Abstract
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 L16 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 mm3/min to 36.3132 mm3/min for Inconel 601; from 1.3389 mm3/min to 29.3128 mm3/min for Inconel 625; from 1.1844 mm3/min to 31.5995 mm3/min for Inconel 718; and from 1.2654 mm3/min to 25.9459 mm3/min for Inconel 825. Surface roughness was found to vary from 4.9667 µm to 14 µm for Inconel 601; from 4.7 µm to 11.5333 µm for Inconel 625; from 6 µm to 12.3667 µm for Inconel 718; and from 3.7333 µm to 13.2 µm for Inconel 825. Optimal parameters setting determined as: [Vg = 80 V; IP = 7A; Ton = 200 µs; τ = 75%; Fp = 0.6 bar] for Inconel 625; [Vg = 70 V; IP = 7A; Ton = 500 µs; τ = 80%; Fp = 0.6 bar] for Inconel 718; [Vg = 60 V; IP = 7A; Ton = 400 µs; τ = 80%; Fp = 0.5 bar] for Inconel 601, and [Vg = 90 V; IP = 5A; Ton = 300 µs; τ = 70%; Fp = 0.3 bar] for Inconel 825, respectively.
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