Thermoforming is a moulding technique that consists of vacuum shaping sheets of plastic at high temperatures. The action of the vacuum pumps allows for a perfect adhesion with the mould made of MDF, resin, or aluminium to provide the shape to the finished.
Phases of the production in thermoforming
The plastic sheet is heated to a temperature that allows it to become malleable and moldable when it comes into contact with the mould. The heating temperature is maintained constant and is regulated based on environmental factors and the characteristics of the material used.
During the drawing phase, the plastic sheet is subjected to a flow of compressed air that inflates it like a “balloon”. This phase allows the already heated plastic material to be uniformly distributed during the subsequent forming phase.
The plastic material, which is heated to the right temperature and stretched to perfection, is subjected to the vacuum process that makes it correctly adhere to the mould and allows for its shaping. The vacuum pump makes it possible to remove the air entrapped between the sheet and the mould.
In this phase, the forced aeration system enters into action. This system quickly cools the sheet of plastic material that was thermoformed in the previous stage, which is then detached from the mould. This phase makes sure that the forming does not show any deformation at the time of release.
Once the plastic sheet has been thermoformed, it is ready for the cutting and finishing phase that is carried out with the CNC machine. During this phase, the excess material is removed to obtain the finished piece. At this point, the part can be subjected to pad, or silkscreen embossing worked with cuts for particular applications or assembled with other pieces to obtain the desired semi-finished product.
Advantages of the thermoforming mould
Materials used for the mould
Acrylonitrile butadiene styrene - ABS
Acrylonitrile butadiene styrene or ABS is a typical thermoplastic polymer used to create light and rigid objects such as pipes, musical instruments, and toys such as the famous LEGO bricks. ABS is a copolymer derived from polymerized styrene together with acrylonitrile in the presence of polybutadiene, and therefore can be defined as terpolymer. ABS is widely used in the manufacturing of products with rapid prototyping machines that use production techniques such as FDM (Fused Deposition Modeling).
Polystyrene - PST
Polystyrene is styrene polymer.
It is a thermoplastic aromatic polymer with a linear structure. At room temperature it is a glassy solid; it acquires plasticity and is capable of flowing when it reaches temperatures above its glass transition temperature, about 100°C; it begins to decompose at a temperature of 270°C.
Polystyrene is used in many application fields due to its mechanical and electrical properties.In the food industry, it is used to make plastic cutlery and plates, egg cartons, and yogurt pots.
In the manufacturing industry, it is used wherever a rigid and economical plastic is needed, such as for CD and DVD containers, license plates, and plastic models.
Production can be done by thermoforming or injection moulding.
Density: 1.04 g/cm³
Polymethylmethacrylate - PMMA
The polymethylmethacrylate or PMMA is a plastic material formed by the polymers of methyl methacrylate, methacrylic acid methyl ester.
It is also known under the trade names Plexiglas. Examples of its applications include the taillights of automobiles, the barriers in the stadiums and the large windows of the aquarium, and one of the largest markets is the bathroom industry where it is used for the production of bathtubs and shower trays. It was used in the production of laserdiscs and is occasionally used in the production of DVDs.
The acrylic paint essentially consists of a suspension of PMMA in water, stabilized with suitable surfactant compounds, given that the PMMA is hydrophobic.
Density: 1,18 g/cm³
Melting point: 160 °C
Molar mass: 100.12 g/mol
Boiling point: 200 °C
Polyethylene terephthalate - PTG
The PETG is a variant of the polyethylene terephthalate, a copolymer of the polyester family, suitable for contact with food. It has excellent transparency, high impact resistance, good fire behavior, and excellent thermoforming properties.
It is the ideal product for the following uses: display devices, price tags, shelf dividers, signals, advertising writings, food containers and trays, pharmaceutical applications, flat and fit machine covers, and panels for the separation of environments.
PETG sheets can be thermoformed quickly, with low energy consumption and in extreme drawing conditions. Production times are short, and shapes can be easily reproduced without pre-drying.
Density: 1.38 g/cm³
Melting point: 260 °C
It is an acrylonitrile butadiene styrene or ABS to which a layer of transparent PMMA is applied, providing it with:
– Increased hardness
– Scratch resistance
– Good UV stability
– Greater resistance to breakage