Study On Discharge Characteristics And Servo Control Of Micro EDM Using Electrostatic Induction Feeding Method

Micro electrical discharge machining (Micro-EDM) is one of the most effective methods for micro machining. With the development of Micro Electro Mechanical System (MEMS) and increasing need for microscopic parts, demands for micro-EDM are growing increasingly. In recent years, how to improve the processing capacity of micro-EDM has become a research focus. In order to obtain smaller discharge craters, the electric discharge energy per pulse must be reduced as much as possible. The electric discharge energy per pulse can not be reduced further during to the stray capacitance in the relaxation type pulse generator, which is generally used in micro-EDM equipment. This means that the minimum electric discharge energy per pulse is determined by the stray capacitance, indicating a limit to miniaturization.The electric feeding is carried out with the feeding electrode by electrostatic induction method in micro-EDM using electrostatic induction feeding method. When discharge occurs, the influence of stray capacitance in circuits can be eliminated because there is no conduction current between feeding electrode and tool electrode. The energy stored in stray capacitance can not affect the discharge energy per pulse. In addition, discharge current which pulse width is very narrow generates easily by this method. This method has better micro processing capacity comparing to micro-EDM whose minimum discharge energy is determined by the stray capacitance.In this paper, micro-EDM using electrostatic induction feeding method has been realized, three types of voltage pulse have been obtained. The phenomenon of multi-discharges during a voltage pulse and the open voltage raising step by step after discharge when the frequency is high have been analysed. The regularity of energy liberation and changes of dielectric strength was researched, the time for the recovery of dielectric strength has been estimated according to the phenomenon of the open voltage raising step by step after discharge. In order to control the gap width automatically, the servo control of gap width was carried out according to the discharge characteristics, meanwhile, the influence of servo parameter and pulse frequency on servo machine speed was investigated. Micro rods with 5.8μm in diameter 100μm in length and 5.1μm in diameter 120μm in length were obtained by successfully by block and wire electrical discharge grinding using electrostatic induction feeding method and micro through-hole with 8.6μm in diameter was processed on a stainless steel feeler 20μm in thickness.