Chatter stability of metal cutting and grinding (original) (raw)

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.

Dynamics Aspect of Chatter Suppression in Milling

Harmful chatter vibrations in milling should be avoided or suppressed. Therefore dynamic aspect of milling model with vibrating workpiece are analysed in this paper. The idea, successfully implemented to orthogonal cutting, now is used for more complicated discontinuous system. The obtained results which not always give wanted response are presented as the stability lobes and bifurcation diagrams. Finally, parameters of workpiece excitation are tested to find chatter suppression zones and specific dynamic phenomena.

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 expressions for chatter analysis in milling operations with one dominant mode

Journal of Sound and Vibration, 2016

In milling, an accurate prediction of chatter is still one of the most complex problems in the field. The presence of these self-excited vibrations can spoil the surface of the part and can also cause a large reduction in tool life. The stability diagrams provide a practical selection of the optimum cutting conditions determined either by time domain or frequency domain based methods. Applying these methods parametric or parameter traced representations of the linear stability limits can be achieved by solving the corresponding eigenvalue problems. In this work, new analytical formulae are proposed related to the parameter domains of both Hopf and period doubling type stability boundaries emerging in the regenerative mechanical model of time periodical milling processes. These formulae are useful to enrich and speed up the currently used numerical methods. Also, the destabilization mechanism of double period chatter is explained, creating an analogy with the chatter related to the Hopf bifurcation, considering one dominant mode and using concepts established by the Pioneers of chatter research.

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.

Time and frequency domain models for chatter prediction in milling

In order to avoid chatter vibrations, usually a process planning is performed before manufacturing. This involves some calculations based on the tool and the machine dynamics that yield the stability lobes diagram. On this purpose, two approaches are available: one based on the time domain, and another based on the frequency domain. A matter of current discussion is which one of them is better according to the desired target. All of the above is argued in this paper, explaining the stability lobes diagram calculations and gathering the main advantages and drawbacks of each technique. These ideas are clearly explained by a comparison between analytical calculations and experiments carried out using the DS630 horizontal machining centre of Danobat Group.

Continuous model for analytical prediction of chatter in milling

International Journal of Machine Tools and Manufacture, 2009

A novel analytical approach for prediction of chatter in milling process is presented. Existing approaches use lumped-parameter models to define the dynamics of tools/workpieces. In this paper a continuous beam model is employed for prediction of milling operations dynamics. The tool boundary conditions are elastic support at the tool/holder/spindle interface and free support at the other end. Employing the continuous model eliminates the need for tool tip frequency response function (FRF) measurements in tool-tuning practice, especially in micro-milling, where FRF measurement is practically very difficult. Tool/holder/spindle interface parameters, once identified, can be used for other tool lengths. The impact hammer test is used to identify stiffness and damping parameters of the tool/holder/spindle interface. Using the new analytical approach and picking single-frequency solution (SFS), stability lobes are obtained for a slotting operation. The resulting lobes are compared to those obtained by the well-proven lumped-parameter model. In addition to a good general agreement between the two approaches, the continuous model prediction is more conservative for critical depth of cut, which is attributed to its ability to consider all participating modes in the response and so represents a more accurate representation of the system.

Chatter Stability of 5-Axis Milling Using Multi-Frequency Solution

5-axis milling is a common manufacturing process especially in machining of complex surfaces. In such operations, chatter is an important problem as it affects the surface quality of the finished part. The application of stability diagrams is an efficient tool to predict chatter free cutting conditions. Although several stability models have been developed for milling operations, they are limited to 3 axis milling applications. In an earlier study by the authors, a stability model for 5 axis milling was presented using single frequency solution. Due to the time varying nature of the milling dynamics, a multi frequency system response may be obtained for cases where radial depth of cut is small. These frequencies show up in the system response in the form of addition and subtraction of the chatter frequency and harmonics of the tooth passing frequency. In the present study, dynamics of 5-axis milling is modelled analytically considering multi-frequency effects. The existence of multi frequency response is demonstrated using experiments and numerical solutions. The effect of multi frequency dynamics on the stability diagrams are shown by the analytical solutions and time domain simulations.

Chatter in machining processes: A review

Chatter is a self-excited vibration that can occur during machining operations and become a common limitation to productivity and part quality. For this reason, it has been a topic of industrial and academic interest in the manufacturing sector for many years. A great deal of research has been carried out since the late 1950s to solve the chatter problem. Researchers have studied how to detect, identify, avoid, prevent, reduce, control, or suppress chatter. This paper reviews the state of research on the chatter problem and classifies the existing methods developed to ensure stable cutting into those that use the lobbing effect, out-of-process or in-process, and those that, passively or actively, modify the system behaviour.

4 Time Domain Chatter Stability Comparison Turning and Milling Processes

Chatter stability of metal cutting and grinding (original) (raw)

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