Effect of pulsed powder ultrasound on plasma morphology and its changing mechanism

Arc plasma shape under pulsed and continuous ultrasound field was studied in this research using a self-developed welding device which combines arc and ultrasound field coaxially. The results show that, compared with the arc of conventional tungsten inert gas welding, the shape of arc under pulsed power ultrasound field relates to the pulse frequency. From 1 to 20 Hz, the arc plasma expands and contracts periodically in one pulse. When more than 20 Hz, the arc plasma contracts as the pulse frequency increases. During high-pulse frequency, the arc shape becomes steady and similar to those in the continuous ultrasound field. When at 500 Hz, the contraction ratio of arc projected area under pulsed power ultrasound field reaches 38 %, compared with 30 % of the same power continuous ultrasound field; i.e., in high-frequency, low-power pulsed power ultrasound can obtain arc control effect similar to high power continuous ultrasound, raising usage efficiency of ultrasound energy. The mechanism of ultrasonic influence on arc is analyzed based on sound pressure and acoustic streaming.