Variable Polarity Plasma Arc Flat Position Welding Process Of Thin Plate Aluminum Alloy

Compared with other fusion welding, VPPA (Variable Polarity Plasma Arc) welding process has many advantages, such as concentrated energy, higher arc stiffness, more penetration as well as smaller deformation etc, which can realize the two-sided appearance welding by one side without groove. VPPA welding has succeeded applies the welding productions of outside storage of aerospace craft which has the widespread application prospect.In this paper, the welding source system comprises a Variable Polarity Plasma arc welding power source, wire feeder, semiautomatic welding tractor as well as hannover welding quality analyzer and so on in experimentation. The welding power source use double inverter technical, output constant-current. The first inverter control circuit through PWM and PFM in company with to control IGBT driving circuit of power source. The second inverter control core is microcontroller 80C196KC which output Variable Polarity current. The microcontroller 80C196KC procedure can independently adjust the positive and negative polarity electric current peak-to-peak value and the positive and negative polarity electric current time ratio separately.In this paper, the aluminum alloy thin steel plate was welding used by variable polarity plasma arc flat position welding technology. The influence which the welding parameters such as welding current, flux of plasma gas and wire feed rate etc to appearance of weld are analyzed. The welding current is Key aspect of the appearance of weld in aluminum alloy thin steel plate VPPA welding. The plasma arc force and arc voltage has the relationship with flux of plasma gas. The other welding parameters such as Wire feed rate, tungsten Contraction quantity, nozzle inside diameter welding speed etc have the material effect to the stability of weld pool and the appearance of weld. In these parameters any parameter's change can influence forces and thermal balanced in the weld pool. The stability of the keyhole weld pool is based on the balance between forces and thermal. Adopts the reasonable welding process parameter and the regulatory measures is the important premise of establishing stable weld pool and Realizing the good appearance of weld. The aluminum alloy VPPA welding process character under different currents is also preceded. Through a mass of experiments, we obtained the optimum welding parameters of 3mm thickness aluminum alloy. the experimental optimum parameter is: positive polarity current84A,negative polarity current110A ,wire feed rate176cm/min, welding speed 35cm/min, tungsten Contraction quantity 2mm.The mechanics performances of plasma arc and thin plate aluminum alloy variable polarity plasma arc stability of the appearance of weld are analyzed in this paper. The relationship between the welding current and the flux of plasma gas can be get and provided a guideline for choose of the welding parameters when using VPPAW. It is found that with the electric current increases, the multiple of plasma arc center intensity of pressure increases is smaller than the electric current multiple's square slightly, and the flux of plasma gas in proportion to the plasma arc pressure basically. The German hannover welding quality analyzer has used to real-time record welding parameters which comprise weld current, the voltage and arc short circuit transition time etc. Positive and negative polarity current and the voltage change rule are analyzed in VPPAW process.Aluminum alloy welded joint mechanical properties and microstructure properties are tested, has carried on the synthesis evaluation to the aluminum alloy VPPA weld joint. It is found that the tensile strength of aluminum alloy VPPAW is equate in the base metal . The microstructure of welded joint is compact. It is have not welded defects such as pore and inclusion etc in weld.