Selective thermally oxidized tool surfaces for dry deep drawing

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Friction and wear have significant influence on tool life in sheet metal forming. Thus lubrificants are generally used to extend the tool life. Since the use of harmful lubricants does not correspond with the target of sustainable production, methods for dry forming are investigated.Within the scope of this project, the production and the use of tool coatings, which are produced by selective thermal oxidation, are investigated. The oxidative heat treatments of the tool surfaces need to take place at a defined oxygen partial pressure. Therefore the treatments are carried out under a protective gas atmosphere (nitrogen) and monosilane doped nitrogen, respectively. With this approach, it is possible to generate oxide coatings with a defined chemical composition and thickness.The results from the first project period show that oxide layers produced under well-defined process conditions feature friction coefficients, which are similar to those measured on the tool surfaces after applying lubricants.In the second phase of this subproject, an innovative heat treatment method has been developed. Initially, a continuous heating process was used to create the oxide layers. This method, however, requires an extensive processing time and an increased amount of process gases. In comparison, the new heat treatment method employs a tube furnace, which allows for the production of oxidecoated specimens with reduced protective gas consumption. In addition, an inductive heating unit was installed in the heating system to decrease process time. Moreover, various surface modifications were investigated in the second phase of the project including friction and wear experiments. Further analysis is needed to understand the behaviour of these coatings under dry metal forming conditions, and thus to ensure transferability to industrial application in the long-term. This aspect, will be one of the key aspects of the research project in its third phase. Specifically, a modular deep-drawing tool equipped with oxidised mold inserts will be developed. By manufacturing different components with various geometries using this tool system it is possible to increase the load collective on the generated oxide layers successively and thus investigate the behaviour of the layer system in a conventional deep-drawing process.At the same time, the heat treatment process to tailor the oxide layers will be adapted with respect the application. Furthermore, the developed numerical model, which was validated on test specimens, will be applied to the geometries investigated in this phase as well. Finally, the rejuvenation process of the layer system will be investigated, to provide for a validated tool life prediction.