Abstract

Thermoforming is widely used industrial manufacturing process in which tub-shaped components are manufactured by heating a plastic sheet in the oven and formed to the desired shape through vacuum or pressure. Heating of the sheet is the most important phase which determines product quality and process efficiency. In order to automate the process to improve the product quality and process efficiency, the development of a mathematical model of heat propagation to the sheet and inside the sheet is imperative. Heat transfer takes place through the combination of convection, conduction and radiation energy, which conducts and absorbed inside the sheet and greatly depends on material properties, oven air temperature and velocity and sheet color. A mathematical model based on variable material properties including density, specific heat and thermal conductivity is developed and validated against experimental data. The effect of both oven air temperature and velocity is studied by simulating the already developed and validated variable properties mathematical model for different values of oven air velocity and temperature. The sheet color effect is also studied by considering two extreme cases of black color sheet and white color sheet and validated by simulating the models and comparing the results against experimental data. The sheet heating model based on exact solution to conduction equation with constant material properties and convection heat as boundary condition is also developed and validated against experimental data.