In-Process Monitoring of Changing Dynamics of a Thin-Walled Component During Milling Operation by Ball Shooter Excitation

Abstract

During the milling of thin-walled workpieces, the natural frequencies might change radically due to the material removal. To avoid resonant spindle speeds and chatter vibration, a precise knowledge of the instantaneous modal parameters is necessary. Many different numerical methods exist to predict the changes; however, small unmodelled effects can lead to unreliable results. The natural frequencies could be measured by human experts based on modal analysis for an often interrupted process; however, this method is not acceptable during production. We propose an online measurement method with an automatic ball shooter device which can excite a wide frequency range of the flexible workpiece. The method is presented for the case of blade profile machining. The change of the natural frequencies is predicted based on analytical models and finite element simulations. The measurement response for the impulse excitation of the ball shooter device is compared to the results of impulse modal tests performed with a micro hammer. It is shown that the ball shooter is capable of determining even the slight variation of the natural frequencies during the machining process and of distinguishing the slight change caused by different clamping methods. An improved FE model is proposed to include the contact stiffness of the fixture.

Analysis of the Displacement of Thin-Walled Workpiece Using a High-Speed Camera during Peripheral Milling of Aluminum Alloys

“…The thin walls being the subject of the study were made on a sample having a rectangular base with smooth sides. As the research shows [ 11 ], the differences in the mounting of a very similar sample with thin walls influenced in less than 5% the difference in the frequency analysis, which allows for assuming no significant influence of the mounting method on the results obtained in the study.…”

“…As described earlier, the formation of chatter during the machining of thin-walled workpieces has a very negative impact on the quality of their surface. In order to minimize this risk, the authors [ 11 ] focus on the study of the natural frequency of thin walls with their various dimensional variants with the use of an automatic ball launcher. The results obtained using this method do not differ from the traditional method of measurement with the use of a modal hammer, additionally they were compared to analytical methods (including FEM).…”

Cloud-based process design in a digital twin framework with integrated and coupled technology models for blisk milling

“…Therefore, in most cases it is sufficient to analyze the first and second eigenmode to describe the dynamic behavior of the component (Scippa et al, 2014). The calculation of resonant vibrations of tool and workpiece and their frequency response functions (FRFs) for each position of the toolpath is essential to describe vibrations occurring during the cutting process (Biermann et al, 2010;Bachrathy et al, 2020;Wang et al, 2020). In terms of improving the dynamic vibration behavior in milling of thin-walled workpieces, the adaptive control of the spindle speed is one key approach to prevent resonance of both tool and workpiece and tracking their relative displacement (Scippa et al, 2014).…”