What is Vacuum Forming?

Vacuum forming, also known as thermoforming, is a technique to shape a variety of plastics to a mold called a buck. Vacuum forming is used by hobbyists, designers, and engineers, as well as in industrial settings. A vacuum form table is not a complicated piece of technology -- it requires mechanisms to heat plastic and pour it over a sample, and a chamber from which all the air can be pumped out to form a vacuum, ensuring that the plastic adheres closely to the buck. Even homemade vacuum form tables can be so precise that small pores from organic samples will appear in the final cast.

Thermoforming is among the oldest of plastic shaping techniques. Most of the plastic products we see in our daily life are produced using this technique. Common plastics shaped using this technique include polystyrene, polyethylene, polycarbonate, and acrylic. First-time users often use the inexpensive plastic styrene. In more expensive machines used in industrial process settings or for specialized purposes, a variety of fine-tuned pneumatic, hydraulic, and thermal controls are used.

The process begins by fixing a sheet of plastic of uniform thickness onto a sturdy frame. This frame is inside the vacuum chamber. Then the frame is heated and slowly lowered over the buck, until the frame touches the bottom of the chamber and the soft plastic is draped over it.

Next, air is pumped out of the chamber, adhering the plastic to the buck in a precise mold. If the mold contains too deep a hole, "blowouts" may occur, in which the plastic rips and the process must be restarted. Because of blowouts, there are limitations on the shape of the mold. The vacuum in the box can be created by something as off-the-shelf as a vacuum cleaner. A high-intensity vacuum is rarely necessary.

After the mold is completed, the plastic must be allowed to cool. When the plastic is cooled, it is removed vertically from the sample. Vacuum forming does not create a form that encircles the entire mold, but only one side, because the sample must lie on the bottom of the vacuum chamber unless a special stand is used. When the plastic is difficult to remove from the mold, a knife must be used to score the perimeter first.