Self-exited Vibration Research Articles

Estimation of vibration stability in turning using operational modal analysis

• OMA is used for the identification of self-exited vibration during turning. • The dominant poles of the turning system are identified from process vibrations. • This method can potentially forecast chatter when vibrations are still stable. Unstable vibrations in machining operations, known as chatter, may cause damages to the tool, workpiece, or the machine tool. Chatter is usually avoided by selecting the appropriate spindle speed and depth of cut determined by the dynamic models of the machining process. Due to modeling uncertainties or variations of the process dynamics, chatter may happen even when stable cutting conditions are used in the process planning stage. Therefore, it is critical to detect chatter during the process and take corrective actions in the shortest possible time. The existing chatter detection methods process various signals such as sound, vibration, and force to extract chatter indicators during the process, however these methods detect chatter only after vibrations become unstable. In this paper, a new chatter detection method is presented based on the identification of the dynamics of turning processes using Operational Modal Analysis (OMA). Because this new method estimates the stability margin of the process, rather than the stability/instability of vibrations, it determines the level of stability of the cut before vibrations become unstable. The performance of the presented chatter detection method is studied using numerical simulations and machining experiments.

Numerical Investigation of Orthogonal Cutting Processes with Tool Vibration of Ti6Al4V Alloy

This article investigates the vibration cutting process of Ti6Al4V alloy numerically and theoretically. The Coupling Eulerian-Lagrangian finite element models with one-tool and double-tool are established, to simulate the cutting processes with tool forced vibration and self-exited vibration respectively. It is shown that low-frequency forced vibration aggravates the periodic shear banding instability and increases the cutting force amplitude, whereas high-frequency forced vibration can improve the machined quality. Furthermore, the self-exited vibration due to fluctuating cutting thickness with low frequency promotes the shear banding evolution in chip. The self-exited vibration stability limit is found dependent on the frictional behavior, penetration resistance and the inherent vibration sources of tool-workpiece system. These simulation results show good agreement with theoretical models, which provide practical guidelines for improving vibration machining.

Center Track Analysis and Simulation Considering Effect of Vortex and Perturbation of Cutting Fluid on BTA Boring Bar

In order to reveal the motion center track of boring bar during heavy-duty deep-hole boring trepanning processing, a new model is proposed considering both linear item and cubic item to describe nonlinear factors of the bars stiffness. The study mainly investigates two factors: vortex instability caused by outside cutting fluid, and perturbation instability caused by inside cutting fluid of the boring bar. Vibration amplitude of the bar changes with the nonlinear stiffness coefficient while the bar works at the same rotation speed. The results of numerical calculation and simulation are obtained, when the processing parameters match the combinative operation parameters under the different motion status. It shows the bar interaction with external cutting fluid while it is subjected to unbalanced force. These behaviors will induce self-exited vibration of bar, meanwhile the center track will be a closed curve loop. Boring bars vibration is always in a certain vibration amplitude. The maximum vibration amplitude is near the region of ω/2 and 2ω in the x direction.

Axial Vibration Characteristics of a Metal Diaphragm Coupling

In this article, a metal diaphragm coupling is introduced. It is assembled by interference fit with the shafts. Based on two axial vibration styles, self-exited vibration and external exited vibration, of the coupling, physical model of the coupling is established. Stiffness and damping of the coupling are also solved and analyzed. Then, natural vibration of the coupling is researched and natural frequencies are acquired by analyzed and simulated method. Finally, axial vibration response of the coupling was presented based on a calculation example. Techniques are presented which permit the coupling designer to predictably modify the coupling and thereby make in-place retrofits should an axial resonance condition occur in the field.

G305 送風機配管系の白励振動により圧縮された空気を駆動源とする船舶用推進装置(GS3-1 流体機械,一般セッション)

G305 送風機配管系の白励振動により圧縮された空気を駆動源とする船舶用推進装置(GS3-1 流体機械,一般セッション)

Design and Analysis of the Digging Spring Tooth of Stubble Harvester

The developed corn stubble harvester can simultaneously finish such as the digging, picking up, cleaning, collection and Stripy laying stubble process and so on, but it cost more man-hour time because of the high digging resistance and high engine power consumption in digging stubble works. The digging spring tooth for corn stubble harvester including self-exited vibration S-shaped spring handle and curved chisel-shaped bionic tooth is designed based on the mechanism of drag reduction of self-excited vibration and bionic drag reduction for reduce digging resistance and power consumption, and the statics analysis of digging spring tooth is done by ANSYS software, the stress and strain distribution diagrams show the design is reasonable.

Oscillation Characteristic of Single Free Piston Engine Generator

An oscillation model of a single free piston engine generator which is coupled with a linear generator is presented in this paper. Based on the dynamics and energy equilibrium, the oscillation model is described by the mass spring damping system. It demonstrates that the generator could be regarded as a single freedom self-exited vibration system. The excitation is the periodical combustion in the cylinder. And the system reaches a limit loop after several cycles. The frequency and amplitude characteristics with the effects of key variables are shown. It provides a power map as function of the stiffness and mass, which will be applied into the match design and optimization.

444 タービンモデルロータの翼振動診断について(翼運動,OS-18 ロータダイナミクス,総合テーマ「伝統を,未来へ!」)

This paper deals with abnormal vibrations encountered in experiments in the each case of in-plane blade system, out-of-plane blade system. In the case of the in-plane blade system, -1X resonance occurs caused by gravity. In the case of the out-of-plane blade system, two types of abnormal vibrations appear. One is -2X resonance at -2Ω=-ω_b due to unbalance of the shaft and anisotropy support. The other is a flow-induced self-exited vibration caused by galloping. Both occurred at the same time and both leads to the entrainment phenomenon. These abnormal vibrations are identified by our analysis technique. Our analysis technique can easily confirm that abnormal vibrations are resonance/self-excited vibration or forward/backward vibration.

G1001-3-5 翼軸連成振動の計測と診断((3)振動解析・制振・防振2)

It is well known that zero and one nodal diameter (k=0 and k=1) modes of blade system interact with shaft system. We discus experimentally and theoretically the k=1 modes of blade system. If we excited the shaft at the rotational speed of Ω=|ω_b-ω_s|, we examined that the exciting frequency ν=ω_s induced shaft-blade coupled resonance. In addition, we encountered the abnormal vibration below. In the case of the in-plane blade system, blades resonate at Ω=ω_b attributed to deformation caused by gravity. In the case of the out-of-plane blade system, blades are generated at Ω=ω_b/2 due to unbalance of the shaft and asymmetry of the bearing stiffness, and a nonlinear self-exited vibration occurred by galloping due to the cross-section shape of blade tip. Both occurred at the same time and the entrainment phenomena were identified. This paper also includes experimental data of 45deg. blade system.

Finite element analysis of machine and workpiece instability in turning

Chatter is a well-known and self-exited vibration. The stock removal rate is highly affected by this phenomenon. In this paper instability analysis of machining process is presented by dynamic model of turning machine. This model, which consists of machine tool's structure, is provided by finite element method and ANSYS software, so that, the flexibility of machine's structure, workpiece and tool have been considered. The model is evaluated and corrected with experimental results by modal testing on TN40A turning machine in which the natural frequencies and the shape of vibration modes are analyzed. Finally, the stability lobes obtained from this model are plotted and compared with experimental results.

3832 大形テンタゲートの複合発散振動に関する大形3次元モデル実験(J15-4 流体関連の騒音と振動(4)-機器・設備-,J15 流体関連の騒音と振動,2005年度年次大会)

3832 大形テンタゲートの複合発散振動に関する大形3次元モデル実験(J15-4 流体関連の騒音と振動(4)-機器・設備-,J15 流体関連の騒音と振動,2005年度年次大会)

Analysis of Chaffer in Tandem Cold Rolling Mills.

This paper is concerned with chatter in tandem cold rolling mills, which has been recognised to have close relation with friction conditions in roll bites. However, the relation between rolling conditions and the stability of vibration has not been clearly understood. Therefore, an attempt is made to understand how the rolling conditions can be related with vibration phenomena, through numerical simulations Firstly, a theoretical model is constituted to simulate the vibrational behaviour of a five-stand continuous rolling mill, and the stability of the mill vibration is evaluated, introducing a disturbance to the static rolling conditions. The results of the calculation show that the vibration is greatly influenced by rolling speed and friction coefficient. With increase in rolling speed, the mill vibration tends to be self-excited. Also, the results show that optimal range of friction coefficient exists in which the vibration is damped and the mill is stable against the disturbance. Secondly, a simple self-exited vibration model is proposed and the stability index is proposed for further understanding of the phenomena. An analytical approach is made to predict the stability of the rolling process. With this model, it is shown that the rolling force and the delay of the response to the change in gap have a major effect on self-exited vibration. Also, the calculated optimal range of friction coefficient in the continuous rolling simulation can be explained by using the analytical model.

Shimmy Phenomenon on Steering System of Two-Wheeled Vehicles.

The shimmy that appears in two-wheeled vehicles has been regarded as a self-exited vibration, but this has yet to be clearly proven. Here, we provide experimental and theoretical analyses based on three experiments. It is found that the shimmy phenomenon can be clearly defined by the experimental analyses. It is impossible for previous theoretical models to describe the shimmy phenomenon. Therefore, we propose a new tire model which includes the dynamics of side force and self-aligning torque. From the results of the theoretical analyses, it is found that the model describes the shimmy phenomena not only qualitatively but also quantitatively. Furthermore we analyze the influence of the design parameters of the tire and their main influences on shimmy. Consequently, it is clarified that cornering stiffness, tire lateral and torsional rigidity, relaxation length of lateral displacement of contact patch, tire lateral damping and moment of inertia around the steering axis all have strong influences on shimmy.

Dynamic Motion of a Nonlinear Mechanical System with Time Delay. Analysis of the Self-Excited Vibration by an Averaging Method.

A nonlinear mechanical system with time delay shows noise and chatter vibration. A long-time delay might destroy the system. Therefore, it is important to analyze the nonlinear system with time delay. However, the nonlinear system with time delay is described by a differential-difference equation which is difficult to solve. In this paper, we deal with the forced, self-excited vibration of a one-degree-of-freedom system with time delay in the nonlinear restoring force term, apply an averaging method for a functional differential equation to the system, and obtain the stability condition of self-exited vibration.

Whirling Vibration in Drilling. Part 1: Cause of Vibration and Role of Chisel Edge

The whirling vibration of the drill in the beginning of the drilling operation is experimentally investigated. Special attention is paid to how vibration develops as the drill proceeds into the workpiece. Three types of drills with different web thicknesses are used, and the characteristics and cause of the vibration are discussed. Whirling vibration, which has an elliptical orbit, is a self-exited vibration accompanied by a phase lag with respect to the revolution of the workpiece. The vibration energy is provided by the regenerative effect at the major cutting edge, while the chisel edge acts to dampen the vibration.

Adhesion and Dynamic Phenomena during Slippage of Electrical Rolling Stock : 3rd Report: Self-excited Vibration during Slippage of Electric Locomotive Trucks

When the driving axles of an electric locomotive slip, self-excited vibration will occasionally occur in its trucks. To suppress such selfexcited vibration, detailed theoretical calculations of the vibrations during slippage of typical trucks were made and stability criteria were sought by simplifying the system. (1) Theoretical expressions were derived for the vibrations during slippage of typical trucks, that is, individual quill spring drive type trucks, and individual axle-hung motor type trucks, and numerical calculations regarding actual examples were made. The calculated and observed results generally agree with each other, revealing that the behavior of trucks can be predicted through theoretical calculations. (2) Stability criteria were sought for several problematical mode of vibration, that is, the torsional vibration of both individual and monomotor driving systems and the pitching of an axle-hung motor about the axle. The validity of the stability criteria was proved by comparing them with actual examples, and some instances of success in suppressing self-exited vibration were disclosed.