Comparing Chatter Stability of End-Milling Processes of different number of teeth (original) (raw)
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Effects of Radial Immersion and Cutting Direction on Chatter Instability In End-Milling
Proceedings …, 2002
Low radial immersion end-milling involves intermittent cutting. If the tool is flexible, its motion in both the x-and ydirections affects the chip load and cutting forces, leading to chatter instability under certain conditions. Interrupted cutting complicates stability analysis by imposing sharp periodic variations in the dynamic model. Stability predictions for the 2-DOF model differ significantly from prior 1-DOF models of interrupted cutting. In this paper stability boundaries of the 2-DOF milling process are determined by three techniques and compared: (1) a frequency-domain technique developed by Altintas and Budak (1995); (2) a method based on time finite element analysis; and (3) the statistical variance of periodic 1/tooth samples in a time-marching simulation. Each method has advantages in different situations. The frequency-domain technique is fastest, and is accurate except at very low radial immersions. The temporal FEA method is significantly more efficient than time-marching simulation, and provides accurate stability predictions at small radial immersions. The variance estimate is a robust and versatile measure of stability for experimental tests as well as simulation. Experimental upmilling and down-milling tests, in a simple model with varying cutting directions, agree well with theory.
Chatter Stability Characterization of a Plastic End-Milling CNC machine
The desire to carry out this work arose from an observation during a practical work on a typical plastic end milling CNC machine. It was noticed that under certain conditions of cutting, operation of the machine became noisy with increasing depth of cut and eventual perforation of workpiece therefore the basic aim is to generate stability characterization of the machine in the form of a chart on the plane of cutting parameters on which stable operation is demarcated from the unstable operation . In modelling this machine, a slot creating mode of operation is used since the machine is mainly used for creating logos which are basically collection of slots. The significance of the resulting stability chart lies in the result that the cause of the aforementioned noisy operation is due to unstable parameter combination. For example a laboratory operation at spindle speed of 1500rpm and depth of cut of 1.5mm was noisy while that at spindle speed of 1500rpm and depth of cut of 1mm was serene. The stability chart generated for the system thus shows close agreement with both practice and theory. A unique impact this work will have on the reading community will be in the area of validity of the resulting stability chart on the basis of MATLAB dde23 numerical simulation. The parameters of the end milling process are; tool mass tool natural frequency damping factor and workpiece cutting coefficient .
Stability limits of milling considering the flexibility of the workpiece and the machine
International Journal of Machine Tools and Manufacture, 2005
High speed machining of low rigidity structures is a widely used process in the aeronautical industry. Along the machining of this type of structures, the so-called monolithic components, large quantities of material are removed using high removal rate conditions, with the risk of the instability of the process. Very thin walls will also be milled, with the possibility of lateral vibration of them in some cutting conditions and at some stages of machining. Chatter is an undesirable phenomenon in all machining processes, causing a reduction in productivity, low quality of the finished workpieces, and a reduction of the machine-spindle's working life.
COMPARISON OF UP-MILLING AND DOWN-MILLING MODES OF END-MILLING PROCESS
End-milling at partial radial immersion is distinguished into up end-milling mode and down end-milling mode thus the need to ascertain the more stable option for laboratory application. The two end-milling modes are theoretically given comparative study for a three tooth end-miller operating at 0.5 and 0.8 radial immersions. The 0.5 and 0.8 radial immersion conditions are chosen so that analysis covers situations in which free flight of tool and simultaneous teeth engagements occur. Model transformation is achieved through the use of Fargue approximation. It results from analysis of 1-DOF model of end-milling that down end-milling is better for workshop application than up end-milling from standpoints of cutting force and dynamic stability. This result is the significance of the study since it conforms to the age long recognition from workshop practices that climb milling operations are more stable than conventional milling operations. Stability results of both modes of operation are given in the form of stability charts in which a transition curve is tracked to demarcate the stable from the unstable domains. Validation of these charts is conducted via time domain numerical analysis of selected points on the parameter plane of spindle speed and depth of cut. Another significance of this study that impacts into the reading community is that a phenomenon called "Approximation parameter (n) banding of accuracy and inaccuracy" is discovered and highlighted as one of the setbacks in the use of Fargue approximation method in milling stability analysis. The major limitation of this study is that a formal explanation could not be given for the discovered "n-banding of accuracy and inaccuracy" of Fargue approximated charts.
It was noticed in laboratory practice that certain conditions of slotting operation of a plastic end milling computer Nu merical control (CNC) machine became noisy with increasing depth of cut and eventual perforation of workp iece thus objective is to generate stability characterization of the machine in the form of a chart on the plane of cutting parameters on which stable operation is demarcated fro m the unstable operation. Chatter stability analysis is carried out here using a recently developed method called Fu ll-discretization. The resulting chart is partit ioned into portions of secondary Hopf and flip bifurcations through MATLAB eigen-value analysis of resulting monodro my operator. These two types of bifurcation are d iscovered to be visible for high speed range while only secondary Hopf bifurcat ion is visible for the lo w spindle speed range. It is also discovered for the studied slotting operation, that critical characteristic mu ltipliers are almost pure imaginary at the turning points of secondary Hopf bifurcation lobes and get closer to the negative real axis when critical points move away from min imu m points. Equation describing the infinitely many but discrete secondary Hopf bifurcation chatter frequencies at min imu m points is postulated. The parameters of the end milling process are; tool mass m = 0.0431kg, tool natural frequency n = 5700 rads −1 , damping factor ξ = 0.02 and workpiece cutting coefficient C = 3.5 × 10 7 Nm −7 4 ⁄ . The stability chart generated for the system shows close agreement with both practice and theory.
Influence of Milling Cutter Dynamics on Stability Lobe Diagrams
2017
In milling, both dimensional accuracy and productivity depend on several parameters of milling. As these parameters influence the material removal rate and the stability of process in terms of vibrations and chatter, it is important to examine the role of these parameters on the level of vibration and chatter. Since 1960s, the researchers have studied chatter problems with a view to understand the mechanism, parameters responsible for this phenomena and its behaviour in milling operation. Out of several methods that can be followed for minimizing and avoiding chatter, stability lobe diagram is considered to be the most reliable way of identifying the cutting parameters for chatter free condition. Since the chatter depends on the interaction of milling cutter with work piece during milling of parts on the milling machine, it is essential to examine the influence of dynamic parameters of milling cutter on the stability of cutting process. This paper covers the generation of stability ...
Prediction of stability limit for multi-regenerative chatter in high performance milling
International Journal of Dynamics and Control, 2014
Chatter is one of the most important factors that inhibit the improvement of productivity and deteriorate the machined surface quality in milling process. In order to obtain good surface quality, classical machining process usually has to take conservative milling parameters. Based on the authors' previous work, this paper presented a new thirdorder discretization method to compute the stability lobes considering multi-regenerative chatter effect. A mathematical model, which is suitable for the dynamic system with non-uniform pitch cutter or cutter run-out, is first established for multi-regenerative chatter. Then, three examples are performed to test the validity of the proposed method. The first example is for the case that the system takes a non-uniform pitch cutter. In the second example, after the modal parameters, run-out parameters and cutting force parameters are gained from experiments, the stability lobes are predicted using the proposed method and subsequently testified by a series of experiments. The third example is for the case of existing cutter run-out. The final computation and experiment results indicate the effectiveness and validity of the proposed method. It is applicable in high performance machining for achieving a good parameter combination.