Machinability analysis of Inconel 601, 625, 718 and 825 during electro-discharge machining: On evaluation of optimal parameters setting

In the present article, machinability of four different grades of Inconel super alloy was experimentally analysed during execution of electro-discharge machining. Experimental design was planned according to the 5-factor-4-level L(16 )orthogonal array. The following process variables were considered: gap voltage, peak discharge current, pulse-on time (i.e. pulse duration), duty factor, and dielectric circulation flushing pressure. Machinability was assessed in consideration with material removal rate, electrode wear rate; surface roughness as well as surface crack density at the EDMed work surface. Satisfaction function approach integrated with Taguchi method was attempted to determine an optimal parameters setting. Surface integrity of the EDMed specimen was studied in purview of surface morphology as well as topographical features. Material migration, formation of precipitates, grain refinement onto the EDMed surface etc. were also discussed. Additionally, direct effects of peak discharge current on various performance measures were presented graphically. Results indicated that disappointing surface morphology was attributed to the EDMed surface as compared to as received parent material). Significant carbon migration was detected at the machined surface due to pyrolysis of dielectric media. Consequently, residuals of carbides were traced at the machined surface. Material removal efficiency was found to vary from 1.8249 mm(3)/min to 36.3132 mm(3)/min for Inconel 601; from 1.3389 mm(3)/min to 29.3128 mm(3)/min for Inconel 625; from 1.1844 mm(3)/min to 31.5995 mm(3)/min for Inconel 718; and from 1.2654 mm(3)/min to 25.9459 mm(3)/min for Inconel 825. Surface roughness was found to vary from 4.9667 mu m to 14 mu m for Inconel 601; from 4.7 mu m to 11.5333 mu m for Inconel 625; from 6 mu m to 12.3667 mu m for Inconel 718; and from 3.7333 mu m to 13.2 mu m for Inconel 825. Optimal parameters setting determined as: [V-g = 80 V; I-p = 7A; T-on = 200 mu s; tau = 75%; F-p = 0.6 bar] for Inconel 625; [V-g = 70 V; I-p = 7A; T-on = 500 mu s; tau = 80%; F-p = 0.6 bar] for Inconel 718; [V-g = 60 V; I-p = 7A; T-on = 400 mu s; tau = 80%; F-p = 0.5 bar] for Inconel 601, and [V-g = 90 V; I-p = 5A; T-on = 300 mu s; tau = 70%; F-p= 0.3 bar] for Inconel 825, respectively. (C) 2019 Elsevier Ltd. All rights reserved.