Twin Sheet Thermoforming, Cycle Time Minimization by Maximizing Heater Cycle Temperature Profile that Prevents Sheet over Temperature

Twin Sheet Thermoforming. Minimization of cycle time for heating sheets of a polymer of various sizes. Providing, improved quality, and cycle time reduction. A process optimization algorithm.

Minimization of the sheet heating cycle time by starting the sheet heating cycle with maximum power and then backing off on power over time to create a transient heating cycle that will keep the surface skin temperatures below a specified limit; until the mid-plane temperature reaches a temperature that is optimal for forming. Use of Finite Element Analysis to model the sheet heating cycle is presented in the paper. Comparisons of finite element models to analytical solutions are also discussed. The sheet heating cycle profile is developed for different size, and thicknesses of material. Minimized cycle times for the different sheets are developed. Different heater systems are discussed and evaluated. The heater cycle profiles that are discussed are designed to avoid overshoot on the skin temperature, and maintain an acceptable mid-plane forming temperature. Using a transient heater cycle profile rather than steady state heater profiles to prevent undesirable surface temperatures from occurring maximizes material quality as well as minimized cycle times for this process.