On Performance of Electrochemical Discharge Micro-Machining Process Using Different Electrolytes and Tool Shapes

1. Introduction

There are lots of advanced materials and alloys, which are utilised for specific purposes. But producing complicated profiles on such materials sometime becomes extremely difficult with the help of usual methods due to poor machineability. The electro-chemical discharge micro-machining (μ-ECDM) process may be considered as one of the alternative processes since it can machine a variety of electrically non-conducting materials such as ceramics, composites and glass, etc., which are widely utilised in the modern manufacturing industries as a substitute of metals. Micro-ECDM process is an advanced multifaceted micro-machining process, which integrates the modes of electro-chemical machining (ECM) and electro-discharge machining (EDM) processes (Bhattacharyya et at., 1999). In μ-ECDM process, the material is removed on account of the collective effects of electrochemical (EC) reactions and electrical spark discharge action (Basak & Ghosh, 1996; Ghosh, 1997; Jain et al., 1999; Kulkarni et al., 2002). Since the job sample is electrically non-conducting two electrodes are used to complete electrolytic cell. Out of two electrodes one electrode serves as cathode, which is generally the tool and other one is anode, which is typically referred as auxiliary electrode. The job sample is dipped into an electrolyte solution along with the auxiliary electrode in a machining chamber and the tool electrode touches the job sample under about 1 mm depth.

Wüthrich and Fascio (2005) dissertated about the complexity of high current density and the emerging application of ECDM process in micro-machining domain. Sarkar et al. (2006) illustrated the effects of various process parameters of μ-ECDM process based on the relationship between the machining parameters viz applied voltage, electrolyte concentration and the process criteria such as MRR, radial overcut and HAZ during micro-drilling on silicon nitride ceramics. Zheng et al. (2008) explored the effects of geometric contour of tool and pulse-off time during micro-drilling on Pyrex glass. Sarkar et al. (2008, 2017) documented that the quality of μ-holes on electrically non-conducting and semi-conducting materials such as Al₂O₃, ZrO₂ and SiC during micro-drilling extensively depended upon applied voltage and electrolyte concentration. Han et al. (2009) improved the machining performances by using pulse voltage, flow of electrolyte to maintain steady sparking and ultrasonically vibrated electrolyte with the tools insulated at side wall during micro-drilling. Sarkar et al. (2009) and Mallick et al. (2017) searched out the suitable power circuit configuration and parametric combination respectively for micro-machining operation on glass by ECDM. Wüthrich and Allagui (2010) demonstrated about the microscopic scale applications of ECDM process to build micro and nanosystems for the utilization in catalyst and biomedical domain. Yang et al. (2011) assured that ECDM process involved the melting of material at high-temperature and faster chemical etching under high discharge of electrical energy. Cao et al. (2013) developed a triplex hybrid process of ECDM and micro-grinding using PCD as tools in order to reduce the machining time and improve the surface quality. Huang et al. (2014) anticipated a new solution for drilling micro-hole by ECDM with high-speed electrode in stainless steel. Jiang et al. (2014, 2015) used tapered tool electrodes to improve the consistency of spark generation and deduced an analytical model of the gas film by incorporating the growth and removal of bubble on electrode, the electrolysis features and the thickness of gas film. Gupta et al. (2016) reported that the quality as well as aspect ratio of micro-hole on glass material machined by ECDM was influenced by pulse duration and the authors suggested to apply large pulse time. Behroozfar et al. (2016) documented about the tool wear of various materials and explained the feasibility of using various tool materials in high voltage to estimate the tool surface temperature. Goud et al. (2016) showed the possibility to enhance material removal rate of electrical discharge machining process after reviewing on material removal mechanism. Hajian et al. (2016) used the magnetic field and higher voltage to make the machined surface smooth at lower electrolyte concentration and to increase the machining depth. Elhami and Razfar (2017) reported that ultrasonic amplitude of 10 μm reduced the thickness of gas film about 65% and achieved the minimum value of gas film thickness during drilling of soda lime glass by using a drill bit of 0.5 mm diameter.