Thermoforming is the process where a thermoplastic polymer sheet is
heated & deformed into a desired shape.
Step 1: Heating a plastic sheet to the temperature where it softens.
Step 2: Stretching the softened polymer against a cold mold surface.
step 3: Cooling the finished part and trimming any excess plastic.
4. Steps of thermoforming
1. Heating: Heating is accomplished by radiant electric
heater which is located at a distance of 125mm (5 in.)
either on one or both sides of the sheet.
2. Forming: After heating, the polymer sheet is converted or
formed into various shapes by either air pressure, vacuum
pressure or by mechanical pressure.
6. Vacuum forming
It is the earliest method of thermoforming.
In vacuum forming, vacuum is created below the preheated
plastic sheet to draw sheet into the cold mold cavity.
Basic steps of vacuum forming
1. A flat plastic sheet is heated by radiant heater, which is
placed on one or both sides of the plastic.
2. The softened sheet is placed over a concave cavity.
3. Vacuum draws the sheet to the sheet to the cold cavity .
4. The product is cooled and any extra plastic parts are
I. Operated at a comparatively low vacuum pressure.
II. Relatively cheap.
I. Region of least thickness occurs near the clamp.
II. Bad finishing or non uniform plastic formation.
III. Uneven wall thickness at the corner of the product.
Figure: thin area at the corner
9. Pressure forming
Alternative to vacuum forming.
Here the air pressure is forced to the preheated sheet into a
cold mold. Here the air pressure is much higher than the
The basic difference from vacuum forming is that the heated
sheet is pressurized from above the mold cavity .
Due to high pressure, the heated sheet can be deformed in a
fraction of a second. (High production rate)
• High production rate.
• Efficient for large parts.
• Low tooling cost.
• Limited shape complexity.
12. Mechanical thermoforming
Here, positive (male) and negative (female) molds are
brought against heated plastic sheet forcing it to the
In mechanical forming, air pressure or vacuum pressure are
not used to deform the plastic sheet.
Air between the die and sheet is evacuated by using
vacuum pump and the sheet conforms to the mold shape.
Formed part is cooled and ejected.
1. Better dimensional control.
2. Opportunity for surface detailing of both sides
of the parts.
1. Two mold halves are required
2. Relatively costly.
15. Materials Used:
• ABS (Acrylonitrile butadiene styrene)
• Cellulose acetate
• LDPE (Low density polyethylene)
• HDPE (High density polyethylene)
• PVC etc.
Applications of Thermoforming
I. Food packaging
II. Automotive parts
III. Aircraft windscreens
IV. Vehicle doors etc.
Advantages of thermo forming:
• Rapid prototype development.
• High production rate.
• Flexible design.
• Low set up cost.
• Less thermal stress.
Disadvantage of thermo forming:
• Not eligible for thermosets.
• All parts need to be trimmed.
• Parts may have non-uniform thickness.