JP2004091929A - Sintering and cold forging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a sintered product of high density. <P>SOLUTION: Metal powder is subjected to temporary compression molding inside a die to form a preliminary preform. A lubricant is applied to the preliminary preform, and the preliminary preform coated with the lubricant is subjected to normal compression molding inside a die. Next, the preliminary preform subjected to the compression molding is temporarily sintered to form a sintered preform for cold forging. The sintered preform is subjected to cold forging, so that the sintered product is produced. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a sintering cold forging method for producing various sintered products, and more particularly to a sintering cold forging method capable of obtaining a sintered product having a high density composition.

  The sintering cold forging method is to form a sintered preform for cold forging by compression molding metal powder and then subject the preform to cold forging and sintering to obtain a final sintered product. Therefore, in order to obtain a product having high mechanical strength, it is desired to obtain a sintered product having a high density composition.

  By the way, in this sintering cold forging method, since the forming and the cold forging of the preform are performed in the die, it is necessary to pay attention to the prevention of seizure between the preform and the die.

Therefore, for example, Patent Document 1 discloses that a preform preformed by compression-molding a metal powder to which 1% of a lubricant is added and mixed is temporarily sintered to form a sintered preform for cold forging. An improved technique for cold forging and sintering after applying a lubricant to the reform is disclosed. According to this improved technique, the cold forging step comprises a temporary compression molding step and a main compression molding step, and between the temporary compression molding step and the final compression molding step, Prior to the forming step, the lubricant is suctioned off from the sintered preform by negative pressure. This prevents the lubricating oil remaining in the preform from crushing and eliminating the minute voids inside the preform to prevent the preform from becoming porous, thereby increasing the density of the product. As a result, a product having a density of 7.4 to 7.5 g / cm ³ is obtained after cold forging.
JP-A-1-123005.

That is, according to the conventional example, 1% of a lubricant is added to the metal powder for compression molding of the preform. This is effective to prevent seizure between the preform and the die when the preform is compression-molded. Crushing disappears, and a high-density preform cannot be obtained. For this reason, when a lubricant is applied to the surface of the preliminary preform to prevent seizure when the preliminary preform is cold forged, the lubricant penetrates into the interior of the preliminary preform, and the lubricant is applied during cold forging. This hinders the increase in density. Therefore, according to the conventional example, the lubricant is sucked and removed before the main compression molding step of the cold forging to increase the density, and the density of the product obtained after the cold forging is increased to 7. It is about 4 to 7.5 g / cm ³ .

  By the way, in order to obtain a sintered product having a further high-density composition by the manufacturing method of the conventional example, it is necessary to increase the forming pressure of the cold forging, and there is a possibility that the product may be cracked during the cold forging. is there. According to the study of the inventors, it has been found that it is important to increase the density of the preform before cold forging in order to obtain a sintered product having a higher density composition.

  However, in the above-mentioned conventional example, the lubricant added at 1% to the metal powder for compression-molding the preform prevents the crushing and extinction of the minute space inside the preform at the time of compression molding. It becomes difficult to obtain. As a result, it becomes difficult to obtain a sintered product having a high density composition after cold forging.

  The present invention has been devised in view of the above conventional circumstances, and has as its object to provide a sintering cold forging method capable of obtaining a sintered product having a higher density composition.

  Therefore, a first aspect of the present invention provides a temporary molding step in which a lubricant and carbon are mixed, and the lubricant is subjected to temporary compression molding in a die of 0.6% or less of metal powder to form a preform. Then, directly, a lubricant application step of applying a lubricant to the preliminary preform, a main molding step of main compression molding the preliminary preform coated with the lubricant in a die, and the main compression molded preliminary preform Producing a sintered product by temporarily sintering to obtain a sintered preform for cold forging, and a cold forging step of cold forging the sintered preform. It is assumed that.

Further, the invention according to claim 2 is characterized in that the density of the main molding step in which the preliminary preform is fully compressed is 7.4 g / cm ³ or more.

Here, in order to obtain a sintered product having a high density, it is preferable not to add a lubricant to the metal powder, but when a lubricant is mixed and added, the content is set to 0.6% or less. The density of the pre preform metal powder obtained by temporary compression molded in die, 5.5 g / cm ^3, preferably about a 5.0~6.5g / cm ^3. When the density of the preform is increased in the preliminary molding step, the lubricant can be prevented from entering the preform as much as possible in the lubricant application step, but the amount of the lubricant added to the metal powder is small. Therefore, seizure is likely to occur between the preform and the die during the temporary molding.

  As the lubricant applied to the preliminary preform, various lubricants used for ordinary cold forging, such as zinc stearate, can be applied.

In the main forming step, the preliminary preform coated with the lubricant is subjected to main compression molding to increase the density of the preform to preferably 7.4 g / cm ³ or more. If the density in the main forming step is low, the lubricant applied to the sintered preform for cold forging before the cold forging step enters the preform, and the density of the product in the cold forging step is reduced. Is not preferred in increasing the

  The preliminary sintering step is preferably performed at 700 to 900 ° C. or lower to prevent diffusion of carbon and obtain a sintered preform for cold forging having a predetermined hardness.

In the cold forging step, after applying a predetermined lubricant to the sintered preform for cold forging, the sintered preform for cold forging is pressure-formed in a die. In the cold forging step, since the density of the preliminary preform is increased to 7.4 g / cm ³ or more, it is possible to forge to a density of 7.5 g / cm ³ or more, and a product having a high-density composition is easily manufactured. Is obtained.

  According to the present invention, a sintered product having a high density composition can be easily obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a process explanatory view of a sintering cold forging method showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a temporary forming step. In the temporary forming step 1, a metal powder is filled in a temporary forming die, and the powder is compacted in the die to form a preliminary preform. When a lubricant is mixed and added to the metal powder, the content is set to 0.6% or less. Increasing the amount of lubricant makes it difficult to increase the density of the resulting preform. In the temporary forming step, a preliminary preform having a density of 5.0 to 6.5 g / cm ³ is formed.

  2 is a lubricant application step. In the lubricant applying step 2, a lubricant such as zinc stearate is applied to a predetermined portion of the preliminary preform obtained in the temporary forming step 1.

3 is a main molding step. In the main forming step 3, the preform to which the lubricant has been applied is inserted into the main forming die and subjected to main compression molding to increase the density of the preform to 7.4 g / cm ³ or more.

  Reference numeral 4 denotes a temporary sintering step of temporarily sintering the preliminary preform having the increased density in the main molding step 3. This preliminary sintering step 4 is performed in a reducing atmosphere at 700 to 900 ° C. to prevent diffusion of carbon and obtain a preform for cold forging having a predetermined hardness.

5 is a cold forging process. The cold forging step 5 is performed by applying a lubricant to a predetermined portion of the cold forging preform after the preliminary sintering step 4 is completed, and inserting the cold forging preform into a forging die. The molding pressure in this case can be variously selected depending on the density of the final product, but in order to obtain a product having a density of 7.5 g / cm ³ or more, pressure molding (forging) is performed at a pressure of 7 ton / cm ² or more. You.

Prior to the cold forging in the cold forging step 5, a lubricant is applied to a predetermined portion of the preform for cold forging in the same manner as in normal cold forging. According to the embodiment, since the density of the preform for cold forging is increased to 7.4 g / cm ³ or more, the applied lubricant stays on the surface without entering the inside of the preform. As a result, the lubricant can lubricate between the preform and the die during cold forging to prevent seizure, and an effective cold forging operation is achieved. Further, since the lubricant does not enter the preform, it is advantageous to make it difficult for the lubricant that has entered the preform to prevent the collapse and disappearance of the minute voids during forging and increase the product density. To be avoided.

Thus, in the cold forging step 5, a product having a density of 7.5 g / cm ³ or more can be easily obtained.

  The product after the cold forging step 5 is sintered at 1100 ° C. to 1300 ° C. in the main sintering step 6 and further subjected to a predetermined heat treatment in a heat treatment step 7.

As a result, a product having a high-density composition in which the density of the sintered body is 7.5 g / cm ³ or more can be easily obtained.

  The results of an experiment under the following conditions will be specifically described.

A metal powder mixed with 0.2% of a lubricant was filled in a die and compacted to form a preform having a density of 5.5 g / cm ³ . After applying zinc stearate to the preliminary preform, the preform is subjected to pressure molding at a pressure of 8 ton / cm ² in the die of the final molding step 3, whereby a preliminary preform having a density of 7.45 g / cm ³ is obtained. Was.

Here, the amount of the lubricant mixed and added to the metal powder was changed, and the amount of the mixed lubricant was 0.2%, 0.3%, 0.4%, 0.5%, and 0.75%. When a certain metal powder was preliminarily compression-molded to form various preliminary preforms and the preliminary preform was fully compression-molded, the relationship between the molding pressure and the density was as shown in FIG. . That is, when 0.6% of the lubricant was mixed and added, a preform having a density of 7.41 g / cm ³ was obtained by setting the molding pressure to 10 ton / cm ² . That is, in order to obtain a preform having a density of 7.4 g / cm ³ at a molding pressure of 10 ton / cm ² , it is possible to obtain a result in which 0.6% of a lubricant can be mixed and added to the metal powder. Was done.

The preliminary preform, that is, the preliminary preform having a density of 7.45 g / cm ³ , is temporarily sintered in a reducing atmosphere at 700 to 900 ° C. to form a sintered preform for cold forging. After applying a lubricant to the sintered preform for use, the product was subjected to pressure molding (cold forging) at a pressure of 7 ton / cm ^{2 in} a die, and as a result, a product having a density of 7.62 g / cm ³ was obtained. When the molding pressure was increased to 10 ton / cm ² , a product having a density of 7.64 g / cm ³ was obtained. When the molding pressure was increased to 14 ton / cm ² , a product having a density of 7.66 g / cm ³ was obtained.

Since the sintered cold forging method according to the present invention can easily obtain a sintered product having a high density composition, a sintered cold forging method for producing various sintered products, particularly a sintered product having a high density composition, It can be conveniently applied to the sintering cold forging method that can be obtained.

It is a process explanatory view of a cold forging sintering method showing an embodiment of the present invention. FIG. 3 is a diagram showing a relationship between molding pressure and density obtained in a main molding step, using an amount of a lubricant mixed and added to metal powder as a parameter.

Explanation of reference numerals

1 Temporary Forming Step 2 Lubricant Application Step 3 Main Forming Step 4 Temporary Sintering Step 5 Cold Forging Step 6 Main Sintering Step

Claims (2)

A lubricating agent and carbon are mixed, and the lubricating agent is preliminarily compression-molded in a die to form a preliminary preform with a metal powder of 0.6% or less;
Then, directly, a lubricant application step of applying a lubricant to the preliminary preform,
A main molding step of main compression molding the preliminary preform coated with the lubricant in a die,
Temporary sintering step of temporarily sintering the compression-formed preform to obtain a sintered preform for cold forging,
A cold forging step of cold forging the sintered preform to produce a sintered product. A sintering cold forging method, wherein a density of a main forming step in which a preliminary preform is fully compressed is 7.4 g / cm ³ or more.

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