Investigation of the fibre type influence on the energy density of the induction heating process through a semi-analytic method

The study investigated the induction welding of carbon fibre-reinforced Polyamide 66 with different types of carbon fibres and fabrics. The major scope of the study was the plastification of the thermoplastic matrix as the first process step of the continuous induction welding. A new semi-analytic method was created to simulate the dependence of the plastification parameters (induction coil, power, weld velocity and coil-workpiece distance) on the fibre and fabric. Numerical and physical methods of Duhovic [1] and Velthuis [2] were used to investigate the complete process of plastification and consolidation. This kind of simulation uses the principle of the finite element method (FEM) [1]. The calculated results are strongly influenced on the one hand by the simplification of the thermal conductivity of the fibre and the matrix in the composite material (constant shape value, constant beam value) and on the other hand by the parameterization of the heat source. The semi-analytic method uses the radial basic function and the physical correlation between the thermal losses and the induced eddy currents at the electric conductive carbon fibers for the calculations. The calibration of the tool was done by testing a series of plastification parameters for different kinds of fibre and fabrics. In-situ temperature measurements through thermocouples and pyrometer were carried out for the melt zone in addition to destructive testing of the resulting joint. Yarlagadda [3] and Ahmed [4] have investigated the induction heating of carbon fibres and have shown three kinds of heating mechanisms: Joule loss/fibre heating, junction heating/dielectric hysteresis heating and junction heating/contact resistance heating. The simulation model investigated the amount of heating based on these three mechanisms. The semi-analytic model was created to use it for weldability check of material combinations and the pre-parameter setup for induction welding at a fully automated production system of composite automotive structural parts [5].