Evaluation of molten pool geometry with induced plasma plume absorption in laser-material interaction zone

The presence of plasma affects laser material processing technology because, according to process parameters, a large portion of the energy emitted by the laser source is absorbed by the plasma plume without hitting the workpiece. The only way to avoid a significant reduction in process efficiency, due to plasma absorption, is thus to decrease the plasma formation by controlling the working parameters. An original analytical system for the prediction of the actual energy transmitted to the workpiece was developed by modelling the plasma plume physical state related to the process parameters. In this way, by determining the laser beam energy lost in the plasma plume and the conduction energy transmitted to the workpiece, an evaluation of the laser material interaction could be carried out. The developed model allows to evaluate the geometry of the molten pool by means of the computation of the interface between the solid and the remelted material. The effect of the plasma plume presence, by comparison with a modelisation without plasma implemented in similar way by the authors, was to reduce the molten pool and in particular the penetration depth and it permits to have close simulation results to experimental data. For the model validation several experiments were performed on an austenitic stainless steel with a CW CO2 laser source. The experimental activity was developed by varying process speed and power level up to 1200W when in the range of conduction welding.