Selective influencing of stiffness and damping at joints by modifying the contact surface micro-geometry on components made of heat-treated steel

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Cutting machine tools are used for the production and finishing of components respectively. They are subject to increasing requirements. These result from a growth in the use of both high-strength and difficult-to-machine materials, the reduction of manufacturing time due to high speeds or metal removal rates, and stricter design specifications with regard to the tolerances and roughness values to be maintained. Passive damping is of particular importance in this context. Joints like the contact surfaces of machine elements connected by screws contribute significantly to damping. But, good joint damping typically leads to reduced joint stiffness. Previous studies in this field indicate that a combination of strong joint damping and high stiffness is possible by applying a suitable surface finish or micro structuring. However, fundamental scientific principles for the design of such surfaces are currently lacking. Firstly, finite element simulations on a microscopic scale are carried out to model the contact conditions. As a result, an understanding of the mechanisms influencing joint damping and stiffness is obtained. Based on this, surface geometries are defined and implemented in terms of manufacturing technology. The surfaces are designed in such a way that they can be generated directly during final machining. Pressure measurement foils are used to analyse the load-dependent stress distribution in the joint. Based on extensive frequency response analyses of both the individual and the assembled specimens, natural frequencies and damping ratios are extracted. These represent the objective functions in a parameterised FEA model on a macroscopic scale and thus serve the identification of pressure-dependent joint damping and stiffness. As a result, causal relationships exist between the surface finish, the surface pressure and the joint damping and stiffness. These relations enable the design of surfaces suitable for production, which entail particularly strong vibration damping while retaining the joint stiffness. Consequently, the behaviour of machine tools can be improved in such a way that increased demands on components in terms of tolerances and surface properties can be realised while taking into account economic constraints.