Investigation on the effect of laser pulse shape during Nd:YAG laser microwelding of thin Al sheet by numerical simulation

Abstract

In the welding of thin A3003 Al sheet by a Nd:YAG laser beam, the laser pulse shape plays an important role in enhancing the welding penetration stability. In order to evaluate the effect of laser pulse shape during Nd:YAG laser welding of a thin Al sheet and to predict the welding performance by numerical simulation, a three-dimensional finite differential method (FDM) analysis is presented for heating with different laser pulse shapes and related welding parameters. The simulated results give good agreement with experimental results, where a sound weld shape and crack-free weld pool are obtained. The simulation results show that the welding stability is greatly affected by the modulation of laser pulse shape for the same laser energy and welding parameters. As a rectangular laser pulse is modulated to have three stages with high, medium, and low power levels for the first, second, and third stages, respectively, more energy is absorbed in the melt pool, and the cooling rate is reduced. While a high power level at the first stage increases the laser beam absorption, the thermal energy of the third stage prevents fast cooling of the melt pool. Also, evaporation is prevented by proper modulation of the laser pulse. If the laser pulse is modulated properly, the optimum melt-pool size and cooling rate can be obtained; also, the desired weld depth and welding stability are achieved for the conduction welding mode. The numerical simulation method can be used to determine the proper conditions for good welding performance.