Research On Micro Hole With Large Aspect Ratio Machining Technology Of Ultrasonic Vibration Assited EDM

Micro-EDM relies on the high temperature and high pressure produced by electrode and workpiece discharge to process materials,which are not in direct contact with each other.It has unique advantages in machining difficult to machine materials such as high strength,high hardness,high plasticity and high adhesion represented by TC4 titanium alloy,and is widely used in Aerospace and other fields.With the development of aerospace technology,there are more and more applications of micro holes with large depth diameter ratio.When traditional Micro-EDM is used,the products of electrical erosion are easy to gather at the bottom of the hole,the machining state is deteriorating rapidly,short circuit,arcing and secondary discharge occur frequently,and the machining efficiency and accuracy are low.In this paper,the combination of ultrasonic technology and micro EDM technology can effectively avoid the occurrence of abnormal discharge and improve the efficiency and accuracy of micro hole machining with large depth diameter ratio.Based on the basic theory of discharge in medium,the mechanism of ultrasonic vibration assisted micro EDM is studied.The effects of ultrasonic vibration on discharge channel,discharge gap,material removal process,material removal rate,electrode loss and surface roughness were studied.The results show that the introduction of ultrasonic vibration increases the dispersion of the discharge point,improves the inter electrode processing state,and promotes the throwing out of the corrosive substances.At the same time,the pumping effect of ultrasonic vibration improves the inter electrode working fluid environment,thus reducing the electrode loss and improving the material removal rate.Based on the design theory of ultrasonic vibration system,the ultrasonic vibration system is designed and simulated.According to the technical requirements of ultrasonic vibration assisted Micro-EDM,the ultrasonic vibration system composed of ultrasonic generator,PZT-8 piezoelectric transducer with frequency automatic scanning tracking and timing control,ultrasonic horn made of step composite titanium alloy material and so on are selected.The specific structural dimensions of ultrasonic transducer and horn are designed and simulated by ABAQUS.The natural frequency and the maximum displacement response of the horn are obtained.Based on the single factor experiment,the influence of process parameters on the performance of ultrasonic vibration assisted Micro-EDM is studied.The results show that with the increase of pulse width,the material removal increases first and then decreases,the relative electrode loss rate increases continuously,the taper angle decreases first and then increases,and the amount of overcut increases first and then decreases;with the increase of pulse interval,the material removal increases first and then decreases,the relative electrode loss rate and taper angle decrease continuously,and the amount of overcut increases continuously;with the increase of peak current With the increase of ultrasonic amplitude,the material removal rate continues to increase,the relative electrode loss rate continues to decrease,the taper angle and the amount of overcut continue to increase;with the increase of ultrasonic amplitude,the material removal rate continues to increase,the relative electrode loss rate,the taper angle and the amount of overcut continue to decrease.Based on the orthogonal experiment and signal-to-noise ratio analysis method,the process optimization of ultrasonic vibration assisted Micro-EDM is studied.The effects of pulse width,pulse interval,peak current and ultrasonic amplitude on material removal rate,relative electrode loss rate,taper angle and overshoot are studied.The signal-to-noise ratio of material removal rate is obtained according to the formula of large characteristic signal-to-noise ratio,and the signal-to-noise ratio of relative electrode loss rate,taper angle and overcut are obtained according to the formula of small characteristic signal-to-noise ratio.Finally,the maximum material removal rate,the minimum electrode loss rate,the minimum taper angle and the minimum overcut are obtained,and the reliability of the process optimization results are proved by the verification experiment.