Dry sheet metal forming of aluminum by smooth DLC coatings

Currently a high amount of lubricants is used in aluminum forming processes to ensure a long tool lifetime and a high product quality. These technological and economical goals are traded for a negative environmental impact caused by the usage of lubricants. One approach to reduce the environmental impact is the utilization of dry forming of aluminum. Therefore, alternative methods for a tribological optimization need to be implemented like the deposition of tool coatings. Diamond like carbon (DLC) coatings are well known for their exceptional tribological properties. However, state of the art DLC coatings fail due to rapid formation of aluminum adhesions. In this paper, the nanoscopic roughness of DLC coatings will be presented as a critical property for preventing the formation of aluminum adhesions and enabling dry forming of aluminum. For this purpose, an amorphous hydrogenated carbon (a-C:H) coating will be deposited, subsequently polished and characterized to validate the impact of the material selection and surface treatment on the coating roughness. For an evaluation of the tribological properties, polished and unpolished a-C:H coatings will be tested in application oriented strip drawing and industry-oriented deep drawing tests. These tests demonstrate the capability of smooth a-C:H tool coatings to enable dry forming of aluminum with a reduced environmental impact.