The Metal Injection Molding process
|The following items represent the production steps of the metal injection molding process:
More About The Process
The feedstock is mixed from fine metal powder, typically <22 micrometers, with a proprietary binding agent. The latter can be based on water, wax or other system. Different feedstocks will have specific characteristics, i.e., viscosity, injection pressure and temperature, and debinding process. The powder loading is 55-65% by volume or 90% by weight for steels.
Molding is done in a conventional injection molding machine. The mold is designed similar to that for plastic but with allowances made for shrinkage and the cooling requirements for a feedstock highly loaded with metal particles. Molding can be done on both vertical and horizontal machines.
The parts are removed from the mold. At this point they are called “green” parts. Before the part can be sintered, the bulk of the binder has to be removed. With Polymer Technologies’ advanced binder system, the debinding is a simple step, providing the capability and considerable advantage for manufacturing heavier/thicker wall parts. In other systems, the binder has to be extracted by liquid or gaseous solvent, water or thermally, or a combination thereof. The debound part is called “brown”.
The brown part is placed on a custom designed ceramic trays and processed in a high temperature furnace. Sintering is typically done in a high vacuum furnace or a continuous hydrogen furnace
Sintering temperatures go up to 2500 degrees F. During the sintering process, the metal particles fuse together, the part shrinks 15% linearly, and density is increased to 98% or better.