Study On Arc Behavior Of Special Tungsten Electrode GTAW

TIG is a traditional non-molten gas shielded arc welding method.It has many advantages such as stable welding process,good weld formation and high degree of automation.The shape of the tungsten electrode in TIG welding determines the welding current density distribution and the arc pressure distribution.The basic laws of heat transfer and force transmission of arc with different tungsten electrode shapes are significantly different.In order to obtain the basic laws of heat transfer and force transmission of TIG welding under different tungsten shapes,the basic laws of welding arc behavior of hollow tungsten,bifurcated tungsten and double tungsten argon arc welding are studied in this paper.Based on FLUENT fluid simulation software,the arc models of hollow tungsten electrode GTAW,bifurcated tungsten electrode GTAW and twin-electrode TIG are calculated,and the arc shapes of three tungsten electrodes under different parameters are photographed.The arc pressure on the workpiece surface is measured by means of arc pressure measuring device,which verifies the accuracy of the arc model.Firstly,the distribution of current density field,temperature field,velocity field and pressure field of hollow tungsten electrode GTAW under different welding current,inner gas flow rate and inner hole diameter is studied.The results show that the arc current density field,temperature field,velocity field and pressure field increase significantly with the increase of welding current in the range of 100A-220 A.With the increase of welding current by 30 A,the maximum arc temperature increases by about 1400-2600 K,and the maximum plasma velocity increases by about 65-101m/s.The influence of gas flow rate in hollow tungsten electrode on the arc shape is mainly in the area below the tungsten electrode hole.With the increase of gas flow in the inner hole,the current density,temperature and velocity on the central axis of arc decreased.With the increase of internal gas flow rate of 0.1L/min,the maximum temperature of arc decreases by about 1650 K and the maximum plasma flow rate decreases by 20m/s.When the inner hole diameter of hollow tungsten electrode increases,the current density,temperature,plasma velocity on the central axis of the arc and the pressure on the tungsten extreme part and the workpiece surface all decrease obviously.When the diameter of inner hole increases from 0.5mm to 1mm,the maximum arc pressure on the workpiece surface decreases from 548 Pa to 291 Pa.Then,the distribution of current density field,temperature field,velocity field and pressure field of bifurcated tungsten electrode GTAW arc under different welding current,shielding gas flow rate and tungsten electrode spacing is studied,and compared with ordinary TIG.The results show that the pressure acting on the workpiece surface by bifurcated tungsten GTAW arc is much lower than that by conventional tungsten argon arc welding,and the current density,temperature and pressure distribution of bifurcated tungsten GTAW arc on the workpiece surface show a relative contraction trend in the X-axis direction.When the welding current increases,the current density,temperature,plasma velocity and arc pressure of the arc all increase significantly.When welding current increases by 30 A,the maximum arc temperature increases by about 1400-1800 K and the maximum plasma velocity increases by about 51-67m/s.The effect of shielding gas flow rate on arc is not obvious.With the increase of shielding gas flow rate,the temperature field,velocity field and pressure field of arc only increase a little.When the bifurcation spacing of tungsten electrodes increases,the maximum temperature of arc,the maximum plasma velocity and the arc pressure on the workpiece surface decrease significantly.When the bifurcation spacing increases from 0.5mm to 1mm,the maximum arc pressure on the workpiece surface decreases from 275 Pa to 190 Pa.Finally,the welding behavior of twin-electrode TIG is studied.The asynchronous arc initiation process of twin-electrode TIG is obtained by Xiris camera.It shows that the right electrode completed the arc initiation through the conductive channel formed by the left arc,and the shape of the left arc is affected.The temperature field,velocity field and pressure field of twin-electrode TIG under different welding current is calculated.The results show that the highest temperature,the maximum plasma velocity and the maximum arc pressure of the arc all occur at the tungsten electrode extremity,and the reverse plasma flow appears above the arc.With the increase of welding current,the arc temperature,plasma velocity,arc pressure and reverse plasma velocity above the arc have been significantly increased.In the range of welding current 100A-140 A,with the increase of welding current by 20 A,the maximum temperature of arc increases by 1171 K and 1262 K,the maximum plasma velocity increases by 24m/s and 39m/s,and the maximum arc pressure on workpiece surface increases by 33 Pa and 59 Pa.Under the condition of non-equal current,the highest temperature,maximum velocity and maximum pressure of welding arc occur at the tungsten extremity where the current is high.The current density and arc pressure on the workpiece surface are asymmetrically distributed,and the peak value all occurs at the left of the workpiece center.