Vacuum Casting

How does vacuum casting work?

A master pattern is built first, either by SLA printing or CNC machining. Two-part silicone is poured around the master and cured for 8 to 16 hours. The master is removed, leaving a silicone cavity. PU resin and hardener are mixed under vacuum at 5 to 10 mbar to pull out dissolved air, then poured into the mold while still under vacuum. The part cures in a 60 to 80°C oven for 1 to 4 hours, then is demolded, trimmed, and finished. Each silicone mold runs 15 to 25 parts before replacement.

What file formats do you accept?

STEP is preferred for the 3D part file. STL is also accepted. A PDF drawing is needed alongside the 3D file for parting line preferences, insert locations, surface finish callouts, and tolerance-critical dimensions. If you have an existing master pattern or a physical sample, contact us before submitting an RFQ and we can advise on the best path forward.

Which materials are available?

PU resin families: ABS-like (tensile strength 50 to 65 MPa, Shore D 80 to 85, for rigid housings and brackets), PP-like (Shore D 70 to 75, for snap fits and living hinges), transparent PU (for light pipes and lens prototypes), and rubber-like PU (Shore A 30 to 90, for seals, grips, and soft-touch components). Silicone casting is available for parts that require true silicone material properties. If your target production resin is not listed, include it in the RFQ and we will match the closest PU formulation.

What tolerances can vacuum cast parts hold?

General tolerance is ±0.15% of nominal dimension, minimum ±0.3mm on features over 100mm. First shots off a fresh mold run tighter; parts near the end of mold life drift wider as the silicone stretches. Critical features under 100mm can hold ±0.1mm with controlled mold temperature and degassing. Anything tighter than ±0.1mm requires post-cast machining. PU resin shrinks 0.15 to 0.25% during cure; master pattern dimensions are scaled up to compensate.

How long does it take to get first parts?

First parts in 7 to 10 business days from file approval. Master pattern build takes 3 to 5 days. Silicone mold cure takes 1 day. Casting, curing, and finishing takes 1 to 3 days depending on quantity and resin. Simple single-resin parts on a fast schedule can arrive in 5 business days. Multi-color or painted parts add 1 to 2 days for finishing.

How many parts can one silicone mold produce?

15 to 25 parts per mold under standard conditions. PP-like and rubber-like resins are harder to demold and wear the mold out 20 to 30% faster, reducing yield to 10 to 18 parts per mold. For orders above 25 pieces, additional molds are cut from the same master. Total runs above 100 parts are better served by rapid injection molding with aluminum tooling, which costs less per part at that volume.

What surface finish do cast parts have?

The cast part replicates the master pattern surface 1:1. An SLA master at Ra 1.6μm produces cast parts at Ra 1.6μm. A hand-polished master produces glossy cast parts. A textured master transfers texture to every shot. Post-cast finishing options: primer and paint (any RAL color), pad printing, soft-touch coating, and chrome-effect painting. Specify the surface finish requirement in the RFQ, including any texture reference or gloss level.

Can vacuum cast parts have metal inserts or threaded features?

Yes. Metal threaded inserts are installed post-cast using heat-set or press-fit methods, same as injection-molded parts. Inserts can also be cast in place if the location is designed into the mold. Direct-cast threads in PU resin work for light-load applications but wear after repeated assembly cycles. For any thread that will see repeated engagement, specify a metal insert in the drawing.

Do you sign NDAs before reviewing design files?

Yes. Send an NDA request to [email protected] before uploading files. We return a signed copy within 24 hours on business days. Files can also be uploaded through our secure RFQ portal.

How do vacuum cast parts compare to injection-molded parts in testing?

Fit and form test accurately. ABS-like PU resin handles assembly tests, snap-fit evaluations, and ergonomic reviews. Functional testing for load, fatigue, UV resistance, and long-term chemical exposure does not transfer: PU compression set is higher than production rubber, UV resistance is weaker than molded ABS or PC, and creep under sustained load is more pronounced. Plan validation testing around what vacuum cast parts can actually show. Parts that need to pass production-equivalent mechanical testing should run in rapid injection-molded resin instead.