Experimental Study On Keyholing Plasma Arc Welding Assisted By Pulsed Power Ultrasonic Vibration

Enhancing the penetration capability of the plasma arc is of great significance for the welding and manufacturing of medium and thick plate structures.The research group invented the ultrasonic vibration assisted perforation plasma arc welding(U-PAW)process in the early stage,and achieved good process results.How to further improve the efficiency of sound energy utilization and the penetration capability of plasma arc is a problem worthy of further study.This paper proposes a new technology of pulsed power ultrasonic vibration assisted PAW(PU-PAW),which takes advantage of the high peak power output of the pulsed power supply to realize the effective use of ultrasonic energy and the effective improvement of the penetration capability.A laser vibrometer was built to measure the vibration information of the tungsten tip in both continuous and pulsed power modes,and the appropriate power ultrasonic frequency was selected.The plasma arc image acquisition system was used to shoot plasma arc images at different ultrasonic power frequencies.The distribution of arc pressure under different conditions was measured.The results show that,compared with continuous power ultrasonic vibration,after pulsed power ultrasonic vibration is applied,the plasma arc column area continues to shrink,the arc pressure is increased,and the peak pressure increases more significantly.DC plasma arc welding and open-loop controlled pulse keyholing welding experiments were carried out on stainless steel workpieces with thicknesses of 6 mm and 8 mm.Under the same process situation,the application of 5 Hz pulse ultrasonic vibration can achieve stable perforation in a shorter time,and obtain keyholes on the back with a larger exit area and a smaller backward offset;under the equal welding current,applying 5 Hz pulsed ultrasonic vibration still achieves complete keyholing with the improvement of weding speed,which improves the welding efficiency.Compared with continuous ultrasonic vibration,pulsed ultrasonic vibration is applied under the same welding parameters,open-loop controlled pulse keyholing PAW achieves perforation and maintains a stable pulse-per-hole mode.A pulsed ultrasonic vibration-assisted controlled pulse keyholing PAW welding test was carried out on a stainless steel workpiece with a thickness of 8 mm.It was found that after applying pulsed ultrasonic,compared with continuous ultrasonic vibration,the welding peak current decreased by 5.9%-8.3%,compared with the conventional controlled pulse keyholing PAW dropped by 12.15%-15.4%;when the welding velocity was rised by 10%-20%,the peak welding current was reduced by 13%.It shows that compared to applying continuous ultrasonic vibration,applying pulsed ultrasonic vibration improves the utilization efficiency of sound energy.It can use lower peak current and faster welding speed to achieve a pulse-per-hole welding mode.The above consequence proves that applying pulsed ultrasonic can improve the utilization of ultrasonic sound energy,further reduce welding heat input,improve welding efficiency,and broaden the application range of plasma arc welding.