JPH04224082A - Method for forming press formings - Google Patents

Abstract

PURPOSE:To perform press-forming in the wider range of forming condition without generating cracks in the case that two sheets different in sheet thickness and different in quality of material are superposed, welded and these two welded sheets are subjected to press forming into the prescribed shape. CONSTITUTION:The metal sheet positioned at the side to be more easily affected with the cracks to be generated in the press forming between two metal sheets 2, 4 is composed of the metal sheet 2 whose allowable strain quantity is larger.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention involves superimposing and welding two plates of different thicknesses, materials, etc., and
The present invention relates to a method of forming a press-formed product by press-forming a sheet of plate material into a predetermined shape.

0002

[Prior Art] In recent years, from the viewpoint of improving the material yield in the press forming process, a forming method has been proposed in which multiple plates are welded in advance and the welded and integrated plates are press-formed. . For example, JP-A-59-220
No. 229 discloses a technique for butt welding a plurality of plate materials by laser welding prior to press forming.

[0003] In addition to the above-mentioned butt welding, a method can be considered in which two plates are overlapped and welded by spot welding or the like, and the two welded plates are press-formed into a predetermined shape.

0004

[Problem to be Solved by the Invention] In this way, when two plates welded together are press-formed, the area where the maximum strain occurs due to the press-forming generally exists in one of the plates. . If the two plates are made of the same material and have the same thickness, as the press forming conditions become stricter, cracks will first occur at the location where the maximum strain occurs. In press forming, it is necessary to set press forming conditions within a range in which there is no risk of such cracks occurring.

[0005] As mentioned above, in the case where two plates welded together are press-formed, it is possible to use plates with different thicknesses and materials in order to reduce material and mold costs. This is possible, but if the thickness, material, etc. of the two plates are different, the maximum allowable strain for each plate will also be different, so the press forming conditions should be determined taking these conditions into account. Must be set. and,
In this case, it is desirable to ensure as wide a range as possible as the molding conditions.

The present invention has been made in view of the above circumstances, and involves overlapping and welding two plates having different thicknesses, materials, etc., and shaping the welded two plates into a predetermined shape. The object of the present invention is to provide a method for forming a press-formed product, which enables press-forming within a wider range of forming conditions without causing cracks.

[0007]

[Means for Solving the Problems] The method for forming a press-formed product according to the present invention is to select the one of two plates that is located on the side where conditions are worse for cracks that may occur during press-forming. The above objective is achieved by constructing the plate with a plate material having a larger strain tolerance.

That is, it is a method for forming a press-formed product, in which two plates having different strain tolerances are overlapped and welded, and the two welded plates are press-formed into a predetermined shape. , if two plates of the same material and thickness are overlapped and welded, and these two welded plates are press-formed into the predetermined shape, then the press-formed part of these two plates is The welding and the press forming are performed by placing the plate material with a larger strain tolerance among the two different plate materials on the side where the plate material where the maximum strain occurs is located. It is characterized by:

[0009] The above-mentioned "strain tolerance" refers to the maximum strain that can be produced in the plate without causing cracks in the plate. This "strain tolerance" has a larger value, for example, as the thickness of the plate increases or as the plate is made of a material with greater ductility.

0010

As shown in the above configuration, according to the present invention, two plates made of the same material and having the same thickness are overlapped and welded, and the welded two plates are If press molded into a predetermined shape, these two
Of the two different plates, the one with a larger strain tolerance is placed on the side where the part where the maximum strain will occur due to the press forming is located, and Since press forming is performed, it is possible to press form without creating cracks compared to the case where two sheets of plate material are welded in the opposite positional relationship and press formed. The range of molding conditions that can be achieved can be greatly expanded.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a process diagram showing an embodiment of the press molding method according to the present invention.

[0013]This press molding method is first shown in Fig. 1(a).
As shown in , two plates 2 and 4 made of the same material but with different thicknesses are partially overlapped with the thicker plate 2 facing upward, and both plates 2 and 4 are overlapped at this overlapped portion.
Spot weld 4 at multiple locations.

Next, as shown in FIG. 2(b), these two spot-welded plates 2 and 4 are attached to the thicker plate 2.
The two sheets are press-molded at the same time so that they are facing upward to form a press-formed product 6 having an upwardly convex cross-sectional shape.

FIG. 2 is a perspective view showing the punch 12 (FIG. 2(a)) and die 14 (FIG. 2(b)) used in the press forming. As shown in the figure, the punch 12 and the die 14 are formed with mold relief parts 12a and 14a, which make the cross-sectional shape of the press-formed product 6 thicker, as shown in Figure 1(b). The plate material 2 side and the thin plate material 4 side are formed to have substantially the same shape.

FIG. 3 is a perspective view showing an inner panel of a center pillar of a vehicle body, which is a specific example of the press-formed product 6, and FIG. 4 is a sectional view taken along the line IV--IV.

In FIG. 4, the corner outer surface indicated by arrow A is the area where the largest strain occurs due to the press forming. In this embodiment, the plate 2 where this maximum strain occurs is the thicker of the two plates 2 and 4, so its plastic deformation follows the large strain on the outer surface of the corner. This makes it possible to prevent cracks from occurring.

As detailed above, according to this embodiment,
For example, if two plates of the same material and thickness are overlapped and welded, and these two welded plates are press-formed into a predetermined shape, the pressed plate of these two plates The plate material 2, which is the larger one of the two plate materials 2 and 4 with different thicknesses (i.e.,
Since welding and press forming are performed by arranging the plate material with a larger strain tolerance, weld the two plate materials 2 and 4 in the opposite positional relationship and perform press forming. Compared to the case where this is done, the range of molding conditions under which press molding can be performed without causing cracks can be greatly expanded.

In this embodiment, since the plate material 2 and the plate material 4 are welded by spot welding,
The press forming causes stress concentration in each spot weld (nugget). This stress concentration occurs between the two plates 2,
This occurs due to the difference in the degree of strain shown in Figure 1.
This is most likely to occur at the spot welds on both left and right walls of the press-formed product 6, as shown by arrow B in FIG. However, in this embodiment, since the thicker plate material 2 is located on the outside, breakage at the spot weld B is less likely to occur than in the opposite case.

This point will be explained below based on experimental results.

(1) Experimental conditions As shown in Figure 5(a), thick plate (t=1.4mm)
and a thin plate (t = 0.7 mm) with a lap width of 12 mm, and spot welded at four locations symmetrically with a pitch of 30 mm (current value 7700 A, pressing force 200 kg, energization cycle 13 cycles). Ta2
As shown in Figure 5(b), the two plates are press-formed to have an upper width of 60 mm, a left and right flange width of 15 mm each, and an overall length of 5 mm.
00 mm A press molded product with a height of 40 mm was molded.

[0022] The pressure during press molding was 300 tons,
Three cushion pressures were used: 10, 20, and 30 tons, and the positions of the thick and thin plates were also changed.

(2) Experimental results As shown in Figure 6(a), when the thick plate is on the outside (arranged as shown in Figure 5), the cushion pressure is 30 tons.
In this case, the spot weld (B) broke, but at a cushion pressure of 10 or 20 tons, press forming could be carried out without any breakage. On the other hand, when the thin plate was on the outside, the spot weld (B) broke at all cushion pressures of 10, 20, and 30 tons.

FIG. 6(b) shows a spot weld (B).
This is a graph plotting the strain caused by multiple samples. The horizontal and vertical axes in the figure are shown in Figure 6 (
c) As shown in , the horizontal axis represents vertical strain, and the vertical axis represents horizontal strain.

[Brief explanation of the drawing]

[Fig. 1] A process diagram showing an example of the method for forming a press-formed product according to the present invention.

[Fig. 2] A perspective view showing the punch and die used in the above example.

[Fig. 3] A perspective view showing a specific example of a press-formed product formed according to the above embodiment.

[Figure 4] IV-IV line sectional view in Figure 3

[Figure 5] Diagram showing experimental conditions for experiments conducted in connection with the above example

[Figure 6] Diagram showing the experimental results of the above experiment

[Explanation of symbols]

2, 4 Plate material 6 Press molded product

Claims (1)

[Claims] [Claim 1] A method for forming a press-formed product, in which two plates having different strain tolerances are overlapped and welded, and the two welded plates are press-formed into a predetermined shape. If two plates of the same material and thickness are overlapped and welded, and these two welded plates are press-formed into the predetermined shape, then out of these two plates, the shape of the press-formed plate is The welding and press forming are performed by placing the plate material with a larger strain tolerance among the two different plate materials on the side where the plate material where the maximum strain occurs is located. A unique method for forming press-formed products.