AbstractsEngineering

Thermoforming is a process of forming thermoplastic sheets into three-dimensional shapes by heating it to tender soft and pliable, and then, forcing the sheet into or over the shape of a mold by applying differential pressure or vacuum. Sheet reheat is the most important step in thermoforming because its result can affect all subsequent processing steps. In order to develop an advanced in-cycle and cycle-to-cycle control strategy, one needs to track the desired sheet temperature profiles throughout the reheat cycle, and identify and characterize the process and material parameters that vary from cycle-to-cycle and batch-to-batch. Absorptivity of the polymer sheet material and the heat flux incident on the sheet are the two important factors that need to be monitored and estimated properly in order to integrate into the absorptivity based model for the sheet reheat phase. Estimation of the heat flux can be used to generate the heat gain matrix relating the energy given to the heating elements and temperature of the sheet. This thesis develops methods to estimate absorptivity and heat flux in order to improve model based control systems.