A SELECTION METHODOLOGY FOR LUBRICATING OILS IN COLD METAL-FORMING PROCESSES

A selection methodology for the evaluation of lubricating oil performa nces has been developed in order to help engineers in the definition o f 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 lubrica ting 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 roug hness of the specimen. The tribological behaviours are related to the physicochemical characteristics of lubricating oils. Moreover, the rea ction 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) 19 98 Elsevier Science S.A.