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What is Thermoforming and what is it used for?

Thermoforming is a plastic manufacturing process where a thermoplastic sheet is deformed into a specific shape. The process starts with the heating of a flat plate like sheet of plastic which is then manipulated by either applying pressure or using a vacuum. The process is also know by a number of other names such as:-

The process of Thermoforming

The thermoforming process can be broken down into two basic steps, heating and forming. The heating apparatus consists of radiant heaters. The heaters are attached to the top section of apparatus and placed at equal distance from each other. Plastic sheet is the raw material used and is secured on the top of the mould cavity with the help of the clamps. For deformation purpose the force is created ether using a vacuum only or vacuum with air pressure. Whichever process is used, holes are drilled into the bottom of the mould. The plastic sheets are held in place by clamps as the radiant heaters apply heat to the surface. When the sheet is soft enough it is pulled down into the mould by vacuum pressure. As a result of pressure the sheet takes the shape of mould and is removed after solidification.

 

Applications for Thermoforming

There are many different products/processes which make use of thermoforming such as:-

Materials

There are also many different materials which can be used in the thermoforming process which include:-

Mechanical Design Guidelines

To ensure you get the best out of the thermoforming process there are a number of guidelines to consider. These include:-

Process Variations

It will come as no surprise to learn that there are now a number of variations on the base process. This allows the process to be adapted to best suit an array of different products/materials. Some of the variations include:-

Negative Pressure Process

The negative pressure process for thermoforming is where a vacuum is created inside the mould to force the plastic sheet to take the shape of mould. The pressure limit for this process is about 1 atm. To make the vacuum inside the mould, air is removed using a suction pump attached to holes drilled in the mould base.

Positive Pressure Process

This thermoforming process uses air pressure in order to deform the plastic sheet by what is called the positive pressure process. It is also known as the blow forming process as it resembles the blow moulding technique often seen with glass. Advantages of using positive pressure, instead of a vacuum, revolve round the availability of high pressure of about 3 atm to 4 atm. To apply pressure a hole is drilled at the top section of the mould, to remove the trapped air inside the mould, vent holes are provided at the bottom of the mould.

Positive and Negative Mould

Positive moulds are convex shaped with plastic sheets deformed over the shape of the mould.  Negative moulds are concave shape moulds where the plastic sheet is deformed against the concave shape of the mould. Negative moulds can use any type of pressure whereas positive moulds need negative pressure. During manufacturing if a positive mould is used, the final product will have inner surface dimensions the same as the mould. If a negative mould is used then the outer surface of the final product will have same dimensions as the mould.

Mechanical Thermoforming

Mechanical thermoforming is a third process variation where negative and positive moulds are used together to press the heated plastic sheet. Air pressure/vacuum are not used in this process, rather the mould parts are pressed on both sides of a plastic sheet to force it into the mould shape.

Economics of the Process

As with any commercial process, the pros and cons are often outweighed by the commercial cost. So when it comes to thermoforming the economics are as follows:-

Advantages of Thermoforming

Now we get down to the bottom line, the advantages of thermoforming and exactly what it has to offer for an array of commercial processes:-

Disadvantages of Thermoforming

To balance this review of thermoforming we also need to take a look at the disadvantages of the process which are:-