Search

The tuned mass damper (TMD) has been used in machining processes for reducing forced vibration, suppressing chatter, and improving machined surface quality. In micro-milling process, the tiny size of the cutting tool-tip and the high rotating speed bring challenges in implementing the TMD. Besides, the TMD needs to have two degrees-of-freedom (DOFs) for reducing vibrations of micro-mill in two orthogonal directions. This paper presents the chatter suppression for micro-milling by attaching a two-DOF TMD to the tool shank and rotates with the cutting tool. The frequency response function (FRF) at the tip of the micro-mill clamped by an aerostatic spindle is predicted using receptance coupling analysis. A two-DOF TMD is designed via graphical approach based on the FRF result at the tool-tip. The natural frequencies and damping ratio of the TMD are optimized under different spindle speeds in order to enhance the cutting stability. The chatter stability of micro-milling is predicted considering the gyroscopic and centrifugal effects of the TMD structure. Modal tests and micro-milling experiments are conducted to validate the effect of the TMD on chatter stability. The results show that the TMD is able to improve the critical depth of cut by 13 folds, and satisfy the compact design requirement for micro-milling. • Shank-mounted TMD satisfies the specific geometric requirement in micro-milling. • Design of TMD using graphical approach based on synthesized FRFs of substructures. • The centrifugal and gyroscopic effects of TMD on chatter stability are studied. • Chatter-free axial depth of micro-milling operation is enhanced by 13 folds. [ABSTRACT FROM AUTHOR]

Passive chatter suppression by addition of tuned mass dampers has proven effective in enhancing machining stability of thin-walled workpieces. However, the damper installed on a fixed position may fail to offer effective and robust chatter suppression, as the cutting position varies during machining. This challenge is compounded by the steep dynamics variation of the workpiece along the radial direction caused by material removal in cutting zones. The present paper presents a comprehensive study on improving the chatter stability of milling thin-walled casing workpieces by employing a sucker-mounted damper, which allows a quick and easy repositioning for following the instantaneous cutting zone. An inverse multi-point receptance coupling method is developed to predict the frequency response function of the workpiece equipped with the sucker-mounted damper at the instantaneous cutting position, while accounting for the material removal effect. The damper's parameters are optimized using a new strategy focused on stability lobe diagrams to maximize the chatter-free cutting depth within a specified spindle speed range. This strategy aims to maximize material removal rate while adhering to the constrained speed range imposed by practical processing systems. The structure of damper, which embodies the optimum parameters, is implemented from configuration to dimensions using the screw theory. A series of modal test and milling experiment with and without the damper are conducted to verify the validity and reliability of the sucker-mounted damper. The results indicate that the damper is able to improve the material removal rate by up to 220.0%, and satisfy the requirement of robust performance, flexible repositioning and secure attachment for milling large thin-walled workpieces. [ABSTRACT FROM AUTHOR]

Highlights • A general design routine for multi-DOF TMD is proposed. • The multi-DOF TMD is designed via the graphical approach. • Frequencies of the TMD are formulated analytically. • A three-DOF TMD is implemented for damping single mode. Abstract The multi-degree-of-freedom (MDOF) tuned mass damper (TMD) has demonstrated a more effective performance than single-DOF and multiple SDOF TMDs. For a damping mass in the space, there are maximum six DOFs; however, only along the vibration direction of the main structure can the motion of the TMD be utilized to control the vibration mode. Therefore, the maximum available DOFs of a TMD for mitigating single translational mode are three (i.e. one translational DOF and two rotational DOFs). A general routine of suppressing single vibration mode by multi-DOF TMD is presented, especially, a three-DOF TMD is used for example. Based on the non-dimensional dynamic model, the design parameters of the TMD are optimized via the simulated annealing algorithm according to the H∞ criterion. The graphical approach is utilized to design the configuration of the TMD with prescribed DOFs. Stiffness and natural frequencies are formulated analytically by the compliance matrix method, based on which the dimensions of the TMD are determined. It is demonstrated that the SDOF and two-DOF TMDs are special cases of the three-DOF TMD from the point of mathematical modeling, numerical optimization and design methodology. Theoretical formulation is verified by conducting hammer tests on the TMD under various geometry configurations. After employing the three-DOF TMD, 86.5% reduction of the amplitude of the frequency response function (FRF) of an I-shaped part is achieved, which shows 29.5% improvement than previous two-DOF TMD. [ABSTRACT FROM AUTHOR]

Abstract: A new-type nonlinear tuned mass damper (TMD) containing an additional element of elastic support dry friction compared with the common linear TMD is proposed to suppress machining chatter. The design and tuning process of this nonlinear TMD have used a combination of analytical modeling with experimentally measured frequency response function (FRF) of the machining system. Theoretical studies and experimental results show that the proposed nonlinear TMD can remarkably improve the machining stability by effectively suppressing the magnitude of the real part of the FRF of the damped machining system. [Copyright &y& Elsevier]

• Novel oppositely oriented series MTMDs with compact structure and minimized parasitic vibration. • Formulation of parasitic and primary vibrations for quantitative geometry design of MTMDs. • Practical routine for parameter design and evaluation of MTMDs considering background modes. • Vibration suppression of a parallel machine tool with closely spaced and position-dependent modes. Passive vibration control of the parallel machine tool is challenging due to its closely spaced vibration modes and position-dependent dynamics. Owing to the advantages of significant vibration suppression, high robustness, and no need for additional damping materials, the series multiple tuned mass dampers (MTMDs) appear to be an effective solution to this problem but suffer from large-sized structure and significant parasitic vibrations. This paper proposes a novel type of oppositely oriented series MTMDs with a compact structure and minimized parasitic vibrations, with the effectiveness and robustness of the traditional type retained. An analytical model of the parasitic and primary vibrations of the series MTMDs is presented for quantitative geometry design. The dynamics of the actual main structure and the analytical MTMDs are integrated, followed by the parameter optimization and performance evaluation of the MTMDs considering the effect of background vibration modes. The oppositely oriented series dual-mass TMDs are implemented to suppress the machining vibrations of a parallel machine tool. Modal tests indicate that 72.7% amplitude of the target mode is reduced by the series dual-mass TMDs, which shows a 10.8% improvement compared to the SDOF TMD with equal damper mass. A maximum of 70.1% vibration reduction is achieved in slot milling experiments. [ABSTRACT FROM AUTHOR]