Electrochemical Micromachining Performance Optimization: Impact of Cathode Profile and Rotation on Machining Speed and Accuracy

Introduction

Micromachining is a technology deals with machining of conducting materials in micron range. The micro machined components finds application in biomedical, automobile, defence and ornamental industries. Among various micromachining techniques electrochemical micromachining (ECMM) is found to be superior for its advantages of no tool wear, higher machining speed, good surface finish and no residual stress. ECMM works on a principal of Faradays law of electrolysis in which cathode act as tool electrode and workpiece is considered as an anode (Jain et al. 2012). The material removal on the workpiece takes place due to ions dissociation with the help of applied voltage. In ECM process a cathode material is chosen based on the ability to permits the electrolytic breakdown of water and liberation of hydrogen. The hydrogen bubbles evolution and the electrolysis of water produces hydroxide ions. The ions from the anode combine with hydroxide ions formed from the electrolysis of water to produce metal hydroxides. These precipitate away of the electrolyte, eliminating the ions from the electrolyte and avoiding them from cathode deposition (Leese & Ivanov 2016). In ECMM process the anodic dissolution takes place in the range of size 1-999µm with applied voltage in the range of 0-10 Volts (Bhattacharyya et al.2004). The narrow gap between the cathode and anode place an important role in material removal and it is called inter electrode gap (IEG). The optimized gap is essential for achieving higher material removal rate (MRR), by increasing the IEG the MRR is significantly affected. The electrolyte namely active and passive electrolyte is considered in the ECMM process (Shunmugam & Kanthababu, 2019). Passive electrolytes such as sodium nitrate, sodium chlorate, weak acid were considered for ECMM apart from active electrolytes (strong acids such as sulphuric acid, hydrochloric acid and sodium chloride). In case of ECMM the stagnant electrolyte is found to show more efficacy compared to flow electrolyte. Sometimes pulsating electrolyte flow is also preferred over the continuous flow of electrolyte. The electrolysis is initiated by potential difference between the electrodes, there are two types of power supply considered for the ECMM namely direct current and pulse power supply. The pulse power supply is found to be suitable for micromachining which offer higher MRR and good surface quality. The pulse power supply in the range of millisecond, microsecond and nanosecond were used for the machining based on the application. The various factors that affect the performance of ECMM are machining voltage, current, pulsed power supply, electrolyte type, temperature and concentration, cathode profile, IEG gap width and workpiece material. In this chapter the effect of cathode profile and rotation is discussed, since in ECMM process cathode shape, temperature, coating and rotation has shown the significant improvement in the MRR and accuracy. The fishbone diagram shown in figure 1, shows the input parameters for improving the ECMM performance.

Figure 1.

Fishbone diagram for ECMM

(Source: Reprinted from Arunchalam et al 2018)