Study On Welding Arc Character Of Coupling Arc AA-TIG Welding

In recent years, because of the faults of A-TIG welding which include complexityof coating process, too long time for development of surfactant formula, controllingintroduction quantity of surfactant hard and inaccuracy and so on. Those limits A-TIGwelding widely used. Arc assisted activating TIG welding, namely AA-TIG welding isproposed a new type of activating welding method.In order to further improve the welding production efficiency, on the previousbasis, this research group had been done experiment research for double welding torchcoupling arc AA-TIG. Its welding speed is higher than ordinary TIG welding. Itassembles two tilted welding torch, which generates the coupling arc through the twotungsten pole of inclining plank. In welding direction, the assisted arc which isshielded by mixed gases which include the inert gas （such as Ar, He） and active gas（such as CO₂, O₂） is in the front with smaller welding current. In primarily TIGwelding arc which is shielded by the inert gas （such as Ar, He） is in the behind with thelarger current. In the welding process, two welding torches weld at the same time. Thiswelding process is very stable and the productivity is further improved than theordinary TIG welding.Arc characteristic is great significance to study the mechanism of coupling arcAA-TIG weld shape and the improvement of the welding method. This paper hadstudied the arc characteristics of the coupling arc AA-TIG welding basis on these trialsand made a simple analysis about the advantages of the method. The mechanism of itsweld forming is discussed combined with the arc characteristic. Test consists of threeparts:Firstly, the measurement and analysis platform for coupling arc AA-TIG weldingarc characteristics is built, main including coupling arc shape acquisition system, thearc pressure measurement system, the anode current density measurement system, theanode temperature field measurement system, the arc voltage acquisition system andthe welding process test platform.The second is the measurement and analysis of the coupling arc AA-TIG weldingarc characteristic which includes five parts:（1） Collection of coupling arc AA-TIGwelding arc shape, the results show that: Under2mm tungsten spacing conditions, thecoupling arc AA-TIG arc shape is similar with the traditional single-arc which showed a bell-type and it is little impacted by welding current and the arc length. But under4mm tungsten spacing conditions, due to the factors of the main arc and assisted arcasymmetric, with the arc length and current changes the coupling arc shape deflectedand the arc shape towards to the main arc side. Compared to the traditional single-arcTIG, the coupling arc axial cross-sectional area gradient is smaller.（2） The coupled arcAA-TIG welding arc pressure measurement, the results show that: Compared with thetraditional single-arc, the coupling arc AA-TIG welding arc pressure was significantlylower. At2mm tungsten spacing conditions, with the welding current decreases, thearc length increases and the oxygen content of assisted arc reduce the arc pressure peakdecreases. With the tungsten electrode spacing increases, the coupling arc AA-TIG arcpressure distribution transition from Gaussian distribution to a bimodal distribution.（3）Coupling arc AA-TIG welding current density of the anode measurements, the resultsshow that: At2mm tungsten spacing conditions, the distribution of the anode currentdensity of the coupling arc AA-TIG welding is belong to Gaussian distribution. Withthe welding current increased, the peak value of the current density was significantlyincreased. With the arc length increased the peak of the current density reduced. Theinfluence of oxygen flow rate on peak current density is small. With the tungstenelectrode spacing increases, the current density distribution transition from theGaussian distribution to the bimodal distribution. And the peak value of the currentdensity of the main arc is bigger than the peak value of the current density of theassisted arc.（4） Measurement of the anode temperature distribution of the coupling arcAA-TIG welding, the results show that: Under the same welding procees, thetemperature of the traditional single-arc TIG welding is higher than the coupling arcAA-TIG welding at the central point on the workpiece. With tungsten electrodespacing increases the center temperature of the coupling arc decreases, the edgetemperature elevated. The smaller of the tungsten electrode spacing the temperature ismore focused.（5） Acquisition of the coupling arc AA-TIG arc voltage, the results showthat: The coupling arc AA-TIG welding arc voltage of the main arc is greater than theassisted arc voltage and both of them are less than the traditional single-arc TIG arcvoltage under the same current conditions. With the arc length increases, the variationvoltage of the main arc and the assisted arc is the same of the coupling arc AA-TIGwelding.The third is the welding process test validation. The process test results show that:compared to traditional single-arc TIG welding, the welding efficiency of the coupling arc AA-TIG welding is improved and the applications range is wider. Its penetration is2-3times of the conventional TIG welding and the penetration depth of coupling arcAA-TIG welding can reach8mm at one welding on the304stainless steel. At500mm/min welding speed, weld surface forming is good and weld penetration increased.At1200mm/min welding speed, it is one-side welding of2mm stainless steel platewith two-side forming.Finally a brief analysis of the forming mechanism of the coupling arc AA-TIGweld combined with arc characteristics show that: the mechanism of coupling arcAA-TIG weld penetration increased is the introduction of oxygen change the surfacetension-temperature gradient coefficient of the stainless steel pool. The Marangoniconvection changes and the liquid metal flows to the bottom of weld, whichsignificantly increases the weld penetration. The weld forming is good of coupling arcAA-TIG welding at high speed because of the arc characteristics and oxygen elements.Oxygen reduces the viscosity of the molten metal and arc pressure significantlyreduced the pool metal rear force. Thus the molten metal is easier to reflux to fill thepool to improve weld forming. These show that the coupling arc AA-TIG weldingprocess can ensure welding quality and improve welding productivity, reduceproduction costs. It is a potential development value of the welding method.