Metal Injection Molding (MIM)

Metal injection molding (MIM) forms small, complex metal parts by molding metal powder feedstock, then debinding and sintering to near-net shape.

Overview

Metal injection molding (MIM) produces dense metal parts by injecting a metal-powder/binder feedstock into a mold, then removing the binder and sintering to full density. It excels at small, intricate geometries—fine features, thin sections, and multi-feature parts—that would be costly to machine, with good surface finish and repeatability at volume.

Choose MIM when you need high quantities of net-shape metal components where machining would drive cycle time or scrap, and when part size stays within typical MIM envelopes (often grams to tens of grams). Tradeoffs: tooling cost and lead time are significant, sintering shrinkage must be controlled (dimensions depend on process capability and geometry), and sharp thickness transitions, large flat parts, and very tight position tolerances may require secondary machining or grinding. Material selection is narrower than wrought stock and properties depend on sintered density and heat treat.

Common Materials

  • 17-4 PH stainless
  • 316L stainless
  • 4140 alloy steel
  • M2 tool steel
  • Ti-6Al-4V
  • Tungsten heavy alloy

Tolerances

±0.005 in

Applications

  • Firearm trigger/sear components
  • Orthodontic brackets
  • Watch cases and small hardware
  • Surgical instrument jaws and handles
  • Consumer electronics hinges and brackets
  • Automotive sensor housings and levers

When to Choose Metal Injection Molding (MIM)

MIM fits high-volume production of small metal parts with complex geometry, fine features, and thin walls where near-net shape eliminates extensive machining. It’s a strong choice when consistent repeatability and good surface finish matter and the part can tolerate process-driven shrinkage control and potential secondary ops for critical datums.

vs Standard Injection Molding

Choose MIM when the part must be metal for strength, wear, temperature, or corrosion performance and you still want injection-molded complexity at volume. Standard injection molding wins on cost and speed when plastic properties meet requirements and tighter cosmetic control is needed without sintering variability.

vs Overmolding

Choose MIM when the primary structure needs to be an all-metal component with integrated features that would otherwise require multi-piece assemblies. Overmolding is better when you need a hard/soft interface, sealing, grip, or electrical insulation integrated onto an existing substrate.

vs Insert Molding

Choose MIM when you want to avoid managing inserts, insert-loading labor, and interface failure risks by consolidating features into a single metal part. Insert molding is preferable when you need metal threads/bushings in a plastic body or when the insert must be a different metal/material than the molded matrix.

vs Compression Molding

Choose MIM when you need high feature density, fine detail, and tight repeatability that benefit from injection-style filling and near-net shaping. Compression molding is generally aimed at thermosets/elastomers or simpler geometries where flow length and knit-line concerns differ.

vs Transfer Molding

Choose MIM when you need complex 3D geometry in metal with consistent molding and a production path to high density after sintering. Transfer molding is typically used for thermosets and encapsulation applications where metal mechanical properties are not the driver.

Design Considerations

  • Keep wall thickness as uniform as practical to reduce distortion during debind/sinter and improve dimensional control
  • Avoid large flat areas and long unsupported spans; add ribs or curvature to improve sintering stability
  • Use generous internal radii and avoid sharp corners to reduce stress concentrations and cracking during sintering
  • Define critical datums and tolerances clearly and expect secondary machining on tight location/flatness requirements
  • Plan for ejection and gating like injection molding; avoid features that trap the part or force complex slides unless volume justifies it
  • Confirm part mass/size early and call out required density, heat treat, and surface finish so the supplier can quote the right sinter cycle and secondary ops