Laser cutting of titanium with pulsed and modulated pulsed Nd:YAG lasers

Recent test results demonstrate the differences between laser cutting of Ti with different pulsed formats at 1.06 mu m wavelength. The Precision Laser Machining (PLM) consortium is dedicated to investigating improved processing obtained with the use of diode-pumped Nd:YAG lasers having high beam quality and high average power. One of the PLM lasers developed at TRW was used to determine the best parameters for laser cutting 0.034 " Ti. Average power was available up to 340W. Pulse repetition rates were 322 Hz with pulse lengths of 454 mu s, while the modulated laser output had a 142 kHz micropulse train within the pulse envelope. Beam quality was sufficient to permit a 100 mu m spot size to be used with f/10 focusing. Ar assist gas was used. At each setting of the laser average power the cutting tests usually were tried at 11 different speeds, up to 3 "/second. The highest speed for which cutting is possible at a given average power is the threshold speed for that power. The cut specimens were evaluated for dress for a variety of rear surface Ar cross flow conditions. Each cut specimen also was evaluated for excess heating indicated by metallurgical and/or surface chemistry changes. Cutting at speeds above a critical minimum speed for each setting of laser average power greatly reduces degradation due to excess heating. Goad cutting is possible between the threshold speed and this minimum speed (both a function of average power). Data for threshold and minimum speed were obtained for the pulsed and the modulated pulsed laser output. These tests also determined evidence of optimum conditions for cutting with a rear cross flow of Ar that substantially eliminates rear surface dress on the edge of the kerf. The quality of the cut edge was evaluated by inspection of its polished crossection..