Analysis of Debris Motion in Vibration Assisted Reverse Micro Electrical Discharge Machining

Abstract

The reverse micro EDM (R-MEDM) has emerged as an important process for machining of high aspect ratio arrayed features and textured surfaces. In R-MEDM process, accumulation of debris particles in the inter-electrode gap drives the process towards instability and also the sticking of debris particles on machined microrod increases its surface roughness. Vibration assisted R-MEDM can help to overcome the issues of debris accumulation, produce debris free surfaces and enabled a creation of textured/engineered surfaces. The objective of this paper is to quantify the debris size distribution, number of debris particles generated per discharge and further simulate the debris and dielectric flow under the influence of electrode vibrations in R-MEDM process. Debris particles of estimated sizes, numbers and ejection velocity are injected into channel and simulated under the influence of electrode vibrations. Simulation results show that the electrode vibrations impart oscillatory motion to dielectric fluid and debris particles. During upward motion of plate electrode, dielectric fluid is pushed out of inter-electrode gap while the flow reversal takes place in the inter-electrode gap when plate electrode starts to move in the downward direction. The debris particles also show similar reciprocating motion whereas such motion of debris is completely absent in a fixed inter-electrode gap (no electrode vibration) condition. It is found that displacement of the plate electrode from bottom to middle position (at 6 kHz frequency and 1 μm amplitude) resulted in 6.4 and 3.4 time increase in maximum dielectric velocity and average velocity of debris particles in particular. The flow reversal and the reciprocating motion improves the overall process stability of R-MEDM process.