Authors:
Martin Sparkes
Markus Gross
Steven Celotto
Tao Zhang
William O’Neill
Centre for Industrial Photonics, Institute for Manufacturing, Department of Engineering, University of Cambridge, Cambridge, CB2 1RX, United Kingdom

A 2.2 kW fiber laser was used in a series of inert cutting trials on stainless steels of section thicknesses in the range of 6–10 mm. Variations in the cutting performance with changing gas pressure, focal position, and nozzle diameter were investigated. Results showed the difficulties associated in cutting with high brightness lasers, specifically in obtaining full melt eject through narrow kerfs; two distinct melt eject failure mechanisms were observed: (I) Failure of melt removal in the upper region resulted in melt ejecting out of the top surface and (II) poor base ejection giving recast and dross problems on the base of the cut. Detailed scanning electron microscope images of these phenomena are presented. A computational fluid dynamic model is used to show distinct differences in the theoretical gas performance at the center of the cut, displayed by most models, and at the edges where the melt eject is taking place. Melt eject is also shown both experimentally and theoretically to be improved for these experiments by the use of smaller nozzles for our experimental range. With a change in focal position strong correlations between the theoretical laser path, and the cut edge with variation in focal position were observed. The performance of the melt eject is shown with respect to speed, pressure, and kerf width. Improved quality of the cut edges was achieved with higher speeds, higher pressures, smaller nozzles, and wider kerfs. Even though the processing parameters were not optimized to utilize the benefits of high brightness, cutting speeds were 1.5 times higher than those of the CO₂ with similar powers and processing parameters.