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Vacuum Forming Plastic Vacuum Forming is an industrial technique which may be used for batch production or mass production. A sheet of thermoplastic held by the use of toggle clamps is heated until the plastic becomes malleable (soft and flexible). The air is then sucked out from underneath the plastic using a vacuum pump. The plastic then takes the shape of the mould. This process enables thermoplastics to be formed into shapes such as packaging, storage trays and seed trays, yoghurt pots, party hats and fancy dress masks

Step1 Put the former in the vacuum forming machine and clamp the plastic into position.

Step 2 Heat the plastic until it softens to a 'rubber like' state.

Step 3 Remove the heat and raise the former into the softened plastic.

Step 4 Turn on the vacuum. The plastic will be drawn around the shape of the former.

Step 5 When cooled, unclamp the plastic and remove the former. Trim to the required size and shape

How it works: the movie! Steps 1-5

Moulds The Plastic Vacuum formed shape will only ever be as good as the mould or pattern. It is very important that the mould is correctly made. The mould may be made from plywood, hardened clay or m.d.f. In Industry the mould may be made from steel or lead. A Steel mould will tend to last longer than a wooden mould. Stages of making the mould. 1. The sides of the mould must slope slightly. This is to allow the plastic shape to be removed after vacuum forming. These are called Draft Angles. 2. The mould must be well sanded, polished or smoothed depending on the materials used. Any surface detail which is left on the mould will be transferred to the plastic product. 3. The mould may have small drill holes in it to allow the air to be easily sucked through it by the vacuum pump. This will create an improved definition or shape. These holes are called Vent Holes. These holes also prevent small pockets of air being trapped when the sheet forms. 4. The mould must not be too deep, otherwise the excess plastic (polystyrene) will stick together at the corners. This is called WEBBING. This also affects the thickness of the sheet on the vertical surfaces as it is drawn down.(polystyrene)

Examples of vacuum formed trays A vacuum forming mould. Note holes to let air out

The moulds: key points Moulds are usually made from wood or metal … we use MDF ( medium density fibreboard ) It is easy to cut and shape with a file and glass paper Always make sure that the sides slope so that the mould can drop out after you have vacuum formed your shape.

Ideal mould shape Shapes you can and can't mould... Almost any shape can be produced, but not necessarily in one piece. It must be possible to release the plastic from the mould. This generally means no undercuts in the shape of the mould; parallel vertical faces can also cause difficulties.

Bad moulds

Things that can go wrong When the plastic is moulded over a tall, steep shape, depending on the plastic being used, it can form curtain- like forms. The pic shows it better than words...

Planning for manufacture? Task: Produce a flow chart that illustrates the step by step process of manufacturing the mould you will need.