On-line monitoring of keyhole instabilities during laser beam welding

Abstract

Two years ago a paper was given about a German Canadian Cooperation between the UoW (University of Waterloo) and the ILT (Fraunhofer institute of laser technique). A new method of monitoring the welding process based on a CCD-camera was presented. Experience gained with this system revealed two difficulties as regards the availability of the method within a production line. Firstly, the difference between the illumination power of the melt pool and the keyhole makes it interesting to use a camera with a higher optical dynamic range. Secondly, it is useful to have a big image field for adjusting the system and for observing different positions of the welding process. On the other hand, it is necessary to obtain a frame rate of about 1kHz in order to detect all faults of the process. These two demands (a high frame rate and a big image field) contradict one another. A solution could be a camera, which is able to generate subframes. These difficulties could be solved with a camera based on the CMOS technique. Prometec constructs an industrial application with a CMOS-camera using the methods of the cooperation. The new system will be introduced during this presentation. First results shows the availability for manufacturing and the advantages of the system are worked out.