Simultaneous micro-EDM and micro-ECM in low-resistivity deionized water Minh Dang Nguyen n , Mustafizur Rahman, Yoke San Wong National University of Singapore, Department of Mechanical Engineering, 9 Engineering Drive 1, 117576 Singapore, Singapore article info Article history: Received 3 August 2011 Received in revised form 11 November 2011 Accepted 14 November 2011 Available online 2 December 2011 Keywords: Micro-EDM Micro-ECM Hybrid machining Deionized water Short pulses abstract Micro-EDM and micro-ECM are two suitable machining processes for micro- and nano-fabrication. Each process alone has some undesirable effects which confine its capability. By appropriate combination of these two processes, the adverse effects can be significantly mitigated. However, micro-EDM operates in non-conductive dielectric fluid whereas micro-ECM employs conductive electrolyte. Because of two rather divergent requirements, micro-EDM and micro-ECM are usually used sequentially. By using low- resistivity deionized water, which exhibits both characteristics of a slightly conductive fluid and a dielectric fluid, this study aims to combine micro-EDM and micro-ECM in a unique hybrid machining process to achieve improved performance in both surface finish and machining accuracy. Through the analysis of material removal phenomenon in micro-EDM using low-resistivity deionized water, it is found that there is a conversion of material removal mechanism from mere micro-EDM to hybrid micro-EDM/ECM when low feedrate is applied. Arising from this observation, a novel hybrid machining process, named as simultaneous micro-EDM and micro-ECM (SEDCM), has been developed. Three key factors of SEDCM, namely low-resistivity deionized water, low feedrate and short voltage pulses, are identified. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Micro-electrical discharge machining (micro-EDM) and micro- electrochemical machining (micro-ECM) are two suitable machin- ing processes to fabricate micro-features and micro-compo- nents [1]. Each process has differing characteristics in its material removal mechanism. The former removes the material from the workpiece by electric discharges whereas the latter uses the electrochemical reaction to dissolve material. In micro-EDM, material is removed by vaporization and melting during each electric discharge. Therefore, the machined surface is made up of thermally damaged layers consisting of the white layer and the heat affected zones [2]. Micro-cracks and residual stresses are also observed in these distinctive layers [3]. As a result, the fatigue strength of the machined part is reduced. In addition, after each discharge, a small amount of material is removed leaving a crater on the surface. Hence, the generated surface is covered with numerous overlapping discharged craters [4]. Consequently, the surface machined by micro-EDM usually has high surface roughness due to its asperity. On the other hand, the material is removed not only from the workpiece but also from the electrode, which manifests as electrode wear. This influences the machining shape and accuracy, especially in micro-EDM drilling and milling. In micro- ECM, the material is removed based on the dissolution of metal from anode. The dissolution rate of electrochemical reaction is relatively low, especially as short pulses, low voltage and small current must be used in micro-ECM to assure required accuracy [5–7]. Hence, the material removal rate of micro-ECM process is considerably lower than micro-EDM. Although the throwing power is small, the dissolution occurs in an area larger than the facing zone of the tool electrode [1]. Therefore, accuracy is another obstacle in micro-ECM. However, micro-ECM has some valuable advantages. Since the material removal mechanism is based on ionic dissolution, the surface machined by micro-ECM is very smooth [8]. The generated surface does not have thermally affected layers and it is stress-free with no burr as well as micro-cracks. In addition, during machining, only gas evolution occurs at the cathode surface. Thus, there is no tool wear in micro-ECM [9]. Hence, an appropriate combination of micro-EDM and micro-ECM could yield the advantages of these two processes while mitigating their adverse effects. Many attempts have been made to combine micro-EDM and micro-ECM in the last two decades [10–12]. How- ever, it has encountered a challenging obstacle due to their different material removal mechanisms. Non-conductive dielectric fluid is used in micro-EDM whereas conductive electrolyte is employed for micro- ECM. Therefore, micro-ECM has typically been used as a sequential process of micro-EDM only. The primary aims of these studies are to lower the surface roughness and remove the thermally damaged zones created during EDM. The earliest research used mate-electrode Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ijmactool International Journal of Machine Tools & Manufacture 0890-6955/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2011.11.005 n Corresponding author. Tel.: þ65 16 4644. E-mail addresses: dang@nus.edu.sg, nmdang85@yahoo.com (M.D. Nguyen), mpemusta@nus.edu.sg (M. Rahman), mpewys@nus.edu.sg (Y.S. Wong). International Journal of Machine Tools & Manufacture 54-55 (2012) 55–65