Product Code: ICA12_606

Diagnostics of the CO2-Laser Cutting Process by Evaluating the Back-Reflected Laser Power
Authors:
David Schindhelm, GSaME Graduste School of Excellence Advanced Manufacturing Engineering; Stuttgart Germany
Rudolf Weber, IFSW Institut fuer Strahlwerkzeuge; Stuttgart Germany
Thomas Graf, IFSW Institut fuer Strahlwerkzeuge; Stuttgart Germany
Presented at ICALEO 2012

In this report we analyze the information content of back reflected laser light during high-power CO2-laser cutting of metal sheets. A fast sensor which is mounted coaxially to the beam path of a CO2-laser cutting machine behind a scraper mirror detects the back reflected laser power from the interaction zone of the CO2-laser with the work piece. The origin of the back reflected laser power (cutting front or workpiece surface) was analyzed for different materials (mild steel, stainless steel, aluminum) and thicknesses (1 and 3 mm). It was seen that only 10% is reflected from the cutting front in the kerf. The main part (>90%) is reflected from the overlapping area of the laser beam with the workpiece surface outside the cutting kerf. The back reflected laser power strongly depends on the feed rate, the surface roughness and the focal position. This relationship can be used to online measure the absolute position of the focal plane as well as detecting an undesired focus shift during laser cutting. Furthermore, the correlation of the backreflected laser power with cutting for defects such as "lost cut" due to the closed cutting kerf will be shown.