Vacuum casting: production-quality plastic parts from silicone moulds
Vacuum casting makes production-quality plastic parts from silicone moulds. How it works, how our moulds cut time and cost, and when it beats injection moulding.
By BlacksmithAI · · 6 min read · اقرأ بالعربية
Key takeaways
- Vacuum casting pours polyurethane resin into a silicone mould under vacuum: production-quality plastic parts without a steel mould.
- The classic limit is the mould: a silicone mould is commonly quoted at around 20 to 25 casts before it wears out.
- We rebuilt the silicone mould around that limit: longer-lasting moulds, AI-designed moulds, parallel moulds and circular upcycling of worn silicone.
- And the process around it: scan-checked first parts, mould life tracking, masters printed from the parametric model, multi-cavity moulds and colour in the resin.
- The result: 500 to 2,000 parts, typically in 2 to 3 weeks from design approval. In our comparisons, about 6.8× cheaper than injection moulding and 3.5× faster than 3D printing for runs in this range.
It is the process behind most "looks-like, works-like" plastic parts: housings, covers, clips, seals and lenses that have to look and behave like the moulded product, in quantities where a steel mould does not make sense. Vacuum casting is also called urethane casting or polyurethane casting; the names describe the same process.
How vacuum casting works
- The master. A perfect copy of the part is made from the CAD model, usually 3D printed or machined, then finished to the surface the final parts should have.
- The silicone mould. Liquid silicone is poured around the master and cured. The mould is cut along its parting line and the master is taken out, leaving a cavity of the exact shape.
- The cast. Two-part polyurethane resin is mixed, degassed and poured into the mould inside a vacuum chamber. The vacuum pulls the air out, so the resin fills thin walls and fine detail without bubbles.
- Cure and demould. The resin cures, often in an oven, the mould is opened and the part comes out. Gates and vents are trimmed and the part is finished.
- Repeat. The same mould makes the next part, until it wears.
What vacuum casting makes well
- PP-like parts: tough and slightly flexible, for clips, caps and living hinges.
- ABS-like parts: rigid and impact resistant, for housings, covers and brackets.
- Rubber-like parts: soft-touch in a range of hardnesses, for seals, grips and feet.
- Clear parts: for lenses, windows and light pipes.
- Detail and finish close to injection moulding, because the silicone copies the master exactly.
- Size: parts up to about 50 cm with us, and larger on request.
The limit everyone hits: the mould
Silicone is soft, which is why it releases fine detail and undercuts so well, and also why it wears. Each cast ages the mould a little: heat, resin and demoulding take their toll. A silicone mould is commonly quoted at around 20 to 25 casts. For a handful of prototypes that is plenty. For 1,000 parts it means dozens of moulds, each one time, labour and silicone, and each one a chance for parts to drift.
That is why vacuum casting has traditionally been sold for prototypes, and why we rebuilt the silicone mould to make it a production process.
What we changed in the silicone mould
Longer-lasting moulds
Our moulds are built to make more parts before they wear. More parts per mould means fewer moulds per run, less silicone and labour per part, and more parts that come out of the same cavity, so they match each other more closely.
AI-designed moulds
Where a mould splits, where the resin goes in and where the air gets out decides whether a cast comes out clean. We design those from the CAD model with AI rather than by eye: parting lines, gates and vents placed from the part's geometry. Fewer failed casts, cleaner surfaces, and good parts from the first moulds instead of after a round of trial and error.
Parallel moulds
A single mould casts one part at a time. We make several identical moulds from the master and cast them side by side, so a run of hundreds or thousands advances in parallel instead of in a queue. That is what puts 500 to 2,000 parts within 2 to 3 weeks of design approval.
Circular moulds
A worn mould is usually thrown away. We reclaim the silicone and upcycle it into new tooling. Less waste, lower material cost per part, and a process that suits the industrial capability we want to build in Egypt and the GCC.
What we changed around the mould
Scan-checked first parts
The first part off every mould is scanned and compared with the CAD model, using the same check AI Reverse Engineering runs on scans. You get the result as a measurement of how closely the part matches the design, and a problem is caught on part one, not part 500.
Mould life tracking
Every mould counts its casts. We retire a mould before its wear shows in the parts, so part 2,000 matches part one.
Masters printed from the parametric model
The master is printed straight from your approved parametric model, not hand-made. A design change is a new master from the updated model, not a hand-modified pattern, so the change is exact and quick to make.
Multi-cavity moulds
Small parts are cast several to a mould, so each pour makes more than one part. Fewer pours per run, and a lower cost per part on small items.
Colour in the resin
Parts are coloured through the resin rather than painted, so the colour runs all the way through and does not chip or scratch off.
Vacuum casting vs 3D printing vs injection moulding
| 3D printing | Injection moulding | Blacksmith vacuum casting | |
|---|---|---|---|
| Tooling | None | A steel or aluminium mould, paid up front | Silicone moulds from a master |
| 500–2,000 parts take | Long: every part is printer time | Weeks for the mould, then fast | Typically 2–3 weeks from design approval |
| Cost for 500–2,000 | Flat per part, does not fall | Dominated by the mould | About 6.8× lower than moulding in our comparisons |
| Materials | Printing resins and powders | The real thermoplastics | PP-like, ABS-like, rubber-like, clear |
| Finish | Layer lines or grainy | Excellent | Close to moulded |
| Best for | Prototypes, a few dozen | Tens of thousands | 500 to 2,000, bridge runs, spares |
The full comparison is in 500 to 2,000 plastic parts: 3D printing, injection moulding or vacuum casting?, and why to cast before you tool up is in bridge production.
From a part in your hand to a vacuum-cast run
No CAD? Start from the part. AI Reverse Engineering builds an editable model from photos, a scan or a STEP file; you approve it; the master, the moulds and the parts follow. That is vibe-CADing carried all the way to production, and it is how we work. See small-batch production for how a job runs, or contact us for a quote.
Frequently asked questions
What is vacuum casting?
Making plastic parts by pouring polyurethane resin into a silicone mould under vacuum, so the resin fills every detail without bubbles. The mould comes from a master of the part, so no steel tooling is needed.
How many parts can a silicone mould make?
A silicone mould is commonly quoted at around 20 to 25 casts. Ours are built to last longer, and we cast several identical moulds in parallel, which is how we make runs of 500 to 2,000 parts.
How long does vacuum casting take?
For runs of 500 to 2,000 parts, typically 2 to 3 weeks from design approval.
Is vacuum casting the same as urethane casting?
Yes. Vacuum casting, urethane casting and polyurethane casting are names for the same process: resin cast into silicone moulds under vacuum.
Is vacuum casting cheaper than injection moulding?
For hundreds to a couple of thousand parts, usually yes, because there is no steel mould to pay for. In our comparisons, about 6.8× lower total cost for runs of 500 to 2,000. For tens of thousands, injection moulding wins.
How do you check vacuum-cast parts?
The first part off every mould is scanned and compared with the CAD model, and every mould counts its casts so it is retired before wear shows in the parts.
Can vacuum-cast parts be coloured?
Yes. We colour parts through the resin rather than painting them, so the colour runs all the way through.
Do you offer vacuum casting in Egypt and the GCC?
Yes. We make vacuum-cast parts locally for customers in Egypt and the GCC. Every run is quoted per project.
Get a quote for your run
500 to 2,000 plastic parts, typically 2 to 3 weeks from design approval, made locally in Egypt and the GCC. Tell us the part, the material and the quantity.