Detection of micro gap weld using magneto-optical imaging during laser welding

Accurate seam tracking plays a critical role in acquisition of good weld. During laser butt joint welding, the laser beam focus must be controlled to follow the weld trajectory. The key problem to be solved is the automatic identification of weld position. An approach to detect the micro gap weld (gap width is less than 0.05 mm) based on magneto-optical imaging (MOI) is proposed. The laser butt joint welding of carbon steel was carried out. A magnetic excitation device was used to magnetize the weldment, and it was found that magnetic field distribution at the weld was different from other regions. The magnetized weldment was detected by using a magneto-optical sensor, and magneto-optical images of the weld were captured. By analyzing and processing weld MO images with low contrast and strong magnetic field noises, the weld center position could be detected accurately. Weld MO images at different laser welding speeds were investigated to analyze the varieties of image characteristics. Experimental results indicated that the magneto-optical imaging technique could be applied to detect the micro gap weld accurately, which provides a novel approach for automatic identification and tracking of micro gap weld during laser welding.