Computational stability analysis of chatter in turning (original) (raw)
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Linear analysis of chatter vibration and stability for orthogonal cutting in turning
International Journal of Refractory Metals & Hard Materials, 2011
The productivity of high speed milling operations is limited by the onset of self-excited vibrations known as chatter. Unless avoided, chatter vibrations may cause large dynamic loads damaging the machine spindle, cutting tool, or workpiece and leave behind a poor surface finish. The cutting force magnitude is proportional to the thickness of the chip removed from the workpiece. Many researchers focused on the development of analytical and numerical methods for the prediction of chatter. However, the applicability of these methods in industrial conditions is limited, since they require accurate modelling of machining system dynamics and of cutting forces. In this study, chatter prediction was investigated for orthogonal cutting in turning operations. Therefore, the linear analysis of the single degree of freedom (SDOF) model was performed by applying oriented transfer function (OTF) and \tau decomposition form to Nyquist criteria. Machine chatter frequency predictions obtained from both forms were compared with modal analysis and cutting tests.
Chatter Stability in Turning and Milling with in Process Identified Process Damping
Journal of Advanced Mechanical Design, Systems, and Manufacturing, 2010
Process damping in metal cutting is caused by the contact between the flank face of the cutting tool and the wavy surface finish, which is known to damp chatter vibrations. An analytical model with process damping has already been developed and verified in earlier research, in which the damping coefficient is considered to be proportional to the ratio of vibration and cutting velocities. This paper presents in process identification of the process damping force coefficient derived from cutting tests. Plunge turning is used to create a continuous reduction in cutting speed as the tool reduces the diameter of a cylindrical workpiece. When chatter stops at a critical cutting speed, the process damping coefficient is estimated by inverse solution of the stability law. It is shown that the stability lobes constructed by the identified process damping coefficient agrees with experiments conducted in both turning and milling.
A 3D Turning Model for the Interpretation of Machining Stability and Chatter
Nonlinear Science and Complexity - Proceedings of the Conference, 2007
Turning dynamics is investigated using a 3D model that allows for simultaneous workpiece-tool deflections in response to the exertion of nonlinear regenerative force. The workpiece is modeled as a system of three rotors connected by a flexible shaft. Such a configuration enables the motion of the workpiece relative to the tool and tool motion relative to the machining surface to be three-dimensionally established as functions of spindle speed, instantaneous depth-of-cut, material removal rate and whirling. The model is explored along with its 1D counterpart, which considers only tool motions and disregards workpiece vibrations. Different stages of stability for the workpiece and the tool subject to the same cutting conditions are studied. : 05.45.-a, 46.32.+x
Time Domain Chatter Stability Comparison of Turning and Milling Processes
2012
The delay differential equations describing the turning and milling processes are solved using MATLAB and results compared. The same set of parameter combinations are used for turning tool, one tooth, three tooth and six tooth milling tools in generating graphical trajectories of cutting process. This resulted in the comparison that gave rise to the conclusion that under full-immersion conditions milling stability characteristics get closer to that of turning as the number of teeth of milling tool increases.
Analytical prediction of part dynamics for machining stability analysis
2010
An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle in order to obtain frequency response functions (FRF), which are needed in chatter stability analyses. For this purpose, a structural modification method that is an efficient tool for updating FRFs is used. The mass removed by machining is considered to be a structural modification in order to determine the FRFs at different stages of the process. The method is implemented in a computer code and demonstrated on different geometries. The predictions are compared and verified by FEA. Predicted FRFs are used in chatter stability analyses, and the effect of part dynamics on stability is studied. Different cutting strategies are compared for increased chatter-free material removal rates considering part dynamics.
Study of Chatter Analysis in Turning Tool And Control Methods – A Review
2012
Machine tool chatter is one of the major constraints that limit productivity of the turning process. It is a self-excited vibration that is mainly caused by the interaction between the machine-tool/workpiece structure and the cutting process dynamics. The frictional and impact chatter are mainly due to the nonlinearity of the dry friction and the intermittent contact between the cutting tool and the workpiece. There are some methods that can limit the chatter. In this paper we introduce and compare some of these methods.
Stability Analysis of the Vibration-Assisted Turning Process
2016
ARTICLE INFORMATION ABSTRACT Original Research Paper Received 20 July 2016 Accepted 21 August 2016 Available Online 02 October 2016 Chattering is a kind of self-excited vibration encountered in different machining processes such as milling and turning. This type of self-excited vibration rapidly develops after commencement and destabilizes the whole process. This phenomenon leads to, among other issues, increased noise, wavy surface finishes, discontinuous chips, and failure in the tool or machine parts. The depth of cut is the main parameter in the occurrence of chattering in machining processes. Avoiding the critical depth of cut ensures the stability of the process. Process modeling is a way to obtain the critical depth of cut. The vibration-assisted turning process has many advantages and is of a different nature than the conventional machining. In this paper, the vibration-assisted turning process is modeled and numerically solved and the critical depth of cut is obtained. Vali...
The International Journal of Advanced Manufacturing Technology, 2016
Productivity of high-speed turning operations is limited by the onset of self-excited vibrations known as chatter. Unless avoided, chatter vibrations may cause large dynamic loads damaging the machine spindle, cutting tool or workpiece and leave a poor surface finish behind. Cutting force magnitude is proportional to the thickness of the chip removed from the workpiece. This paper presents a new procedure to determine dynamic cutting force coefficients (DCFC) required for process simulation by mechanistic modelling. In this study, a two degree of freedom complex dynamic model of turning with an orthogonal cutting system is considered. The complex dynamic system consists of a dynamic cutting system force model based on shear angle (φ) oscillations and penetration forces caused by the tool flank's contact with the wavy surface. The dynamic cutting force coefficients are identified by operating a series of cutting tests at the desired frequency, while changing φ oscillations and penetration forces. It is shown that the process damping coefficient increases as the tool is worn, which increases the chatter stability limit in cutting. The chatter stability of a dynamic cutting process is solved using the Nyquist law and time domain simulation (TDS) techniques and compared favourably against experimental results at low cutting speeds. Finally, comparisons among the proposed mechanistic model and experimental results show a good agreement with the analytically established SLD and, thus, validate the effectiveness of the proposed model.
Stability analysis of machine-tool vibrations in the frequency domain
IFAC-PapersOnLine, 2015
The identification of the stability lobes for machine-tool vibrations is presented for interrupted turning processes with round inserts. An analytic cutting force model for round inserts is derived, where the directional factors depend nonlinear and non-homogeneous on the depth of cut. Furthermore, the effect of vibrations in the cutting speed direction on the chip thickness modulation is taken into account, which leads to a state-dependent delay. A multifrequency solution is presented for the stability analysis of metal cutting processes, where the cutting force is characterized by periodic coefficients and state-dependent delays.