What’s Metal Injection Molding?

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Metal injection molding (MIM) is a process that uses pulverized metal and binder material to create small, detailed parts. Powder metallurgy is used to determine which metals can be made into powder for MIM. The raw material is injected into a mold and cooled before the binder is partially removed and the metal is sintered to create a strong, dense part. MIM is a flexible and cost-effective technology for producing intricate and complex parts.

Metal injection molding (MIM) is a process by which metal is pulverized, mixed and placed into a mold to create solid parts and pieces of equipment. The blend of powdered metal and binder material, known as the raw material, is in limited quantities, making metal injection molding ideal for small, detailed parts. Applications of this process include machine parts, dental instruments and firearms equipment and generally all involve small and complex parts.

Powder metallurgy is the technique of determining what types of metal can be made into powder for the metal injection molding process. Different strategies are available to create a metallic powder, such as physical deposition, grinding, atomization, chemical reactions or centrifugation. The type of powder strategy strongly depends on the type of metal to be pulverized and its specific qualities.

Once the metal powder is produced it is mixed with a binder, which is a material made up of various waxes and plastics. The resulting mixture, called the raw material, is then ready to be injected into the mould. Due to the similarities between the raw material and the molten plastic used in regular injection molding, the same injection molding equipment can be used for metal injection molding. The raw material is injected into the molding equipment in a small amount called a shot, which is then allowed to cool inside the mold.

After cooling is complete, the binder material is partially removed from the part, usually with a solvent or chemical reaction, but occasionally the part is heated to dissolve the binder. The part now contains a significant fraction of void comprising approximately 2% to 4% of the total volume in a process step known as the brown phase. The metal is then made stronger and denser through a sintering process. During sintering, the metal is heated to a temperature just below its melting point, until the surface of the metal particles fuses together while maintaining the structural integrity of the part. The end result is a metal part that contains up to 99% solid density.

Once small changes have been made, the part is completed and ready to be used. Because metal injection molding involves the use of molds, it is a more flexible technology and ideal for intricately designed and complex parts. Other metal technologies often require high costs to obtain the same resulting products, so metal injection molding is becoming an increasingly popular technique for producing these parts.

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