IMPACT OF THERMAL FOCAL SHIFT ON LASER CUTTING PROCESSES WITH HIGH BRIGHTNESS LASERS

摘要

The increasing use of high brightness lasers withpower in the kilowatt range for laser fusion cuttingprocesses leads to advantages concerning yield andquality. Conversely these laser sources are verysusceptible to external disruptions and therefore tendtowards instable processing This becomes noticeablein the thermal focal shift which is influenced by manydifferent factors during the process and can easilyextend the Rayleigh length. The authors report oninvestigations of influences on the thermal focal shiftusing different optical configurations in laser cuttingwith single mode and multi mode high power fiberlasers. Changes of the beam caustic could be observeddue to the optical components in the laser processinghead including the fiber end block. In consequence ofthe measured drift of up to multiples of the Rayleighlength the focal shift has a high impact on the cuttingresults. Investigations about the impact of this drift onfusion cutting processes for metal sheets withthicknesses of 0.1 mm to 1.5 mm were conducted anda feasible technique for experimental determination ofthermal instabilities such as the laser induced focalshift could be demonstrated.