PVD hard coatings applied for the wear protection of drawing dies

Cold drawing is a standard technique for manufacturing of copper profiles, the components of large segmented commutators using the conical dies with a half reduction angle of 10°. Adhesion wear of the working surface of the die was observed at the positions of highest contact pressures. We tried to improve the wear resistance of such dies by deposition of CrN. The TiAlN, TiAlN/a-C and a CrN/a-C double-layer hard coating were also tested for comparison. The performance tests were made under real manufacturing conditions in the Kolektor factory in Idrija (Slovenia). We found that a rather thin hard coating is enough to increase the lifetime of cemented carbide die by more than 100%. Scanning electron microscope (SEM) was used to determine the coating thickness of polished cross-section and damages of worn dies after service. The roughness of the die working surface was measured on half dies (longitudinally cut) by profilometer.