The pragmatic bridge between prototype and injection molding.
20–50 polyurethane copies that look, feel and function like ABS, PC, PP, PMMA or rubber. Silicone tooling built in 3 days. No hard-tool cost. Ideal for pilot runs, trade shows, beta users and crowdfunding fulfillment.
Vacuum casting
Four stages from master part to cast copies. Unlike injection molding, no hard tooling is built — the silicone mold is soft and molded around the master pattern.
How vacuum casting works.
Four stages from master part to cast copies. Unlike injection molding, no hard tooling is built — the silicone mold is soft and molded around the master pattern.
Master pattern
SLA printed or CNC machined master part with target surface finish. Any cosmetic detail on the master reproduces in every casting.
Silicone mold
Master suspended in mold frame, RTV silicone poured under vacuum to eliminate bubbles. 24-hour cure, then cut open along parting line.
Casting cycle
PU resin mixed with pigment, degassed under vacuum, poured into mold via gravity feed. Cured at 60–80 °C for 1–2 hours.
Finish & ship
Parts demolded, gates trimmed, flash removed, cleaned. Optional paint, pad print, silk screen. Individually packed.
Polyurethane resins that mimic production plastics.
ABS-like PU
The default vacuum-cast resin. Mimics ABS stiffness, surface finish, and machinability. White, black, or any pigment.
PC-like PU
Clear or tinted. Mimics polycarbonate optical clarity. Lightly tinted versions for lens prototypes, display covers.
PP-like PU
Slightly flexible like polypropylene. Living hinge prototypes, closures that need repeated flex.
PMMA-like PU
Optically transparent, hard, polishable. Mimics acrylic for optical prototypes, displays, lightguides.
Rubber-like PU
Elastomeric PU covers the full rubber hardness range. Grips, seals, gaskets, overmolded parts.
Glass-filled PU
Glass-bead or milled-fiber filled for structural rigidity. Mimics PA66-GF30 for bracket prototypes.
Flame-retardant PU
Halogenated or phosphorus FR package. Required for electrical enclosures, lighting fixture prototypes.
High-temp PU
Elevated heat-deflection temperature. Under-hood automotive prototypes, appliance interior parts.
Food-contact PU
FDA 21 CFR 175-177 compliant for food contact. Food packaging prototypes, kitchen appliance parts.
PU resins are formulated to match the look, feel and mechanical behavior of common injection-molding plastics. They are not identical — but close enough for functional prototypes, pilot runs, and user studies.
When vacuum casting is the right call.
Pilot runs & market validation
20–50 parts to validate product-market fit before committing to $15K injection tooling. Lets you iterate one more time if users flag issues.
Trade show & investor demos
Fully finished, painted, pad-printed demo units in 10 days. Indistinguishable from production-injection parts to anyone not an engineer.
Crowdfunding fulfillment
Kickstarter early backers (first 50–100 units). Ship polished beta units while production tooling builds.
Complex geometry at low volume
Geometries expensive to CNC (deep pockets, thin walls, complex curves) cast easily in silicone molds.
Multi-color or multi-material assemblies
Cast one part in Shore A rubber, another in Shore D rigid, bond or interlock. Cheaper than multi-shot injection tooling.
Pre-production validation
Get parts in the final injection-molded geometry before production starts. Test fit, assembly, and cosmetic before tooling commitment.
Medical pre-clinical trials
Small batch of anatomically accurate devices for animal or cadaver studies. Biocompatible PU grades available.
Not every project needs vacuum casting. Below is where it dominates other processes on cost, speed, and practicality.
The pragmatic bridge between prototype and — questions
What is vacuum casting and when should I use it?
Vacuum casting (also called urethane casting or RTV silicone molding) uses a silicone mold made from a master pattern (typically SLA printed or CNC machined) to cast polyurethane copies that mimic injection molded plastics. Use it when you need 20–50 functional parts in ABS-like, PC-like, PP-like or rubber-like materials — the sweet spot where 3D printing becomes expensive and injection molding tooling isn't justified.
How many parts can a silicone mold produce?
Typical silicone tool life is 20–30 castings per mold. Larger or complex parts may limit a mold to 15 castings. For runs beyond 30 parts, we build a second or third silicone mold from the same master — still dramatically faster and cheaper than injection tooling.
What materials can you cast?
Polyurethane resins that mimic: ABS (various Shore D hardnesses), Polycarbonate (tough, clear or pigmented), PP (flexible, chemical-resistant), PMMA (transparent optical), TPE/rubber (Shore A 30–90), glass-filled PA (structural), flame-retardant PU (UL 94 V-0), food-contact PU. Colors mixed to Pantone on request. Transparent, translucent, and opaque options.
What is the lead time for vacuum casting?
Standard lead time is 7–10 business days from CAD approval. Day 1–2: master part printed via SLA. Day 3–4: silicone mold built around master. Day 5–10: casting runs with curing cycles (1–2 parts per mold per day for typical parts). First articles shipped from day 8–10.
What tolerances can vacuum casting hold?
Typical tolerance is ±0.15 mm or ±0.3% of dimension, whichever is greater. Slightly looser than CNC but tighter than FDM 3D printing. Surface finish matches the master (typically SLA-smooth at Ra 2–5 µm after polish). For cosmetic or mating features below 0.1 mm, CNC machine those surfaces instead.
Can vacuum cast parts be painted or finished?
Yes. PU parts accept paint, silk screen, pad print, clear coat, and chrome paint. Parts can be tumbled, bead blasted, or hand-finished. Color can be cast-in (throughout part) or painted afterwards. For Pantone-matched color, casting pigment is more consistent than painting.
When should I switch from vacuum casting to injection molding?
Practical crossover is around 100 parts. Below 100: vacuum casting total cost (master + silicone mold + cast parts) is lower than injection tooling + parts. Above 100: aluminum rapid tooling injection molding becomes cheaper per part and enables production materials (true ABS, PP, PC) instead of PU mimics.
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