Effects of machine component damping on dynamic behaviour and process stability of machine tools

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The accuracy and performance of machine tools are determined by the interaction between the cutting process and the dynamic compliance of the machine structure. Chatter vibrations may occur due to large dynamic compliances which are caused by insufficient stiffness or damping. These self-excited vibrations limit the machine performance, cause a bad surface quality of the workpiece and reduce tool life. In order to calculate and optimize the dynamic behavior of a machine tool in the development process, knowledge of stiffness, mass and damping of all structural components and joints lying in the force flux is necessary. While mass and stiffness values are usually well known, validated and parameterized accurate damping models are still missing. In order to reduce these deficits, the research group "Damping effects in machine tools" is being funded by the German Research Foundation. Within the subproject "Methods for the measurement of damping effects in machine components" methodological foundations were developed by the Laboratory for Machine Tools (WZL), RWTH Aachen, for parameterizing damping models of machine tool components. Here, a significant influence of different design variants and various lubrications were detected on the damping of components. In this project, the method to repeatable determine damping and the knowledge about damping effects of feed axis components will be used to improve the dynamic behavior of machine tools. For this purpose two different machine tools of the application partners will be examined, a machining center and a lathe. The damping behavior of the feed axis components of both machines will be determined with the help of test benches. Based on the knowledge of the damping effects, machine components will be selectively modified. For example, the monorail guidance system might be replaced by different design variants which ensure an improvement of the dynamic behavior of the entire machine tool. The dynamic behavior of the modified machine tool will be measured and as a result it will be investigated whether the dynamic compliance and the process stability of the machine tool can be manipulated by the simple modification of components.