Influence of absorption mechanisms on the temperature distribution on the keyhole wall during laser deep penetration welding

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The energy input into the keyhole determines the keyhole properties, especially the wall temperatures, and also the occurrence of defects. Due to a lack of methods for directly evaluating the keyhole wall temperatures, it is not clear how the different absorption mechanisms contribute to the energy input and the temperature distribution. It is also not understood how process defects correlate to the keyhole wall temperature.Therefore, the aim of the project is to qualitatively describe the correlations between the laser energy input and the temperature distribution in the keyhole to open a possibility of forming a stable keyhole and thereby reduce pore formation. The experimental determination of the temperature distribution during welding will be done with several pyrometric measurements in tantalum tubes positioned in holes in the base material. Thus, the temperatures in the melt pool to the temperature on the keyhole wall can be locally measured. An absorption model is able to describe the temperature distribution depending on the absorption mechanisms. Comparing the measured and the modelled temperature fields the proportion of the absorption mechanisms contributing to the overall energy absorption can be evaluated. In addition, the temperature distribution during the evolution of process pores is observed to characterize the pore formation process.