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Vacuum Forming

Nov 17th 2015 at 5:36 AM

Vacuum Forming is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mold, and forced against the mold by a vacuum (suction of air). The vacuum forming process can be used to make a wide variety of products such as product packaging, speaker casings and car dashboards. The first commercial manufacturer of vacuum-formed plastics was Robinson Industries of Coleman, Michigan,USA.

Materials

The process uses thermoplastics, such as: acrylic, polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP) and crystalline polyester (CPET). Fibre reinforcing the material will give added strength and rigidity.

Process Variations

The heating method used can vary from infrared heaters to ovens with heating elements on the top and bottom of the sheet or only on the top. The use of thick sheets requires a top enclosure and compressed air as part of the process, an additional force may be required to draw the heated plastic sheet over the cold mould.

Thermoforming is a process used for thin section components such as packaging.

Economic Factors

Equipment and tooling costs for vacuum forming are moderate to high but lead times are usually within days depending on the complexity of the mould used. There is some skilled labour required for the process but this can be reduced with automation.

Production rates are 20–300 components/hour and the process becomes economical at medium to high production volumes, batches of 1000–10000. The process lends itself to excellent material utilisation with less than 3 % of material wasted however the waste material is not directly recyclable. The finishing process is low cost but there is no capability in the process for in mould trimming.

Vacuum 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.

Plastic Vacuum forming is where a flat sheet of extruded plastic is heated until pliable, it is then allowed to shape by applying a vacuum. Once the forming has been cooled and hardened once again, you are able then to trim the part to the desired profile. The limitations of vacuum forming are that undercuts are not normally possible and a degree of taper on any vertical face is usually warranted.

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