Vacuum Casting

Vacuum casting reproduces plastic parts in silicone molds under vacuum, delivering bubble-free, cosmetic-quality prototypes and low-volume production from polyurethane resins.

Overview

Vacuum casting uses a 3D-printed or machined master to create a silicone mold, then casts polyurethane resins under vacuum to remove air and prevent bubbles. It produces accurate, cosmetic-quality plastic parts that closely mimic injection-molded ABS, PP, PC, rubber, or clear acrylic. Typical runs range from 1–30 parts per mold, with lead times in days, not weeks.

This process fits low-volume production, pilot runs, and appearance or functional prototypes where surface finish and material behavior matter. It handles undercuts and complex geometries easily, but silicone mold life and PU resin selection limit total volumes and operating temperatures. Tolerances are looser than hard tooling, and part-to-part variation grows as the mold wears. Expect good cosmetics, reasonable accuracy, limited temperature/chemical resistance, and a finite mold life traded against very low tooling cost and fast turnaround.

Common Materials

  • ABS-like polyurethane
  • PP-like polyurethane
  • Clear polyurethane (PMMA-like)
  • Elastomeric polyurethane (Shore A)
  • High-temperature polyurethane
  • Flame-retardant polyurethane

Tolerances

±0.005" to ±0.010"

Applications

  • Consumer electronics housings and enclosures
  • Automotive interior trim and bezels
  • Clear light lenses and display windows
  • Overmold-like soft grips and gaskets
  • Low-volume functional brackets and covers
  • Marketing and show-model prototypes

When to Choose Vacuum Casting

Choose vacuum casting for low-volume plastic parts (roughly 1–100 units) that need injection-mold-like appearance and feel without paying for hard tooling. It suits complex geometries, undercuts, and multi-material “soft-touch” concepts where surface finish, color, and transparency matter. Use it when you can live with moderate tolerances and limited material temperature/chemical performance in exchange for low tooling cost and fast lead time.

vs Silicone Mold Casting

Pick vacuum casting when you need bubble-free parts, thin walls, and reliable surface finish, especially for clear or cosmetic components. Standard silicone mold casting without vacuum struggles with trapped air, leading to voids, incomplete fills, and more rework on complex or fine-detail parts.

vs Injection Molding

Pick vacuum casting for pre-production and low-volume runs where hard tooling cost and lead time are hard to justify. It gives you production-like plastics and cosmetics quickly, while you finalize design before investing in steel molds.

vs CNC machining

Pick vacuum casting when the geometry is organic, highly contoured, or full of undercuts and internal features that would require complex setups or multiple machined pieces. It is also better when you need several identical plastic parts in a short time with molded-in textures or consistent color rather than machined tool marks.

vs 3D printing

Pick vacuum casting when you need multiple copies with better surface finish, closer-to-production materials (rigid, clear, or elastomeric), and consistent color throughout the batch. It is effective when you already have one good 3D-printed master and want short-run, customer-facing parts without visible layer lines.

Design Considerations

  • Aim for uniform wall thickness (1.5–4 mm) to minimize sink, warpage, and inconsistent cure in polyurethane castings
  • Include at least 1–2° of draft where possible to reduce stress on silicone molds and improve part release
  • Avoid very sharp internal corners; use generous fillets (≥0.5 mm) to extend mold life and reduce tearing
  • Keep minimum feature sizes around 0.5–0.8 mm and clearly mark critical-to-function features and tolerances on drawings
  • Call out color, gloss, texture, and transparency requirements explicitly so the shop can select the right resin, pigment, and finishing steps
  • Flag any press-fit, threaded, or high-load areas early; these may need metal inserts or local design changes to survive in urethane