Torch Design And Droplet Transfer In Ultrasonic-MIG Hybrid Welding

The MIG welding is a traditional and efficient welding method. The wire melting speed is very high because of the high current density of the wire and arc, thus the deposition efficiency is high and penetration and welding distortion is better. The ultrasonic vibration in the welding process expanded the range of welding condition, promoted the free transfer of drop and improved the frequency of dip transfer. The ultrasonic characterizations such as acoustic radiation force and the acoustic streaming effects changed the arc shape and the drop transfer form.First, the ultrasonic-MIG welding system was designed. It included the structural design of transducer and amplitude transformer. The transducer and amplitude transformer were regarded as one dimensional vertical vibration cross-section bar. The theoretical dimensions were calculated, and then optimized by ANSYS finite element analysis. Finally, the dimensions of amplitude: the frontendplate was 73mm; the back cover plate was 18mm; the diameter of mesopore was 6mm; the length of amplitude transformer was 125mm; the diameter of mesopore was 6mm. the error of simulation frequency was only 0.35%. The dimensions satisfied for the design requirement. The design of welding torch was completed. The circuit and water cooling system were designed on the basis of no affect on ultrasonic vibration. The double shielding gas form was adopted.The dripping test was conducted under static conditions to study the regularities of acoustic radiation force distribution in ultrasonic field. The results showed that: the direction of acoustic radiation force was alternative; the direction was opposite in adjacent 1/4 wavelength. The effect of acoustic radiation force was obvious in standing-wave field. The influence of the height of radiation side and nozzle to ultrasonic-MIG was studied, and the optimized heights: the height of radiation side was 30mm; the height of nozzle was 11mm.The comparison experiments of normal MIG and ultrasonic-MIG under different welding parameters were conducted. The characteristics of different droplet transfer in ultrasonic-MIG were studied. In dip transfer, the arc shrinking was obvious; the range of cathode cleaning was narrowed; the dip transfer frequency was improved; the drop transfer was homogeneous; the peak current was decreased 70A equally in short circuit. In globular transfer interval of high voltage, the length of arc was shorted; the droplet transfer frequency was increased; the spreadability of welding bead was better. In spray transfer, the current was decreased by about 20A; the radius of arc center was decreased; the stiffness was improved; the wandering of arc caused by cathode cleaning was weakened; the spreadability of welding bead was better; the weld reinforcement was decreased. At last, the preliminary study to the reason for arc shrinking was made in ultrasonic-MIG from the aspects of arc energy balance and the force balance for plasma. The mechanism of acoustic flow effect and arc plasma action in ultrasonic was put forward. The physical nature of the arc shape change in ultrasonic was explained based on principle of minimum voltage.