JP2008264857A - Press forming method having excellent shape fixability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a press forming method for preventing warping and twisting of a longitudinal wall part occurring in a press-formed product. <P>SOLUTION: The press forming method is provided for press-forming a member having a U-shaped section or a V-shaped section at least in a part thereof, wherein in a first pressing step, a recess having the predetermined length L1 and width and depth is press-formed so that horizontal sections of a pair of longitudinal wall parts 11, 11 form closed sections, and thereafter, at least one press forming is performed so that the length L2 in the longitudinal direction of the longitudinal wall parts 11, 11 is increased (L2>L1), and thereby the residual stress due to the press forming is mitigated, and the spring-back can be considerably reduced. In the press forming step of increasing the length of the longitudinal wall parts 11, 11, a three-divided punch having a punch of a wedge shape 5 in a center part may be used. Thereafter, trimming is performed so that ends of the longitudinal wall parts form a product shape of an open section. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for press forming a metal plate, and particularly to press forming for preventing a spring back generated during press forming of a high-strength steel plate or an aluminum alloy plate and ensuring a good shape freezing property. Is.

  In recent years, the use of high-strength steel plates and aluminum alloy plates for automobile bodies has increased, and shape freeze defects after press forming have become a problem. Defective shape freezing is a problem in which dimensional accuracy cannot be obtained, and not only significantly deteriorates the appearance quality of the final product, but also causes welding defects in assembly operations performed after molding. Therefore, prevention of shape freezing failure is regarded as important.

  Springback, which is known as a shape defect frequently observed in bending, is a phenomenon that occurs because the residual stress generated in the metal plate during bending is elastically deformed and deformed during unloading. The cause is that the stress is unevenly distributed in the thickness direction. In general, when bending is performed by press working, if the metal plate is released, elastic recovery of the metal plate causes opening of the shoulder portion of the punch and wall warping. In order to solve this problem, Patent Document 1 discloses a press molding method in which a horizontal slide die is used and the horizontal slide die is slid in the width direction of the product at the bottom dead center of the molding, thereby correcting the wall warp of the vertical wall portion. Is disclosed.

However, the springback is not only the “angle change” of the shoulder portion 1 and the “wall warp” of the vertical wall portion 2 shown in FIG. A phenomenon referred to as “twist” 3 that is a springback also becomes obvious, and the invention disclosed in Patent Document 1 cannot prevent this springback. Patent Documents 2 and 3 disclose a technique using a press horizontal die (same as the above horizontal slide die) as a method for bending a metal tube. This technique can also obtain the same effect as that of Patent Document 1, but cannot reduce three-dimensional springback (twist).
JP-A-6-246355 JP 2004-98139 A JP 2005-95956 A

  An object of this invention is to provide the press molding method which prevents the curvature and the twist of a vertical wall part which generate | occur | produce in a press molded product.

In order to solve the problem, the gist of the present invention is as follows.
(1) A method for press-forming a member having a U-shaped cross-sectional shape or a C-shaped cross-sectional shape in at least a part thereof, and having a predetermined length so that a horizontal cross section of a pair of vertical wall portions becomes a closed cross section After the concave portion having the length L1, the width and the depth is press-molded, it is press-molded at least once so that the longitudinal length L2 of the vertical wall portion is longer than the length L1, and then the end of the vertical wall portion A press molding method having excellent shape freezing property, wherein trimming is performed so that the portion has a product shape with an open cross section.
(2) In the press molding step of increasing the length of the vertical wall portion, a press die having a three-part punch having a wedge-shaped punch in the center is used, and has excellent shape freezing property (1) The press molding method as described.
(3) In the press molding step of increasing the length of the vertical wall portion in the longitudinal direction, the length of the vertical wall portion is changed by changing the amount of movement of the wedge-shaped punch. The press molding method according to (2), which is excellent in.
(4) In the press molding step of increasing the length of the vertical wall portion, press molding is performed while pressing the vertical wall portion with a punch and a pad, and the shape freezing property according to (2) or (3) is excellent. Press molding method.

  According to the present invention, a good hat-shaped molded part having excellent dimensional accuracy can be obtained.

The present invention is described in detail below.
The present inventors have studied a press molding method for preventing warpage and twisting of a vertical wall portion of a hat-shaped part having a U-shaped cross-sectional shape or a C-shaped cross-sectional shape in part, and can solve these problems. I found out how.

  In the conventional press molding method, the spring back product (a) as shown in FIG. 3 is subjected to a list (b) which is a spring back correction process (the process of performing press molding again to reduce the spring back. A “restrictive process” (referred to as “list”) was performed, and parts were built by a trim process (c) in which the flange portion was trimmed to a final shape. On the other hand, in the present invention, as shown in FIG. 4, the recess 12 having a predetermined length L1, width and depth is press-molded so that the horizontal section of the pair of vertical wall sections 11 and 11 becomes a closed section. (A). In addition, the horizontal cross section of the recessed part 12 will be in the state closed in the loop shape by press-molding so that the horizontal cross section of the vertical wall parts 11 and 11 may become a closed cross section in this way. Then, the lengthening process (b) which shape | molds a to-be-processed material is performed so that the length of the longitudinal direction of the vertical wall parts 11 and 11 may become long (L2> L1). And the trim process (C) which trims the edge part of the flange part 13 and the vertical wall parts 11 and 11 so that it may become a final component shape is performed. In addition, by removing the end portions of the vertical wall portions 11 and 11 in this trimming process, both ends in the longitudinal direction of the pair of vertical wall portions 11 and 11 are in an open state (open cross section). It has been found that by performing these steps (a), (b), and (c), the spring back is reduced (the invention according to (1)).

  In the present invention, after the molded product is deep-drawn in a state where the horizontal cross section of the pair of vertical wall portions 11, 11 maintains a closed cross section, the molded product is stretched along the longitudinal direction of the vertical wall portions 11, 11 in the expansion process. By pulling, the residual stress in the plate thickness direction of the product and the residual stress in the longitudinal direction existing in the punch bottom, the vertical wall portions 11 and 11 and the flange portion 13 of the product can be relaxed. Thereafter, by trimming to a member having a U-shaped or C-shaped cross-sectional shape, a product superior in shape freezing property can be obtained compared to the conventional press molding method.

  The invention according to the above (2) has a three-part punch having a wedge-shaped punch in the center part in a press molding process (enlargement process) for increasing the length of the vertical wall portions 11 and 11 in the longitudinal direction. It is characterized by using a press die.

  In the expansion step, in order to pull the vertical wall portions 11, 11, the molding load of the main press must be converted in a direction perpendicular to the stroke. In the present invention, the punch is disassembled into three as shown in FIG. 5, and the wedge-shaped punch 5 comes into contact with the divided punches 6a and 6b, so that the divided punches 6a and 6b are in the stroke direction (downward on the paper surface). It was designed to be able to apply a tensile tension 7 to the vertical wall portions 11 and 11 by moving in the direction perpendicular to the paper (left and right direction on the paper surface). For parts that are curved in the longitudinal direction, wedge-shaped punches 5 and punches 6a and 6b divided into straight parts of the parts are arranged at the curved parts of the parts, and wedge-shaped punches are provided at the straight parts that are the expansion points. The punch 5 was designed so as not to interfere.

  In the invention according to (3), in the press molding process (expansion process) in which the longitudinal length of the vertical wall portions 11 and 11 is increased, the amount of movement of the wedge-shaped punch 5 is changed. It is characterized by changing the length.

  In order to significantly reduce the springback according to the present invention, the tension tension in the expansion process must be applied to the punch bottom portion, the flange portion 13 and the vertical wall portions 11 and 11 of the member. The load of this tensile tension is related to the tensile strain (the amount of expansion). If the tensile strain in the longitudinal direction of the member is 0.5% or less, the residual stress of the entire product cannot be alleviated, If the tensile strain is 5% or more, the risk of breakage or necking of the member increases, so the tensile strain is preferably in the above range.

  In the invention according to (4), in the press molding process (expansion process) for increasing the length of the vertical wall portions 11 and 11 in the longitudinal direction, press molding is performed while pressing the vertical wall portions 11 and 11 with a punch and a pad. It is characterized by that.

  In order to apply tensile tension to the entire member in the expansion process, punches 5, 6a, 6b and pads 9a, 9b are used as shown in FIG. It is preferable to hold down the end portions 11 and 11.

  As an example of the present invention, press forming was performed using a steel plate having a plate thickness of 1.2 mm and a tensile strength of 590 MPa class, and a product having a cross-sectional shape of a square shape as shown in FIG. 7 was manufactured. In order to examine the effects of the present invention, as shown in FIGS. 4A to 4C, the molded product is deep-drawn so that the horizontal section of the pair of vertical wall portions becomes a closed section in the first press molding. Then (FIG. 4 (a)), the member was expanded so as to increase the product length by using the three-part punch shown in FIG. 5 in the second press molding (FIG. 4 (b)). Finally, the flange portion and the end portion of the vertical wall portion were trimmed (see FIG. 4C). The amount of expansion (L2-L1) was 10 mm, and the wrinkle presser was 20 tons. Moreover, the pad used for an expansion process was arrange | positioned on both surfaces, as shown in FIG. 6, and the pad pressure was set to 1 ton, respectively. For comparison, an example of press molding was performed so that the product shown in FIG. 7 was obtained by one press molding.

  As evaluation items, displacement amounts W1 to W4 at the punch shoulder R stop of the product end surface before and after the spring back were measured, and the average value was defined as the twist amount. Moreover, the displacement amount from the reference | standard in a 50 mm height position from the punch bottom of a product end surface was measured, and the average value was made into wall curvature. The amount of displacement was evaluated with respect to the reference plane, with the upward displacement as plus and the downward displacement as minus.

  The measurement results of Example 1 are shown in Table 1. According to the present invention, the dimensional accuracy is improved as compared with the comparative example, and a hat-shaped molded part having excellent dimensional accuracy can be obtained.

The schematic diagram explaining wall curvature and an angle change is shown. The schematic diagram explaining twist is shown. The schematic diagram of the product explaining the conventional press molding is shown. (A) Drawing process, (b) List process, (c) Trim process. Sectional drawing of the vertical wall part of the product explaining this invention is shown. (A) Drawing process, (b) expansion process, (c) trimming process. Sectional drawing of the press die explaining this invention is shown. 1 shows a cross-sectional view of a pad illustrating the present invention. The schematic diagram of the components used for the Example is shown.

Explanation of symbols

1 shoulder
2 Vertical wall
3 Torsion 4 Ideal shape 5 Wedge-shaped punch 6a, 6b Divided punch 7 Tensile tension 8 Part shape 9a, 9b seen from the top view Pad 10 Pad force 11 Vertical wall 12 Recess 13 Flange L1 Work before expansion Longitudinal length L2 of the material (vertical wall portion) Longitudinal length A of the workpiece (vertical wall portion) after expansion A straight portion B of the vertical wall portion of the product Concave in the longitudinal direction of the vertical wall portion of the product Curved part C The curved part convex in the longitudinal direction of the vertical wall part of the product

Claims (4)

  A method for press-forming a member having a U-shaped cross-sectional shape or a C-shaped cross-sectional shape at least in part, wherein a predetermined length L1, After the recess having the width and the depth is press-molded, it is press-molded at least once so that the length L2 of the longitudinal wall portion is longer than the length L1, and then the end of the longitudinal wall portion is opened. A press molding method with excellent shape freezing property, characterized by trimming to have a product shape of a cross section.   2. The shape freezing property according to claim 1, wherein in the press molding step of increasing the length of the vertical wall portion, a press die having a three-part punch having a wedge-shaped punch at the center is used. Press molding method.   The shape freezing according to claim 2, wherein the length of the vertical wall portion is changed by changing a moving amount of the wedge-shaped punch in the press forming step of increasing the length of the vertical wall portion in the longitudinal direction. Press molding method with excellent properties.   4. The press molding method with excellent shape freezing property according to claim 2, wherein in the press molding step of increasing the length of the vertical wall portion, press molding is performed while pressing the vertical wall portion with a punch and a pad.

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