Study Of Underwater Ultrasonic Frequency Pulsed Plasma Arc Cutting Method And Technology

The modern plasma arc cutting technology developing direction is towards to efficiency, high quality and low cost. With the advantages of high efficiency, low thermal distortion and low noise, little dust and low arc radiation, underwater plasma arc cutting technology has been widely used in industry. However, there're some disadvantages in underwater plasma arc cutting. Firstly, a dc power supply is generally employed by underwater plasma arc cutting which leads to undesirable cut shape because of the limitation of insufficient compression degree and inclined axial direction. Secondly, quality problems such as wide bevel angle, tough dross clear and higher hardness occur since the cutting process is proceeding under the water.This paper constructed an underwater system based on the principle of dry ultrasonic frequency pulsed plasma arc cutting. Therefore, the ultrasonic frequency pulsed modulation of the arc was realized by paralleling an ultrasonic frequency pulse generator with an ordinary cutting power supply. To analyze the effects of water and ultrasonic frequency pulse, air and oxygen plasma arc cutting experiments were carried out in the the dry and wet circumstances respectively. The dc cutting and the ultrasonic frequency pulsed experiments were also conducted in every case. In the course of the experiments, cut formation was compared, including top and bottom kerf widths, left and right bevel angles, left and right straightnesses, and dross attached level. Then cut hardness was measured and the microstructure of cutting heat affected zone was observed. Finally, the relationship between microstructure variation and hardness was discussed.Experimental results show that, with the effect of ultrasonic frequency pulsation, plasma arc cut formation improves obvisouly. Take underwater oxygen plasma arc cutting for example, the maximum improvement percentages of bottom kerf width, right bevel angle, right straightness are up to 27.8%, 84.8% and 65% respectively at the speed of 60cm/min. At the same time, dross volume decreases and dross state changes of underwater air plasma arc cutting. However, amplitude of ultrasonic pulse has little effect on dross attached level. In addition, cut hardness decreases, heat affected zone width reduces and the size of grain gets smaller during underwater cutting.