How Suspended Particles Affect Surface Morphology in Powder Mixed Electrical Discharge Machining (PMEDM)
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LECTRIC discharge machining (EDM) is one of the extensively used, nonconventional material removal processes. It can be successfully employed to machine electrically conductive parts regardless of their hardness. A relatively new advancement in the direction of process capabilities is the addition of fine powder in the dielectric fluid of EDM. This new hybrid material removal process is called powder-mixed EDM (PMEDM) and is also termed as additive EDM. PMEDM was originally invented during the late 1970s as a revolutionary technique for achieving mirror-like surface finish at relatively high machining rates. Erden and Bilgin[1] reported the experimental and theoretical investigations to determine the effect of impurities in dielectric fluid of EDM in 1980. Copper, aluminum, iron, and carbon powder were mixed into the commercial kerosene oil as artificial impurities, and machining was performed using brass and copper electrodes on steel work material. They observed that the added powder improves the breakdown characteristics of the dielectric fluid, and so the surface quality and the machining rate increased with increase in the concentration of the added powder. However, the machining becomes unstable at excessive powder concentration due to occurrence of short circuits. Jeswani[2] investigated the effect of the addition of fine graphite powder into kerosene oil and reported that by addition of 4 g/L of fine graphite powder into the dielectric liquid increased the inter space for electric discharge initiation and lowered the breakdown voltage. Mohri et al.[3] BU¨LENT EKMEKCI, Associate Professor, and YUSUF ERSO¨Z, MSc Student, are with the Department of Mechanical Engineering, Bu¨lent Ecevit University, 67100 Incivez, Zonguldak, Turkey. Contact e-mail: [email protected] Manuscript submitted March 6, 2012. Article published online July 21, 2012. 1138—VOLUME 43B, OCTOBER 2012
indicated that a fine and corrosion-resistant surface could be produced by silicon powder addition in dielectric liquid. Narumiya et al.[4] revealed that under specific working conditions, aluminum and graphite powders yield better surface finish than the silicon powder. Schumacher[5] indicated that the powder particle facilitates the ignition process by creating a higher discharge probability and lowering the breakdown strength of the insulating dielectric fluid. Kobayashi et al.[6] investigated the effects of suspended powder in dielectric fluid on material removal rate and surface roughness. It was reported that the surface finish of SKD-61 material gets improved with the use of silicon powder. Yan and Chen[7,8] studied the effect of suspended aluminum and silicon carbide powders on EDM of SKD11 and Ti-6Al-4V. It was observed that the material removal rate improves considerably whereas the surface roughness increases. Ming and He[9] revealed that the additives (conductive and inorganic oxide particles) increase the material removal rate and decrease the tool wear rate. Uno and Okada[10] investigated the effect of silicon powder mixing on the surface generatio
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