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Thermoforming

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thermoforming

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Thermoforming

  1. 1. Thermoforming Thermoforming is the process where thermoplastic polymer sheet is heated & deformed into desired shape. Process : • Heating plastic sheet to the temperature where in softens. • Stretching the softening polymer against a cold mold surface. • Cooling the finished part and trimming excess plastics.
  2. 2. Figure : one Stage thermoforming machine Steps of thermoforming : 1. Heating :Heating is accomplished by radiant electric heater which is located by at the distance of 125mm(5 in.) from the sheet. 2. Froming :after heating ,the polymer sheet is converted or formed into various either air pressure,vacccum or mechanical .So,according the forming techniques,thermoforming are 3 types 3. Vaccum forming 4. Pressure forming 5. Mechanical forming
  3. 3. Vaccum froming  It is the earliest method of thermoforming.  In vaccumforming, vaccum is created below the preheated plastic sheet to draw sheet into the cold mold cavity . The basic steps of vaccum forming are, 1. A flat plastic sheet is heated by radiant heater, which is placed on one or either side of the plastic of 125mm distance. 2. The softened sheet is placed over a concave cavity. 3. Vaccum draws the sheet to the sheet to the cold cavity . 4. The product is cooled and extra plastic parts are trimmed.
  4. 4. Figure: Vaccum forming
  5. 5. Vaccum forming : Advantage: 1. Operated comparatively low vaccum pressure. 2. Relatively cheap. Disadvantage: 1. Uneven wall thickness at the corner of the product. 2. Bad finishing or non uniform plastic concentration. 3. Therefore the thinnest area occur at the corner, near the clamp Thin corner Fig: thin area at the corner
  6. 6. Pressure forming • Alternative to vacum forming. • Here,the air pressure is forced to the preheated sheet into cold mold. Here, the air pressure of pressure is much higher than the vaccum forming. • The basic difference between vaccum forming is the heated sheet is pressured from above the mold cavity . • Due to high pressure, the heated sheet can be deformed in fraction of second.(High production rate)
  7. 7. Figure:Presure forming
  8. 8. Pressure forming: Advantage: • High production rate . • Efficient for large parts. • Low tooling cost. Disadvantage: • Limited shape complexity.
  9. 9. Mechanical thermoforming • In mechanical forming, air pressure or vaccum pressure do not use to drag the plastic sheet. • Here, positive(male) and negaive (female) molds are brought against s heated plastic sheet,forcing it to the assumed shape. • Air between the die and sheet is evacuated by using vacuum pump , and sheet conforms to the mold shape. • Formed part is cooled and ejected.
  10. 10. j Mechanical thermoforming: (1) heated sheet is placed above a negative mold, and (2) mold is closed to shape the sheet.
  11. 11. Mechanical froming Advantages: • Better dimensional control. • Opportunity for surface detailing of both sides of the parts. Disadvantages: • Two mold halves are required • Relatively costly.
  12. 12. Materials Used: • ABS (Acrylonitrile butadiene styrene) • Cellulose acetate • LDPE (Low density polyethylene) • HDPE (High density polyethylene) • PVC etc. Applications: Thermoforming has many applications like I. Food packaging II. Automotive parts III. Aircraft windscreens IV. Vehicle doors etc.
  13. 13. Thermoforming: Advantages: • Flexible design . • Rapid prototype development • High production rate • Low set up cost • Less thermal stress. Disadvantage: • Not eligible for thermosets • All parts need to be trimmed • Parts may non uniform thickness.

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