What is the Process of Vacuum Forming?

Thermoforming is one of the most common methods of processing plastic materials. Basically, vacuum forming is the simplified version of thermoforming. In this process, a sheet of plastic is heated until it becomes pliable after which a given amount of pressure is applied to form the plastic over a plug mould. It is a simple process which can allow people to take on simple jobs. It involves the following key processes:

• The thermoplastic material is inserted in the forming clamp when it is in cold state or at room temperature.
• Its temperature is raised gradually until it reaches the forming temperature. The heating process is done using heaters; it can be a single heater or a twin heater depending on the type of material.
• The air which had been trapped within the forming system is evacuated using the vacuum system and hence creating a difference in pressure.
• The formed plastic is allowed to cool after which a reverse air supply system is activating to eject the formed plastic from the mould.

Advantages of vacuum forming process
There are very many other forming processes such as moulding, injection and rotational. However, this process is mostly used due to the following reasons:

• Since this process requires low amount of pressure, it requires low cost tooling.
• Most moulds which are used in this process can be constructed from cheap material since they are exposed to low amount of force during the forming process. Furthermore, constructing the mould is simple and hence saving on time.
• It is one of the cheapest way of prototyping.
• A wide range of parts can be formed using a number of materials and hence, the process allows for flexibility in both construction and cost. 
• Customizing various shapes is easy since various tools which are used in the process can easily be modified.

Even though this process is being used in very many plastic forming processes, it has some disadvantages which are still being addressed. During the forming process, there are sections which must be cut from the formed sections besides finding mechanisms to deal with the extruded sections. If precaution is not taken, it may result into some additional costs.
Factors to consider during the process:
Clamping process; the clamp must be powerful enough to handle the sheet of plastic to be heated. All the necessary precautions must be taken to ensure that any accidental damage do not occur during the process e.g. interlocking for the automated clamping system.
Heating process; it must be done evenly over the entire sheet of plastic to be formed. Most heaters use infrared elements. It is important to go for heating systems whose heating temperature can be controlled. For faster heat penetration into the plastic, using twin heaters could be a noble idea.
Sheet level; the plastic should not sag. In case it goes below the sheet level, a sufficient amount of air should be injected to lift it.
Pre-stretch process; this is to ensure that the plastic has reached the forming temperature and that the thickness is even throughout the entire plastic sheet.
Vacuum process; after pre-stretching, the vacuum should be applied with a differential pressure maintained at about 0.686m of mercury.
Cooling and release; in a good system, fans are installed to hasten the cooling process. The formed plastic should be removed after it has cooled.
For sure, this an important forming process since most plastic products we used in our day to day activities are produced through vacuum forming.