Study on Micro-EDM Technology with High Spindle Speed Using Non-Contact Electric Feeding Method

Author:Feng Guang Lei

Supervisor:yang xiao dong

Database:Doctor

Degree Year:2019

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Pages:135

Size:4266K

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With the development of MEMS technology,the demand for micro-motors,micro-sensors and other small parts is increasing.Micro-EDM is very suitable for machining the small parts due to its non-contact,independent of the hardness of the material being processed and better controllability.However,due to the small machining scale and the weak discharge explosion force,the debris in the working gap often accumulate in the gap and cannot be flushed easily,which leads to unstable discharge state.As a result,the machining speed is reduced and the tool electrode wear is increased,which seriously limits the application range of micro-EDM technology.Based on non-contact electric feeding method,high spindle speed micro-EDM technology can realize electrode rotational speed of tens of thousands of revolutions per minute or more.High electrode rotational speed can effectively improve the discharge state,improving machining efficiency and reducing electrode wear.This is very important for expanding the practical application of micro-EDM and expanding its application fields.Based on the analysis of the principle of micro-EDM using non-contact electric feeding method,this dissertation firstly analyzes the theoretical modeling of micro-EDM using non-contact electric feeding method without considering distributed capacitance and distributed inductance,and clarifies the charging/discharging characteristics of micro-EDM using non-contact electric feeding method in that conditions.Considering the small discharge energy,the distributed capacitance and distributed inductance in the discharge circuit may affect the discharge,and then the theoretical modeling analysis of micro-EDM using non-contact electric feeding method under the influence of distributed capacitance and distributed inductance is carried out,and the influence law of distributed capacitance and distributed inductance on the charging/discharging characteristics of micro-EDM using non-contact electric feeding method is clarified.According to the principle and charging/discharging characteristics of micro-EDM using non-contact electric feeding method,this dissertation designed a machining system for micro-EDM using non-contact electric feeding method with high spindle speed,which mainly includes: high-frequency pulse power supply,non-contact electric feeding and non-contact measuring device,tool electrode holder device,and servo control system based on non-contact measuring.Through the simulation analysis of the non-contact measuring equivalent circuit,the size of the measuring electrode was determined.Based on the measuring voltage,the servo control of the micro EDM using non-contact electric feeding method is realized,and the influence of the measuring circuit on the discharge is avoided.And,finally a stable micro-EDM with high spindle speed can be achieved.In order to clarify the influence of the relative linear velocity of the tool electrode and the workpiece on the electrode wear in micro-EDM with high spindle speed,this dissertation established a thermal analysis model of single-pulse electrode side discharge under moving heat source,and conducted simulation analysis of electrode surface transient temperature field distribution under different spindle speed.The simulation results showed that the greater the electrode rotational speed,the greater the linear velocity of the electrode surface,the smaller the heat flux density input to the electrode surface,the smaller the electrode melting zone along the axial and radial dimensions of the electrode,the larger the size along the electrode surface linear velocity direction;When the linear velocity of the electrode surface is increased to 20 m/s,the temperature of the molten region on the electrode is lower than the melting point of the electrode material,and machining without electrode wear can be realized.Comparing the experimental results of the linear velocity of the electrode surface in electrode side discharge milling,it can be seen that increasing the electrode surface linear velocity can achieve smaller electrode wear,and can make the electrode surface roughness smaller.The radial wear along the electrode and the surface roughness of the electrode after machining become smaller,which can explain that the depth of the discharge crater becomes shallower as the linear velocity of the electrode surface increases.The experimental result is consistent with the temperature field simulation results.In order to clarify the effect of electrode rotational speed on flushing debris particles from the gap in the micro-EDM drilling with high spindle speed,this dissertation established a model of the working gap flow field in micro-EDM with side flushing and simulation analyzed the influence of the electrode rotating speed on the flow field and the distribution of the discharge debris particles in the gap.The simulation results showed that as the electrode rotational speed increases,the discharge particles are more likely to enter the free surface from the frontal and lateral gap.That is,in micro-hole machining,the discharge debris are more likely to flush from the gap during high-speed rotation of the spindle.Through the experimental results of micro-hole machining at different speeds,it can be seen that increasing the spindle speed can effectively improve the machining speed and reduce the probability of occurrence of short circuit,which indirectly proves that increasing the rotating speed can promote the removal of the discharge particles.And the experimental result is consistent with the flow field simulation results.In order to realize the micro electrode machining with high spindle speed,this dissertation carried out the research of block electrical discharge grinding(BEDG).In the case where the spindle rotation speed is 60000r/min,a micro rod of 5μm in diameter,80μm in length and 16 in high aspect ratio is machined.In order to clarify the influence of spindle rotational speed on machining characteristics of micro-holes machining,this dissertation analyzed the effect of spindle rotational speed on the material removal rates,the electrode wear,the taper of the machined holes and the surface roughness of the hole wall,and the results showed that the higher the spindle rotational speed,the greater the material removal rate,the smaller the electrode wear,the smaller the taper of hole and the surface roughness of the hole wall.At the same time,it analyzed the effect of spindle rotational speed on the material removal rates and the electrode wear in different electrode diameters and different hole depth,and the results showed that increasing the spindle rotational speed has a better effect on increasing the material removal rate of the larger electrode diameters and deeper hole machining,and has a better effect on reducing electrode wear of smaller electrode diameters and deeper hole machining.Finally,it was further verified that the high electrode rotational speed was good for flushing the debris from the gap and improving the stability of the discharge state by the comparison experiment of machining the small holes using the edging electrode and the cylindrical electrode.In order to clarify the influence of the spindle rotational speed on machining characteristics in micro-EDM milling,this dissertation firstly studied high spindle speed micro-EDM milling using electrode end,analyzed the influence of the spindle rotational speed on the electrode wear and the machining surface roughness and the results showed that increasing the spindle rotational speed was good for reducing the electrode wear and the surface roughness of the machined surface.Then,it studied high spindle speed micro-EDM milling using electrode sidewall,analyzed the influence of the electrode surface linear velocity on the material removal rate,electrode wear and machining surface quality,and the results showed that increasing the linear velocity of the electrode surface was good for the improvement of the material removal rate,the reduction of the electrode wear,and obtaining a better surface quality.