Modulation of the laser power to prevent hot cracking during laser welding of tempered steel

It is shown that a temporal modulation of the laser power can prevent the formation of hot cracks during deep-penetration laser welding of tempered steel. For this purpose, the influence of the modulated laser power on the cumulated length of the hot cracks in the weld seams was quantified. Varying amplitude and frequency of the modulation significantly changes the pattern and length of the hot cracks. Moreover, hot cracks can be prevented entirely in a specific range of the modulation frequency that depends on the welding speed. Our results indicate that the reduction of hot cracks might be related to a change of the fluctuating length of the weld pool, which was detected by means of thermographic imaging. (C) 2017 Laser Institute of America.