Optimized Sheet Temperature Distribution for Thermoforming

The heating phase of the thermoforming process is crucial to control the forming step and wall thickness distribution of the final product. Controlling and numerically predicting the in plane and through thickness time dependent temperature distribution is however complicated by the need for specific material properties (e.g. wavelength dependent absorption characteristics) and processing boundary conditions (e.g. convective heat transfer coefficient, amount of emitted heat flux by the heater elements). In order to cope with these challenges, the present study presents an explicit finite difference (FD) model to predict the temperature evolution of the sheet. The model parameters are updated using a single set of initial temperature measurements for different power settings of a single heater element. The good correlation between the modelled and experimental data indicates a successful model updating procedure. To validate the updated parameters, the model was used to predict the transient temperature of the thermoplastic sheet for 27 different heater element configurations. The comparison to experimental data indicated that the model is capable of accurately predicting the temperature of the sheet during the heating phase of the thermoforming process.