Suppress Chatter Vibration Research Articles

Mechanism to suppress regenerative chatter vibration due to the effect of air-cutting and multiple regeneration during low frequency vibration cutting

Recently, the application of low frequency vibration has been attempted in the turning process. The tool is vibrated in the feed direction by numerical control to break up long continuous chips that adversely affect the surface quality and tool wear, etc., by generating a duration of cutting edge leaving workpiece. In order to achieve higher machining efficiency in vibration cutting, however, it is necessary to focus on chatter stability. When chattering occurs, a higher frequency chatter vibration is superimposed on the low-frequency tool vibration caused by the feed motion of the servo drive. However, the chatter amplitude decreases due to system damping, because the cutting force does not act in the air-cutting section of vibration cutting. In addition, tool displacement is regenerated not only before one spindle rotation, but also before two or more rotations in vibration cutting. Therefore, the application of low frequency vibration has an important influence on the chatter stability. The purpose of this study is to reveal the detailed effects of vibration conditions on the stability limit, and identify the vibration conditions that achieve high chatter stability. We consider the effect of the air-cutting and multi-rotation delayed regeneration described above, in which chatter displacement occurring more than two spindle rotations before is regenerated, and analyze regenerative chatter vibration during vibration cutting in the frequency domain. In this study, the phase difference φ of tool motion in vibration cutting is focused as an important vibration condition parameter that affects the stability limit. In the conventional condition (φ = π), the air-cutting ratio is limited to a relatively low value, and only the dynamic displacements before one and two spindle revolutions are regenerated. On the other hand, setting φ appropriately under the condition φ≠π, the air-cutting ratio is increased. Furthermore, the dynamic displacement is regenerated not only before one and two spindle rotations but also before three or more spindle rotations. These results indicate that proper setting of the phase difference φ is effective in suppressing regenerative chatter vibration due to the effects of both the air-cutting phenomenon and multi-rotation delay. Finally, cutting experiments show that the phase difference φ specified by the analysis was effective in suppressing chatter vibration. In summary, the application of low frequency vibration with an appropriately set phase difference φ is an effective strategy for suppressing chatter vibration without reducing the material removal rate in the turning process.

Influence of flank texture patterns on the suppression of chatter vibration and flank adhesion in turning operations

In this paper, we propose a practical texture design on the tool flank face for suppressing chatter vibration and flank adhesion. To avoid chatter vibration during cutting, the process damping phenomena can be utilized, where the tool flank face contacts the surface of a finished workpiece to provide a damping effect. As a new technology for an effective process damping, the tool flank texture-assisted technique has been proposed, and its excellent performance in suppressing chatter vibration has been demonstrated. However, issues that can lead to adhesion and tool damage pose challenges from a practical viewpoint. To overcome such issues, this paper proposes new texture geometries that improve the practical performance: parallel line type, vertical line type, and dot type. The results of a series of finite element analyses showed that the effectiveness of process damping depends on the vibration amplitude and wavelength. The proposed flank textures were fabricated on tool flank faces, and turning tests were carried out. The experimental results showed that the proposed tool is stabler than the conventional untextured tool and that it can more effectively improve the critical cutting speed, reduce the vibration amplitude, and decrease the surface roughness after cutting. With the appropriate design of the texture distance, adhesion and tool damage were hardly observed, and a stable and practical cutting could be realized.

Chatter Stability Prediction Method of the Spindle-Tool Holder-Tool System with Interface Contact Characteristics

To predict chatter stability and suppress chatter vibration, a chatter stability prediction method for the spindle-tool holder-tool system with interface contact characteristics is constructed. A five-DOF model is constructed to determine the spindle-bearing interface dynamic contact stiffness considering the coupling effect of spindle and bearing. A fractal multiscale tool holder-spindle interface dynamic stiffness model is proposed considering time-varying cutting force. The fractal dimensions and cutting force coefficient parameters are identified from the power spectrum experiments and cutting force tests. The cutting force is solved according to the milling stability model. Dynamic model of the spindle-tool holder-tool system is found by the finite element method. Based on extended Floquet theory, chatter stability of the spindle system is studied. Effect of interface parameters, radial cutting depth, and feed rate on milling stability is researched. Milling force tests and milling stability tests are performed in order to verify the reliability of the method. Results find that the increase of front bearing preload and spindle-tool holder’s interference fit are effective to improve the milling stability. The optimal feed rate and the critical radial cutting depth are found. The model proposed in this paper can be used as an instruction for predicting and suppressing the chatter vibration and optimizing cutting parameters and also is helpful for designing the spindle-tool holder-tool system.

Self-acting optimal design of spindle speed variation for regenerative chatter suppression based on novel analysis of internal process energy behavior

Spindle speed variation (SSV) is a well-known effective and flexible technique to suppress chatter vibration by disrupting regenerative effect. In most research, the SSV is properly designed by a large number of complex stability simulations including identification of machine dynamics with time consumption or costly experiments while varying design parameters; hence, this approach cannot be on-line or integrable in the machine tools for autonomous self-suppression of chatter vibration. This paper presents a programmable optimal design methodology for sinusoidal spindle speed variation (SSSV), which only requires measuring the chatter frequency and can incorporate the machine constraints into the design procedure. The design concept is based on the minimization of kinematic internal process energy balance during SSSV cycle for efficient chatter energy dissipation. For this purpose, the modulation index, which is originally defined for frequency modulation (FM) technology in radio communication engineering, is introduced into SSSV as a novel index. The novel design criteria in terms of SSSV frequency are also proposed for robust chatter suppression without a momentary destabilization during SSSV cycle, called as beat vibration. A series of time-domain SSSV simulation and boring tests are carried out in depth for verification. It can be concluded that, the parameter candidates suggested by the proposed design procedure can optimally dissipate the chatter with little beat vibration.

Modeling and active control of chatter vibrations of piezoelectric stacked machining arm in micro-turning process

Self-excited vibrations known as chatter are considered as the most detrimental issue in micro-turning processes. Occurring unpredictably, they adversely affect the tool life, productivity rate and surface quality of the machining processes. In this paper, a novel machining arm is modeled as a piezoelectric stacked rod which is subjected to a chatter force in the orthogonal micro-turning process. Due to the fact that machining processes are affected by various sources of uncertainties, H∞ robust control approach is used to suppress the chatter vibrations of the machining arm in the presence of tool wear and dynamic model parameter variations. Also, input control force of the system is provided by exciting the input voltage of piezoelectric layers of the rod. In order to be certain that the designed controller succeeds in suppressing vibrations of the effective structural modes, behavior of the first three modes of vibrations are considered in the final response of the machining arm. In the following, performance of the robust H∞ controller is compared with a modified PID controller. Simulation results show that the H∞ controller improves the robustness and performance of the system against uncertainties. The PID controller extends the stability region of the sharp tool and fails to achieve this purpose for the worn tool although its performance is acceptable in suppressing chatter vibrations.

Flank face texture design to suppress chatter vibration in cutting

Process damping is useful in improving chatter stability in a low cutting speed range. This paper presents a texture design on tool flank faces that can effectively generate process damping. A convex structure on the flank face dampens chatter vibration even at general cutting speeds. An orthogonal cutting simulation utilizing a finite element analysis was conducted to estimate process damping force coefficients that are the functions of cutting and vibration conditions and tool geometry. Sufficient damping effect was predicted using the proposed texture via a chatter stability analysis in frequency domain. Face turning experiments verified the significant chatter suppression effect.

Multi harmonic and random stiffness excitation for milling chatter suppression

Abstract In cutting process, as one of the most unfavorable factors, the regenerative chatter results in serious degradation of the part surface quality, tool life and machining efficiency. According to the previous research, single frequency stiffness excitation (SFSE) is able to suppress chatter vibration effectively, where the stiffness varies in sine, cosine, square and triangle waveforms. However, the real vibrations in milling process are very complex and the SFSE can vary just in simple forms without considering phase variation. In order to mitigate chatter more effectively, this paper proposed multi harmonic stiffness excitation (MHSE) and random stiffness excitation (RSE). Due to the existence of delay item, the stiffness excitation parameters cannot be optimized with analytic methods. Therefore, with regard to MHSE, the Fourier series is used to expand the function of stiffness variation and the genetic algorithm is employed to optimize the frequency, amplitude and phase. From SFSE to MHSE, the stiffness variation can also be extended to RSE, where the variation waveform seems periodic on the whole time domain but stochastic within one period. This function of stiffness excitation cannot be described by specific parameters; thus, the random walk methodology is implemented for random waveforms optimization. The optimized random waveform is used to guide the stiffness variation for increasing the stability lobe diagrams (SLD) and suppressing chatter vibration. The simulation results show that the SLDs with MHSE and RSE are higher than those under SFSE. Finally, the milling experiments are implemented on a three-axis milling machine to validate the optimized parameters on chatter suppression. Under stiffness excitation, the chatter frequency in milling process vanishes, which shows that the proposed method can suppress chatter effectively.

Active Damping of Milling Vibration Using Operational Amplifier Circuit

The problem of chatter vibration is associated with adverse consequences that often lead to tool impairment and poor surface finished in a workpiece, and thus, controlling or suppressing chatter vibrations is of great significance to improve machining quality. In this paper, a workpiece and an actuator dynamics are considered in modeling and controller design. A proportional-integral controller (PI) is presented to control and actively damp the chatter vibration of a workpiece in the milling process. The controller is chosen on the basis of its highly stable output and a smaller amount of steady-state error. The controller is realized using analog operational amplifier circuit. The work has contributed to planning a novel approach that addresses the problem of chatter vibration in spite of technical hitches in modeling and controller design. The method can also lead to considerable reduction in vibrations and can be beneficial in industries in term of cost reduction and energy saving. The application of this method is verified using active damping device actuator (ADD) in the milling of steel.

Chatter Avoidance in Parallel Turning With Unequal Pitch Angle Using Observer-Based Cutting Force Estimation

Parallel turning is garnering attention as one of the most important technologies for multitasking machine tools. This is because a potential exists to enhance the stability limits compared to the turning operation using a single tool when cutting conditions are properly selected. Although stability prediction models for parallel turning have been developed in recent years, in-process monitoring and in-process chatter techniques are almost not discussed. In this study, to suppress chatter vibration, an unequal pitch turning method was proposed. In this method, the upper tool was controlled based on the optimum pitch angle calculated from spindle speed and chatter frequency. Chatter frequency was identified from estimated cutting force by a disturbance observer (DOB). From the result of the parallel turning test, it is clear that chatter vibration can be avoided by controlling the upper tool based on optimum pitch angle. Meanwhile, the pitch angle difference that can suppress chatter had a certain range. Subsequently, the robustness of the optimum pitch angle difference is experimentally evaluated by both the continuous moving test and the stepwise moving test of the pitch angle.

Programmable Optimal Design of Sinusoidal Spindle Speed Variation for Regenerative Chatter Suppression

Continuous spindle speed variation, especially under sinusoidal speed law, is a well-known effective and flexible technique to suppress chatter vibration by disrupting regenerative effect in high-lobe-number zone. In most researches, its optimal design parameters (i.e. amplitude and frequency of spindle speed variation) are selected to maximize cutting depth by using complex stability simulations, which take much time and require machine tool dynamics. In this paper, novel simple criteria, only according to chatter frequency and nominal spindle speed, is proposed to select optimal amplitude and frequency of sinusoidal spindle speed variation (S3V). Under assumption that the variation amplitude and frequency is low in practice, modulation index for S3V can be introduced by analogy between S3V and frequency modulation technique in radio engineering. Then, the proposed formula to select optimal parameters is introduced based on kinematic process energy analysis with modulation index as an argument of Bessel function. Although the proposed method does not give information about stability limit, it has potential to contribute to intelligent active chatter suppression by automatic selection of S3V parameters combined with chatter monitoring system. Some boring tests were conducted to verify the proposed formula.

Numerical investigation of chatter suppression in milling using active fixtures in open-loop control

Among the chatter suppression techniques in milling, active fixtures seem to be the most industrially oriented, mainly because these devices could be directly retrofittable to a variety of machine tools. The actual performances strongly depend on fixture design and the control logic employed. The usual approach in the literature, derived from general active vibration control applications, is based on the employment of adaptive closed-loop controls aimed at mitigating the amplitude of chatter frequencies with targeted counteracting vibrations. Whilst this approach has proven its effectiveness, a general application would demand a wide actuation bandwidth that is practically impeded by inertial forces and actuator-related issues. This paper presents the study of the performance of alternative open-loop actuation strategies in suppressing chatter phenomena, aiming at limiting the required actuation bandwidth. A dedicated time-domain simulation model, integrating fixture dynamics and the features of piezoelectric actuators, is developed and experimentally validated in order to be used as a testing environment to assess the effectiveness of the proposed actuation strategies. An extensive numerical investigation is then carried out to highlight the most influential factors in assessing the capability of suppressing chatter vibrations. The results clearly demonstrated that the regenerative effect could be effectively disrupted by actuation frequencies close to half the tooth-pass frequency, as long as adequate displacement is provided by the actuators. This could sensibly increase the critical axial depth of cut and hence improve the achievable material removal rate, as discussed in the paper.

Investigating Actuation Strategies in Active Fixtures for Chatter Suppression

Active fixtures represent one of the most industrially relevant alternatives among active chatter control techniques in milling, even though control logics and actuation strategies could directly reflect on their effectiveness. Closed-loop controls targeted in the chatter frequency range are commonly adopted for this purpose, but this approach lacks of applicability when chatter frequency exceeds the achievable actuation bandwidth. The purpose of this work is to investigate the effectiveness of potential low-frequency actuation strategies in suppressing chatter vibrations. A dedicated time-domain simulation model, developed and validated by authors, is used to test different actuation strategies in order to highlight the most relevant factors in assessing actuation effectiveness. The simulation results demonstrated that employing actuation frequencies close to the first half-harmonic of the tooth-pass frequency could disrupt the regenerative effect. This allows the mitigation and suppression of chatter phenomenon, increasing the critical axial depth of cut, as discussed in the paper.

切削抵抗と工具挙動の解析結果に基づくボールエンドミル形状の最適化 (第1報)

Various shaped ball end mills having a large helix angle, multiple flutes and their irregular intervals of the cutting edges are produced and widely used. However, relationships among these variably geometrical components of the tool, cutting forces and tool behavior during milling have not yet been systematically explained. This investigation deals with the tool configuration which makes effect on reducing the movement of the tool axis caused by tool deflection and suppressing chatter vibration. In this report, milling process with ball end mills whose circumferential cutting edges arranged at equal intervals is mainly treated, and cutting forces in the case of one to six circumferential cutting edges are estimated by using a cutting model proposed in previous papers. Then, to clarify the effect of the number of circumferential cutting edges on tool behavior, finite element models of ball end mills having three or four cutting edges are constructed by using geometrical data of the cross-section of a standard-type end mill. Furthermore, the data of cutting forces predicted is applied to these models to analyze the deflection of the tool axis. It is shown that the fluctuation in cutting forces and the tool axis trajectories can be considerably reduced in the case of providing four circumferential cutting edges. In addition, cutting forces of two flutes ball end mill having unequal interval of the cutting edges are estimated, and relationship between interval of the cutting edges and fluctuation of cutting forces is discussed.

Suppression of Chatter Vibration by Fuzzy Sliding Mode Control in Machining Processes

Chattering elimination of machining processes is an important issue in turning operation, due to the damages caused by this phenomenon. Limited productivity rate, decrease in tool life, poor surface quality and noisy workplace are some adverse effects of the chatter vibration. In this paper two control strategies are developed to suppress chatter vibration in turning process including a worn tool. A single degree of freedom model of the turning process including tool wear is briefly described. In the first stage, sliding mode approach used to control the system, and in the second stage fuzzy sliding mode approach is used. The simulation results indicate that the fuzzy sliding mode performs better than the direct sliding mode controller.

Mechanistic modelling for cutting with serrated end mills – a parametric representation approach

Rough end mills with a serrated profile along the cutting edge are broadly used for suppressing chatter vibrations encountered during machining. The serrated profile of the cutting edge has a phase shift from one flute to the next and interferes with the regeneration of waviness of the cut surface. The edge serration alters periodically along the axial direction and therefore calculation of chip load for serrated tools is different from that of traditional tools. In the present paper, serrated cutting edges are analytically defined and geometrically modelled as a B-spline curve. The chip load along the serrated cutting edge is computed by a newly proposed universal algorithm. The presented algorithm computes the instantaneous chip load for any geometry including straight, helical, and serrated. The validity of the presented model is investigated geometrically using solid modelling techniques. In addition to geometrical model verification, milling tests for regular, serrated cylindrical, and serrated tapered ball end mills were conducted to validate the model's accuracy. The simulation results confirmed that the presented model can calculate the chip load with high accuracy and can be implemented effectively for force simulations of serrated cutters.

Spindle speed variation and adaptive force regulation to suppress regenerative chatter in the turning process

Chatter suppression in machining processes results in more material removal rate, high precision and surface quality. In this paper, two control strategies are developed to suppress chatter vibration in the turning process including a worn tool. In the first stage, a sinusoidal spindle speed variation around the mean speed is modulated to disturb the regenerative mechanism. The optimal amplitudes of the speed modulations are found based on a genetic algorithm such that the input energy to the turning process is minimized. In the second stage, to improve the response of the system which is associated with small ripples under the steady state condition, an adaptive controller is designed. In this stage, the provided external force (e.g., by a piezo-actuator) is the input variable. Results are provided for each control strategy. It is shown that if both control approaches are applied simultaneously, chatter vibration is suppressed in less time without any ripples at the steady state condition.

An Experimental Study on Suppression of Chatter Vibration with Different Helix Angles End-Mill

In this study we attempted to suppress chatter vibration in end-milling of austenitic stainless steels with an end-mill having different helix angles. We showed there were two types of chatter vibration in end-milling with a conventional end-mill with regular helix angle. The two types of chatter vibration depend on the cutting speed. We detected these two types of chatter vibration by the developed monitoring method using laser Doppler vibrometers. We classified the two types of chatter vibration according to chatter generating tendency, frequency and vibration mode. We showed that chatter vibration generated at lower cutting speeds was regenerative chatter vibration. On the other hand, chatter vibration generated at higher cutting speeds was another type. We showed that a end-mill with different helix angles could prevent generative chatter vibration at lower cutting speeds and was also effective in suppressing chatter vibration at higher cutting speeds.

An Experimental Study on Suppression of Chatter Vibration with Different Helix Angles End-Mill

In this study we attempted to suppress chatter vibration in end-milling of austenitic stainless steels with an end-mill having different helix angles. We showed there were two types of chatter vibration in end-milling with a conventional end-mill with regular helix angle. The two types of chatter vibration depend on the cutting speed. We detected these two types of chatter vibration by the developed monitoring method using laser Doppler vibrometers. We classified the two types of chatter vibration according to chatter generating tendency, frequency and vibration mode. We showed that chatter vibration generated at lower cutting speeds was regenerative chatter vibration. On the other hand, chatter vibration generated at higher cutting speeds was another type. We showed that a end-mill with different helix angles could prevent generative chatter vibration at lower cutting speeds and was also effective in suppressing chatter vibration at higher cutting speeds.

Mechanics and Dynamics of Serrated Cylindrical and Tapered End Mills

Serrated end mills are effectively used in suppressing chatter vibrations in roughing operations. Mechanics and dynamics of serrated cylindrical and tapered helical end mills are presented in the article. The serrated flute design knots are fitted to a cubic spline, which is then projected on helical flutes. Cutting edge geometry at any point along the serrated flute is represented by its immersion angle and tangent vectors in radial, tangential and helical directions. The chip thickness removed by each cutting edge point is determined by using exact kinematics of dynamic milling. The cutting forces are evaluated by orthogonal to oblique cutting mechanics transformation. The experimentally proven model is able to predict the cutting forces and chatter stability lobes in time domain. It is shown that the proposed model can be used in evaluating the performance of serrated end mills during their stage.

Suppression of Chatter Vibration in Drilling

In this study, from the viewpoint of suppressing chatter vibration in drilling, the effects of cutting conditions on the initiation boundary of chatter vibration were investigated experimentally. Furthermore, the application of an impact damper on drills was attempted to suppress chatter vibrations.