| Since the laser technology was applied to welding area in1970, laser welding, was widely used in various industry fields in the industrial developed countries, with its high quality, high precision, low distortion, high efficiency and high speed, and many other features. What’s more it has great potential for development. With the development of the laser itself, laser welding as a kind of advanced special welding technology, will play a vital role in the future field of material connection.Welding is an important processing manufacturing technology, which has many characteristics, such as poor working conditions, large workload, and higher quality requirements and so on. Laser welding is a welding technology method commonly used in welding industry, and laser beam is used as the controlled object to realize welding automation control which is an important means of welding automation. Among them, the precise seam tracking is the premise of high quality for welding, namely, the laser beam must be controlled to follow the seam in the whole welding process. Therefore, the accurate weld position should be detected automatically. Especially as the demand of the precision welding workpiece and reducing the cost, the welding problem of no groove and tight butt-weld micro gap is increasingly prominent. When butt-weld micro gap is welded, weld wire can be unfilled, more small welding deformation and more even weld joint can be obtained, and joint defect detection after welding and repair work can also be reduced. Thus the welding efficiency and economic benefits.can be significantly increased. However welding is a complex thermal processing technology at the same time, many interference will appear in the process of welding, such as, thermal deformation, strong radiation, arc, soot and splash, which is very difficult to achieve accurate detection of weld position. Especially for the laser welding, with the high laser power density, small light spot diameter and allowed weld path deviation, usually when the deviation between the laser beam and the weld is more than0.2mm, welding failure will be caused. So the technology of automatic detection the butt-weld gap and seam tracking is very important, however the traditional visual sensor detection method are difficult to realize the recognition of this weld. An approach of detecting the micro weld joint (weld gap less than0.1mm) based on magneto-optical (MO) imaging is investigated during laser butt-joint welding of low carbon steel. MO imaging principle for weld position detection was introduced and Magneto-optical sensor was used to capture the dynamic images of weld joint. Magneto-optic weld image sequence was analysed and the interested area of image was selected to processing. According to the weld image gray distribution features, weld position transition zone was extracted, and the midpoint of transition zone was defined as a weld location point, then the weld location point was deemed as center point of the weld seam position during detecting welding position. The influence of different welding conditions on the weld position detection was also studied. Through methods of regression analysis and curve fitting, the mathematical correlation between the seam bias and the characteristic parameters was studied. Laser welding test results showed that magneto-optic imaging technology used in different experimental conditions, the position of the weld would be effectively detected. A model of the relationship between the weld position characteristic parameter and seam tracking offset was established. It provides a new method for real-time controlling welding laser beam following seam in actual industrial and has certain theoretical and practical significance. |
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