Study On The Influence Mechanism Of Pulsed Plasma Gas On VPPA

Variable polarity plasma arc welding(VPPAW)has the advantages of energy concentration and so on.It is widely used in aerospace and other fields because of its high efficiency welding and cathode cleaning in aluminum alloy welding.However,due to the coupling of many process parameters,the fault tolerance margin of this method is small,which leads to the poor arc stability in the welding process.Therefore,it is still necessary to use other auxiliary methods to improve the stability of the arc and the weld pool to maintain the weld formation.All kinds of welding gases are essential materials in gas shielded welding.The auxiliary GTAW / GMAW welding method which controls the welding gas flow has been proved to have good process effect.As a special welding gas of VPPAW,is it feasible to apply plasma gas flow control in VPPAW process to improve the above problems of VPPAW? It is center part of this paper.The experimental system of PPG-VPPAW is designed and built,which includes welding system,data acquisition system and pulsed plasma gas control system.Combined with the characteristics of VPPAW,the independent control of plasma gas flow and the coupling control of plasma gas variable polarity current are realized.Based on the research of pulsed plasma gas direct current plasma arc welding(PPG-PAW),the mechanism and welding process characteristics of pulsed plasma gas on variable polarity plasma arc are further studied.The physical characteristics and weld quality of PPG-PAW were studied.The experimental results show that the arc voltage,arc force and macro shape all show the same frequency oscillation with the pulse plasma gas.Compared with the conventional PAW,the pulsed plasma gas does not affect the overall thermal output of the arc and the arc force oscillates.Therefore,the thermal force decoupling control of the plasma arc is realized to a certain extent.Under the same welding conditions,PPG-PAW is more constrained when the plasma gas is turned off,and the welding seam is narrower when the fixed-point burning is performed.The influence of the turn-off and turn-on of the pulsed plasma gas on the arc force output characteristics and the change of the arc shape is studied.Based on this,the control method of pulsed plasma gas to plasma arc is established.By coupling the plasma gas and the variable polarity current,it is found that PPG-VPPAW overlaps the periodic oscillation caused by the pulse plasma gas on the basis of the original variable polarity.In addition to the characteristics of PPG-PAW,different ion gas cut-off points can regulate the heat distribution of VPPAW positive and reverse polarity arc.Compared with conventional PAW,PPG-VPPAW is more restrained in negative phase and more divergent in positive phase.The results of the experiment on 5A06 aluminum alloy without filling wire and piercing welding show that the welding process of PPG-VPPAW is more stable,the weld joint has formed a uniform fish scale on the front,the periodic oscillation of arc force improves the fluidity of the weld pool better,and the corresponding weld width and porosity are further reduced.