A critical evaluation of the double cup extrusion test for selection of cold forging lubricants

The performance evaluation of cold forging lubricants and coatings as well as determination of the friction coefficients is necessary for production as well as finite element (FE) simulations. The double cup extrusion test (DCET) has been widely used to evaluate cold forging lubricants, since it was believed to accurately emulate the practical conditions (severity of deformation and surface expansion) found in most cold forging applications. However, recent research and previous studies using finite element (FE) simulation as well as experiments indicated that the interface pressure conditions and surface generation in the DCET may not be comparable to those found in cold forging. Thus, the aim of this work was to evaluate the DCET by studying the influence of various geometrical and process parameters on the cup height ratio and contact pressure at the tool–workpiece interface. Based on this evaluation, recommendations are made on how to re-design the DCET and make it more sensitive to changes in interface friction.