In situ visualization of multiple reflections on the cut flank during laser cutting with 1 μm wavelength

Instabilities of the laser cutting front cause loss of quality due to the formation of striations on the cut flank. The mechanisms of striation generation during laser cutting are still not yet fully understood. In this paper, the frequently disputed and not completely clarified effect of multiple reflections in the cut kerf during laser cutting with 1 μm wavelength is investigated during cutting of 6 mm thick stainless steel using a laser power of 5 kW and nitrogen assist gas. To visualize the laser cutting process, the trim-cut technique was invented many years ago and has been and still is continuously improved by different authors. During a trim-cut, the laser beam is moved in parallel along an existing sheet flank and cuts off a stripe of less than a standard kerf width. The cutting front and the transition to the resultant cut flank are directly visible. In order to maintain a kerf-guided supersonic gas jet along the melt film and simultaneously enable the in situ observation of the cutting kerf wit...