Friction reduction in lubricated tribological contacts by micro textured surfaces

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The modification of component surfaces in lubricated tribological systems can improve the tribological behavior and reduce friction losses. This can be achieved by tribological layers or by discrete microtextures applied to the component surface. With regard to larger quantities, these microtextures have to be realized by forming processes such as micro coining, which can be integrated into conventional manufacturing processes. Up to now, basic knowledge is missing in order to understand the manufacturing challenges in combined forming processes during component production. In addition, a deeper understanding of the effects as well as the optimal design of surface microtextures in lubricated tribological contacts is lacking.The aim of the research project is to gain basic scientific knowledge with regard to the effect of surface microtextures in EHL contacts, as well as their manufacturability using forming processes. In cooperation with industrial partners, the obtained basic knowledge is transferred to industrial applications. A more realistic determination of the effects of microtextures in rolling-sliding contacts is achieved by the expansion of a TEHL simulation model by the influence of thin layers, roughness and solid-solid contact as well as dynamic operating conditions. Exemplary for the cam/tappet-contact, over the cup surface locally optimized microtextures are derived, taking into account the manufacturing limitations. Latter are investigated for an extrusion-coining process, in which a more homogeneous and precise texture shaping on the component by an inverse texture optimization is strived. In addition, a combined process including deep drawing, ironing and coining which has a lower material flow in the coining area is compared with the extrusion process. The objective is to identify process-specific influencing variables on the texture shape. In addition, the wear behavior of the coining punches is examined using a wear test-rig. The overriding objective of the study is to gain knowledge on the achievable accuracy of the texture geometry as well as on the application behavior of the tools based on numerical models and simplified bench tests. The analysis of the application behavior of the components in terms of friction and wear in a complete test chain from model, over component, to aggregate testing-rigs serves to validate the numerical design. Finally, the obtained knowledge about suitable and simultaneously technically feasible microtextures is validated for different application cases using experimental setups.