Parameters Optimization And Control For Multicomponent Material Micro-arc Plasma Discharge Polishing

Multicomponent materials are widely used in the production of important industrial parts due to their good physical,chemical and mechanical properties such as aero engine impellers,high-temperature alloys and 3D printed titanium alloy parts.In the manufacturing,the surface smoothness of these multi-component materials is extremely high(Ra/Sa<0.01?m).Therefore,the surface smoothness of multicomponent materials has become the focus of research in recent years.In micro-arc plasma discharge polishing process,liquid-solid channels between the workpiece and the electrolyte are formed,by plasma discharging in the channels realizes the polishing of multi-component materials.Since the electrolyte is a neutral or weak acid weak alkaline salt solution with a lower concentration and can be recycled by supplementing electrolyte,the micro-arc plasma discharge polishing is a special environmentally friendly processing method for polishing workpieces with high quality and high efficiency.This processing method can not only solve the problems of low mechanical polishing efficiency and the inability of polishing workpieces with complex surface shapes,but also solve the inevitable pollution problem of electrolytic polishing.What's more,micro-arc plasma discharge polishing leads to higher polishing efficiency and surface quality than that of common electrolytic polishing,which has broad application prospects.In this paper,the mechanism of micro-arc plasma discharge polishing is analyzed from different perspectives,explains the establishment of the plasma discharge channel,breakdown and workpiece removal process are explained from a macro perspective;the movement process and reaction state of the internal electron,ion and plasma are explained from a micro streamer discharge principle;the mechanism of material removal and micro-planarization is analyzed from the perspective of micro-arc plasma discharge.Designed experiments according to the influencing factors including solution concentration,power supply parameters and processing time of micro-arc plasma discharge,and built a test platform.In the experiment,304 stainless steel is taken as the experimental research object to study the influence of various parameters on the surface roughness of polished workpiece and material removal rate.The orthogonal experiment method is adopted to determine the main factors that affect the polishing results as power supply parameters,polishing time and submergence depth of the workpiece.Through the central combination experiment,the optimal power supply parameters are obtained,the power voltage is 310 V,the pulse frequency is 50 kHz,the pulse duty cycle is 50%,and the optimal polishing time is 5-10 min.The optimal electrolyte composition for TC4 titanium alloy is studied,and the power parameters of the polishing process were optimized,the optimized power parameters are close to that of the 304 steel polishing.The single pulse process of plasma discharge polishing of multi-component materials is studied.According to the real-time current and voltage changes measured by the experiment and the volt-ampere characteristic curve of discharge machining,each pulse discharge process of micro-arc discharge is divided into discharge preparation process,transition process,and stable discharging process.The characteristics of electrical parameters in each stage are analyzed theoretically,and the corresponding stages are capacitance stage,micro-arc discharge stage,and resistance stage.Modeling and MATLAB simulation of the dive depth and discharge polishing power parameters of each stage were carried out respectively.The accuracy of the established models is verified by comparing the simulation results with the current and voltage parameters measured by experiments.A model predictive controller for the discharge gap and gap current of micro-arc discharge polishing is established,and a generalized predictive control algorithm for submergence depth and current is designed.The gap variance of the discharge gas film is controlled by changing the submergence depth and submergence speed of the workpiece,then the current value is stabilized near the optimal value.According to the discharge gap model and the generalized predictive control model,the generalized predictive control experiment of the gap model is carried out.The experimental results show that the model predictive controller can control the current,and it is feasible to control the discharge gap current by controlling the submergence depth.Comparing the surface roughness of the workpiece after polishing under different currents,when the reference current I0=4A,the surface quality is optimal.