Thermoforming

What is thermoforming?

Thermoforming or vacuum forming is a process that moulds preheated sheet/foil in a (vacuum) mould to a product.

The Thermoforming process consists of four steps:

1. Heating the sheet/foil

The sheet/foil is heated to approximately 450°C. The heat makes the sheet/foil supple so it can be transformed. A conveyor chain pulls the sheet/foil through a vacuum forming machine. In order to hold the sheet/foil, the chain makes little holes on the edge of the sheet/foil.

2. Moulding the product

A tenter frame holds the sheet/foil. Only the piece that is in inside it is moulded. The machine brings the moulded piece against the sheet/foil surface and sucks the space under the sheet/foil vacuum. Result: the sheet/foil is pulled into the moulded piece. During the moulding process, the machine may also blow moulding air to get the sheet/foil into the cavity of the moulded piece even better.

3. Product punching

With in-line punching, a punching station that punches out (cuts out) the products is in the vacuum forming machine. With off-line punching, uncut sheets/foil come out of the vacuum forming machine. These are punched later (for example with a flat punch). The remnants around the punched project are called the skeleton. Small hooks (nicks) ensure that the punched products briefly remain in the frame. They serve as grip for transporting the product to the stacker.

4. Stacking the product

A lot of vacuum forming machines are equipped with an integrated stacker. This separates the vacuum formed products from the frame. The end product comes out of the frame neatly stacked. The skeleton is then rolled up and is ready for recycling.

The vacuum forming mould

A vacuum forming mould is actually a mould set in five parts:

1. Base plate or fixing plate. All other parts are mounted on this. The base plate is fastened in the vacuum forming machine.
2. Cooling plate. The cooling water runs through the cooling plate. It assures a constant temperature of the mould. After all, fluctuations in temperature have a negative influence on the demoulding of the product.
3. Moulded piece. Vacuum holes are bored into this to make sure that the sheet/foil is sucked into the moulded piece. The moulded piece determines the ultimate shape of the product.
4. Tenter. The tenter frame pinches off the sheet/foil. Only the clamped piece is transformed.
5. Upper die. An upper die can be used as an extra aid in shaping the product. It pushes the sheet/foil into the cavity which means the sheet/foil is pulled into the moulded piece more quickly. It is especially recommended for difficult and relatively deep moulds.

Types of vacuum forming machines

There are two kinds of vacuum forming machines. The difference lies in the way the sheet/foil is processed.

Standard machines work with sheets/foil on rolls. The thickness of the sheet/foil varies between 100 micron to 1.8 mm.

Plate machines work with sheet/foil plates. They are mainly used for larger products and for applications with thicker sheet/foil. The plates can be up to 6 mm thick.

Choice of materials

These materials are suitable for vacuum forming:

• PVC - polyvinylchloride
• PET (A, G, GAG) - polyethylene terephthalate
• PP - polypropene
• PS - polystyrene

Vacuum formed products

• blisters ;
• transport packaging (everything with a bundling and/or protective function) ;
• salad containers and other food packaging (for ex. for packaging ready-to-eat meals) ;
• liners ;
• counter displays ;
• specials such as sealing plugs, lids, plastic machine parts.

Do you want to find out more about vacuum forming? Or would you like to have a product vacuum-formed? Then get in touch with the number one specialist via http://www.bwa.be.