Metal Casting

Metal casting forms metal parts by pouring molten alloy into molds, enabling complex geometries and large parts with relatively low per‑part cost at volume.

Overview

Metal casting creates parts by melting metal and pouring it into a mold cavity that defines the final shape. It covers processes like sand, die, investment, permanent mold, centrifugal, and shell mold casting, each optimized for different alloys, sizes, complexity, and production volumes. Casting is especially strong for complex internal passages, thick sections, and large parts that would be wasteful or impossible to machine from solid stock.

Use metal casting when you need complex shapes, integral features, or large parts in metals like aluminum, steel, iron, or bronze, and you have low-to-high production volumes. Expect looser as-cast tolerances and rougher surface finishes than machining, with critical surfaces usually finished by machining. Tooling and pattern costs are the main upfront tradeoff, so casting pays off as volumes increase or when the geometry would be very expensive to fabricate by other methods.

Common Materials

  • Aluminum 356
  • Gray iron
  • Ductile iron
  • Carbon steel 1020
  • Stainless steel 304
  • Bronze C954

Tolerances

±0.005" to ±0.030" depending on process, section size, and mold type

Applications

  • Engine blocks and cylinder heads
  • Pump and compressor housings
  • Valve bodies and manifolds
  • Gearbox and motor housings
  • Impellers and turbine wheels
  • Industrial brackets and mounting lugs

When to Choose Metal Casting

Choose metal casting when you need complex 3D geometry, internal passages, or large solid sections in metal and can accept moderate as-cast tolerances. It suits everything from prototypes (with low-cost tooling options) up to high-volume production once dedicated molds or dies are justified. It works best when critical surfaces can be machined and the rest of the part can remain as-cast.

vs Polyurethane/Urethane Casting

Pick metal casting when you need structural metals, higher temperature resistance, wear resistance, or long-term production durability that polymers cannot handle. Metal casting has higher tooling cost and lead time than urethane casting but supports much larger production runs, higher loads, and harsher environments.

vs CNC machining

Choose metal casting when the geometry would require extensive material removal, deep cavities, or complex internal passages that are hard or impossible to machine. Casting reduces material waste and cycle time for bulky or complex shapes, with CNC used only where tight tolerances or fine finishes are needed.

vs Metal 3D printing

Choose metal casting for production-scale quantities, larger parts, and lower cost per part once tooling is in place. 3D printing suits very low quantities and extreme complexity; casting becomes more economical and robust for traditional industrial shapes and when you can live with casting-grade feature resolution.

vs Sheet metal fabrication

Use metal casting when you need thick sections, complex 3D forms, or fluid passages that can’t be made from bent and welded sheet. Casting produces monolithic parts with fewer welds and fasteners, improving stiffness and sealing where fabricated assemblies would be cumbersome.

vs Plastic injection molding

Select metal casting when your part must endure high temperatures, high loads, or abrasive environments that plastics cannot survive. Casting carries higher melt temperatures and different tooling, but provides superior mechanical strength, dimensional stability under heat, and long-term durability.

Design Considerations

  • Target uniform wall thickness and gradual transitions to minimize shrinkage porosity, hot spots, and distortion
  • Include adequate draft (typically 1–3°) on all mold-pulled surfaces to simplify ejection and reduce tooling wear
  • Avoid sharp internal corners and isolated heavy sections; use generous radii and cored-out pockets to improve feed and solidification
  • Add machining stock on critical surfaces and holes so shops can hit tight tolerances with secondary machining
  • Specify only necessary tight tolerances and surface finishes to keep tooling complexity and scrap rates under control
  • Indicate preferred parting line, gating-restricted areas, and critical datum features on the drawing to help foundries design efficient tooling and fixturing