Injection Molding of Metal PowdersAn alternative to the use of pressure techniques to form a green compact is the use of injection molding. This technique uses the technology of plastic injection molding by combining metal powders with a polymer binder to produce a slurry-type mixture that can be injected into a complex die. Unlike plastics, however, the size of the parts produced by this method is somewhat restricted. Complex geometries including undercuts, holes, and reentrant angles may be produced using appropriate slide tooling on the die. Following injection, a binder removal operation at relatively low temperatures (400-600T) is done.
Next, a sintering operation is conducted that is much the same as that for conventional PM processing. In injection molding of PM, shrinkage between the original injection molded dimensions and final sintered dimensions may be as much as 20%; therefore, careful tool design is needed. The polymer-PM blend must produce a predictable shrinkage preform. The range of materials applicable to this process is limited only by the use of any fine powder material that can be sintered. These include steels, both stainless and carbon steel, and alloy steels as well as superalloys, tungsten carbides, and so on. The technique has also been used with ceramic materials such as aluminum oxide.
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