Description of Vacuum Forming

Written by marion sipe
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Description of Vacuum Forming
Its low cost makes vacuum forming useful for creating prototypes. (plastic chairs image by Adrian Hillman from Fotolia.com)

Vacuum forming is a technique that allows the easy moulding of plastics into products, or the creation of packaging in which a product will be sold. It has a wide variety of uses, from creating plastic toys, to creating form-fitting packaging, to the making of prosthetics for the disabled. The process is widely used in many industries from automotives and robotics to cosmetics, athletic equipment and toy manufacturing.

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The Machine

Vacuum forming machines come in many shapes and sizes. Some are big enough to fill a wall and create multiple parts, such as in the automotive industry. Others are no larger than an average table. In general, the machine works by heating a piece of thermoplastic until it becomes flexible and then pressing it onto a mould. A vacuum pump then pulls out all the air so the thermoplastic fits precisely to the mould.

Moulding Methods

Molds can be either “male” or “female” meaning that they either form the plastic around their shape, or the plastic is pressed into their shape by the vacuum. For instance, when a tray is made for a given product, a model of that product made of heat-resistant material would be placed in the vacuum forming machine. The heated plastic presses down onto the model, conforming to its shape. Such a model is “male.” However, in making something like a football helmet, a “female” mould of the helmet could be made and the plastic pressed down inside it by formation of the vacuum.

The Materials

There are a variety of thermoplastics used for vacuum forming, depending on the finished product. Making a single-use tray for packing baked goods doesn’t require much of the plastic: it merely has to retain its shape. However, making something more durable, such as a sign for a store, requires a harder plastic, one able to endure the elements. Materials may include polycarbonate (Lexan), polythene and polypropylene, all of which must be heated to the right temperature to become pliable enough to mould.

Three-Dimensional Objects

While containers, trays and helmets are all easily made using vacuum forming, some three-dimensional objects require more than a single piece. These three-dimensional objects require at least two sides that are then joined together. Such objects are hollow, making them lighter weight, but they can still be quite strong.

Finishing the Product

Once the plastic cures, or hardens as it cools to a normal temperature, it’s removed from the mould. Air is pumped back in, separating the mould and the plastic, sometimes with the help of a spray on agent that keeps the two from sticking together. Vacuum forming can create sharp details, so if the mould was shaped beforehand, there is no need for hand-shaping of the product. Also, because the colour and texture of the finished product can be formed in, there’s no need for painting. This reduces the costs of finishing the product, making vacuum forming economical.

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