DIAGNOSTICS OF THE CO_2-LASER CUTTING PROCESS BY EVALUATING THE BACKREFLECTED LASER POWER

摘要

In this paper we analyze the information content ofback-reflected laser light during high-power CO_2-lasercutting of metal sheets. A fast sensor which is mountedcoaxially to the beam path of a CO_2-laser cuttingmachine behind a scraper mirror detects the laserpower which is reflected back from the interactionzone of the CO_2-laser beam with the workpiece.The origin of the back-reflected laser power isanalyzed for different materials (mild steel, stainlesssteel, aluminum) and thicknesses (1 and 3 mm). It wasobserved that only a small fraction of 10% of the totalback reflection originates from the cutting front in thekerf. The main part (＞90%) is reflected from theoverlapping area of the laser beam with the workpiecesurface outside the cutting kerf.The amount of back-reflected laser power stronglydepends on the feed rate, the surface roughness and thefocal position. This relationship can be used to onlinemeasure the relative position of the focal plane as wellas to detect an undesired focus shift during lasercutting.Furthermore, the correlation of the back-reflected laserpower with cutting defects such as "lost cut" due to theclosed cutting kerf will be discussed.