Study Of Efficient Welding Technology Of Rail Transit Vehicle Bogie By Compound External Magnetic-field

The bogie is one of the key parts of rail transit vehicles.With the rapid development of rail transit vehicles,the production efficiency of bogies is facing huge challenges.In the atmospheric environment,the bogie structure,especially the welded joints,is corroded.To meet the requirements of the bogie service environment,weathering steel has become one of the preferred materials for welded bogie frames due to its high strength,good toughness,and strong resistance to atmospheric corrosion.The T-joint of the bogie is welded by the multi-pass gas metal arc welding(MP-GMAW),which has a low heat input and can inhibit the growth of crystal grains,but the welding efficiency is poor.Obviously,increasing the welding speed by increasing the welding current to control the heat input is a simple way to improve the welding efficiency.The main problem of the MP-GMAW process welding bogie T-joint:When the welding speed is high,defects such as undercut or insufficient fill of the weld toe will appear.This restricts the improvement of bogie welding efficiency.Therefore,improving the existing MP-GMAW process to achieve efficient welding is of great significance to the production of bogies.The external magnetic field(EMF)assisted GMAW is an advanced welding process in which an external magnetic field is applied during the welding process.By adjusting the welding arc,droplet or molten pool behavior to improve weld formation or refine the microstructure and other advantages.The process has the advantages of low cost,simple device,and easy operation.Studies have shown that applying EMF in the welding process is a simple and effective method to improve welding efficiency.Therefore,this subject optimizes the structure of the external magnetic field generator that can be integrated with the welding gun nozzle,and increases the accessibility of the welding gun.During the welding process,a pulsed compound magnetic field combining a parallel magnetic field and a transverse magnetic field can be generated at the same time.The magnetic field can adjust the arc behavior,the horizontal spreading of the liquid metal in the molten pool and the longitudinal flow behavior.This project has carried out the T-joint technology of GMAW welding bogies controlled by the external compound magnetic field,and analyzed the influence of the external compound magnetic field excitation current and excitation frequency on the weld formation of the T-joint MP-GMAW.The research found that for the filling welding,the compound magnetic field excitation is applied.The study found that when the excitation frequency of the external compound magnetic field is 15 HZ and the excitation current is 30 A,the filling welding speed can be increased to 0.72 m/min;when the magnetic frequency is 15 HZ and the excitation current is 40 A,the cover welding speed can be increase to 0.6 m/min.A temperature field acquisition system,an arc acquisition system and an electrical parameter acquisition system were built to gather the molten pool temperature,arc and excitation current and other related parameters of the welding process.The influence of the external compound magnetic field on the temperature distribution and arc behavior of the molten pool was analyzed,and the influence mechanism of the external compound magnetic field on the weld forming is preliminarily revealed.It is found that under the action of the compound magn etic field,the arc will swing left and right perpendicular to the welding direction,and the welding direction changes from the original backward dragging behavior to forward tilting behavior.The lateral temperature distribution is more uniform,which is conducive to the lateral spreading of liquid metal,and effectively suppresses defects such as undercut and insufficient welding toe filling.Analyze the microstructure and physical and chemical properties of T-joint in magnetically controlled high-efficiency welding by means of microstructure and physical chemistry analysis.When an external compound magnetic field is applied,the normalizing area of the filling welding is increased,the coarse-grained region in the middle of the weld decreases,the coarse-grained region on both sides increases,and the weld structure is refined.To a certain extent,the columnar crystals are broken,and the magnetic field has little effect on the content and distribution of gold in the welding seam.The mechanical properties of the welded parts were tested,and the mechanical properties were found to be good.The electrochemical corrosion resistance of the weld was studied,and it was found that the corrosion resistance of the magnetron high-efficiency welding weld was slightly lower than that of the low-speed welding,and was within the acceptable range of the use requirements.