JPH0810851A - Press formation of metallic sheet - Google Patents

Abstract

PURPOSE:To form even a metallic sheet consisting of a high-strength metallic material to a prescribed shape and size with good accuracy at a low cost in a short time. CONSTITUTION:The point where the residual stress to deform molded goods generates by elastic recovery of the formed metallic sheet after parting from molds is previously recognized in the method for press forming the metallic sheet 1 to form the molded goods having prescribed shapes by using metal molds. This part is irradiated with plural pieces of high energy beams satisfying the following equation bw/t>=3.33XbH/t (0.3<=bH/t<=0.7) where, bW: bead width, t: sheet thickness, bH; penetration depth, in the bead shape when the metallic sheet to be formed is pressurized down to the bottom dead point of press forming.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for press-forming a metal plate, which press-molds a metal plate into a predetermined shape and size using a mold.

[0002]

2. Description of the Related Art When a metal plate is used as a raw material and a product having various shapes and sizes is obtained by press molding, when a molded product is taken out from a mold after molding, the molded product has a shape different from the shape and size of the mold. It is well known that deformation due to so-called elastic recovery phenomenon occurs, resulting in defective shape of a molded product.

These shape defects are usually because when the molded product is taken out of the mold, the restraining force received from the mold is removed and elastic recovery due to residual stress occurs.
Due to this elastic recovery, the molded article has a wall warp phenomenon in which the flat surface of the side wall portion has a curvature, and the angle between the two surfaces sandwiching the ridge of bending is different from the angle of the mold, so-called springback. Deformation phenomena such as an angle change, a twisting phenomenon in which two cross sections intersecting at right angles to the longitudinal axis rotate, and a ridge line warp in which the bending axis ridge line of the molded product has a curvature different from the ridge line of the mold occur.

Conventionally, in order to prevent shape defects due to these elastic recovery phenomena, as a measure from the viewpoint of material characteristics of the metal plate, a low yield point material or a high elastic modulus material is selected and the elastic recovery amount is selected. There is a method of suppressing. Further, as one of the measures from the viewpoint of the molding method, there is a method of using a high energy beam. The technology up to now is a method to improve the shape of the molded product by irradiating a high energy beam to the part where the phenomenon of wall warpage or angle change of the press molded product occurs after mold release and causing shrinkage deformation. , Was a method of improving the formability of the molded product after release by irradiating the place where residual stress is expected to occur at the molding bottom dead center with a high energy beam to release the residual stress ( See JP-A 1-233019).

[0005]

In recent years, there has been a tendency for the strength of press-formed metal sheets to be increased in order to reduce the weight of parts and improve their strength. For example, automobile parts are 350 to 590 (N / mm ² ) grade as a metal plate that is press-molded in order to improve fuel efficiency by reducing the weight of the vehicle body and increase vehicle body strength to ensure passenger safety. The high-strength steel sheet of No. 1 has been widely used, and more recently, the use of high-strength steel sheet of 780 to 1180 (N / mm ² ) grade has been studied.

As described above, when the strength of the metal plate used is increased, the elastic recovery amount of the molded product is increased, and the degree of shape / dimension failure due to the elastic recovery phenomenon is increased. Therefore, as the strength of the metal plate increases, it becomes more difficult to obtain a molded product having a predetermined shape and dimensional accuracy. Therefore, there is a method of utilizing a high-energy beam as one of the measures from the molding surface, as in the above-mentioned conventional technique. However, conventionally, the irradiation condition (energy density, focus position, bead shape, irradiation pattern, etc.) of the high energy beam was not specified at all, and the place where residual stress was generated at the molding bottom dead center was grasped in advance and By irradiating the whole with a high-energy beam, the residual stress was completely released, and a molded product having a predetermined shape and size was obtained. Therefore, the irradiation amount of the high energy beam is extremely large, and there are many problems such as cost, irradiation time, and appearance of the product.

The present invention solves the problems of the above-mentioned conventional techniques, and even a metal plate made of a high-strength metal material can be formed into a predetermined shape and size with high precision, at low cost, and in a short time. An object of the present invention is to provide a method for press-forming a metal plate that enables the above.

[0008]

In order to achieve the above object, the present invention takes the following means. That is, the press-molding method for a metal plate according to the present invention is a press-molding method for forming a metal plate into a molded product of a predetermined shape by using a mold,
The place where residual stress that elastically recovers the molded metal plate after releasing from the mold and deforms the molded product is grasped in advance, and when the metal plate to be molded is pressed to the bottom dead center of the press molding, b _W /T≧3.33×b _H / t (0.3 ≦ b _H / t ≦
0.7) Here, several high-energy beams satisfying b _W : bead width t: plate thickness b _H : penetration depth are irradiated.

[0009]

The function of the present invention will be described as follows. The metal plate that is press-formed during press-forming follows the shape of the mold at the bottom dead center of press-molding and has the same predetermined shape and size as the bending angle of the mold, but undergoes particularly large deformation. Residual stress that elastically recovers and deforms the molded product is generated at the location at the time of subsequent mold release.

In the present invention, the place where such a residual stress occurs is grasped in advance, and when the metal plate to be molded is press-molded, when the metal plate to be molded is pressed to the bottom dead center of the press-molding, as shown in FIG. the occurrence point of the molded metal plate 1 of residual stress as indicated _{by, b W /t≧3.33×b H /t(0.3≦b H /} t ≦
0.7) Several beads 2 having a shape satisfying the formula 1 are irradiated.

Where b _{W is the} bead width, t is the plate thickness,
b _H: penetration is the depth. As a result, the metal to be formed is heated by receiving the energy of the high-energy beam applied to the place where the residual stress is generated, and the strain of the processed structure of this part is released to become a stable structure with less strain. The bead width b _{W of the} metal to be formed which was irradiated with the high energy beam under the condition satisfying the formula 1 was 3.33 times the penetration depth b _H or more, and the irradiation was stable over a relatively wide range with a single irradiation. You can get a tissue. Under the irradiation condition that the bead width b _W is 3.33 times or less of the penetration depth b _H , the high energy beam hits the surface of the metal plate to be formed and then is reflected in the direction of penetrating the plate thickness. , The bead width b _W becomes extremely narrow. Therefore, the effect of reducing the strain to an extremely narrow range can be obtained by one irradiation, and the effect of suppressing the elastic recovery amount is small.

It is generally known that the amount of elastic recovery after release from the mold is determined by the magnitude of the residual stress difference between the front and back surfaces of the metal sheet to be formed at the bottom dead center of forming. Therefore, the relationship between the residual stress difference between the front and back of the metal sheet to be formed at the forming bottom dead center in draw bending where elastic recovery is likely to occur and the amount of elastic recovery after release (here, wall warpage) is shown in the figure. It is 2. Even in recent years when the strength of the metal plate used for press forming is increased and difficult forming is required, the difference in residual stress between the front and back of the metal plate at the bottom dead center of press forming is shown in Fig. 2 in most of the forming. It is 800 (N / mm ² ) or less as shown. Figure 2
If it is possible to reduce the residual stress difference between the front and back surfaces of the metal sheet to be formed at the bottom dead center of the press molding by 30% or more, the amount of elastic recovery after release should be at a level that does not pose any problem for actual press-formed products. It becomes possible to suppress. Than this, the depth b _H penetration it is necessary to more than 30% of the plate thickness.

When the penetration depth b _H is larger than 70% of the plate thickness, the elastic recovery amount is small, but excessive high-energy beam is irradiated, which leads to an increase in cost and especially the metal plate to be formed. In the case of thin plates, the risk of cutting increases. The irradiation of the high-energy beam satisfying the above conditions is performed when the press molding is pressed to the bottom dead center, so the metal plate to be molded with reduced residual stress that causes elastic recovery fits well in the mold. It will be released later, the shape and dimensions of the mold
The accuracy will correspond to the dimensions.

Incidentally, in the present invention, in order to grasp in advance the place where the residual stress which elastically recovers the molded metal plate after releasing from the mold and deforms the molded product is grasped, the analysis by simulation and the empirical rule in the mold design stage. The method of grasping based on the above, or the method of performing preforming with a mold and analyzing the preforming result to grasp. Further, in the present invention, the metal plate is a cold and hot rolled plate, not only a surface-treated steel plate subjected to plating, but also a plate-shaped metal such as titanium, aluminum or copper, and a high energy beam Means an energy beam such as a laser beam, an electron beam, or a plasma beam that gives heat to an object to be irradiated.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 This example is an example applied to a product having a shape in which a wall warp phenomenon is likely to occur during press forming, that is, a shape requiring draw bending.

FIG. 3 is a view showing the molded product 3, and the test materials are cold rolled steel sheets of 440N grade and 590N grade having a plate thickness of 0.8 (mm). At the bottom dead center of the press molding, the bead shape is b _H = 0.
4 (mm), b _W = 1.5 (mm), condition 2 is b _H
= 0.2 (mm), b _W = 1.5 (mm), and under the condition 3, b _H = 0.4 (mm) and b _W = 1.0 (mm), the laser beam was irradiated.

As the condition 4, ordinary molding without laser beam irradiation was carried out. With respect to each of the molded products obtained by these moldings, the curvature of the vertical wall portion represented by 1 / ρ in FIG. 3 was measured and defined as the wall warp amount. FIG. 4 is a graph showing the wall warp amount 1 / ρ under each condition based on the above measurement results.

As shown in FIG. 4, in the case of the condition 1 which satisfies the irradiation condition of the laser beam of the present invention, the wall warp amount 1 / ρ is extremely small as compared with the cases of the conditions 2 and 3. Recognize. Example 2 This example is an example of a rectangular container in which a twist phenomenon is likely to occur during press molding.

FIG. 5 is a view showing the formed rectangular container 4, and the test materials are cold rolled steel sheets of 440N grade and 590N grade having a plate thickness of 0.8 (mm). At the bottom dead center of the press molding, the bead shape is b _H = 0.4 (mm) and b _W = 1.6 (mm) as condition 1 and b _H = 0. 2 (mm), b _W = 1.6 (m
m), as condition 3, b _H = 0.4 (mm), b _W = 0.
The laser beam was irradiated so as to be 8 (mm).

As the condition 4, ordinary molding without laser beam irradiation was carried out. For each of the molded products obtained by these moldings, the twist angle θ with respect to a predetermined flatness represented by θ in N in FIG. 5 was measured. FIG. 6 is a graph showing the twist angle θ under the angular condition based on the above measurement result.

As shown in FIG. 6, it can be seen that the twist angle θ is extremely small in the case of the condition 1 satisfying the laser beam irradiation condition of the present invention as compared with the cases of the conditions 2 and 3. In general, when such a high-energy beam is irradiated, some burn marks are left on this portion, but the appearance is not significantly deteriorated.

[0022]

As described above, according to the present invention, it is possible to remarkably reduce wall warpage, twisting, springback, etc. due to elastic recovery that occurs after mold release of a processed product in press molding of a metal plate. , It is possible to obtain a processed product of a predetermined shape and size with good accuracy, at low cost, and in a short time, and it is possible to carry out without being restricted by the material characteristics such as the type and strength of the metal plate as the material. .

[Brief description of drawings]

FIG. 1 shows a shape of a bead when a metal plate to be molded is irradiated with a high energy beam.

FIG. 2 is a graph showing the relationship between the difference in residual stress between the front and back surfaces of a metal sheet to be formed and the amount of wall warpage at the forming bottom dead center in draw bending.

FIG. 3 shows a molded product according to the first embodiment of the present invention.

FIG. 4 is a graph showing the wall warpage amount under each condition of the first embodiment of the present invention.

FIG. 5 shows a molded product of a second embodiment of the present invention.

FIG. 6 is a graph showing a twist angle under each condition of the second embodiment of the present invention.

[Explanation of symbols]

 1 Metal Plate to be Formed 2 Bead 3 Press Formed Product (Draw Bend Forming) 4 Press Formed Product (Rectangular Container)

Claims (1)

[Claims] 1. A press molding method in which a metal plate is formed into a molded product of a predetermined shape by using a mold, and a location where residual stress that elastically recovers and deforms the molded product after mold release of the molded metal plate is generated in advance. grasped advance, when pressurized to be molded metal plate to press forming bottom dead _{center, b W /t≧3.33×b H /t(0.3≦b H /} t ≦ this part
0.7) Here, the high-energy beam is irradiated under the condition that b _W : bead width t: plate thickness b _H : penetration depth, and a high-energy beam is irradiated.