Numerical Simulation Of Transient Behavior Of PPCA-TIG AC Arc Plasma

AC TIG welding is a common method used to weld aluminum alloys,but due to the limited current-carrying capacity of tungsten electrodes and the dispersion of argon arcs,the welding penetration is shallow and the production efficiency is low.Powder Pool Coupled Activating TIG welding(PPCA-TIG welding,Powder Pool Coupled Activating TIG welding)introduces the activating flux into the arc and the molten pool system through the outer gas.The sequential action of the activating flux on the welding arc and the molten pool makes the penetration depth significantly increase,which can greatly improve production efficiency.In this paper,through establishing a two-dimensional arc plasma transient model based on actual welding conditions,the periodic change process of the plasma characteristics of the AC PPCA-TIG arc and the influence of the main process parameters on it are studied with numerical simulation methods.It lays the foundation for understanding the transition behavior of the active flux in the AC PPCA-TIG welding arc and molten pool system and its influence mechanism on the weld formation in the future.This will be of great significance to promote the research and application of AC PPCA-TIG welding of aluminum alloys.First,a two-dimensional transient arc model of AC TIG welding is established and simulated research was carried out to obtain the arc characteristic distribution of arc temperature field,electric potential field,velocity field,pressure field and current density.Secondly,a transient arc model of AC PPCA-TIG welding is established for simulation research.In this model,the transition of active flux particles is not considered,that is,both the inner nozzle and the outer nozzle output inert gas,and the arc characteristic distributions are obtained.The results show that,compared with AC TIG welding,AC PPCA-TIG welding has a stronger cooling effect on the arc,the arc shrinks,the arc voltage increases,the current density increases,the temperature in the center area of the arc increases,the speed increases,and the arc pressure increases.The arc temperature field distribution of AC PPCA-TIG welding changes periodically with time.The larger the current,the larger the arc shape and the higher the arc temperature.Compared with the results obtained by using the high-speed camera system,the simulation results are in good agreement with the test results.The maximum temperature and arc voltage of the AC PPCA-TIG welding arc change periodically with time.When the welding current increases,the maximum temperature of the arc increases.However,compared with the change of welding current,the change of the maximum temperature of the welding arc is delayed.The maximum temperature of the arc decreases to the lowest after a little time after the current crosses zero.The higher the arc temperature before the current crosses the zero,the more obvious the delay effect.Then,the influence of main process parameters on the transient arc plasma characteristics of PPCA-TIG welding is studied.The process parameters of welding current,outer gas flow,arc length and coupling degree are adjusted,and their influence on the characteristics of transient arc plasma is analyzed.The results show that increasing the welding current will expand the arc's high temperature range in the EN section,EP section,the zero-crossing section of the rising edge and the zero-crossing section of the falling edge.The arc axis temperature increases as a whole,and the sheet surface pressure increases.The maximum temperature of the arc changes periodically with time,and the larger the welding current,the higher the maximum temperature of the arc at the same time.The change of the outer gas flow rate will only affect the arc periphery.The outer gas flow rate increases,and the outer area of the arc root shrinks slightly,and there is no effect on the temperature field distribution in the central area of the arc.The temperature distribution of the arc axis and the change of the maximum arc temperature with time under different outer gas flow rates are basically the same.The increase in the arc length of the welding arc will move the high temperature area of the arc upward,and the high temperature area of the lower part of the arc will shrink to a certain extent,but the overall volume of the arc increases,and the action area under the arc is larger.As the arc length increases,the temperature on the side near the electrode rises slightly,while the temperature on the side near the plate decreases.The maximum arc temperature changes with time in the same law,but the longer the arc length,the higher the maximum arc temperature at the same time.The change of coupling degree does not have a significant effect on the distribution of arc temperature field.