What is Vacuum Forming?

Plastic is usually molded by thermoforming.

Vacuum molding, also known as thermoforming, is a technique for molding a variety of plastics into a mold called a buck. Vacuum molding is used by hobbyists, designers and engineers, as well as in industrial settings. A vacuum table is not a complicated technology – it requires mechanisms to heat the plastic and pour it over a sample, and a chamber from which all the air can be pumped to form a vacuum, ensuring the plastic adheres well to the buck. Even homemade vacuum tables can be so accurate that tiny pores from organic samples will show up in the final mold.

Thermoforming is among the oldest plastic shaping techniques. Most of the plastic products that we see in our daily lives are produced with this technique. Common plastics molded with this technique include polystyrene, polyethylene, polycarbonate, and acrylic. First-time users often use cheap plastic styrene. On more expensive machines used in industrial process settings or for specialized purposes, a variety of pneumatic, hydraulic and thermally tuned controls are used.

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

Air is then pumped out of the chamber, adhering the plastic to the core in a precise mold. If the mold contains a hole that is too deep, “breaks” can occur, in which the plastic tears and the process must be restarted. Because of the breakages, there are limitations in the shape of the mold. The vacuum in the box can be created by something as common as a vacuum cleaner. A high-intensity vacuum is rarely needed.

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After the mold is completed, the plastic should cool down. When the plastic is cooled, it is removed vertically from the sample. Vacuum forming does not create a shape that surrounds the entire mold, but only one side, because the sample must be at the bottom of the vacuum chamber unless a special support is used. When the plastic is difficult to remove from the mold, a knife should be used to mark the perimeter first.

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