Product Code: ICAL08_M306

High Speed Video-based Melt Pool Surveillance in Laser Spot Welding
Authors:
Nicolaj C. Stache, RWTH-Aachen University, Institute of Imaging & Computer Vision; Aachen Germany
Jens Gedicke, Fraunhofer Institute for Laser Technology; Aachen Germany
Jonas Dieckelmann, RWTH-Aachen University, Institute of Imaging & Computer Vision; Aachen Germany
Robert Firnich, RWTH-Aachen University, Institute of Imaging & Computer Vision; Aachen Germany
Alexander Olowinsky, Fraunhofer Institute for Laser Technology; Aachen Germany
Peter Abels, Fraunhofer Institute for Laser Technology; Aachen Germany
Til Aach, RWTH-Aachen University, Institute of Imaging & Computer Vision; Aachen Germany
Presented at ICALEO 2008

Laser welding processes are today increasingly observed with cameras. To this end, systems are employed, which mostly observe the laser-induced process radiation. Algorithms to evaluate such acquired images are under development, but they only indirectly allow to draw conclusions about the current state of the melt pool thus leading to corresponding uncertainty. To observe the melt pool directly, we previously tested an approach for monitoring it coaxially with additional illumination. The thus gained information is much more meaningful as it relies on the measurement of geometrical information. These directly measured data are much better suited to derive conclusions about the actual process state. Furthermore, applicable real time approaches with throughput rates of 5000 frames per second and beyond are difficult to realize yet especially depending on the type of information to be monitored. We therefore developed a framework, which complements the required throughput rates with a high degree of fault tolerance for determining the desired melt pool parameters such as position, size, size evolution, and a quality criterion with respect to sputters. The underlying principle is a robust contour point detection method, combined with a smart outlier regression and an algorithm for fitting a circle model to the melt pool. Laboratory results are presented, which confirm the proposed procedure.