1. Thermoforming 2.810 Fall 2002 Professor Tim Gutowski

2. Thermoforming Process Plan Hardware Requirements Tool Trim Fixture Set-up Mount Tool in Thermoformer Mount Trim Fixture Run Fixture Sheet; Heat; Form; Cool; Trim

3. Thermoforming Heater Plastics sheet Clamping Vacuum * ** * Source: R. Ogorkiewicz, “Engineering Properties of Thermoplastics.”; ** http://www.arrem.com/designguide/dgprocesscap.htmhttp://www.arrem.com/designguide/dgprocesscap.htm Thin corner

4. Thermoforming

5. Variations on the process Drape Forming Vacuum Forming Vacuum Snap-Back Forming Billow Vacuum Forming

6. Variations on the process Plug-assist Vacuum FormingPlug-assist Pressure Forming Pressure Reverse Draw with Plug-assisted

7. Production Equipment

10. Heat Transfer in Thermoforming Heating Cooling

11. Temperature regimes for polymers Log E(t) TemperatureTgTm Semi-crystalline Polymer Log E(t) Temperature Tg Tg+60  C Amorphous Polymer

12. Viscoelastic Effects During processing Unloaded sample Coiled polymer chain Extended polymer chain Loaded sample Polymer chains tend to exist in coiled configurations. Loading the sample can extend the chain and alter the mechanical behavior. Generally, abrupt, high rates of loading will extend the chain and lead to elastic effects. On the other hand, gradual slow rates of loading allow the chain to more or less retain its coiled configuration, with a resulting primarily viscous response

13. Simple Viscoelastic System

14. “FAST” t << Elastic “SLOW” t >> Viscous “INBETWEN” t ~ Viscoelastic

15. Temp. Dependence of Time constant, Arrhenius Rubber elasticity Approximation (For better accuracy, use Time-Temp shift, WLF eqn.) Example: PMMATemp 40  C114 yrs 100  CT g 135  C3.5 millisec