QLIP - Quality assurance in laser beam cutting by means of in-situ polarization measurement

Funded within the framework of Sparkling Science Project partners:  HTL Donaustadt, opens an external URL in a new window and HTL Ettenreichgasse, opens an external URL in a new window

Project end: December 2019

Today, laser cutting is one of the standard processes in industrial material processing due to the high flexibility that can be achieved, the excellent automation capability and the high quality of laser-cut components. Laser cutting is also a highly dynamic process with a large number of parameters, which means that quality monitoring systems face very high challenges. In addition, since direct observation of the processes in the kerf is very difficult, the thermal emissions from the kerf were used to determine the cut quality during laser beam cutting.

For this purpose, the emitted and polarized thermal radiation from the kerf was recorded and evaluated during laser cutting of steel sheets. By using an active optical element (SCPEM = Single Crystal Photo-Elastic Modulator) and a polarizer, the polarization state of the thermal radiation was converted into a modulated signal and detected with a photodiode and then recorded. The selected measurement method allowed the thermal radiation emitted by the cutting front to be recorded at a high sampling rate, which meant that even highly dynamic processes of the melt pool could be captured. Evaluation algorithms were used to calculate the ratio of the polarization components from the signal curves and thus determine the inclination of the cutting front. By correlating the cut quality determined in laser beam cutting tests and the calculated cutting front inclination, a quality criterion was found. These results can also be used to improve existing simulation models of laser cutting, which can then be used to extend our understanding of the process.