Thermoforming Process (step-by-step)

thermoforming-thumb-200Vacuum Forming Plastic Process (step-by-step)

  • A material blank which has a length and width greater than the finished part is loaded into a clamp frame to be carried through the process.
  • The blank in the clamp frame moves into an oven where it is heated to the forming temperature. At the forming temperature, the material is softened and pliable, but remains in a sheet configuration and is not melted.
  • The material is then moved from the oven to the forming station. The softened blank is then sealed on the deck of the tool. In some instances, low pressure air will prestretch the material to enhance wall thickness uniformity on the finished part.
  • A vacuum is drawn between the blank and tool to form the softened material against the tool surface. In pressure forming, while the vacuum is drawn to avoid air entrapment, positive air pressure is applied on the non tool side of the material to force the material against the tool surface.
  • An option for the process when using female tools is to use a ‘pusher’ or ‘plug assist’ on the non tool side of the blank to control and improve material distribution in the finished part.
  • The (now) formed part, while still in the clamp frame, is removed from the forming tool.
  • The clamp frame releases (opens) for part removal.
  • The formed part is now ready for the next step – trimming.

What is Vacuum Forming?

engineering-quality-largeVacuum forming is a technique that is used to shape a variety of plastics. In school it is used to form/shape thin plastic, usually plastics such as; polythene and perspex. Vacuum forming is used when an unusual shape like a ‘dish’ or a box-like shape is needed. Below you can see the stages involved in vacuum forming.

To the right is an example of a vacuum formed toy. The simple ‘lorry’ mould has been placed in a vacuum former and a compressed polystyrene sheet has been placed above it. The polystyrene has been heated and then vacuum formed to the shape of the mould.

Many everyday items have been vacuum formed in this way. Look around your home – list some examples. as a guide – some food products are packaged in vacuum formed materials.