Chatter vibration

Chatter is one of the most important limitations in machining processes causing poor surface finish, decreased tool life, and damage to the machine tool. Additional operations are required to clean the marks left on the surface however this may not be possible in cases of severe chatter. In short, chatter vibrations result in reduced productivity, increased cost, and inconsistent product quality. 

Chatter is a self-excited vibration type resulting from the dynamic interaction between the cutting tool and the work material (Tobias 1965 Koenigsberger and Tlusty 1967). For forced vibrations arising in mechanical systems, the excitation is independent of the response, i.e., the vibrations do not affect the forces. In self-excited chatter vibrations, on the other hand, the chip thickness becomes modulated... 

The term chatter prediction describes a range of simulation methods, which are used to predict chatter vibrations (instabilities). These methods are based on the dynamic compliance of the machine tool structure as well as on the dynanucs of the machining process. The whole machine behavior can be expressed in terms of mathematical descriptions (coupled structure-process models), from which stability lobe diagrams can be derived. 

As shown above, the cause of chatter is associated to the machining process and its history as well. However, the intensity of chatter vibrations is characterized by all components within the force flux (tool, machine tool, and workpiece structure) respectively their compliance. To determine the stability of the coupled overall system (see Fig. 1), both subsystems have to be modeled. 

Fig. 2 Regenerative chatter vibrations occurring during an orthogonal cutting process with one SDOF xi...

Fig, 4 Regenerative chatter vibrations occurring during a two-dimensional milling process with two DOF x and X2 (Altintas 2012)... 

This equilibrium becomes unstable at a certain b, and a sinusoidal vibration starts growing up, which is called chatter vibration. The stability limit, i.e., the maximal width of cut where the equilibrium is stable, can also be found by a stability analysis (Schmitz and Smith 2009). We assume that a distortion results in a damped or excited sinusoidal vibration with a starting amplitude a and an angular velocity a> ... 

Machine tool vibrations can conveniently be measured or monitored by an accelerometer, a gap sensor or a microphone. The vibration mark left on the machined surface is often measured or observed to estimate the vibration amplitude and frequency. Figure 3 shows an example of the regenerative chatter vibration mark left on a face-milled surface. The vibration frequency can be estimated from the measured vibration pitch and the cutting speed. 

The number of peaks in a related series and the relative intensity of these peaks are functions of the shape of the grooves or tool marks. Changes in this pattern are an excellent diagnostic for tool wear, chip drag, chatter, vibrations, and a number of other characteristic and potential problems in the machining process. 

In contrast, self-excited vibration called chatter vibration often occurs on the boring bar of a cutting tool being used to expand the bores in metal parts. It is especially disturbing in iron boring operations. When chatter vibration is excited, it not only affects the finishing... 

Utilizing the vibration damping ability of VEM (visco-elastic material, a pressure-sensitive adhesive of acrylic resin), as shown in Fig. 5.19, boring bars with an extremely high stability against chatter vibration have been developed. 

Fig. 5.21. Stability for chatter vibration of boring bar with adhesive bonded...

Regardless of the frequency, there are desirable vibrations (aka Good Vibrations), and there are undesirable vibrations. There are vibrations which make our teeth chatter, vibrations that make us nauseous, and vibrations that make our heart go pitter-patter (which is usually a good thing, but not always). There are vibrations which are resonant, consonant, dissonant, damped, undamped, muted, baffled, treated, untreated, amplified, modified, distorted, and/or ignored. 

The high elastic modulus, compressive strength, and wear resistance of cemented carbides make them ideal candidates for use in boring bars, long shafts, and plungers, where reduction in deflection, chatter, and vibration are concerns. Metal, ceramic, and carbide powder-compacting dies and punches are generahy made of 6 wt % and 11 wt % Co ahoys, respectively. Another apphcation area for carbides is the synthetic diamond industry where carbides are used for dies and pistons (see Carbon). 

Schnarre,/. (Elec.) buzzer. schnarren, v.i. rattle, jar, buzz, vibrate, scfanattera, v.i. cackle chatter. 

Plain slideways are preferred in the majority of applications. Only a thin film of lubricant is present, so its properties - especially its viscosity, adhesion and extreme-pressure characteristics - are of vital importance. If lubrication breaks down intermittently, a condition is created known as stick-slip , which affects surface finish, causes vibration and chatter and makes close limits difficult to hold. Special adhesive additives are incorporated into the lubricant to provide good bonding of the oil film to the sliding surfaces, which helps to overcome the problems of table and slideway lubrication. On long traverses, oil may be fed through grooves in the underside of the slideway. 

Diamond, as single crystal or as a polycrystalline compact (PCD) is an excellent cutting material but is expensive and requires closely controlled speed and absence of chatter and vibration for optimum performance.PI It has limited oxidation resistance as it begins to oxidize in dry-grinding operations between 500 and 700°C, and the use of coolant is recommended to remain below these tern-... 

Figure 10.5 shows a vibrating string system with a discontinuous nonlinear interaction. As the string vibrates, it chatters against the secondary bridge... 

Chatter, Fig. 3 Chip thickness in turning, boring, and nulling under the effect of vibrations... 

Although orthogonal theory demonstrates fundamentals and basic relations of chatter, dynamic cutting and chatter stability of industrial machining operations require multidimensional analysis due to their complex geometry. Figure 3 shows the chip thickness variation under the effect of vibrations in two directions. In these cases, components of each dynamic displacement in the chip thickness direction must be considered. These vibrations may come from the tool or workpiece side in more than one direction. The stability... 

Stable depth of cuts obtained in chatter tests can be used to determine the process damping and the indentation force coefficients between the flank face of the tool and the material (Budak and Tunc 2010). In addition to the cutting speed and the vibration frequency, which determine the wavelength, clearance angle and edge hone... 

Chatter Prediction, Fig. 5 Free vibrations of a linear, viscously damped system, where (a) represents the stable case, (b) the marginally stable case, and (c) the unstable case... 

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