High-dynamic-imaging Based Detection Of Deep Penetration K-TIG Welding Pool State And Study Of Its Variation Mechanism

As a welding method with high energy input,deep penetration K-TIG welding(keyhole tungsten inert gas,K-TIG)plays an important role in the butt welding process of medium thickness metal plates.Deep penetration K-TIG welding does not need to process grooves.It can fully weld the plate at one time and form the front and back at the same time,which can speed up the production speed of medium and thick plate welding.It is widely used in shipbuilding and large container manufacturing industry.In order to improve welding productivity,the automation of deep penetration K-TIG welding process has become the development direction in actual production,and the detection of molten pool state is the key to realize automation.The weld pool state includes the position offset of the weld pool relative to the gap to be welded and the penetration degree of the weld pool.However,deep penetration K-TIG welding process is accompanied by strong arc light brought by highenergy arc,which covers most of the information of molten pool in the visual inspection of welding process;At the same time,the keyhole shape formed in the molten pool of deep penetration K-TIG welding largely determines the quality of the welded joint.The existing welding detection methods are difficult to completely overcome the influence of arc light to observe the forming inside the molten pool.In this paper,the change of weld pool state in KTIG welding is taken as the research object,and the welding high dynamic imaging technology is studied to realize the detection of weld pool offset and the prediction of weld pool penetration in the process of deep penetration K-TIG welding,and the deep mechanism of weld pool state change is studied from the perspective of numerical model.Firstly,a measurement method of irradiance distribution in welding scene based on camera response curve is proposed,and the fundamental reason why the current visual detection methods are not applicable is explored.On this basis,the welding high dynamic imaging technology is proposed,and the universality of the technology in different application scenarios is studied,and the best process window for parameter setting is obtained.Finally,the contrast experiment proves that the high dynamic imaging technology can improve the dynamic range of welding image.Then,the side detection method of molten pool migration based on high dynamic imaging technology is studied.The arc center under high dynamic imaging technology is used to locate the molten pool position.Algorithms are designed to extract the arc center position and the center position of the gap to be welded,and then experiments are carried out to compare the weld pool offset detection results under high dynamic imaging technology and ordinary camera imaging technology,so as to verify the improvement of high dynamic imaging technology on weld pool offset detection.Then,the method of weld pool penetration pre side based on high dynamic imaging technology is studied.By designing the feature extraction algorithm based on onedimensional pixels and the calibration method in three-dimensional space,the sizes of deep penetration K-TIG welding pool and keyhole under different welding current,welding speed and workpiece thickness are obtained.The penetration of molten pool is predicted by establishing BP neural network and inputting characteristic parameters.After comparing different feature parameter inputs,it is found that the features obtained based on high dynamic imaging technology have the highest prediction accuracy and model convergence speed.Finally,the change mechanism of molten pool state under high dynamic imaging is studied,and the deep influencing reasons of molten pool offset and molten pool penetration under different welding parameters are explored.The double ellipsoidal heat source model with automatic tracking free interface is used to simulate the deep penetration K-TIG welding process.It is found that heat input and arc pressure under different process parameters are important factors to change the shape of molten pool.The changes of molten pool shape caused by molten pool offset are deeply analyzed,and the reasons for different molten pool permeability under different parameters are explained.