Vacuum forming is a plastic moulding technique where a sheet of heated plastic is pressed down onto a pattern, or mould. Air is then sucked out of the area beneath the plastic, pulling it tightly down onto the pattern, closely following its shape. The result is a fast and technologically simple (hence, low cost) manufacturing technique that is used in a broad variety of applications such as blister packs, storage containers, drinking glasses and more. Using a vacuum forming machine is straightforward process once you're aware of the basic principles.
Produce your mould in a solid, heat-resistant material such as wood, making sure to use "draft angles" on its sides. This means that the base of the mould needs to be its widest point, and any angling of the sides must get narrower as they approach the top. If your mould flares outward and gets wider toward the top, you will not be able to remove it from the plastic. Place your mould on the platform in the forming machine.
Insert a plastic sheet into the upper portion of the vacuum former and clamp it firmly into position. It should form a "ceiling" above your mould, and there should be no visible gaps around the edges.
Turn on the heating element in the vacuum former and wait for the plastic to heat up to a malleable state. You will be able to tell it is done when the surface of the plastic starts to shimmer slightly, and you may notice a slight droop in the centre. Turn off the heat and raise the mould platform upward, pushing the pattern into the suspended plastic. Lock the platform in the upper position.
Turn on the vacuum pump. This will pull out all the air from between the mould and the plastic, pulling the sheet tightly against the surface of the mould. Allow the pump to continue running for two to three minutes, or until the plastic is at room temperature. Switch off the pump.
Detach the clamps and remove the plastic sheet from the forming machine. If your mould was properly shaped, the cooled plastic should already be squeezing it out of the recessed shape. Remove the mould and trim off the excess plastic.
Vacuum forming machines become very hot during use. Take proper care and use hand and eye protection when working with heated plastics.