Study of surface integrity, temperature distribution and parametric optimization during Electrical Discharge Machining (EDM) of Inconel 718, using Taguchi method coupled with TOPSIS approach

Super alloys are increasingly utilized in the nuclear, aerospace, and chemical sectors, with Inconel 718 being a prominent example. Classified as a “difficult to machine” material, it has prompted extensive research globally aimed at enhancing its machinability. Inconel 718 exhibits significant toughness, hardness, and work hardening, coupled with low thermal conductivity, which complicates its machining using conventional methods. Consequently, non-traditional machining techniques, such as Electrical Discharge Machining (EDM), are employed to address these challenges. This research aims to determine appropriate process parameters, such as Open Circuit Voltage (OCV), peak current (Ip), pulse-on time (Ton), duty factor (t), and flushing pressure (Fp), to optimize machining performance in the electro-discharge machining of the super alloy Inconel 718 utilizing a pure copper tool electrode. The experiments were structured using an L25 orthogonal array design, with each parameter adjusted across five different levels. The evaluation of machining performance was based on material removal rate (MRR), electrode wear rate (EWR), and surface roughness (Ra) of the EDMed Inconel 718 product. An innovative optimization strategy that integrates the TOPSIS method with Taguchi's philosophy has been employed in this study. The thermal analysis of the work surface generated by Electrical Discharge Machining (EDM) has been performed, indicating a notable rise in temperature at the junction of the tool and the work piece. The findings were evaluated in relation to three primary parameters: temperature distribution, directional heat flux, and total heat flux across the work surface. The hybrid Taguchi–TOPSIS optimization approach identified the optimal parameter combination as OCV = 90 V, Ip = 4 A, Ton = 350 μs, duty factor = 55 %, and flushing pressure = 0.4 bar, which yielded improved machining performance. The optimization resulted in a maximum material removal rate (MRR) of 87.541 mm 3 /min with reduced electrode wear rate (EWR) and surface roughness (Ra) compared with other experimental conditions. Furthermore, the thermal and SEM analyses revealed lower surface crack density and reduced white layer thickness under optimal machining conditions, indicating improved surface integrity of the EDMed Inconel 718 surface.