SMART & SUSTAINABLE MACHINING USING MINIMUM QUANTITY LUBRICATION (MQL): OPPORTUNITIES AND RESEARCH TRENDS: A REVIEW

ABSTRACT MQL (Minimum Quantity Lubrication) systems have been found to be effective and environmental friendly methods of machining with low use of cutting fluids, while still producing high-quality work. As more environmentally friendly manufacturing seeks to reduce waste, significant advances in hybrid lubrication technologies, including nanofluid-based and smart-machining approaches, are enabling better performance with reduced waste. This review paper will focus on gathering and summarising up-to-date information on MQL machining, evaluating advanced lubrication/cooling strategies available today, identifying new areas of research, and outlining current gaps and future directions. A thorough review of the scientific literature, including studies evaluating results achieved with traditional MQL systems, hybrid CryoMQL systems, nanofluidassisted lubrication, hybrid nano-lubricants and machining systems based on the principles of Industry 4.0 was conducted. The performance of various machining methods was compared, including overall MQL machining performance, sustainability benefits, tool life, surface finish quality, energy efficiency and overall ease of implementation in industry. The study demonstrated that the application of hybrid CryoMQL technology offers substantial advantages over traditional cooling technologies, including longer tool life, reduced cutting temperatures (below 30%), and improved surface finish. The use of nanoparticle-enhanced lubricant products (e.g., containing graphene, CNTs, HbN, or MoS2) significantly improves lubrication and tribological performance during cutting, resulting in lower friction and reduced tool wear. Additionally, AI, machine learning, digital twins, and IoT-based monitoring systems are increasingly used in machining processes to enable realtime monitoring, predictive maintenance, and process Optimisation. Keywords: Minimum Quantity Lubrication (MQL), Sustainable Machining, Smart Manufacturing, Nano-Lubricants, Industry 4.0 Machining