A selection methodology for lubricating oils in cold metal forming processes

A selection methodology for the evaluation of lubricating oil performances has been developed in order to help engineers in the definition of the right lubrication strategy. The methodology is exposed through a cold forward extrusion process with a 75% reduction in area. Specific friction tests are performed according to the physical and mechanical contact conditions characterising the extrusion process. Four lubricating oils available on the market are investigated. Three criteria are proposed to characterise the performances: the friction coefficient, the occurrence of two types of surface defects, and the resulting roughness of the specimen. The tribological behaviours are related to the physicochemical characteristics of lubricating oils. Moreover, the reaction mechanisms of the different additives and the influences on the regimes of lubrication are discussed. Finally, the optimum lubricating oil with regards to the forward extrusion process is selected. (C) 1998 Elsevier Science S.A.