An Experimental Investigation during Micro Machining of E-Glass-Fibre-Epoxy Composite on Developed Electrochemical Spark Machining Setup

An Experimental Investigation during Micro Machining of E-Glass-Fibre-Epoxy Composite on Developed Electrochemical Spark Machining Setup

Alakesh Manna (PEC University of Technology, India) and Vivek Narang (PEC University of Technology, India)
DOI: 10.4018/ijmmme.2012040103
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Abstract

In the present research, specially designed square cross-section with centrally micro hole brass tool and different diameter round shape micro tools made of IS-3748 steel were used for micro electrochemical spark machining (ECSM) of electrically non conductive e-glass-fibre-epoxy composite. To analyze the influences of the various process parameters of ECSM setup, the specific numbers of experiments have been carried out on developed ECSM setup. The ECSM performance characteristics such as material removal rate, hole depth, and over-cut on hole radius during machining of e-glass-fibre-epoxy composite under varying process parametric conditions are reported in this paper. From the test results, it is found that at higher setting value of D.C. supply voltage, moderate setting value of electrolytic concentration and 180 mm gap between tool (cathode) and auxiliary electrode (anode) the material removal rate is higher. Utilizing the test results mathematical models for MRR and over-cut on hole radius have been developed to express the effect of ECSM process parameters. Different SEM photographs of the micro holes show the surface texture of the machined holes and shape of the generated special shape contour.
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1. Introduction

Advanced engineering materials like ceramics and composites are gradually becoming very important materials for their scope and use in aerospace and automotive industries due to their high fatigue strength, thermal shock resistance, high strength to weight ratio, etc. However, with the rapid technological acceptance of ceramics and composites in industrial applications, the machining of ceramics and composites have been of ardent importance for modern manufacturing engineers and applied researchers working in this field. The different traditional methods are usually employed for producing the composite and ceramic parts but it has been difficult to achieve necessary tolerance and other closer dimensional accuracy feature in practice through such processes. Again, e-glass-fibre-epoxy composite is an electrically non-conductive material and conventional machining of fibre-epoxy composites leads to delamination and fuzzing. Even non conventional machining processes like EDM, ECM, WEDM, etc., are not suitable to machine electrically non conductive materials. Therefore, to meet the requirement of machining of the advanced e-glass-fibre-epoxy composite a hybrid machining setup has been developed and utilized for experimental investigation. This hybrid machining process is known as electrochemical spark machining (ECSM) process.

The basic principle of material removal in ECSM process is electrochemical dissolution of the work-piece due to the combined effects of electrochemical reaction and electrical spark discharge action. This combined effect takes place when applying sufficient D.C. voltage to the electrolytic cell in proper polarity, i.e., positive terminal connected to the auxiliary electrode (anode) and negative terminal connected to the tool (cathode). When the applied voltage reaches beyond a certain level reduction of electrolyte take places and liberates hydrogen gas bubbles at the cathode, and generates electrolytic gas around the surface of the electrode. There is evolution of oxygen gas and formation of oxide films at the auxiliary electrode surface while machining of electrically non-conducting materials. When the number of hydrogen bubbles formed at the electrode becomes sufficiently large, the resistance at the tool-electrolyte interface becomes very high due to constriction caused by the insulating effect of the gas bubbles. This leads to an increase in the Joule heating around the tool electrode to temperature levels which cause formation of electrolyte in vapors. This leads to formation of a spark due to the inductance in the tool-electrolyte circuit similar to that in an electrical circuit.

From the literature survey, it is evident that some research on electrochemical discharge machining (ECDM) has been carried out by the previous researchers but still a lot of applied research in the above field is required so as to explore the successful utilizations of the process in the area of machining of non conductive materials. Keeping in view some of the published research works in brief are listed.

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