Improving reliability of heat and fluid flow calculation during conduction mode laser spot welding by multivariable optimisation

Several uncertain parameters affect the reliability of heat transfer and fluid flow calculations during conduction mode laser spot welding because their values cannot be prescribed from fundamental principles. These parameters include absorptivity of the laser beam, effective thermal conductivity and effective viscosity of liquid metal in the weld pool. Values of these parameters are usually adjusted by trial and error so that the computed results agree with the corresponding experimental values. Here it is shown that by integrating multivariable constrained optimisation with convective heat transfer and fluid flow calculations, the values of the uncertain parameters can be obtained from a limited volume of experimental data. The optimisation technique requires numerically calculated sensitivity values of weld dimensions with respect to absorptivity, effective thermal conductivity and effective viscosity and minimises the discrepancy between the predicted and the measured weld dimensions. The numerical heat transfer and fluid flow model embodying the optimised values of the uncertain parameters could accurately compute values of weld dimensions for new welding conditions. Reliability of heat transfer and fluid flow calculations can be significantly enhanced by determining the values of uncertain parameters from a limited volume of experimental data using a multivariable optimisation technique with a numerical heat transfer and fluid flow model.