A mixed lubrication model for cold strip rolling

A review for each lubrication regime in metal forming processes is given. In the "mixed" lubrication regime, part of the interface load is carried by asperity contact and part by the pressurized lubricant in surface valleys. Because of the need to control surface topography, this is the most important regime in practical metal forming.; An analytical model for cold strip rolling in the mixed lubrication regime is developed. The average Reynolds equation for Christensen surfaces with arbitrary Peklenik surface pattern parameter is combined with an analysis for asperity flattening under conditions of bulk plastic flow to treat lubrication in the mixed regime. An inlet zone analysis and the influence of pressure on viscosity as well as a viscoplastic friction model are included. By using special numerical techniques, the model can be used over a wide speed range. A simple analysis is also applied to predict the surface finish of the rolled strips by neglecting surface roughening and the effect of displaced material on the surface's geometry.; A series of oil drop tests accompanied with the roughness measurements confirm the theoretical prediction of the model. These were carried out by rolling 1100-H14 aluminum strips with purely longitudinal, purely transverse or isotropic surfaces made by lapping, pack rolling or sand-blasting. A variety of lubricants were used to cover a wide range of the non-dimensional rolling speed. The results for the lapped strips and pack rolled strips agree well with the theory while some adjustments have to be made for the hardened sand-blasted strips. Corrections to the Peklenik surface pattern parameter have to be considered in predicting the film thickness in the low speed range. The tests for the outlet speed ratio show a discrepancy between the theory and experiments for the transverse lay, possibly due to assumptions regarding asperity flattening. Both the model and experiments show that surface texture has an important effect in metal rolling.