A comparative study of surface deformation and quality of brass workpiece in contact with coated dies by pin-on-disc testing

Abstract

Manufacturing technology must ensure the production of parts with required characteristics: dimensional accuracy, overall strength, and surface quality. The surface layers in metal forming generally remain at the surface. The quality of the deformed surface is therefore determined by the initial surface and the history of the various forming processes undergone. Surface roughness influences surface quality and wear of metal forming products. Pin-on-disc tests at a range of temperatures were employed to study the influence of die coatings on the surface quality of a two-phase brass alloy during forging operation. The pins were made in H13 hot work tool steel and given duplex surface treatments including plasma nitriding and physical vapor deposition (PVD) coatings. The discs were machined from CuZn38Pb2 forging brass. Mechanical properties, surface roughness, and compositional properties of pins were determined by nanoindentaion, two-dimensional profilometer, and scanning electron microscopy equipped with energy-dispersive X-ray detector, respectively. At 25 °C, wear track parameters were more affected by the changes in Young’s modulus and the surface roughness of the pins. At 250 °C, the highest tendency to adhesion was observed in H13 steel pin. At 700 °C, oxidation of the pins influenced the wear track parameters on the discs. R a parameters inside the wear tracks were constant at 25 and 250 °C, but R ku parameters were maximum for the wear tracks of disc in contact with plasma nitriding and H13 pins at 25 and 250 °C, respectively. At 700 °C, the lowest surface quality was for the disc in contact with H13 steel pin. It was concluded that in forging process of brass alloys, the surface quality and deformation behavior of workpiece were improved by applied PVD coating on the surface of the die.