JPS642452B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a drawing method, and more specifically, to a drawing method, and more specifically, to bending to the bottom side so as to have a U-shaped cross section, and to connect the two bending lines at the time of the bending. A product obtained by bending a U-shaped cross section upward along orthogonal folding lines, such as a continuous box-shaped cross section (hereinafter referred to as a "hat cross section") with a partially saddle-shaped convex shape. The present invention relates to a drawing method for press forming a product having a saddle shape (hereinafter simply referred to as a saddle shape).

For example, as shown in Figure 1, a method for drawing a partially saddle-shaped product with a continuous cross section is to divide the saddle-shaped part into two left and right parts at the center.
Alternatively, divide the saddle-shaped part into three separate parts,
There is a split method in which each divided piece is individually drawn, a method in which the first stage is drawn to a large bending radius and a second stage is drawn to the shape of the final product, or step drawing and double-action methods. One-piece methods such as drawing methods are known in the art.
However, with the above-mentioned splitting method, there is an increase in the number of molds and the resulting increase in mold manufacturing costs, an increase in the welding process due to the increase in the number of parts, and furthermore, an increase in the work space and equipment costs due to the increase in the welding process. There are many problems that lead to a rise in product costs, such as an increase in In addition, there were problems such as wrinkles and stretch cracks easily occurring, making it difficult to obtain the desired product.

This invention was made in view of the above circumstances, and an object of the present invention is to provide a drawing method that can perform forming without causing wrinkles or elongation cracks during integral single-action press processing. The purpose of this product is to bend the product to be drawn and formed into a U-shaped cross section toward the bottom side, and to bend the U-shaped cross section along two bending lines during the bending process. A bulging portion is formed at the location where the bending is to be performed to form a shape that is curved back to the upper surface side along a line perpendicular to When molding is carried out by bringing the part into contact with the lower die punch, the bulging part is also stretched, thereby preventing wrinkles and stretch cracks due to elongation or compression, or an imbalance thereof. .

That is, for example, when drawing the entire shape of the product 1 shown in FIG. 2
It is normal to have a gently curved shape, but
Since the timing at which the wrinkle pressing surface and the lower die punch hit is different, the material is gathered from the earlier timing to the later timing, and wrinkles are generated in the shaded areas in FIG. 2. Therefore, in the present invention, a material (material board) is placed near the area where wrinkles are likely to occur, in the area extending from the slope 4 following the top surface 3 of the saddle-shaped portion in FIG. 2 to the flat surface 5 on the lower end side.
A bulge was formed at the same time or slightly before the molding was started by rolling down the material, and the wrinkles were eventually absorbed by stretching the bulge. In other words, by making the bulge function as an elongation allowance, elongation and compression at or near the inclined surface 4 and flat surface 5 at the final stage of molding are facilitated, thereby balancing elongation and compression and eliminating wrinkles. This prevents the occurrence of cracks and stretching cracks.

The present invention will be described in more detail below, taking as an example the case where the product shown in FIG. 1 is drawn. first,
To explain the mold used, Fig. 3 is a sectional view with half of the mold in the longitudinal direction omitted, and Fig. 4 is a cross-sectional view taken along the - line in Fig. 3 with the upper die raised to the upper limit. In this sectional view, the upper surface of the lower die punch 11 provided on the lower die body 10 is formed in the same shape as the product 1, and the upper die 12 has a recess 13 having a shape corresponding to the upper surface of the lower die punch 11. , and is configured to be able to move up and down with respect to the lower die punch 11. A lower blank holder 15 is disposed around the outer periphery of the lower die punch 11, and is pushed up by a dike (not shown) via a cushion pin 14, and its upper surface serves as a lower die wrinkle pressing surface 16, and the lower blank holder 15 serves as a wrinkle pressing surface 16 for the lower die. A tension bead 17 is formed on the wrinkle pressing surface 16, and the outer circumference of the lower surface of the upper mold die 12 facing the lower mold wrinkle pressing surface 16 is an upper mold wrinkle pressing surface 18. A protrusion 19 corresponding to the tension bead 17 is formed on 18 .

A portion of the lower die punch 11 that corresponds to the portion extending from the inclined surface 4 to the flat surface 5 of the product 1, that is, a portion that spans both sides of the portion corresponding to the folding line when folding back to the upper surface side. A sub-punch 20 is disposed as a pre-drawing member so as to be able to protrude and retract. This sub-punch 20 has an upper end surface that is inclined at an angle (for example, 15° to 35°) that is approximately equal to the wrinkle pressing surfaces located on both left and right sides of the sub-punch 20,
It is housed in a cavity 21 formed in the lower punch 11, is pushed up by a spring 22 disposed on the lower surface thereof, and is prevented from coming off by engaging the shoulder with the upper surface of the cavity 21. It is said that Note that here, the spring 22
The elastic force is preferably about 1/6 to 1/3 of the cushioning force required for normal drawing. Therefore, when the sub-punch 20 is pulling the upper die 12 upward and while the rigidity of the product 1 being molded is weaker than the elastic force of the spring 22,
Its upper end surface protrudes from the upper surface of the lower die punch 11, more specifically from the upper surface of the portion where the timing of contact with the material plate is the latest.

The reference numeral 23 in FIGS. 3 and 4 indicates a spring retaining pin, and the reference numeral 24 in FIG. 4 indicates a slide plate for movable the roller blank holder.

Next, the method of the present invention using the above mold will be explained. The material plate 25 placed on the lower blank holder 15 is gripped by the wrinkle pressing surfaces 16 and 18 by lowering the upper die 12, and then the lower blank holder 15 is lowered against the cutting force of the die cutting. As a result, the material plate 25 comes into contact with the lower die punch 11, and as a result, it begins to be bent downward along two bending lines that are substantially parallel to each other. In that case, immediately after the start of bending, that is, at the initial stage of forming, the sub-punch 20 as the pre-drawing member protrudes from the upper surface of the lower die punch 11, and the elastic force of the spring 22 pushing up the sub-punch 20 is stronger than the rigidity of the material plate 25. 3, the material plate 25 is partially pushed up relatively by the sub punch 20, as shown by the dashed line in FIG. 3, and as a result, a bulge 26 is formed as shown in FIG. As is clear from the arrangement position of the sub-punch 20, the position of this bulging portion 26 is from the inclined surface 4 to the flat surface 5 of the final product 1, and this is the position that will eventually be formed into a U-shaped cross section. Corresponding to the position of bending to the bottom side and folding back to form the U-shaped cross section into a shape that is curved back to the top side as shown in the figure, the touch timing to the lower die punch 11 is the latest. It's the location. However, at this stage, the material plate 25 is not particularly positively bent in the longitudinal direction, but elongated by the sub-punch 20.

When the upper die 12 is further lowered, the material plate 2
5 is further bent and the drawing process progresses, the rigidity of the material plate 25 increases, and the upper die 1
2 acts, so that the sub punch 20 is finally pushed down against the elastic force of the spring 22 and retreats into the lower die punch 11. In the final stage of the forming process, the bulging portion 26 is bent downward to form a U-shaped cross section near the point where the bulged portion 26 is formed, and the U-shaped cross section is bent upward as shown in the figure. The folding and bending to form a straight shape proceed simultaneously, and elongation and compression occur in a complicated manner, but ultimately the bulge 26 is stretched and becomes the desired shape, so the bulge 26 is Elongation and compression due to the shape change caused by stretching and resolving occur in just the right amount, and as a result, the occurrence of wrinkles and stretch cracks can be prevented. This phenomenon can be said to be that the wrinkles and elongation cracks are absorbed by the bulged portion 26.

As described above, the method of the present invention is a method in which the portion that is hit by the lower die punch 11 at a later timing is stretch-molded in the initial stage of molding, and the bulging portion 26 is formed there to prevent the occurrence of wrinkles and stretch cracks. Therefore, in carrying out the method of the present invention, the mold used may be any mold as long as it can form the bulge as described above, and the pre-drawing member for this purpose is the sub-punch 20. However, the present invention is not limited to this, and for example, the lower die punch may be divided into a plurality of parts, and the divided pieces at the portions where the contact timing is normally delayed may be made to protrude upward in advance, and may be used as the pre-squeezing member as described above. Further, the means for pushing the pre-squeezing member upward is the spring 2.
2, and mechanical means such as a cam may also be used. Furthermore, the present invention is not limited to the case where the product 1 having the shape shown in FIG. Folding and bending to form a straight shape occur at the same location,
In addition, it can be applied to the case where a product having a shape in which the timing of hitting the lower die punch at that location is later than at other locations is drawn.

As explained above, according to the drawing method of the present invention, bending toward the lower side to form a U-shaped cross section and folding back to form a shape in which the U-shaped cross section is warped toward the upper surface side are performed. When drawing a product with a shape such as a saddle, which is formed at the same location and the timing at which the bottom punch hits that spot is later than the timing at other locations, the timing at which the bottom punch hits the bottom punch is delayed. At the beginning of molding, a bulging part is stretched and molded at the location.
Since the bulging part is stretched and eliminated at the final stage of molding, the elongation and compression at that part occur in a well-balanced manner, with just the right amount and not enough, and as a result, the material stretches even in the part that is conventionally used as a contraction molding part. It can even out the appearance of wrinkles and effectively prevent the appearance of wrinkles.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of a saddle-shaped drawn product, FIG. 2 is an enlarged view of the part shown in FIG. 1 to show where wrinkles occur, and FIG. Figure 4 is a cross-sectional view taken along the line - in Figure 3 with the upper die pulled up to its upper limit, Figure 5 is a cross-sectional view of the intermediate product at the initial stage of drawing. It is a perspective view showing a part. DESCRIPTION OF SYMBOLS 1...Product, 11...Lower die punch, 12...Upper die, 20...Sub punch (predrawing member), 25...Material board, 26...Bulging part.

Claims (1)

[Scope of Claims] 1. With the peripheral part of a flat material plate being held between the upper and lower wrinkle pressing surfaces, the upper and lower wrinkle pressing surfaces are lowered relative to the lower die punch to press the material plate into the lower die. By pressing the material plate against the upper surface of the punch and further pressing the material plate against the upper surface of the lower punch using an upper die, the material plate is bent downward along two bending lines that are substantially parallel to each other. Bending to form a U-shaped cross section, and folding to form a shape in which the U-shaped cross section is curved upward along a folding bending line that is substantially orthogonal to each of the two bending lines. When performing the drawing process, prior to the bending and fold-back bending, a bulge that bulges toward the upper surface side is preliminarily formed on a portion of the material plate that spans both sides of the portion corresponding to the fold-back bend line. A drawing method characterized in that the bulging portion is stretched and disappears by forming the material plate, and applying the bending and folding back bending to the material plate.