Correlation between plume fluctuation and keyhole dynamics during fiber laser keyhole welding

In order to reveal the fluctuation mechanism of the plume induced during fiber laser keyhole welding, dynamic behaviors of both the plume and the keyhole were simultaneously observed by using the multiple-imaging method. The results show that the fluctuation period of the plume was the same as that of the laser-induced vapor moving down on the keyhole front wall (KFW). The tilt angle of the plume was the largest when the laser-induced vapor was close to the orifice. As the laser-induced vapor moved toward the bottom of the KFW, the tilt angle of the plume decreased gradually. The correlation between the plume fluctuation and the dynamics of the laser-induced vapor on the KFW was not affected by parameters such as welding speed, laser power, and focal length. Further analysis shows that the periodic drilling behavior of the laser spot on the KFW is the main reason for the periodic fluctuation of the plume.