Research On Micro-Hole Machining Process And Servo Feed Method By EDM In Gas-Liquid Two-Phase Medium

With the development of MEMS technology,mechatronics products become more and more sophisticated,precise and high-performance over time.In aerospace,medical equipment,electronic industry and national defense equipment,the application of micro-hole is increasing.Materials with high strength and high hardness are widely used,which makes the micro-hole machining is facing the great challenge..As a commonly used method for micro-hole processing,Electrical Discharge Machining(EDM)usually takes fluid as dielectric medium to maintain machining stability,but it causes large electrode wear and environmental problems.Taking high-pressure gas as dielectric medium,Kunieda put forward the EDM in gas,which significantly reduces the electrode wear and even gains negative electrode wear.Because of small discharge gap in gas,it is hard to maintain the processing stability,which decreases processing efficiency.Based on the characteristics of liquid and gas medium,the characteristics of EDM under different gas-liquid mixing ratio are studied in this thesis,in order to obtain fast processing speed and low electrode wear.Based on the discharge characteristics of gas and liquid,the discharge characteristics of gas with tiny droplets and water with tiny bubbles are analyzed.An experimental platform was built according to the requirements of EDM in gas-liquid two-phase media,which can provide working medium with different volume ratios between deionized water and air.Finally,deionized water,fog(deionized water accounts for 10% of the volume)and bubble water(deionized water accounts for 90% of the volume)are chosen as working medium.In order to analyze the effect of flushing liquid on the working fluid supply system,the flow field in the discharge gap was simulated with the actual processing parameters as boundary conditions.The results confirm the discharge is performed in two-phase medium;there are no discrete phase droplets or bubbles accumulated in large numbers.The influence of capacitance,charging current and servo reference voltage on EDM micro-hole machining is studied by using machining speed,electrode loss and machining quality as evaluation parameter.In order to make a reasonable comparison of different media,orthogonal experiments are designed to analyze the influence degree of each factor and to find the optimum parameter combination in each medium.The relationship between processing speed,electrode wear and working depth in different media was investigated by fixing processing time and fixing feed depth.Compared with EDM in deionized water,the electrode wear in fog can reduce up to 27% and the processing time in the bubble water could be shorten up to 17%.The micro holes produced in deionized water have smaller taper.According to the characteristics of micro-hole machining by EDM in gas-liquid two-phase medium and the deficiency of the control system of machine tool,the servo control system of machine tool is improved by introducing PID control.In order to improve the shortage of PID control,fuzzy control is introduced to adjust the PID parameters online.Through the process experiment,processing time can be reduced by 38% at most compared with the original servo system,better machining results have been achieved.