The Precitec (New Hudson, MI; www.precitec.us) Laser Weld Monitor (LWM) was recently installed on the Rofin CO2 laser Remote Welding System (RWS) in the Autotek Industrial facility located in Puebla, Mexico (see May ILS page 26). The LWM system was installed to provide in-process monitoring of every single laser welded part for determining good versus bad parts. Volkswagen has required Autotek to implement a quality monitoring system for the laser welded parts produced on the Rofin RWS. The parts are inner door stiffeners consisting of high-strength steel. The weld joint is an overlap type with the parts containing a stamping to provide a 0.1mm gap between the two parts to allow for gas to escape. The parts are galvanized and thus require this gap during the laser welding process. The LWM sensor is co-axially mounted within the RWS and thus is protected from weld slag and smoke. The LWM utilizes two distinct sensors for monitoring the UV and NIR radiation generated during the actual weld, and a sampling rate of 20kHz is possible. Another option with the LWM is to monitor the laser power during the weld to correlate with the UV and NIR sensor signals. The LWM is successful in detecting various process changes such as loss of shield gas, parts not properly seated, loss of laser power, laser out of focus, lack of penetration, and others.
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