JP2012131316A - Manufacturing method for torsion beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for torsion beam, capable of reducing tensile residual stress at a lug section by only cold forming, without stress relief heat treatment.SOLUTION: The torsion beam has such a product shape as to be straight in the longitudinal direction and that both ends in the width direction form a curl-shaped lug section 1c at a part thereof in the longitudinal direction and that a remaining width portion is of U-shaped cross-section shape of a single layer, by forming a metal plate blank (workpiece 1). First, a region to form the lug section of the blank is worked by curling and a portion in the width direction is then bent into a U-shaped cross-section. At the same time, a U-shaped bottom outer face side of the U-shaped cross section is bent to form the outside thereof by bending work in the longitudinal direction. Next, bending correction processing is implemented to straighten a portion in the longitudinal direction, thereby applying a residual plastic flexural strain of 0.2-0.6% to the lug.

Description

  The present invention relates to a method for manufacturing a torsion beam. More specifically, the present invention relates to a method of manufacturing a torsion beam. In particular, both ends in the width direction are curled ears in a part of the length direction, and the remaining width portion in the width direction is a single layer U. The present invention relates to a method for producing a torsion beam that can advantageously produce a torsion beam having a product shape such as a letter-shaped cross-sectional shape by molding using a blank of a metal plate. The U-shape also includes a V-shape (the same applies hereinafter). The molding process is performed cold (the same applies hereinafter).

  As an equivalent to the torsion beam having the above-mentioned product shape, it is described in Patent Document 1 that “a cross strut made of steel for a torsion beam type axle, wherein the cross strut extends over most of its length. Having a single-layer cross-sectional profile in the shape of a letter, the cross-sectional profile comprising two legs and one arcuate heel section connecting the legs "(Patent Document 1 [0001] ) "At the free end of at least one leg is provided with a length section curved in the shape of a hollow profile, and the length section is in the region of its end face, on the inner surface or outside of the leg. There is known a technique (Patent Document 1 [0006]) that is made to be bonded to the surface. In this description, “the length section curved in a hollow profile” and “the length section is joined to the inner surface or the outer surface of the leg in the region of the end surface” Applies to the ear.

  In the torsion beam having the above-mentioned product shape, a single-layer U-shaped cross-sectional shape that does not have the ears at both ends, or a two-layer U-shaped cross-sectional shape is formed by crushing the pipe in the tube diameter direction. At the same time, the weight of the material for obtaining the same rigidity can be made smaller than that in which hollow portions corresponding to the ear portions are formed at both ends of the cross-sectional shape (Patent Document 1 [0005]).

JP 2005-29155 A

The conventional method for manufacturing the torsion beam having the above product shape is to form a curled ear by forming a width direction end portion in a longitudinal direction of a blank of a metal plate, that is, a curling process, This is a method of bending the width direction into a U-shaped cross-section while restraining the direction straight.
However, a large tensile residual stress due to the curling process remains in the ear portion of the molded product, and the fatigue resistance is deteriorated. Therefore, it is necessary to perform a stress removing heat treatment to reduce the tensile residual stress, There was a problem of hindering performance and cost reduction.

The inventors have intensively studied to solve the above-mentioned problems, and as a result, have come up with a means capable of reducing the tensile residual stress of the ear portion only by cold forming without performing the stress-relieving heat treatment. Made.
That is, the present invention forms a blank of a metal plate, is straight in the longitudinal direction, and in the longitudinal direction, both end portions in the width direction are curled ears and the remaining width portion is a single-layer U-shape. In forming a torsion beam having a product shape that is a cross-sectional shape, first, the region of the blank to be the ear is curled, and then the width direction is bent into a U-shaped cross-sectional shape, and at the same time, the U-shaped cross-sectional U-shape The residual plastic bending strain of 0.2 to 0.6% is applied to the ear by bending in the longitudinal direction with the bottom outer surface side bent outward and then performing straightening to straighten the longitudinal direction. A method of manufacturing a torsion beam.

  In the present invention, when the metal plate is a steel plate and the radius of curvature of the longitudinal bend after unloading is R and the height of the U shape is h in the longitudinal bending step, e = (h / (2R + h) ) × 100 (%), and the bending in the longitudinal direction may be performed so that the geometric bending strain e after unloading is 2 to 6%.

  According to the present invention, it is possible to manufacture a torsion beam having excellent fatigue resistance without performing the conventionally required stress relief heat treatment, which contributes to improvement in productivity and cost reduction.

Schematic of the molding process showing an example of an embodiment of the present invention Graph showing the relationship between the residual stress ratio γ and the residual plastic bending strain ε

  FIG. 1 is a schematic view of a molding process showing an example of an embodiment of the present invention. The planar shape of the workpiece 1 (metal plate blank) before forming shown in FIG. 1A is set based on a figure obtained by developing a three-dimensional product figure after forming on a plane, as in the prior art. As shown in FIG. 1 (d), the product shape is straight in the longitudinal direction, and both end portions in the width direction form curled ears 1c in a part of the longitudinal direction (the central portion in the longitudinal direction in this example). The width portion is a single-layer U-shaped cross-sectional shape. In this example, since the portion without the ear portion 1c in the product longitudinal direction (both ends in the longitudinal direction in this example) has an elliptical cross-sectional shape, U corresponding to this in the longitudinal direction of the blank has U portions with ear portions 1c. It has a wider width than the central portion in the longitudinal direction of the blank having a letter-shaped cross-sectional shape.

With respect to the workpiece 1 (blank) of FIG. 1 (a), first, as shown in FIG. 1 (b), the region to be the ear portion 1c is subjected to curling to form the ear portion 1c. This processing is performed by, for example, press processing (ear part forming press processing).
Thereafter, as shown in FIG. 1 (c), the width direction of the central portion in the longitudinal direction including the ear portion 1c is bent into a U-shaped cross section, and at the same time, the U-shaped bottom outer surface side of the U-shaped cross section is bent outward. Then, as shown in FIG. 1 (d), a bending correction process is performed to straighten the longitudinal direction to obtain a product. At this time, in the bending process in the longitudinal direction, the residual plastic bending strain (residual plastic bending strain after unloading) of the ear portion 1c after the subsequent bending correction process is 0.2 to 0.6%. Thus, by setting the amount of bending, a residual plastic bending strain of 0.2 to 0.6% can be applied to the ear portion of the product.

In addition, although the shaping | molding process with respect to the longitudinal direction part (this example both ends of a longitudinal direction) which does not form the ear | edge part 1c is a shaping | molding process to an elliptical cross-sectional shape in this example, it is a shaping | molding process to other cross-sectional shapes. It may be.
FIG. 2 is a graph showing the relationship between the residual stress ratio γ and the residual plastic bending strain ε determined in a bending straightening simulation experiment. The residual plastic bending strain ε is the maximum principal strain of the ear after unloading measured by the strain gauge cutting method or the X-ray method, while the residual stress ratio γ is obtained by cutting out the portion of the maximum principal strain. From the stress value corresponding to the release strain (maximum value of the maximum principal stress) σ and the yield strength YS of the material measured in the tensile test, γ = (σ / YS) × 100 (%) . As shown in the figure, the residual stress ratio γ decreases along the curve in the figure as the residual plastic bending strain ε increases, and in the range where ε is 0.2% or more (range Z in the figure), γ is 50%. It becomes the following. In the above-described conventional method (a method in which the longitudinal direction is constrained to be straight and the width direction is formed into a U-shaped cross-section after curling), γ exceeds 50%. Since ε is limited to 0.2% or more, γ can be reduced to 50% or less, and the stress relief heat treatment can be omitted.

If ε is excessively large, buckling or the like occurs during bending in the longitudinal direction, leading to shape defects. Therefore, ε is limited to 0.6% or less.
In order to manage the residual plastic bending strain ε at the ear of the molded product to 0.2 to 0.6%, for example, in the case of a normal steel torsion beam, in the longitudinal bending stage (FIG. 1 (c)), the removal is performed. The geometry after unloading is calculated by the following formula: e = (h / (2R + h)) × 100 (%) where R is the radius of curvature of the longitudinal bend after loading and h is the height of the U-shape. The longitudinal bending process may be performed so that the geometric bending strain e is 2 to 6%.

  As an example, in the embodiment shown in FIG. 1, a blank of a steel plate having a tensile strength of 690 MPa class and a thickness of 3.5 mm is used as a raw material, and the residual plastic bending strain ε is variously changed as shown in Table 1, and a torsion beam for a small class vehicle. Manufactured. With respect to the manufactured torsion beam, a fatigue test simulating the residual stress ratio γ of the ear portion and a repeated stress load state estimated to be received by the torsion beam mounted on the small class vehicle is performed to determine the endurance life (number of times). Examined. The results are shown in Table 1. From the table, it can be seen that the examples of the present invention have a much higher durability life than the comparative examples and the conventional examples, and no defective shape occurs.

1 Work material (using a metal plate blank)
1c Curled ear

Claims (2)

  A metal plate blank is formed and processed in a straight line in the longitudinal direction, with both end portions in the width direction forming curled ears in a part of the longitudinal direction and the remaining width portion having a single-layer U-shaped cross-sectional shape. In forming a torsion beam having a shape, first, the region to be used as the ear portion of the blank is curled, and then the width direction is bent into a U-shaped cross-sectional shape, and at the same time, the U-shaped bottom outer surface side of the U-shaped cross-sectional shape is bent. It is characterized by imparting a residual plastic bending strain of 0.2 to 0.6% to the ear part by performing a bending process in the longitudinal direction to be outside and then performing a bending correction process to straighten the longitudinal direction. Torsion beam manufacturing method. When the metal plate is a steel plate and the radius of curvature of the longitudinal bend after unloading is R and the height of the U-shape is h in the longitudinal bending step, e = (h / (2R + h)) × 100 ( %), The torsion beam according to claim 1, wherein the bending in the longitudinal direction is performed so that the geometric bending strain e after unloading is 2 to 6%. Manufacturing method.

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