An Insight on Current and Imminent Research Issues in EDM

1. Introduction

Electrical discharge machining (EDM) is one of the most extensively used non-conventional material removal processes.EDM mainly consists of two major components: machine tool and a power supply (Figure 1). The machine tool holds a shaped electrode and a workpiece whereas power supply provides energy for performing the machining. The power supply uses a transformer to convert AC supply to DC supply through rectifier. Based on type of polarity namely straight polarity and reverse polarity either terminal of power supply is connected to electrode and workpiece.

Figure 1.

Schematic diagram of EDM

Both the electrode and workpiece are completely submerged under dielectric. The commonly used dielectric are hydrocarbon oil, silicon based oil and de-ionized water. A servo controller is used to maintain a constant gap between the electrode and workpiece. Depending upon the voltage and the gap an electric field is established between the tool and workpiece (Yunxiao et al., 2018; Jha et al., 2011). As the electric field is established free electrons on the tool are subjected to electrostatic forces and electrons having less bonding energy are plucked out from the tool and accelerated towards the workpiece through the dielectric medium. As they gain more velocity while moving towards the workpiece, collisions occur between the electrons and dielectric molecules resulting in the ionization known as dielectric breakdown (Hamid, 2017; Ganguly, 2012). This cyclic process increases the concentration of electrons and ions at the gap creating a channel known as “plasma”. The electrical resistance of plasma is very less, therefore electrons with high energy move from negative terminal to positive terminal and highly energize ions will flow from positive to negative terminal. The kinetic energy of the electrons and ions on impact with the surface of the work and tool gets converted into thermal energy which increases the temperature of workpiece and tool resulting in erosion of material due to instant melting and vaporization of the respective material. The material is removed in form of debris. When the power supply is withdrawn, the plasma channel expands and collapsed generating pressure which flushes the debris out from machined surface (Ganguly, 2012). Simultaneous erosion of workpiece and tool increases gap between them and thus the electrode is lowered automatically by servo controller to maintain this gap and the process continues. One of the main advantages of this process is that there is no direct contact between tool and workpiece and thus there is no forces in machining and even soft and delicate materials can be machined. EDM is widely used in machining of dies, moulds, parts of aerospace, automotive industry and surgical components. Important trends in EDM was marked in 1990 and since then numerous works have been established in EDM (Rajurkar, 1994). Irrespective of wide use of EDM, there is still a scope of improvement in line with latest developments in areas of science and technology. Based on this important research areas are identified and addressed in this chapter. Section 2 presents these research issues in detail and section 3 summarizes the study undertaken. An insight on few important future research issues is also presented in section 4.

2. Various Research Issued In Edm

For convenience of understanding various issues are presented separately in subsections: