26 February 2013 Online characterization of laser beam welds by NIR-camera observation
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Abstract
We have investigated process monitoring of laser beam welding with a TruDisk disk laser to detect process faults. Additionally to monitoring laser beam welding processes by a conventional VIS camera an NIR (near-infrared) camera reveals new information. Our sensor detects thermal radiation between 1100 and 1700 nm from the weld zone, which represents surface temperatures above 1000 K. Using the thermal radiation from the process we can observe all major weld defects without auxiliary illumination. The camera is integrated in a standard TRUMPF welding optics for on-axis observation. A real-time image processing system analyzes the camera images regarding welding irregularities and delivers information to characterize the weld process and its result. Actually, we perform an online passive heat-flow thermography that uses the process itself as the heat source and that probes the thermal attributes of the seam. By this means we can detect regions of bad fusion (“false friends”) virtually during the welding process. In addition to conventional thermography we have investigated the use of ratio pyrometry by using to NIR-cameras that observe the process in two different spectral bands. By considering the pixel-per-pixel ratio the influence of surface effects it greatly reduces and we obtain images of the weld zone with an absolute temperature scale. We have compared ratio pyrometry measurements with conventional thermography.
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Friedhelm Dorsch, Holger Braun, Steffen Keßler, Dieter Pfitzner, Volker Rominger, "Online characterization of laser beam welds by NIR-camera observation", Proc. SPIE 8603, High-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications II, 86030R (26 February 2013); doi: 10.1117/12.2004196; https://doi.org/10.1117/12.2004196
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