Papers by Keyword: Chatter Suppression

Abstract: This paper presents the improvement in chatter vibration damping using different types and arrangements of magnets, as well as comparison with normal cutting conditions in turning of stainless steel AISI 304. Chatter is defined as the self-excited violent relative motion between the cutting tool and work-piece. It is the common vibration problem that limits the productivity of machining processes, since it leads to shortened tool life, poor surface finish, breakage and premature damage of cutting tool, as well as mechanical deterioration. The occurrence of chatter during metal cutting process also causes instability of the machine tool system. Though there has been a large number of works on identifying the causes of chatter and its behavior, there is still no consensus among researchers on this very vital issue of machining. Previously, the incidence of chatter was thought to be due to forced vibration, BUE formation, cutting speed, and cracking during chip formation. Different ways to overcome this problem have been investigated, such as using piezoelectric inertia actuators, feed-forward neural network controllers, and work-piece preheating methods. In this research, permanent magnets with different size, strength, and composition are mounted around the cutting tool. A vibration sensor (accelerometer) is placed at the bottom of the tool to record the suppression of chatter amplitude in turning operation. It is shown that magnetic force can modify the frequency response function of the cutting tool resulting in improved cutting stability in turning operations. Chatter can then be effectively suppressed due to increased cutting stability.

Abstract: This paper presents the results of experimental investigations of vibration analysis conducted on Engine Lathe Harrison M390 using variable cutting speed, feed rate and depth of cut at constant tool overhang of 120mm as the machining parameters ascertain the effectiveness of TiN coated carbide insert in turning of hardened steel AISI 304. The experiments were designed based on the Response Surface Methodology (RSM) approach using DESIGN EXPERT (DOE) software to enhance statistical model using the capabilities of RSM to compare the effectiveness of application of a combination of a bottom and a side magnet with respect to the tool holder in terms of reduction of chatter amplitude. The experiments were performed under application of magnetic field from two permanent magnets with magnetic strength of 1200 Gauss each with one located at the bottom and the other at the side of the cutting tool with distance 1cm from the tool. The dimension of the bottom magnet was 25 x 25 x 50mm and that of the side magnet was 87 x 50 x 17mm. The vibration amplitude data for the two conditions were compared to identify the influence of magnet on chatter reduction. The results reveal that a maximum of 87% and an average of 50% reduction of chatter acceleration amplitude were achieved with the said arrangement of the magnets. Furthermore, empirical mathematical model of maximum chatter amplitude was developed for machining with magnet application to predict the cutting parameters with the lowest value of chatter amplitude and maximum material removal rate.

Abstract: In this paper, a torus is designed as an adding mass to modify the dynamic characteristics of the tool-holder system in free boundary condition and in fixing boundary condition. The torus is fixed on the holder of a given face milling cutter, which may change the mass distribution and the stiffness distribution of the system, to adjust the frequency and damping ratio of the tool tip. Although the dynamic characteristics of the tool tip are significantly influenced by holder-spindle interface, the influence of the tool-holder can’t be neglected. In this attempt, by adding mass on the tool holder, the first order frequency decreased by 37% in free boundary condition and 6.7% in fixing boundary condition. The first damping radio increased by 48% in free boundary condition and 4.5% in fixing boundary condition. Chatter suppression is verified in the cutting process by adding mass on the holder.

Abstract: This paper investigates the regenerative chatter in a plunge grinding process. The effect of the contact force on the onset of chatter vibration is clarified by a proposed continuation algorithm, and the boundary for the chatter-free region in which the grinding process is stable is obtained. By varying the rotational speed of the workpiece continuously, the chatter vibration with the values of the system parameters being near the boundary is suppressed, namely, the chatter-free region is expanded by this spindle speed variation control strategy.

Abstract: 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.

Abstract: The most common tunings for the TMD in the field of vibration suppression are H_∞ and H₂. However, regenerative machine tool chatter is a complex problem with many variations, which therefore requires a new tuning for the optimum chatter suppression. The real part based tuning is investigated numerically by employing the minimax numerical approach, which aims to maximize the minimum real part of the primary structure under the harmonic excitation. The performances of multiple TMDs system are discussed. A face milling case is employed to verify the benefits of multiple TMDs in increasing the chatter free depth of cut. It is concluded that multiple TMDs configuration are more effective than single TMD in chatter control.

Abstract: In this paper the chatter stability of turning and full-immersion milling operations with spindle speed variation is studied. We present a method to calculate the stability lobes in the limit of very low and very high frequencies of the delay modulation. These approximations help to classify the results of numerically exact methods, as for example semi-discretization or multi-frequency approaches. For slowly time-varying delay, the position of the stability lobes is understandable from a simple connection between the lobes for constant and time-varying delay. Furthermore, this method can be used to estimate the efficiency of an application of spindle speed variation and helps to find optimal parameters for it.

Abstract: This paper deals with deformation control and chatter suppression in the milling of thin-walled blade. The purpose is to generate tool paths that can control machining deformation and suppress chatter during milling. To achieve this object, symmetrical spiral milling approach is proposed to release residual stress on both sides of the blade in the same machining circle to control machining deformation. Besides, in order to suppress chatter during milling of thin-walled blade, nonuniform-allowance is left on both sides of the blade during machining, this can effectively increase the rigidity, thereby chatter cannot easily occur during machining. Machining experiments showed that the proposed approaches can dramatically improve the machining quality, decrease deformation and suppress chatter in the milling of thin-walled blade.

Abstract: The paper deals with semi-active chatter absorber based on an electrodynamic transducer built around high-energy permanent magnets. Also, a fuzzy logic control system for the absorber control system has been designed. The principal advantage of fuzzy control is the possibility to implement practical experience gained by machine operators in the control algorithm. Hence, the possibility of factoring such quantities, as vibrations experienced by selected points of the machine-tool, and sound emitted by working machine into the analyzed chatter absorber fuzzy control system has been studied in the paper. The control system has been tested by way of simulation with the use of the process and cutting force models.

Abstract: Self-chatter is a serious problem in cutting process. This paper aims to solve the problem by establishing time series model of vibration acceleration signal in cutting process based on Hidden Markov Model (HMM) technology and achieve the purpose of chatter recognition and prediction. Features which can indicate cutting state are extracted from the acceleration signal. HMM parameters are obtained by model training, and the reference models database is built. Then cutting state recognition is performed according to the feature matching level. Simulations and experiments are conducted, and the results show that the proposed method is feasible and it could get high recognition