The Research Of Synchronous Magnetic Pulse Control In The Medium Current CO₂ Welding Short Circuit Liquid Bridge

CO₂ gas shield welding iswidely used in low-carbon steel and low alloy steel and other ferrous materials because of its high-efficiency and low-cost. However, CO₂ gas shield welding has the drawbacks of big welding spatter and bad appearance of welding, thus limiting the CO₂ gas shield weldingdevelopment in the industrial. In this paper, external longitudinal magnetic field is introduced to reduce welding spatter rate and improve the appearance of welding. The base metal is Q235 in the welding experiment. Thedroplet transfer process and welding arc of CO₂ gas shield welding with and without the action of external longitudinal magnetic field was shot with high-speed camera, and compare the difference in every phase of short-circuit transfer.And according to the pictures, the size r1 of radius of droplet on the arcing stage, r2 of contact radius at early stage of short circuit, r3 of minimum radius of equatorial plane of liquid bridge, r4 of contact radius at bottom of liquid bridge was measured. Based on the analysis of forces exerted on the droplet, the influence of external magnetic field on the liquid bridge can be concluded. The results show that when the low frequency magnetic field is imposed, with increasing the magnetic field frequency,the droplet radius increases reaches the maximum value with the magnetic field frequency of 60 Hz, and has the largest globular droplet volume at this time. With increasing the magnetic field frequency, the liquid bridge formation period shortens,and the droplet transfer process at the early stage of short circuit is promoted. When the high frequency magnetic field is imposed, the minimum radius of equatorial plane in liquid bridge shrinkingperiod reduces, and the droplet transfer process at the terminal stage of short circuit is promoted.External longitudinal magnetic field can change the shape of welding arc, and then it can improve the welding formation, when the low frequency magnetic field is imposed, with the increase of excitation current, upper arc constriction, thebottom of arc divergence, gradually change to the bell shape, and the extent of the rotation of the welding arc becomes more severely, and the welding width gradually become bigger.When the magnetic field strength is certain, the welding arc change to the bellshape. The spatter of CO₂ short-circuit transition is main produced in the early and late phase of short-circuit.At the beginning of the short-circuit, the contact surface of droplet and molten pool is very small, the instantaneous spatter is easy to happen, but the spherical droplet extend in horizontal after low frequency magnetic field is introduced, so that the spatter is reduced. At the end of the short-circuit transition, the liquid is magnetic compression after high frequency magnetic field is introduced, it can effectively promote theshort circuit transfer of droplet, so it can reduce the CO₂ welding spatter. The experimental result shows that when the welding current is 190 A,exciting current is 5A, magnetic field frequency is 100 Hz, the welding spatter rate is the minimum 3.1%.