Self-lubricating PVD Coatings in Interaction with Textured Workpiece Surfaces for BulkMetal Forming

Abstract

Bulk metal forming of steel, in particular forward extrusion, is characterized by high material utilization and resource efficiency. Currently, high quantities of mostly ecologically harmful lubricants are required, leading to the demand for lubricant-free forming. Two approaches are being pursued to achieve the objective of lubricant-free extrusion of steel. One approach focuses on the tool, the other on the workpiece.With regard to the tools, physical vapour deposition (PVD) can be used to apply self-lubricating hard coatings on forming tools. The workpiece-side approach uses texturing of the workpiece surfaces. In this work, one self-lubricating PVD hard coating as well as four different textured workpieces were investigated. The coating was produced in an industrial coating unit. Using a self-designed tool model with the same dimensions as real forming dies with two extrusion shoulders, the coating thickness distribution and the change in coating properties as a function of complex geometry of the forming dies were analysed. Using a pin-on-cylinder tribometer, which represents an open tribological system and simulates the loads of dry bulk metal forming of steel, the interactions between PVD hard coatings and textured workpiece surfaces were investigated. The combination of two approaches of tool coating and workpiece texturing leading to reduction of wear and friction.