Machine Tool Chatter and Surface Location Error in Milling Processes (original) (raw)
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Machine Tool Chatter and Surface Quality in Milling Processes
Manufacturing Engineering and Materials Handling Engineering, 2004
Two degree of freedom model of milling process is investigated. The governing equation of motion is decomposed into two parts: an ordinary differential equation describing the stable periodic motion of the tool and a delay-differential equation describing chatter. Stability chart is derived by using semi-discretization method for the delay-differential equation corresponding to the chatter motion. The stable periodic motion of the tool and the associated surface location error are obtained by a conventional solution technique of ordinary differential equations. Stability chart and surface location error are determined for milling process. It is shown that at spindle speeds, where high depths of cut are available through stable machining, the surface location error is large. The phase portrait of the tool is also analyzed for different spindle speeds. Theoretical predictions are qualitatively confirmed by experiments.
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.
2007
This paper investigates the effectiveness of Sinusoidal Spindle Speed Variation (SSSV) technique as a chatter suppression method in milling process. On this purpose, a twofold study was carried out: on the one hand, a simulation analysis, and on the other, experimental machining. First, a time domain model of the cutting process was modified to include simulation capabilities concerning spindle speed variation. The results obtained by SSSV techniques mainly depend on the relationship between the chatter frequency and the tooth passing frequency. The SSSV-based strategy for chatter avoidance was embedded in a Computer Numerical Control (CNC) to run experimental tests. They were carried out to show the SSSV technique performance, focused on both high and low spindle speeds. To summarise, this technique lifts the asymptotic stability limits mainly at low spindle speeds.
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 Improvement of a Slender Milling Tool via a Dynamics Variation Mechanism
Research Square (Research Square), 2023
In this study, a milling tool with variable mass and stiffness is developed for chatter reduction. The proposed milling tool is hollow with a solid core threaded inside it. As the core is screwed in or out of the tool body, the equal mass and stiffness of the tool are changed. Therefore, the tool's frequency response function (FRF) is changed to affect the stability lobe diagram (SLD) position. Moving the SLDs can stabilize an unstable cutting process. With respect to the FRFs obtained from modal test, the idea is proven using an experimental and analytical approach. The optimum core position for every spindle speed is also presented. The developed tool stability is then investigated in a realistic cutting condition. The cutting process sound analysis and surface finish visual inspection results reveal the performance of the proposed system in chatter reduction of a slender milling tool.
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 modelling in micro-milling by considering process nonlinearities
International Journal of Machine Tools and Manufacture, 2012
This paper presents a new approach for chatter modelling in micro-milling. The model takes into account: the nonlinearity of the uncut chip thickness including the run-out effect; velocity dependent micro-milling cutting forces; the dynamics of the tool-holder-spindle assembly. The uncut chip thickness is determined after considering the full kinematics of the cutting tool including the runout effect. The micro-milling cutting forces are determined by: (i) a finite element (FE) prediction of the cutting forces in orthogonal cutting at different cutting velocities and uncut chip thicknesses; (ii) describing the relationship between cutting forces, cutting velocities and uncut chip thicknesses into a nonlinear equation; (iii) incorporating the uncut chip thickness model into the relationship of the cutting forces as function of the cutting velocity and the uncut chip thickness. The modal dynamic parameters at the cutting tool tip are determined for the tool-holder-spindle assembly and used for solving the equation of motion. The micro-milling process is modelled as two degrees of freedom system where the modal dynamic parameters for the tool-holder-spindle assembly and the micromilling cutting forces are considered. Due to nonlinearities in the micro-milling cutting forces, the equation of motion is integrated numerically in the time domain using the Runge-Kutta fourth order method. The displacements in the x and y directions are obtained for one revolution-per-tool. Statistical variances are then employed as a chatter detection criterion in the time-domain solution. Scanning electron microscope (SEM) inspection is carried out to observe potential chatter marks on the micromilled AISI 4340 steel surfaces at different spindle speeds and depths of cut. The predicted stability lobes and the experimentally obtained stability limits resulted in satisfactory agreement. The influence of the run-out effect on the stability lobes at different feed rates was investigated, which demonstrated the capability of the developed chatter model to consider quantitatively the run-out phenomenon. The results showed that the stability limits decrease by increasing the run-out length.
Procedia CIRP, 2016
In milling processes, the desired machined surface cannot be perfectly achieved even in case of chatter-free machining due to the thermally induced errors, the trajectory following errors and the most significant one: the cutting force induced vibration errors. In case of vibration, the error is represented by the so-called Surface Location Error (SLE), which is the distance between the machined and the required surface position. In case of roughing operations, these errors can have a significant impact on the surface position due to the interaction between the subsequent SLEs. The machined surface depends on the previously resulted SLE through the variation of the radial immersion. In this paper, the series of the consecutive SLEs are investigated in a multi-degree-of-freedom model. The dynamical behaviour of the milling tool is described by frequency response functions. The variation of the SLE values is governed by a discrete map, which may lead to an unpredictable final surface position. The parameter range where this unpredictable final SLE occurs is presented together with the traditional stability chart representing the chatter-free domains of cutting parameters. With the proposed methods, the traditional stability chart can be improved, from which chatter-free and CSLE-stable technological parameters can be selected.
The Effect of Spindle Speed Variation on Chatter Suppression in Rotating-Tool Machining
Spindle speed variation (SSV) is one of a number of promising strategies to suppress chatter. Most previous research on SSV stability analysis for nonintermittent machining processes has focused on stationary-bar boring or turning. However, nonintermittent rotating-tool machining is also a common process. This paper investigates the effect of SSV in nonintermittent rotating-tool machining, using rotating-bar boring as an example. This paper takes advantage of the rotating-frame approach and the resulting constant delay in the angle domain to investigate the SSV effect on system stability for rotating-bar boring. The results show that the SSV effect on rotating-bar boring flattens the stability lobes and lifts the tangential stability limits
Multiple chatter frequencies in milling processes
Journal of Sound and Vibration, 2003
Analytical and experimental identifications of the chatter frequencies in milling processes are presented. In the case of milling, there are several frequency sets arising from the vibration signals, as opposed to the single well-defined chatter frequency of the unstable turning process. Frequency diagrams are constructed analytically and attached to the stability charts of mechanical models of high-speed milling. The corresponding quasiperiodic solutions of the governing time-periodic delay-differential equations are also identified with some milling experiments in the case of highly intermittent cutting.