Reduction of friction in EHD-contacts by microstructured surfaces of components: design, layout and manufacturing by forming

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In the first project phase it has been shown that specific applied microstructures can reduce friction in cam tappet contacts as a representative of rolling sliding contacts. Furthermore, the feasibility of a simulation-based dimensioning and design of microstructures for EHD contacts could be demonstrated. In addition, the feasibility of a process-safe production of components with microstructured surfaces in one process step has been proved. For the design of microstructures their geometry and arrangement has to be adapted to the particular load spectrum of application. An identification of advantageous microstructure types only by experiments is too time consuming and inefficient. In fact, the effect of microstructures has to be understood by a simulation-based approach upon which generalized design rules for microstructured surfaces are derived. A parameterized model of the EHD contact extended by non-Newtonian flow of lubricants and starved lubrication effects allows the calculation of various load cases, microstructure shapes and arrangements. It provides the basis for establishing a suitable meta-model. Through this meta-model the ability to optimize the design of microstructures is created, waiving any additional detailed simulations. However, manufacturing of theoretically advantageous microstructures reaches its limits due to their filigree geometries. Therefore, the process limits of micro laser ablation, micro electrical discharge machining and micro coining are determined and the influences of process parameters on accuracy of microstructures are analyzed. In terms of mass production of components with microstructured surfaces manufacturing by forming in a combined extrusion micro coining process is persued. Thereby, the mutual influence of the individual processes and the targeted control of the material flow are investigated. Concerning operation of microstructured components wear mechanisms that modify the shape of microstructures during stress duration represent the durability determining factor. Tribological testing of microstructured components on a cam follower test rig allows the analysis of the operational behavior and the change of microstructure shape due to wear effects under conditions near operation. Objectives of the project are the development of a validated methodology to optimize the form of microstructures and their arrangement for individual load spectra, the definition of design guidelines for microstructured surfaces of components and establishing of a manufacturing matrix for microstructured surfaces displaying suitable manufacturing processes depending on the size, number and arrangement of microstructures.