Method for producing highly porous metallic moulded bodies close to the desired final contours
The invention relates to a method for producing highly porous, metallic molded bodies. The inventive method consists of the following steps: a metallic powder used as a starting material is mixed with a dummy; a green body is pressed out of the mixture; the green body is subjected to conventional mechanical machining, the dummy advantageously increasing the stability of the green body; the dummy material is thermally separated from the green body by means of air, a vacuum or an inert gas; and the green body is sintered to form the molded body and is then advantageously finished. Suitable materials for the dummy are, for example, ammonium bicarbonate or carbamide. The mechanical machining carried out before the sintering advantageously enables a simple production close to the desired final contours, even for complicated geometries of the molded body to be produced, without impairing the porosity, and without high wear of the tools. The workpiece is advantageously sufficiently stable in terms of pressure for the green machining as the dummy material is still present in the pores of the green body during the machining.
1. A method of producing a high porosity metallic molded body with the following process steps:
mixing a metal powder used as the starting material with a particulate place holder with a particle size of 50 μm to 2 mm and selected from the group which consists of carbamide, biuret, ammonium carbonate and ammonium bicarbonate to form a mixture,
pressing from the mixture consisting essentially of said metal powder and said particulate place holder a green body with a compressive strength sufficient to allow machining thereof,
subjecting the green body to a conventional mechanical machining,
removing the place holder material thermally from the green body in air or under vacuum or under a protective gas to produce a machined green body with open porosity, and
sintering the green body to form the molded body while maintaining the open porosity.
2. The method according to claim 1 , in which the place holder is removed at a temperature below 300° C.
3. The method according to claim 1 , in which stainless steel 1.4404 (316L) or titanium is used as the metallic starting powder.
4. The method according to claim 1 , in which the molded body is produced by sawing, boring, turning, milling or grinding in the green state to close to its final contour.
5. The method according to claim 1 , in which the sintering is carried out in a bed of ceramic balls.
6. The method according to claim 1 , in which the molded body following sintering is trovalized or ground smooth.
7. The method according to claim 2 wherein the place holder is removed at a temperature below 105° C.
8. The method according to claim 7 in which the place holder is removed at a temperature below 70° C.