Electrode Vibration In Micro Hole Drilling By EDM

Electrical discharge machining (EDM) is used to remove material from any electrically conductive material without mechanical contact between the tool electrode and workpiece. Micro EDM can drill micro holes and generate micro features in metallic materials regardless their hardness and strength. It is applied to drill micro holes in fuel nozzles and machine micro molds.In EDM, the material is melted and partially vaporized by discrete discharges between the workpiece and the electrode, both immersed in dielectric. Although no mechanical force exists between the tool and the workpiece, there are electrostatic force, electromagnetic force, dielectric flushing force, spark force and reaction force from the expansion and collapse of the bubbles.In wire EDM, these forces act on the long thin wire causing wire vibration, resulting in low machining accuracy. The same problem is also found in drilling of micro hole with a high aspect ratio when a long and thin electrode is used. However, there is no theoretical model to describe this phenomenon.In this paper, The NC program is developed based on the existing horizontal Micro-EDM machine tool. Which includes Coordinate display and set the origin, rapid positioning, single step feed, the tool electrode processing, micro hole machining, the spindle rotation control, position detection, stop processing, Signs of NC machining process. All related experiment can be conducted based on the NC program.In this paper, a theoretical model is proposed to analyze the dynamic behavior of electrode during micro hole drilling by EDM. Extensive experiments are carried out to verify this model. And the model is applied to calculate dimensions of electrode when drilling micro holes with desired diameters.Relative error of experimental results and theoretical ones is less than 3% in 14 of the 15 group verification experiment and 8 of the 9 group applied experiment. The reasons causing the relative errors are analyzed in this paper, and the applicability of the theoretical model is explored under different experimental conditions.This paper also explores the effect of different experimental conditions on electrode vibration, such as different voltage and different capacitance. This study found that amplitude of the electrode increases with the voltage, and first decreases then increases with increase of capacitance.