Metal Casting

Metal casting forms near-net-shape metal parts by pouring molten alloy into molds, enabling complex geometries and large sizes with moderate tolerances and tooling-driven economics.

Overview

Metal casting makes metal parts by melting an alloy and pouring it into a mold cavity that defines the part shape. Common variants include sand, die, investment, permanent mold, centrifugal, and shell mold casting; they range from low-tooling, flexible sand molds to high-tooling, high-rate die casting.

Choose metal casting when the geometry is hard to machine efficiently (complex external shapes, internal passages, ribs), the part is too large or heavy for practical machining from billet, or you need near-net-shape economics at moderate to high volumes. Casting is also a good fit when specific alloys, mass properties, or section thickness transitions matter.

Tradeoffs: tolerances and surface finish are typically looser than machining, and cast parts often need secondary ops (machining critical faces/holes, heat treat, impregnation). Risk drivers include shrinkage, porosity, warpage, and draft requirements; good foundry DFM and clear inspection datums keep these manageable.

Common Materials

  • A356 Aluminum
  • A380 Aluminum
  • 316 Stainless Steel
  • 17-4 PH Stainless Steel
  • Ductile Iron
  • C932 Bronze

Tolerances

±0.010" to ±0.030"

Applications

  • Automotive transmission housings
  • Pump and valve bodies
  • Impellers
  • Machine tool bases
  • Hydraulic manifolds
  • Bearing housings

When to Choose Metal Casting

Metal casting fits parts that benefit from near-net-shape metal with complex geometry, thicker sections, or large overall size. It’s a strong choice when volumes justify molding/tooling setup and you can machine only the critical features. Plan for foundry-driven constraints (draft, parting lines, gating/risers) and secondary finishing where needed.

vs Polyurethane/Urethane Casting

Choose metal casting when the part must be metal for strength, temperature, wear, conductivity, or regulatory/material requirements. Metal casting also scales better for long-term production and higher loads, while urethane casting is typically faster for cosmetic prototypes and low-volume plastic-like parts.

vs CNC Machining

Choose metal casting when machining would waste significant material, require excessive cycle time, or struggle with complex near-net shapes (deep cavities, organic surfaces, large ribs). Cast a near-net blank and machine only datums, bores, and sealing faces to control cost.

vs Metal 3D Printing (Additive Manufacturing)

Choose metal casting when you need lower unit cost at production volumes, larger parts than typical printer envelopes, or well-known foundry alloys and property data. Casting is often faster to industrialize for repeat production once tooling and process parameters are locked.

vs Forging

Choose metal casting when geometry complexity, internal features, or large section changes dominate the design. Casting can achieve shapes that would require extensive machining after forging, at the expense of the grain-flow benefits forgings provide.

Design Considerations

  • Add draft on external and internal faces early; call out where draft is not allowed and expect machining there
  • Control wall thickness and transitions; avoid abrupt thick-to-thin changes to reduce shrinkage, hot spots, and porosity
  • Place parting lines away from critical sealing surfaces and tight-tolerance features; plan machining stock on those areas
  • Specify datums and inspection features that will be machined, not as-cast surfaces, for repeatable measurement
  • Use generous radii at internal corners to improve mold fill and reduce stress concentrations and cracking
  • Define cosmetic expectations and allowable surface texture; as-cast finish varies by process and drives secondary finishing cost