High-speed Pulsed Tandem TIG Welding Process Based On Coordination Control Of Tandem Pulsed Welding Current

Stainless steel plates and pipes are widely used in pressure equipment,industrial architecture,furniture decoration,foods,medical and other industries because of its excellent corrosion resistance,high strength and good plasticity.Tungsten inert gas welding(TIG)is the main welding process of thin stainless steel plate currently,due to its advantages of stable welding process,low cost and high welding quality,especially suitable for welding production of thin-walled plate and pipe.For the low current carrying capacity of tungsten electrade,it is difficult to obtain good weld appearance by increasing speed and current simultaneously for single TIG welding.In addition,there are some problems such as coarse grain and low corrosion resistance of weld bead caused by high welding heat input.For the development of modern manufacturing industry and the demand on welding method with high quality and efficiency,and a high-speed pulsed tandem TIG welding process(tandem P-TIG)was proposed by controlling tandem pulsed welding current on the basis of the high speed tandem TIG welding process,which can be applied to high efficient welding production of thin-walled stainless steel pipes.In tandem P-TIG welding process,the main leading TIG arc at the peak stage is used to ensure the full penetration and the good back weld appearance,while the assistant TIG arc at the base stage reduces the unnecessary heat input and its interference to the main TIG molten pool.When the main leading TIG arc transfers to the base stage,the assistant TIG arc reaches its peak current stage to heat the trailing region of molten pool continuously and prolong the existence t:ime of the molten pool to ensure the liquid metal flow back.In addition,the assistant TIG arc at the peak current produces a high forward driving force for the molten pool to prevent the molten pool from piling up to the tail,and promotes its backflow of molten pool.So the joint themo-mechanical control of molten pool can be realized to prevent the formation of undercut and humping defects effectively in high speed TIG welding process with low heat input.The communication protocol between two inverter pulsed direct-current TIG welding power sources with the same specification was established,which can realized the coordination controls of frequency,phase difference between the main TIG arc and the assistant TIG arc.And the experiment platform for the high-speed tandem P-TIG welding process was set up based on the coordination control of pulsed welding current.High speed welding experiments were carried out at different phase and duty ratio of two different pulsed welding current,and the experimental results show that the thermo-mechanical joint control of molten pool by assistant pulse arc is effective.The interaction between the main TIG arc and the assistant TIG arc is weak when they are not at the peak stage at the same time,which can avoid the disorder of molten pool caused by the interference between two arcs,and it is easy to obtain good weld appearance.During the butt welding process of 304 stainless steel plate with the thickness of 1.2 mm,good weld appearance without undercut and humping defects can be obtained at the welding speed of 3.0 m/min.Compared with single TIG welding process,the welding speed is increased by 150%,the heat input is reduced by 17.5%;Compared with the tandem TIG welding process,tandem P-TIG welding process heat input is reduced by 14.5%at the same welding speed.The elongation,tensile strength and hardness of the tandem P-TIG welded joints are equivalent to that of tandem TIG welding,and the average grain sizes in the weld center and heat affected zone are decreased by 12%and 17.2%,respectively.The grain morphology of weld bead indicates that the opposite grains do not form in the solidification process of the tandem P-TIG weld bead at the welding speed of 3 m/min,the dendritic grains on both sides of the weld bead center are symmetrically grow up to the upper of the weld bead center on its axis.Compared with the traditional single TIG weld bead,the strength of tandem P-TIG weld is higher,and compared with the tandem TIG weld bead,the average grain size of tandem P-TIG weld is smaller.The experimental results indicate that high-speed tandem P-TIG welding process,which can not only have the advantage of the tandem TIG welding,suppresses the formation of the defects in high-speed welding,but also reduce the welding heat input and realize the high speed TIG welding with low energy consumption.