An efficient finite element model of surface pit reduction on stainless steel in metal forming processes

The reduction of surface pits in cold metal forming processes with oil lubrication is modelled using the finite element method. The model has four key elements: an oil cavity, a rigid smooth tool, an elastic-plastic workpiece and the model for leakage of oil via the interface between the tool and workpiece. The oil cavity is modelled as one hydrostatic fluid element. The oil leakage from the pit is realized by a fluid link to the environment. This approach is much faster than previous models in which the interface is regarded as a porous elastic layer. Results confirm that the pit depth decreases with bulk strain. The reduction in the pit depth increases with decreasing pit slope or increasing oil permeability. Predictions from the model are in line with measurements of pit area taken from plane strain compression tests on stainless steel.