Experimentation and Analysis into Micro-Hole Machining of Ti-6Al-4V by Micro-EDM Using Boron Carbide Powder Mixed De-Ionized Water

Experimentation and Analysis into Micro-Hole Machining of Ti-6Al-4V by Micro-EDM Using Boron Carbide Powder Mixed De-Ionized Water

G. Kibria (Mechanical Engineering Department, Aliah University, Kolkata, India), I. Shivakoti (Mechanical Engineering Department, Sikkim Manipal Institute of Technology (SMIT), Rangpo, East Sikkim, India) and B. Bhattacharyya (Production Engineering Department, Jadavpur University, Kolkata, India)
DOI: 10.4018/ijmmme.2014010102
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Abstract

In micro-electrical discharge machining (micro-EDM), dielectric plays a significant role during the machining process as different types of dielectrics encounters different chemical compositions, cooling rates and dielectric strengths. Therefore, while employing these different dielectrics, dissimilar process responses are accounted when machining in EDM at micron level. The present paper investigates micro-EDM characteristics such as material removal rate (MRR), tool wear rate (TWR), overcut (OC), taperness and machining time (MT) during micro-machining of through holes on Ti-6Al-4V superalloy employing de-ionized water based dielectric other than conventional hydro-carbon oil i.e. kerosene. The paper also includes the comparative study of the micro-EDM machining characteristics employing boron carbide (B4C) powder as additive in de-ionized water dielectric at different discharge energies. The results show that MRR and taper of micro-hole are better and TWR is less employing B4C additive in the dielectric than pure one, i.e. the productivity is improved and same micro-tool can be used for machining an array of micro-holes. Surface topography and recast layer formed during micro-hole machining by micro-EDM has also been investigated based on optical and SEM micrographs. Energy dispersive spectroscopy (EDS) analysis of machined surface as well as tool electrode surface has been done and the results show that there is significant amount of infusion of tungsten element onto the machined surface. A significant amount of carbon element is found onto the tool electrode surface.
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1. Introduction

With the trend of rapid development of micro-machining technology, the demand of precision miniaturized products has grown tremendously. Again, the innovation of hard-to-machine materials has thrown a challenging task to the manufacturing engineers to fabricate micro-components by micro-machining of these materials. Micro-EDM is one of the established and emerging advanced micro-fabrication processes, which are being utilized to manufacture micro-sized features in products made of hard materials like titanium superalloys, etc. Micro-EDM utilizes the spark erosion phenomenon for removing material from electrically conductive workpiece through a dielectric medium. As the material removal process is non-contact type between the micro-tool and workpiece, it produces no mechanical stresses in workpiece, thereby reducing chatter or vibration problems during machining.

Since micro-EDM process is performed into a dielectric fluid, the types of dielectric fluids influence the machining performances criteria. Typically, in EDM, generally hydrocarbon oil kerosene is used as the dielectric fluid. However, in micro-EDM, the use of kerosene dielectric creates several problems such as (1) deposition of carbide layer on workpiece surface that reduces material removal rate, (2) adhesion of carbon particles on micro-tool surface that makes the discharge inefficient and (3) formation of harmful vapours such as CO and CH4 that create toxic environment around the machining area, etc. (Zhang et al., 2006; Chung et al., 2007). To promote better micro-machining performances and safe machining environment, experimental investigations are going on employing different non-hydrocarbon based dielectric oils. The oxygen-based fluid, i.e. de-ionized water is one of them that can be applied as dielectric liquid during micro-machining in EDM. The oxygen-based dielectrics improve the electrical discharge phenomena in the machining gap and further results in better machining efficiency in EDM (Kunieda et al., 1991; Chen et al., 1999).

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