Effects of pulse shaping on Nd:YAG spot welds in austenitic stainless steel

The effects of temporal pulse shape on weld dimensions and weld quality of Nd:YAG laser spot welds produced in AISI 304 stainless steel have been examined over a range of power densities and pulse times. Four different temporal pulse types were used: normal rectangular'' pulses with a characteristic leading-edge power spike, rectangular pulses with no spike, ramped-up pulses and ramped-down pulses. Pulse shaping had no significant effect on the weld dimensions or weld quality of the conduction-mode welds. Removal of the leading-edge power spike from rectangular'' pulse shapes tended to reduce the weld diameter and crater area of keyhole-mode welds, but had little effect on other measures of size or quality. However, the diameter, penetration and melt area of keyhole-mode welds made with ramped-up or ramped-down pulse shapes were consistently greater than those made with the rectangular pulse shape. Also, the penetration and melt area of keyhole-mode welds made with the ramped-up pulse shape were greater than those made with the ramped-down pulse shape. Keyhole-mode welds made with ramped-up pulse shapes had the greatest occluded gas porosity, but the smallest crater areas. Alternatively, welds made with the ramped-down pulse shape exhibited the least porosity, but the greatest crater areas.