CastcraftVacuum Forming Explained

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Vacuum forming (also known as thermoforming) is a way to make thin plastic products by heating a plastic sheet until it is soft, then lowering the plastic sheet over a pattern at the same time the air is withdrawn from between the plastic and the pattern. When the air is withdrawn, a vacuum is created, and the plastic sheet is pressed to the pattern by atmospheric pressure. Vacuum forming typically makes "one-sided" or "shell" type parts, as shown below.

Vac formed model airplane parts
Vac form model airplane parts

You have seen many commercial products made by vacuum forming, including:

"Blister" and "bubble" display packaging, plastic cups, plates, and bowls, food trays, tubs, containers, garden pots and plant starter trays, remote control car, boat, and plane bodies, soft candy molds, soap molds, candle molds, hot tubs and spas, shower liners, ornaments, decorations, and props.

What can you make with a homemade machine?

You can make the same kinds of things as described above, especially molds and model parts. Many molds produced for making plaster castings, concrete stepping stones, and candies are made by vacuum forming. Most remote control car bodies are produced by vacuum forming. The only limitation is the size of the plastic sheet that your machine will accept. If the biggest plastic your machine can accept is 2 feet by 4 feet, you couldn't make a hot tub!

Also, anything made by vacuum forming cannot have undercuts or perfectly vertical sides. The plastic forms tightly to the shape of the pattern. Vertical sides in the pattern would create so much friction that you wouldn't be able to remove the part from the pattern. An undercut is like a wedge, with the wide part of the wedge on top. The plastic would wrap tightly to the narrow part of the wedge, and you wouldn't be able to get the narrow formed plastic over the wide part of the wedge. If you need to make a mold of something with undercuts or vertical sides, a rubber mold is best.

You can build a vacuum forming machine in your home workshop. The Do-It-Yourself Vacuum Forming book shows how and why these machines work, and how to build a simple one. The Hobbyist Vacuum Forming Machine Plans show exactly how to build a medium-sized machine capable of forming up to 1/4" thick plastic sheets, with pictures, diagrams, detailed instructions, and sources of supply. The Professional Vacuum Forming Machine Plans show how to build a larger machine, and also include pictures, blueprints, diagrams, and sources of supply.

The practical difference between the Hobbyist and Professional machines is the size of the plastic sheet that can be formed. The Professional machine can form bigger sheets of plastic, which means you can make bigger parts or more copies of smaller parts with each forming run.

What's the difference between commercial machines and a homemade machine?

Big, extremely expensive commercial / industrial machines do everything automatically. They load the plastic, heat the plastic, control the vacuum, press the plastic, knock out the part after it is formed, and so on. With a homemade machine, YOU load it, turn on the heater and vacuum, lower the plastic over the pattern, remove the pattern, and trim the part. BUT - The parts you make can have the same detail and quality as those made on a commercial machine, maybe even better!


Related Links:

Vacuum Forming Books

Plans for building vacuum forming machines