Investigation on the sliding of aluminium thin foils against PVD-coated carbide forming-tools during micro-forming

This paper reports an investigation on the tribological properties of Al thin foils (0.2 mm nominal thickness) in sliding contact with PVD-coated carbide forming-tools, with reference to the applications in the manufacture of miniature/micro-products, particularly through micro-forming. The study addresses the evolution of the friction coefficient between both surfaces under dry lubrication conditions, its influence on the surface quality of the processed material and the damage produced on the tool due to sticking phenomena. Uncoated, CrN-coated and WC-C-coated tools were tested, using a pin-on-disc configuration to monitor the evolution of the relative friction coefficients under different contact pressures. It was shown that the contact sliding of Al foils on the untreated carbide tool produced a significant transfer of Al to the tool, leading to a rapid degradation of both tool and foil surfaces, even faster than that produced on bulk aluminium. Conversely, the sticking of Al was retarded using low friction magnetron sputtered WC-C-coated carbides. Other PVD coatings such as CrN failed under similar operation conditions. Aluminium transfer to the WC-C-coated tool surfaces during sliding seemed to be a non-continuous process, which appeared after certain sliding distances. Temperature accelerated the Al transfer to the WC-C tool surfaces, probably due to the increase of the thermoplastic behaviour of Al above 100 °C, which led to an increase of the adhesive interaction with the WC-C coating.