Investigation of bio-based cooling lubricants for the machining of aircraft stainless steels

Water-miscible cooling lubricants are used in approx. 90% of metalworking processes mainly for lubrication and cooling of the contact zone between tool and workpiece. The base oils of the widely used water-miscible emulsions are often of mineral origin and represent a significant share of the CO2-fingerprint in production systems in terms of their extraction, processing and the possibility of recycling. Cooling lubricants are furthermore negatively discussed regarding to their health compatibility. Those disadvantages of conventional cooling lubricants drive the research for replacing mineral base oils with vegetable base oils, which contribute to a safer work environment and greener production. In this work, both conventional cooling lubricants and several water-miscible emulsions with various edible and non-edible vegetable-based oils were prepared and characterized regarding their suitability as cooling lubricants for the milling of aircraft stainless steels. Comprehensive experimental investigations were carried out to determine the process forces and the resulting tool wear as technical performance indicators for the test evaluation.