Dry forming of aluminum

Abstract

Aluminum parts are used in a wide range of applications. However, the strong adhesion of aluminum to numerous tool materials is challenging for production processes. To ensure an economic production of aluminum sheet parts a high quantity of lubricants is currently needed. The additional process steps and operating resources associated with their use considerably reduce the sustainability of production. Ecological advantages achieved by lightweight construction during the use phase of aluminum products lose their value drastically when the entire life cycle is considered. The aim of the research project is therefore the development, qualification and transfer of a surface technology system solution for the optimization of tools, whereby the use of lubricants is dispensed with and an environmentally friendly production of aluminum parts is achieved. Within the scope of the research project, the basic wear mechanisms during the lubricant-free forming of aluminum sheets were investigated and strategies for industrial implementation were explored. Starting point of the investigations was a holistic view of the tribological system. In addition to process-driven variables such as contact normal stress and temperature, a significant influence of the semi-finished product in terms of surface chemistry and topography was found. The inert and particularly smooth design of the tribological contact plays a decisive role in this respect. On the sheet side, the native aluminum oxide layer ensures a separation of the reactive aluminum matrix and its performance was improved by additional electrolytic treatment. Further-more, the adhesive wear was significantly reduced by providing sheet material with a high proportion of ma-terial close to the surface. On the tool side, amorphous hydrogenated carbon (a-C:H) caotings were deposited to provide an inert surface. In order to additionally create a nanoscopic smooth tool surface economically, different action strategies along the process chain for tool production were investigated. In addition to various approaches for optimizing the coating process, these strategies consist of a roughness-oriented material selection and different polishing processes that are variable in the process sequence. All investigations were based on a sequential qualification method (tribometer, strip drawing, application) in order to narrow down the scope of solutions for application tests. Finally, the mechanical-chemical polishing of a-C:H coated forming tools was qualified for industrial application in deep-drawing tests.