Vacuum forming is a simplified version of thermoforming.
Thermoforming is a manufacturing process for thermoplastic sheet or film. The sheet or film is heated between infrared heaters to its forming temperature. Then it is stretched over or into a temperature-controlled, single-surface metal mold. It is held against the mold surface unit until cooled. The formed part is then trimmed from the sheet. The sheet trim is usually reground, mixed with virgin plastic, and reprocessed into useable sheet . There are several categories of thermoforming, including vacuum forming, pressure forming, twin-sheet forming, free blowing, and simple sheet bending. whereby a sheet of plastic( Plastic is a term that covers a range of synthetic or semisynthetic polymerization products. They are composed of organic condensation or addition polymers and may (often) contain other substances to improve performance or economics. There are few natural polymers generally considered to be "plastics".) is heated to a forming temperature, stretched onto or into a single-surface mold (Molds, or moulds, are various fungi that cover surfaces as fluffy mycelium and usually produce masses of asexual, sometimes sexual spores. The molds are not an actual taxonomic or phylogenetic grouping – they can be found in the divisions Zygomycota, Deuteromycota or Ascomycota. The presence of mold usually implies decay, although some molds are used deliberately, for example in cheese-making, and for the production of antibiotics.) and held against the mold by applying vacuum.
Normally, draft angles must be present in the design on the mould, otherwise release of the formed plastic and the mould 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.