Design and manufacturing of radial shafts seals mating surfaces using manufacturing processes with geometrically defined cutting edges - Diregeo

• Applicants: Professor Dr.-Ing. Bernd Sauer; Professor Dr.-Ing. Andreas Schubert
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering ; Engineering Design, Machine Elements, Product Development
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 430170022

For the sealing of shafts in pressure-free areas or sections with minor pressure difference typically radial shafts seals (RSS) are applied. The specific design of RSSs leads to an axial carriage of the lubricant due to the shaft rotation, always directed in the direction of the oil storage. However, the surface microstructure of the mating seal surface (MSS) can result in a carriage effect as well, mainly attributed to a certain twist of the surface microstructure in turning. Surface macro-twist can be defined as a periodic, directional structure such as feed marks. In difference to that, micro-twist represents microstructures with its main direction providing a deviation of rectangularity with reference to work piece rotational axis. Consequently, the MSS are intended to be realized without twist; while up to date, no uniform thresholds are defined concerning macro- and micro-twist. Plunge grinding is typically considered as default process for finish machining of MSS, as typically hardened steels are applied. A predefined dressing and an adaption of the cutting process can typically reduce the twist. From an economical point of view, there are several disadvantages such as high investment, reduced flexibility, and due to comparably long spark-out, times reduced economic efficiency. The substitution of grinding by hard turning provides significant potential for cost reduction. However, up to date there is lack in a comprehensive understanding of the interactions between the process parameters, the surface microstructure, and the functional properties of the MSS. The end user information concerning the required surface specific values as well as information on the selection of tools and cutting parameters are limited. The aim of the proposed research is an in-depth understanding of the correlations between the process parameters in hard turning, the resulting surface microstructure of the MSS, and its functional properties in use. Accordingly, cutting experiments, bench tests, and computer aided process and elastohydrodynamic simulation (EHD) shall be applied. Another goal is the determination of the surface parameters for the function-related description of hard-turned MSS. For longitudinal turning, the influence of the macro-twist on the pumping rate and the friction torque should be examined by a variation of the cutting parameters and the tool corner geometry. Moreover, a predefined modification of the stochastic component of the roughness should be achieved by applying different cutting edge geometries and grain sizes of the CBN cutting material taking the tool wear into consideration. The findings should be used for the qualification of the start-stop-turning (SST), a special process for the machining of MSS. In this context, SSD represent a turning process enabling the generation of MSSs characterized by a zero lead angle, which already provided comparably low pumping ratios in preliminary investigations.

• DFG Programme: Research Grants