What is Vacuum casting?

What is Vacuum casting?

Vacuum casting, sometimes referred to as Urethane Casting or Polyurethane Casting,using silicone moulds to make plastic and rubber components under vacuum. It is an extremely adaptable manufacturing process capable of mimicking the injection moulding to produce complex parts in polyurethane resins and cast nylon.

Due to the process being under vacuum, it produces high-quality bubble-free casting with smooth surface texture similar to painting effect.Vacuum casting can be extremely useful and worth considering when selecting rapid prototyping processes for plastic or rubber parts.

Advantages of Vacuum Casting

Vacuum Casting Process

There are three steps to making polyurethane vacuum cast parts: making the master pattern, making molds and casting the parts.

01 Master Patterns

Patterns are 3D solids of your CAD designs. They are usually made by CNC machining or with 3D plastic printing such as SLA/SLS. You can supply your own patterns or we can make them for you. Patterns need to be able to withstand heating to 40°C.

A master pattern can be any physical solid of your design. They are often made either by CNC machining or some form of 3D printing such as SLA. Note, however, that a pattern made from 3D printing will not be quite the same as the CNC counterpart, since the later process uses round cutting tools that cannot make very tight radius corners.

02 Making the Molds

Casting molds are made from liquid silicone. This silicone is poured around the master pattern inside of a casting box, and then allowed to cure in an oven for 16 hours. Once dried, the mold is cut open and the master removed, leaving behind an empty cavity in the exact negative shape of the original.

First the pattern must be carefully prepared, and that means sanding and sealing the surface with primer.  Once it’s ready, it’s placed into a casting box and liquid silicone is poured around it. Depending on the size of the part, it can take 12~24 hours to fully cure inside of an oven. Once dried, the mold is cut open and the master removed, leaving behind an empty cavity in the exact negative shape of the original.

03 Vacuum Casting Tolerances

The finished dimensions of vacuum cast parts are dependent on the accuracy of the master pattern, the part’s geometry and the type of casting material used.

Generally a shrinkage rate of 0.15% is to be expected.

What is Vacuum casting?
What is Vacuum casting?

Typical technical specification

Typical technical specification

Time frame Within 24 hr – 5 working days for up to 30-50 parts

Material choice Wide variety of materials available

Accuracy ±0.3% (with a lower limit of ± 0.3 mm on dimensions smaller than 100 mm)

Minimum wall thickness To ensure that the mould is filled properly, a wall thickness of at least 0.75 mm is necessary. But best results are achieved with a recommended wall thickness of 1.5 mm

Maximum part dimensions The size of the mould is limited by the dimensions of the vacuum chamber

Typical quantities Up to 50 parts per mould

Surface structure Gloss to Matt surface finish can be obtained

Materials of vacuum casting

Vacuum casting polyurethanes resins (Transparent PU, Soft plastic PU, ABS PU, PP/PE PU, Polycarbonate PU)
MaterialSupplier (Country)Material SimulationStrength ShoreFlexion(MPA)TC MaxProduct color descriptionAdvantage/DisadvantageShrinkage
PU8150Hei-CAST (Japan)ABS83 shD179085Amber,white and blackGood resistance1
UP4280Axson (France)ABS81 shD220093Dark AmberGood resistance1
UP5690Axson (France)PP75-83 shD600--130070White/BlackGood resistance1
PU8400Hei-CAST (Japan)Elastomer20-90shA//Milky white/BlackGood Bend1
T0387Hei-CAST (Japan)Elastomer30-90shA//ClearGood Bend1
PX 527Hei-CAST (Japan)PC85 shD2254105White/BlackHigh T℃ 105°1
PX223HTHei-CAST (Japan)PS/ABS80 shD2300120BlackIdealTG 120°1
PU8263Hei-CAST (Japan)ABS83 shD180085White94V0 flame retarding1
PX330Axson (France)Loaded ABS87 shD3300100Off WhiteV 0 far 251
PX522HTAxson (France)PMMA87 shD2100100ClearColoration TG100°0.996
PX521HTAxson (France)PMMA87 shD2200100ClearColoration TG100°0.996


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