Temporal evolution of the temperature field in the beam interaction zone during laser material processing

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Abstract
This paper presents a numerical simulation of the temperature field resulting from the impingement of a laser beam on a metal surface. The calculations were based on a hydrodynamic physical model of laser-material interaction, which includes the effect of evaporation recoil pressure on melt flow and the related convective heat transfer. The computations follow an experimentally verified physical model of melt hydrodynamics and the model of laser-induced evaporation developed by Anisimov. The simulations indicate that convective heat transfer which is induced by recoil pressure is significant for absorbed laser intensities from 0.5 MW cm-2 to 10 MW cm-2. This range corresponds to laser welding, cutting and drilling due to melt ejection (hydrodynamic drilling). The simulations also show that the motion of the melt from the centre of the beam interaction zone towards the periphery results in a secondary maxima in the temperature distribution, which in turn can lead to instability of the melt flow and temperature field fluctuations. The model also predicts that the cooling rate in and around the fusion zone is strongly influenced by the recoil-pressure-induced melt flow. At the centre of the beam interaction zone, the cooling rate is much higher (~10 times), and at the periphery, much slower than predicted by a pure heat conduction model.