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.
» History: The metal injection molding 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.
» Metal Injection Molding 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. As shown in this MIM schematic, metal powders are blended and mixed with a polymer and additives.
Then they are processed on conventional injection molding machines used for thermoplastic materials into so-called green parts. The polymers serve as a binder that allows the metal powders to be injection-molded. The binder is removed from the green parts in a continuous process under a highly defined and controlled temperature-time profile. Subsequently, the parts are sintered to their final density. The choice of materials and alloying systems is virtually limitless.
» Advantages of Metal Injection Molding: The window of economic advantage in metal injection molded parts lies in the complexity and small size of the part. 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).
As a metal forming process, Metal Injection Molding (MIM) combines the material flexibility of powder metallurgy and the design flexibility of plastic molding. With properties comparable, or better than, those of wrought steel, the MIM process is ideally suited to producing small and complex-shaped parts with outstanding mechanical properties.
