Evaluation of cam and roller surfaces by wear testing and functional characterisation

Paper in proceeding, 2008

Friction and wear are constant problems encountered in camshaft development. The contact between roller and cam is a mix of sliding and rolling which leads to a wide range of failure modes. The uniqueness of this contact is also due to variations all around the cam of a multitude of parameters such as load and radius. A previous study described surface topography as a function of cam shape. The different types of wear mechanisms are strongly linked to contact pressures which are also dependent on roughness. The aim of the paper is to develop a rough contact model which will be utilized as a tool to rank surfaces and their ability to face wear problems. In order to verify the tool, rough contact results are compared to roughness parameter variations due to wear produced in a cam roller rig test. The surface measurements used for this study are made by a non-contact light interferometer. The Greenwood-Williamson contact model has been developed in a deterministic way and the elasto-plastic behaviour of the material has been integrated to the model. The outputs of the simulation give a ranking of surfaces which is compared to their roughness variations due to wear. The study shows that the model developed is a reliable tool to rank and define surface quality since the results are correlated to wear. However, the results show as well some discrepancies which could be corrected in the future by integrating to the model two new features: a rough to rough contact including sliding between surfaces. This new model should be verified by an accurate experimentation using relocation between unworn and worn surfaces.