The Studying Of Temperature Distribution And Control Technique During Polymer Sheet Heat Process

Thermoforming is a process in which a flat sheet of plastic material is heated and then formed into useful tub-shaped plastic parts. This thesis focuses only on the details of the heating stage, which has a direct influence in quality of the final product. It also has direct influence in the energy consumption and production rate of the equipment.The objective of sheet reheat control is to heat the centerline temperature within the sheet to the minimum forming temperature as fast as possible, while ensuring that the surface temperature remains below the maximum forming temperature. First of all, temperature distribution during polymer sheet reheat phase in thermoforming should be researched. There are three basic modes of heat transfer that affect the temperature of the sheet, which are:conduction in the interior sheet, convection between the sheet and the ambient air, and radiation that from the heater to the sheet. In order to analyzing the temperature distribution of the interior sheet, the sheet is divided into N isothermal layers along its thickness. With layer as unit, the temperature variation during reheat process is considered. Electro-thermal model and finite element model of polymer sheet temperature distribution during heating phase are discussed. Finally, the mechanism model of temperature distribution during polymer sheet reheat phase in thermoforming is established by employing analysis method. And this model is implemented in a simulation tested based on software LabVIEW8.6 for performance evaluation. The results of simulation show that the curves of temperature distribution during polymer sheet reheat phase in thermoforming. So the model can be tuned to the parameters of the actual sheet-heater system.The study of the temperature control of heater is based on the temperature distribution during polymer sheet reheat phase in thermoforming. The traditional control method such as percentage control and PID control can be used to control the temperature of heater. But Aiming at the nonlinear and long dead time system, perfect result can't be achieved using traditional control strategy. Then, iterative learning control are studied based on the system.The temperature distribution during heating phase is obtained by simulation analysis of the model. Temperature control technique based on the temperature distribution of the sheet, especially iterative learning control technique has a very good control performance and robustness.