Effect of laser spot weld energy and duration on melting and absorption

To facilitate pulse Nd-YAG laser spot weld development, it is common practice to adjust the pulse energy, duration, and focus spot size. An accurate understanding of the effect of these parameters on melting, weld appearance, and heat input is thus required. Calorimetric measurements of the net heat input to 304 stainless steel workpieces for laser spot welds have been completed. A pulse Nd-YAG laser was used with varying pulse energies from 1 to 5·5 J, and pulse durations of 2·2 and 7·0 ms. Measurements showed the absorption for spot welds produced using the pulsed Nd-YAG laser to vary from 38 to 67% and to be relatively insensitive to beam intensity. Analysis of the continuous point source equation for conduction heat flow in solids was used to predict the weld size for the pulse energy and duration measured in the experiment. Calculations of the weld pool volume from the weld metallography were used to determine the melting for each spot weld. Comparisons of the measured weld size with the three-dimensional model predicted size indicated that the observed weld pools are larger than is expected from the measured workpiece energy. Analysis of the experimental data and the theoretical model has revealed a substantial increase in melting for short duration pulses versus long duration pulses of the same energy. The benefit of laser spot welding parameter optimisation is hence indicated.