Current tool coatings
For the coating of tools for the cold forming of aluminum sheets, a wide variety of hard thin films have been established. As lubricants are currently applied in order to reduce adhesion, these tool coatings are not only optimized with regard to high resistance to abrasive wear but also with respect to bonding and interaction with the additives contained in the lubricant. At present, there is a development trend towards reducing the lubricant consumption. There are, however, no established industrial tool coatings which could enable a complete renouncement of lubricants. With the current technological status, even layers of diamond-like carbon (DLC) cannot completely prevent adhesive tool wear.
Within the framework of the Priority Program SPP 1676 from the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG), the Fraunhofer IST carries out further development of amorphous hydrocarbon layers (a-C:H) with the realization of lubricant-free aluminum forming as its objective. Over the course of the latest developments, it was possible to verify that the nanoscopic surface roughness is a significant influencing factor on the adhesion tendency of a-C:H layers. Adhesive layer wear can be prevented and low friction (see adjacent Figure in the middle) can be achieved in the lubricant-free contact with aluminum through a reduction in the nanoscopic surface roughness as shown in adjacent Figure above. For the deposition of correspondingly smooth a-C:H coating systems, various strategies for action, consisting of an optimized coating process and a subsequent surface treatment, were developed and qualified for actual application.
Transfer of results to industrial forming processes
The roughness requirements represent another optimization variable in addition to the coating properties which have formed the focus of attention so far, e. g. hardness, wear resistance, adhesion, etc. Furthermore, the surface quality of the forming tool plays an important role in the transfer of development results to real forming processes. In order to fulfill these requirements, a holistic optimization of the layer-tool bond is necessary. The selection of the tool material, the manufacture of the tool, the actual coating process and the post-treatment of the a-C:H tool coating must thereby be included. The Fraunhofer IST has acquired many years of experience in comprehensive tool optimization with numerous industrial partners. As a result, it has already been possible to demonstrate the lubricant-free deep-drawing of high-alloy aluminum sheets in initial application tests (see adjacent Figure below).
The Fraunhofer IST plans to implement the described results in the industrial manufacture of aluminum components.