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Metal Injection Molding (MIM)
Metal Injection Molding (MIM) combines the shape and design flexibility of thermoplastic injection molding with the mechanical properties of high performance powder metals, offering a cost-effective solution for a variety of industries.
Metal Injection Molding Process
Mixing
MIM feedstock begins with micron-sized particles of alloys such as 316 stainless steel or elements such as iron, chromium, and nickel.
The metal powders are blended with thermoplastics selected to provide the proper viscosity, green density, and green strength.
High shear mixers and low temperature heaters combine to effectively blend as many as ten components into one homogenous feedstock.
Molding
Similar to plastic injection molding, feedstock is forced through a heated barrel and injection nozzle by a reciprocating screw and plunger. Friction provides additional heat to keep the thermoplastics in the feedstock molten.
Molded or’green’parts are ejected and robotically unloaded to minimize handing damage.
The thermoplastic polymers and waxes in the feedstock allow runners and gates to be reused, eliminating scrap material providing additional savings.
Debinding
Necessary during molding, thermoplastic binders must be removed before sintering to ensure excellent mechanical properties in the finished component.
Binders can be removed using either a thermal, solvent, or capillary process.
Removing low temperature binders creates a 'brown' part containing a porous network of metal particles held together by high temperature binders.
Sintering
The initial stages of sintering remove the remaining binders from the brown parts as they are heated to soak temperatures as high as 2475°F.
Time at temperature provides the energy that drives the micron-sized metal particles to create metallurgical bonds. Components usually reach 96 to 99% of the metal's theoretical density.
Removing binders and driving the sintering process to this degree of completion cause the MIM parts to shrink, often as much as 15 to 20%. |