Research on ultrasonic characteristics during ultrasonic assisted MIG welding

Ultrasonic assisted metal inert gas welding (U-MIG), as a new welding method, introduces corresponding acoustic effects to weld pool applying added ultrasonic field. Systematic experiments researched the effect of ultrasound on arc shape, droplet transfer and joints macroscopic morphology is designed to better understand the characteristics of ultrasonic under different welding conditions. Arc images recorded by high-speed camera are processed and analyzed. It revealed that the compression effect of ultrasound on arc increases with the welding voltage increases. However, with the increase in the wire feed speed, welding current increases, the arc compression effect becomes smaller and smaller. The analysis of force mechanism of droplet transfer shows that an additional force is provided to promote droplet transfer under the action of the ultrasonic wave. When the welding current is 200 A, this additional force reaches its maximum, the value is about 2.8×10^-3 N. If the welding current is continuously increased, the additional force will be gradually decreased. Compared with macro-morphology of weld with different wire feed speeds, it reveals the variations welding current can not be infinitely increased, and there is an optimum parameter values. The acoustic field analysis is conducted based on plane standing theoretical. With increasing temperature, acoustic radiation force gradually decreases, which may counteract the effect of the additional force. The weld pool film model is applied to investigate the relationship between arc, droplet transfer and weld pool oscillation. The effects of ultrasound on arc and droplet transfer can change the oscillation characteristics of weld pool. It shows indirectly the changes of the macro-morphologies of weld joints. By experiments and theoretical analysis, this result has laid a solid foundation for the further development and application of U-MIG welding process.