Study On The Behavior Of Arc And Droplet Transfer In MIG Welding With External Magnetic Field

In recent years,as a new welding technique,magnetic controlling welding technique can effectively change the shapes and motion states of welding arc and droplet,refine the primary solidification structure and improve the mechanical properties of the welding by the interaction between the external magnetic field and the welding arc and droplet.Study the interaction effect of MIG welding with different styles external magnetic field and it is helpful to enrich and perfect the mechanism of magnetic controlling welding and to lay a theoretical foundation for popularizing the practical application of magnetic controlling welding.In this paper,the MIG welding of low carbon steel is taken as the research object,and the reasonable welding parameters are selected through the experiment.The influence of different magnetic field directions and excitation current on the welding arc,droplet shape and movement mode of MIG is obtained respectively by photographed in welding process with high speed photography.The results show that in a certain range of magnetic field parameters,with the increase of excitation current,the welding arc expands outward and rotates,and its shape changes from conical to bell shaped.The droplet deviates from the center of the welding wire,moves around the wire axis,and turns from spherical to ellipsoid.By comparison,it is the same influence for the different directions of external constant longitudinal magnetic field on the shapes of welding arc and droplet,but different on the way of motion.Observe the influence of the alternating magnetic field on the welding arc and spray transfer in MIG welding by a high speed photography,and establish models of charged particles in the arc and liquid metal conducting fluid to analyze the movement mechanism.It is found that the welding arc expands periodically and contracts with the effect of excitation current and excitation frequency,and changes along the axis of the welding wire clockwise and counterclockwise.The liquid metal conducting fluid at the end of the welding wire deviates from the wire and makes rotation motion.When the liquid metal conducting fluid is short,it approximates the shape of a straight line;When the liquid metal conducting fluid is long,its rotational motion curve approximates the spiral line.The arc brightness region and shape will change with the change of liquid metal conducting fluid motion.The MIG welding experiment is carried out when the welding current is 320 A,the welding voltage is 35 V,the welding speed is 0.7m/min,and the argon flow rate is18L/min.When the excitation frequency is 40 Hz and the excitation current is 0.6A,the weld face is smooth,and the space between the fish scales becomes more uniform and compact.The external magnetic field also has a certain influence on the appearance of weld.With the increase of the excitation current,the weld width increases first and then decreases and the penetration decreases first and then increases.The weld primary solidification structure is refined under the effect of electromagnetic stirring.When the excitation current is 0.6A and the excitation frequency is 60 Hz,the primary solidification structure of the weld is fined the highest.The hardness of the welded joint should be greatly improved,the maximum is 281.47 HV when the excitation frequency is 60 Hz and the excitation current is 0.6A.