The Metal Injection Molding process

The following items represent the production steps of the metal injection molding process:

  • Formulation and Mixiing of feedstock from metal powder and binder
  • Inject feedstock in to mold
  • Mold “Green” Part
  • Debind  (Aqueous, Solvent, Thermal) “Brown” part to remove major portion of proprietary binder
  • Sinter in vacuum (Batch System) or controlled atmosphere (Continuous Pusher) furnaces
  • Secondary operations
  • Heat Treat
  • Finish or Coating operations as needed

More About The Process

Feedstock
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
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.


Horizontal Machine (left) and Vertical Machine (right)


Injection Mold with Mechanical Cams (left)
Injection Mold with a Mechanical part in “Green” state (right)

Debinding
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”.

Sintering
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


CM Furnaces Continuous Hydrogen Pusher 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.