Suppressing vibration modes of spindle-holder-tool assembly through FRF modification for enhanced chatter stability Yaser Mohammadi, Milad Azvar, Erhan Budak (1)* Manufacturing Research Laboratory, Sabanci University, Istanbul, Turkey 1. Introduction Chatter is considered as one of the most catastrophic threats to part quality and process productivity in metal cutting operations [1]. Developing various methods to tackle the chatter problem, therefore, has been in the centre of researchers’ interest for a long time. There is a definite link between chatter free behaviour of a cutting process and dynamics characteristics of machine’s components such that high flexibility of the structure can drastically decrease the stable MRR [2]. Thus, modifying the dynamics characteristics of the machine tool can be considered as a chatter mitigation method. One way to modify dynamic response of the machine tool is to utilize the natural dynamic interaction among tool, tool holder and spindle creating dynamic absorber effect which is the subject of this paper. Tool length tuning can be one of the ways to match machine tool structure modes to suppress FRFs. In the literature, tool length tuning has been used extensively as a chatter mitigation technique. Tlusty [3], Davies [4] and Smith [5] adjusted the tool length such that the deepest stability pocket coincided with the maximum spindle speed in order to fully exploit the machine tool power. In the mentioned papers, the approach is based on tuning the tool length such that its natural frequency matches with integer multiple of the tool passing frequency [3], rather than utilizing the absorber effect due to the componential modes interactions. However, there are a few researchers who investigated the dynamic interaction among the machine tool components using tool tuning. Schmitz [6] noticed that the dynamic absorber effect caused by the modal interaction between substructures of a machine tool could result in a stiffer system, and consequently increased the stability limit. Similarly, Erturk [7] demonstrated that by varying the lengths of the machine tool’s components, individual modes of components can interact dynamically creating an absorber effect. Results in Refs. [6] and [7] are accurate and verified experimentally, however, without a systematic procedure requiring a time-consuming process of trial and error to tune the tool length. In this paper, a systematic and generalized methodol- ogy is presented in order to fully exploit the absorber effect due to dynamic interactions among machine tool components. In this approach, in addition to the tool length, all geometrical parameters of the tool-holder-spindle assembly, i.e. tool diameter and tool holder and spindle dimensions, are included in the analysis to maximize the dynamic rigidity, and thus stable MRR. The important reason to tune the tool holder and spindle back tail dimensions is due to the fact that, in many applications, especially aerospace, there is an inevitable need to use long and slender cutting tools wherein tool length cannot be shortened sufficiently to achieve the desired effect. The presented procedure eliminates the time consuming trial and error based tuning procedure and provides a fast and accurate way to select system components for maximum machining stability. 2. Assembly’s FRF prediction Receptance Coupling Substructure Analysis (RCSA) is an accurate method to predict the dynamics response of a machine tool assembly [8]. In this method, the dynamic response of the individual substructures can be calculated either analytically or experimentally and then elastically coupled considering the joint parameters and bearings to obtain full assembly’s FRF [8,9]. In order to identify the contact parameters, at the tool–tool holder interface, for example (c rot , c trans , k rot , k trans in Fig. 1), one can CIRP Annals - Manufacturing Technology xxx (2018) xxx–xxx A R T I C L E I N F O Keywords: Chatter Milling Frequency response function A B S T R A C T Modifying dynamic response of a machine tool is of great importance for chatter mitigation. Tool tip frequency response function (FRF) can be suppressed by capitalizing on the absorber effect due to dynamic interactions among vibration modes of spindle, holder and tool. In this paper, a practical method is presented to modify the system’s FRF by selecting proper dimensions for assembly component without extensive testing. Robustness of the method is demonstrated through simulation and test results. Milling stability tests were also conducted where significant improvements in chatter free Material Removal Rate (MRR) is achieved. © 2018 Published by Elsevier Ltd on behalf of CIRP. * Corresponding author. E-mail address: ebudak@sabanciuniv.edu (E. Budak). G Model CIRP-1712; No. of Pages 4 Please cite this article in press as: Mohammadi Y, et al. Suppressing vibration modes of spindle-holder-tool assembly through FRF modification for enhanced chatter stability. CIRP Annals - Manufacturing Technology (2018), https://doi.org/10.1016/j.cirp.2018.03.003 Contents lists available at ScienceDirect CIRP Annals - Manufacturing Technology journal homepage: http://ees.elsevier.com/cirp/default.asp https://doi.org/10.1016/j.cirp.2018.03.003 0007-8506/© 2018 Published by Elsevier Ltd on behalf of CIRP.