Suppression Mechanism Of Low Current Auxiliary TIG Arc On Undercut Defect In High Speed MIG Welding And Process Optimization

The metal inert-gas welding(MIG)welding is the most widely used welding process in the manufacturing industry because of its low cost,high adaptability and easy automation.However,the undercut will occur when the welding speed is beyond a certain critical value,which becomes a main obstacle for its application in high speed welding.In this paper,the low current TIG-assisted high-speed MIG hybrid welding is carried out to suppress the undercut defect and the suppression mechanism of the undercut defect was analyzed from the aspects of mass transfer,heat transfer and force-action condition.The optimization of TIG-MIG hybrid welding process was conducted to obtain the satisfactory weld beads without the undercut to achieve the high speed welding.A double-torch holding device for the TIG-MIG hybrid welding was designed and optimized,and the electrical parameter acquisition equipment was also optimized and reorganized.The visual observation system and the temperature field measurement system were established to investigate the temperature distribution,metal transfer,fluid flow,and the force status on the formation and suppression of undercut defect.The influence of the temperature field of the weld pool surface on the undercut was investigated.The results show that the temperature gradient of the weld pool edge plays an important role in the formation of the undercut.The low current auxiliary TIG arc can reduce the temperature gradient of the edge of the high-speed MIG pool so the undercut was prevented.In addition,the observation of the molten metal flow on the weld pool surface based on the tracer particles also proves that the low current TIG arc can promote the spreading and filling of the liquid metal to the edge of the weld pool,so the temperature gradient of the molten pool edge was reduced.The influence of the force status on the undercut defect was also experimentally analyzed.The results show that the arc force and the droplet impact play the major role in the formation of the undercut defect compared with gravity and surface tension.The auxiliary of low current TIG can reduce the arc force to mitigate or even inhibit undercut defect during the high-speed welding process.The orthogonal test was curried out to investigate the influence of weld process parameters(TIG welding torch inclination.TIG current,wire-pole spacing and tungsten distance workpiece distance)on undercut defect.The hybrid process parameters were optimized based on the orthogonal test results.A set of welding process parameters can be determined conveniently and easily for a given welding condition.