Study of discharge characteristics and multi objective optimisation of machining parameters in ultrasonic vibration assisted micro electrical discharge machining

Abstract

Micro-EDM is a non-traditional manufacturing technique that uses the heat energy of the plasma to remove material. When there is a sufficient electric potential between two electrodes, the dielectric in between becomes ionised, resulting in the formation of a plasma channel. The net discharge energy produced is the result of the current and voltage present at the inter-electrode gap (IEG). The current and voltage waveforms obtained from the oscilloscope are used to calculate the discharge energy. A small part of this discharge energy gets converted as plasma temperature, which facilitates material removal in micro-EDM. Because plasma is the only source of heat, its properties must be studied. In the present study, Optical Emission Spectroscopy is used to calculate the temperature of the plasma. This article explores the scope of a hybrid micro EDM process, where an ultrasonic vibration is integrated to the tool electrode. A systematic approach using Response Surface Methodology is employed for modelling and analysis of plasma properties and material removal in micro EDM. Two types of input parameters were chosen: Voltage and pulse on time being the electrical parameters, and Amplitude and Frequency as the vibrational parameters. Dielectric used is deionised water. A single spark experiment was performed on Nitinol Shape Memory Alloy and tool used was of same material. Ultrasonic vibration was provided to the tool using a piezoelectric actuator. It was found that electrical parameters have a significant impact in determining plasma properties and material removal properties. Vibrational parameters play a vital impact in enhancing the crater’s surface features.