JPH06142812A - Manufacture of torsion bar for power steering device - Google Patents

Abstract

PURPOSE:To prevent the generation of an internal defect called 'cuppy' in the torsion bar of a power steering device which is manufactured through swaging. CONSTITUTION:Swaging is applied to a steel material which is composed of a carbon steel for mechanical structures or an alloy steel for mechanical structures, and the torsion bar is manufactured. The steel material to be used is the one satisfying the tensile strength of 70kgf/mm<2> or less and the drawing value of 65% or more. Consequently, when the steel material having these conditions is used, the plastic fluidity at the time of swaging is improved and the generation of cuppy defects is controlled, and therefore, highly reliable torsion bars are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a torsion bar used in a power steering system.

[0002]

2. Description of the Related Art Conventionally, a torsion bar for a power steering device has been manufactured by a method such as cutting or grinding, but in recent years, a new method for manufacturing a torsion bar by swaging has been proposed. (JP-A-2-211922). In this method, the grip portion and the parallel portion are press-forged from the front end of the polished steel bar having a constant thickness, and the grip portion following the parallel portion is also press-forged (swaging) at the same time, and the front end grip portion By cutting the length up to the end grip, a plurality of torsion bars are continuously obtained from one polished steel bar.

[0003]

SUMMARY OF THE INVENTION In the above conventional method,
Since the torsion bar is continuously manufactured from a single polished steel bar, effects such as cost reduction can be achieved. However, when a torsion bar for a power steering device is manufactured by swaging, the area reduction rate of the product after processing reaches 60 to 80% with respect to the cross-sectional area of the polished steel bar of the material, so that plastic fluidity When a bad material or a material with poor internal quality is used, internal cracking called "cuppy" may occur in a portion that cannot follow the plastic flow during swaging. When such internal defects (cuppies) occur, there is a problem that the fatigue strength of the torsion bar is significantly reduced.

The present invention has been made to eliminate the above-mentioned drawbacks. By limiting the mechanical properties of the steel material as a material to a specific range, the plastic fluidity is improved, the occurrence of cuppies is suppressed, and the reliability is improved. It is intended to obtain a torsion bar for a high power steering device.

[0005]

A method of manufacturing a torsion bar for a power steering apparatus according to the present invention is characterized in that a steel material made of carbon steel for machine structure or alloy steel for machine structure is swaged so that both ends A torsion bar having a large-diameter connecting portion and a small-diameter spring portion in the middle is manufactured.
In particular, the steel material is characterized in that it has a tensile strength of 70 kgf / mm ² or less and a mechanical reduction ratio of 65% or more.

[0006]

In the above manufacturing method, since the mechanical properties of the steel material used as the material satisfy the above conditions, it is possible to follow the plastic flow during swaging cold plastic working, and thus it is called "cuppy". There is no risk of internal defects.

[0007]

EXAMPLES An example of the present invention will be described below.
FIG. 1 is a diagram for explaining each step of the method for manufacturing a torsion bar 2 for a power steering apparatus (see FIG. 2) according to one embodiment of the present invention. First, in a first step, a steel material as a material is received. , Swaging is performed in the second step, and as shown in FIG. 2, the intermediate small-diameter spring portion 2a and the large-diameter connecting portions 2 at both ends thereof that are respectively connected to the input / output shafts of the power steering apparatus.
b, 2c and the small diameter spring portion 2a and the large diameter connecting portion 2
A torsion bar shape having R portions 2d and 2e connecting b and 2c is obtained.

Subsequently, in the third step, the material is cut and the fourth step is performed.
In the process, quenching and tempering treatment is performed to ensure spring characteristics. In the subsequent fifth step, shot peening is performed after the heat treatment for the purpose of improving the torsional fatigue strength. After the above steps, ultrasonic flaw detection is performed as the sixth step and centerless grinding is performed as the seventh step to complete the torsion bar for the power steering apparatus.

As the steel material received in the first step, carbon steel for machine structure or alloy steel for machine structure is used, and in particular, it is used for forming a torsion bar by swaging which is cold plastic forming. It is preferable to use chromium / molybdenum steel or the like, which has special consideration of plastic slidability and surface scratch removal during cold plastic working. The steel material as the material of the torsion bar is manufactured by the following steps. First, the wire rod obtained by hot rolling is spheroidized by a continuous annealing furnace. Next, a steel bar is obtained by the steps of shot blasting, cold drawing and cutting. Further, a polished steel bar is obtained by performing centerless grinding and eddy current flaw detection. This polished steel bar is used as a material for swaging.

Next, the mechanical properties of the above material (steel material) will be examined. As shown in FIG. 3, the occurrence of the above-described cuppy is related to the area reduction rate during swaging and the material properties (tensile strength and drawing value). When a torsion bar for a power steering device is formed by swaging, the swaging area reduction rate is up to 80.
In order to prevent the occurrence of cuppies, it is essential to limit the tensile strength to approximately 70 kgf / mm ² or less and the aperture value to approximately 65% or more. Become. The hardness is 90H
It is desirable to set it to RB or less. The area reduction rate means a value represented by the following formula. Area reduction = {1- (D / d) ² } x 100 (%) where D: diameter of spring part after swaging (Fig. 2
D) Material diameter (see Figure 2)

Swaging is performed on the steel material having the above mechanical properties. 4 to 6 show an example of an apparatus for performing swaging processing.
The dies 4 are arranged, and the back side of each die 4 is supported by the wedge 6 and the backer 8, respectively. A spring 10 fitted in each hole 4a is interposed between the adjacent dies 4 and urges the circular space (space for receiving the work) formed by the three dies 4 in a direction to expand the circular space. ing. The outer periphery of each backer 8 is a roller 1
When the roller 12 hits the backer 8, the die 4 is pushed toward the center and hits the work (steel material) 14, and when the roller 12 comes off the backer 8, the die 4 moves backward. To do. By repeating such forward and backward movements of the die 4, the work 14 is struck in the diametrical direction to reduce its cross section. As an example of the processing operation, for example, the work 14 held by the chuck 16 is rotated (about 5 rpm) while reciprocating in the left and right directions in FIG. 6, and the die 4 is advanced and retracted at a high speed of several thousand hundreds of times per minute. Move it and hit the work 14. FIG. 7 is a diagram showing a molding state in each processing step in the swaging processing step, and in each of the first to fifth steps, the processing indicated by hatched portions in the drawing is sequentially performed.

After the shape shown in the fifth step in FIG. 7 is obtained by swaging, the above-mentioned third step and the subsequent steps are sequentially performed to complete the torsion bar for the power steering apparatus. In this embodiment, as a material for swaging, a steel material satisfying a tensile strength of about 70 kgf / mm ² or less and a drawing value of about 65% or more is used, so that plastic flowability is good and swaging is performed. It is possible to obtain a highly reliable torsion bar for a power steering device by suppressing the generation of cuppies due to the edging process. The shape of the device for performing the swaging process and each step of the swaging process are not limited to those shown in the drawings, and other processing devices may be used, or different processing steps may be taken.

[0013]

As described above, according to the present invention, the mechanical properties of the steel material as a material for manufacturing the torsion bar by swaging are the tensile strength of 70 kg.
By limiting to those satisfying the condition of f / mm ² or less and the aperture value of 65% or more, the plastic fluidity during swaging processing is improved, the occurrence of cuppy is suppressed, and highly reliable power steering. A torsion bar for the device can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing steps of a method for manufacturing a torsion bar for a power steering apparatus according to an embodiment of the present invention.

FIG. 2 is a front view showing a state in which a steel material as a material is swaged by the above manufacturing method.

FIG. 3 is a graph showing the relationship between the swaging area reduction rate and the material physical properties (tensile strength and drawing value) with respect to the limit of occurrence of cuppies.

FIG. 4 is a vertical cross-sectional view showing a simplified device for performing swaging processing.

FIG. 5 is a front view showing a simplified device for performing swaging processing.

FIG. 6 is a perspective view showing a die of the apparatus.

FIG. 7 is a diagram sequentially showing each step of a swaging process step.

[Explanation of symbols]

 2 torsion bar 2a small diameter spring part of torsion bar 2b large diameter connecting part of torsion bar 2c large diameter connecting part of torsion bar

Claims (1)

[Claims] 1. A carbon steel for machine structure or an alloy steel for machine structure, which has a tensile strength of 70 as a mechanical property.
By swaging the steel material satisfying the conditions of kgf / mm ² or less and the drawing value of 65% or more, a torsion bar for a power steering device having a large diameter connecting portion at both ends and a small diameter spring portion in the middle thereof is provided. Method of manufacturing.