Research On Electric And Magnetic Field Assisted Laser Welding Process Of Austenitic Stainless Steel

In recent years,with the rapid development of laser welding technology,electric and magnetic assisted laser welding technology has been widely valued by researchers at home and abroad.The introduction of electric and magnetic fields in laser welding can control the formation of plasma and affect the flow of molten pool,thus improving and promoting the weld morphology,porosity defects,joint strength and the stability of welding process.In this paper,from the perspective of the interaction between electric field and laser welding plasma,the influence mechanism of electric field on the flow of laser welding pool is explained;at the same time,according to the influence mechanism of magnetic field on the flow of laser welding pool,weld morphology and porosity defects,the internal relationship of the influence of magnetic field intensity on the welded joint is revealed by combining numerical simulation with experiment.The main research work is as follows(1)The experimental platform of electric field assisted laser welding was built.In the case of electric field reverse connection(plate connected with high potential,laser head connected with low potential),it was found that a large number of free electrons moved downward and gathered in the keyhole,which affected the keyhole fluctuation behavior and led to the instability of welding joint quality.On this basis,the influence of electric field intensity on weld cross-section morphology,porosity and mechanical properties of welded joint was explored by changing the direction of electric field.According to the charged nature of plasma,a two-dimensional model of particle motion in electric field was established.The influence mechanism of electric field on welded joint was explained from the perspective of the influence of electric field on plasma motion.The actual test and simulation results were compared The results show that the electric field can affect the movement of free electrons in the plasma,change the electron concentration above the keyhole and at the nozzle,and affect the laser scattering and absorption.With the increase of applied voltage,the weld penetration,joint width and joint strength show the same change law,which first increases and then decreases,while the weld width continuously increases with the increase of applied voltage,and the cross section of the weld increases The porosity increased.When the applied voltage is 200 V,the welding quality is the best.After increasing the voltage between the plate and the nozzle,it is found that the current is generated in the loop.According to the calculation,with the increase of the applied voltage,the potential difference between the nozzle and the plate decreases,so the variation laws of weld morphology,porosity,tensile strength and plasma characteristics are opposite to those of the positive electric field.(2)The results show that the magnetic field can increase the weld penetration and the width of the bonding zone,reduce the weld width,and the weld morphology changes from "wine cup" to "V" shape,but at the same time,it will lead to the increase of the weld porosity.Based on the theory of fluid heat transfer and fluid flow,the molten pool flow model of magnetic field assisted laser welding is established.According to the influence of magnetic field intensity on the cross-section morphology of laser weld,the temperature field and flow field distribution of molten pool under different magnetic field intensity are simulated from the perspective of the influence of magnetic field intensity on the flow behavior of molten pool.The magnetic field distribution can be seen from the actual test and theoretical analysis The Lorentz force generated in the molten pool will inhibit the flow of the molten pool,resulting in the change of weld morphology and porosity.The simulation results are in good agreement with the experimental results.