Experimental studies on electro-discharge machining of Inconel 825 super alloy using cryogenically treated tool/workpiece

Abstract

The present work studied effects of Cryogenic Treatment (CT) of tool/workpiece on machinability of Inconel 825 super alloys during Electro-Discharge Machining (EDM). The ease of machining was evaluated in terms of multiple performance features viz. Material Removal Rate (MRR), roughness average (Ra), Surface Crack Density (SCD) and White Layer Thickness (WLT) developed over machined surfaces. Considering three process parameters namely, peak discharge current (Ip), pulse-on duration (Ton) and duty factor (τ), EDM experiments were conducted using the following tool/work combinations: (i) Normal Tool and Normal Workpiece (NTNW), (ii) Cryogenically Treated Tool and Normal Workpiece (CTTNW), and (iii) Normal Tool and Cryogenically Treated Workpiece (NTCTW). Apart from investigating parametric effect on various machining responses, attempt was also made to carry out a comparative study on chemical composition, metallurgical aspects, residual stress and micro-indentation hardness of the machined specimens obtained by using NTNW, CTTNW and NTCTW, respectively. Effects of cooling rate (ramp-down) during cryogenic treatment cycle of the workpiece were also examined. Morphology of the machined surface was studied through scanning electron microscopy. Moreover, effects of cryogenic treatment of tool electrode were discussed from the viewpoint of shape retention capability, wear and extent of carbon deposition onto the bottom surface of the tool electrode.