Finite Element Simulation of Nd:YAG laser lap welding of AISI 304 Stainless steel sheets

Laser beam welding (LBW) is one of the most important manufacturing processes used for joining of materials. It is also a remarkably complicated, nonlinear operation involving extremely high temperatures. Since its invention more than two decades ago, laser beam welding has been more of an art than a science. Laser welding of austenitic stainless steel AISI 304 the candidate material of this research work is used in several areas, including electronics, medical instruments, home appliances, automotive and specialized tube industry. An industrial 2kW CW Nd:YAG laser system, available at Welding Research Institute (WRI), BHEL Tiruchirappalli, is used for conducting the welding trials for this research. After proper tuning of laser beam, laser welding experiments are conducted on AISI 304 grade sheets for lap joint configuration to evaluate the influence of input parameters such as beam power, welding speed and spot diameter of the beam on weld bead geometry i.e. bead width (BW) and depth of penetration (DOP). Three dimensional finite element simulation of high density heat source is performed for laser welding technique using finite element code SYSWELD for predicting the temperature profile on AISI 304 stainless steel sheets. The temperature dependent material properties for AISI 304 stainless steel are taken into account in the simulation, which has a great influence in computing the temperature profiles. The latent heat of fusion is considered by the thermal enthalpy of material for calculation of phase transition problem. A Gaussian distribution of heat flux using a moving heat source with a conical shape is used for analyzing the temperature profiles. Experimental and simulated values for weld bead profiles are analyzed for stainless steel material for different beam power, welding speed and beam spot diameter. The results obtained from the simulation are compared with those from the experimental data for laser welding of lap joint configuration and it is observed that the results of numerical analysis (FEM) are in good agreement with experimental results, with an overall percentage of error estimated to be within ±5%. Key-Words: Laser welding, Heat source, SS 304, lap joint, FEM, SYSWELD, Nd:YAG laser