Laser Drilling Simulation Considering Multiple Reflection of Laser, Evaporation and Melt Flow

In this paper, laser drilling was analyzed by considering multiple reflections and evaporation of the material. In the keyhole formation process, the variation of the hole shape and the variation of the absorption of the laser power distribution in the wall were examined. The flow velocity distribution of the molten metal was also examined. Moreover, the effect of material on the hole shape was examined. The main results obtained are as follows: (1) At the stage where the depth of the hole is comparatively shallow, the power at the bottom of hole increases by the effect of multiple reflection. (2) When the hole becomes deep, the effect of multiple reflections becomes remarkable and the absorption factor increases. The absorptance increases due to multiple reflections to a value of about 0.75. (3) When the hole becomes deep, the flow field shows that the circulation of molten metal that rises near the walls of the keyhole and by surface tension, moves away from the keyhole at the surface, forming an eddy. (4) Because the thermal diffusivity of aluminum is larger than iron, the energy lost by thermal diffusivity increases, and the energy used for evaporation decreases. Moreover, the melting point of aluminum is lower than that of iron. Therefore, in case of aluminum, the molten pool broadens and the hole becomes narrow.