The Application Of High-frequency Magnetic Field In High-Speed TIG Welded Pipe

Tungsten Inert Gas Arc Welding (TIG for short) is a method that uses pure tungstenor active tungsten such as thorium-tungsten and cerium-tungsten as the non-consumableelectrode, uses inert gas such as argon or helium as the shielding gas. It is very popular inmodern industry. It has many advantages of high quality in welding joint and fitting foralmost all metal materials joining, especially in sheet steels or thin-walled tubes.Nevertheless, the TIG welding has a smaller weld penetration and a lower productivity. Alot of effective methods such as active TIG (A-TIG), ultrasonic TIG (U-TIG), heatedwire TIG and high-speed TIG are adopted to increase the welding productivity.High-speed TIG welding is the way to improve efficiency by enhancing the weldingspeed which is usually above1m/min. Welding stainless steel tube with a wall thicknessof2mm, with the improvement of the welding speed, there will be a transparentcondition in the tube is incomplete penetration, and simultaneously weld is notcontinuous and undercuts tendency, thus limiting the improvement of the welding speed,impacting the welding efficiency. The topic for this problem expand research, dedicatingto the TIG welding arc energy density, thus increasing the weld penetration, increasingthe angle of the weld melt, reducing the weld undercut tendency to increase the weldingspeed, improving production efficiency.A large number of references at home and abroad were searched. The way ofmagnetic fields added in TIG arc welding were put forward. The arc characteristics andlaws of the influence of magnetic fields on welding formation were investigated deeply.The TIG arc theory under the external magnetic fields was enriched and an effective wayof extending the range of TIG welding application was developed.Electromagnetic field equipment with a wide range of adjustable parameters for TIGwelding was developed. The technical parameters are as below:Input voltage of power source:220V/50Hz, no-load voltage:60V(DC), directcurrent range:0~200A, load duration rate:100%, frequency scope:0~20KHz, duty cycle: 10~70%. The equipment has functions of outputting direct current and intermittentalternative square waveform. Magnetic heads matching with TIG welding gun weredesigned.Shot the shape of the magnetic field within the range of0-100Hz TIG arc with ahigh-speed camera system, and analysis the arc movement mechanism. The arc heatdistribution of the arc not in the magnetic field and the applied high-frequency magneticfield with testing device of arc heat distribution is measured. The arc heat distributionplus high frequency magnetic field is more concentrated. Applying a high frequencymagnetic field can also increase the pneumatic pressure of the arc column center peak.Welding current is60A, the magnetic field frequency is350Hz, the magnetic fieldstrength is30mT, protecting gas flow is10L/min. Arc pneumatic pressure is bimodaldistribution, when in the470Hz, doublet disappeared, the pneumatic pressure distributionbecomes Gaussian distribution, and continues to rise as the frequency peak, pneumaticpressure increases to about3000Hz, the pneumatic pressure peaks beyond the pneumaticpressure is not applied magnetic field arc. When the arc current density is appliedmagnetic field in the frequency6KHz, it significantly increases.The magnetic arc compression effect Plus high frequency transverse magnetic fieldis confirmed, and this magnetic compression can effectively increase welding speed andimprove the high-speed TIG welding incomplete penetration undercut tendency, andweld discontinuities. When welding current is90A, protecting gas flow is10L/min,high-frequency magnetic field strength is30mT, the frequency is6KHz, welding speed is4.5m/min, welding formation is very good.