Plastic vacuum casting is a two-stage process that requires, first, the production of the master and mould, and then the creation of the finished part itself. A master pattern of the finished product must first be created. This is often designed in a CAD application and produced using a 3D printer, then used as a master to create the silicone rubber mould. Each mould can be used multiple times before it starts to lose definition. After this, it will need replacing to avoid degrading the quality of the mould.
If you want to reproduce something that already exists, instead of creating a master pattern you can prepare the original for reproduction by covering any gaps with tape and removing imperfections that will affect the smooth finish of the copy. The parting line, which forms the edge of the finished part, is marked out using coloured tape, as this will be visible through the silicone used to create the mould. The master is then suspended inside a bolster and covered with liquid silicone rubber.
The bolster is placed in the casting chamber, from which all air is removed to create a vacuum, extracting any bubbles from the silicone. The mould is cured before the master pattern is removed, leaving a void within the mould, which is filled with resin to create the reproduction.