shape with a small curvature. Similarly, the side surfaces 8a-8c may have a certain degree of curvature in a cross section perpendicular to the longitudinal direction. In other words, the side surfaces 8a-8c may be configured as curved surfaces (R-surfaces) exhibiting a predetermined curvature. Furthermore, the side surfaces 8a-8c do not need to be completely straight along the longitudinal direction, and may have a curved shape with a certain degree of curvature in the longitudinal direction. Similarly, the vertices 7a, 9a-9c may be configured as convex surfaces exhibiting a certain degree of curvature.

The pressed product 1 having the above shape is manufactured through at least a first press process S1 in which a plate-shaped workpiece 10 (see Figure 4 described below) is drawn to form a bulge 11 (see Figure 2) that bulges out more than the protrusion 3, and a second press process S2 in which the plate-shaped workpiece 10 (intermediate pressed product) with the bulge 11 formed therein is pressed to reshape the bulge 11 into the protrusion 3 (here, the corner 7).

(S1) First Pressing Step In this step S1, the plate-shaped workpiece 10 is subjected to drawing to form a bulging portion 11 (see FIGS. 2 and 6) that bulges out more than the protruding portion 3, which is the final product shape, in the portion of the plate-shaped workpiece 10 where the protruding portion 3 will ultimately be formed. In this embodiment, as shown in FIGS. 2 and 6, the bulging portion 11 has a generally convex curved shape and is located closer to the protruding side than any of the flat portions 4 to 6 that form the corner portion 7 of the protruding portion 3 (see the A-A cross-sectional view indicated by the solid line and the two-dot chain line in FIG. 6 and the B-B cross-sectional view indicated by the solid line and the two-dot chain line in FIG. 7).

In addition, in this process S1, an inclined surface portion 12 that chamfers the bulge portion 11 is formed on a portion of the bulge portion 11 (see Figures 2 and 6). In this embodiment, the bulge portion 11 is formed on the plate-shaped workpiece 10 by drawing, and the inclined surface portion 12 is also formed on a portion of the bulge portion 11. In this case, the inclined surface portion 12 is formed so as to chamfer the apex 11a of the bulge portion 11 (shown by the two-dot chain line in Figure 6). In this case, in this embodiment, the inclined surface portion 12 is formed so that it forms the vertex 7a of the corner portion 7. Figures 2 and 6 illustrate an example in which the inclined surface portion 12 is formed so that the vertex 7a of the corner portion 7 is located on the peripheral edge 12a of the inclined surface portion 12.

In addition, in this embodiment, the inclined surface portion 12 is formed in a state in which it is inclined in a direction closer to the first side portion 8a than the second side portion 8b and the third side portion 8c (see Figure 2). In this case, the difference in inclination angle θ between the inclined surface portion 12 and the first side portion 8a (see Figure 6) is preferably set to, for example, 10° or more and 30° or less.

It is also preferable to set the dimensions (range) of the inclined surface portion 12 so that the difference (actual cross-sectional length difference) between the actual cross-sectional length of the inclined surface portion 12 and the actual cross-sectional length of the corner portion 7 at the end of the second press process S2 is 20% or less of the actual cross-sectional length of the corner portion 7. In the embodiment shown in FIG. 6, when viewed in a cross section (A-A cross section) along the first side portion 8a of the inclined surface portion 12, it is preferable to set the dimensions of the inclined surface portion 12 in a predetermined direction so that the value obtained by subtracting the actual cross-sectional length L21 of the corresponding base portion 2 and first side portion 8a from the actual cross-sectional length L11 of the inclined surface portion 12 is 20% or less of the actual cross-sectional length L21. Furthermore, as shown in Figure 7, when viewed in a cross section (cross section B-B) perpendicular to the first side 8a of the inclined surface portion 12, the dimensions of the inclined surface portion 12 in a predetermined direction should be set so that the actual cross-sectional length L12 of the first flat surface portion 4, the second flat surface portion 5, and the inclined surface portion 12 minus the actual cross-sectional length L22 of the first flat surface portion 4, the second flat surface portion 5, and the first side 8a is 20% or less of the actual cross-sectional length L22. Of course, the above-mentioned numerical ranges are merely examples, and should be adjusted appropriately depending on, for example, the material and thickness of the plate-like workpiece 10.

In the illustrated example, the inclined surface portion 12 has a flat shape, but the shape, position, and size of the inclined surface portion 12 are not limited to those described above. Naturally, the inclined surface portion 12 can have any shape, position, and size as long as it is effective in suppressing the occurrence of wrinkles in the second press process S2.

Next, an example of the manufacturing procedure (design procedure) for the inclined surface portion 12 will be explained with reference to Figure 3.

First, as shown in Figure 3, the bulge portion 11 is conveniently created with three curved surface portions 13a to 13c (Step 1). In this case, a first side portion 14a is formed between the first curved surface portion 13a and the second curved surface portion 13b, a second side portion 14b is formed between the second curved surface portion 13b and the third curved surface portion 13c, and a third side portion 14c is formed between the third curved surface portion 13c and the first curved surface portion 13a. Furthermore, the top 11a (here, vertex 11a) of the bulge 11 and the first vertex 15a between the base 2, the first curved surface 13a, and the second curved surface 13b are connected to each other via the first side 14a, while the vertex 11a and the second vertex 15b between the base 2, the second curved surface 13b, and the third curved surface 13c are connected to each other via the second side 14b, and the vertex 11a and the third vertex 15c between the base 2, the third curved surface 13c, and the first curved surface 13a are connected to each other via the third side 14c.

After creating the bulge 11 as described above, a first imaginary line L1 is drawn connecting the vertices 7a of the corners 7 of the product shape and the vertices 11a of the bulge 11 (Step 2). Then, a second imaginary line L2 perpendicular to the first imaginary line L1 created in Step 2 is drawn (Step 3). In Figure 3, the second imaginary line L2 is drawn perpendicular to the first imaginary line L1 and passing through the vertices 7a of the corners 7. Two intersections P1 and P2 between the second imaginary line L2 and the bulge 11 are then determined (Step 4). In Figure 3, the intersections P1 and P2 between the second side 14b and the third side 14c of the bulge 11 and the second imaginary line L2 are determined. Finally, the triangle obtained by connecting the intersections P1 and P2 obtained in Steps 1 to 4 with the first vertex 15a of the bulge 11 is defined as the inclined surface 12 (Step 5). Alternatively, the cross section obtained by cutting the bulge 11 along an imaginary plane including the triangle is used as the inclined surface 12. In this way, the inclined surface 12 is created based on the product shape (corner 7) and the bulge 11.

Figure 4 shows a cross-sectional view of a press-forming apparatus 20 for drawing a plate-shaped workpiece 10 in the first press step S1. This cross-sectional view is taken at the same position as the A-A cross section along the first edge 8a of the press-formed product 1, which represents the final product shape. The press-forming apparatus 20 includes a lower die 21, an upper die 22, and a blank holder (not shown). The lower die 21 and the upper die 22 have corresponding press-forming surfaces 23, 24 facing each other. In this case, the upper end of the forming region 23a of the inclined surface portion 12 of the press-forming surface 23 of the lower die 21 is the highest position of the press-forming surface 23 (the position closest to the upper die 22) (see Figure 4). Note that the terms "upper" and "lower" are used here merely for convenience to aid in understanding the pressing direction. Of course, the actual installation and use of the press-forming apparatus 20 are not limited to the above.

Next, an example of press working (drawing) using the press forming device 20 shown in Figure 4 will be described with reference to Figures 4 and 5.

First, as shown in Figure 4, a plate-shaped workpiece 10 serving as a blank is placed in a predetermined position on the lower die 21. At this point, the plate-shaped workpiece 10 has a flat shape with no irregularities, and portions not shown are held by a blank holder (not shown) and the upper die 22. The plate-shaped workpiece 10 is also separated from the press-forming surface 23 of the lower die 21. From the state shown in Figure 4, the plate-shaped workpiece 10 is moved downward relative to the lower die 21 and pressed against the press-forming surface 23 of the lower die 21. In this case, the plate-shaped workpiece 10 may be lowered, or the lower die 21 may be raised.

Through the above-described operation, the plate-shaped workpiece 10 is first pressed against the highest portion of the press-forming surface 23. In this embodiment, the forming region 23a of the inclined surface portion 12 is provided continuously from the highest position of the press-forming surface 23 (see Figure 4). Therefore, after the plate-shaped workpiece 10 is pressed against the highest portion, the drawing process proceeds while the plate-shaped workpiece 10 is pressed in surface contact against the forming region 23a of the inclined surface portion 12 (see Figure 5). Therefore, the drawing process is performed while minimizing the concentration of load on the plate-shaped workpiece 10, resulting in a plate-shaped workpiece 10 (intermediate press-formed product) having the bulge portion 11 and inclined surface portion 12 as an integral part, without cracking.

(S2) Second Pressing Step In this step S2, the plate-shaped workpiece 10 (intermediate press-formed product) having the bulged portion 11 and inclined surface portion 12 formed therein is pressed to reshape the bulged portion 11 including the inclined surface portion 12 into the protruding portion 3 (corner portion 7 in this embodiment) that will become the final product shape. This results in the pressed product 1 shown in Figure 1. In principle, any press-forming method can be used in the second press-forming step S2, and bending, for example, can be used.

As described above, in the drawing method for a plate-shaped workpiece 10 according to this embodiment, when forming the protrusion 3 on the plate-shaped workpiece 10 by drawing, a bulge 11 that bulges out more than the protrusion 3 is formed on the plate-shaped workpiece 10, and an inclined surface 12 that chamfers the bulge 11 is formed on a portion of the bulge 11. By providing the inclined surface 12 that chamfers the bulge 11 in this manner, the actual cross-sectional length L11 of the bulge 11 of the plate-shaped workpiece 10 after the first press step S1 can be made shorter than the actual cross-sectional length of a conventional bulge (e.g., the actual cross-sectional length L31 of the convex portion 30a shown in FIG. 8). Therefore, the difference between the actual cross-sectional length L21 of the plate-shaped workpiece 10 after the second press step S2 is made smaller than conventional, thereby preventing the occurrence of wrinkles during the second press step S2. Furthermore, because the inclined surface 12 is part of the bulge 11, the inclined surface 12 still prevents cracks from occurring due to the bulge 11. As described above, the drawing method for a plate-shaped workpiece 10 according to this embodiment makes it possible to form a protrusion 3 (corner 7) on the plate-shaped workpiece 10 by drawing while preventing the occurrence of cracks and wrinkles.

Furthermore, in this embodiment, the corner 7 formed between the three flat surfaces 4-6 is the target (protrusion 3) of the drawing method according to the present invention, and in the first press step S1, the inclined surface 12 is formed to form part of the corner 7 (see Figure 2), thereby reducing the distance between the inclined surface 12 and each of the flat surfaces 4-6 or each of the side surfaces 8a-8c (here, the distance from the first side surface 8a). This minimizes the amount of deformation of the plate-shaped workpiece 10 when reshaping the inclined surface 12 into the corner 7, while preventing cracks and wrinkles. This improves the press quality of the pressed product 1 and enables the above-described press processing to be carried out stably.

The above describes one embodiment of the present invention, but the method for drawing a plate-shaped workpiece according to the present invention can also adopt configurations other than those described above, as long as they do not deviate from the spirit of the method.

For example, in the above embodiment, the corner 7 formed between the three flat surfaces 4-6 is illustrated as the protrusion 3 to be formed by drawing. However, the present invention is not limited to this. For example, the present invention may also be applied to the edge portion (first side 8a, the area near the first side 8a of the first flat surface 4, and the area near the first side 8a of the second flat surface 5) formed between the first flat surface 4 and the second flat surface 5. That is, although not shown, in the first press step S1, a bulging edge portion that bulges out more than the edge portion between the first flat surface 4 and the second flat surface 5 is formed by drawing on the plate-shaped workpiece 10, and a sloped surface that chamfers the edge bulge is formed on part of the edge bulge. In the second press step S2, the plate-shaped workpiece 10 with the bulged edge portion formed is pressed to reshape the edge bulge into an edge portion that serves as the protrusion 3. This makes it possible to form the plate-shaped workpiece 10 into a shape that includes the edge portion by drawing while preventing cracks and wrinkles from occurring at the edge portion.

Of course, the application of the present invention is not limited to corners 7 and edge portions. As long as the protrusions 3 are formed on the plate-shaped workpiece 10 by drawing, the shape of the protrusions 3 is arbitrary. The number and size of the protrusions 3 are also arbitrary.

In addition, while the above embodiment illustrates the case where one bulge 11 and inclined surface 12 are formed for one protrusion 3, this is of course not limited to this. For example, although not shown in the drawings, depending on the shape of the protrusion 3, two or more bulge 11 may be provided for one protrusion 3. Furthermore, one or more inclined surface 12 may be formed for each bulge 11.

In addition, while the above embodiment illustrates the use of bending in the second press step S2, this is not necessarily limited to this. Any press processing method can be used as long as it is possible to reshape the bulge 11 having the inclined surface 12 into the protrusion 3.

The drawing method of the present invention can also be applied to any plate-shaped workpiece of any material, shape, or size that is generally suitable for drawing. In fact, the drawing method of the present invention can also be applied to forming protrusions 3 in plate-shaped workpieces using drawing, even when the shapes or dimensions are generally considered difficult to draw due to issues with cracks or wrinkles.

1 Pressed product 2 Base 3 Projection 4 First plane part 5 Second plane part 6 Third plane part 7 Corner part 7a Vertex part 8a First side part 8b Second side part 8c Third side part 9a First vertex part 9b Second vertex part 9c Third vertex part 10 Plate workpiece 11 Swelling part 11a Top part 12 Inclined part 12a Peripheral part 13a, 13b, 13c Curved part (bulging part)
14a, 14b, 14c Side part (bulging part)
15a, 15b, 15c Vertex portion (bulging portion)
20 Press-forming device 21 Lower mold 22 Upper mold 23, 24 Press-forming surface 23a Forming area 30a of inclined surface portion Convex-shaped portion 30b Convex-shaped portions L1, L2 Virtual straight lines L11, L12 Actual cross-sectional length (after first press process)
L21, L22: Actual cross-sectional length (after the second press process)
θ Tilt angle difference

Claims (2)

A method for forming a protrusion , which is a side portion formed between two flat surfaces and an edge portion consisting of a region near the side portion, or a corner portion formed between three flat surfaces, on a plate-shaped workpiece by performing drawing as a press process on the plate-shaped workpiece,
a first pressing step of forming a bulging portion that is larger than the protruding portion on the plate-shaped workpiece by drawing;
a second press step in which the plate-shaped workpiece on which the bulging portion has been formed is pressed to reshape the bulging portion into the protruding portion,
In the first press step , as the chamfering of the bulging portion, the bulging portion having the inclined surface portion is formed, which has a shape obtained by replacing a convex curved surface portion as a part of the bulging portion including the apex of the bulging portion having a shape that would be assumed if the chamfering was not performed with an inclined surface portion ; and
A method for drawing a plate-shaped workpiece, characterized in that the inclined surface portion is formed so as to form a part of the edge portion or the corner portion as the protrusion . 2. The drawing method according to claim 1, wherein in the first press process, the inclined surface portion is formed so that a difference in inclination angle between the inclined surface portion and the flat surface portion or the side portion formed between the two flat surface portions is 10° or more and 30° or less .