| Microstructure products are widely used in aviation,military industry,biomedicine,microelectronics,semiconductor and other fields.Among which the microstructure machining of difficult-to-cut metal materials is a difficult point in the field of industrial manufacturing.Microelectrochemical machining theoretically removes materials in the form of ions(nanoscale),and in principle,this machining method has advantages for the machining of difficult-to-cut metal materials.In the previous experiments,the research team confirmed that the introduction of magnetic field can improve the accuracy of micro-electrochemical machining,In order to explore the mechanism of magnetic field to improve the precision of micro-electrochemical machining,this thesis studied the shaping law of magnetic-field assisted micro-electrochemical machining from the theoretical point of view,respectively,from the aspects of differential equation of magnetic field affecting micro-electrochemical machining shaping law,magnetic-field assisted micro-electrochemical machining simulation,magnetic-field assisted micro-electrochemical machining law experimental research,etc.,the main research content is as follows:(1)In order to study the influence of magnetic field on the shaping process of micro-electrochemical machining,the equation of ion motion trajectory in the electromagnetic field and the differential equation of the shaping law of magnetic-field assisted micro-electrochemical machining are derived.The electric field force and Lorentz force formula were used to derive the equation of the motion trajectory of charged ions in the magnetic field at any angle and any rotation speed,and the numerical solution of the motion trajectory equation was solved by using MATLAB software.Based on magnetohydrodynamics and Fick’s theorem,combined with Faraday’s law,the differential equation of orthogonal horizontal magnetic-field assisted micro-electrochemical machining in motion is derived.The results show that the radius of curvature of the ion trajectory is affected by the time and the strength of the magnetic field,the ion drop point and reaction area are affected by the gap between the poles,and the magnetic field increases the mass transfer coefficient while reducing the thickness of the diffusion layer,which jointly accelerates the electrolysis reaction.(2)In order to study the influence of magnetic field on the shaping law of micro-electrochemical machining,COMSOL software is used to carry out three-dimensional and two-dimensional multi-field coupling simulation analysis.The effects of four schemes,namely horizontally opposed homopolar and heteropolar magnetic fields,up-and-down opposed homopolar and heteropolar magnetic fields,on the magnetic field distribution in the machining area,the flow velocity streamline distribution of electrolyte and the distribution of electrolyte pressure were studied by using magnetic field,flow field and primary current density.The ion reaction region is used to characterize the corrosion machining position,and the influence of magnetic field on ion trajectory and drop point in micro-electrochemical machining is simulated,and the results show that the Lorentz force is conductive to the fluid so that the static electrolyte forms a stable and regular fluid.The rotating magnetic field enlarges the scanning area of ions,leading to a larger processing area,and the rotating magnetic field makes the distribution of ion drop points lag.The presence of magnetic field makes the effect of machining gap size on micro-electrochemical machining more significant.(3)In order to study the influence of key parameters on magnetic-field assisted micro-electrochemical machining,a single-factor experiment was designed.Screened out the basic machining parameters by the pre-experiment,and then the effects of magnetic field motion,different magnetic field strength and different initial gap on the forming machining were studied.The machining results show that the fixed magnetic field can effectively reduce the lateral clearance and improve the machining accuracy.The variation of the fixed magnetic field intensity has no obvious effect on the size of the lateral clearance.In this experiment,the maximum reduction of the lateral clearance is 18.7μm when the fixed magnetic field intensity is 0.05 T.The rotating magnetic field can effectively improve the average machining depth and increase the machining efficiency,and there is a wireless relationship between the rotating magnetic field intensity and the lateral clearance.The change of initial machining clearance has no obvious effect on the diameter of micro pit entrance.In this experiment,when the initial machining clearance is 100μm and the rotating magnetic field intensity is 0.1T,the average machining depth increases by 16.3μm maximum.And the microstructure profile is greatly optimized.The experimental results are consistent with the simulation results.At the same time,the shaping law of magnetic field compound micro-electrochemical machining is summarized: the fixed magnetic field improves the machining accuracy by improving the flow field movement,and the change of the fixed magnetic field intensity has no obvious effect on the lateral clearance.With the increase of initial machining clearance,the machining efficiency first increases and then decreases,and the change of initial machining clearance has no obvious effect on the lateral clearance.The rotating magnetic field can greatly improve the machining efficiency and optimize the workpiece structure.The average machining depth first increases and then decreases with the increase of the magnetic field intensity.There is no linear relationship between the influence of the rotating magnetic field intensity on the inlet diameter of the micro pit.Within the range that does not affect normal machining,with the increase of initial machining clearance,the machining efficiency first increases and then remains unchanged,and the change of initial machining clearance has no obvious influence on the lateral clearance.(4)In order to obtain the ideal combination of machining parameters,the three-factor hybrid orthogonal experiment of magnetic field motion state,magnetic field strength and initial gap was completed.Taking the lateral clearance and average machining depth of the machining workpiece as the measurement index,the gray correlation method was used to analyze the data and complete the optimization of the combination of single-target and multi-target parameters,and the influence order of each parameter on the shaping process was analyzed,and the optimal machining parameters were magnetic field strength 0.1T,rotating magnetic field(15RPM),and initial machining gap 60μm.The comprehensive verification experiment of magnetic field composite micro-electrochemical machining was carried out using the optimal machining parameter combination.The experimental results showed that the lateral clearance of magnetic field composite micro-electrochemical machining was reduced by 56.8%,and the average machining depth was increased by 118.5%.Theoretical research and experimental results show that the magnetic field affects the shaping law of micro-electrochemical machining by changing the ion motion trajectory and improving the flow field environment.The theoretical equation explains that the magnetic field can increase the speed of electrolytic reaction by increasing the mass transfer coefficient and decreasing the thickness of diffusion layer,and the simulation shows that the Lorentz force generated by the magnetic field can make the electrolyte form stable flow field to improve the machining accuracy,the single-factor experiment is completed and the experimental results are more consistent with the theoretical derivation and simulation results,and the final machining results are obtained in the experiment after optimizing the parameters: The lateral clearance decreased from 57.3μm to 28.1μm,decreased by 56.8%,and the average machining depth increased from 10.8μm to 23.6μm,increased by 118.5%.The experimental results are consistent with the forming law of magnetic field composite micro-electrochemical machining. |
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