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Process diagnosis and control for removal processes with excimer laser radiation


Waidelich, W.:
Laser in der Technik. Vorträge des 11. Internationalen Kongresses Laser 1993
Berlin: Springer, 1994
ISBN: 3-540-57444-1
ISBN: 0-387-57444-1
S.411-416 : Abb.,Lit.
Internationaler Kongreß Laser <11, 1993, München>
Fraunhofer ILT ()
beam shaping; energy conversion; measurement workpiece handling; process computing system; reflection; surface treatment

Many basic aspects of surface treatment with Excimer laser radiation have been investigated and it has been shown that the processing results are affected by variations of the processing variables as well as by irregularities of the workpiece. Therefore the development of on-line process control systems is of great importance for an increase in reproducibility and further acceptance of Excimer laser processing in production line. To ensure high machining quality and short machining time the processing result and all significant processing parameters has to be analyzed and controlled in realtime. One promising technique of surface treatment is scale removal to improve the corrosion resistance of austenitic steel. For this application the varying thickness and composition of the scale layer require an adaption of the processing parameters (fluence and number of laser pulses per site) to the local surface conditions. A process diagnosis based on Plasma Emission Spectroscopy (PES) is build up for this application. Another application of interest is selective removal of corrosion layers on historical glass paintings to increase light transmission. Because the corrosion layers have varying composition and thickness a process diagnosis with a probe laser and an optical sensor is used to measure the transmittivity of the layer. A process control system is build up for real time diagnosis of removal processes with Excimer laser radiation. The system is applied to descaling of steel. For selective removal of corrosion layers on glass a closed loop control has been developed to guarantee a high processing quality without damaging the glass.