Performance of low-friction coatings in the dry drilling of automotive Al–Si alloys

摘要

Due to the high financial and environmental cost of cutting fluids, there is a considerable driving force in many machining industries for a reduction in their use. However, any such reduction will be commercially acceptable only if the overall performance of machining operations can be maintained in dry conditions. This might be achieved through the use of coatings on cutting tools. TiB2-based coatings have been promoted as effective in improving the performance of tools used to machine Al alloys. In this work such coatings were deposited on high-speed steel drills by closed-field unbalanced magnetron sputter ion plating. Further drills were coated with commercial low-friction Graphit-iCi, and Dymon-iCi or MoSTicoatings, and others left uncoated. These were tested in the dry drilling of automotive Al–Si alloys. The measured performance criteria were the tool lifetime and the dimensional accuracy of the drilled hole. Endof- tool-life in most cases was brought about by blockage of the drill flutes with adherent Al. Results show that, while all the coatings offer significant improvements over uncoated tools, exceptional results were achieved using the Graphit-iCi coating. When compared to TiB2-coated tools in air-cooled conditions this coating improved tool life by over 400% and reduced the number of undersized holes by a similar amount. EDX analysis of used tools revealed that these coatings survived intact; therefore the improvements in performance are probably due to the reduced adhesion between the coatings and the aluminium.