A Modeling Approach for Analysis and Improvement of Spindle-Holder-Tool Assembly Dynamics

doi:10.1016/S0007-8506(07)60437-5

CIRP Annals

Volume 55, Issue 1, 2006, Pages 369-372

https://doi.org/10.1016/S0007-8506(07)60437-5 Get rights and content

Abstract

The most important information required for chatter stability analysis is the dynamics of the involved structures, i.e. the frequency response functions (FRFs) which are usually determined experimentally. In this study, the tool point FRF of a spindle-holder-tool assembly is analytically determined by using the receptance coupling and structural modification techniques. Timoshenko's beam model is used for increased accuracy. The spindle is also modeled analytically with elastic supports representing the bearings. The mathematical model is used to determine the effects of different parameters on the tool point FRF and to identify contact dynamics from experimental measurements. The applications of the model are demonstrated and the predictions are verified experimentally.

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An accurate description of machine tool dynamics is essential for health monitoring, chatter prevention, and improvement of manufacturing accuracy. The standard identification approach of experimental modal analysis at the standstill of the machine does not realize the possible variations in the dynamics due to operational conditions. The in-process identification methods in the literature, on the other hand, are associated with implementation difficulties in industrial environments due to the required complex and specially-designed setup, limited excitation forms, or excessive measurement efforts. This paper proposes an industrial-friendly method to estimate the in-process structural dynamics of machine tools, considering practical demands and implementation limits. Knowing that the operational dependency of the dynamics is associated with the machine and spindle structure, the machine–spindle and holder–tool structures are considered two distinguished subsystems. The cross Frequency Response Function (FRF) of the coupled structure, between the tooltip and spindle flange, is determined by measuring forced vibrations during milling operations. The milling forces are considered as excitation input and the process is designed to be stable and chatter-free so that the simulated forces can be accurately used in the identification. Then, the receptance coupling theory is utilized to develop an optimization algorithm. Given the model of the coupled structure, the evolutionary optimization tunes the modal parameters of the machine–spindle dynamics and joint parameters until the predicted cross FRFs match the experimentally determined FRFs. The direct FRF at the tooltip is predicted using identified in-process machine–spindle dynamics through the receptance coupling method. The identified in-process dynamics are used to predict stability diagrams for different tooling systems and, moreover, to design an augmented Kalman filter to estimate cutting forces. Comparison of estimated SLDs and cutting forces with chatter test results and dynamometer measurements validate the outcomes of the proposed identification method. This paper demonstrates that the system dynamics under operational conditions can be successfully identified without requiring costly setup, specially-designed workpieces or operations, and destructive chatter tests.
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Citation Excerpt :
It is composed of the portion of the artifact beyond the spindle flange (component II) and the spindle-machine (component III), where the spindle-machine receptances are required to predict the tool tip receptances for arbitrary combinations of tools and holders inserted in the selected spindle-machine. In 2006, Budak et al. [94] described an analytical method that employed Timoshenko beam theory, RCSA, and structural modification techniques to model spindle-holder-tool assemblies in machining centers to predict the tool point FRF. The method was applied to optimize the spindle geometry and bearing locations for maximum dynamic stiffness at a desired frequency or frequency range.
This paper provides a chronological review of publications that implement and advance the receptance coupling substructure analysis (RCSA) approach first applied to tool tip receptance (or frequency response function) prediction for milling applications in 2000. The review topics mimic the RCSA approach, where the tool, holder, and spindle-machine receptances are coupled analytically, and include: tool-holder receptance modeling; connection modeling; spindle-machine receptances; and applications. The review paper summarizes contributions from multiple, international authors (198 papers) to these topics. It also provides a comprehensive resource for those beginning an investigation into RCSA.
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Citation Excerpt :
The RC method has been widely used to predict tool-tip frequency response of end-mills [29]. The models can be further expanded to multi-point RC methods to include dynamics of tool holder by assuming rigid contacts [30] or elastic contact between the tool-holder and the spindle assembly [31–32]. A Kalman filter is also designed and applied to the displacement signals of the spindle housing, integrated from the acceleration signals, to indirectly obtain the cutting forces [33].
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A Modeling Approach for Analysis and Improvement of Spindle-Holder-Tool Assembly Dynamics

Abstract

Annals of the CIRP

Annals of the CIRP

Annals of the CIRP

Annals of the CIRP

International Journal of Machine Tools and Manufacture

International Journal of Machine Tools and Manufacture

Journal of Sound and Vibration