Novel experimental set-up to investigate the wear of coatings for sheet metal forming tools

摘要

The use of hard coatings to improve the service-life of forming tools has increased significantly in metalforming processes, both for bulk- and sheet- metal applications. However, while the knowledge on the most relevant coating technologies, namely the Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD), has been developed and improved, the approaches to select the coatings for a specific forming operation still remain not well established, being mainly based on trial and error experiences. Finite Element Method (FEM) analyses may represent an effective support in the coating selection thanks to the possibility of investigating the influence of the different process parameters, but the need of testing procedures and reliable models to describe the mechanical and tribological phenomena at the interface between the dies and the workpiece is still relevant. The paper presents a novel experimental set-up for the evaluation of the wear resistance of coated tools in sheet metal forming operations. A progressive stamping process was taken as reference case and analysed by numerical simulation in order to evaluate contact pressures and sliding speed at tools-blank interface. The diamond-like-carbon coating a-C:H:Ti was chosen as reference and deposited by PVD magnetron sputtering technique. The novel set up was designed and tested by using the parameters obtained from the numerical simulation. The results showed a good correlation with tribological and mechanical stresses applied on the reference industrial case, allowing the evaluation of the coating performances.