From home hobbyists to large corporations, vacuum forming has been used as an efficient, economical way to make plastic parts. Manufacturers vacuum-form plastic trays, packaging, signs and thousands of other items. The basic machine is a simple system consisting of a clamp frame, heater and vacuum system which can be used with countless different molds. The mold determines the shape of the finished part and can be reused for many years.
To begin the molding process, the operator sets a mold on the vacuum forming machine's mold table and clamps a plastic sheet into the machine's frame. An electric heater heats the plastic until it softens. The operator lowers the frame onto the mold, stretching the plastic so it conforms to the mold's shape. A vacuum pump draws air out from under the sheet, and it fits the mold exactly. When the plastic cools, the operator releases the molded plastic piece from the machine.
Molds can be made of many common materials, such as plastic, wood or metal, as long as they're stable and heat-resistant. Typical mold sizes range from a few inches to more than a foot. The size of the plastic sheet dictates the maximum mold size, and the mold designer must not create a mold so large or tall that the stretched sheet can't fit around it. If you're molding small items, it makes sense to arrange several small molds on the molding table to make the most of every plastic sheet. The molds must also have strategically placed vent holes so the air can be drawn out evenly, avoiding bubbles.
The mold shapes have some limitations. For example, steeper draft angles, or angles measured from vertical, make the plastic more difficult to release from the mold. Angles under five degrees are not recommended. You must also avoid horizontal voids or dips into molded shapes, as the mold would not release the plastic.
Vacuum forming machines use thermoplastic sheets, which means that the plastics soften when heated. They include polystyrene, acrylonitrile butediene styrene (ABS), polyethyene terepthalate glycol (PETG) and acrylic. The sheet thickness is generally limited to under an eighth of an inch.
You can obtain plans or kits to build a vacuum forming machine for home hobbyist use. Though more limited than commercial machines, their affordability opens up opportunities for amateur and semiprofessional users. Many craftspeople and model builders use them to create good-quality plastic parts.