Vacuum Forming & Blow Moulding

These processes are closely related to Pressing in that they rely on pressure forces into contact with a mould. In vacuum forming this is done by sucking the sheet material onto the mould whilst in blow moulding this is done by raising the pressure to force the material against the mould.
Tooling costs are much lower than for presswork but the forces involved are very much lower which limits the materials that can be used and the shapes produced.
The diagram below shows the equipment used for vacuum forming. Note that the corners of the mould are rounded, tapered and air vents are included in positions where air may become trapped. Whilst thermoplastic sheet is the most common material, alloys of aluminium, zinc and stainless steel can be vacuum formed although this is expensive. The mould can be made from any material which can withstand the relatively low temperatures and stresses involved.