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

在第一个项目阶段，已经证明了特定的应用显微结构可以减少作为滚动滑动接触代表的凸轮挺杆接触的摩擦。此外，基于仿真的EHD触点尺寸和微结构设计的可行性也得到了验证。此外，还证明了在一个工艺步骤中安全生产具有微结构表面的部件的可行性。对于微结构的设计，它们的几何形状和排列必须适应特定的应用载荷谱。仅通过实验来确定有利的微观结构类型既耗时又低效。事实上，微观结构的影响必须通过基于模拟的方法来理解，在此基础上推导出微观结构表面的广义设计规则。基于非牛顿流体润滑和缺乏润滑效应的EHD接触参数化模型，可以计算各种载荷情况、微观结构形状和布置。它为建立合适的元模型提供了基础。通过这个元模型，微结构优化设计的能力被创建，放弃任何额外的详细模拟。然而，制造理论上有利的微结构达到其极限，由于他们的细丝几何形状。为此，确定了微激光烧蚀、微电火花加工和微铸造的工艺极限，分析了工艺参数对微结构精度的影响。针对具有微结构表面的零件的批量生产，采用复合挤压微压成形工艺进行了研究。因此，研究了各个过程的相互影响和物料流的目标控制。在微结构构件的工作过程中，改变微结构形状的磨损机制是耐久性的决定因素。在凸轮从动件试验台上对微结构部件进行摩擦学测试，可以分析操作行为和在接近操作条件下由于磨损影响而引起的微结构形状变化。该项目的目标是开发一种经过验证的方法，以优化微结构的形式及其对单个负载谱的排列，定义组件微结构表面的设计指南，并建立微结构表面的制造矩阵，根据微结构的大小、数量和排列显示合适的制造工艺。

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.