JP2000254752A - Die for two stage cold forging and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a die capable of working well without having contact between a material and the die for a shaft part in two stage reduction forging and to provide a forging method by the die which conducts good two stage reduction without generating jamming. SOLUTION: In two stage reduction, when working with a punch stroke specified by S<1.2.D0+H1, the die, which satisfies the formula of 271R1+281R2+221θ1+1000θ2-30837<0 wherein a cross sectional area reduction R1(%) of a first tapered part and a die half angle θ1 (deg) of the die, a cross sectional area reduction R2(%) of a second tapered part and a die half angle θ2 (deg) of the die, is excellent in two stage reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a two-stage shaft having different diameters while reducing the diameter of a cylindrical material by cold forward extrusion, whereby the mold does not contact the material at the first shaft. The present invention relates to a mold excellent in two-step drawing workability and a processing method using the mold.

[0002]

2. Description of the Related Art When a gear shaft or the like is manufactured by forging, a two-stage drawing process is performed in a preliminary forming process. In the two-stage drawing process performed by cold forging, since it is desired to limit the surface pressure of the punch below the breaking limit,
It is important to design the dies and the material as little as possible. This two-stage drawing is a process in which two steps of surface reduction are performed in a single forging process. However, if the taper is designed with an inappropriate cross-section reduction ratio and a half angle of the die, the material expands in the first shaft. Touch the die with
In some cases, molding cannot be performed due to the surface pressure exceeding the breaking limit of the punch and die. In such a case, that is, when the material comes into contact with the die at the first shaft portion in the two-stage drawing, it is generally determined that the two-stage drawing cannot be performed.

Whether or not the material is in contact with the first shaft portion depends on the die half angle of the second taper portion and the reduction rate of the cross section, and the degree of work hardening in the material caused by the surface reduction processing of the first taper portion. It is difficult to predict because it works. Work hardening occurs unevenly near the surface of the material, and the degree of hardening caused by the hardening is greatly affected by the half angle of the die and the reduction rate of the cross section of the first tapered portion. That is, the deformation behavior of the material at the first shaft portion differs depending on the combination of the half-width of the dies of the first and second tapered portions and the reduction ratio of the cross section. Conventionally, it has been difficult to estimate the effects of these factors and predict the optimal mold shape. For this reason, hitherto, it has been common practice to repeatedly perform processing experiments using actual machines and to select an optimal mold shape and material empirically, which greatly increases the development cost and time.

There is no problem in the case where the material is constantly swelling in the width direction at the first shaft portion during the pressing, but the material continues to swell at the first shaft portion during the pressing and the material and the die are squeezed. May come into contact with each other, making two-stage drawing impossible. For this reason, a method of using a range in which a clogging does not occur in an unsteady deformation region by performing rolling down with a short stroke length such as a former is also applied. Therefore,
An appropriate punch stroke length is also an important factor in the two-step drawability, but the determination of the punch stroke length also required the development of trial and error.

[0005]

When performing forging two-step drawing, it is desired to design the diameter of each shaft portion in an arbitrary combination. However, the influence of each factor affects the forming conditions in a complicated manner, and each taper portion is formed. It is difficult to obtain the optimum die half-angle and the optimum cross-section reduction rate at the same time, and an increase in time and cost in die design is inevitable. Therefore, an object of the present invention is to clarify a combination of a half angle of a die and a reduction ratio of a cross-section that can be formed in a two-stage drawing process, and to provide a mold that can be favorably processed without a material being in contact with a die at a first shaft portion. To provide. Also, even if machining in the unsteady deformation region in the mold,
An object of the present invention is to provide a forging method at a stroke length of a punch that can obtain good two-stage drawability without causing clogging.

[0006]

SUMMARY OF THE INVENTION The present invention provides a CAE (calculation assisting technology), which has undergone many technological innovations in recent years and has a remarkable technological progress, so that the die half angle and the cross section of the first and second tapered portions of a two-stage drawing die are reduced. Using the rate as a parameter, the forming limit of the two-stage drawing when the material was pushed in with a punch stroke length at which the material and the die did not come into contact with each other in the first shaft portion even in a region where the material undergoes unsteady deformation was examined. The molding limit was expressed by a regression equation so that the obtained results could be used under arbitrary conditions, and the mold shape at the molding limit of the two-stage drawing was derived. By comparing the obtained result with the actual forging result, it was possible to obtain an index of a mold having excellent two-step drawing workability.

That is, a means for solving the above-mentioned problems of the present invention is a metal used in a two-stage drawing process for forming two-stage shafts having different diameters while reducing the diameter of a cylindrical material by cold forward extrusion. In the mold, the cross-sectional reduction rate R ₁ (%) and the half-angle θ ₁ (deg) of the die, and the cross-sectional reduction of the second tapered portion of the die when processing with the punch stroke length S (mm) of Equation 2 A mold excellent in two-stage drawability, characterized by satisfying the following expression 1 between the ratio R ₂ (%) and the die half angle θ ₂ (deg).

[0008]

## EQU1 ## 271R ₁ + 281R ₂ + 221θ ₁ + 1000θ ₂ -30837 <0

According to the second aspect of the present invention, when a material having a diameter D ₀ (mm) is processed in the two-stage drawing die according to the first aspect, the length H of the first shaft portion of the die is set. A two-stage drawing cold forging method characterized in that forging is performed such that the stroke length S (mm) of the punch with respect to ₁ (mm) satisfies Equation 2.

[0010]

S <1.2 · D ₀ + H ₁

The operation of the present invention will be described below.
FIG. 1 is an explanatory diagram showing a two-stage aperture model. As shown in FIG. 1, the diameter of the first shaft portion 6 of the mold or die insert 3 and 1.05 times the diameter D ₁ out first tapered portion. The material 1 is pushed into the die insert 3 by the punch 2, so that the initial diameter D ₀ of the material 1 is reduced to the diameter D ₁ , which is the outlet diameter D ₁ of the first taper portion 4, and the second taper portion 5. The material 1 is transferred from the diameter D ₁ to the diameter D ₂ which is the second tapered portion outlet diameter D _2.
Change to At this time, the cross-sectional reduction rates R ₁ (%) and R ₂ (%) of the material 1 in each shaft portion are defined by Expressions 3 and 4, respectively.

[0012]

Equation 3] _{R 1/100 = 1- (D} 1 / D 0) 2

[0013]

Equation 4] _{R 2/100 = 1- (D} 2 / D 1) 2

[0014]

[Table 1]

Table 1 shows the limitations of the two-step drawing.
And the cross-sectional reduction rate R of the first tapered portion 4 ₁(%) And half die
Angle θ₁(deg), the cross-sectional reduction rate R of the second tapered portion 5_Two(%)and
Die half angle θ_TwoWhen each parameter of (deg) is changed variously
In the case where a two-stage drawing is possible, that is, the material 1
When processing is performed without contacting the dies,
The material 1 swells at the first shaft 6 with the processing and the die
And two-stage drawing is not possible because of the closed extrusion
The case is indicated by x. However, ● indicates that material 1 expands with the reduction.
Although unsteady deformation continues to occur,
Molding is possible with a punch stroke length S. That is,
● is the first shaft part at the stroke length S shown in Equation 5.
6 allows good two-stage drawing without contact between the material 1 and the die
And the regression equation for the molding limit is
It becomes 6.

[0016]

S = 1.2 · D ₀ + H ₁

[0017]

## EQU6 ## 271R ₁ + 281R ₂ + 221θ ₁ + 1000θ ₂ -30837 = 0

Accordingly, when rolling down with the stroke length S represented by the inequality of the equation (2), the range of ● or が with good two-step drawability can be represented by the inequality of the equation (1).

[0019]

## EQU1 ## 271R ₁ + 281R ₂ + 221θ ₁ + 1000θ ₂ -30837 <0

[0020]

S <1.2 · D ₀ + H ₁

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. The two-stage drawing is performed by cold forging,
Steel 1 is used as the material 1. The material 1 is pressed into the die insert 3 by the punch 2 by the punch stroke length shown in Table 2 to change the material initial diameter D ₀ to the first tapered portion exit diameter D ₁ , and further passes through the first shaft portion 6. Then, the diameter is reduced to the diameter D ₂ of the second taper portion, and the diameter of the second shaft portion 7 is formed.
The punch 2 and the die insert 3 are carbide tools, and the material is SCM415. The deformation resistance value is σ = 88
0.94ε ^0.114 . Lubrication is performed by applying a metal soap to a zinc phosphate film. Material 1 and die insert 3 of tool
Is approximately μ = 0.10.

[0022]

[Table 2]

[0023]

EXAMPLE A two-stage drawing was carried out under the conditions shown in FIG.

Example: Test condition no. 1. Test conditions N
o. 2, test condition No. 3 and test condition No. 3 Under the conditions satisfying the formulas 1 and 2 as shown in FIG. 4, the contact between the die insert 3 and the material 1 was prevented by the first shaft portion 6 in each case, and the two-stage drawing was completed as intended. Note that the material in this example is SCM415 of steel as shown in Table 2, but SCM420 and SUS304 and SUS316 are also used as SCM415 as steel.
Similarly to the above, two-step drawing can be performed under the conditions satisfying the formulas 1 and 2.

[0025]

## EQU1 ## 271R ₁ + 281R ₂ + 221θ ₁ + 1000θ ₂ -30837 <0

[0026]

S <1.2 · D ₀ + H ₁

Comparative Example 1: Test condition no. 5 and test condition No. 5 Under the conditions shown in Expressions 2 and 7, as in the case of 6, in both cases, the material was swollen in the first shaft portion 6 and came into contact with the die insert 3 together with the processing, so that the two-stage drawing was impossible.

[0028]

S <1.2 · D ₀ + H ₁

[0029]

(Formula 7) 271R ₁ + 281R ₂ + 221θ ₁ + 1000θ ₂ -30837> 0

Comparative Example 2: Test condition no. 7 and test condition no. As shown in FIG. 8, under the conditions represented by Expressions 1 and 8, the two-stage drawing was impossible because the material expanded in the first shaft portion 6 and came into contact with the die insert 3 during processing.

[0031]

## EQU1 ## 271R ₁ + 281R ₂ + 221θ ₁ + 1000θ ₂ -30837 <0

[0032]

S> 1.2 · D ₀ + H ₁

[0033]

As described above, according to the present invention, a mold having excellent two-stage drawing and a punch stroke length which can be processed without contact between the material and the die at the first shaft portion in the two-stage drawing. However, the processing design and the die design of the two-stage drawing can be performed in a short time and at low cost, and an excellent effect which has not been achieved in the past can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an embodiment of the present invention;
3 shows a model of a stepped stop.

[Explanation of symbols]

1 material 2 punch 3 die insert 4 diameter theta ₁ out initial diameter D ₁ first tapered portion of initial height D ₀ material of the first tapered portion 5 second tapered portion 6 first shaft portion 7 second shaft portion L material No. 1 taper part die half angle D ₂ second taper part exit diameter θ ₂ second taper part die half angle H ₁ length of first shaft part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4E087 AA10 BA15 BA17 CA17 CA22 CB03 CB11 CB12 DA05 DB06 DB24 EC17 EC18 EC43 EC50 EC54 ED01 ED31 ED33 HA31

Claims (2)

[Claims] In a two-stage drawing process, a first tapered portion is formed.
Section reduction rate R₁(%) And die half angle θ₁(deg), 2nd table
Cross section reduction rate R_Two(%) And die half angle θ _Two(deg)
Satisfying the molding limit equation of Equation 1 as a parameter.
A two-stage drawing cold forging die. (Equation 1) 271R₁+ 281R_Two+ 221θ₁+ 1000θ_Two-30837 <0 2. The method according to claim 1, wherein, when a material having a diameter D ₀ (mm) is machined in the two-stage drawing die, the first die of the die is used.
Punch stroke length S with respect to shaft length H ₁ (mm)
(2) a two-stage drawing cold forging method, wherein (mm) is forged such that a relationship satisfying Expression 2 is satisfied. S <1.2 · D ₀ + H ₁