Effect of Pulsed Ultrasound on Plasma Morphology and Its Changing Mechanism

Arc plasma shape under pulsed and continuous ultrasound field were studied in this research using 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 ultrasound field relate to the pulse frequency. From 1 Hz 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 become steady and similar to those in continuous ultrasound field. When in 500 Hz, the contraction ratio of arc projected area under pulsed ultrasound field reaches 38 %, comparing with 30 % of the same power continuous ultrasound field, i.e., in high frequency, low power pulsed ultrasound can obtain arc control effect similar to high power continuous ultrasound, raising ultrasound energy efficiency. The mechanism of ultrasonic influence on arc is analyzed based on sound pressure and acoustic streaming.