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Thermoforming

Thermoforming. 2.810 Fall 2002 Professor Tim Gutowski. Thermoforming Process Plan. Hardware Requirements Tool Trim Fixture Set-up Mount Tool in Thermoformer Mount Trim Fixture Run Fixture Sheet; Heat; Form; Cool; Trim. Thermoforming. *. Heater. Clamping. Plastics sheet. Vacuum.

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Thermoforming

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

  4. Thermoforming

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

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

  7. Production Equipment

  8. Heat Transfer in Thermoforming Heating Cooling

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

  10. Viscoelastic Effects During processing Unloaded sample Coiled polymer chain Loaded sample Extended polymer chain 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

  11. Simple Viscoelastic System

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

  13. Temp. Dependence of Time constant, l Arrhenius Rubber elasticity Approximation (For better accuracy, use Time-Temp shift, WLF eqn.) Example: PMMA Temp l 40C 114 yrs 100C Tg 135C 3.5 millisec

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