Consider metal-injection molding for high-volume small parts with complex, difficult-to-machine geometries. It can be a very cost-effective alternative to die casting, investment casting, machining and press-and-sinter processes. You can mold in cross-drilled holes, radii, blind holes and internal features with tight tolerances using metal molding. Because of the cost of the mold, however, you want to think in terms of minimum quantities of about 10,000.
Most common engineering metals are available as small powders: stainless steel, copper, tungsten alloys and even Kovar iron-nickel-cobalt super alloy. Metals that are reactive and volatile are generally avoided: beryllium, mercury, lead, manganese, zinc, aluminum, tantalum and oxides of tin. Binders used in MIM are a mixture of plastic and wax and constitute about 50 percent of the feedstock. Shrinkage rates are predictable, and mold cavities are sized accordingly.
Hardnesses of MIMed parts can be improved through secondary processes. For example, 17-4 PH stainless parts achieve 29-32 HRC as sintered. With heat treating, the values rise to 38-42 HRC. State-of-the-art molders can achieve ±0.003 to ±0.005 inches/inch and wall sections from 0.030 to 0.250 inches.
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