JPH07112232A - Method for partialy forging hollow product - Google Patents

Abstract

PURPOSE:To prevent the defective shape and thickness and the under fill caused by partial upsetting except the working part by making the friction coeefficient between a blank and a mandrel smaller in a partial forging for hollow product. CONSTITUTION:In the partial forging in the axial direction by executing the forging while restricting the hollow blank 1 from the outside with the die and regulating from the inside with the mandrel 3, each of the friction coefficients between the die and the blank and between the blank and the mandrel is adjusted by varying kind of lubricant, coating method and tool temp. At the time of defining muo for the friction coefficient between the die 2 and the blank 1 and mui for the friction coefficient between the blank 1 and the mandrel 3, the above items are adjusted so as to satisfy mui<muo and muo<=0.35 in the case of mui>0.1 and so as to satisfy muo<=0.35 in the case of mui<=0.1. By this method, the pressing-in of the blank 1 with the mandrel 3 is almost eliminated and the upsetting to the part except the working part is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for partially forging a hollow product used for thickening an open end of a pipe-shaped material or a cup-shaped material.

[0002]

2. Description of the Related Art Conventionally, a partial forging method called upset processing has been used to increase the thickness of the end of a pipe-shaped material (for example, Japanese Patent Laid-Open No. 4-4936). This will be described with reference to FIG.

The raw material 1 is heated, and the portions other than the end portions of the raw material 1 are inserted into the small diameter portion 2a of the mold 2 and restrained. Insert the small diameter part 3a of the mandrel 3 into the end of the raw material 1
While controlling the inner surface of the end portion with a, the large diameter portion 3 of the mandrel 3
The end surface of the material 1 is pressed by b, and the end portion of the material 1 is set in the large diameter portion 2b of the mold 2.

[0004]

In the method for partially forging such a hollow product, a portion ahead of the portion to be processed is also installed in the mold to increase the thickness. As a result, the wall thickness and shape become poor, and the original upset amount is insufficient, resulting in lack of thickness.

In order to solve this problem, the constraint by the mold is strengthened, the material flow in the upset direction is regulated, the extra upsetting allowance is secured in consideration of the deformation of the portion other than the processed portion, and the processed portion is not Generally, measures such as making the temperature higher than the processed part to prevent deformation of the non-processed part are taken.

However, if the constraint by the mold is increased, the molding load increases, and in some cases, the material protrudes from the mold through the gap between the mold and the mandrel. The partial forging method disclosed in Japanese Patent Application Laid-Open No. 4-4936 is to apply a lubricant to the outer surface or the inner and outer surfaces of the material in order to prevent this protrusion, but in this method, as will be described later, parts other than the processed part Upsetting cannot be prevented.

On the other hand, the measure for securing an extra upsetting margin is a measure for preventing wall thinning, and is not a measure for preventing upsetting of a portion other than the machined portion, so that a defect in wall thickness and shape cannot be prevented. In addition, the material yield is reduced.

[0008] As a measure for providing a temperature difference between the processed part and the non-processed part, there are problems that heating is troublesome and deformation of the boundary part cannot be accurately controlled.

Due to these secondary problems, none of the conventional measures can be said to be effective measures.

It is an object of the present invention to prevent hollow parts other than the processed part from being swollen without increasing the constraint by the mold and without making a temperature difference between the processed part and the non-processed part. It is to provide a forging method.

[0011]

[Means for Solving the Problems] In order to prevent the upsetting of a portion other than the processed portion regardless of the strengthening of restraint by the mold and the temperature difference, the present inventors conducted various model experiments. As a result, the following findings were obtained.

In pushing the material in the upset direction, which causes upsetting of a portion other than the processed portion, wear between the inner peripheral surface of the mold and the outer peripheral surface of the material, and the inner peripheral surface of the material and the outer peripheral surface of the mandrel. Friction has a great influence. In FIG. 1, friction between the inner peripheral surface of the small diameter portion 2a of the mold 2 and the outer peripheral surface of the material and friction between the inner peripheral surface of the material and the outer peripheral surface of the small diameter portion 3a of the mandrel 3.

Regarding the roles of the mold and the mandrel in these friction regions, the mold restricts the spread of the material and the material flow in the upset direction, while the mandrel conversely expands to the outer peripheral side of the material and pushes in the upset direction. is doing.

Therefore, when the coefficient of friction μo between the mold and the material is small, the material is pushed by the mandrel and the portion other than the processed portion is also installed. Also, when the friction coefficient μi between the material and the mandrel is large, the material is pushed by the mandrel.

Therefore, in order to prevent upsetting of a portion other than the processed portion, it is effective to make the friction coefficient μi of the material and the mandrel smaller than the friction coefficient μo of the mold and the material. That is, by setting μo> μi, upsetting of the portion other than the processed portion can be almost prevented regardless of the constraint strengthening by the mold and the temperature difference. However, this is not the case when the friction coefficient μi between the material and the mandrel is extremely small. That is, μo <μi may be satisfied.

Regarding the friction coefficient μo between the mold and the material,
Restriction is required from the viewpoint of preventing seizure. Japanese Patent Laid-Open No. 4-4
The partial forging method disclosed in Japanese Patent No. 936 enhances the lubricity between the die and the material and reduces the friction coefficient μo between the die and the material. The idea is to make the friction coefficient μo between the material and the mandrel smaller than this friction coefficient μo. Therefore, seizure can be prevented, but upsetting of parts other than the processed part cannot be prevented.

The present invention was made on the basis of the above findings. Partial forging of a hollow product in which a hollow material is restrained by a mold from the outside and regulated by a mandrel from the inside while a part of the material in the axial direction is forged. In the method, when the friction coefficient between the mold and the material is μo and the friction coefficient between the material and the mandrel is μi, when μi> 0.1, μi <μo and μo ≦ 0.35
Is satisfied, and when μi ≦ 0.1, μo ≦ 0.35 is satisfied.

[0018]

FIG. 2 shows the relationship between μo and μi in the present invention. The shaded area is the scope of the present invention.

Regarding μo, it is necessary to be 0.35 or less in order to prevent seizure between the mold and the material.

When μi is 0.1 or less, there is almost no pushing of the material by the mandrel regardless of the size of μo, and upsetting of parts other than the processed part is prevented.

When μi exceeds 0.1, by setting μo> μi, pushing of the material by the mandrel is almost eliminated, and upsetting of parts other than the processed part is prevented.

Μo and μi can be arbitrarily adjusted by changing the type of lubricant, the coating method thereof, the tool temperature, and the like. For example, water-soluble graphite has better lubricity than oil-based graphite. Further, even if the same lubricant is applied to the tool and the material, the lubricity is better than when it is attached only to the tool. Regarding the tool temperature, when the temperature exceeds 300 ° C, the water-soluble graphite becomes difficult to adhere to the tool, and the lubrication performance deteriorates.
If the temperature is higher than 00 ° C, the lubrication performance deteriorates.

The partial forging method of the present invention can be applied not only to the pipe-shaped material but also to the cup-shaped material. Further, not only the thickening processing as shown in FIG. 1, but also the molding processing without thickening such as mouth widening, and the molding processing with thickening can be used.

[0024]

EXAMPLES Examples of the present invention will be shown below, and the effects of the present invention will be clarified by comparison with Comparative Examples.

When the cup-shaped material extruded backward is subjected to the upset process shown in FIG. 1 to increase the thickness of the open end of the material, the friction coefficient μo between the mold and the material and the friction coefficient μi between the mold and the mandrel are variously changed. .

Table 1 shows the processing conditions, Table 2 shows the method of adjusting the friction coefficient, and Table 3 shows the processing results. The friction coefficient was previously obtained by a ring compression test.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

Since No. 1 had μo> 0.35, seizure occurred on the mold. No. 2 has μo ≦ 0.35, but μo <μi
Therefore, the part other than the processed part was set up, and the part was thickened (Fig. 1) and the processed part was lacked. No. 3
Is μi> 0.1, and μi = μo, (μo
(Since the condition of> μi is not satisfied), the portion other than the processed portion was installed, the thickness was increased in that portion, and the processed portion was slightly chipped.

On the other hand, in Nos. 4 to 6, μi> 0.1
However, since the conditions of μo ≦ 0.35 and μo> μi are satisfied, the constraint by the mold is not strengthened, and the temperature difference between the processed portion and the processed portion is not given, Almost no parts other than the processed part were installed, and neither thickening of the part other than the processed part nor lack of thickness of the processed part occurred. Since No. 7 had μi = 0.1, the moldability was good even with μo = μi.

[0032]

As described above, the method for partially forging a hollow product according to the present invention focuses on the relationship between the coefficient of friction between the die and the material and the coefficient of friction between the material and the mandrel, and adjusts the relationship to make the die It is possible to prevent upsetting of the parts other than the processed part regardless of the strengthening of restraint due to and the temperature difference. Therefore, the defective shape and wall thickness and the lack of thickness due to the upsetting of the portion other than the processed portion are prevented, and the secondary problems such as the increase of the molding load and the deterioration of the profile of the temperature boundary portion do not occur.

[Brief description of drawings]

FIG. 1 is an explanatory view of a partial forging method.

FIG. 2 is a graph showing a range of a friction coefficient in the partial forging method of the present invention.

[Explanation of symbols]

 1 Material 2 Type 3 Mandrel

Claims (1)

[Claims] 1. A method of partially forging a hollow material in which a hollow material is restrained from the outside by a die and regulated by a mandrel from the inside, and a part of the material in the axial direction is forged. μo, where μi is the coefficient of friction between the material and the mandrel, μi <0.1 and μi <0.35 are satisfied, and μi ≦ 0.1 is satisfied.
A method for partially forging a hollow product characterized by satisfying 0.35.