Research Of Integrated Multiphysics Welding Model With Plasma Arc,Keyhole And Weld Pool

The keyhole plasma arc welding can form a keyhole that penetrates the weld pool of the workpiece.It can achieve one-sided welding with both sides formation of the medium thickness plates without opening the groove,and has great potential for application in the industrial field.In the plasma arc welding process,keyhole is the key to form a large welding penetration,and the shape of the keyhole has a crucial influence on the quality of the weld.However,in the keyhole plasma arc welding,the keyhole is affected by the narrow process parameter range and poor stability,which greatly restricts the application of plasma arc welding technology.Plasma arc,weld pool and keyhole always affect each other during the welding process,and their thermophysical mechanism involves complex electro-magnetic-thermal-mechanical multiphysics coupling.Therefore,accurately describing the multiphysics interaction mechanism of gas-liquid-solid multiphase in the welding process has important theoretical guiding significance and engineering practical value for welding quality optimization.Based on the characteristics of plasma arc welding process,the plasma arc welding experimental system was built and a series of welding experiments were carried out to provide verification data for subsequent calculations.A three-dimensional integrated axisymmetric mathematical model of plasma arc-keyhole-weld pool for the keyhole plasma arc welding pattern was established,considering the influence of Marangoni force,surface tension,electromagnetic force,buoyancy force and gravity,and applying VOF method to tracking the gas-liquid two-phase interface between the arc and the weld pool.Using the integrated welding model,the dynamic evolution of the temperature field,flow field and electromagnetic field of the plasma arc and the weld pool and the shape of the keyhole in the case of fixed-point plasma arc welding are calculated.By coupling to solve the hydrodynamic equations,heat transfer equations and electromagnetic field equations,the various physical effects of gas-liquid-solid multiphase in the welding process are accurately described,and the heat transfer characteristics and the formation mechanism of the weld pool in the keyhole welding pattern are revealed.The validity of the integrated model is verified by experiments.Aiming at the moving plasma arc welding process,considering the movement of the welding gun relative to the workpiece,an integrated model of three-dimensional moving plasma arc welding is established,and the electro-magnetic-thermal-mechanical coupling between the plasma arc,the weld pool and the keyhole is analyzed in detail.Due to the relative movement of the welding torch and the workpiece,the front part of the plasma arc shrinks and the rear part expands.There is a significant deviation between the center of the keyhole and the center line of the welding torch;the inclination of the front and back walls of the keyhole in the weld pool is different;the maximum value of plasma arc pressure on the wall of the keyhole is located in front of the outlet of the keyhole on the bottom;the maximum values of current density and electromagnetic force on the surface of the weld pool are located in front of the key hole;two sets of mobile plasma arc welding experiments were carried out to verify the correctness of the integrated model.For the calculation of electromagnetic field,a method of combining magnetic vector equation and Biot-Savart equation is proposed to calculate the magnetic field B.The effects of the three electromagnetic methods on the thermal physical properties of plasma arc welding are analyzed and compared in detail,and a certain quantitative difference is found.Finally,by comparing the arc pressure on the surface of the workpiece and the shape of the fusion line with the experimental data,it is verified that the proposed method has higher accuracy.