Metal injection molding (MIM) is a net-shape process that combines fine metal powder with a polymer binder to form feedstock, injection-molds it into a green part, then debinds and sinters it into a dense metal component. Typical MIM parts weigh under ~100 g, hold about ±0.3% as-sintered tolerance, and reach over 97% of theoretical density.
A manufacturing process that mixes fine metal powder with a polymer binder to form feedstock, injection-molds the feedstock into a shaped green part, then debinds and sinters it into a dense metal component. MIM suits small, complex, high-volume parts, usually under about 100 g.
The homogeneous, granulated mixture of fine metal powder (typically 1–20 µm) and a thermoplastic binder system that is fed into an injection molding machine. Feedstock usually contains around 60% metal by volume.
The polymer and wax component of feedstock that makes it flow during molding and holds the powder together until it is removed. Common binder systems are wax-polymer, catalytic, or PEG-based.
The as-molded part after injection, consisting of metal powder held together by binder. It is oversized relative to the final part because the part shrinks during sintering.
The part after debinding, when most of the binder has been removed but a small backbone (about 2–3%) remains to keep the shape stable before sintering.
The process of removing binder from the green part by heat, solvent, or a catalytic reaction. Partial debinding leaves a brown part that can still be handled before sintering.
Heating the brown part in a controlled atmosphere at 1200–1400 °C (depending on alloy) so the metal particles bond and densify into a solid part. MIM parts shrink isotropically by roughly 15–20% linearly during sintering.
The density of the finished part relative to the theoretical density of the alloy. Well-controlled MIM typically reaches above 97% of theoretical density, and higher with hot isostatic pressing.
The uniform dimensional contraction that occurs during sintering. MIM shrinkage is isotropic, so tooling is designed oversized by a predictable, material-specific factor.
Producing a part close to its final dimensions so that little or no machining is needed. Sintering-based MIM is a near-net-shape process.
The hardened steel die, machined by CNC and EDM, into which feedstock is injected. Tooling cost is fixed and is amortized over the production volume.
The shaped void inside a mold that forms the part. A single tool can have multiple cavities to produce several parts per molding cycle.
The small channel through which feedstock enters the mold cavity. It is trimmed off after molding.
The main feed channel that carries molten feedstock from the machine nozzle to the runners and gates.
The permissible dimensional variation of a part. Typical MIM as-sintered tolerance is ±0.3%, and tolerances tighter than that can be reached with secondary machining.
A low-carbon austenitic stainless steel widely used in MIM for its corrosion resistance, common in medical, marine, and consumer parts.
A precipitation-hardening martensitic stainless steel used in MIM where high strength and hardness are required after heat treatment.
Alloys such as Fe-Si, Fe-Ni (permalloy) and Fe-Co that are easily magnetized and demagnetized. MIM produces complex soft-magnetic parts for motors, sensors and inductors.
A hard, wear-resistant cermet of tungsten carbide grains bonded with cobalt. Cemented carbide MIM parts are used for nozzles, cutting tools and wear components.
A post-sintering process that applies high temperature and isostatic gas pressure to close residual porosity, raising density toward 100% and improving fatigue life.
The slight taper on the vertical walls of a mold that lets the molded part be ejected cleanly.
The cross-sectional thickness of the part walls. Uniform walls of roughly 1–5 mm mold and sinter most reliably.
Any cutting, grinding, or drilling performed after sintering to add features or hold tolerances tighter than the as-sintered capability.
The controlled gas inside the furnace during sintering, often hydrogen, nitrogen, or vacuum. It prevents oxidation and controls the carbon content of the part.
An early, low-temperature stage of debinding in which the polymer binder is thermally decomposed and driven off.
The volumetric fraction of metal powder in the feedstock, often around 60%. It strongly affects shrinkage and defect rates.
The condition of a MIM part directly after sintering, before any secondary operations.
MIM gives design freedom and near-net shape at high volume for small, complex metal parts, cutting machining cost and material waste.
Common MIM materials include 316L and 17-4PH stainless steels, low-alloy steels, titanium alloys, copper, tungsten carbide (WC-Co) and soft magnetic alloys.
Typical as-sintered MIM tolerance is ±0.3%. Tighter tolerances can be achieved with secondary machining after sintering.
MIM is best for small, intricate parts, generally under about 100 g, produced in medium to high volumes.
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