What is vacuum casting?
Vacuum casting is a way to make small series of plastic parts in polyurethane (PU). Liquid casting resin is poured into a silicone mould inside a vacuum chamber. The vacuum draws out air bubbles, so the resin also fills thin walls and fine details.
The result looks very much like an injection-moulded part: a clean surface, an even colour and properties close to the final product. But you don't need a steel or aluminium mould. At Makernaut, vacuum casting is done through selected, ISO 9001-certified partners.
How does vacuum casting work? In four steps
- Master model. First a flawless master is made, usually by SLA printing or CNC machining. Every detail of the master reappears in every cast part.
- Silicone mould. The master is suspended in a casting box and liquid silicone is poured around it. Once cured, the mould is cut open along a parting line and the master is removed.
- Casting under vacuum. The mould is closed, placed in the vacuum chamber and filled with PU resin. Once cured, the part is taken out of the flexible mould.
- Finishing. Sprues and flash are removed. Painting, inserts or a quality check follow where needed.
What determines the price of vacuum casting?
Vacuum casting costs consist of two parts: one-off costs for the master and the mould, and a price per cast part. The more parts you get from one mould, the smaller the share of those one-off costs per part.
| Factor | Effect on the price |
|---|---|
| Master model | One-off. A large or complex master costs more to print and finish smooth. If you supply your own master, that step drops away. |
| Silicone mould | One-off per mould. Larger parts need more silicone; undercuts and extra parting lines make the mould more labour-intensive. |
| Quantity | One mould typically lasts 20 to 25 castings. Need more, and an extra mould is added. |
| Size and weight | More volume means more resin and longer curing time per part. |
| Material, colour and hardness | Standard PU is the baseline. Clear, rubber-like, a specific Shore hardness or a custom colour take extra work or a pricier resin. |
| Finishing | Painting, texture, inserts or printing come on top of the casting price. |
So there is no fixed price per part. Two parts of the same volume can come out differently if one has a simple parting line and the other three undercuts. That's why vacuum casting at Makernaut works with a custom quote: you'll have it within one working day.
How to keep vacuum casting costs down
- Limit undercuts. Every extra parting line makes the mould more complex.
- Keep walls evenly thick. It casts more easily and distorts less while curing.
- Match your quantity to the mould's life. For 20 parts one mould is enough; ask for slightly more and you're already paying for a second.
- Choose a standard colour, or have parts painted afterwards if only one variant needs it.
- Only ask for tight tolerances where they really matter. Vacuum casting typically achieves ±0.2 to 0.5 mm.
Which materials can you vacuum cast?
PU casting resins mimic the properties of common plastics. So you don't pick 'ABS', but a resin that behaves like ABS.
- ABS-like: rigid and strong, for housings, holders and mechanical parts.
- PC-like: clear with high impact strength, for covers and light guides.
- PP-like: flexible and chemically resistant, for clips and hinges.
- Rubber-like: elastic, in various Shore A hardnesses, for seals and grips.
When does vacuum casting pay off?
Vacuum casting sits between 3D printing and injection moulding. It pays off mainly for small series, typically from 1 to 100 parts.
| Your situation | Choose |
|---|---|
| One or a few parts, design still changing | 3D printing |
| Small series with the look and feel of a moulded part | Vacuum casting |
| Clear or rubber-like parts in a small series | Vacuum casting |
| Marketing samples or a pre-series for a launch | Vacuum casting |
| Large, steady volumes in the final material | Injection moulding |
Vacuum casting is also a handy bridge. While the final injection mould is being made, you already have parts to test, show or sell. And if you find a design flaw at that stage, you change the master rather than a steel mould.
Mind the limits: parts up to about 600 × 600 × 300 mm, and PU resins that resemble the final material without being it. If your part must be certified in the actual production material, final testing will need injection-moulded parts.
In summary
The price of vacuum casting is made up of one-off costs for the master and mould, plus a per-part price that depends on size and material. It pays off for small series that need to look like a moulded part, and as a bridge to series production. Upload your model to Quotebase and request a quote; you'll have it within one working day.