Residual stress and distortion calculation of laser beam welding for aluminum lap joints

A numerical simulation model of the laser beam welding (LBW) process is developed, aiming to a reliable prediction of the residual stress and distortion fields. As LBW is a thermo-mechanical process, a thermal analysis is conducted to analyze the spatial temperature distribution history, coupled to a mechanical analysis to calculate the residual stresses and distortions. An innovative and efficient keyhole model, independent of any empirical parameter, is introduced for the prediction of the keyhole size and shape required for the thermal analysis. All the major physical phenomena associated to the LBW process, such as, heat radiation, thermal conduction and convection heat losses are taken into account in the model development. The thermal and mechanical material properties are introduced as temperature dependent functions, due to the high temperature variations and the material phase changes occurring during the welding. The simulation algorithm is programmed as a macro routine within the ANSYS finite element code. The model is validated for the case of butt joint welding DH-36 steel plates and its efficiency is demonstrated for the lap-joint welding of two aluminum 6061-T6 plates. The main advantage of the developed model is its generality and flexibility, as it is independent of any empirical parameter, enabling its application in parametric studies of a wide range of LBW problems of different geometrical, material and joint type, requiring only the basic mechanical and thermal material properties.