Research On The Mechanism And Process Of Short Electric Arc High-efficiency Milling

With the rapid development of the manufacturing industry,facing the urgent demand for large amount removal of difficult-to-machine materials such as nickel-based high-temperature alloys,the low machining efficiency of traditional electrical discharge machining(EDM)has become the main bottleneck restricting the further development of EDM technology.Short electric arc machining is a novel EDM method with high energy arc discharge as the energy carrier,which not only inherits the advantages of traditional EDM without the limitation of material hardness,strength,and toughness,but also can realize the rapid removal of large amount of material residue,and has become an important technical means for the efficient machining of difficult-to-machine materials.In this paper,aiming at the insufficient research on the mechanism of gas-liquid mixed media breakdown process,discharge channel characteristics,and energy distribution law in short electric arc high-efficiency milling,as well as the problems of large electrode loss and poor surface quality of the machined workpiece during the processing,the machining mechanism and process are systematically and deeply studied,which laid the theoretical and experimental foundation for promoting the further application of short electric arc high-efficiency milling technology.The formation of plasma discharge channel by breakdown medium is a prerequisite for discharge machining.In this paper,the dielectric breakdown mechanism and discharge characteristics in short arc high-efficiency milling of gas-liquid mixed two-phase flow medium are investigated.Based on the breakdown theory of gas medium and liquid medium,starting from the mechanism of discrete phase action in two-phase flow medium,the potential in two-phase flow medium is solved by Laplace’s equation with Gauss’ s law,the expression of the electric field strength of two-phase flow medium is established,the breakdown mechanism of two-phase flow medium is analyzed,and the theoretical analysis results are verified by machining experiments in different mediums.By collecting the voltage-current waveforms during the discharge process,the discharge characteristics of single pulse and continuous pulse are analyzed,and it is found that the discharge processing can also be realized in the super low voltage state,and the whole continuous-pulse discharge process is a coexisting process of open circuit,spark discharge,arc discharge,and instantaneous short circuit.To clarify the coupling mechanism and distribution pattern among the multiphysics in the discharge process and their effects on material erosion,this paper investigates the physical field distribution characteristics of the discharge channel and the material erosion process in short electric arc high-efficiency milling.Based on the magnetohydrodynamic theory,coupling the temperature,flow,electric,and magnetic fields and considering the heat transfer effect between the arc plasma and the electrode and the workpiece,the electrode-arc plasma-workpiece coupling model of short electric arc high-efficiency milling is established,and the temperature,velocity,pressure,electric field strength,and magnetic field strength distribution laws of the discharge channel during the discharge process are obtained.By further analyzing the temperature field of the coupled model,the erosion law of the material at both electrodes during the discharge process is obtained,and the heat source distribution characteristics of the short electric arc high-efficiency milling are determined.The simulation results are confirmed through experiments,confirming the reliability of the proposed model.The discharge channel size and energy distribution ratio are closely related to the discharge conditions,which directly affect the machining effect of the parts.This paper investigates the discharge channel expansion characteristics and energy distribution law of short electric arc high-efficiency milling based on single-pulse discharge.Single-pulse discharge experiments have been designed and carried out to investigate the effect of electrical parameters on crater morphology and to reveal the material etching characteristics of short electric arc high-efficiency milling.A single-pulse discharge temperature field model is established,and by comparing the actual crater radius and depth between simulation and experiment,a method for solving the discharge channel radius and energy distribution ratio is proposed,and the laws of voltage,pulse width,and current on the anode and cathode discharge channel radius and energy distribution ratio are obtained,and the relevant regression models are built.Compared with the corresponding model for low-energy conventional EDM,the proposed model not only considers the effects of pulse width and current,but also considers the effects of voltage for the characteristics of short electric arc discharge,which can realize the accurate prediction of the radius of high energy short electric arc discharge channel and energy distribution ratio.To solve the problem of poor machining accuracy of parts caused by large electrode loss,this paper investigates the electrode loss characteristics and its compensation strategy for short electric arc high-efficiency milling.The reasons for the change in electrode shape during electrode loss are analyzed via combination of experimental results and a gap electric field model.Through comparison experiments,the effects of different flushing methods and electrode rotation directions on the machining effect are studied,and the optimal flushing method and electrode rotation direction are determined.With the relative loss of electrode and machining efficiency as process indexes,the influence of voltage,duty cycle,frequency,and flushing pressure on process indexes under different polarities is studied through single-factor and orthogonal experiments,and the primary and secondary relationships of the effects of each factor on process indexes and the optimal parameter combinations for each process index are acquired,and the process models of electrode loss and machining efficiency under different polarities are established,and the reliability of the optimal parameter combinations and process models are verified through experiments.The reliability of the optimal combination of parameters and process model is verified through experiments.Based on this,further based on the fixed-length compensation method,the mathematical model of electrode loss compensation for single-groove milling and plane milling is established through the electrode equal loss theory and the geometric relationship between the electrode bottom profile and the workpiece,and the accuracy of the proposed compensation model is confirmed by the compensation experiment.To enhance the surface quality of the finished parts while taking into the purpose of high-efficiency and low-cost machining,this paper investigates the short electric arc high-efficiency milling process.The effects of machining parameters on surface quality are investigated through process experiments,and the microscopic characteristics of the machined surface of nickel-based high temperature alloys are analyzed.On the foundation of the above research,the most significant factors affecting the machining efficiency and surface quality as well as the respective advantages of the two polarities are combined to propose a combined high-voltage positive polarity and ultra-low-voltage negative polarity machining process,and sample machining verification experiments and comparative experiments with EDM machining effects are conducted to confirm that the process can provide a practical method for high-efficiency,low-cost,and high-quality machining of parts.