Experimental Investigation on Centreless Electro Discharge Texturing of Thin Walled Inconel-600 Tubes

Introduction

Bryan and Evan (1999) defined surface texturing as producing engineered surfaces with deliberately created multiple features (micro holes, micro asperities) of sizes ranging from millimetre to nanometre with better control of surface design for the fulfilment of specific functional requirements. Surface texturing is also termed as structuring or patterning. According to OPSD Westinghouse (1982), surface texturing apart from engineered pattern, includes irregularities in the form of roughness, waviness, lay and flaws as a result of machining processes as well as due to the nature and condition of machine tools. Electro discharge texturing (EDTex) or electro-erosion texturing is a recently evolved variant of electro discharge machining (EDM) used for optimisation of surface texture along the work surface (cold mill rolls) through high degree of process control by selecting appropriate operating variables such as peak current and on-time relative to surface roughness (R_a). Gohil and Puri (2015) stated that EDTex and EDT are variants of die sinking EDM and are suitable for burr free manufacture of rotationally symmetric components of hard-fragile materials. Electro discharge turning is presently being used to produce aerospace honey-comb seals. According to Evin (2015), resultant R_a and peak count (PC) (number of peaks cm^-1) are the roughness parameters of EDTex. Characteristics of EDM process have been experimentally evaluated by many researchers. Chakraverti and Soni (1994) conducted an experimental study on EDM with rotary as well as stationary tool electrode to investigate the process behaviour. They reported that material removal rate (MRR) with rotary tool electrode increased at the cost of surface finish due to efficient spark and effective flushing action of dielectric . Qu et al. (2002, pp702-707) developed rotary spindle cylindrical Wire EDM to produce rotary symmetric parts of high strength electrically conductive materials. They found that material removal rate was higher compared to two dimensional wire electro discharge machining (2D- WEDM), and it was sensitized by spindle run out accuracies. Macro-ridges, surface craters, recast layer and heat affected zone (HAZ) were observed along the machined surface. Qu et al. (2002, pp 708-714) during their extended experimental study for roundness and surface finish, found that relatively short pulse on duration and lower feed motion were important in improving roughness and geometrical accuracies. Guu and Hocheng (2001) observed significant improvement in MRR with increase of workpiece speed (rpm) during their study of electric discharge machining of D2 steel using copper electrode.