For continuous radial immersion milling operations, the dominant mode shape becomes difficult to determine when stiffness of the tool and workpiece are comparable, and this can pose a great challenge for ensuring machining processes stability. In this paper, we propose a rapid method to obtain time-varying modal parameters of the workpiece by combining experimental measurements with the receptance coupling method. Firstly, the contact parameters between the workpiece and vise were identified by a so-called dynamic coupling matrix. Then the mode shapes and the time-varying natural frequency of the workpiece were determined using the modal parameters of workpiece. Finally, the stability lobe diagrams (SLDs) were computed using the modal parameters and then were validated by undertaking immersion milling experiments. The experiments showed a more conservative and practical SLD for general workpiece under continuous radial immersion, where the workpiece mode had not always dominated the machining process. Based on the proposed method, we also explored two modifications in form of additional cylinder masses and passive support, to suppress chatter. Both modifications were effective in enhancing the minimum boundary of the conservative SLD, and the modification of passive support worked better. Although the modification of the workpiece could improve the stability boundary, it indirectly affected the dynamics of the milling tool through the interaction area between the workpiece and milling tool.
The authors would like to thank the Federal Ministry of Economic Affairs and Energy (BMWi) and the AIF Projekt GmbH for funding this scientific paper as part of the research project "UltrahardMill" of the central Innovation Programme for SMEs. The authors appreciate Dr.-Ing. Michael Löser and Dipl.-Ing. Zhongyan Zhu from TU Dresden for discussing and modifying the content of the manuscript. Besides, Mr. Daniel Schmidt from Fraunhofer Institute for Machine Tools and Forming Technology (IWU) provided us with lots of generous help to carry out the experiments.
- Continuous immersion milling
- Receptance coupling
- Stability lobe diagram
- Chatter suppression