Vacuum forming, or thermoforming, is a plastic molding technique used by hobbyists, designers, engineers, and in industrial settings. The process involves heating a sheet of plastic, draping it over a mold, and using a vacuum to adhere it to the mold. Common plastics used include polystyrene, polyethylene, polycarbonate, and acrylic. The process has limitations on mold shape and requires cooling before removing the plastic from the mold.
Vacuum forming, also known as thermoforming, is a technique for molding a variety of plastics into a mold called a buck. Vacuum forming is used by hobbyists, designers and engineers as well as in industrial settings. A vacuum table isn’t a complicated piece of technology: It requires mechanisms for heating the plastic and pouring 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 tightly to the pail. Even homemade vacuum tables can be so accurate that tiny pores of organic samples will appear in the final cast.
Thermoforming is one of the oldest plastic molding techniques. Most of the plastic products we see in our daily life are made with this technique. Common plastics molded in this technique include polystyrene, polyethylene, polycarbonate, and acrylic. Novice users often use cheap plastic styrene. In more expensive machines used in industrial process settings or for specialized purposes, a variety of optimized pneumatic, hydraulic and thermal controls are used.
The process begins by affixing 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 buck, until the frame touches the bottom of the chamber and 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 a hole that is too deep, “blowouts” can occur, where the plastic tears and the process must be restarted. Due to the blowouts, there are limitations on the shape of the mold. The vacuum in the box can be created by something ready made like a vacuum cleaner. A high intensity vacuum is rarely needed.
After the mold has been completed, the plastic must be allowed to cool. When the plastic has cooled, it is removed vertically from the sample. Vacuum forming does not create a shape that surrounds the entire mold, only one side, because the sample must lie on the bottom of the vacuum chamber unless a special holder is used. When the plastic is difficult to remove from the mold, you need to use a knife to score the perimeter first.
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