JP2012071327A - Method of press-forming metallic sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of press-forming a metallic sheet, which is inexpensive and has general applicability and with which excellent shape freezing property is obtained.SOLUTION: In the method of press-forming the metallic sheet, after previously specifying the region of a flat part or a vertical wall which is optimum to mitigate residual stress in parts manufactured by press-forming the metallic sheet A by a press forming analyzing method, an opening is provided to the position of the metallic sheet equivalent to the region of the flat part or the vertical wall, and the metallic sheet A obtained by welding a metallic sheet B which is lower in strength, is press-formed at the opening.

Description

  The present invention relates to a press forming method of a metal plate, and more particularly to a press forming method of a metal plate that provides excellent shape freezing property.

  It is well known that when a metal plate is press-molded, the molded product undergoes springback, twisting, etc. due to elastic recovery, and a predetermined dimensional shape cannot be obtained, that is, a shape freeze defect occurs.

  In recent years, in steel plates for automobiles that have been strengthened, the problem of defective shape freezing has been highlighted, and there is an increasing demand for press forming methods for metal plates that can provide excellent shape freezing properties. Therefore, for example, in Patent Document 1, in a press forming method in which a metal plate is formed into a predetermined shape using a mold, residual stress that elastically recovers after the formed metal plate is released and deforms the formed product. There has been proposed a press forming method of a metal plate in which the occurrence location of the metal plate is grasped in advance, and when the metal plate to be formed is pressed to the bottom dead center of press forming, a high energy beam is irradiated on this portion. Patent Document 2 includes a hat-shaped metal part that is formed of a ceiling portion, a vertical wall portion, and a flange portion, and is press-formed into a U-shaped or C-shaped cross-sectional shape, and at least the vertical wall portion A hat-type metal part having a plurality of holes with a width of 10 mm or less that has a reduced residual stress after press molding and a shape-free metal part and a method for manufacturing the same have been proposed.

JP-A-8-10851 JP 2008-778 JP 2007-229724

  However, the press molding method described in Patent Document 1 requires a device that irradiates a high energy beam such as a laser beam or an electron beam, which increases costs and increases the bottom dead center of press molding in all press molding. It is not possible to irradiate a high energy beam to the necessary part when pressed, and it is not versatile. In addition, the hat-type metal part described in Patent Document 2 has a plurality of holes (voids) having a width of 10 mm or less in the vertical wall portion, so that the strength is lowered, so it cannot be applied to an automobile strength member, etc. poor.

  An object of the present invention is to provide a press forming method of a metal plate that is inexpensive, versatile, and has excellent shape freezing property.

  As a result of intensive studies to achieve the above object, the inventors of the present invention proposed a flat part or a vertical wall part optimal for alleviating residual stress in a press-formed product. 3 is specified in advance by the press forming analysis method described in 3, and an opening is provided at the position of the metal plate A corresponding to the portion of the flat portion or vertical wall portion, and a different metal plate with lower strength is provided in the opening. It has been found that it is effective to press-mold metal plate A welded with B.

  The present invention has been made based on such knowledge, and in a part produced by press-molding the metal plate A, the portion of the flat portion or vertical wall portion that is optimal for the relaxation of residual stress is specified in advance by the press-forming analysis method. In addition, an opening is provided at the position of the metal plate A corresponding to the portion of the flat portion or the vertical wall portion, and the metal plate A in which a lower strength metal plate B is welded to the opening is press-formed. A metal plate press forming method is provided.

  In the metal plate press forming method of the present invention, the strength of the metal plate B is preferably 75% or less of the strength of the metal plate A.

  According to the present invention, it is possible to provide a press forming method for a metal plate that is inexpensive, versatile, and has excellent shape freezing property. The press molding method of the present invention is suitable for manufacturing a structural member of an automobile.

  It is well known that shape freeze defects such as springback and torsion that occur when a metal plate is press-formed are based on non-uniform residual stress in the molded product. Therefore, the press molding analysis method using the FEM stress analysis described in Patent Document 3 proposed by the present inventors is suitable for the portion of the flat portion or vertical wall portion that is optimal for relaxation (uniformization) of residual stress in the molded product. In advance, an opening is provided at the position of the metal plate A corresponding to the portion of the flat portion or vertical wall portion, and a metal plate A in which a different metal plate B having a lower strength is welded to the opening is provided. If the press molding is performed, the residual stress is relieved at a site where different metal plates B having lower strength are welded, so that the shape freezing failure can be reduced.

  In the press molding method of the present invention, an opening is formed in the material metal plate A (a hole is formed), and the metal plate A in which a low-strength metal plate B is welded is used. A special device such as an energy beam irradiation device is also unnecessary, and versatility is not impaired. In addition, since the opening is closed with a metal plate B having a certain level of strength, there is almost no decrease in strength, and there is no problem when applied to a strength member of an automobile.

  Setting the strength of the metal plate B to be welded to the opening to 75% or less of the strength of the metal plate A as a raw material is more effective for reducing the residual stress. In addition, what is necessary is just to set the number and magnitude | size of an opening part suitably according to the magnitude | size and shape of a press molded product.

Claims (2)

  The part of the flat part or vertical wall part that is optimal for the relaxation of residual stress in the part produced by press-molding the metal plate A is specified in advance by the press molding analysis method, and corresponds to the part of the flat part or vertical wall part. A metal plate press forming method, comprising: providing an opening at a position of the metal plate A to be pressed, and press forming the metal plate A welded with a lower strength metal plate B into the opening.   2. The method for press-forming a metal plate according to claim 1, wherein the strength of the metal plate B is 75% or less of the strength of the metal plate A.