Study On High Frequency Pulse Twin-electrode TIG Welding Process Of Stainless Steel Sheet

Modern industry has put forward higher requirements for welding production rate.Traditional TIG welding is easy to cause hump and other defects in high speed and high current welding.Twin-electrode TIG welding(T-TIG)is developed on the basis of single tungsten electrode TIG.Two power sources are used to provide two tungsten electrodes with power respectively.Coupling arc is generated in the only nozzle,which greatly reduces the arc force and is helpful to restrain hump defect.High frequency pulse twin-electrode TIG welding(HFPT-TIG)with superimposed HFP can further increase the penetration,and not only can the mechanical properties of the weld be improved but also the grain is refined,which has a broad application prospect.In this paper,the physical characteristics of HFPT-TIG arc and the influencing factors of weld formation are studied.By using orthogonal test,the optimized welding parameters are obtained.Not only the the mechanical properties but also microstructure of HFPT-TIG joint are compared with those of traditional TIG and T-TIG welding joints.It provides a new idea for high efficiency and high quality welding of thin plate.The arc shape of HFPT-TIG with different welding parameters was photographed by high-speed camera system.The arc force distribution was obtained by arc force acquisition device,and the static characteristics of arc were measured by means of electric signal acquisition device.The results show that the front face of HFPT-TIG arc is“bell jar shape" and the side face is“triangle shape" when the tungsten electrode spacing is 2mm.When the tungsten electrode spacing is 6 mm,the front surface of the arc is "nose shape" and the side surface is "round shape".The high frequency pulse makes the arc contract obviously,and the degree of contraction in Y direction(The vertical direction of the tip connection of two tungsten electrodes)is greater than that in X direction(The direction of the tip connection of two tungsten electrodes).The stiffness of HFPT-TIG arc increases and the arc drag is restrained in high speed welding.The peak value of arc force of T-TIG is much lower than that of traditional TIG.The arc force of HFPT-TIG is slightly higher than that of T-TIG,and the peak value shifts to the side of tungsten electrode with HFP.The electrode spacing has a great influence on the arc force.The electrode spacing increasing from 2mm to 6mm,the range of X direction is expanding and the range of Y direction is reduced.The arc force increases slightly with the increase of HFP frequency and HFP amplitude.The static characteristics of HFPT-TIG arc are "U" shape,which is between traditional TIG and T-TIG;the change of tungsten electrode spacing,HFP frequency and HFP amplitude has little effect on the arc voltage.Surfacing experiments were carried out on 2mm thick 304 stainless steel plate to analyze the influence of different welding parameter on the surface forming and cross-section morphology of HFPT-TIG weld.The results show that HFPT-TIG can inhibit the generation of welding defects,and the weld has the best shape and larger penetration when the tungsten electrode tip line is parallel to the welding direction and the HFP is applied to the leading tungsten electrode.The tungsten electrode spacing has a great influence on the stability of welding process.When the total equivalent welding current is 130A+130A,the tungsten electrode spacing is 2mm and the arc length is 3mm,the weld penetration(1.79mm)of HFPT-TIG is 46.7%higher than that of T-TIG(1.22mm),and the average grain size of central weld is reduced from 11.6?m to 9.8?m.The optimized parameter of 1mm thick and 2mm thick stainless steel butt welding with HFPT-TIG were obtained by orthogonal test.Compared with traditional TIG welding and T-TIG welding,the welding speed of HFPT-TIG is increased,and the heat input required to ensure penetration is reduced.The microstructure of HFPT-TIG joint is mainly austenite and skeletal ferrite or strip ferrite.Fine grain zone is near the fusion zone;the grain size of columnar crystal distributed in the weld center is smaller than T-TIG,and the width of HAZ is more narrow than T-TIG.The tensile strength of HFPT-TIG joint can reach more than 97%of the base metal,and the fracture morphology is uniform and dense dimples,showing the characteristics of ductile fracture.The average hardness of the joint is higher than that of traditional TIG and T-TIG joints,and the hardness peak appears near the weld center.The results show that not only has HFPT-TIG welding process the advantages of good joint quality but the efficiency is markedly high,so that the process must be popularized in the industrial production.