MAGNETIC CONTROL OF ARC PLASMA AND ITS MODELLING

This paper describes the control of arc plasma by a cusp-type magnetic field. The cusp-type magnetic field, which is produced by four magnetic poles, changes the cross-section of arc plasma from the conventional circular shape to an elliptical shape. Previous studies using solenoid coils to produce a cusp-type magnetic field reported that magnetized arc plasma provides deeper penetration. However, the solenoid device developed for the cusp-type magnetic field was too large, in comparison with the size of the welding torch used for production welding. In the present study, magnetized arc plasma with the use of high-performance permanent magnets is experimentally and theoretically investigated. It is confirmed experimentally by tungsten inert gas (TIG) arc welding that permanent magnets can produce arc plasma with an elliptical cross-section. In a series of experiments, a good bead appearance was obtained in high-speed welding with magnetic control. A three-dimensional numerical model of arc plasma was also constructed to determine the optimum arrangement of the magnets. It was analytically shown that the elliptical shape of the magnetized arc plasma and its effect on welding depended on the magnet height from the base metal and the magnetization direction.