Exploratory Study Of Micro-hole Drilled By Micro-EDM In Powder-mixed Dielectric

Micro-hole is widely used in industry.There are various micro drilling processes available for different size of hole,material and accuracy,including mechanical processes and special machining technology.One of them is micro electrical discharge machining(EDM),which has the ability of processing any electrically conductive materials regardless of their strength and hardness.Micro EDM are widely used in aerospace,medical devices and mechanical machining,owing to its cheap equipment.However,it is a challenge to drill deep micro hole by micro EDM due to the difficulty of debris and bubbles removal in working area.In this paper,tube electrode has been used to transfer dielectric into discharge area,which can force bubbles and debris to remove and update dielectric.Powder is mixed in dielectric and bought into discharge area.Powder-mixed dielectric will affect discharging,and effect hole sidewall.Original machine tool has been improved to adapt the experimental requirements.Rotary spindle with sealing performance is designed and motor is chosen according to torque.Theoretical formulas of radial run-out in three situations are derived on cantilever theory.Base on these formulas,director is designed and fabricated with radial run-out less than 10?m.Liquid cycle system is designed which can achieve pressure from 0 to 2MPa.Micro EDM program based on LabVIEW is written,and velocity and open circuit are matched optimally.In this paper,micro EDM in powder-mixed dielectric has been proposed to overcome the problems of deep hole drilling.Some processing results are studied,like electrode wear,diameter of entrance and exit,machining time,surface roughness and recast layer.Research finds that dielectric mixed with diamond is benefit to reduce electrode wear.With increase of diamond particle size,electrode wear decreases.When the particle size is 10?m,electrode wear length is 76.7% less compared with the dielectric without powder,and 71.1% less with particle size of 1?m.Reduction of electrode wear is that carbon particles converted from diamond can reduce and compensate tool wear by attaching to the electrode.Hole diameter of entrance is reduced,because reduction of debris composed of electrode and workpiece material lower the probability of secondary discharge in hole entrance.As diamond particle size increases,the diameter variation between entrance and exit tend to be stable.With the increase of particle size,machining time decreases first and then increases.When the particle size is 5?m,material removal rate increases by 27.2% compared with dielectric without powder.Particles in dielectric stick to hole sidewall,which affects the accuracy of surface roughness measurement.By observing SEM photos of hole sidewall and surface roughness of part,we find that surface quality machined with powder is better than that without powder.Powder mixed in dielectric has less influence on recast layer,and recast layer thickness of hole entrance is maintained at 8.5±1?m.