Metal Injection Molding

Metal injection molding (MIM) is a metalworking process by which finely-powdered metal is mixed with a measured amount of binder material to comprise a "feedstock" capable of being handled by plastic processing equipment through a process known as injection molding. The molding process allows dilated (oversized due to binder) complex parts to be shaped in a single step and in high volume. After molding, the powder-binder mixture is subjected to steps that remove the binder (debinding) and sinter densify the powders. End products are small components used in various industries and applications. The nature of MIM feedstock flow is defined by a physics called rheology. Current equipment capability requires processing to stay limited to products that can be molded using typical volumes of 100 grams or less per "shot" into the mold. Rheology does allow this "shot" to be distributed into multiple cavities, thus becoming cost-effective for small, intricate, high-volume products which would otherwise be quite expensive to produce by alternate or classic methods. The variety of metals capable of implementation within MIM feedstock are broad, but mostly stainless steels, as common in powder metallurgy; they contain the same alloying constituents found in industry standards. However, oxygen is often a difficulty and is often not specified, but can be a problem for corrosion resistance. Subsequent conditioning operations are performed on the molded shape, where the binder material is removed and the metal particles are diffusion bonded and densified into the desired state with typically 15% shrinkage in each dimension.

The metal injection molding market has grown from $9 million USD in 1986, to $382 million USD in 2004 to more than $1.5 billion USD in 2015. A related technology is ceramic powder injection molding, leading to about $2 billion USD total sales. Most of the growth in recent years has been in Asia.

An early developer of the process during the 1970s was Dr. Raymond E. Wiech Jr., who refined MIM technology as co-founder of a California company named Parmatech, the name being condensed from the phrase "particle materials technology". Wiech later patented his process, and it was widely adopted for manufacturing use in the 1980s.

MIM gained recognition throughout the 1990s as improvements to subsequent conditioning processes resulted in an end product that performs similarly to or better than those made through competing processes. MIM technology improved cost efficiency through high volume production to "net-shape", negating costly, additional operations such as machining although MIM is weak in terms of tight dimensional specifications.

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