Study On The Mechanism And Technology Of Deep Penetration TIG Welding Of Medium-Thick Steel Plate With High Thermal Conductivity

Deep penetration TIG welding is a new welding method for medium-thick metal plates.On the basis of traditional TIG welding,deep penetration TIG welding is equipped with specially designed welding torch and large diameter tungsten electrode to obtain higher current density,so that the workpiece can be penetrated by the arc force during the welding process.Deep penetration TIG welding has the advantages of high efficiency,economy,good weld forming and high weld quality,which has a wide application prospect in the welding of medium-thick metal plate.At present,deep penetration TIG welding is mainly used in the welding of low thermal conductivity metal materials such as stainless steel and titanium alloy.However,for the welding of high thermal conductivity metal materials such as low carbon steel,nickel alloy and aluminum alloy,the welding process is unstable.In this paper,the reason that deep penetration TIG cannot stabilize the welding of medium-thick metal plate with high thermal conductivity is analyzed.According to the experimental phenomena in the welding process and the simulation of temperature field distribution in the deep penetration TIG welding process by ANSYS Fluent,it is found that the heat accumulated on the workpiece at the later stage of welding and the size range of hole are affects the stability of the welding process.According to the results of theoretical analysis,two solutions are proposed to improve the stability of deep penetration TIG welding of high thermal conductivity metal: 1)adding flux to the back of the workpiece to be welded;2)modifying the surface of the workpiece to be welded.After that,Q235 low carbon steel was used for validation the proposed two modified deep penetration TIG welding.The microstructure and properties of the welded joints are studied.The results are given as follows:(1)By adding flux on the back of the workpiece to be welded,the surplus heat at the welding pool can be effectively reduced by the melting heat absorption of flux.The stability of heat in the welding position makes the size of the small hole stable,so as to ensure the stability of the deep penetration TIG welding process.Finally,the stable welding of 8 mm thick Q235 low carbon steel with deep penetration TIG was realized in the welding current range of 430 A to 480 A.(2)Through the surface modification of welding parts,the thermal conductivity of the workpiece to be welded is reduced,the heat accumulation in the welding process is reduced,and the gravity of the molten pool is reduced;at the same time,the surface tension and viscosity of liquid metal in the molten pool are increased,and the size range of stable existence of small holes is enlarged.The small hole on the back of the workpiece is finally balanced under the joint action of various forces,and the deep penetration TIG welding process is stable.Finally,the stable welding of 8 mm thick Q235 low carbon steel with deep penetration TIG was realized in the welding current range of 430 A to 450 A.