Selective thermally oxidized tool surfaces for dry deep drawing

在板料冲压成形过程中，摩擦磨损对刀具寿命有重要影响。因此，通常使用润滑剂来延长刀具寿命。由于有害润滑剂的使用与可持续生产的目标不一致，因此研究了干法成形的方法。在本项目的范围内，研究了选择性热氧化工具涂层的生产和使用。刀具表面的氧化热处理需要在规定的氧分压下进行。因此，处理分别在保护气体气氛(氮气)和单硅烷掺杂氮气下进行。第一个项目期的结果表明，在明确的工艺条件下生产的氧化层具有摩擦系数，与涂抹润滑剂后在工具表面上测得的摩擦系数相似。在这个子项目的第二阶段，已经开发了一种创新的热处理方法。最初，使用连续加热过程来产生氧化层。然而，这种方法需要较长的处理时间和增加的处理气体量。相比之下，新的热处理方法使用管式炉，允许生产氧化处理的样品，减少保护气体的消耗。此外，在加热系统中安装了感应加热单元，以缩短加工时间。此外，在该项目的第二阶段还研究了各种表面改性，包括摩擦和磨损实验。需要进一步的分析来了解这些涂层在干金属成形条件下的行为，从而确保长期可转移到工业应用中。这方面，将是第三阶段研究项目的关键方面之一。具体地说，将开发一种配备氧化模具刀片的模块化拉深工具。通过使用该工具系统制造具有不同几何形状的不同部件，可以连续增加生成的氧化层上的载荷集合，从而研究在常规深拉深工艺中的层系统的行为。同时，将根据应用调整用于定制氧化层的热处理工艺。此外，所开发的数值模型，并在试件上进行了验证，也将应用于本阶段所研究的几何形状。最后，将研究层系的返老还童过程，以提供有效的刀具寿命预测。

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.