Identification of modal parameters of machine tools during milling

点击翻译按钮获取中文摘要

Vibrations in machine tools limit the working accuracy and the productivity. They significantly contribute to wear of tools and machine parts. Furthermore, they affect the environment by noise and ground vibrations. The experimental modal analysis (EMA) represents an established method for the investigation of the dynamic behaviour of machine tools. As the EMA assumes linear, reciprocal, time-invariant, causal and stable behaviour of the investigated subject, machine tools are assessed at standstill, when conducting EMA. Therefore, the effects occurring during machining like changed modes due to gyroscopic effects, changing stiffness of parts with non-linear behaviour caused by the different static preloads, differences in inertial mass resulting from the additional masses of the work piece, the work piece fixation, the tool etc. as well as different damping properties inclusively process damping are ignored.In principal, the Operational Modal Analysis (OMA) offers a possibility for consideration of such effects during a measurement analysis due to capturing the dynamic behaviour of a machine tool in the operating point related to the real cutting conditions. Performing OMA on machine tools requires new approaches for broadband excitation by the cutting process, for consideration of the time-variant behaviour of a machine tool and for the treatment of the fact, that the operating load of a machine tool, particularly the cutting process, is distinct from the excitation being assumed in OMA. While the broadband excitation and the time-variant behaviour have been addressed within own preliminary work, this project focusses on the development of two new methods for treating an excitation, that is concentrated on a few measuring points when modal parameters are identified from vibration signals captured during operation of a machine tool. In this context, new mathematical tools for the two methods are going to be developed and the excitation character (statistic and deterministic) as well as the effect of disturbances are investigated.The two new methods are going to be developed by using simulation models and experiments. Afterwards, the methods are validated in experiments on a machine tool.Beside the consideration of the effects related to the operation of a machine tool, the successfully and reliably application of OMA in machine tools can significantly contribute to monitoring of machine tools condition and machining processes using values for system description like modal parameters. Moreover, the OMA can be used for a periodic updating of digital twins in order to reflect the real structural-mechanical properties of a machine tool.