Metal Injection Molding (MIM) is a mature technology used to produce high quantities of small and complex components. The main materials used in MIM are ceramic powders, metal powders, and polymers. The advantages are dimensional accuracy and little to no post processing.
Until the development of 3D printing, MIM was the main way of making complex geometrically shaped parts. Thus, one of the larger disadvantages is that the cost of developing molds for MIM can be costly.
MIM begins with the use of a raw material usually in the form of metallic powder compacted into pellets.
The MIM process typically consists of 3 steps:
Printing— The raw material must be prepared before it is put into the molds. Often, the preparation consists of adding in an organic binder. The binder and raw material are mixed to ensure maximum homogeneity with the final result being a feedstock that is usually pellets. The pellets are fed into a hopper. Then the molding process begins where the pellets are pushed or injected into the mold under pressure. The result is an object referred to as “green,” which still contains the binder. The choice of binder is important as it can lead to premature separation of the binder and metal powder, affecting the final quality of the part.
Debinding—Debinding is the process that removes most of the binder present in molded part. Debinding helps reduce deformation, crumbling, swelling or breakage of the part.
In solvent debinding, the binder is dissolved in a solvent such as acetone and heptane, or even water. In many cases, solvent debinding only removes some of the binder.
Often thermal debinding is used to finish the binder removal or to handle it altogether. The part is placed in a furnace to burn out the binder. The result is a solid, metallic part.
Sintering—is the stage used to compact the part, often up to a density of 95%, sometimes up to 99%. This stage eliminates any residual binding material.