Asperity deformation, lubricant trapping and iron fines formation mechanism in cold rolling processes

Contact conditions in cold rolling are decisive to improve quality and final aspect of rolled strip. The control of contact conditions is obtained by a good combination of process parameters, such as normal and tensile force, forward slip and lubrication regime. To understand and to optimise contact at roll–strip interface, a simulation test was developed in our laboratory. The upsetting rolling test (URT) permits reproduction of the main contact conditions for cold rolling. The URT is able to simulate and to define the influence of rolling parameters on the iron residue quantities, and on the quality of the final surface. In accordance with finite element simulations, we can estimate a mean Coulomb’s friction coefficient. A very good correlation was found between experimental and numerical results. A complementary finite element model has been developed to predict the local behaviour of surface asperities during cold rolling. In this simulation at local scale, the roughness and trapping of lubricant are introduced, in addition to the pressure force and forward slip. It has been found that forward slip and reduction ratio modify the plastic strain behaviour of asperity through pressure and shear force. Thus, we are able to define the quantity of iron residues, as a function of the local plastic strain and the plastic energy solutions.