| With the rapid develop ment of manufacturing industry,steel output is increasing day by day.Nearly 50%of steel processing needs welding,and welding processing volume is increasing sharply.Therefore,it is particularly important to improve welding efficienc y.GMAW is widely used in metal manufacturing industry because of its high welding efficiency and stable process.In the process of GMAW welding,the direct way to improve the cladding efficiency is to increase the wire feeding speed,welding current and stick out length.However,when the welding current exceeds the second critical current and droplet trans fer is changed into rotating jet transfer,the arc is unstable and the weld formation becomes worse.In this paper,the external magnetic field of high current GMAW is studied,and it is found that the external magnetic field is a scientific and effective means.The commercial MIG/MAG welding machine was modified,the wire feeding speed was increased from 22m/min to 50m/min,and a magnetic control device with adjustable frequency and intensity was developed to apply different frequencies and strengths to the GMAW welding process under high current.The longitudinal alternating magnetic field obtains a relatively stable rotary jet transition,and performs high-speed photography and voltage and current signal acquisition for the welding process.Observe and analyze the magnetic field of different frequencies and intensities on the droplet transition,arc shape,welding spatter,weld formation,the influence of weld mechanical properties and electrical signals.Summarize the law and provide guidance for the application of longitudinal alternating magnetic fields to GMAW welding productio n.When the excitation current is 5A and the applied frequency is 1000Hz alternating magnetic field,the rotating radius of the arc decreases,the stiffness and stiffness of the arc increase,the arc is relatively more stable during the transition of the rotating jet,the liquid cone at the end of the welding wire is stable,the spatter rate decreases,the penetration of the weld increases and the weld formation improves.At the same current,the metal evaporation rate increases slightly compared with that without magnetic field.The excitation current is 9A,the voltage and current waveforms of different frequencies are relatively stable,the droplet transition is relatively stable,and the stability of welding process is well controlled.Under the condition of 1000Hz frequency,with the increase of magnetic field intensity,the overall trend of weld penetration increases,the change of weld width is not obvious,and the ratio of depth to width increases,which indicates that the stronger the magnetic field,the better the weld formation.When the excitation current is 5A and 9A,the weld width ratio increases with the increase of frequency,which is better than that without magnetic field,and the weld shape is improved.By applying the longitudinal alternating magnetic field and X-ray detection,the weld formed well and the weld width narrowed under MAG welding.According to the order of base metal,heat-affected zone and weld,the hardness curve of weld cross-section is symmetrical,and the overall trend of hardness curve is "cap eaves".The hardness at weld seam is higher,the hardness in HAZ is lower than that at weld seam.When excitation current is 9A,the hardness at 100Hz is higher than that at 500Hz,1000Hz and without magnetic field,which is related to the stirring degree of magnetic field to liquid metal crystallization.When alternating magnetic field is applied,the weld structure grows into columnar crystal with fine structure and good performance.Applying different parameters of magnetic field,the area of heat-affected zone decreases,the grain size is coarse,and the grain boundary is obvious.The application of longitudinal alternating magnetic field has a positive effect on the weld performance.The splashes and fume generated during the GMAW welding process were studied.When the form of the droplet transition is different,the main sources of splashing are different.The metal splash particles are scooped out and solidified rapidly,and the surface has a special morphology,and the sheet is irregular like a hexagon,and the composition is mainly oxide.When the particles are small,the specific surface area is large and easy to adhere;when the particle size of the splash is small,sedimentation is likely to occur.When the arc is burned,the end of the wire forms a spot with a high current density,and the temperature at the spot is high.As the welding current increases,the amount of metal evaporation increases,the metal vapor continuously generates,and the area where the metal evaporates is mainly concentrated at the tip of the wire,the surface of the bath and the arc column area.Metal evaporation removes most of the alloying elements such as Si and Mn in the wire,and both Si and Mn are effective deoxidizing elements.Therefore,metal evaporation removes the alloying elements and affects the O content in the weld,which in turn affects the weld performance.The particle size of GMAW welding fume mainly concentrates on 10μm～90μm.The composition is mainly Fe oxide and Mn oxide.The highest probability distribution of soot particles is 10μm～60μm particles.The particle size of soot particles is related to the droplet transfer mode.With the increase of current,the range of fume particle size is enlarged. |
