Electrical Impedance Modeling of Electrochemical Spark Micromachining Process

Electrical Impedance Modeling of Electrochemical Spark Micromachining Process

Anjali Vishwas Kulkarni (Indian Institute of Technology Kanpur, India)
DOI: 10.4018/978-1-5225-1639-2.ch012
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Abstract

Electrochemical spark micromachining (ECSMM) process, an advanced machining process, has been used for micromachining. Various kinds of machining power sources, different workpiece materials and different tool materials have been used to study the performance of the process. The nature of the sparking has been investigated by studying the online, transient process current in synchronization with the machining supply voltage. Based on the study of the transient current, the spark formation process is identified as discrete and repetitive. The spark formation comprises of many physical and chemical phases in a single spark cycle. The online process current has been mathematically analyzed to formulate the electrical model of the process to understand the overall process mechanism. The electrical impedance in each phase of a single spark cycle is modeled. This semiempirical modeled impedance is compared against the impedance computed by taking the ratio of the measured online voltage and current data during single spark formation.
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Introduction

The electrochemical spark micromachining (ECSMM) process is an advanced microfabrication process, suitable for machining of wide range of materials. The modeling of the process in the light of electrochemistry (Fascio, Wuthrich, & Bleuer, 2004), heat source (Basak & Ghosh, 1992; Jain, Dixit, & Pandey, 1999; Yadav, Jain, & Dixit, 2002) have been performed by various researchers. However the holistic approach is lacking in understanding the process mechanism as the material removal mechanism in ECSMM is a complex phenomenon. Moreover, sparking is not a continuous process as it is considered; rather it is a discrete phenomenon. Complexity arises primarily due to the presence of various physio-chemical phases involved in forming the discrete sparking and secondly due to the non-thermal nature of these sparks. In the existent literature, the spark energy is considered to be of thermal nature. Also the thermal analysis and material removal are considered to be due to this thermal source (Basak & Ghosh, 1992; Jain, Dixit, & Pandey, 1999). But this is not the case as it has been found experimentally that the spark is a non thermal discharge. This has been established (Kulkarni, 2009) while making an attempt to measure the spark temperature by a pyrometer. Pyrometer failed to measure the temperature as the radiation is a non thermal type. Instead it is a repeated discharge process similar to that of the breakdown of the hydrogen gas bubble isolating the tool tip from the surrounding electrolyte. Moreover electro chemical systems are known to exhibit complex non-linear behavior. These nonlinearities arise due to electro hydro dynamism, ionic reactions, bubble generation, their growth and their breakdown phenomena. The spark formation cycle is a series of such activities. The present mechanism has been studied by presenting the electrical impedance during each phase of one cycle of the spark formation. The electrical impedance in each stage of a single spark cycle is modeled using MATLAB software. This semiempirical modeled impedance is compared against the impedance computed by taking the ratio of the measured on line, transient and synchronized voltage and current data during single spark formation.

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