Theory Of The Detection Of Plasma Cloud And Fuzzy Control In Plasma Arc Welding

Nowadays, the stability of arc and welding quality plays a crucial role on the plasma arc welding from the research of the controls of welding process in the world. And it is uneasy to maintain the process of stable welding and to gain a good quality of welding line.The control of welding process and quality is an important problem in the keyhole plasma arc welding. Therefore, controls of the keyhole are an urgent task by means of detecting the state of the keyhole. It is a short cut to improve the welding quality in the plasma arc welding. So people are focused on detecting the size of the keyhole. On the basis ofinterplay between the plasma arc and penetration, the paper analyzes the formation of the plasma cloud in plasma arc welding. The state of plasma cloud is changed when the shape of the pool is changed. The relation between plasma cloud and the shape of pool is pointed out. If work piece is not yet penetrated, the plasma cloud must be existed above the work piece on theoppose direction of welding velocity; On the other hand, if work piece is penetrated, the plasma cloud can.t be existed while plasma efflux must be existed.With the help of the phenomenon, if plasma cloud can be detected, work piece is penetrated, or the work piece is not penetrated. The paper analyzes that the welding time, welding current and welding velocity have an influence on the penetration.From views of plasma arc velocity and plasma arc force, plasma cloud is ejected from the maximal tangent angle of molten pool in the oppose direction of welding velocity when work piece is unpenetrated. The formation of the pool and penetration can determine the angle of plasma cloud ejection.Therelations between the welding current and angle of ejection plasma cloud are fit out by least double multiplication. If the probe is located in the plasma, there is a negative electromotive force in the probe. The paperfirst introduces the model of plasma sheath to explain the mechanism of phenomenon. It offers the formula to compute plasma cloud voltage. The value has only something to do with temperature and plasma component. It is up to the level of voltage and easy to be detected. On the above basis, a device of detecting plasma cloud without power is designed. It is simple and reliable, and has a good future of application in industry. The angle of plasma cloud can reflect the penetration. The location tungsten probe, welding velocity and welding current can change the angle of plasma cloud. The paper studies the rule of melting probe in high temperature plasma cloud. The II Abstract result indicates that the device without power can detect the high temperature plasma if the location of probe is sound. The experiment proves the theory of the sheath. The welding current, welding velocity, and the location of probe can change sheath voltage on the experiment. According to the formula between welding current and the angle of plasma cloud ejection, the theory of fuzzy control is introduced to plasma welding. Detection of...