2. Topic

3. Definition
Thermoforming is the process where a thermoplastic polymer sheet is
heated & deformed into a desired shape.
•Process:
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.
Figure: Stagethermoformingmachine

5. So accordingto the formingtechniques
thermoformingare 3 types
Vacuum forming
Pressure forming
Mechanical forming

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
trimmed.

7. Figure:Vaccumforming

8. Advantage:
I. Operated at a comparatively low vacuum pressure.
II. Relatively cheap.
Disadvantage:
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.
Thin corner
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
vacuum forming.
 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)

10. Figure : Pressure forming

11.  Advantage:
• High production rate.
• Efficient for large parts.
• Low tooling cost.
 Disadvantage:
• Limited shape complexity.

12. Mechanical thermoforming
Here, positive (male) and negative (female) molds are
brought against heated plastic sheet forcing it to the
assumed shape.
 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.

13. Figure : Mechanicalthermoforming: (1)Heatedsheetisplacedabovea
negative mold (2)moldisclosedtoshapethesheet.
• J

14.  Advantage
1. Better dimensional control.
2. Opportunity for surface detailing of both sides
of the parts.
 Disadvantages
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.

16. :
 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.