Parameterized multipoint-line analytical modeling of a mobile heat source for thermal field prediction in laser beam welding

The thermal effects of the “keyhole” full penetration welding mode, which is characteristic of high-power CO₂ laser, are simulated introducing a multipoint-line thermal source model based on heat conduction, parameterized by the distribution of the laser beam power, and the setting of the source system layout, and to be fitted on experimentally detected cross sections of the heat-affected or fusion zones of the weld. The proposed model allows to express the thermal field according to the moving reference system fixed on the overall heat source, and to analyze the temperature profiles that develop in some detection points fixed on the workpiece, as time varies during the welding process. By this way, it can be useful in evaluating the thermal effects that result from the variation of the main welding parameters (beam power, welding speed, plate thickness), with the aim of simplifying the selection of the optimal process conditions. As an application, reference is made to a cross section of a joint between plates of AISI 304 L austenitic steel. The fitting procedure allows to set the power distribution and layout parameters of the most suitable source combination (obtained by superposition of a line and two point sources). The value of the absorption coefficient also is assumed as fitting variable, so to overcome the complex problem of evaluating the beam power actually absorbed by the material on keyhole mode welding. Finally, the fitted model is applied to carry out a detailed thermal field analysis in the welded plates.