Remote Optical Detection of the Fusion State in Laser Deep Penetration Welding

We introduce a novel technique for the determination of the fusion state of laser welded blind joints (e.g. overlap joints) by measuring the vibrations of the workpiece during the welding process. In case of incomplete fusion, the workpiece vibrations differ significantly from the vibrations observed during a sound weld. The detection of the vibrations is performed by observing a speckle pattern on the workpiece surface. The movement of this pattern allows remote detection of the workpiece oscillations close to the keyhole. Those oscillations contain information on the fusion state of the weld.