A noncontacting ultrasonic sensor system is being developed for online inspection of thick section welds made by a robotic gas metal arc welding (GMAW) system. The sensor system consists of a pulsed laser for generating the ultrasound and an electromagnetic-acoustic transducer (EMAT) for receiving it. The sensor will follow closely behind the weld head and inspect the solidified weld bead for flaws. The main advantage of this technique is that flaws can be found and repaired before they are covered by subsequent welding passes. This is expected to be much simpler and less likely to induce further flaws than current practice since a large amount of otherwise good weld metal need not be removed to reach and repair a flaw. The system also monitors the welding process, i.e., detection of a large number of flaws indicates that the process is no longer operating as planned. In this paper, the technique for detecting incomplete sidewall penetration is demonstrated and methods for improving the system are discussed.
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