Vacuum Casting Services

Where vacuum casting sits

There are three ways to get a plastic part, and they are arranged by quantity.

3D printing has no tooling at all. It is the cheapest route to one part, and the only route to some geometries, but the surface and the material properties are those of an additive process.

Injection moulding uses a steel tool. The tool is a substantial investment, and it only pays back across a production volume — but once it exists, parts are cheap, consistent and available in production materials.

Vacuum casting sits between them. A silicone tool is cast around a master pattern and used to produce a limited number of parts. The tool costs a fraction of a steel mould, the parts come out with a production-like surface and a wider choice of material properties than a printed part, and the quantity it suits is roughly tens of pieces rather than thousands.

That middle position is what makes the process useful. It is the route for the quantities that are too many to print one at a time and too few to justify steel — sales samples, pilot builds, field trials, market tests, and the bridge period while production tooling is being cut.

How the process works

The sequence matters, because every part inherits the quality of the master.

1. The master pattern is made. Usually machined on our floor, which gives the best dimensional accuracy and the best surface; printed where the geometry suits additive better.
2. The silicone tool is cast around it. The master is suspended in a frame and silicone is poured around it; once cured, the tool is cut open and the master removed. A two-part tool is normal for a simple part, with more sections where the geometry needs them.
3. Parts are cast under vacuum. Resin is poured into the closed tool inside a vacuum chamber, which draws it into every detail and pulls out trapped air. The tool is then opened and the part removed.
4. The part is finished. Flash is removed, and any feature that has to be accurate — bores, sealing faces, threads — is machined on our floor.

The vacuum step is what distinguishes the process from simple silicone casting. Casting a resin that cures under vacuum is a different thing: the pressure differential is what makes the part fill fine detail without voids. The process is arranged through our vetted partner network and managed as one job with any machining that follows.

Materials, and one advantage worth knowing

The confirmed range covers polyurethane systems and the engineering plastics in our standard range, and the full list is on the materials page.

One property of the process is worth pulling out because it changes how a programme can be run: the same silicone tool can produce parts in several different materials. Colour, hardness and flexibility can be varied from one tool, which makes it practical to trial a colourway or a durometer with a customer before committing to production tooling, without the cost of a second tool.

That is a genuine advantage over injection moulding, where changing the material usually means a different set of process parameters and sometimes a different tool. Where a programme is still deciding what the part should feel like, casting from one tool in three materials is a cheap way to answer the question.

Tolerance, and what has to be machined

Because the tool is flexible, vacuum casting reproduces fine detail well — undercuts, lettering, texture and thin features all come through. What it does not do is hold a tight dimensional tolerance, for the same reasons a casting does not: the material shrinks as it cures, and the tool itself moves slightly.

The practical rule is the one that applies to any cast part:

Treat the casting as the shape and the machining as the accuracy.

Features that have to be exact are machined afterwards, and those features are held to ±0.01 mm with ISO 2768-m as the general tolerance block — see tolerances we hold. What that covers in practice:

Feature	Route
Outer form, ribs, bosses, texture	As cast from the tool
Bores and bearing seats	Machined after casting
Sealing faces and mating surfaces	Machined after casting
Threads	Cut after casting
Cosmetic faces	As cast, or painted to the master’s texture

The master pattern is where the accuracy comes from. Machining the master gives every part from the tool the best chance of being right, which is why we machine masters rather than printing them where the accuracy matters.

Design rules for a cast part

Plan the tool split before the design is fixed. The master has to come out of the tool and the part has to come out of the tool afterwards. Where the split line and the pull direction fall is a design decision, and it affects where the flash appears and which faces can be cast cleanly.

Wall thickness should be as uniform as the design allows. Uneven sections cure unevenly and shrink differently, which shows up as distortion and sink.

Deep, narrow features are harder than they look. The vacuum helps fill fine detail, but a deep narrow slot still has to be filled and released, and the tool has to survive being opened around it.

Decide which faces are seen and which are functional. The cosmetic faces should be cast against the tool; the functional faces can be machined afterwards, which is where the tolerance belongs.

Plan the finishing early. Textured, painted and as-cast parts each have their own requirements, and painting a vacuum cast part is common where the appearance has to match a production component.

Quantities, tooling and lead times

The silicone tool is quoted separately so you can see the true cost per part across the run rather than a blended figure. Tool life is finite and the expected number of parts is confirmed with the quotation, which is what makes the comparison with injection moulding meaningful rather than approximate.

Orders for cast parts start from a single piece, because the tool is the only fixed cost and it exists once. Where the cast parts then need machining — bores, faces, threads — that stage follows the same rules as any machined order: 50 pieces per style and material for production, samples from a single piece in 5–10 days, and production in 25–35 days after sample approval.

A machined master pattern takes 5–10 days, and the tool and first parts follow from it. Every order ships with pre-shipment photos of the actual parts before dispatch, and a material certificate where the supplier issues one; the quality documents page covers what else can be supplied on request.

How to start

Send the model or drawing, the quantity, what the part has to do, and whether the appearance has to match a production component. Say at the enquiry whether the material choice is still open — where it is, casting the same tool in two or three materials is a cheap way to settle the question before production tooling is committed. The reply comes back within 24 hours with DFM feedback on the tool split, the wall thicknesses and which features should be machined after casting.