JPS59150623A - Press forming device - Google Patents

Abstract

PURPOSE:To perform press forming which generates no plane distortion at all by heating locally at least one point in a partial forming section or plane distortion generating section to the temp. higher by a specific temp. or above than the periphery thereof. CONSTITUTION:The plane distortion generated in a press-forming article in which a plane occupies a greater part and which is formed partially is possibly the light buckling owing to a residual compressive stress. Therefore if said part is shrunk, the residual compressive stress can be relieved and the plane distortion can be eliminated. More specifically at least one point in the partially forming section or the plane distortion generating section is locally heated during forming and is formed by providing a temp. difference from the non-heated part, by which the locally heated part is deformed while said part is kept thermally expanded during forming. When the temp. is made uniform upon ending of the forming, the thermally expanded section is shrunk and the residual compressive stress which is ought to be generated by elastic recovery after the forming is removed. The above-described temp. difference is essentially regulated to >=20 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is capable of preventing and eliminating corrugated surface defects (surface distortion) that occur during press forming of a metal plate in which the flat portion occupies the majority and partial forming processing is performed. The present invention relates to a press molding method.

For press-formed products that are mostly flat and partially overhang, drawing, bending, etc., and complex processing thereof,
Minor surface waving defects (hereinafter abbreviated as surface distortion) occur around the partially molded area.

Examples of such press-molded products include automobile outer panels such as door outer barrels, bonnets, trunk lids, and rear fenders.

In order to remove the surface strain in these molded products, methods using low yield point materials have been adopted as material countermeasures, but it is difficult to completely eliminate surface strain, and it is difficult to completely eliminate the surface strain, and it is difficult to completely eliminate surface strain. be. Furthermore, with the recent increase in the use of high-strength steel plates as a weight reduction measure, this surface distortion problem has become the biggest issue in forming.

If it were possible to completely remove surface distortion during press forming, it would not only improve the aesthetic appearance of press-formed products, but also greatly expand the flexibility in selecting materials for forming them.
It becomes possible to replace conventional materials with low yield points and high formability with high strength materials due to the problem of surface strain, and it also becomes possible to downgrade the materials. Furthermore, from the standpoint of mold design, it becomes possible to expand the degree of freedom in the shape of the film.

An object of the present invention is to provide a press forming method in which no surface strain occurs at all, and its feature is that at least one of the partial molding area or the area where surface strain occurs is locally formed from the surrounding area. The purpose is to mold the product at a high temperature of 20°C or higher.

As described above, in the press molding method of the present invention, the area where surface strain occurs is locally heated during molding so that the temperature difference with the non-heated area is 20° C. or more.

The surface strain that occurs in press-formed products that are mostly flat and partially formed is considered to be slight buckling due to compressive residual stress. Therefore, if this portion is contracted, the compressive residual stress will be released and the surface strain will disappear. If the area where surface strain occurs is locally heated during molding and molded with a temperature difference from the non-heated area, the locally heated area will deform while undergoing thermal expansion during molding, and if the temperature becomes uniform at the end of molding, The thermally expanded portion contracts, and the compressive residual stress that would have been generated due to elastic recovery after molding is removed.

In addition, the cause of compressive residual stress, which is a factor of surface strain, is due to the non-uniform elastic recovery or It is believed that the cause is a slight surplus of meat. Therefore, if only the molded portion is locally heated and molded so that it shrinks after cooling, the compressive residual stress and surface strain are eliminated.

The reason why the temperature difference between the locally heated portion and the non-heated portion was set to 20° C. or more is as follows.

When we investigated the surface strain of press-molded products of various plate materials and the temperature required to eliminate it, we found that a temperature difference of at least 20°C was required. In addition, if the forming temperature exceeds 200°C in actual forming, the lubricating effect of the lubricating oil normally used for press forming may deteriorate, and the formability may be worse than that without lubrication, so the maximum temperature is not so high. It can't be expensive.

Note that the term "flat" used in this specification means that the entire surface appears flat compared to the locally molded portion, and includes curved surfaces with large curvature.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the shape of the molded product of Example 1,
It is a model shape of a car door.

In Figure 1, the dimensions of each part are A = 1750mm, B
-950mmC=30++u++, R=2600m
m, and the dimensions of the handle are a-170ms, b = 6
5 mWl, handle depth c = 11 mm (as shown in the XX cross section). When forming in this way, the surface strain is the first
It occurs in the shaded area above and below the handle in the figure. At this time, when position ① of the lower part of the handle #=10 mm is measured using a shape measuring machine, a measurement line approximately as shown by the solid line in FIG. 2 is obtained. A hypothetical shape in which no surface distortion occurs is shown by the broken line in FIG. The surface strain was evaluated by measuring the maximum value Δh of the difference between the broken line and the solid line in FIG. 2. Similarly, for the upper part of the handle, the profile of the shaded area is convex with respect to the virtual shape, but since the surface distortion of the upper part of the handle and that of the lower part are the same, only the lower part of the handle will be described below. Furthermore, the magnitude of surface distortion was smaller in the upper part of the handle, and when the surface distortion in the lower part of the handle was removed by the molding method of the present invention, the distortion in the upper part of the handle was definitely removed. Table 1 shows the tensile test results using JTS No. S test pieces with the shape shown in Figure 1.
It was press-molded and the surface strain was measured. Press molding is 300
The process was carried out using a 200-ton double-acting mechanical press.

Table 1, FIG. 3 shows a cross section of a mold for carrying out the present invention, taken along the cross section XX in FIG. This molding is generally performed using a die 1 and a punch 2. The handle portion where surface distortion occurs is formed by an embossing punch 3 provided on a die and a cavity 4 of the die.

In the present invention, the embossing punch 3 is not integrated with the die 1, but is fitted with the die 1 via a heat insulating material 7, and a heating element 5 made of nichrome wire is embedded in the embossing punch 3. The heating element 5 is energized and heated by a conducting wire 6.

Using the mold with the structure shown in Fig. 3, it is shown in Table 1.
FIG. 4 shows the results of press forming the material by varying the temperature of the embossing punch 3. As is clear from FIG. 4, in material (2), surface strain was completely eliminated at a temperature difference of 20°C. Furthermore, even in the case of material (3), which had the most severe surface strain, the surface strain was removed with a temperature difference of 45°C. When the temperature difference is even higher, no surface strain occurs at all. If the temperature difference increases, the shrinkage will also increase, which can be expected to have a negative effect on the shape, such as the formation of whiskers, but this did not occur in this experiment. The reason for this is not clear, but it is thought that the excess shrinkage was absorbed by other molded parts and did not have any adverse effects. When the temperature difference exceeded 200°C (molding temperature 225°C), the material broke during the molding of the handle due to deterioration of lubrication.

In this example, only the handle was locally heated, but a mold as shown in FIG. 5 was also tested.

In other words, without making any changes to the handle part, the nichrome heating element 5 is embedded in the heating plate 8, which contains the surface distortion and is wider by 201 cm vertically and horizontally, at the lower part of the handle on the die side where the surface distortion occurs, and is insulated. It was fitted into the die 1 via the material 7.

FIG. 6 shows the results of a test similar to that shown in FIG. 3 using the mold shown in FIG. 5, and the same effect was obtained. In the above two tests, the non-heated parts other than the heated part were cooled with compressed air. In the present invention, since the temperature difference between the locally heated portion and the non-heated portion is important, in actual production sites, air cooling or water cooling of the non-heated portion is effective. In addition, the heating element does not have to be a nichrome heating element, but can also be heated air,
Anything that can be heated to 200 to 300°C, such as heated steam, can be used.

Furthermore, although the method of heating the mold is shown above, it goes without saying that the principle of the present invention can also be applied to a method of heating a local part of the workpiece immediately before molding with the same effect.

FIG. 7 shows another embodiment of the present invention, which is applicable to molding an automobile trunk lid panel. In the case of this example, surface strain occurred at position 9, and according to the measurement at the measurement line N-kidney passing through the center of the surface strain, Δh = 0.04 mm for material ■. In this case, as shown by the broken line 10, the mold was provided with a heating plate that was about 10 mm larger both vertically and horizontally as shown by the broken line 10, and by heating only that part from around 30° C., the surface strain was eliminated.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the shape of the molded product for an automobile door, Figure 2 is a diagram showing the shape along line H in Figure 1, and Figure 3 is a diagram showing the shape of the molded product for the automobile door in Figure 1. Figure 4 is a diagram showing the results of press molding of the mold shown in Figure 3 taken at various temperatures of the embossing punch, Figure 5 is a diagram taken along the X-X line of the mold. FIG. 6 is a diagram similar to FIG. 4 when the mold shown in FIG. 5 is used; FIG. 7 is a molded product of an automobile trunk lid panel. It is a figure showing a shape. (Main reference number) 10. Dice, 20. Punch, 39. Emboss punch, 41. Cavity, 5, heating element, 60. Conductor, 70. Insulation material, 80. heating plate. Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Masahiko Arai 0 No. 60 7th Prisoner Proceedings Amendment Form Stamped October 72, 1981 1, Indication of Case Patent Application No. 24720 of 1982 2,
Title of the invention Press molding method 3, relationship with the amended case Patent applicant address 5-15 Kitahama, Higashi-ku, Osaka Name (211)
) Sumitomo Metal Industries Co., Ltd. Representative Kumagai Preamble 4, Agent address 703 New Belmode Building, 3-3 Kojimachi, Chiyoda-ku, Tokyo 102 6, Subject of amendment Patent claim section of specification, Detailed description of invention section, The column for the brief description of the drawings, Drawing 7, and the contents of the amendment (11) Claims are amended as shown in the attached sheet. (3) "Compressive residual stress" written in page 4, line 9 of Book 11 should be corrected to "indirectly compressive residual stress in the area where surface strain occurs." (4) Add the following sentence after “Stress is also removed.” on page 4, line 10 of the specification. If it is formed so as to shrink after cooling, the compressive residual stress at the area where surface strain occurs will be indirectly resolved, and surface strain will also be removed.''(5) "Figure 7 is" as stated in page 9, line 8 of the specification. (6) The “mold” described in page 9, line 12 of the specification is corrected as “Fig.
As shown in Figure (a), the correct name is ``Mold''. (7) Add the following sentence next to "Resolved." written on page 9, line 15 of the specification. ``Also, in this example, as shown in FIG.
I tried molding it by heating it to around 5°C, but the surface distortion was resolved in the same way. ” (8) “Figure 7 is” written in page 10, line 8 of the specification is corrected to read “Figure 7 (a) and (b) are respectively”. (9) Figure 7 of the attached drawings is corrected as shown in the attached sheet. Claims In forming a press product of a metal plate in which the flat surface occupies most of the area and partial forming processes such as stretching, drawing, bending, and combinations thereof are performed, the partial forming process part or The molding process is carried out in a state in which at least one area around the forming area including the area where surface defects occur due to slight waviness or around the area where surface defects occur near the forming area is at least 20 degrees Celsius higher than other areas. A press forming method for metal plate materials. Figure 7 (a) (b)

Claims (1)

[Claims] In forming a press product of a metal plate in which a flat surface occupies most of the area and partial forming processes such as stretching, drawing, bending, and combinations thereof are performed, the partial forming process part or the forming process part A method for press forming a metal plate material, characterized in that at least one of the surrounding areas of the forming process, including areas where surface defects occur due to slight waviness, is heated to a temperature of 20° C. or more higher than other areas.