JPH0873902A - Method for molding powder by metal mold - Google Patents

Abstract

PURPOSE: To obtain sintered parts having a uniform density and high accuracy by using an inexpensive press machine and molding powder molded goods having intricate shapes and a large size by metal molds. CONSTITUTION: The sintered hard alloy to be packed into the female mold of the metal molds to be pressurized by the press machine is mixed and kneaded with an org. binder of 30 to 60vol.% in volume of the sintered hard alloy. As a result, the flow property of this mixture is increased and the pressurizing force by the press machine is rapidly transmitted to the inside of the metal molds and, therefore, the powder molded goods having the uniform density and the excellent dimensional accuracy are obtd. even if the shape is intricate and the size is large. The sintered parts 2 having the uniform density and the excellent dimensional accuracy are eventually obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a powder molding method using a metal mold, more specifically, to reduce cracking.
Moreover, the present invention relates to a powder molding method using a metal mold capable of molding a powder molded product having a uniform density at a lower pressure.

[0002]

2. Description of the Related Art As is well known, powder molding methods include, for example, a die press molding method in which a hydraulic press machine is used for embossing, and an organic binder is mixed with the powder to impart plasticity,
There are known an extrusion molding method in which a mixture is extruded from a nozzle to be molded, an injection molding method in which a mixture of a powder and an organic material is heated to a high temperature to be liquefied, and the mixture is poured into a mold under pressure to be molded. By the way, in the case of powder metallurgy, it is desirable to shape the powder into a shape as close to the final product as possible in order to reduce the number of processing steps in the subsequent process. This is especially required for powder molded products made of hard materials such as cemented carbide and ceramics, which harden due to sintering and become difficult to machine. Therefore, the size of the powder filling chamber of the mold is set in consideration of the shrinkage amount of the powder molded product due to sintering.

Incidentally, when powder is molded by a die press molding method, it is general that an organic binder is not added to the powder because the powder is not required to have so much fluidity. If an organic binder is added to the powder, it is inevitable. Since the density of the powder molded product becomes low and a degreasing step is required, it is said that it is better not to add it as much as possible. However, since some fluidity is required when filling the mold, paraffin is added to the powder in an amount of several Vol% of the volume of the powder.

[0004]

The above-mentioned powder molding methods are useful as such, but each has the disadvantages described below. For example, it is extremely difficult to form a round bar or a tube by a press forming method using a press machine which is the cheapest as a device. Further, by the extrusion molding method, a shaft molded product such as a long round bar can be molded, but a powder molded product having a complicated three-dimensional shape cannot be molded. Also,
With the injection molding method, powder molded products with complicated shapes can be molded, but the device itself is complicated, large, and expensive,
In addition to the fact that only a small powder molded product can be molded, it has to be molded at a high temperature, which makes it difficult to operate and handle the device itself.

The cheapest facility that is easy to handle, that is,
It is preferable that a large-sized powder molded product having a complicated shape can be easily molded by a die press molding method using a press machine with low pressure. However, as described above, in the past, even if a high pressure was applied, the shape was complicated and it was not possible to form a large-sized powder molded product with high accuracy. Therefore, in consideration of the obtained dimensional accuracy, it is necessary to perform molding in a size in which the machining allowance of the subsequent process is set to be large, which is an obstacle to the cost reduction of the final product.

Therefore, an object of the present invention is to provide a powder molding method using a mold which enables molding of a large-sized powder molded product at a low pressure with a simple shape using a simple press machine. To provide.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and therefore, the gist of the method for molding powder with a die according to claim 1 of the present invention is that cemented carbide powder is used. An organic binder having a capacity of 30 to 60 Vol% of the volume of the cemented carbide powder is mixed and kneaded, and the mixture obtained by mixing and kneading is filled in a mold and pressed by a pressing machine.

Further, the gist of the method for molding powder with a die according to claim 2 of the present invention is that ceramic powder is mixed and kneaded with 10 to 20% by volume of the organic binder of the ceramic powder, and then mixed and kneaded. It is characterized in that the mixture obtained in (1) is filled in a mold and pressed by a press machine.

[0009]

As described above, in forming alloy powder by a press using a die, the female die of the die is filled with the powder and pressed, but especially in the case of a powder molded product having a complicated shape, the alloy powder is used. Due to the friction between each other or the alloy powder and the mold, the pressing force is not sufficiently transmitted to the inside of the mold and a part insufficient for filling occurs, so that the powder molded product may crack, or the packing density may be uneven. Occurs.

On the other hand, according to the powder molding method of the first aspect of the present invention, the cemented carbide powder is mixed and kneaded with 30 to 60 Vol% of the capacity of the cemented carbide powder. The mixture obtained by mixing and kneading is filled in a mold and pressed, and according to the powder molding method of claim 2 of the present invention, the ceramic powder has a capacity of 10 to 20 Vol. % Organic binder mixed
The mixture obtained by kneading, mixing and kneading is filled in a mold and pressed, but since the mixture is clay-like, it is easily deformed and flows even with a low pressure.

[0011]

EXAMPLES Examples 1 to 3 relating to a method for molding powder by a mold of the present invention will be described below with reference to FIG. 1 which is a side view of a powder molded article.
FIG. 2 (a) of the relative density measurement position explanatory diagram of the sintered product obtained from the powder molded product and FIG. 2 (a) of the sintered product obtained from the powder molded product of the alloy molded by the present invention and the conventional method. 2) of the relative density explanatory graph of the position corresponding to ()). However, since the pressing machine used for molding the powder is well known, the description of its configuration will be omitted.

First, the first embodiment of the present invention will be described. Reference numeral 1 shown in FIG. 1 is a powder molded product of cemented carbide, and the powder molded product 1 has a disk-shaped large diameter portion 1a and a large diameter portion 1a. It is composed of a small diameter portion 1b having a cylindrical shape protruding from the center of the large diameter portion 1a, and the material of the powder molded article 1 and its molding / sintering process are as follows.

That is, 88% by mass of WC powder having an average particle size of 0.7 μm and 12% by mass of Co powder having an average particle size of 1.3 μm were mixed by a wet tristar for 5 hours and dried,
50 vo of this cemented carbide mixed powder to the dried cemented carbide mixed powder
An organic binder prepared by mixing 1% of an organic binder, that is, 50 vol% of paraffin, 20 vol% of stearic acid, and 30 vol% of polypropylene was mixed and kneaded at 100 ° C. for 3 hours. Then, the mixture thus obtained is filled into a female mold of a mold, and the mold is filled with a uniaxial hydraulic press machine at 1.96 × 10 ⁷ Pa.
The powder molded product 1 was molded by applying a pressure of (200 kgf / cm ² ). Next, this powder molded product 1 was degreased at 400 ° C. for 1 hour and then sintered at 1400 ° C. for 1 hour.

The second embodiment of the present invention will be described. The difference between the second embodiment and the first embodiment is that WC powder and C
This is to reduce the mixing ratio of the organic binder to the cemented carbide powder consisting of o powder, and is intended to grasp the lower limit of the mixing ratio of the organic binder. That is,
Whereas the mixing ratio of the organic binder in Example 1 was 50% by volume of the cemented carbide powder,
In Example 2, the mixing ratio of the organic binder to the cemented carbide powder was set to 25 Vo, which is the volume of the cemented carbide powder.
1%, 30 Vol%, and 45 Vol%.

Explaining Example 3 of the present invention, contrary to Example 2 described above, Example 3 aims at grasping the upper limit of the mixing ratio of the organic binder to the cemented carbide powder. Then, the mixing ratio of the organic binder is set to 60 vol% and 65 vol% of the capacity of the cemented carbide powder.

Then, in order to verify the quality of each of the 10 sintered products obtained in Examples 1 to 3 (this method),
1.96 x 1 by the conventional die press molding method (conventional method)
The sintered product obtained by the present method and the sintered product obtained by the conventional method were manufactured by pressurizing at a pressure of 0 ⁸ Pa (2000 kgf / cm ² ), molding, and then sintering. The appearance and the structure of the above were compared. The results are shown in Table 1 below.

[0017]

[Table 1]

According to the above Table 1, the mixing ratio of the organic binder to the cemented carbide powder is 30 Vol% to 60 Vol.
%, The pressing force for molding is 1/10 that of the conventional method.
However, compared with the conventional method,
It is well shown that a sintered product 2 having an excellent appearance and structure can be obtained.

Next, the relative density of the sintered product obtained by the present method and the conventional method will be explained. The relative density measurement position is, as shown in FIG. Position, B
There are four positions: position, C position, and D position. Among the sintered products in Examples 1 to 3 above, when the mixing ratio of the organic binder is 25 Vol%, the solid line and the black square represent 30 Vol%.
In the case of, the solid line and the white circle, in the case of 45 Vol%, the solid line and the white square, in the case of 50 Vol%, the solid line and the double circle, 60 V
The solid line and the white triangle for the case of ol%, the solid line and the solid triangle for the case of 65 Vol%, and the solid line and the solid circle for the sintered product by the conventional method are as shown in FIG. 2B. The relative density is obtained by the Archimedes method.

According to this figure, in the case of this method, the mixing ratio of the organic binder to the cemented carbide powder is 30 Vol%.
If it is less than 25 Vol%, as in the case of the conventional method, there is a large variation at each position and there is not much difference from the conventional method. If it exceeds 30 Vol%, that is, 65 Vol%, there is little variation in the relative density, but the overall It is low. However, if it is 30 Vol% to 60 Vol%, it is well understood that the density is higher than that of the conventional method, there is no crack, the density variation is small, and it is far superior to the conventional method. That is, it is well understood that the fluidity of the cemented carbide powder is increased by mixing the organic binder, and the pressure applied by the press is effectively transmitted to the inside of the mold. The mixing ratio of the organic binder is 60V.
In the case of ol%, the sintered product could not be completely densified, and some pores were recognized.
Since it can be eliminated by pressurizing and heating with HIP, it was confirmed that there is no practical problem.

By the way, the mixing ratio of the organic binder to the cemented carbide powder should be changed according to the material and particle size of the cemented carbide powder and the molding temperature of the cemented carbide powder. Considering the degree of shrinkage during sintering of the molded product, the preferable mixing ratio of the organic binder is 40 to 60 Vol%, and the more preferable mixing ratio of the organic binder is 45 to 55 Vol%.
Is.

In the above, the case of forming a cemented carbide powder obtained by mixing WC and Co has been described as an example, but in order to further clarify the effect of the present invention, the ceramic powder is also formed and sintered. It was confirmed that in each case, it was superior to the powder molded product molded by the conventional method. Less than,
Explaining Example 4 relating to the ceramic powder, first, 100% by mass of Al ₂ O ₃ powder having an average particle size of 0.5 μm was mixed with Seranda (made by Yuken) as an organic binder, and the mixture was heated at 5 ° C.
And kneaded for 3 hours. Then, the mixture thus obtained was filled into a female mold of a mold, and this mold was molded by a uniaxial hydraulic press machine at 1.96 × 10 ⁷ Pa (200 kgf / 200 kgf /
cm ² ) and pressurizing in the same manner as in Examples 1 to 3.
A powder molded product 1 having the shape shown in FIG. 1 was molded. In this example, the mixing ratio of the seranda was ₃ % of 10 vol%, 15 vol% and 20 vol% of the volume of the Al ₂ O ₃ powder.
It is a kind.

Next, the powder molded article 1 thus obtained was degreased at 400 ° C. for 1 hour and then sintered at 1500 ° C. for 1 hour. Then, the sintered product (this method) after sintering and 1.96 × 10 ⁸ Pa by the conventional press molding method (conventional method) are used.
The appearance and structure were compared with the sintered product obtained by sintering after molding at (2000 kgf / cm ² ). The quality is as shown in Table 2 below, and it is well understood that this method is superior to the conventional method as in Example 1.

[0024]

[Table 2]

Next, the relative densities of the sintered products obtained by the present method and the conventional method are similar to those in Examples 1 to 3, and the positions A, B, C and D shown in FIG. Each of the four positions was measured, and the mixing ratio of the sender in this method was 8
Solid line and black triangle for Vol%, solid line and white square for 10 Vol%, solid line and white circle for 15 Vol%, solid line and white triangle for 20 Vol%, 23 Vol
A solid line and a black square in the case of% and a solid line and a black circle in the case of the sintered product by the conventional method are shown in FIG.

According to this figure, in the case of this method, when the mixing ratio of the organic binder to the alloy powder is 8 Vol%, there is a large variation at each position as in the case of the conventional method, and there is no great difference from the conventional method, and it is 23 Vol%. In the case of 1, the relative density has little variation, but it is low as a whole, but if it is 10 Vol% to 20 Vol%, it has a higher density and no cracks than the conventional method, and there is little variation in the density. It can be seen that it is far superior to. The more preferable mixing ratio of the sender to the Al ₂ O ₃ powder is 10 to 15 Vol%.

As described above, according to the present method, the equipment is easy to handle and inexpensive, the pressure is much lower than that of the conventional method, and the sintered product having a complicated shape and a large size with excellent quality is obtained. It becomes possible to obtain a powder molded product that makes it possible to obtain the final product cost effectively. Further, as described above, since the pressing force may be 1/10 of the conventional case, a low-capacity one-axis hydraulic press machine will suffice, and there will be a reduction in equipment costs and running costs.
It will be possible to further contribute to the cost reduction of the final product.

By the way, if the molding temperature of the powder molded product is too low, the fluidity of the mixture decreases, and conversely, if it is too high, the mixture is liquefied and a good powder molded product cannot be obtained. Since the technical idea of the present invention can be applied to the molding of powder molded products of various shapes, the shape of the powder molded product is limited by the above-mentioned embodiment. is not.

[0029]

As described in detail above, the first aspect of the present invention
According to the powder molding method of the above, the cemented carbide powder is mixed and kneaded with an organic binder in an amount of 30 to 60 Vol% of the volume of the cemented carbide powder, and the mixture obtained by mixing and kneading is formed into a mold. According to the method of molding powder according to claim 2 of the present invention, the ceramic powder is filled with an organic binder in an amount of 10 to 20% by volume of the ceramic powder, and the mixture is mixed and kneaded. The mixture obtained in this way is filled in a mold and pressed, but since the mixture is clay-like, it easily deforms and flows by pressure and moves to the inside of the mold. With the pressure, a large-sized powder molded product having a complicated shape can be molded with high accuracy, and it can greatly contribute to the cost reduction of the final product by improving the accuracy of the sintered product.

[Brief description of drawings]

FIG. 1 is a side view of a powder molded article according to Examples 1 to 3.

FIG. 2 (a) is an explanatory view of relative density measurement positions of the sintered products according to Examples 1 to 3, and FIG. 2 (b) is a sintered product at a position corresponding to FIG. 2 (a). It is a relative density explanatory graph figure.

FIG. 3 is a graph for explaining relative density after sintering of a ceramic powder molded article according to Example 4.

[Explanation of symbols]

 1 ... Powder molded product, 1a ... Large diameter part, 1b ... Small diameter part 2 ... Sintered product

Front page continued (72) Inventor Akira Egami 179-1 Kanegasaki Nishioike, Uozumi-cho, Akashi-shi, Hyogo Inside the Akashi Plant, Kobe Steel, Ltd. (72) Inventor, Kazuhiko Asano 1-3-3, Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo No. 18 Kobe Steel, Ltd. Kobe Head Office

Claims (2)

[Claims] 1. A cemented carbide powder is mixed and kneaded with an organic binder in an amount of 30 to 60 Vol% of the volume of the cemented carbide powder, and the mixture obtained by mixing and kneading is filled in a die and pressed. A method for molding powder by a die, which comprises pressurizing with a die. 2. A ceramic powder is mixed with an organic binder in an amount of 10 to 20 Vol% of the volume of the ceramic powder.
A method for molding powder by a mold, which comprises kneading, mixing a mixture obtained by mixing and kneading, and pressing the mixture with a press.