Metal injection molding or (MIM) is a manufacturing process which combines the versatility of plastic injection molding with the strength and integrity of machined, pressed or otherwise manufactured small, complex, metal parts. Competing processes include pressed powder sintering, investment casting, turning and machining.
The process involves combining fine metal powders with a plastic binders which allow the metal to be injected into a mold using 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. The products of metal injection molding are up to 98% as dense as wrought iron and used in a broad range of applications (including medical, dental, firearms, aerospace, and automotive just to name a few.)
The window of economic advantage in metal injection molded parts lies in the complexity and small size of the part. 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 cost 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 (threads (both internal and external), miniaturization, branding).
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