JPH06344068A - Die for cold forging - Google Patents

Abstract

PURPOSE:To shorten a process because a die member is unnecessary to manufacture it by dividing from the first stage, by arranging notch on the outer peripheral part crossed on the plane passing through a stress concd. part generated in the inner diameter part of the die member as a means for amplifying the stress generated at the stress concd. part. CONSTITUTION:The die member 1 has the notch 4 for amplifying the stress generated at the stress concd. part on the outer peripheral part which is perpendicular to the axial direction of the die member 1 and is crossed on the plane passing through the stress concd. part 3 generated in the inner diameter part 5 of the die member 1. At the time of heating by using the die, uniform and neat crack runs to the tip part of the notch 4 from the stress concd. part in the die member by the load and the die member 1 can be divided to the upper and the lower parts in the inner part of the die. As a result, the die for cold forging composed of high accurate split type die member without the difference of step on the split surface as the upper and the lower mating parts can be obtd., and the reduction of number of the parts and the shortening of die making processes can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal mold for plastic working, in particular, a metal mold used for cold forging.
The present invention relates to a cold forging die subjected to stress concentration.

[0002]

2. Description of the Related Art Cold forging involves applying pressure to a metal material with a die tool at room temperature or below the recrystallization temperature of the material.
It is a processing method of extruding or filling along the shape of a mold member to make an article of a predetermined shape.

Generally, since a die for cold forging has a large forging pressure, the outer periphery of the die member is reinforced by a cylindrical member to prevent the die member from being damaged. However, in the case where there is a portion where stress is concentrated due to forging pressure, such as a sudden change in cross section, of the inner diameter portion of the die member, uneven lateral cracks occur in that portion, and this causes The crack becomes large and the mold member becomes unusable.

Conventionally, the structure of the mold member for preventing this kind of cracking is as described in "Compression mold" published by Japan Machinist Co., Ltd. A split mold member is used which is divided into and combined with each other.

[0005]

In the method of dividing the mold member into the upper mold and the lower mold from the beginning as in the prior art, the upper mold and the lower mold are separately arranged in order to obtain the accuracy of the mold. Since it has to be processed with high precision, a die manufacturing process is required more than an integral die member, and the die manufacturing cost becomes high. Also, in order to prevent cracking and seizure that occur when forging hard-to-process materials such as stainless steel, restrictions on the processing rate at the section where the cross-section of the inner diameter of the die member suddenly changes and application of lubricant such as molybdenum disulfide to the pressed material Are required, and the processing cost becomes high. On the other hand, in order to prevent cracking and seizure, a coating treatment such as TiN (titanium nitride) or TiC (titanium carbide) may be performed on the inner diameter of the die member. In this case, the die for cold forging is used. When the coating treatment is performed after the completion of manufacturing, foreign matter such as cutting powder is jetted into the coating treatment furnace from the divided surfaces of the upper die and the lower die of the die member, and the treatment furnace is contaminated. After performing the coating process on the upper die and the lower die alone, the upper die,
If a cylindrical member is press-fitted to the outer periphery of each lower die, the inner diameter joints of the upper die and the lower die do not match due to variation in dimensions due to the press-fitting, and a step occurs, which causes seizure. Also, the coating must be removed to correct the step. As described above, it is almost impossible to manufacture a cold forging die which is coated.

It is an object of the present invention to reduce the number of parts of a cold forging die, shorten the die manufacturing process and reduce the die manufacturing cost, and have a coating process in a divided type. It is to provide a die for cold forging with high accuracy and long life.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a cold forging die in which a die member is reinforced at least once with a tubular member on the outer periphery of the die member.

The mold member according to the present invention has an outer peripheral portion which is perpendicular to the axial direction of the mold member and which intersects with a plane passing through a stress concentration portion generated in the inner diameter portion of the mold member, A notch is provided as a means for amplifying the stress generated in the stress concentration portion.

[0009]

According to the cold forging die according to the present invention, when it is manufactured as an integrated die member having a notch in the outer peripheral portion and completed as a cold forging die, it is pressed. A uniform and clean crack runs from the stress concentration part of the mold member to the tip of the cut under load, and the mold member can be divided into upper and lower parts inside the mold. As a result, it is possible to obtain a cold forging die including a highly precise split die member having no step on the split surfaces serving as the upper and lower seams.

[0010]

EXAMPLE A die for cold forging according to an example of the present invention will be described below.

FIG. 1 shows the structure of a cold forging die according to this embodiment. The mold member 1 has a large-diameter inner wall 10, a small-diameter inner wall 11, an inner diameter part 5 composed of a stress concentration part 3, and an outer peripheral taper surface of the mold member 1 having a notch 4, which is subjected to a forging load from a pressed material 14. It has twelve. The outer peripheral taper surface 12 of the mold member 1 and the inner peripheral taper surface 13 of the tubular member 2 are press-fitted with the taper to form a cold forging mold.

FIG. 2 is a plan view of (a) using a cold forging die.
It shows that the forging part 15 shown in (b) can be obtained from the to-be-pressed material 14 shown in FIG.

FIG. 3 shows a partially cutaway perspective view of the die member 1 made of a superhard material. The same parts as those in FIG. 1 are designated by the same reference numerals. The mold member 1 has a notch 4 on the entire circumference of the outer peripheral taper surface 12, and the inner diameter portion 5 composed of the large diameter inner wall 10, the small diameter inner wall 11 and the stress concentration portion 3 is made of TiN (titanium nitride), It is coated with TiC (titanium carbide) or a composite layer thereof. Here, a manufacturing process of the mold member 1 to be coated will be described. First, in the die member 1, the inner diameter portion 5 is roughly processed, and the outer peripheral tape is
After finishing the finishing surface 12 and the notch 4, the mold member 1
The outer peripheral taper portion 12 is press-fitted into the inner peripheral taper surface 13 (FIG. 1) of the tubular member 2 (FIG. 1) and temporarily assembled. next,
In the temporarily assembled state, the inner diameter portion 5 of the mold member 1 is finished to have a predetermined size in consideration of the coating thickness. After finishing, the mold member 1 is pulled out from the tubular member 2 and subjected to a coating process to complete the manufacturing process of the mold member 1. Incidentally, the processing of the notch 4 may be performed before or after the mold member 1 is extracted from the tubular member 2 and coated. Further, if the notch 4 is processed before the sintering of the cemented carbide material, the material is soft and the processing is easy. Notch 4
Can be processed with a cutting device such as a micro cutter.

FIG. 4 shows a vertical cross-sectional view of a main part of the mold member 1.
The same parts as those in FIG. 1 are designated by the same reference numerals. Mold member 1
The notch 4 processed into the outer peripheral taper surface 12 passes through the joint between the inner corner R receiving the stress concentration and the large-diameter inner wall 10, and on the virtual surface 20 vertical to the axial direction, or in the vicinity thereof. The notch tip 6 is preferably located. It is desirable that the shape of the cut 4 is, for example, a triangular shape having a depth h and a tip angle θ, and that the entire circumference is substantially uniform. If the depth of the notch 4 is too deep, the die member 1 may be damaged due to the influence of the press-fitting load when the die member 1 and the tubular member 2 are combined. Therefore, the large-diameter inner wall of the die member 1 1 / thickness t
3 is good. Further, the smaller the tip angle θ of the cut 4 is, the more uniform the mold member 1 can be by the stress concentration on the cut tip 6, but it is sufficient if it is practically 30 ° or less.

FIG. 5 shows an example of the shape of the notch 4. It is desirable that the tip angle θ of the notch 4 be distributed vertically with respect to the virtual surface 20, but it may be offset toward the lower side as shown in FIG. Further, as shown in (c), the shape may be a parallel cut with the tip being r. However, it is desirable that the tool r at the tip of the cut shown in (d) is as small as possible.

FIG. 6 shows the structure of the cold forging die after the die member 1 is divided by the forging load. The same parts as those in FIG. 1 are designated by the same reference numerals. When the cold forging die described with reference to FIG. 1 is subjected to a forging operation, a split surface 30 that is a uniform lateral crack is generated in the cut 4 from the stress concentrating portion 3 in several shots or several tens of shots, and the die member 1 is divided into an upper die 1a and a lower die 1b with this dividing surface as a boundary, and a cold forging die composed of divided die members is obtained.

FIG. 7 shows another embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals. The mold member 1 has two stress concentrating portions 3 and two notches 4 on an imaginary plane passing through the stress concentrating portions 3, and is divided into three when a forging load is applied. Further, a plurality of tubular members 2 are also configured. Further, the combination of the die member 1 and the tubular member 2 may be straight press fitting, shrink press fitting, or taper press fitting.

[0018]

According to the present invention, since it is not necessary to divide the die member from the beginning, the number of parts is reduced, the die manufacturing process is shortened, and the die material cost and the production cost are reduced accordingly. It is possible to provide a cold forging die capable of achieving the above.

Further, it is possible to provide a mold for cold forging which is a split mold and which has a coating process which requires no lubricant and has a high precision and a long life.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of a cold forging die according to an embodiment of the present invention.

FIG. 2 is a perspective view of a pressed material and a forged component during the cold forging of FIG.

3 is a partially cutaway perspective view of the mold member of FIG. 1. FIG.

FIG. 4 is a longitudinal sectional view of a main part of the mold member of FIG.

5 is a shape view of a cut of the mold member of FIG. 1. FIG.

FIG. 6 is a vertical cross-sectional view showing the structure of the cold forging die after the die members of the cold forging die of FIG. 1 are divided by the pressure load.

FIG. 7 is a vertical cross-sectional view of a cold forging die showing another embodiment.

[Explanation of symbols]

1 ... Mold member, 2 ... Cylindrical member, 3 ... Stress concentration part,
4 ... Notch 5 ... Inner diameter part, 6 ... Notch tip, 20 ... Virtual surface,
30 ... Dividing surface.

Claims (4)

[Claims] 1. A mold member and a mold for cold forging in which a cylindrical member is reinforced at least once or more on the outer periphery of the mold member,
Occurring in the stress concentration portion at the outer peripheral portion where the die member is perpendicular to the axial direction of the die member and intersects with a plane passing through the stress concentration portion generated in the inner diameter portion of the die member A cold forging die having a means for amplifying stress. 2. A die for cold forging according to claim 1, wherein the means for amplifying the stress is a notch provided in the outer peripheral portion. 3. The cold forging die according to claim 1, wherein the die member is made of a super hard material. 4. The cold forging die according to claim 1, wherein the inner diameter portion of the die member is coated.