Influence of Workpiece Surface Topography on the Mechanisms of Liquid Lubrication in Strip Drawing

The workpiece surface topography is an important factor controlling the mechanisms of lubrication in metal forming processes. In the present work, the microscopic lubrication mechanisms induced by lubricant trapped in pockets of the surface in strip drawing are studied. The experiments are performed with macroscopic model pockets in the surface studying the influence of the shape of the pockets on the lubrication mechanisms. A large radius of curvature on the rear edge and a small angle to the edge of the lubricant pocket induce a large area of backward escape of lubricant caused by MicroPlasto HydroDynamic Lubrication (MPHDL). On the other hand, when the radius on the edge is small MPHDL is impeded and MicroPlasto HydroStatic Lubrication (MPHSL) appears instead implying forward escape of the lubricant. The occurrence of these mechanisms are quantitatively explained by a mathematical model combining a slab method of analysis of the strip drawing process and an analysis of lubricant escape by Reynolds equation.