The Study Of The Process And Stability In Aluminum Alloy Variable Polarity Plasma Arc Welding

Compared with other fusion weldings, VPPAW(Variable Polarity Plasma Arc Welding)is characterized by concentrated energy density, high arc stiffness, big single weld penetration depth as well as little postwelding deformation etc, which can realize the double-side molding with welding by one side in the event of square groove. VPPAW is a extensive application prospects welding process which has beening applied in the welding productions of outside storage of aerospace craft.The equipment used in this paper consists of Variable Polarity Plasma arc welding power source, variable polarity plasma arc welding torch, wire feed system, cooling system, semi-automatic trolley, arc force sensor, as well as hannover welding quality analyzer etc. By the double-inversion technology, the major welding power source can export constant external characteristics. Within it, first inverter control circuit control IGBT driving circuit of power source with combined controlling means through PWM and PFM; the second inverter control core is microcontroller 80C196KC which can output variable polarity plasma arc current. The parameters like current amplitude of positive and reverse polarity as well as time ratio of positive and reverse polarity can be justified regulated independently.In this paper 3 mm thickness and 5 mm thickness aluminum alloy plate are tested by plat welding. Influence which have been exerted on weld forming by the parameters: welding current, plasma Gas flow rate, frequency of variable polarity have been analyzed, the most important factor that affect the weld forming in aluminum alloy variable polarity plasma arc welding process is welding current. To a great extent, the parameters: plasma gas ratio, variable polarity frequency and time, wire feed speed, nozzle aperture as well as welding velocity can affect the stability of molten pool and welding seam molding. In this paper, on the promise of obtaining the high quality of weld shaping is to establish stability welding pool. Reasonable process parameters and controlling means were adopted. By a large plenty of experiments for 3 mm thickness and 5 mm thickness aluminum plates the optimal technology parameters were acquired.The strained condition of welding puddle in level of variable polarity plasma arc welding in this paper was analyzed. In the process of welding arc force is much larger than in vertical welding, in addition to the coaction with gravity of liquid molten pool, so the surface tension of liquid metal can hardly bear the resultant forces of the two and keep the balance of force on the surface of welding poll, also the welding beam is apt to collapse. Therefore, the study of the stability in level of VPPAW is particularly significant. The premise of stability in aluminum alloy VPPAW is to keep the balance of the heat and force, while the arc force is the most vital factor with respect to the balance of the heat and force on molten. Influence that welding parameter, wire feed equipment, welding source have exerted on stability in aluminum alloy VPPAW was analyzed, and the quality of the proposed use of Hannover, Germany, the welding process in real time detection and analysis, to some extent the stability of the welding process can be assessed.Mechanical properties of welding joint was measured and microscopic structure of welding bead was observed. Overall appraisal was made to the quality of the aluminum alloy VPPA welding joint. With the analysis the conclusion can be drawn that: mechanical properties of aluminum alloy VPPA welding joint is good and is the same as the mother-plate, the microscopic structure of the welding bead is compact and without other defects like gas pockets.