Investment Casting

Investment casting (lost wax) produces complex, near-net-shape metal parts with fine detail, tight tolerances, and excellent surface finish from reusable wax patterns.

Overview

Investment casting, or lost wax casting, uses disposable wax patterns and ceramic shells to produce highly detailed, near-net-shape metal parts. It excels at complex geometries, thin walls, internal passages, and fine surface finishes with minimal machining. Typical surface finishes around 125–250 µin and tight, repeatable tolerances make it popular for precision components.

Choose investment casting when you need intricate features, moderate to high part value, and annual volumes from tens to many thousands. Tooling cost is higher than sand casting but usually lower than high-pressure die casting, with better accuracy and more alloy flexibility than many other casting routes. Tradeoffs include higher per-part cost than coarse processes, limited section thickness range, and size constraints compared to large sand castings. It is ideal for stainless steels, nickel superalloys, and other difficult-to-machine or hard-to-cast materials where machining from solid or alternative casting methods would be expensive or less precise.

Common Materials

  • Stainless Steel 304
  • Stainless Steel 17-4 PH
  • Carbon Steel 1020
  • Inconel 718
  • Ti-6Al-4V Titanium
  • Cobalt-Chrome

Tolerances

±0.005" for first inch, ±0.002"/inch thereafter

Applications

  • Turbine blades
  • Medical implant components
  • Valve bodies and pump impellers
  • Firearm receivers and triggers
  • Industrial hardware and brackets
  • Aerospace hinge and latch components

When to Choose Investment Casting

Choose investment casting for small to medium-sized metal parts with complex geometry, fine details, or thin walls that need good accuracy and surface finish. It fits best for annual volumes from prototype/short run (with rapid tooling or printed patterns) up to many thousands where tooling cost can be amortized. It is especially attractive when using difficult alloys or when you want to reduce downstream machining time.

vs Sand Casting

Choose investment casting over sand casting when you need finer detail, smoother surface finish, and tighter tolerances, especially on smaller or intricate parts. It is better for thin walls, small features, and precision components where machining allowance needs to be minimized.

vs Die Casting

Choose investment casting over die casting when you need steel, stainless, nickel, or titanium alloys instead of aluminum or zinc, or when you cannot justify very high tooling costs and production volumes. Investment casting also handles more complex geometries and thicker sections without the high injection pressures and die wear issues of die casting.

vs Permanent Mold Casting

Choose investment casting instead of permanent mold casting when the part has complex cores, undercuts, or fine details that are difficult or impossible to achieve with rigid metal molds. It is also preferable for hard-to-cast alloys and when you need better detail resolution at moderate production volumes.

vs Centrifugal Casting

Choose investment casting over centrifugal casting when you need detailed external geometry, features, and complex shapes rather than primarily hollow, axisymmetric sections like tubes, bushings, or rings. Investment casting is better suited for parts where dimensional accuracy of external surfaces and small features is critical.

vs Shell Mold Casting

Choose investment casting over shell mold casting when surface finish, feature resolution, and tolerance are more critical than absolute lowest tooling cost. It offers better detail on small parts and more flexibility with intricate geometries and internal passages formed via wax patterns and ceramic cores.

Design Considerations

  • Keep wall thickness generally between 0.060" and 0.250" and avoid abrupt transitions; use gradual thickness changes and fillets to reduce shrink defects
  • Add uniform draft (typically 1–2°) where possible on external features to help wax pattern ejection and shell removal
  • Specify realistic tolerances and surface finish; tighten only critical features to keep tooling and inspection costs under control
  • Use generous radii at internal corners (≥0.040") and avoid sharp re-entrant corners to improve mold filling and reduce stress concentrations
  • Provide clear datum schemes and machining stock on critical surfaces that will be finished after casting, typically 0.020–0.060"
  • Group similar parts in families and design common gating/fixturing features to reduce tooling complexity and lower per-part cost