Many manufactured goods employ pulsed laser spot welding in joining and it is important to monitor the weld quality. The weld quality is highly related to the thermal history of the weld and there have been many trials to monitor the quality using an infrared (IR) sensor. Though the emitted thermal radiation is a function of the emissivity and the surface temperature, the measuring condition has an important influence on the detectable radiation. To increase the reliability of monitoring, it is useful to find the robust feature that is immune to the change of measuring condition. This paper suggests an in-process monitoring method using a point IR sensor for the pulsed laser spot welding of thin metal sheet. The suggested monitoring method is robust to the change of the measuring condition and it can detect the variation of the absorbed energy as well as any serious defect in the weldment.
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