A New Method In Electrochemical Discharge Micro Machining In Glass And Its Mechanism

Nowadays,the wearable smart devices and smart phones prevail in consumers everyday life.Non-conductive hard brittle Micro-Electro-Mechanical System(MEMS)materials such as glass have many favorable properties such as high hardness,high brittleness,wear resistance,chemical inertness,electrical insulation,optical transparency and bio-compatibility.However,they are hard to process in micromachining.Electrochemical discharge machining(ECDM)is a micromachining process especially for non-conductive materials like glass,quartz and some ceramics.It is featured by high efficiency,high flexibility and low cost.Nevertheless,it has not been applied to large scale industrial applications due to its low machining accuracy,machinable depth,and low repeatability.In this study,we proposed a series of micromachining techniques for insulating hard brittle materials based on electrochemical discharge effect,which improved significantly the comprehensive processing performance.In this dissertation,the physics and chemistry of electrochemical discharge effect were briefly introduced.Nowadays,gravity-feed drilling is the most commonly used method for micro hole drilling with ECDM.However,experiments show that gravity-feed set-up may lead to many issues that lower the repeatability of machining.In this chapter,a new method is proposed to achieve effective micro-drilling,under the name of counter resistant microhole drilling.Furthermore,the varied force acting on machining process was investigated.The experiments demonstrated that reproducible machining was significantly improved over the conventional gravity-feed method.Meanwhile,a systematic analysis of this new drilling method was characterized.The experiments showed that force is one of the key factors that influences the drilling process,especially in the hydrodynamic regime.The unstable gas film around tool electrode in which the electrical discharges take place is unpredictable as the machining depth increases,resulting in inaccurate geometry and inconsistent machining.The material removal rate is significantly decreased due to the insufficient electrolyte flow around tool tip in the hydrodynamic regime.These are serious drawbacks of the process that need to be improved.This chapter presents an analytical analysis of the magnetohydrodynamic(MHD)effect in the ECDM process.The mechanism of the MHD effect in electrochemical discharge machining was investigated.The highspeed camera was used to record the formation of gas film on the tool electrode with or without magnetohydrodynamics effect.The experimental results showed that MHD effect induced by the magnetic field improved significantly electrolyte circulation and higher machining efficiency was also achieved.Furthermore,it has been observed that the thickness of gas film was decreased by high speed camera.In addition,the radius of the machined hole was reduced from 528 ?m to 430 ?m;the machining time decreased from 50 s to 16 s.The counter resistant feeding method and magnetic field could be applied simultaneously by the newly designed set-up.This hybrid method enhanced significantly the accuracy and throughput of drilling process,as well as improved the roundness of the machined hole.The material removal rate is significantly decreased due to the insufficient electrolyte flow around tooltip in the hydrodynamic regime.This will result in a heat affected zone starts to grow gradually.The cracks and roundness error are both significant.The recent research shows that electrolyte circulation can be improved using magnetic field through the magnetohydrodynamics(MHD)effect.However,the mechanism of the MHD effect in ECDM has not been investigated adequately.In this paper,a theoretical model of bubble formation and motion are presented.The critical voltage and the most effective machining zone under MHD effect are estimated.The theoretically predicted results are consistent with the experimental observations.It is experimentally determined that the optimal magnetic field intensity is around 0.28 T for the best machining speed and accuracy.