Vacuum forming

From Plastics Wiki, free encyclopedia

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, 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. 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].

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.
• Webs may form around the mold, which is due to the overheating of the plastic and so must be carefully monitored. Webbing can also occur when a mold is too large or parts of the mold are too close together.

References

1. J.L. Throne, Understanding Thermoforming, Hanser Gardner Publications, Inc., Cincinnati OH, 1999.

External links

• Vacuum Forming Basics
• Vacuum Forming Guide w/ Pictures
• Vacuum Forming Process Description
• Vacuum Forming Tools & Thermoforming tools - A Video How-To