Formech 450 Installations-, Betriebs- und Wartungshandbuch - Seite 9

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Tools

Formech 450

Tools for vacuum forming should always be solidly constructed as the operating air pressure

reaches approximately 100 kg over an area 100mm x 100mm (one ton per square foot)

All tools should be mounted on a baseboard. They cannot have undercuts and must be

produced with slightly angular sides ('draft angle') to aid release. Vent holes are needed to

allow the air to be evacuated from pockets and sharp angles on the tool. Providing these

holes are kept small they will not leave marks on the surface of the finished moulding.

Tools made from wood or medium density fibreboard (MDF) are easily constructed and can

give short runs of good quality mouldings at a low cost. (See note below)

The use of close-grained wood will avoid grain patterns appearing on the mouldings.

Plaster of Paris may be used for one-offs but the plaster must be allowed to properly dry out.

(See note below)

Metal tools have the advantages of carrying fine detail and being more resistant to both

distortion and surface damage. Metal tools should be pre-heated before use. A cool metal

mould will absorb some of the heat from the plastic sheet before it can take up the full

definition.

Resin tools combine most of the advantages of metal moulds with relative ease of

manufacture. Various resinous materials are commercially available especially for vacuum

forming tool production.

NOTE: Porous mould materials such as wood and plaster should be properly sealed to

prevent the vacuum pump from sucking out any moisture or sawdust, loose plaster etc. The

vacuum circuit may quickly become choked with dust or slurry if moulds are not properly

sealed.

Repairs to the vacuum circuit can be costly.

As the plastic cools after forming it will contract, gripping the tool tightly. If the tool has been

made with sloping sides and has a good surface finish it will release more easily. Where the

draft angle must be kept to a minimum a release agent may be used to assist release.

Sealed moulds will usually release more easily. Silicon based release agents may be used

on more difficult moulds.

Silicon based release agents are rapidly absorbed by porous

(unsealed) moulds, rendering them ineffective.

The use of talc as a release agent is not recommended. It may clog the vacuum circuit.