Study On The Arc Behavior Of Variable Polarity TIG Welding

There are more and more studying on variable polarity welding of Al, one of kinds of the widely used metals, however, these studies are mainly focused on variable polarity power source in our country instead of the welding process of variable polarity welding.This dissertation present a study about the arc behavior of VPTIG welding, with the help of data collecting unit with which current and voltage data are collected, and high-speed camera with which welding arc images are captured. not only arc's images but also that of weld pool'After studying the arc behavior when Al is welded by sine wave power, this dissertation finds that in low current range, there is a longer period of zero current at the time of changing polarity. The higher the current is ,the shorter this period is.The study of VPTIG welding consists of three parts. The first is, when Al is welded by normal VPTIG, the changes in current, voltage and arc shape. It has been discovered that there is a peek current after passing zero, the larger the frequency is, the smaller the peek is.The second is, when steel is welded by means of VPTIG of argon, the changes in current, voltage and arc shape. It has been found that current passes zero extremely fast, welding arc does not extinguish.The third is, when Al is welded by means of VPTIG method of helium, the changes in current, voltage and arc shape. It has been discovered that arc shape of helium is different from that of argon. arc color in center area is blue or purple, and arc color far from center area is green in DCEN period, arc color is orange in DCEP period. According to these studies, this paper gives a model to judge arc stability,and proves that it matches real situations. Arc stability has relationship with frequency, peek of arc voltage, peek of current, speed of current passing zero, shielding gas.