Investigation on friction behaviour of deep drawing radii using volatile media as lubricant substitutes

Abstract

Abstract Understanding and controlling tribological systems and thus the friction conditions during deep drawing processes represent two important challenges for stable and economical forming processes. In order to optimise the friction conditions in sheet metal forming processes, mineral oils with additives and oil-water based emulsions are usually used. When using such conventional lubricants two major disadvantages may emerge on the one hand, environmental aspects due to the partly environmentally hazardous additives have to be considered and on the other hand, cleaning steps after forming processes to enable further production steps such as welding, gluing and painting are not avoidable. To solve these problems, the Institute for Metal Forming Technology (University of Stuttgart) is currently investigating the use of volatile media as lubricant substitutes. Thereby, media are used which volatilise into the gaseous state without any residue after forming. In the present work, friction conditions at tool radii are particularly considered, since highest surface pressures between workpiece and tool usually occur at these areas. In this context, the work deals with experimental investigations on the tribological friction conditions at tool radii while using volatile lubricants, such as CO2 and N2. To keep the multitude of possible influences on the tribological system as low as possible, the investigations were carried out on a deflected strip-drawing testing rig. The aim of the investigations was the characterization of the tribological system and the friction conditions at tool radii under varying boundary conditions such as surface pressure and injection angle of the lubricant.