Vacuum forming
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Vacuum forming is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, stretched onto or into a single-surface mold, and held against the mold by applying vacuum between the mold surface and the sheet.
Normally, draft angles must be present in the design on the mold, (A recommended minimum of 3°) otherwise release of the formed plastic and the mold is very difficult.
Vacuum forming is usually – but not always - restricted to forming plastic parts that are rather shallow in depth. A thin sheet is formed into rigid cavities for unit doses of pharmaceuticals and for loose objects that are carded or presented as point-of-purchase items. Thick sheet is formed into permanent objects such as turnpike signs and protective covers.
Relatively deep parts can be formed if the formable sheet is mechanically or pneumatically stretched prior to bringing it in contact with the mold surface and before vacuum is applied [1].
Suitable materials for use in vacuum forming are conventionally thermoplastics, the most common and easiest being High Impact Polystyrene Sheeting. This is molded around a wooden mold and can form to almost any shape.
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[edit] Common Problems Encountered with Vacuum forming
- Moisture Absorption: Absorbed moisture can expand forming bubbles within the plastic's inner layers. This may be solved by drying the plastic for an extended period at high but sub-melting temperature.
[edit] See also
[edit] References
- J.L. Throne, Understanding Thermoforming, Hanser Gardner Publications, Inc., Cincinnati OH, 1999.
[edit] External links
- Vacuum Forming Guide w/ Pictures
- Vacuum Forming Process Description
- Fabrication Guide for Polycarbonate
- A Vacuum Forming Guide
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