Combination of PVD tool coatings and biodegradable lubricants in metal forming and machining

The main goal of the work presented in this paper is to enable the use of biodegradable, additive-free lubricants for metal forming and cutting processes. Deficiencies in the tribological performance of these alternative cutting and forming lubricants shall be compensated for by the application of newly developed PVD tool coatings. In doing so, some of the functions that the lubricant used to perform, especially wear protection, need to be transferred to the coatings. In order to test many different coatings and lubricants under the tribological conditions of metal forming and cutting processes, a tribometer based on the pin-on-disc set-up has been developed. In the field of metal forming, fundamental studies based on SEM and TEM analysis have been carried out which describe the mechanisms of adhesive wear and the mechanism of possible coating failures. On the basis of these mechanisms, it is possible to determine what is required in the development of coatings and lubricants. In addition, example results from the lubricant tests are presented with respect to wear and friction behaviour. The application of PVD coatings in machining operations represents the state-of-the-art. Consequently, ester-lubricated turning and drilling tests have been carried out using many different PVD coatings. Besides conventional coatings, newly developed multilayer systems that are mainly based on TiAlN and amorphous Al2O3 have been used. Pre-selections have been made using the tribometer. Example results from both the tribometer and cutting tests are presented.