Abstract
Thermoforming is a very popular method of plastics processing, because it is simple and inexpensive. There is a growing interest for thermoforming in the case of applications which are more and more technical, i.e. for automotive industry. This implies to better control and optimize the process. One key step is the heating of the plate in order to reach the viscoelastic state of the material, the heat required for this change of state being mainly transferred in a radiative form.
Therefore the energy distribution in the plate should be carefully optimized. Classical methods based on the “view factors concept” are known to be difficult to operate in the case of complex geometries and/or spectral diffusion sources. In this study, an approach using the “ray tracing method” is used. The principle of this method consists in discretizing the heating source surface and associating to each element several rays which carry a given amount of energy. Each ray interferes with the plate, directly or after reflection on the reflectors, and transfers its energy to the plate. The energy distribution on the plate surface is easily deduced and the temperature field can be calculated, providing the bases for the inverse problem which is more interesting from the process point of view : starting from a required temperature distribution on the plate, the adequate sources (emissivity, shape…) and their relative locations with respect to the heated plate will be predicted.
