An investigation into the behaviour of selected boundary regime lubricants when cold forging steel under rolling-sliding conditions

A study of PVD coatings, solid-in-liquid suspensions, and an ashless phosphate ester in oil at the upper die- workpiece interface when cold rotational rotary forging martensitic steel. The aim was to gain tribological insight for advanced near net-shape process development. The test method was a cylinder upsetting operation using an industrial-scale press, and lubricants were applied via in-process spraying. Forming cycle torque requirements were lowest when water-based suspensions were employed. However, there was a positive correlation between friction and homogeneity of through-thickness deformation, and oil-based dispersions generated superior surface roughness. A tribological synergism occurred using MoS2 micro-platelets and an ashless phosphate ester mixed in mineral oil. This lubricant achieved higher quality surface finish and greater protection against adhesive wear than did each component dispersed separately.