Formech's step by step guide to the principles of the vacuum forming process

The Principles

In order to produce a vacuum formed product, four key elements are required:

Select the relevant section above in order to obtain a full understanding of the process.

Mould

Moulds (sometimes called tools or patterns) can be made from a variety of different materials; wood, clay, plaster, epoxy resin, aluminium, plasticine.

Wood is one of the more commonly used materials in schools and colleges when students are designing their own products, as it is easy to work with, economical and readily available. It can produce high quality vacuum formed products. The best kind of wood to use is one with a close, even grain so that no imperfections appear on the finished product. This is particularly important when using clear materials. Hardwoods such as Jelutong and Obeche are ideal.

The mould surface should be dry and free from dust particles wherever possible. If using MDF, a suitable sealant should be applied to the mould in order to prevent particles becoming dislodged inside your machine, which could cause problems with the vacuum pump.

During cooling, the thermoformable material shrinks tight around the mould. This can make it difficult to remove the finished part. To make this easier, it is necessary to put a slight angle on any vertical part of the mould. This is called a draft angle and should be a minimum of five degrees.

For a more robust mould, which will last for hundreds of formings, epoxy resin is a cost effective solution. A high definition vacuum forming is taken in plastic from a prototype mould e.g. clay or wood. The epoxy resin mixture is made up, according to the manufacturer's instructions and poured into the mould. For large moulds, it makes sense to pack it out with blocks of wood, making the process cheaper and also resulting in a lighter mould. After curing, the plastic is removed and the epoxy resin mould is ready for use.

In order to obtain a moulding with good surface detail, all of the air must be removed during the forming cycle. It is possible to prevent air from becoming trapped in corners and recesses of the tool by drilling vent holes from the recesses through to the base of the tool. Provided these vent holes are small, they will not leave any marks on the mouldings.

Vent holes are essential for providing a high degree of definition on the finished product, as they allow the plastic to pull tightly into all areas of the mould. The easiest way of drilling the holes is to use a length of spring steel or piano wire with a flat hammered end. This type of drill can flex enough to prevent breaking when drilling awkward holes.

If you require any further information regarding moulds please contact us.

Thermoformable Material

A thermoformable material is one which can be moulded upon the application of heat. The most commonly known thermoformable material used in vacuum forming is plastic. There are many different types of plastic which are suitable for vacuum forming - see the table below for more details. It sometimes comes as a surprise to learn that foam can also be vacuum formed. It is widely used by the theatre and film industries for making costumes, film sets and props.

Most Popular Materials used by Schools, Colleges & Universities

If you require any further information regarding thermoformable material please contact us.

Heat

A heat source must be present in order to soften the material to be vacuum formed. On the Formech range of machines this heat source comes from a series of powerful infrared ceramic elements which are housed inside a heater box. Heat is emitted up to 300°. The wavelength of the infrared heat penetrates through the surface of the plastic sheet enabling the Formech range of machines to form plastic up to 6mm in thickness. Different plastics have different forming temperatures. It is impossible to give exact heating cycle times for the different materials as so many different factors can affect the result, but the table below can act as a general guide.

If you require any further information regarding heating please contact us.

Suction / Vacuum

Once heated, the sheet of material will have a natural tendency to drape over the mould. However, in order to achieve a high definition moulding, which shows all the details on the mould, it is necessary to suck the air out from between the plastic and mould in order to achieve a higher degree of detail. On a vacuum forming machine, the plastic is sucked tight around the mould with the use of a vacuum pump. Formech machines contain powerful vacuum pumps which are capable of drawing down the plastic to produce a high degree of detail on the finished mould.

All Formech machines contain a mould release facility which will reverse the suction and blow air back through the vent holes, to release the moulding from the tool.

If you require any further information regarding heating please contact us.