Wang Lin, Gao Xiangdong, Chen Ziqin
Opt Express. 2018 Jan 8;26(1):347-355. doi: 10.1364/OE.26.000347.
The keyhole status is a determining factor of weld quality in laser-metal active gas arc (MAG) hybrid welding process. For a better evaluation of the hybrid welding process, three different penetration welding experiments: partial penetration, normal penetration (or full penetration), and excessive penetration were conducted in this work. The instantaneous visual phenomena including metallic vapor, spatters and keyhole of bottom surface were used to evaluate the keyhole status by a double high-speed camera system. The Fourier transform was applied on the bottom weld pool image for removing the image noise around the keyhole, and then the bottom weld pool image was reconstructed through the inverse Fourier transform. Lastly, the keyhole bottom was extracted from the de-noised bottom weld pool image. By analyzing the visual features of the laser-MAG hybrid welding process, mechanism of the closed and opened keyhole bottom were revealed. The results show that the stable opened or closed status of keyhole bottom is directly affected by the MAG droplet transition in the normal penetration welding process, and the unstable opened or closed status of keyhole bottom would appear in excessive penetration welding and partial penetration welding. The analysis method proposed in this paper could be used to monitor the keyhole stability in laser-MAG hybrid welding process.
小孔状态是激光-熔化极活性气体保护电弧（MAG）混合焊接过程中焊缝质量的一个决定性因素。为了更好地评估混合焊接过程，本文进行了三种不同的熔透焊接实验：部分熔透、正常熔透（或全熔透）和过度熔透。利用包括金属蒸汽、飞溅和底面小孔在内的瞬时视觉现象，通过双高速相机系统评估小孔状态。对底部熔池图像进行傅里叶变换以去除小孔周围的图像噪声，然后通过傅里叶逆变换重建底部熔池图像。最后，从去噪后的底部熔池图像中提取小孔底部。通过分析激光-MAG混合焊接过程的视觉特征，揭示了小孔底部闭合和打开的机理。结果表明，在正常熔透焊接过程中，小孔底部的稳定打开或闭合状态直接受MAG熔滴过渡的影响，而在过度熔透焊接和部分熔透焊接中会出现小孔底部不稳定的打开或闭合状态。本文提出的分析方法可用于监测激光-MAG混合焊接过程中的小孔稳定性。
