Vacuum casting (often shortened to vac casting) copies a master pattern in a silicone mould to make batches of 10 to 500 polyurethane parts close to injection-moulded quality. Lead time is confirmed at quote, and 20 small parts can take about a week. Small parts hold about ±0.2 mm, and large castings up to ±0.7 mm.
We're a UK vacuum casting company in Cambridge producing vacuum cast parts in polyurethane, silicone and epoxy. We make a silicone mould from a master pattern, such as an SLA print, then cast resin into it under vacuum to draw out air bubbles and pick up fine detail. Each mould makes a run of parts with a production-like surface finish and mechanical properties.
Vacuum casting at Complete Fabrication, at a glance
“A good master is one that has been designed or amended to suit the vacuum casting process. If the design works with the process rather than fighting against it, the results are better, the processing is easier and the unit price comes down.” Jim, Workshop Operations Manager
Medical device prototypes
Consumer product development
Aerospace and automotive components
It gives you small batches that look and feel closer to production, without committing to full tooling too soon.
Browse the casting materials and data sheets, or see what affects the price.
Small features and critical dimensions transfer cleanly from the master pattern to the finished part.
Polyurethane, silicone and epoxy resins selected to match the performance your prototype needs.
We give you a firm timeline at quote, so you can plan testing around it.
Why choose a UK vacuum casting supplier?
Vacuum casting since the 1980s
David Kent started casting resins under vacuum when he founded the company, and developed the process with a leading supplier of vacuum casting machines. We were the first to achieve two-shot vacuum casting, using self-coloured polyurethanes of different Shore hardness in one part.
David Kent also cast turbine blades for the Whittle Laboratory at the University of Cambridge. Glass-filled resin was cast into CNC-machined hard tools for dimensional accuracy, with Kevlar and a steel locking pin cast into each blade. The resin was not designed for hard tools, which made it a tricky job, and more than 100 blades in two to three designs were made over two to three years.
Today most of our production work is vacuum cast: scientific and medical instrument housings and components, in runs of tens to the low hundreds, self-coloured and ready to assemble.
Vacuum cast parts we have made
Owlstone breath analysers: self-coloured casework cast with an injection-moulded surface texture, in resin processed to keep impurities out. The work started as one- and two-off prototypes and grew over five years into production runs of 10 to 30, with tolerances held tight across every casting. Vacuum casting bridged the gap between trials and higher-volume manufacture.
I-Dration water bottle: we grew the bottle in two parts on our in-house Viper SLA machine, vacuum cast them in clear PU and bonded the top and bottom for a watertight seal. The drinking nozzle was cast in a self-coloured flexible PU.
Prism 200 casework (Cambridge Consultants): a high-value product that had to work in some of the most hostile conditions imaginable. The case had to meet an IP rating and survive environmental and drop testing. We made SLA masters with the agreed texture, fit-checked them with the client, then vacuum cast the case sets in PX 212 resin. Testing showed one weak area, so we added a woven glass-fibre reinforcement in the casting. The moulds are among the largest we make. We have made around 10 multi-part case sets a year for ten years, numbering into the low hundreds.
Medical device teams use vacuum casting for clinical-trial and user-testing batches of 10 to 500, in biocompatible and clear grades. See medical device prototyping.
Casting batches for hall tests and user trials are covered on our trial batches page, and our design for manufacture guide explains how to design parts for casting.
Examples of vacuum cast prototypes and small batches built for testing, review and real use
Find answers about our vacuum casting capabilities and process
No. Our vacuum casting uses polyurethane, silicone and epoxy resins poured into silicone moulds, which suits plastic and rubber-like parts. For metal parts we CNC machine from solid, and small SLA parts can be plated in copper, nickel or gold for a metallic finish.
No. Investment casting pours molten metal into a ceramic shell built around a wax or resin pattern. Vacuum casting draws liquid resin into a silicone mould under vacuum to make plastic and rubber-like parts. We do vacuum casting, not investment casting.
We make a master pattern, usually an SLA print, finish it to the surface you want, then pour liquid silicone around it to make a mould. Once the silicone cures, the mould is cut open and the master removed. Resin is then cast into the mould under vacuum, which draws out air bubbles and picks up fine detail.
Around 20 castings per mould. Some resins are harder on the silicone, so the number depends on the geometry and the resin and can be fewer. For larger batches we make more moulds from the same master.
Single castings up to 800 × 550 × 550 mm, with shots of up to 3.5 kg. Larger items can be cast in sections and joined.
Yes. We cast clear polyurethanes, such as 6095 clear casting resin, for covers, windows and transparent housings. The I-Dration water bottle, for example, was vacuum cast in clear PU from SLA masters.
Yes. We cast polyurethane elastomers such as Poly PT Flex, from about Shore A20 to A85, and RTV silicones across most Shore hardnesses, for grips, seals and soft-touch parts. See flexible gaskets.
No. Silicone moulds flex, so parts release without draft. Adding draft still helps if the part will be injection moulded later.
1.5 mm is a good starting point, with 0.75 mm possible in small, non-load-bearing areas. Large castings need thicker walls so the resin can flow through the whole part without bubbles.
Yes. We were the first to achieve two-shot vacuum casting, combining self-coloured polyurethanes of different Shore hardness in one part, for example a rigid body with a soft-touch grip.
Yes. The resin is pigmented before casting, so the colour runs right through the part and many parts need no painting. We mix colours in-house, and parts can also be painted to a Pantone or RAL reference.
Yes. Cast resin doesn't tap well, so we always use threaded inserts in cast parts. Brass inserts can be cast in place, as on the Owlstone breath analyser casework.
Vacuum forming heats a plastic sheet and pulls it over a mould, which suits thin shells and trays. Vacuum casting draws liquid resin into a silicone mould, which gives solid parts with fine detail, varied wall thickness and production-like properties. We specialise in vacuum casting.
Shrinkage is rarely an issue. We only compensate the master in a few cases, mainly long, thin castings, where a small percentage change adds up along the length.
Around 1 to 2% of castings are rejected and remade, mostly large, complex shapes. We record the materials, pattern and mould numbers, who made the parts and the check results for every batch.
Yes. The master patterns and silicone moulds can be handed over to you on request, along with the batch records.
Yes. We vacuum cast polyurethane, silicone and epoxy parts at our workshop in Whittlesford, a short drive south of Cambridge, in batches of 10 to 500.
Yes. The workshop is a two-minute walk from Whittlesford Parkway station. We also offer same-day delivery in the local area and overnight delivery across the UK, with delivery charges shown in your quote.
Reach out to discuss your vacuum casting project
Send us your design and we'll provide a cost and a timeline
