From one SLA master to a batch of Vacuum Cast parts

An SLA prototype can help you check the shape, fit and appearance of a new component. But what happens when one part isn’t enough?

You might need a set of housings for assembly trials, samples for customers to handle, or components for a small pilot build. If the design is settled, Vacuum Casting offers a way to turn an SLA master into a batch of polyurethane parts without investing in production tooling.

The SLA master sets the standard

Vacuum Casting starts with a master pattern, usually made using SLA 3D Printing. The master is prepared and finished to represent the parts you want to receive. A silicone mould is then formed around it, capturing its shape and surface detail.

This makes the master worth careful attention. If a visible face needs a smooth, painted finish, or a texture needs to appear on every casting, those requirements should be agreed before the mould is made. Marks or imperfections on the master can also be carried through to the cast parts.

An SLA prototype that’s been used for testing isn’t automatically the best casting master. Depending on its condition and finish, it may be better to make a dedicated master from the approved CAD design.

How does one master become a batch?

Once the SLA master is finished, it’s placed in a box and surrounded with liquid silicone. The silicone is cured, then the mould is opened and the master removed.

For each part, liquid polyurethane is prepared, coloured if required, and poured into the mould under vacuum. The vacuum removes trapped air, allowing the material to fill the mould. After curing, the casting is removed, inspected and finished.

The mould can be used again for further parts. Its useful life depends on the component’s geometry and the polyurethane grade, so the number of parts available from one mould is assessed for each project. Typically, a mould may be reusable up to 25 times.

When is Vacuum Casting useful?

The route becomes particularly interesting when the design is stable, and you need several similar parts. Examples include:

Housings or covers for assembly and fit trials
Samples for customer demonstrations
Components for a limited number of test units
Pilot batches before committing to injection mould tooling
Flexible parts such as grips, seals or protective components
Parts that need cast-in inserts or overmoulded features

Polyurethane grades can be selected to provide different levels of rigidity, flexibility, colour and finish. This gives you more options than simply making further copies in the original SLA resin.

For example, an SLA housing might establish the design and appearance. Vacuum Cast copies could then be used across several assembly trials or supplied to a group of testers. If the design changes after their feedback, you can assess the revision before committing to a production tool.

Should you just print more SLA parts?

Sometimes, yes. If you only need one or two additional parts, or the design is still changing regularly, further SLA prints may be the more practical route. Vacuum Casting adds the time and cost of preparing a master and making a silicone mould.

The intended use matters too. A Vacuum Cast part is made from polyurethane, which can simulate the behaviour or appearance of a production plastic, but it isn’t identical to an injection moulded part made in that plastic. If testing requires the exact production material and manufacturing process, that should be discussed at the outset.

Quantity, geometry, material properties, finish and timing all affect the choice. There’s no fixed number of parts at which every project should switch from SLA to Vacuum Casting.

Plan the batch before making the mould

The most useful time to discuss Vacuum Casting is when the SLA design is being approved, before the master is prepared. Tell us:

How many parts you need now and whether you expect another batch
What the parts will be used for
Which dimensions and assembly features matter most
The rigidity or flexibility required
The colour, texture and finish you want
Whether inserts, overmoulding or other assembly work is needed
Your deadline and likely future production route

These details help us advise on the master, polyurethane grade, mould design and lead time. Vacuum Casting projects are quoted individually because the part and finishing requirements can vary considerably.

Take the next step from prototype to batch

The first SLA part helps you decide whether the design works. When you need to put that design into more hands, Vacuum Casting may provide the next step.

Send us your CAD file, intended quantity and details of how the parts will be used. We can advise whether further SLA 3D Printing, Vacuum Casting or another process is the most suitable route.

Call us on 01763 249760, email office@prototypeprojects.com, or request a quote.