JP2007021568A - Method for forming member of hat-shaped section having excellent shape freezing property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method capable of suppressing a warp of a three-dimensional shape of a member of a hat-shaped section having a bent part in the longitudinal direction of the member used, in particular, for a vehicle body member of a car. <P>SOLUTION: In the forming method of a member of a hat-shaped section having excellent three-dimensional shape freezing property and having a bent part in the longitudinal direction of the member, the member is formed so that the radius r (mm) of a punch shoulder is larger than the radius R (mm) of a shoulder of a product in a first stage forming; and formed so that the radius is equal to the radius R (mm) of the shoulder of the product, in a second stage forming, with the same width in the first stage by using a punch, a die, and a fold-pressing tool. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a molding method for improving the shape freezing property of a cross-sectional hat-shaped member having a bent portion in a member longitudinal direction used for a member of an automobile body.

In recent years, a cross-sectional hat-shaped member is often used as a structural member of an automobile body. However, this cross-sectional hat-shaped member is formed into a shape as shown in FIG. 1, but this cross-sectional hat-shaped member 1 has a bent portion 2 in the longitudinal direction of the member. For example, when the cross-sectional hat-shaped member 1 having a length of 500 mm, a hat head width of 50 mm, and a wall length of 70 mm is formed and processed to have a radius Rb of the bent portion (bending angle: about 145 °): 300 mm, As shown in FIG. 2, a springback due to residual stress occurs, and a twist in the three-dimensional direction occurs in the longitudinal direction around the bending point, and the springback amount at the tip reaches about 5.5 mm. That is, the correction of the warp shape in the three-dimensional shape cannot be completely limited by the correction of the warp in the conventional two-dimensional shape (opening of the U-shaped cross section in the AA cross section in FIG. 1). . As described above, ensuring the shape freezing property is a very important technical issue in forming the cross-sectional hat-shaped member.
The amount of springback was defined as the value of the amount of warpage in the vertical direction from the desired shape at the tip of the product.

  In order to ensure this shape freezing property, for example, in Patent Document 1, a metal having a hat-shaped cross-section is formed by using a punch having a convex portion with a semicircular cross-section that is convex toward the metal plate at the head. Use the punch to bring the convex part of the punch into contact with the plate part, perform the pre-processing to form the convex part in which the part that becomes the hat head part of the metal plate protrudes outward, and then obtain the predetermined hat shape A processing method for applying a finishing process has been proposed. However, this processing method is a processing method for a cross-section hat-shaped member having a constant shape in the axial longitudinal direction, and can only be applied to two-dimensional plate warpage. The bending portion 2 in the longitudinal direction of the member as shown in FIGS. This is a technique that cannot be applied to improve the torsion in the three-dimensional shape in the longitudinal direction of the cross-sectional hat-shaped member.

  Thus, while there is an increasing need to improve the shape freezing property of a cross-sectional hat-shaped member having a three-dimensional bent portion in the longitudinal direction of a member used for a member of an automobile body, a proposal for improving this has been made. The current situation is not.

JP 2004-181502 A

  In view of the above problems, the present invention provides a molding method for improving the shape freezing property of a cross-sectional hat-shaped member having a bent portion in the longitudinal direction of the member, particularly used for a member of an automobile body.

  The present invention has been made to solve the above-mentioned problems, and the gist of the present invention is a method for forming a cross-sectional hat-shaped member having a bent portion in the longitudinal direction of the member. Used, the punch shoulder r (mm) is formed larger than the shoulder radius R (mm) of the product in the first stage molding, and the shape is frozen to the shoulder radius R (mm) of the product in the second stage molding. A method for forming a cross-sectional hat-shaped member.

  According to the present invention, three-dimensional torsion due to a spring back in the longitudinal direction of a cross-sectional hat-shaped member having a bent portion can be greatly reduced.

As described above, the present invention is a method of forming a product having a hat-shaped cross section and a bent portion in the longitudinal direction of the member using a punch, a die, and a wrinkle pressing tool. mm) is larger than the shoulder radius R (mm) of the product, and is molded into the shoulder radius R (mm) of the product in the second stage molding. FIG. 4 shows a sectional view of the operation of the cross-section hat-shaped member according to the present invention. In FIG. 4, 3 is a steel plate to be formed, 4 is a die, and 5 is a punch.
The punch shoulder r (mm) that is largely formed by the first stage molding is preferably applied over the entire length in the longitudinal direction including the bent portion, but can also be applied only in the vicinity of the bent portion.

  In normal molding, as shown in FIG. 3A, a large tensile stress is generated mainly at the punch bottom of the bent portion, and a large compressive stress is generated at the flange portion corresponding to the die face of the bent portion. These tensile-compressive stresses become driving forces, causing a large torsion of the product in the longitudinal direction starting from the bent portion, and the shape accuracy of the product deteriorates.

  Accordingly, the present inventors have intensively studied to minimize the tension-compression stress balance, forming the molding into two stages, and including the bent portion in the first stage molding as shown in FIG. The radius r (mm) of the punch shoulder is set to be larger than the shoulder radius R (mm) of the final product over the entire length in the longitudinal direction, preferably 1.2 to 3.5 times as large as R. In the second stage of the normal molding as shown in FIG. 5B, the punch width is the same as the first stage and the shoulder radius of the product is molded so that only the tensile stress acts. By forming with the same punch as R (mm), the final shape as shown in FIG. 5C is obtained, and the tension-compression stress balance acting on the punch bottom of the bent portion is as shown in FIG. 3B. The tensile stress at the center of the punch bottom at the bent part is extremely small compared to the shoulder part. Tensile at shoulder stress at Jo is a central tension that compressive stress acts - can be minimized stress balance of compression. By adopting such a molding method, it is possible to significantly reduce the twist caused by the spring back of the product longitudinal by correcting the tensile stress generated in the punch bottom portion of the bent portion in the compression direction.

A cross-sectional hat-shaped member having a punch bottom length of 50 mm and a flange height of 70 mm as shown in FIG. 1 and a bent portion having a radius of 300 mm at the center in the longitudinal direction was manufactured by molding. The bending angle of the bent portion was 145 ° as in FIG. The molding of the example of the present invention is the first stage molding as shown in FIG. 5A, and the radius r (mm) of the punch shoulder of the bent portion is 2R, which is twice the radius R of the punch shoulder of the final product: 5R: Form a large size of 10 mm and apply a tensile stress to the bottom of the punch. Next, as shown in FIG. 5 (b), the punch width is the same as the first stage and the punch shoulder radius R is the same as the final product. Was used to correct the tensile stress generated at the bottom of the punch in the compression direction. The shape of the die was the same as the product shape, and was formed with a wrinkle pressing force of 200 [kN] using a wrinkle pressing tool (not shown).
The comparative example was molded under the same conditions as in the examples except that the punch having the same shape as the punch used in the second stage molding of the example of the present invention was molded in one stage.
As a result, as shown in FIG. 6, the springback amount of the comparative example, which is a conventional molding method, was very large at about 5.5 mm, whereas the example of the present invention was improved by about 1.8 mm to about 70%. Was able to achieve a surprising and remarkable effect.

The figure which shows the product shape of a cross-section hat-shaped member. The figure which shows the state of the spring back after shaping | molding of a cross-sectional hat type | mold member. It is a figure which shows the cause stress of the springback in shaping | molding of a cross-sectional hat type | mold member, (a) is a figure which shows the stress state in the conventional shaping | molding method, (b) is a figure which shows the stress improvement state in this invention. The action sectional view of a section hat type member. It is a figure which shows the shaping | molding state in this invention, (a) is a figure which shows a 1st step shaping | molding state, (b) is a figure which shows a 2nd step shaping | molding state, (c) is a figure which shows a final product and the stress state in the state. . The figure which shows the springback improvement effect by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cross-section hat-shaped member 2 Bending part 3 Steel plate 4 Dice 5 Punch

Claims (1)

In a method for forming a cross-sectional hat-shaped member having a bent portion in the longitudinal direction of the member, the member is formed using a punch, a die and a wrinkle pressing tool, and the radius r (mm) of the punch shoulder is set to the shoulder of the product in the first stage forming. Cross section with excellent shape freezing characteristics, characterized in that it is formed larger than the radius R (mm), is formed in the second step, the same width as the first step, and the shoulder radius R (mm) of the product. A method for forming a hat-shaped member.

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