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Metal injection molding (MIM) is a metalworking process which is used to create small, complex metal parts in high volumes for use in a variety of industries and applications. The MIM process is typically described as the combination of powder metallurgy and the plastic injection molding process. The process was invented in 1973 by Karl Zueger, but was not adopted for manufacturing use until the 1980s. Competing processes include pressed powder sintering, investment casting, turning and machining.
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Process
The process involves combining fine metal powders with plastic binders which allow the metal to be injected into a mold using equipment similar to standard plastic injection molding machines. After the part is molded and before the binders are removed, the part is referred to as a 'green part'. The next step is to remove the binders with solvents and thermal processes. The resultant metal part is sintered at temperatures great enough to bind the particles but not melt the metal.
Applications
The window of economic advantage in metal injection molded parts lies in the complexity and small size of the part. The products of metal injection molding are up to 98% as dense as wrought metal and used in a broad range of applications (including medical, dental, firearms, aerospace, and automotive.) Tolerances as small as +/-.003" per linear inch can usually be held without secondary processes. The difficulty of fabrication through other means may make it inefficient or even impossible to manufacture otherwise. Increasing complexity for traditional manufacturing methods typically does not increase cost in a metal injection molding operation due to the wide range of features possible through injection molding (internal and external threads, miniaturization, branding).
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