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In this paper, the chattering phenomenon in cold rolling is investigated in reference to the finite element method (FEM). The structure of the mill stand is modeled as a system of linear springs and lumped masses while the rolling process is modeled utilizing an implicit FEM. Assembling the two models makes it possible to detect the chatter during the rolling process. The assembled model is capable of perceiving variations in forces generated during the process that deflects the structure of the mill leading to variations at the roll gap and the roll speed. The influences of some rolling parameters on chatter vibration are investigated. Predicted values of the model are in good agreement with that of the experiments as well as the values obtained by other researchers. [ABSTRACT FROM AUTHOR]

Chatter is an unfavorable phenomenon in turning operation causing poor surface quality. Active chatter elimination methods require the chatter to be detected before the control reacts. In this paper, a chatter detection method based on a coherence function of the acceleration of the tool in the x direction and an audio signal is proposed. The method was experimentally tested on longitudinal turning of a stock bar and facing of a hollow bar. The results show that the proposed method detects the chatter in an early stage and allows correcting control actions before the chatter influences the surface quality of the workpiece. The method is applicable both to facing and longitudinal turning. [ABSTRACT FROM AUTHOR]

Chatter is an undesirable dynamic phenomenon in machining processes, which causes cutting disturbance, overcut, quick tool wear, etc., and thus seriously impairs workpiece quality. To mitigate chatter, traditional methods called passive control focus on optimiz-ing working spindle speeds and depths of cut. But they have inherent disadvantages in gaining highly efficient machining. On the contrary, the research in this paper is along the line of active control. Specifically, an adaptive algorithm is developed based on Fou-rier series analysis to deal with the so-called regenerative cutting force which causes chatter. AÍ a result, chatter is remarkably mitigated. The performance improvement is illustrated by numerical simulation in terms of both stability lobes diagram (SLD) and surface location error (SLE). [ABSTRACT FROM AUTHOR]

The dynamic model of 4-h mill, which couples with the rolling process model, the mill roll stand structure model, and the hydraulic servo system model, is built by analyzing the vibration process of cold rolling. By linearization, the multiple input multiple output linear transfer function matrix model of single stand 4-h cold mill system is obtained. With the consideration of strip quality, the model of strip thickness control system is established in a simplified form. Meanwhile, the robust controller based on quantitative feedback theory is designed for the gauge control model. A comparison with PID control-ler shows that the controller has better disturbance attenuation performance for parame-ter uncertainty and external disturbance. [ABSTRACT FROM AUTHOR]

This paper presents a chatter stability prediction method for milling flexible workpiece with end mills having asymmetric structural dynamics. The dynamic chip thickness regenerated by the vibrations of the rotating cutter and the fired workpiece is transformed into the principle modal directions of the rotating tool. The process damping is modeled as a linear function of vibration velocity. The dynamics of the milling system is modeled by a time delay matrix differential equation with time varying directional factors and speed dependent elements. The periodic directional factors are averaged over a spindle period, and the stability of the resulting time invariant but speed dependent characteristic equation of the system is investigated using the Nyquist stability criterion. The stability model is verified with time domain numerical simulations and milling experiments. [ABSTRACT FROM AUTHOR]

Being one of the most important problems in machining, chatter vibrations must be avoided as they result in high cutting forces, poor surface finish, and unacceptable part quality. Using stability diagrams is an effective method to predict chatter free cutting conditions. Although there have been numerous works in milling dynamics, the stability of five-axis ball-end milling has not been studied in detail. In this paper the stability of the five-axis ball-end milling is analyzed using analytical (frequency domain), numerical (time-domain), and experimental methods. The models presented consider 3D dynamics of the five-axis ball-end milling process including the effects of all important process parameters such as the lead and tilt angles. Both single- and multi-frequency solutions are presented. Unlike other standard milling cases, it is observed that adding multi- frequency effects in the solution has marginal influence on the stability diagrams for five-axis ball-end milling operations due to effects of the ball-end milling geometry on the engagement region, thus, on the directional coefficients. The stability limits predicted by single- and multi-frequency methods are compared with time-domain simulations and experiments. Using the models and experimental results, the effects of the lead and tilt angles on the stability diagrams are also shown. The presented models can be used in analysis of five-axis ball-end milling dynamics as well as in the selection of the milling conditions for increased stability. [ABSTRACT FROM AUTHOR]

In this part of the paper series, chatter experiments are conducted in order to verify the proposed stability models presented in the first part (Ozlu, E., and Budak, E., 2007, ASME J. Manuf Sci. Eng., 129(4), pp. 726-732). Turning and boring chatter experiments are conducted for the cases where the tool or the workpiece is the most flexible component of the cutting system. In addition, chatter experiments demonstrating the effect of the insert nose radius on the stability limit are presented. Satisfactory agreement is observed between the analytical predictions and the experimental results. [ABSTRACT FROM AUTHOR]

A novel analytical tool is presented to assess the stability of simultaneous machining (SM) dynamics, which is also known as parallel machining. In SM, multiple cutting tools, which are driven by multiple spindles at different speeds, operate on the same workpiece. Its superior machining efficiency is the main reason for using SM compared with the traditional single tool machining (STM). When SM is optimized in the sense of maximizing the rate of metal removal constrained with the machined surface quality, typical ‘chatter instability’ phenomenon appears. Chatter instability for single tool machining (STM) is broadly studied in the literature. When formulated for SM, however, the problem becomes notoriously mare complex. There is practically no literature on the SM chatter, except a few ad hoc and inconclusive reports. This study presents a unique treatment, which declares the complete stability picture of SM chatter within the mathematical framework of multiple time-delay systems (MTDS). What resides at the core of this development is our own paradigm, which is called the cluster treatment of characteristic roots (CTCR). This procedure determines the regions of stability completely in the domain of the spindle speeds for varying chip thickness. The new methodology opens the research to some interesting directions. They, in essence, aim towards duplicating the well-known ‘stability lobes’ concept of STM for simultaneous machining, which is clearly a nontrivial task. [ABSTRACT FROM AUTHOR]

Describes a quantitative feedback theory controller that minimizes the oscillations within the boundary layer and improves the tracking response. Occurrence of chattering when using the sliding mode control; Introduction of a boundary layer around the sliding surface while keeping the boundary layer attractive to reduce chattering.

Presents a novel analytical model for predicting chatter stability of variable spindle speed machining. Validation of the model using results of numerical time domain simulations; Selection of variable spindle speed trajectory parameters; Applications of the model.

Presents a control system for chatter avoidance in milling. Method for on-line identification of stability lobes; Components of the control system; Simulation of system performance.

A normalized chatter detection index, which is independent of cutting conditions, is critical for machining process monitoring and control. This paper introduces a novel method for on-line machine-tool chatter detection. The method characterizes the significant transition in the cutting dynamics at the onset of chatter by the changes in the instantaneous energy of the machining system. This technique utilizes the relation between the Teager-Kaiser nonlinear energy operator and time-frequency (Wigner) distribution to develop a normalized chatter detection index. The validity of this technique is demonstrated with the actual experimental cutting data obtained from turning and milling processes. [ABSTRACT FROM AUTHOR]