Microbial-based cutting fluids as bio-integration manufacturing solution for green and sustainable machining

Metal working fluids in machining operations, also called cutting fluids (CFs), accomplish the main functions of lubrication between the tool and the work material, cooling down the cutting zone, and washing away the chips from the cutting area. Traditional CFs are either entirely based on mineral oils or, for water-based CFs, contain up to 10% mineral oils. Over time, CFs become contaminated by foreign substances, including bacteria and fungi, causing rancid odour in the work environment and health hazards for the machinists; this contamination is countered by adding biocides, which in turn can be polluting and unhealthy. Conventional CFs, therefore, are potentially pathogenic for humans, deteriogenic for the environment, and costly to dispose of due to the mineral oil and biocide contents. As the global CF consumption amounts to over two million tons/year, the development of greener, more sustainable CFs is highly desired in the manufacturing industry. In this paper, the replacement of mineral oil in CFs with suitable microorganisms providing the lubrication function is studied within a bio-integrated manufacturing approach, with the aim to markedly reduce the negative impact conventional CFs on environment and human health. The turning trials were performed on AISI 1045 steel bars under Small Quantity Lubrication (SQL) conditions using a microbial-based CF containing a microalgae species as lubricant component. The viability and effectiveness of utilising the novel microbial-based CF was positively demonstrated. The cutting forces, tool wear level, surface finish and dimensional accuracy achieved with the microbial-based CF were comparable to or better than for dry cutting and conventional CF.