Bubble evolution in ultrasonic wave-assisted underwater wet FCAW

Ultrasonic wave-assisted underwater wet welding (U- UWW) is a newly developed welding method. The principle of this method is to apply the acoustic radiation force to the arc bubble as an extra retaining force. The dynamic feature of the bubble under an acoustic field was demonstrated and analyzed by visual sensing and welding electrical signals. Comparative experiments indicated that, under the same conditions, the additional ultrasonic wave caused the bubble's motion with a certain angle with respect to the welding torch axis so the welding process was not easily affected by the rising of lateral bubbles. Meanwhile, there was always a relatively large bubble maintained in the weld pool surface. The oscillation of the bubble with small amplitude was observed and no necking was present at the bubble bottom. The measurement results revealed that the ex- ertion of ultrasonic wave resulted in a reduced fluctuation of welding electrical signals and an improvement in the arc burning process. For the variation coefficient, the difference between underwater wet welding and U-UWW became sig- nificant with varying experimental groups, the maximum difference of which occurred at Group 4.