Vacuum Casting

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 Cast Quote Compare all processes

01 · Process

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.

02 · PU materials

Polyurethane resins that mimic production plastics.

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.

ABS-like PU

Shore D 85 · general

The default vacuum-cast resin. Mimics ABS stiffness, surface finish, and machinability. White, black, or any pigment.

PC-like PU

Shore D 85 · transparent

Clear or tinted. Mimics polycarbonate optical clarity. Lightly tinted versions for lens prototypes, display covers.

PP-like PU

Shore D 72 · flexible

Slightly flexible like polypropylene. Living hinge prototypes, closures that need repeated flex.

PMMA-like PU

Shore D 85 · optical

Optically transparent, hard, polishable. Mimics acrylic for optical prototypes, displays, lightguides.

Rubber-like PU

Shore A 30–90

Elastomeric PU covers the full rubber hardness range. Grips, seals, gaskets, overmolded parts.

Glass-filled PU

Shore D 85 · structural

Glass-bead or milled-fiber filled for structural rigidity. Mimics PA66-GF30 for bracket prototypes.

Flame-retardant PU

UL 94 V-0

Halogenated or phosphorus FR package. Required for electrical enclosures, lighting fixture prototypes.

High-temp PU

HDT 120 °C

Elevated heat-deflection temperature. Under-hood automotive prototypes, appliance interior parts.

Food-contact PU

FDA-compliant

FDA 21 CFR 175-177 compliant for food contact. Food packaging prototypes, kitchen appliance parts.

03 · Use cases

When vacuum casting is the right call.

Not every project needs vacuum casting. Below is where it dominates other processes on cost, speed, and practicality.

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.

FAQ

Vacuum casting questions.

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.

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.

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.

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.

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.

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.

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.

The pragmatic bridgebetween prototypeand injection molding.