Vacuum Casting vs Rapid Injection Molding
For runs of 20 to 200 parts, vacuum casting usually suits the low end and rapid injection molding prototyping the high end, with the crossover set by part geometry and material. Vacuum casting starts fast from a silicone mould. Injection molding needs a tool but gives you production resin from the real process.
KEY FACTS
- Vacuum casting, also called urethane casting, makes parts from silicone moulds taken from a master pattern.
- Rapid injection molding makes parts from a metal tool in production plastics.
- HLH Prototypes Co LTD offers a minimum order quantity of 1 for prototypes, typically rising to 100,000 parts.
Silicone moulds wear with use, so vacuum casting suits short runs.
When does vacuum casting make sense?
Vacuum casting makes sense when you need a small batch of good-looking parts quickly and the design may still change. A master pattern is made first, often by 3D printing or CNC, and a silicone mould is cast around it.
Resin is poured under vacuum, which draws out air bubbles and helps it reach fine detail. The trade-off is mould life: silicone wears, and how many parts one mould yields depends on geometry and resin.
When is rapid injection molding the better choice?
Rapid injection molding is the better choice when you need production plastics, tight repeatability or a count at the upper end of your range. The tool is made faster than a full production tool, and parts come from the real moulding process, so you test genuine material behaviour.
The cost is the up-front tool and a longer start. Late design changes are harder once the cavity is cut.
How do the two methods compare?
The table shows the main trade-offs. Exact figures vary by part, so treat it as a guide, not a quote.
| Factor | Vacuum casting | Rapid injection molding |
| Tooling | Silicone mould | Metal tool |
| Best part count | Lower end of 20 to 200 | Upper end and beyond |
| Material | Urethane resins | Production thermoplastics |
| Design changes | Cheap and quick | Costlier once cut |
| Repeatability | Drifts as mould wears | Consistent across the run |
How should you decide for your project?
Start with the material. If the part must be tested in a specific production thermoplastic, choose injection molding whatever the count.
Then look at design stability. A design still being refined suits casting, and a frozen design suits a tool. Our team can look at your drawing and say which route fits before you commit.
Frequently asked questions
Can vacuum cast parts look like production parts?
Yes, with the right finishing. Cast parts can be painted or made in clear resin to resemble moulded parts.
How many parts does one silicone mould make?
It depends on the geometry and resin, so ask us about your design. Silicone wears faster than metal tooling.
What do you need to send for a quote?
A 3D CAD file, the material you want and the quantity. Our team then reviews the project.
Send your drawing for a free review through our HLH Prototypes Co LTD contact page and we will advise on the right process.