JPH0254703A - Production of sintered metal body by injection molding - Google Patents

Abstract

PURPOSE:To produce the metal powder product of an intricate shape which is integral and with which injection molding is impossible by dividing a mixture composed of the metal powder and thermoplastic binder to plural pieces and injection molding the mixtures, then assembling the moldings, joining the moldings by heating and sintering the joined body. CONSTITUTION:A metal powder slurry consisting of the metal powder and the thermoplastic binder is divided to plural pieces and is injection-molded. The divided injection moldings are assembled in a green state and are joined by heating; further, the binder is removed from the assembly and the assembly is sintered in a vacuum to securely join the moldings. The powder sintered product of the intricate shape which is integral and with which the injection molding is impossible or difficult is produced by using a metallic mold having a relatively simple structure in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a metal powder sintered body by injection molding.

[Conventional technology]

A metal sintered body by injection molding is generally manufactured by the following method. A mixture of metal powder, a thermoplastic binder consisting of a thermoplastic resin, wax, etc. is heated to form a slurry, which is then injection molded into a mold, and the molded body is heated.

The binder in the molded body is liquefied or vaporized and removed,
Thereafter, the metal powder is sintered in vacuum or in an inert atmosphere.

Compared to ordinary sintered crystals, which are formed by cold compression molding of metal powder and then sintering, injection molding allows molding of complex shapes because the metal powder slurry is injected under high pressure, and molding is possible in the slurry state. Therefore, fine powder can be used to

It has the characteristics that the sinterability of the powder is improved, the relative density of the sintered body is increased, and the mechanical properties are also improved.

[Problem to be solved by the invention]

Compared to ordinary sintered crystals, which are cold compression molding of metal powder and then sintering, injection molding is a method of molding metal powders by injecting metal powder slurry under high pressure, so complex shapes can be molded. However, there is a limit to the complexity of the shape due to the process of injecting slurry into a mold and taking out the molded body from the mold after solidification.

For example, a product with a shape as shown in Figure 3.

Although it is not impossible to perform injection molding using a core mold, the problem is that the mold becomes very complex and the cost of mold production increases significantly.

[Means to solve the problem]

The present invention was made in view of the above-mentioned conventional problems, and consists of: (1) dividing metal powder slurry into a plurality of parts and injection molding; (2) assembling them in a green state and joining them by heating;
■ Furthermore, it is strongly bonded by sintering.

[Effect]

According to the method of the present invention described above, since the injection-molded metal powder in the green state contains a thermoplastic binder, it deforms slightly when heated, and the distance between the particles at the joint surface becomes closer. Then, the joint surface is easily sintered by subsequent high-temperature heating, and the strength of the joint surface becomes comparable to that of the base material.

These conditions are schematically shown in Figure 2. That is, the second
As shown in Figure (a), the intervals between the four metal particles on the joint surface are not necessarily close at room temperature, but as shown in Figure 2 (b), the thermoplastic resin is heated to a temperature at which it deforms and a slight load is applied. As a result, the distance between the metal particles 4 at the bonding surface becomes closer, and by the subsequent high temperature sintering, the bonding surface is completely adhered and sintered as shown in FIG. 2(c).

〔Example〕

Examples of the present invention will be described below.

A specific example of manufacturing a product in the shape of a bent steel pipe as shown in FIG. 3 will be described below.

For products with this shape, it is not impossible to injection mold them in one piece using a core mold, but the mold would be extremely complicated and the mechanism for removing the product from the mold would also be difficult. The process becomes complicated, and automatic ejection may become impossible in some cases. Therefore, in the present invention, as shown in FIG. 1(a), a product having such a shape is divided and injection molded to obtain a two-part material 2, and then assembled as shown in FIG. 1(b). It is sintered in one piece.

To explain this example more specifically, stainless steel (SUS304L) powder with an average particle diameter of 8 microns is mixed with a mixture of wax and thermoplastic (acrylic resin) in a weight ratio of 90:10. 120~1
The raw materials mixed and granulated at a temperature of 50°C are
At a temperature of 300 to 1,500 °C and a pressure of 9/20°C, injection molding is performed into a mold having the shape of the two-part material 2 as shown in Figure 1 (a), and the material is cooled and solidified in the mold. After that, it is removed from the mold and assembled in a green state as shown in Fig. 1(b), and the molded product is heated gradually to about 500°C while applying a slight load to the joint surface 3 (self-weight is sufficient). At the same time, the distance between the particles on the bonding surface 3 is reduced to bring them into close contact. That is, the thermoplastic binder starts deforming at about 60 to 80°C, and the distance between the particles at the bonding surface becomes closer as shown in FIG. 2(b). After joining in the green state and removing the binder, the metal powder is further heated to about 1200°C in a vacuum to sinter the metal powder. As shown in Figure 2 (c), the distance between the metal particles 4 becomes closer and the relative density increases. increases,
The joint surface 3 is completely sintered.

In this way, for complex shapes that cannot be injection molded in one piece or are very difficult to injection mold in one piece, the structure of the mold can be made relatively simple by dividing them into multiple pieces and injection molding them. , it is possible to produce powder sintered products with complex shapes.

〔Effect of the invention〕

According to the above nine aspects of the present invention, it is possible to produce powder sintered products even with complex shapes that cannot be integrally injection molded or are extremely difficult to be integrally injection molded. It is.

[Brief explanation of the drawing]

FIG. 1 is a conceptual explanatory diagram showing that a product is obtained by integrally joining divided materials as an embodiment of the present invention. Figure 2 is an explanatory diagram showing the behavior of metal particles at (a) normal temperature, (b) temperature at which the thermoplastic resin deforms, and (C) high temperature. It is an explanatory diagram showing an example. 1...Product, 2...Divided material, 3...Joint surface, 4...
...Metal particles Figure 1 Figure 3

Claims (1)

[Claims] Metal sintering characterized by dividing a mixture of metal powder and thermoplastic binder into a plurality of pieces, injection molding them, assembling them, heating and joining them, and further removing the binder and sintering them in a vacuum. How the body is manufactured.