Simulation Based Study on Ultra-Short Pulse Laser Welding of Dissimilar Materials Expending Phase Lag Influence

In this work, the thermal simulation of dissimilar fusion welding system is demonstrated by considering the phase lag effects in ultra-short pulse laser source. When the pulse duration is comparable with the electron relaxation time, the hyperbolic effect cannot be neglected in heat transfer analysis due to femtosecond laser. The non-Fourier effect is considered for heat transfer analysis assuming finite delay in development of temperature within the body. This delay is represented in terms of relaxation times connected to heat flux and temperature gradient. In the present work, the simulation has been proposed by developing 3D finite element based heat transfer model using dual phase lag effect. Since the experimental basis of transient temperature distribution in ultra-short pulse laser is extremely difficult or nearly impossible, the model results have been validated with literature reported results. The model has been used further for the simulation of temperature distribution in femtosecond fiber laser welding of dissimilar aluminum alloy and stainless steel. The results in terms of computed isotherm are compared with experimentally evaluated weld pool geometry for dissimilar materials from independent literature. The influence of other characteristic parameters like pulse frequency, pulse width and relaxation times are assessed for this simulation based study which will effectively reduce the costly experimental effort for differential influence of process parameters. A clear guideline of geometric shape and size of weld pool geometry and peak temperature of the welding system with reference to predictable laser parameters are the effective output of this simulation based study. It was observed that the peak temperature reached in a very short interval of time, in the order of nano-seconds. Such high heating or cooling rate impacts on the microstructural changes of the welded joint. In order to reach certain temperature, multiple pulses are required in the material processing of either very thin film or microwelding to keep the thermal shock distortion as low as possible.