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Top1. Introduction
Abrasive Water Jet Machining (AWJM) is one of the non-traditional machining methods which offers wide range of advantages and considered as promising method for machining difficult-to-machine materials. It does not result in heat affected zone and involves minimum reactive forces. In AWJM, the material is removed by erosion process by the action of high-speed water jet mixed with abrasive particles. The high-speed water jet transfers the kinetic energy to the abrasive particles (typically garnet) and both impinge on to the workpiece (Momber and Kovacevic, 1998). Garnet is frequently used as an abrasive, since it is relatively hard, sharp edged, flowability, availability and reasonable cost (Kanthababu and Chetty, 2006). Commercially, garnet is available in three grades namely mesh # 80, mesh # 100 and mesh # 120. Researches and manufacturers used AWJM process for machining different materials for various applications (Wang, 2003). However, less attention is given in machining of graphite using AWJM. Graphite has unique combinations of properties which includes chemical inertness, high resistance to thermal shock, excellent oxidation resistance, corrosion resistance, high heat conductivity, etc. Graphite is widely used as jigs and fixtures in the electronics industries, spectrographic and electron microscopy components, nuclear research materials, space craft components, rocket nozzles, etc. (Pal and Mukherjee, 1979). Due to the highly abrasive nature of the graphite it leads to severe tool wear during machining with conventional cutting tools. Therefore, researchers and manufacturers preferred non-traditional machining methods for machining graphite.
Literature review related to machining of brittle materials using AWJM, the effect of different size of abrasives and optimization of machining process parameters are briefly presented here. Conner et al (2003) investigated the surface quality and kerf characteristics by varying AWJM process parameters on graphite/epoxy composite sheet. They found that traverse rate is having a significant influence on the kerf quality. They also observed that low traverse rate and finer abrasive mesh size generally yields smoother cut surfaces. Kanthababu and Chetty (2006) studied the influence of single mesh size abrasives in AWJM of Aluminium 6063 T6. They found that single mesh size abrasives behave similar to that of the multi-mesh size in achieving depth of cut, while surface roughness (Ra) is mostly influenced by the single mesh size abrasives. Selvan and Raju (2011) have studied the influence of AWJM process parameters on Granite. They found that high pressure yields in increased depth of cut. They also found that increase in the abrasive mass flow rate in the selected range increases the depth of cut, while the increase in the traverse rate decreases the depth of cut. Ramulu and Arola (1994) studied the influence of AWJM process parameters on kerf taper and Ra while machining graphite/epoxy laminates. They found that the AWJM process parameters are significant with increase in the depth of cut. They also found that high pressure and low traverse rate result in high surface quality while machining thick laminates. From the literature review, it is also observed that the significant input AWJM parameters are found to vary with workpiece material and various combinations of machining parameters.