Study On Thermal Fluid Simulation And Experiment Of Arc Plasma In Electrical Discharge Machining

Electrical discharge machining(EDM)is one of the most widely used non-traditional machining methods at present,and it is based on the high temperature generated by the spark discharge between the two electrodes to remove the material.As the heat source of EDM,the arc plasma is the most direct factor affecting the machining.Therefore,this paper aims to study the characteristics of the arc plasma through simulation and observation experiment.Further,the formation process of the discharge crater was studied,and the influence of the characteristics of the arc plasma on the discharge crater was investigated.The arc plasma model was established by coupling the heat transfer field,the flow field and the electromagnetic field,and the distribution results of physical fields of the arc plasma were simulated.The results show that the temperature of the arc plasma reaches the highest in the center,and gradually decreases from the point to the periphery.The heat flux at the surface of the workpiece is highest at the center point of the discharge area and gradually decreases in the radial direction,and it is the same on the tool electrode.The pressure reaches the maximum at the central axis of the arc plasma,and gradually decreases in the radial direction,and does not change much along the axial direction.The dielectric near the surfaces of the electrodes flows toward the central axis of the arc plasma and the dielectric near the center of the gap flows away from the central axis,thereby forming two symmetrical vortices.The dielectric potential near the central axis of the arc plasma decreases rapidly near the surfaces of the electrodes and slowly near the center of the gap.In addition,the effects of discharge current,discharge gap,dielectric and external magnetic field on arc plasma characteristics were investigated.Among them,after applying the magnetic field,the heat flux and pressure of the arc plasma increase significantly.The discharge crater model was established with the heat flux and pressure simulation results of the above arc plasma model were used as inputs,and the formation process and final morphology of the discharge crater were simulated.The results show that the diameter and depth of the discharge crater increase rapidly at the beginning,and then the increase rate slows down,and the size remains substantially unchanged until the end of discharge,and there is the bulge around the crater.In addition,the effects of discharge current,discharge gap,pulse duration and external magnetic field on the morphology and size of discharge crater were investigated.Among them,after applying the magnetic field,the diameter of the discharge crater reduces obviously,the depth increases obviously,the removal amount of the single discharge increases,the volume and height of the bulge increase.This paper also observes the arc plasma during single pulse discharge using the high-speed video camera.The results show that the arc plasma completes expansion within a few microseconds after the beginning of discharge,and then the diameter of the arc plasma remains substantially unchanged.Then,the arc plasma moves in a similar circular motion between the electrodes constantly,and the amplitude of the motion gradually increases,and the direction of motion constantly changes.The arc plasma quickly disappears until the end of the discharge.In addition,the effects of discharge current,discharge gap,electrode material and external magnetic field on the diameter and motion of the arc plasma were investigated,which were in good agreement with the simulation results.It is also found that the electrode vapors mixed in the dielectric have a great influence on the arc plasma.Further,the discharge crater was observed,it is found that the motion of the arc plasma has a great influence on the morphology and size of the crater.After applying the magnetic field,the entire discharge area shows higher brightness,and as the diameter and the amplitude of motion of the arc plasma reduce,the diameter of the discharge crater reduces,the depth increases,and the removal amount of the single discharge increases.Therefore,the external magnetic field is an effective way to adjust the morphology of the discharge crater.