A MIM part is a metal component produced through metal injection molding, a manufacturing process that combines the design flexibility of plastic injection molding with the strength of solid metal. The process works by injecting a mixture of fine metal powder and plastic binders into a mold, then burning away the binders and fusing the metal particles into a dense, finished part. MIM is best suited for small, complex metal parts produced in high volumes, typically components that weigh between 5 and 15 grams and fit in the palm of your hand.
How a MIM Part Is Made
The MIM process has four distinct stages: compounding, injection molding, debinding, and sintering. Each step transforms the material from a mouldable paste into a solid metal component.
In the compounding stage, very fine metal powder is blended with a plastic binder system to create a material called feedstock. The binder is a mix of polymers that act like glue, holding the powder together so it can flow like melted plastic. This feedstock is then heated and injected into a steel mold, just like you’d inject plastic in conventional molding. The result is called a “green part,” which has the exact shape of the final component but is roughly 20% binder by volume.
Debinding removes most of that binder, either by dissolving it in a chemical bath or by heating the part in a furnace. What remains is a fragile, porous structure of metal particles called a “brown part.” Finally, sintering heats the brown part to temperatures high enough for the metal particles to fuse together (around 1,200 to 1,500°C depending on the alloy) in a controlled atmosphere, often vacuum or argon gas. The part shrinks uniformly as it densifies, reaching near-full density. In some alloys sintered under vacuum, residual porosity drops to as low as 0.1%.
Common Materials
Stainless steel dominates the MIM industry, accounting for roughly 50 to 57% of all MIM parts produced globally. It’s followed by low alloy steels and tool steels, which are common in automotive and industrial applications. Titanium is increasingly used for medical implants, surgical instruments, and dental components because of its strength-to-weight ratio and biocompatibility. Cobalt-chromium alloys (like ASTM F75) serve a similar role in orthopedic and dental implants due to their wear resistance and compatibility with human tissue. Copper alloys round out the most frequently used materials.
Size, Weight, and Precision
MIM parts range from micro medical components weighing as little as 0.030 grams to larger industrial parts up to 300 grams, though the sweet spot is 5 to 15 grams. Length can vary from 2 mm to 150 mm, with the average around 25 mm. If a part fits in your palm, it’s a reasonable candidate for MIM.
Dimensional tolerances typically fall within ±0.3% to ±0.5% of the nominal dimension, which works out to roughly ±0.076 mm per inch. That’s significantly tighter than investment casting, which holds tolerances around ±0.5 mm. Some MIM producers achieve accuracy of ±0.02 mm for critical features, though reaching that level may require secondary machining or polishing after sintering.
Complex Geometry Without Machining
The real advantage of MIM is its ability to produce features that would be expensive or impossible to machine from solid metal. Because the feedstock flows like plastic, the mold can form internal holes, slots, thin walls, and surface details like logos, knurling, and part numbers at no added cost per piece. External undercuts can be created using split molds along the parting line, and some internal undercuts are possible with collapsible cores or slides inside the mold.
Both internal and external threads can be formed directly during molding, though tapping internal threads after sintering is often more precise and cost-effective than building unscrewing mechanisms into the mold. Cored holes reduce wall thickness to achieve uniform cross-sections, which helps parts sinter evenly and cuts material usage. The tooling itself is more expensive to design and maintain than a simple mold, but the savings from eliminating machining and assembly operations downstream often more than compensate.
Where MIM Parts Show Up
In consumer electronics, MIM produces the tiny connectors and electrical contacts inside mobile phones, computers, and other devices. The housings for wireless earbuds are another common application, where MIM delivers a premium metal feel in a shape that would be difficult to machine at scale.
The medical industry relies on MIM for surgical instruments like forceps, scissors, and needle holders, as well as implantable hardware such as screws, pins, and prosthetic components. Titanium and cobalt-chromium alloys are preferred here because they can be sterilized, resist corrosion in the body, and meet biocompatibility standards.
Firearms manufacturers use MIM extensively for trigger components, safeties, and other small, complex steel parts. Automotive applications include turbocharger vanes, sensor housings, and locking mechanisms. In each case, the pattern is the same: small, geometrically complex parts needed in large quantities.
How MIM Compares to Other Methods
MIM competes most directly with CNC machining and investment casting. CNC machining can achieve tighter tolerances and works well for prototypes or low-volume runs, but the per-part cost climbs quickly for complex geometries because each feature requires additional tool paths and setup time. For a part with internal channels, thin walls, and surface textures, machining from a solid block wastes material and labor.
Investment casting uses cheaper raw materials (bulk metal at roughly $3/kg versus MIM powder at around $10/kg for stainless steel) and has lower upfront mold costs, making it more economical for low to medium production volumes. It handles moderately complex shapes well but can’t match MIM’s level of fine detail or tight tolerances without secondary machining.
MIM’s initial tooling investment is higher, but molds last 50,000 shots or more, which drives per-unit costs down as volume increases. The breakeven point varies by part complexity, but MIM generally becomes the most cost-effective option for medium to high volume production runs where each part has features that would otherwise require multiple machining or assembly steps.