Experimental and modelling study of friction evolution and lubricant breakdown behaviour under varying contact conditions in warm aluminium forming processes

Abstract

The lubricant behaviours under varying contact conditions were investigated by conducting pin-on-strip tests between P20 tool steel and AA7075 aluminium alloy using an automated testing system, Tribo-Mate. The effects of temperature changes, and rapid load and speed changes on the coefficient of friction (COF) and lubricant breakdown phenomenon were experimentally studied. The evolutions of COF showed three distinct stages, indicating the transformation from boundary lubrication condition to dry sliding condition. The value of COF at the initial stage was found to increase with increasing temperature. The increase of temperature, contact load and sliding speed caused an earlier breakdown of the lubricant. An interactive friction model was developed to predict friction evolutions at varying contact conditions. A close agreement with errors less than 6.8% were achieved between the model predictions and experimental results.