Research on New Heat Source Model of Variable Polarity Plasma Arc and Welding Forming in Horizontal Position

Abstract

Abstract：In view of the horizontal plasma welding of thick aluminum alloy, the thermal-mechanical characteristics and weld forming process of new type variable polarity plasma arc (VPPA) welding are studied. New kinds of VPPA nozzle were designed to control the arc thermal force characteristics and to improve the stability of horizontal welding. Arc shape, arc force and anodic current density of three kinds of nozzles are compared. It is concluded that the thermal force characteristics of the new type arc have obvious advantages in the horizontal welding forming stability. According to the stability of instantaneous arc pressure waveform and the stability of perforation, it is also found that the arc pressure and the perforation area of the new plasma arc are smaller than those of the normal plasma welding arc, and the shape of the back perforation under the action of the new kind arc is circular and symmetrical. By analyzing the macroscopic contours of perforated welding pool, the direct influence of new arc thermal-force characteristics on the behavior of molten pool is obtained. High-speed photography is used to capture the formation process of the horizontal weld pool, and the results indicated that the higher arc energy and lower arc pressure are more favorable for the formation and stabilization of the molten pool. By observing the flow process and analyzing the force balance of the horizontal molten pool, it is found that the new arc thermo-force character make it easy to balance the molten metal in the flow process. Under the action of the new type plasma arc, it is easy to realize the stable horizontal welding of 8mm aluminum alloy.