A new process damping model for chatter vibration (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.
A simple approach to analyze process damping in chatter vibration
The International Journal of Advanced Manufacturing Technology, 2013
This paper investigates how changes in chatter amplitude and frequency depend on process damping effect in dynamic turning process. For this purpose, the two degrees of freedom (TDOF) cutting system was modeled, and for an orthogonal turning system, the process damping model with a new simple approach was developed. To further explore the nature of the TDOF cutting model, a numerical simulation of the process was developed by this model. This simulation was able to overcome some of the weaknesses of the analytical model. The equations of motion for this cutting system were written as linear and nonlinear in the τ-decomposition form. The variation in the process damping ratios for different work materials was simply obtained by solving the nonlinear differential equations. A series of orthogonal chatter stability tests were performed for the identification of dynamic cutting force coefficients, using AISI-1040, Al-7075, and Al-6061 work materials, at a constant spindle speed. Finally, the experimental results were analyzed and compared with the simulation model, and it was observed that the results obtained through the experiments comply with the simulation model results.
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.
Measurement, 2012
In the previous study, by the same authors, titled ''A new process damping model (PDM) for chatter vibration (Measurement, 44 (8) (2011) 1342-1348)'', a new approach has been presented for obtaining process damping ratios (PDRs). This PDM has been constituted on the basis of the shear angle ðuÞ oscillations of the cutting tool and the alteration of the penetration forces when they penetrate into the wavy surface. Variation and quantity of PDR are predicted by reverse running analytical calculation procedure of traditional Stability Lobe Diagrams (SLDs). In this study, firstly, how the PDM in previous study results with different materials such as AISI-1050 and Al-7075 are examined. Then, two problems are solved: how much of the total PDR of cutting system is caused by the tool penetration and how much is caused by ðuÞ oscillation? Finally, verification of PDR values and PDM are performed by energy equations.
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.
Computational stability analysis of chatter in turning
… and Engineering(USA …, 1997
Machine tool chatter is one of the major constraints that limits 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. This work introduces a general method which avoids lengthy algebraic (symbolic) manipulations in deriving, a characteristic equation. The solution scheme is simple and robust since the characteristic equation is numerically formulated as a single variable equation whose variable is well bounded rather than two nonlinear algebraic equations with unbounded variables. An asymptotic stability index is also introduced for a relative stability analysis. The method can be applied to other machining processes, as long as the system equations can be expressed as a set of linear time invariant difference-differential equations. Associate Technical Editor: S. Smith.
Analyzing the Effects of Tool Holder Stiffness on Chatter Vibration Reduction in Turning
Journal of Metallic Material Research
This paper investigates the effects of tool holder materials on chatter vibration in turning operations. The study uses a complex dynamic turning model with two degrees of freedom for the orthogonal cutting system. Tool holders made from different materials, including Al 5083, Al 6082, Al 7012, and a standard 4140 material, were subjected to chatter vibration to investigate their process damping capabilities. The study found that the standard tool holder 4140 allows for higher stable depths of cut and produces similar process damping values compared to the other tool holders. Finite element analyses (FEA) were performed to verify the experimental results, and the modal and FEA analyses produced very similar results. The study concludes that future research should investigate the effects of tool holders made from high alloy steel alloys on process damping. Overall, this paper provides important insights into the effects of tool holder materials on chatter vibration and process dampin...
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.
On process damping induced by vibration-dependency of cutting direction in milling
Procedia CIRP, 2018
The process damping effect is analyzed for regenerative machine tool chatter in milling via a velocity-dependent cutting force model. This model takes into account that the effective cutting direction depends on the vibrations of the machine tool-workpiece system, which modifies the effective rake angle, the chip thickness, and the cutting force. The model was originally introduced for turning operations where it results in a process damping term that improves the stability of metal cutting at low cutting speeds. Now this model is extended to milling. It is shown that the vibration-dependency of the cutting direction induces a time-periodic process damping term that is negative when the radial immersion is low. This decreases the stability at low cutting speeds, thus the low-speed stability improvement phenomenon in low radial immersion milling can be explained by extended process damping models only.