Influence of Rolling Speed Upon Friction in Cold Rolling of Foils

A theoretical model for simulation of the cold rolling process is presented. A characteristic part comprises the coupling of the bulk plastic deformation and the local plastic deformation of the strip due to impression of roll surface asperities into the work material. The lubricant, which in this case is a liquid, is modeled as a Newtonian fluid. The shear stresses at the roll/strip interface will he a function of the real area of contact, the shear stresses from boundary lubrication and internal shearing in the lubricant film. Simulations have been carried out for rolling with different speeds. The result is a diagram that can be interpreted as a Stribeck curve for cold rolling. The mean friction coefficient in the roll bite decreases with increasing speed to a minimum value i.e., mixed film lubrication prevails. For higher speeds the friction coefficient increases (hydrodynamic lubrication). The influence of roll surface roughness, thickness reductions, and viscosities of lubricant upon the Stribeck curve is also studied. It is concluded that the model can be used to find optimal combination of process parameters for the cold rolling process.