JP3080661B2 - Press molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method in which two sheet materials having different thicknesses, materials and the like are overlapped and welded.
The present invention relates to a method for forming a press-formed product by press-forming a sheet material into a predetermined shape.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of improving the yield of materials in a press forming process, a forming method has been proposed in which a plurality of plate materials are welded in advance and press forming is performed on the welded and integrated plate materials. . For example, Japanese Unexamined Patent Publication No. 59-220229 discloses a technique of butt-welding a plurality of plates by laser welding prior to press forming.

In addition to the butt welding described above, a method in which two sheets are overlapped and welded by spot welding or the like, and these two welded sheets are press-formed into a predetermined shape can be considered.

[0004]

As described above, when a plate material welded in two layers is press-formed, particularly when the cross-section is formed into a convex shape, the maximum strain is generated by the press forming. The site is generally present on either one of the plates. Then, assuming that the two plate materials are the same and have the same plate thickness, cracking occurs first in the plate material in which the maximum strain occurs at a location where the press forming conditions are strict. In press molding, it is necessary to set the press molding conditions within a range in which such a crack is not likely to occur. In addition, when the press forming causes a difference in strain between the two sheet materials, and the difference in strain causes a concentrated stress in a welded portion, a problem that the welded portion is broken may be caused.

[0005] As described above, in a case where a plate material welded in two layers is press-formed, plate materials having different thicknesses, materials, and the like may be used in order to reduce material costs and die costs. It is conceivable, however, that when the sheet thickness, material, etc. of the two sheet materials are different in this manner, the magnitude of the maximum strain that can be allowed for each sheet material also differs. Must be set. And
In this case, it is desired that the range that can be set as the molding conditions be as wide as possible.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has been made by partially overlapping two plates having different thicknesses, materials, and the like, and welding the two plates. In the case of press forming into a convex cross section, without causing cracks, and preventing breakage of the welded portion due to the difference in strain between the two plates caused by press forming, and within a wider range of forming conditions It is an object of the present invention to provide a method for forming a press-formed product, which enables press-forming.

[0007]

According to the present invention, there is provided a method for forming a press-formed product, which comprises the steps of: Among the plate materials, the plate material located on the convex side of the cross-sectional convex shape where the maximum strain occurs is constituted by the plate material having the larger allowable strain, thereby achieving the above object. It is.

[0008] That is, a method of forming a press-formed product, wherein two plates having different allowable strains are overlapped and welded, and the welded two plates are press-formed into a convex cross section. After partially overlapping two plate materials having different allowable amounts and welding and integrating the overlapped portions, the integrated two plate materials are press-formed into the convex shape in section and the welding is performed. When forming a press-formed product in which concentrated stress due to the difference in strain between the two plate materials is formed in the portion, the convex side of the cross-sectional convex shape where the maximum strain occurrence site generated by the press forming will be present, 2
It is characterized in that press forming is performed so that the plate material having the larger allowable strain is located among the plate materials.

The above-mentioned "strain tolerance" refers to the maximum strain that can be generated in a sheet material without causing cracks in the sheet material. The “strain allowable amount” has a larger value, for example, for a plate having a larger thickness and a plate made of a material having higher ductility.

[0010]

As described above, according to the present invention, two plates having different allowable strains are partially overlapped with each other and welded and integrated at the overlapped portions. The two integrated plate materials are press-formed into the cross-sectional convex shape to form a press-formed product in which concentrated stress due to a difference in strain between the two plate materials is formed in the welded portion. Press forming is performed such that the plate material having the larger allowable strain is located on the convex side of the cross-sectional convex shape where the maximum strain occurrence site to be generated exists, so that the position opposite to this is set. Compared to the case of press-molding two plate materials integrated in relation to each other, the range of forming conditions that can form a press-formed product that does not cause cracking of the plate material or breakage of the welded portion is greatly widened Can .

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

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

In this press forming method, first, as shown in FIG. 1A, two plates 2 and 4 made of the same material but having different plate thicknesses are placed such that the thicker plate 2 is on top. The two plates 2 and 4 are spot-welded at a plurality of places at the overlapped portion.

Next, as shown in FIG. 1B, the two spot-welded plates 2 and 4 are simultaneously press-formed so that the thicker plate 2 is on top, and A press-formed product 6 having a convex sectional shape is formed.

FIG. 2 shows a punch used in the press molding.
FIG. 2 is a perspective view showing a die 12 (FIG. 1A) and a die 14 (FIG. 1B). As shown in FIG. 1, the punch 12 and the die 14 are provided with mold relief portions 12a and 14a, which increase the cross-sectional shape of the press-formed product 6 as shown in FIG. The plate 2 side and the thin plate 4 side are formed in 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 line IV-IV of FIG.

In FIG. 4, the outer surface of the corner portion indicated by the arrow A is a portion where the largest strain is generated by the press forming. In the present embodiment, since the plate member 2 where the maximum strain occurs is the thicker plate member 2 of the two plate members 2 and 4, it follows the large distortion of the outer surface of the corner portion due to its plastic deformation. And the occurrence of cracks can be prevented beforehand.

As described in detail above, according to the present embodiment,
If two plates having the same material and the same plate thickness are overlapped and welded, and the two plates thus welded are press-formed into a predetermined shape, if the two plates are pressed, On the side where the plate member where the maximum strain due to forming is to be located is located, the plate member 2 having the larger plate thickness of the two plate members 2 and 4 having different plate thicknesses (that is,
Welding and press forming are performed by arranging the plate material having the larger allowable strain amount), and press forming by welding the two plate materials 2 and 4 in the opposite positional relationship to this. As compared with the case described above, the range of molding conditions in which press molding can be performed without causing cracks can be significantly widened.

In this embodiment, the welding of the plate 2 and the plate 4 is performed by spot welding.
Due to the press molding, stress concentration occurs at each spot weld (nugget). This stress concentration is caused by two plate materials 2,
4 is caused by the difference in the degree of strain.
This is most likely to occur at spot welds on the left and right side walls of the press-formed product 6, as indicated by arrow B in FIG. However, in the present embodiment, since the thicker plate 2 is located on the outside, the breakage at the spot welded portion B is less likely to occur than in the opposite case.

Hereinafter, this point will be described based on experimental results.

(1) Experimental conditions As shown in FIG. 5A, a thick plate (t = 1.4 mm) and a thin plate (t
= 0.7mm) and a lap of 12mm and a pitch of 30mm
Spot welding at four locations symmetrically (current value 7700A,
Pressing force of 200kg, energizing cycle of 13 cycles), press-molding these two spot-welded plates, as shown in Fig. 5 (b), upper width 60mm, left and right flange width 15mm each, total length
A press-formed product having a height of 500 mm and a height of 40 mm was formed.

The pressing force at the time of press molding was 300 tons, and the cushion pressure was set to 10, 20, and 30 tons, and the pressing was performed even when the positions of the thick plate and the thin plate were interchanged.

(2) Experimental Results As shown in FIG. 6 (a), when the thick plate is on the outside (when it is arranged as shown in FIG. 5), the spot welded portion (B) is broken at a cushion pressure of 30 ton. However, the cushion pressure is 10, 20ton
Press molding could be performed without breaking. On the other hand, when the thin plate is on the outside,
The spot weld (B) fractured at all 0 and 30 tons.

FIG. 6 (b) shows a graph in which the strain generated in the spot weld (B) is plotted for a plurality of samples. As shown in FIG. 6 (c), the horizontal axis and the vertical axis in FIG. 6 represent the distortion in the vertical direction, and the vertical axis represents the distortion in the horizontal direction.

[Brief description of the drawings]

FIG. 1 is a process diagram showing one embodiment of a method for forming a press-formed product according to the present invention.

FIG. 2 is a perspective view showing a punch and a die used in the embodiment.

FIG. 3 is a perspective view showing a specific example of a press-formed product formed by the above embodiment.

4 is a sectional view taken along the line IV-IV in FIG.

FIG. 5 is a diagram showing experimental conditions of an experiment performed in connection with the above embodiment.

FIG. 6 is a diagram showing experimental results of the above experiment.

[Explanation of symbols]

 2,4 Board material 6 Press molded product

Claims (1)

(57) [Claims] 1. A method for forming a press-formed product, wherein two plates having different allowable strains are overlapped and welded, and the welded two plates are press-formed into a convex cross section. Then, the two pieces of plate material having different allowable strains are partially overlapped , and then welded and integrated at the overlapped portion.
Press-molding the two plates which is integrated with the convex section
Therefore, the difference in strain between the two plate materials is caused in the welded portion.
That when the stress is concentrated to form a press-molded article occurs, the convex side of the convex section Do that and the maximum strain generated portion occurs Ri by the said press forming is present, among the pre-SL two plate members, Make sure that the plate with the larger strain tolerance
The method forming features and to pulp-less molded product by press molding Te.