| TIG welding process is stable and can get good weld bead surface,however it is low efficient.MIG welding process is high efficient and easy to be used in automatic line,however it is not stable in weldig.With the development of morden industry,traditional welding process can not satisfy the need of high efficiency and low cost.As a result,many welding processes with that strength appear and develop very fast.TIG-MIG hybrid welding process can overcome the shortcomings of single TIG or MIG,and play their respective advantages.So,the process is widely acknowledged in high efficient welding field.But when low current is used in TIG process,DC TIG-MIG hybrid welding process is unstable with severe current interruptions and spatters.Moreover,there are also severe humpings.To change the process parameters and overcome defects like that is with high significance in optimizing TIG-MIG hybrid welding process.TIG AC square wave is good with nearly no zero point region.And the change speed is very fast between the positive and negative polarity,so it can output current with high stability.AC square wave is used to take the place of DC wave in TIG in this paper.AC square wave TIG-MIG hybrid welding process is studied to get more fundamental theory for further optimizing and industry usage.Combined with the weld bead appearance,the stability distinction between DC TIG-MIG hybrid welding process and AC square wave process is analysed from many respects,like the amount of current interruption,the wave of weld parameters and so on.DC TIG-MIG hybrid welding process is more unstable with severer current interruptions,worse weld bead appearance,more spatters and humpings than AC welding process.And when the polarity of AC square wave is set to be 10,the process behavior is the best.The characteristics of AC square wave TIG-MIG hybrid arc and the influence of different polarity are studied.In terms of time,as the polarity goes up,the mutual attractive time of coupled arc becomes longer and the repellent time becomes shorter.In terms of arc shape,as the polarity goes up,the strength of coupled arc is enhanced and the shape of attraction or repellence is more obvious.When polarity is small,the shape of coupled arc is contractive and the heat input is intensive.Droplet characteristic of AC square wave TIG-MIG hybrid welding process and the influence of different polarity are studied.When the wave goes positive,molten MIG wire transit to the rear of the molten pool;when the wave goes negative,the molten liquid metal of the end of MIG wire transit to the front of the molten pool.In AC square wave TIG-MIG hybrid welding process,the droplet of MIG maintains the deviation from tungsten and transits to the rear of molten pool for most of time.As polarity goes up,the time of transition to the rear of molten pool becomes shorter and to the front of molten pool becomes longer.The flow characteristic of molten metal of AC square wave TIG-MIG hybrid welding process and the influence of different polarity are studied to find out how humpings are overcome.When polarity is 0,tapered liquid column of MIG droplet passes into the tail of molten pool.Althoughthe driving effect on the backward liquid flow is smaller because of thick liquid metal layer,the liquid metal flows into the tail to form a wall channel and a molten metal mass,which can easily lead to hump formation.When polarity is 10 and the waveform is in the negative half,the position of the transition droplet into the bath varies within a range,and the continuous thrust of the weld pool will not be formed.The backward flow velocity of molten metal decreases,weld pool lumps will not occur in the weld area.When polarity is 40 and the waveform is in the negative half,MIG droplet passes into the front of molten pool.Thebackward flow velocity of molten metal increases,and it will lead to the formation of liquid metal depressions and finally a hump. |
PDF Full Text Request