Electric discharge phenomenon in dielectric and electrolyte medium

Abstract

Electric discharge is a common tool nowadays for machining of materials. It may be through a liquid medium or through air. Any metals, hard alloys, and non-metals can be machined using the energy of electric discharge. In electric discharge machining (EDM), the discharge occurs between two electrodes through a liquid medium and it is applicable only for electrically conducting materials and alloys. In electrochemical discharge machining (ECDM), the medium is an aqueous electrolyte and it is of two types. In the first type, the discharge occurs between two electrodes. One of the electrodes is the workpiece, and the other is the tool. In the second type, the discharge occurs between one electrode and an electrolyte. It is used for electrically nonconducting materials and the discharge energy is utilized maintaining the nonconducting workpiece in proximity of the discharge. All these electrical discharges are transient phenomena and do not result in a stable discharge in the form of arc. The output parameters depend on the discharge energy that requires precise control to maintain the accuracy of the machining. For micromachining, the control of the discharge is paramount both in terms of energy and pattern. Using various shaped tools, machining media with additives, different types of applied potentials, and supporting mechanical motions are some of the attempts made to improve the machining output. Optimization of these parameters for machining particular materials (or alloys) is a popular field of research. The present work is directed toward the investigation of discharge initiation and development by analyzing the cell current and discharge voltage relationship for both EDM and ECDM. The rectangular direct current (DC) pulse with different frequencies and the duty factor (on–off time ratio) are used for investigation. Observations on the voltage–current relationship are made for the external potential prior to discharge at discharge and above the discharge potential. Though the external potential above the discharge voltage is useful for machining, these observations elucidate the mechanism regarding the initiation of the electric discharge under different conditions. The manner of discharge development in dielectrics and electrolytes is observed to be different. This understanding will aid in deciding the design of the discharge circuit including the external potential and its pattern for certain desired outputs in machining.

Keywords

Electric discharge / Electric discharge machining (EDM) / Electrochemical discharge machining (ECDM) / Pulsed direct current (DC) / Duty factor

Funding

National Institute of Technology Durgapur