Study Of Magneto-optical Imaging Rules Of Micro-gap Weld Under Nonuniform Excitation Magnetic Field

In the welding process, precision seam tracking is the key to obtain good welding quality, and the premise of seam tracking is to accurately recognize the location of the weld. For the micro-gap weld whose gap is less than 0.1mm, there is no efficient recognition method at present. In order to accurately detect the position of micro weld joint, this paper proposes a new method for micro-gap weld seam recognition based on magneto-optical imaging technology.The imaging principle of magneto-optical imaging sensor is Faraday magneto-optical effect, and before collecting micro-gap weld magneto-optical image, the weldment need to be magnetized. And the non-uniformity in the magnetization process of weldment is inevitable because of the asymmetry of excitation field itself and the non-uniformity of weldment materials and other factors, which will affect the magneto-optical imaging of welding seam and go against the precision of welding seam recognition. In order to eliminate the adverse effect of non-uniformity and improve the precision of seam recognition based on magneto-optical imaging, it is necessary to carry out the research of magneto-optical imaging under nonuniform excitation magnetic field first.This paper takes the weldment magnetization method as the starting point, studying the phenomenon and rules of magneto-optical imaging of micro-gap weld under an excitation field that is nonuniform in the horizontal direction. By using some horseshoe permanent magnets, artificially providing a excitation field which is obviously nonuniform in the horizontal direction, and the magneto-optical image of micro-gap weld under nonuniform magnetic field can be obtained. When studying magneto-optical imaging rules of micro-gap weld in nonuniform excitation field, a characterization method for the weld zone slope is proposed, and the weld zone slope is able to accurately determine the magneto-optical imaging effects and changing trends under nonuniform magnetic field. Based on the weld zone slope, proposing a method for developing the quality standard for weld magneto-optical image and selecting the valid weld magneto-optical image with the quality standard. Considering the characteristics of micro-gap weld magneto-optical image under nonuniform excitation field, applying a multi-scale and multi structure elements morphological edge detection operator, effectively extracting the feature information from micro-gap weld magneto-optical image under the nonuniform magnetic field. Finally, according to the magnetic induction intensity distribution in the weld zone and the weld feature information extracted from the magneto-optical image, the prediction model of the weld center offset under nonuniform magnetic field is established.The weld zone slope parameter that can be used to determine the magneto-optical imaging effects is obtained and a method of screening effective seam magneto-optic image is proposed in the study of magneto-optical imaging rules of micro-gap weld under nonuniform excitation magnetic field. Thus, it is possible to acquire the position information of micro-gap weld and predict the weld center offset in each moment under the nonuniform magnetic field. And the research in this paper laid the experimental basis and theory basis for diminishing the adverse effect of the nonuniformity in the recognition of micro-gap weld based on magneto-optical imaging technology.