JP7295425B2 - Manufacturing method of torsion beam - Google Patents

Description

The present invention relates to a torsion beam manufacturing method.

A torsion beam type suspension device is widely used as one form of automobile suspension systems.

A torsion beam suspension system comprises a torsion beam assembly in which a pair of left and right trailing arms that rotatably support left and right wheels are connected by a torsion beam, and a pair of left and right spring receiving portions are joined near the left and right ends of the torsion beam; and a spring and an absorber connecting between the vehicle bodies. The torsion beam is swingably connected to the vehicle body via a pivot shaft extending from the right and left sides of the vehicle body toward the center.

The torsion beam is formed, for example, by plastically working a metal pipe by press molding or hydroforming. It is formed in a substantially V-shaped or substantially U-shaped closed cross section.

Patent Document 1 describes a method of manufacturing a torsion beam that can efficiently manufacture a torsion beam with excellent fatigue characteristics, including a constant shape closed cross-section portion and a shape that is continuous with the constant shape closed cross-section portion and has a different closed cross section. and a shape-changing portion having a connection region with a closed cross-section of . A method of manufacturing a torsion beam is disclosed in which a pulling force is applied along to obtain a torsion beam.

Patent Document 2 describes the production of a torsion beam suspension that reduces residual stress and facilitates the production of a torsion beam. When forming the cross-sectional shape into a substantially V-shape or a substantially U-shape, the pipe is crushed inward in the radial direction to form a recess with the tip opening side open, and then the tip opening side of the recess is formed in the closing direction. A method of manufacturing a torsion beam suspension is disclosed in which the torsion beam suspension is formed into a substantially V-shape or a substantially U-shape.

Japanese Patent No. 6296211 JP 2007-237784 A

Torsion beams are required to be more durable as vehicles become lighter and more dynamic. To meet this demand, torsion beams are increasingly being manufactured from high-strength steel tubes.

In general, when working high-strength steel, cracks are likely to occur at locations in the steel where strain is concentrated during working. In particular, there is room for taking further countermeasures against cracks when manufacturing torsion beams from high-strength steel pipes.

The present invention has been made to solve the above problems, and an object thereof is to provide a method for manufacturing a torsion beam from a steel pipe, which method can suppress the occurrence of cracks. .

In particular, the present inventors diligently studied a method for suppressing cracking that occurs when a torsion beam is manufactured from a high-strength steel pipe. As a result, the present inventors have found that cracks can be prevented from occurring in steel pipes by performing appropriate processing before processing to deform the steel pipes into the final shape. The present invention has been made based on this knowledge and further studies, and the gist thereof is as follows.

(1) a fixed-shape closed cross-section portion whose cross-section orthogonal to the longitudinal direction is a substantially V-shaped or substantially U-shaped closed cross-section having a pair of ear portions and a tip curvature portion at an arbitrary position in the longitudinal direction; and a shape changing portion having a connecting region having a closed cross section that is contiguous with the shape closed cross section and has a different shape from the closed cross section, the method for manufacturing a torsion beam comprising: forming the constant shape closed cross-section portion by applying a displacement from the outside of the steel pipe to the inside of the steel pipe, wherein the step includes a first step of forming a tip curvature portion in the constant shape closed cross-section portion; and a second step of forming a portion other than the tip curvature portion of the fixed shape closed cross-section portion.

(2) The curvature of the pair of ears of the torsion beam at the end of the first step is smaller than the curvature of the ears of the torsion beam at the end of the second step. torsion beam manufacturing method.

(3) The method of manufacturing a torsion beam according to (1) or (2), wherein the curvature of the pair of ear portions of the torsion beam and the curvature of the tip curvature portion are equal at the end of the first step.

According to the torsion beam manufacturing method of the present invention, it is possible to prevent the occurrence of cracks even when manufacturing a torsion beam from a high-strength steel pipe.

1 is a diagram schematically showing a steel pipe and a steel pipe in which a recess is formed; FIG. It is a figure which shows the outline of the metal mold|die and the shape of a steel pipe by a prior art. FIG. 10 is a diagram showing a change in shape when recesses are formed in a steel pipe according to the prior art; It is a figure which shows the outline of the 1st process of the manufacturing method of the torsion beam in this invention. It is a figure which shows the outline of the 2nd process of the manufacturing method of the torsion beam in this invention. FIG. 4 is a diagram showing changes in shape when recesses are formed in a steel pipe by the method of manufacturing a torsion beam according to the present invention; FIG. 4 is a diagram showing the result of calculating the equivalent strain of the torsion beam manufactured by the conventional technology and the torsion beam manufactured by the manufacturing method of the present invention by FEM analysis.

The present invention will be described in detail below. First, a conventional method for manufacturing a torsion beam will be described.

[Conventional manufacturing method of torsion beam]

As shown in FIG. 1, an intermediate portion of a steel pipe 11 as a material is press-molded using a mold to form a concave portion 12 in the steel pipe 11 . The cross section of the concave portion 12 perpendicular to the longitudinal direction of the steel pipe 11 is a substantially V-shaped or substantially U-shaped closed cross-sectional portion having a pair of ear portions and a curved tip portion. FIG. 2 shows the outline of the mold and the shape of the steel pipe. FIG. 2 shows a vertical cross section of the mold and the steel pipe at the position where the fixed shape closed cross section of the steel pipe is formed. The shape of the constant shape closed cross-section portion having the tip curvature portion 13 and the ear portion 14 formed by the molds (upper mold 21 and lower mold 22) used here is almost the same as the final shape of the torsion beam.

FIG. 3 shows a change in shape when the fixed shape closed cross-section portion 12 is formed in the steel pipe 11 . Focusing on the portion 11a of the steel pipe 11, it can be seen that it is bent into a state with a large curvature at the beginning of deformation and then bent back. Although this portion appears to have a flat shape in the final stage of deformation, since strain is introduced by bending-unbending deformation, cracking is likely to occur depending on the material used for the steel pipe 11.

Next, a method for manufacturing a torsion beam according to the present invention for preventing the occurrence of cracks will be described.

[Method for manufacturing torsion beam of the present invention]

The method of manufacturing a torsion beam according to the present invention comprises a constant-shape closed cross-sectional portion whose cross section orthogonal to the longitudinal direction is a substantially V-shaped or substantially U-shaped closed cross-section at an arbitrary position in the longitudinal direction, and a constant-shape closed cross-sectional portion. and a shape changing portion having a connecting region with a closed cross-section having a different closed cross-section shape, wherein at least a part of the steel pipe as a material in the longitudinal direction extends from the outside to the inside of the steel pipe. forming a constant shape closed cross section by imparting a directional displacement.

The step of forming the constant-shape closed cross-section includes a first step of forming the tip curvature portion of the constant-shape closed cross-section, and a second step of forming portions other than the tip curvature portion of the constant-shape closed cross-section. Each step will be described below.

[First step]

The first step is not for shaping the steel pipe as a whole into the final shape of the torsion beam, but for forming the tip curvature portion of the constant-shaped closed cross-section portion. As shown schematically in FIG. 4, a steel pipe 11 is press-formed using dies (upper die 41 and lower die 42). The shape of the tip portion 41a of the upper mold 41 is a shape having a constant curvature. A post-stage portion 41b following the tip portion 41a is a surface substantially parallel to the direction in which the upper die 41 imparts displacement. As a result, in the first step, the steel pipe 11 is deformed by the displacement given by the front end portion 41a of the upper die 41, but depending on the rear step portion 41b, curvature is given to the ear portion having the curvature in the final shape. , the portion that does not have a large curvature in the final shape does not deform significantly.

At this time, in order to suppress large deformation of the portion that does not have a large curvature in the final shape, the curvature given to the ear portion in the final shape should be smaller than the curvature given to the ear portion in the final shape. is preferred. Moreover, it is preferable that the curvature given to the portion which will be the ear portion in the final shape is equal to the curvature of the portion which will be the tip curvature portion in the final shape.

The surface of the rear stage portion 41b does not have to be completely parallel to the direction in which the upper mold 41 applies displacement, but in order not to deform the steel pipe 11 significantly, the angle formed with the direction in which the upper mold 41 applies displacement is − About 5 to 10° is preferable. Here, the angle formed is negative when the rear portion 41b is inclined inward, and is positive when it is inclined outward. The curvature of the tip portion of the upper mold 41 is not particularly limited, but it is preferable that the shape of the tip portion 41a is substantially the same as the tip curvature portion in the final shape of the torsion beam.
[Second step]

The second step, which is different from the first step, is a step of transforming the entire steel pipe into a final shape using molds (upper mold 51, lower mold 52) for shaping the steel pipe 11 into its final shape. The method of this step is not particularly limited, and a known method may be applied. For example, molding by hydroforming is suitable. You may shape|mold by press work. A schematic is shown in FIG. In the first step, the tip curvature portion has a substantially final shape, so the lower mold 52 may be the same as the lower mold 42 used in the first step.

Looking through the first and second steps, according to the conventional torsion beam manufacturing method, the portion 11a is bent into a state with a large curvature at the initial stage of deformation, then bent back, and takes on a flat shape at the final stage. , it can be seen that the torsion beam manufacturing method of the present invention does not undergo large bending-unbending deformation (FIG. 6).

By performing two different steps in this way, bending with a large curvature is not performed at the position where the final shape is almost flat, and a large strain is introduced by bending and unbending. Since there are no cracks during torsion beam manufacturing, cracks can be prevented.

In the above description, the terms "upper die" and "lower die" are used for convenience, but these dies are not limited to being arranged above and below the steel pipe. Needless to say, they may be arranged in the same direction for processing, or may be arranged upside down for processing.

The steel pipe used in the method of manufacturing a torsion beam of the present invention is not particularly limited, but it is suitable for manufacturing a torsion beam using a steel pipe having a plate thickness of about 1.6 to 4.0 mm and a tensile strength of about 590 to 1180 MPa.

When an electric resistance welded steel pipe is used as the steel pipe, the electric resistance welded portion is preferably arranged so as to be the portion with the smallest deformation.

FIG. 7 shows the result of confirming the effect of the present invention by FEM analysis. FIG. 7 shows a steel pipe having a diameter of 92 mm, a plate thickness of 2.0 mm, and a tensile strength of 690 MPa. Equivalent strain at each position is shown.

In the case of the conventional manufacturing method, the equivalent strain was 0.32 at the portion where bending-unbending deformation of the ear portion occurs as shown in (a), but in the case of the manufacturing method of the present invention, (b) As shown, the equivalent strain at the same position was 0.28, confirming that the strain was reduced by about 13%.

REFERENCE SIGNS LIST 11 steel pipe 12 concave portion 13 tip curvature portion 14 ear portion 21 mold (upper mold)
22 mold (lower mold)
41 mold (upper mold)
42 mold (lower mold)
51 mold (upper mold)
52 mold (lower mold)

Claims (2)

A constant shape closed cross-section portion whose cross section perpendicular to the longitudinal direction is a substantially V-shaped or substantially U-shaped closed cross-section having a pair of ear portions and a tip curvature portion at an arbitrary position in the longitudinal direction, and the constant shape closed cross-section. a shape-changing portion having a connecting region having a closed cross-section with a shape different from the closed cross-section, the method for manufacturing a torsion beam comprising:
A step of forming the fixed shape closed cross-section portion by applying a displacement from the outside to the inside of the steel pipe to at least a part in the longitudinal direction of the steel pipe as a material,
The steps are
a first step of forming a tip curvature portion in the fixed shape closed cross section;
a second step of forming a portion other than the tip curvature portion of the fixed shape closed cross-section portion;
with
At the end of the first step, the curvature of the pair of ear portions of the torsion beam and the curvature of the tip curvature portion are equal.
A method of manufacturing a torsion beam, characterized by: 2. The torsion beam according to claim 1, wherein the curvature of the pair of ears of the torsion beam at the end of the first step is smaller than the curvature of the ears of the torsion beam at the end of the second step. manufacturing method.

Images