JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 24, NO. 3, JUNE 2015 661 Modeling Debris Motion in Vibration Assisted Reverse Micro Electrical Discharge Machining Process (R-MEDM) Sachin A. Mastud, Naman S. Kothari, Ramesh K. Singh, and Suhas S. Joshi Abstract— Reverse microelectrical discharge machining (R-MEDM) process is a recent variant of microelectrical discharge machining process capable of fabricating high aspect ratio arrayed microfeatures and textured surfaces. Efficient flushing of the debris particles from the interelectrode gap is essential for process stability, but extremely small interelectrode gaps (∼5 μm) make the dispelling of debris difficult, rendering the R-MEDM process infeasible for machining difficult-to-erode materials and creation of engineered/textured surfaces. It has been experimentally observed that the electrode vibrations facilitate the flushing of debris particles and improve the erosion rate, surface morphology, and dimensional accuracy of the machined features. Despite the obvious advantages, the vibration-assisted R-MEDM process, specifically the debris motion and dielectric flow under the effect of vibration, is not very well understood. Consequently, this paper is focused on computational modeling of the debris motion and its interaction with the dielectric fluid under low-amplitude vibrations imparted via a magnetorestrictive actuator. The effects of frequency and amplitude of the electrode vibration on the debris motion have been quantified. The higher local debris velocities and oscillatory motion due to flow reversal potentially reduce the debris agglomeration. As a result, the normal discharge duration, which is responsible for the material erosion, is increased and fabrication of arrayed features on difficult-to-erode materials and creation of surface texture over large areas become feasible. [2013-0394] Index Terms— Reverse micro electrical discharge machining (R-EDM), vibration assisted EDM, debris simulation, dielectric flow, textured surfaces, micromachining. I. I NTRODUCTION D EMAND for precise miniaturized parts has increased in recent past due to widespread use of ultra-portable mechanical and electrical products/devices. High aspect ratio arrayed micro-features of varying cross section and sizes are required in applications such as electrodes for micromachining processes, printing heads, interface elements in biomedical devices, a source of plasma, etc. [1]–[3]. Micro electrical dis- charge machining (micro EDM) is widely used micromachin- ing process for realization of miniaturized parts. Processes, such as block electrical-discharge grinding (block EDG) [4], Manuscript received December 21, 2013; revised April 7, 2014; accepted June 14, 2014. Date of publication August 7, 2014; date of current version June 1, 2015. Subject Editor H. Seidel. The authors are with the Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India (e-mail: sachiniitmech@gmail.com; namankothari91@gmail.com; ramesh@me.iitb. ac.in; ssjoshi@iitb.ac.in). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JMEMS.2014.2343227 Fig. 1. Fabrication of different features via R-MEDM (a) single microrod (200 μm in diameter and aspect ratio of 5), (b) 8 ×8 array machined on brass. (c) Micro-pillared textured surface on Ti-6Al-4V, (d) magnified view of the textured micro-pillars. micro wire electrical-discharge grinding (micro wire EDG) [5], micro-milling [6] and wire electrical discharge machining (wire EDM) [7] are capable of machining high aspect ratio features. However, these processes fails when machining of densely spaced high aspect ratio arrayed features of non- cylindrical cross section and creation of textured surfaces on micro-parts is required. A recent variant of micro EDM process known as reverse micro electrical discharge machining (R-MEDM) has evolved for machining of such high aspect ratio features and textured surfaces. In R-MEDM, thin metal plates of 0.1-0.5 mm thickness are used as cathode (electrode). Microholes of required dimensions and spacing are initially machined on cathode and aligned over anode (workpiece) surface over which fabrication of microrods is required. Sparking erodes material from anode surface wherever it has interface with cathode surface. Thus, an extruded feature is fabricated on anode surface from each of the microcavity present on the cathode. Fig. 1 demonstrates the capability of R-MEDM process for creation for high aspect ratio features and textured surfaces created in the Machine Tools Laboratory at IIT Bombay. In micro EDM process, material eroded from the anode surface solidifies in the form of particles known as debris. 1057-7157 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.