Numerical and experimental investigation of tandem pulsed Nd:YAG laser welding

This paper presents a three-dimensional finite element model of the heat flow during tandem pulsed laser welding. Model predictions of fusion zone and heat-affected zone dimensions are compared with experimental measurements. When two beams from the same laser are used in tandem to weld a material, it is the intensity distribution of the composite processing beam which is important. This is similar to being able to select the mode of the laser beam, as the relative intensities, spacing and spot size of the two beams can be varied. The potential benefits such a scheme may produce over single beam laser processing are: the possibility of removing potential contaminants to the weld with a minor beam ahead of the main welding beam; the ability to control the heating and cooling rates of the workpiece by employing a minor beam to effectively preheat or postheat the weld; and the modification of the speed and penetration characteristics of single beam laser welding with the same total power. Experiments using a pulsed Nd:YAG laser to produce bead-on-plate welds in AISI 1006 steel were performed to compare with theory. The results suggest that the cooling rates associated with single beam laser welding can be reduced by introducing a minor preheat beam.