Analysis of biobased cooling lubricants in milling stainless steel for aerospace applications - A study of tribology and performance

Due to high thermomechanical loads, metal cutting processes generally require cooling and lubrication solutions to minimize friction between tool and workpiece. Nowadays, the standard in industry is the application of mineral-oil-based coolants, which represent a significant share of the CO<inf>2</inf>-footprint in production systems in terms of their extraction, fabrication and disposal. The demand for ecological innovations pushes the manufacturing sector to apply sustainable and health compatible coolant alternatives based on renewable vegetable oils for safer work environments and greener production systems. In this work, both mineral-oil-based cooling lubricants and several water-miscible emulsions based on vegetable oils were prepared and tested regarding their suitability for milling tasks of aircraft stainless steels. Therefore, comprehensive tribological investigations were carried out to determine the friction conditions in the contact zone between the tool cutting edge and the workpiece. Additionally, extensive experimental investigations were carried out to measure the process forces and the resulting tool wear as technical performance indicators of the cooling lubricants during machining. The study shows the significant potential of bio-based cooling lubricants as high-performance alternatives to conventional cooling lubricants when milling aircraft stainless steels, regarding the improvement of the tribological system of machining processes and the work environment.