Casting

Casting forms near-net-shape parts by filling molds with molten metal or liquid resin, enabling complex geometry at low unit cost in volume.

Overview

Casting makes parts by creating a mold cavity and filling it with molten metal or liquid resin, then solidifying and removing the part. It excels at complex 3D shapes, thick-to-thin transitions, internal features (with cores), and parts that would be expensive to machine from billet. Expect some secondary operations—machining critical datums, drilling/tapping, and finishing—to hit tight fits and surface requirements.

Common sub-processes include metal casting (e.g., sand, investment, permanent mold, die casting) and polyurethane/urethane casting (vacuum casting) for prototype-to-bridge volumes with production-like plastics. Tradeoffs are tooling lead time and cost, process-driven variation (shrink, porosity, draft), and tolerances that typically require machining on functional interfaces. Part size range is broad, from small precision castings to large structural housings.

Common Materials

  • Aluminum A356
  • AISI 1020 steel
  • 316 stainless steel
  • Gray iron
  • Bronze C932

Tolerances

±0.010" to ±0.030" as-cast; ±0.002" to ±0.005" on machined features

Applications

  • Pump and valve bodies
  • Gearbox and motor housings
  • Impellers
  • Manifolds and fluid fittings
  • Machine bases and brackets
  • Enclosures with integrated bosses and ribs

When to Choose Casting

Choose casting when you need complex geometry, integrated features, or large parts where machining from solid would drive high material removal and cost. It’s a strong fit for medium to high volumes once tooling is justified, or for prototype/bridge builds using urethane casting. Plan to machine critical interfaces if you need precise fits, sealing surfaces, or tight positional control.

vs CNC machining

Choose casting when the part is bulky or highly contoured and would require extensive machining time and material waste from billet. Casting also enables internal cavities and near-net ribs/bosses that are impractical to mill without assemblies.

vs 3D printing (additive manufacturing)

Choose casting when you need lower unit cost at scale, broader material property options (especially metals), or production-like repeatability once the process is dialed in. Casting also supports larger parts and better surface/heat-treatment options than many printed metals and polymers.

vs Forging

Choose casting when geometry complexity and internal features matter more than maximum strength and fatigue performance. Castings can integrate shapes that would require multiple forging steps or extensive post-machining.

vs Injection molding

Choose casting when volumes don’t justify injection tooling, when parts are too large or thick for good molding outcomes, or when you need metal parts. Urethane casting can deliver injection-mold-like plastics for prototypes and short runs without hard tooling.

vs Fabrication/weldments

Choose casting when you want fewer parts, better sealing integrity, or reduced weld distortion and inspection burden. Casting can consolidate brackets, housings, and manifolds into a single near-net component with consistent wall thickness.

Design Considerations

  • Add draft on all pulled faces and align the parting line to avoid side actions where possible
  • Keep wall thickness as uniform as practical; use ribs/gussets instead of thick sections to reduce shrink and porosity risk
  • Define machined datums and critical functional surfaces on the drawing; leave enough machining stock on those areas
  • Avoid sharp internal corners; use generous radii to improve flow, reduce hot spots, and increase tool life for secondary machining
  • Design cores and core prints with stability in mind; minimize long, thin cores and provide support where needed
  • Call out cosmetic vs functional surfaces clearly (as-cast finish vs machined/ground) to control cost and quoting assumptions