Pressure forming is a sophisticated version of the vacuum forming process. This process closes the appearance gap with traditional molding techniques. Pressure forming is really an old thermoforming technique which has been used by the thin-gage plastic packaging forming industry for many years.
The mold makers start by creating a pattern based upon drawings and specifications of the custom part. From the pattern, these craftsmen produce either a hardwood or aluminum mold. A wooden mold is used mainly for a customer required prototype or a very low volume production run. The aluminum mold is used for a full production run and when the pressure forming process is necessary.
The pressure forming technique provides for forming heavier sheet from 0.093" thick up to 0.375" thick. The technique is accomplished by forcing a hot sheet against a mold, usually female, by introducing compressed air to the back side of the heated sheet. This method will provide as much as 75 psi working on the sheet surface as compared to the 14 psi in vacuum forming.
Pressure forming can achieve the high quality and detailed look of injection molding, without the expensive tooling costs. By using air pressure on the back side of the sheet during the forming process, textures, undercuts and injection molding details can be achieved.