Research On Multi-physics Coupling Model And Process Optimization Of Profile Electrochemical Machining Based On Gas-liquid Two-phase Flow Theory

Electrochemical machining(ECM)technology has the unique advantages of processing various difficult-to-cut metal materials and no mechanical cutting force.It is the main processing method in the fields of aerospace engine blade,integral blade,gun barrel rifle,small deep hole and special groove.However,the complex process and low forming accuracy of ECM make it more difficult to manufacture difficult-to-cut materials such as titanium alloys and complex shapes.Therefore,it is necessary to study the coupling model of multi-physical field and the process parameters affecting the machining accuracy,optimize the process parameters and improve the accuracy of ECM,according to the interaction of electric field,flow field,temperature field and structure field in ECM.Based on the theory of gas-liquid two-phase flow,several problems of multi-physical field coupling model and the optimization of process parameters for profile ECM are deeply analyzed and studied in this dissertation.The main research contents include the following aspects:(1)The gas volume fraction in electrolyte was calculated.The process of hydrogen generation and its motion characteristics in machining gap are analyzed.A gas-liquid two-phase flow model for ECM was established based on the theory of gas-liquid two-phase flow and Euler-Euler two-fluid model.The boundary conditions were set up to solve the two dimensional distribution of gas volume fraction in turbulent electrolyte.(2)The temperature distribution of electrolyte was calculated.Considering the significant influence of lower flow velocity in the boundary layer on heat transfer,a SST model is proposed to calculate the velocity distribution of turbulent electrolyte.The influence of bubbles on the density and thermal conductivity of electrolyte is also considered.The heat generated in ECM and the heat transfer process are analyzed.The temperature field model of ECM is established,and the two dimensional distribution regularity of electrolyte temperature is obtained by solving the convection-heat transfer equation.(3)A multi-physical field coupling model and a weak coupling iteration method for ECM are proposed.The relationship among electric field,two-phase flow field,temperature field and structure field in ECM process is analyzed.The conductivity distribution affected by temperature and gas volume fraction,and the current density affected by conductivity in the machining gap are calculated.The heat and hydrogen flux varying with the current density are calculated.The instantaneous value of physical quantities in the machining process is solved by iterative method.The dissolution of the anode at each step is calculated,and a new workpiece profile is formed by moving the grid.The workpiece anode profile is predicted by cyclic calculation until the end of processing.(4)The ECM test platform is set up,and the ECM of planar electrode with different processing parameters is studied.The temperature detection system is designed to measure the temperature at the inlet and outlet of electrolyte and the temperature at the sampling points in the workpiece.The simulation study of planar electrode electrochemical machining process is carried out based on the multi-field coupling model of gas-liquid two-phase flow.The validity of the multi-field coupling model is verified by comparing the results of simulation and experiment.(5)Considering the influence of gas volume fraction on the conductivity of electrolyte,the relationship between process parameters and current density distribution on anode surface is analyzed.Based on the multi-physical field coupling model,the effects of processing voltage,feedrate,electrolyte flow velocity and outlet pressure on the current density on the surface of the anode are analyzed.The ECM experiments of blade basin profiles are carried out with different process parameters.The distribution regularity of balanced machining gap and the distribution regularity of anode surface current density in ideal gap are compared.(6)Based on the multi-physical field coupling model,the process parameters of ECM are optimized.The efficiency and accuracy of ECM are selected as the optimization objectives,and the machining voltage,feedrate,electrolyte flow velocity and outlet pressure are selected as the optimization parameters.An optimization model with the average and standard deviation of current density on the surface of anode as the multi-objective objective is established,and the constraints are determined.The optimization results of enumeration method and particle swarm optimization are compared.Finally,the validity of the optimization model is verified by machining the profile with the optimized process parameters.