3D modeling of thermoplastic composites laser welding process - A ray tracing method coupled with finite element method

Laser Transmission Welding process (LTW) is a well know technic for polymer welding. This technic can also be applied to thermoplastic glass fiber composite (polymer + continuous glass fibers). But in this case two phenomenon occur and are able to make the welding in a poor quality: light absorption and light scattering. The two phenomenon occurring into the semi-transparent substrate of reinforced fiber thermoplastic, during the LTW, are numerically examined. A 3D transient thermal model of LTW is achieved with the FEM software COMSOL. A ray tracing software is developed to compute the heat source term used in the FEM simulation. First, the energy distribution coming from the laser irradiation is assessed. Ray tracing techniques allowed us to deal with both absorption and a strong light-scattering caused by the heterogeneity of composite: polymer matrix and glass fibers. Then, the energy balance equation was solved in order to study the heating stage. The present paper proposes an investigation on the influence of the absorption on the heat affected zone. The interest to consider absorption was shown for process optimization purposes and for the use of reinforced composites colored or filled with additives.