Research On The Technology And Mechanism Of High Voltage Excitation Electro-arc Machining

With the development of science and technology,materials with excellent performance was used widely,which caused higher requirements on the processing technology.As for its advantages,include process complex cavities,no macroscopic force and negligible strength,hardness and toughness of processed materials,electrical discharge machining(EDM)has been widely used in the field of high-performance material processing.However,facing the rapid development of modern manufacturing,low processing efficiency has become a bottleneck in the development of traditional electrical processing technology.Electro-arc machining(EAM)was proposed to improve the low machining efficiency of traditional electrical machining,is a new type of electrical machining technology.This technology adopts high-energy electro-arc discharge to remove materials,which has the advantages of fast processing speed,high energy utilization,low electrode relative wear rate,and green discharge medium.It has attracted more and more attention in recent years.However,arc machining has low open circuit voltage,high peak current,and long pulse width,its breakdown gap is small,the flange of craters the erosion particles are large.Therefore,it is easy to cause the deterioration of the gap discharge state and affect the processing stability and processing quality.The high voltage excitation electro-arc machining(HVE-EAM)technology was proposed in this paper.It effectively increases the average discharge gap,disturbs the arc plasma and improves the gap discharge state by superimposing high-voltage pulses in processing process,thereby increasing the processing speed,reducing the relative wear rate of the electrode and the surface roughness is a highly advantageous new EDM technology.The mechanism of HVE-EAM was studied based on the formation,steady state and disturbance of arc plasma,and the morphology of the crater,the research on the machining mechanism of HVE-EAM was carried out.Using the arc theory of plasma physics and the arc plasma model in arc machining,the forming,expanding and maintaining a steady state process of arc plasma was analyzed,the particles interaction in arc plasma was explained,and the relationship between the arc column characteristic parameters and the arc column energy was established.Theoretical research results show that the power source determines the characteristics(arc pressure,are temperature,arc current,arc diameter,the maximum arc length,arc power,and polarity effect)of arc plasma,the arc plasma determines the crater geometry(crater diameter,crater depth,the ratio of depth to diameter,and removal volume),and the machining results(MRR,REWR,and Rz)are determined finally.Using the single-pulse power supply of arc discharge,the arc discharge in different environments was systematically studied,and the needle-surface single-pulse discharge experiments with peak current,pulse width and environmental pressure as factors was carried out.It shows that under low pressure environment,the arc can still erode the workpiece material,which is a big difference from traditional EDM;as the ambient pressure decreases,the arc discharge channel will further expand when the arc becomes stable.The smaller the ambient pressure,the larger the radius of the discharge channel,and the expansion of the discharge channel is almost the same regardless of the anode surface or the cathode surface.Based on this result,the arc plasma expansion model is improved.In addition,the analysis of the craters generated by a single pulse discharge indicates that a smaller ambient pressure will form a smaller melting zone diameter,crater diameter,crater depth,melting volume,removal volume and removal volume ratio and larger discoloration area;and the higher discharge current and longer pulse duration will form a larger discoloration area,melting area,crater diameter,crater depth,white layer thickness,melting volume and removal volume on the surface of the workpiece crater.This shows that the large peak current and the long pulse width will result in a great material removal rate for arc machiningCombining high-power DC power supply and a high-voltage high-frequency pulse power supply,a high-voltage excitation arc high-power combined power supply was proposed,it is suitable for HEV-EAM,and the spindle and working fluid circulation system were improved.Based on the theory of thermo-electronics,the influence of the material characteristics of electrode on the arc discharge in arc machining was analyzed It shows that the current density during arc machining is closely related to the electrode material and its temperature,and the temperature of the electrode material during machining mainly depends on the melting point of the material,the higher the melting point of the electrode material,the higher the temperature,the greater the current density allowed on the electrode due to thermal electron emission;and the experimental prototype was used to explore the effect of different tool materials on the results of EAM.The experiment results verified the thermal electron theory and confirmed the best electrode material.Based on the single pulse experiment results and arc plasma characteristics,the mechanism of superimposed high voltage pulses in EAM was analyzed:superimposed high voltage can increase the average discharge gap,enhance the effect of liquid flushing,promote the movement of the arc root on the electrode surface,and prevent the concentration of discharge.The gap discharge state is improved,and the arc plasma is elongated,which increases the energy of the arc discharge and enhances the polar effect in the energy distribution of the arc column,so that the anode gains energy,the cathode gains energy,and the anode crater becomes larger.The craters become smaller,increasing the MRR and reducing the REWR.The experiment of the high-voltage pulse electrical parameters was carried out,the theory of high-voltage action was verified,and the relationship between the high-voltage pulse electrical parameters and the processing result parameters was obtained.Based on the foundation of fluid dynamics,the fluid field theory of EAM is established.A three-dimensional model of fluid field is established and simulated according to the actual processing conditions.The improved gap fluid field of EAM is also based on the simulation results.Through simulation analysis and experimental comparison of different fluid fields,the rationality of fluid field improvement is verified,and the best fluid field structure suitable for EAM is obtained,which lays the foundation for further research on high-pressure excitation arc milling technology.Single factor experiments with the experimental parameters of peak current,tool rotation speed,flushing pressure,high-voltage pulse,and a comparative experiment was performed on the improvement of the fluid field.The results show that:the increase in peak current leads to an increase in MRR and surface roughness,The REWR of the electrode is reduced;when the electrode speed or flushing pressure is low,the arc discharge is concentrated,which reduces the MRR and increases the REWR;when the electrode speed or flushing pressure is high,the arc breaks frequently,resulting in the actual discharge time is shortened,the MRR will reduce,and the REWR will increase;superposition of an appropriate amplitude high voltage pulse can effectively improve the MRR,reduce the REWR and surface roughness;too high or too low high voltage pulse are not conducive to improving the processing effect;the improved fludi field is superior to the previous field in all aspects.A good flushing environment can eliminate metal particles in time to make the arc processing more stable,resulting in a better processing results;In addition,the improved flow field will also enhance the mechanical arc-breaking effect,transforming the DC arc discharge to a certain extent into a pulsed discharge,effectively improving the deionization process of the discharge,thereby making the processing more stable.