Study On Ultrasonic Aided Electrical Discharge Machining Technology And Mechanism For High Aspect Ratio Holes

Compared with the common electrical discharge machining(EDM),higher efficiency,higher respect ratio,less microcrack and recast layer can be gained with ultrasonic aided electrical discharge machining(UEDM).Workpieces vibration is widely used in the present researches on UEDM,and most researches are focus on the drilling of micro-holes.However,workpiece vibration is not suitable for drilling high aspect holes in complex parts or large size parts.To solve the problems,this paper is focus on UEDM with electrode vibration.An ultrasonic vibration EDM system was developed,which adopted three methods that could be applied simultaneously,including tool electrode ultrasonic vibration,tool electrode rotation,and forced pump flushing.The contactless power transfer method was used,which make the structure of the ultrasonic vibration EDM system compact.As to the design of the core part of ultrasonic vibration system—the ultrasonic transducer,a whole structure model was established,including parts of piezoelectric ceramics,horn,pre-stress bolt,etc.Based on the model,by using modal analysis,an ultrasonic transducer which meets requiements had been designed.In the EDM,electrode wear is inevitable,which causes the length change of an electrode.Electrode wear will vary the resonant frequency of ultrasonic vibration system in UEDM and the amplitude of an electrode may decrease due to the variation of resonant frequency.To solve this problem,the phenomenon of local resonance was used and elaborate analyzed.As well as the local resonance of electrode,the local resonance of drive system of transducer was found.In the local resonance of drive system,the resonance frequency is less influenced by the variantion of electrode length,which indicates that by taking advantages of local resonance,the frequency adjustment of ultrasonic generator can be avoided.And it is found that the amplitude of electrode is relatively stable in the local resonance of drive system.Therefore,the local resonance of drive system was decided to be used in this paper,and the matching circuit of the contactless power transfer was designed correspondingly.Experiments on drilling of high aspect ratio holes were conducted,which verified the feasibility of the local resonance of drive system and the performance of the ultrasonic vibration EDM system.Experimental results showed that the aspect ratio and machining speed were improved greatly with the ultrasonic vibration EDM system.To analyse the machining mechanism of UEDM,a discharge probability model of UEDM was proposed,based on statistics.The effect of vibration amplitude,feedrate,frequency on discharge probability was analyzed with this model.It was found that,compared with common EDM,the discharge probability increase in UEDM,causing a higher material removal rate.