Abstract
<jats:p>Introduction. Environmentally sustainable machining is crucial to improve the manufacturing sector's cost-effectiveness and resource efficiency while mitigating its negative environmental impact. The “eco-index” is a multi-criteria metric that assesses the sustainability of the electrical discharge machining (EDM) of Inconel 718 by quantifying its total environmental and economic impact using a normalized and weighted approach. The purpose of this work is to describe the eco-index for Inconel 718 EDM, which assesses sustainability through environmental indicators such as energy and material consumption, waste generation, emissions, and toxicity, as well as economic indicators including operating and disposal costs along with productivity metrics. However, there are limited studies on sustainability evaluation using the eco-index for Inconel 718 EDM processed with a hybrid nano-dielectric fluid. The methods of investigation. This study investigates the machining performance and environmental sustainability of the EDM process of Inconel 718 using a hybrid nanoparticle-mixed dielectric fluid. A hybrid nano-dielectric fluid was prepared by dispersing Al2O3 and graphene nanoparticles in an equal proportion (total concentration of 0.1%) in EDM oil using a two-step method involving SDS as a surfactant, magnetic stirring, and ultrasonication to ensure a stable suspension. Experiments were conducted on an EDM machine with a copper electrode by varying the pulse on-time (50–150 µs), peak current (3–10 A), and discharge voltage (40–50 V). Key performance responses, including material removal rate (MRR), surface roughness (Ra), tool wear rate (TW), hole cylindricity (ρ), energy consumption (E), and a weighted eco-index (EI), were evaluated to quantify the combined productivity, quality, and sustainability performance. Results and Discussion. The results demonstrate that the hybrid nano-dielectric fluid improves overall EDM efficiency compared to conventional EDM oil by promoting stable discharge behaviour, enhanced heat transfer, and efficient debris flushing, which increases MRR, improves surface finish, reduces tool wear, enhances the cylindricity of the machined hole, and lowers energy consumption, leading to a higher eco-index across most machining conditions. Surface integrity analysis using SEM revealed a substantial reduction in recast layer thickness, which decreased from 17.05 µm (base oil) to 3.91 µm (hybrid nano-dielectric fluid), indicating reduced thermal damage and resolidification. EDX further confirmed nanoparticle involvement through carbon enrichment (graphene deposition) and Al–O signatures (alumina contribution), supporting the proposed mechanisms for improved plasma stability and reduced metallic redeposition. Overall, the hybrid Al2O3–graphene nano-dielectric fluid provides an effective and sustainable approach for the EDM of Inconel 718 by balancing precision, productivity, and environmental efficiency.</jats:p>