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An introduction to Room Temperature Vacuum Casting

This process of molding is applied with the utilization of a vacuum chamber to extract the liquefied material into the mold. The method of vacuum casting is applicable when the mold that is desired has complex details or undercuts. It is also utilized when there is a concern of air entrapment or if the material has fibrous properties or wire reinforces.

A two piece silicone mold is placed in a vacuum chamber while the raw liquefied material is mixed and degassed; this is done when dissolved gasses are removed from liquid materials called degasification applied to prevent gas bubbles formation that is undesirable when a smooth finish is required. After the extraction of gasses is completed, the liquid material is then poured into the mold. The vacuum is then released and the mold is taken out of the vacuum chamber.

After this procedure, the vacuum casting is cured in an oven. Curing is a process of toughening or hardening of the liquefied material. This can also be applied to polyurethane and other plastics like acrylic. The silicone mold can be reused to up to 20 times maximum where it will start to deteriorate and can no longer be useful. 

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In the oven, it takes to up to hours for the liquid material to be cured depending on its size. After an exothermic reaction of the plastics, the cavity is opened and the molded plastic is removed. The silicone cavity is the closed and the procedure done again.

The disadvantage of Vacuum Casting is that it is expensive and is not preferred for mass production. However a substitute is available instead of this method known as Reaction Injection Molding. This process does not require expensive vacuum chambers and mixing facilities. The process utilizes simple plastic injection system with a couple of pressurized chambers.

So in Short

Vacuum casting is a prototyping technology used when you need a short run of your 3d cad model made out of a PolyUrethane with properties close to real injected plastics such as ABS, POM ,PA or TPE’s TPR rubbers

Usually series of 5-100 pieces will be run using this casting technology.

WHAT ARE THE ADVANTAGES OF Vacuum casting?

The main advantages of this process are amuch lower tooling costs and a quicker turn-around than traditional steel mould making. the lead-time to create casted models is around 7-10 days.

The products have an exceptional detail and accuracy which comes close to the final injected plastic parts.

Flexible silicone moulds allow significant undercuts, simplifying mould-making and containing costs.

The process:

The first step of vacuum casting process involves encapsulating/enclosing a master model in a liquid Silicone rubber. Than a vacuum is applied to the mould. The mould is then cured in an oven at around 70°C

Once cured the mould can be split up in 2 or more parts, at which point the master model is removed leaving a mould cavity perfectly replicating the master model.

what is possible with vacuum casting?;

We can make double or triple shot products, we can cast rubber or TPE or TPR like materials. (with 20-80 shore A hardness)

We can vacuum cast optical clear plastics ( same like PMMA) and we can use Inserts in the products.

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