1 Field of the Invention
The present invention relates to a method for efficiently manufacturing a compact from powders which contracts only a little anisotropically.
2 Description of the Prior Arts
In the prior art cold isostatic press method, a resilient mold is filled up with powders such as metallic powder, ceramic powder or the like and sealed. Then, an isostatic press is applied to the resilient mold by the use of a pressure medium at the normal temperature whereby a homogeneous compact is prepared. Hereinafter, the cold isostatic press method is abbreviated as a C.I.P. method. In the forgoing C.I.P. method, however, some idea is required to obtain a compact of desirable shape so that the resilient mold cannot be deformed by the weight of the powders. In this connection, a method wherein a thickness and a strength of the resilient mold are made large to some extent is known. In this method, however, a degree of contraction of the resilient mold relative to a pressure applied thereto is different from a degree of contraction of a fill-up of powders inside the resilient mold, to which a pressure is applied. Due to the difference in the degrees of the contraction, the resilient mold and fill-up do not contract isotropically. Accordingly, the compact is required to be subjected to considerable machining in order to obtain a desired shape and a dimensional accuracy.
A method disclosed in a Japanese Examined Patent Publication No. 297402/87 is pointed out as another method. This method is executed as follows:
(a) A thin-wall resilient mold of a predetermined shape and a ventilative mold support having an inside shape similar to the shape of the resilient mold are prepared;
(b) The resilient mold is inserted into the mold support;
(c) The resilient mold is put close to the inner surface of the mold support;
(d) The resilient mold, which has been put close to the inner surface of the mold support and whose shape is kept, is filled up with powder materials. Then, after air in the resilient mold has been exhausted, the resilient mold is sealed;
(e) The ventilative mold is removed from the thin-wall resilient mold; and
(f) The thin-wall resilient mold is subjected to a cold isostatic press treatment and is removed whereby a compact is prepared.
A great progress in an increase of dimensional accuracy is seen in the method disclosed in the Japanese Patent Application Laid Open No. 297402/87 in comparison with the method wherein the thickness and strength of the resilient mold are made large to some extent. However, since the resilient mold is expanded by the use of the pressure difference and put close to the inner surface of the ventilative mold support, there occurs a phenomenon such that the resilient mold expands, not moving to positions corresponding to due positions of the inner surface of the mold support similar in shape to the resilient mold. When the resilient mold, in which said phenomenon takes place, is subjected to the C.I.P. treatment as it is, there occurs an anisotropic contraction and creases of the resilient mold. The more a desired shape of a compact becomes complicated, the greater this problem is posed.