Sustainable Machining in the Era of Industry 5.0: A Unified Review of Minimum Quantity Lubrication, Nanofluids, and Human-Centric Process Optimisation for Net-Zero Manufacturing

Conventional flood cooling remains the dominant lubrication strategy in machining workshops worldwide, despite more than three decades of documented evidence concerning its environmental and occupational health costs. A single production facility may consume thousands of litres of cutting fluid annually, and the aerosol generated at the work zone carries well-documented associations with respiratory disease, dermatitis, and carcinogen exposure for operators. Over the same period, three categories of technical alternative have each developed substantial evidence bases: minimum quantity lubrication (MQL), nanofluid cutting fluids, and AI-driven process optimisation. No prior review has examined how these three strands fit together, or situated their integration within the Industry 5.0 framework, which holds that manufacturing must serve human well-being and ecological sustainability alongside productivity. This paper addresses that gap. Drawing on 125 primary publications from 2010 to 2025 identified through systematic database searches (methodology described in Section 1.1), the reviewed evidence indicates that nanofluid MQL can reduce cutting fluid consumption by 97 to 99.7 per cent relative to conventional flood cooling while achieving comparable or improved surface finish, tool wear, and cutting force outcomes across titanium alloys, nickel superalloys, stainless steels, and aluminium. This review assesses six nanoparticle classes in bio-based carrier fluids—including locally available West African oils that have received limited attention in the international literature—and examines AI and machine learning approaches for MQL optimisation with explicit attention to worker health outcomes. Eight research gaps are identified and a proposed three-horizon research agenda towards measurably low-impact machining practice by 2035 is presented.