What makes a particular component an ideal candidate for fabrication via Metal Injection Molding (MIM)? We break down our guidelines into four basic areas: complexity, size, production volume, and final properties.
MIM offers the same design freedom as plastic injection molding. The more geometrically complex a part is, the more solid the rationale for manufacturing it via the MIM process. Parts may include cross holes, angle holes, internal threads, irregular shapes, splines, undercuts, side holes or grooves, complex contours, or cantilevers.
Parts that would usually be made by assembling multiple components can be designed as a single MIM part. Some parts that could not be fabricated via any other process can be made through MIM. Complexity that would be cost prohibitive to do via multiple machining operations or by casting and then finishing can be achieved cost effectively through MIM processing.
In general, the weight range MIM parts tend to fall within is 0.1 to 250 grams, although above 100 grams the high cost of the extremely fine powders used in the process begins to neutralize MIM’s cost advantages, unless the complexity is extreme. Parts should have wall thicknesses not less than .13 mm (.005 in.) and not more than 12.7 mm (.5 in.). Due to material flow limitations, the distance from gate to the farthest point on the part should be around four inches. MIM part tolerances are nominally ±0.3%–0.5%, although tighter tolerances can be achieved in some cases if deemed essential.
Medium to high volumes of 10,000 to 2,000,000 parts annually are typically needed in order to be able to amortize costs associated with tooling and start-up engineering. The best economic advantages are achieved at the highest quantities, due to the benefits of larger material purchases, multi-cavity tooling, and dedicated production units.
MIM fabrication is ideal where near-full density, high impact toughness, fracture toughness, and fatigue and corrosion resistance are required. And if non-standard material properties are required, these can be developed with new alloy systems.
MIM is appropriate for materials that are difficult to machine, materials with multi-phase microstructures, or high work-hardening materials. And it delivers a high-quality surface finish (32 rms or better) and cleaner feature detail than investment casting.