Metal Injection Molding (MIM)

Metal Injection Molding (MIM) forms small, complex metal parts by injecting metal powder–binder feedstock into molds, then debinding and sintering to near-full density.

Overview

Metal Injection Molding (MIM) combines plastic injection molding and powder metallurgy to produce small, highly complex metal parts at scale. Fine metal powders are mixed with a binder, injection molded as a “green” part, then debound and sintered to achieve near-full density and strong mechanical properties. Features like undercuts, logos, fine teeth, and internal details are practical in a single net-shape operation.

MIM works best for high-volume production of small components that would be too costly to CNC machine or assemble from multiple pieces. Expect 15–20% shrinkage during sintering, so tolerances are looser than precision machining but good enough for many structural and wear parts. Tooling cost and process development are higher than simple machining or casting, so the economics favor annual volumes from tens of thousands into the millions. MIM is less suitable for very large parts, very low volumes, or parts needing ultra-tight tolerances without secondary machining.

Common Materials

  • 17-4PH stainless steel
  • 316L stainless steel
  • 420 stainless steel
  • Low-alloy steel 4605
  • Soft magnetic iron alloys
  • Cobalt-chrome alloys

Tolerances

±0.003" to ±0.005" on small features; roughly ±0.3–0.5% of dimension after sintering, with critical areas machinable tighter.

Applications

  • Orthodontic brackets and dental hardware
  • Surgical instrument components
  • Firearm triggers, hammers, and safety components
  • Smartphone and consumer electronics hinges and small brackets
  • Automotive sensor housings and lock components
  • Small precision gears and latch mechanisms

When to Choose Metal Injection Molding (MIM)

Choose MIM for small, complex metal parts needing good mechanical strength, high feature density, and medium-to-high production volumes. It shines when machining would require many setups, tiny tools, or assemblies from multiple components. Best for parts under roughly 50 g where tooling cost can be spread over large quantities.

vs Standard Injection Molding

Pick MIM instead of standard injection molding when the part must be metal for strength, temperature, wear, or conductivity. Geometry rules are similar, but MIM supports much higher mechanical performance and operating temperatures than plastic at the cost of higher part and tooling expense.

vs Overmolding

Use MIM when the core part itself must be a complex metal geometry rather than a plastic substrate with a soft or secondary layer. If you need a structural metal component first and may add soft-touch or plastic features later, start with MIM for the metal core and apply overmolding as a separate step if required.

vs Insert Molding

Choose MIM when you want a fully metal part produced in one operation instead of molding plastic around metal inserts. If the design would otherwise require many small metal inserts embedded in plastic for strength or wear, MIM can consolidate those features into a single metal component and then be assembled with plastic separately.

vs Compression Molding

Select MIM over compression molding when you need fine detail, tight feature control, and automated high-volume production of small metal parts. Compression molding suits larger, simpler shapes and composites, while MIM efficiently produces intricate metal geometries with good repeatability.

vs Metal 3D printing (DMLS/SLM)

Use MIM instead of metal 3D printing when you have a stable design and need tens of thousands to millions of parts at the lowest per-piece cost. MIM has higher upfront tooling cost but much lower unit cost and better throughput, while metal AM is better for prototypes, very low volume, or extreme geometries that even MIM tooling cannot support.

Design Considerations

  • Keep wall thickness as uniform as possible; avoid large solid masses to reduce distortion, porosity, and long sintering cycles
  • Design with generous radii and smooth transitions to minimize stress concentrations and improve mold filling and sintering stability
  • Account for 15–20% linear shrinkage; align critical dimensions with the primary mold pull direction and discuss shrink factors with your MIM supplier early
  • Avoid very long, thin cantilevers and knife-edges; thicken or support them with ribs to survive molding, handling, and sintering
  • Plan for secondary machining or coining on only the truly critical features where tolerances tighter than about ±0.003" are required
  • Clearly define functional surfaces, datum schemes, and inspection points on the drawing so the MIM house can target tooling compensation and process control where it matters most