Polyurethane/Urethane Casting

Polyurethane/urethane casting makes plastic-like parts by pouring reactive resin into flexible molds, delivering high detail and fast bridge-production at low volumes.

Overview

Polyurethane/urethane casting (often done as vacuum casting in silicone molds) produces plastic parts by mixing and pouring two-part urethane resin into a mold, then curing at room or elevated temperature. It captures fine texture, small features, and cosmetic surfaces with minimal tooling lead time.

Choose it for prototypes and low-volume production when you need injection-molded-like appearance and functional properties without hard tooling. Typical runs are a few to a few dozen parts per mold, with multiple molds used for higher quantities.

Tradeoffs: dimensional control is moderate and varies with part geometry, resin shrink, and post-cure; tight tolerances usually need secondary machining. Material options cover a wide range (rigid, elastomeric, clear), but they won’t match every thermoplastic’s long-term heat/chemical performance. Mold life is limited, and large flat parts can warp; good gating/venting and consistent wall thickness reduce risk.

Common Materials

  • Rigid polyurethane
  • Elastomeric polyurethane (Shore A)
  • Clear polyurethane
  • Flame-retardant polyurethane
  • Filled polyurethane

Tolerances

±0.005"–±0.015"

Applications

  • Appearance prototypes for consumer products
  • Low-volume housings and enclosures
  • Elastomeric gaskets and seals
  • Overmold-like grips and bumpers
  • Clear lenses and light pipes
  • Bridge production parts before injection tooling

When to Choose Polyurethane/Urethane Casting

Pick polyurethane/urethane casting for prototypes and low-volume parts that need good cosmetics, fine detail, and a range of hardness options. It fits bridge production when lead time matters more than high-volume unit cost and when limited mold life is acceptable.

vs Metal Casting

Choose polyurethane/urethane casting when the part can be polymer and you need faster tooling, lower upfront cost, and better cosmetic surface replication at low volumes. Metal casting is better when you need high-temperature capability, structural stiffness, and true metal properties.

vs Injection Molding

Choose polyurethane/urethane casting to validate design, fit, and appearance before committing to hard tooling, or when volumes are too low to justify an injection mold. Injection molding wins on tight repeatability, high volumes, and broader thermoplastic material selections.

vs CNC Machining (Plastics)

Choose polyurethane/urethane casting when you need multiple copies with molded-like surfaces, complex internal geometry, or soft/clear materials that are difficult to machine. CNC machining is better for tight tolerances, sharp datum control, and quick single-offs without mold development.

vs SLA 3D Printing

Choose polyurethane/urethane casting when you want production-like polyurethane properties (including elastomers) and better durability than typical photopolymer resins. SLA is often faster for one-offs and intricate features, but material performance and long-term stability can be limiting.

Design Considerations

  • Maintain consistent wall thickness to reduce shrink sink and warpage; core out thick sections where possible
  • Add 1–3° draft on mold-pulled surfaces to improve release and extend silicone mold life
  • Define critical datums and plan for post-machining on tight-tolerance features such as bores, sealing faces, and interfaces
  • Avoid large unsupported flat panels; add ribs or gentle curvature to control bowing during cure
  • Call out surface finish and texture expectations (gloss, matte, SPI-like) and provide a cosmetic A/B/C surface map
  • Specify resin type, color, and hardness (e.g., Shore A/D) and note any heat/UV/chemical exposure requirements for proper material selection