切削颤振检测技术综述

为了减小切削颤振给工业生产带来的严重危害,国内外学者投入了大量精力研究其产生机理、颤振特性与控制方法.颤振的信号检测和正确判断是颤振预报和控制的基础,对颤振的检测信号、传感器和颤振信号的分析方法、颤振判别方法进行综述,总结了现有检测和分析方法的优缺点,展望了切削颤振检测技术的发展趋势.     

薄壁件铣削加工颤振控制研究

针对薄壁支架加工过程中出现的颤振现象,通过铣削加工颤振机理分析,并进行切削参数优化,解决了加工过程中的颤振问题。首先通过建立有限元模型,进行零件模态分析,获取零件动态特性;接着通过试验与仿真相结合的方式,获取机床-刀具系统的颤振稳定域;并进行稳定域内参数优化、零件动态特性与切削参数对比分析,最终获取避免加工颤振的切削参数,并进行加工验证试验,解决了加工颤振问题,提高了产品质量。结果表明通过切削参数优化可有效解决加工过程中得颤振问题。     

Effectiveness of continuous workpiece speed variation (CWSV) for chatter avoidance in throughfeed centerless grinding

The continuous rotation speed variation is demonstrated to be an efficient method to avoid regenerative chatter in different machining processes. This paper presents a time-domain dynamic model for throughfeed centerless grinding process that can predict chatter by means of part roundness error evolution. Continuous workpiece speed variation (CWSV) has been implemented in this model to analyze the influence of this disturbing method on the dynamic instability. Experimental results have validated the model and verified the effectiveness of CWSV for chatter avoidance and surface finish and dimensional tolerances improvement. It has been demonstrated that the selection of the optimal variation parameters is an important factor not only for chatter avoidance, but also for the stability of surface finish and dimensional tolerances since workpiece speed variation has a direct influence on throughfeed rate and grinding forces.     

Review of chatter studies in cold rolling

In the past, many different modes of vibration and causes of rolling chatter have been presented, yet no complete and clear picture of the basic mechanics emerged. In order to control chatter in cold rolling operations, a much better understanding of the basic mechanics of the problem is required. To provide, therefore, a ground work for developing such a basic understanding, in this paper, existing models of a mill stand as well as of the rolling process in the open literature are presented. In addition, existing chatter models, which are formulated to investigate chatter as the consequence of the interaction between the structural dynamics of the mills and the dynamics of the rolling process, are also reviewed.     

The measurement of forces in grinding in the presence of vibration

Most investigations of chatter have made the assumption that torsional vibration is not a significant factor. Some recent work has shown that chatter in grinding is affected by a change in the torsional stiffness of the workpiece drive. Also, a theoretical model of grinding chatter has been developed that confirmed the significance of torsional effects. However, the model for the grinding force was assumed to be a dynamic equivalent of a published steady-state model. This paper describes tests conducted to measure the variation in force caused by an oscillation in workpiece speed. The oscillating test results indicate that the torsional vibration of the workpiece may well be a significant effect on chatter in grinding. Moreover, as the grinding force changes with workpiece speed, it may be possible to use variation of workpiece speed at high frequency to reduce chatter.     

轧机工作辊磨削振纹检测与控制

研究分析轧辊磨削振纹产生原因,通过对设备、砂轮、磨削工艺、操作等方面进行改进优化,研制了专用的辊颈振纹检测方法和分级控制规则,有效控制了磨削振纹的产生.     

基于空化效应的功率超声珩磨再生型颤振研究

功率超声珩磨加工过程中的颤振影响因素很多,不仅包含物理磨削过程和机械振动环节,还包含了高频振动和超声波传动系统,是一个非常复杂的复合振动系统。通过建立珩磨颤振动力学模型,重点研究珩磨中空化泡溃灭产生辐射声压对再生型颤振的影响,结果表明:决定功率超声珩磨再生型颤振的主要原因为磨削厚度;空化泡溃灭产生的辐射声压会加剧系统颤振的频率,但对系统颤振的时域图变化趋势和振幅的大小基本没有影响。     

The effect of tool nose radius in ultrasonic vibration cutting of hard metal

A tool edge with a small nose radius can alleviate the regenerative chatter. In general, it is important for conventional cutting to use the smallest possible tool nose radius. However, a sharp tool shape has an adverse effect on tool strength and the instability of machining process still occurs. Previous researches have shown that vibration cutting has a higher cutting stability as compared with conventional cutting. In the present paper, the influence of tool nose radius on cutting characteristics including chatter vibration, cutting force and surface roughness is investigated by theory. It is found from the theoretical investigation that a steady vibration created by motion between the tool and the workpiece is still obtained even using a large nose radius in vibration cutting. This article presents a vibration cutting method using a large nose radius in order to solve chatter vibration and tool strength problem in hard-cutting. With a suitable nose radius size, experimental results show that a stable and a precise surface finish is achieved.     

Industrial experiments and findings on temper rolling chatter

Based on a series of tests, the chatter of temper rolling has been studied. It is shown that the temper rolling chatter is self-excited vibration and its cause is the rolling interface where partial fluid lubrication and viscous-slip co-exist.     

A critical investigation of the phase shift between the inner and outer modulation for the control of machine tool Chatter

The change of spindle speed has been recognized as an effective way to control machine tool chatter. This is because the change of spindle speed can adjust the phase shift between the inner and outer modulation. Chatter can then be suppressed or enlarged by using different phase shifts. However, it still needs to be clarified as to how the change in spindle speed is correlated with the phase shift for suppressing chatter. In this paper, the relationship between the spindle speed and phase shift is clearly studied. As a result, the behavior of chatter due to the adjustment of the phase shift between the inner and outer modulation can be understood in detail. Experimental results performed in drilling and milling operations are presented to illustrate the chatter control using the change of spindle speed.     

Optimisation of variable helix tool geometry for regenerative chatter mitigation

It is well known that regenerative chatter can result in excessive tool wear, poor surface finish, and hence limited productivity during metal machining. Various mitigation methods can be applied to suppress chatter; however, the current paper focuses on applying optimal variable helix tool geometry. A semi-discretisation method is combined with Differential Evolution to optimise variable helix end milling tools so as to avoid chatter by modifying the variable helix and variable pitch tool geometry. The semi-discretisation method is first validated experimentally. The numerical optimisation procedure is then used to optimise tool geometry for a machining problem involving a flexible workpiece. The analysis predicted total mitigation of chatter using the optimised variable helix milling tool at a low radial immersion. However, in practice a five fold increase in chatter stability was obtained, compared to the traditional milling tool.     

Analytical modeling of spindle–tool dynamics on machine tools using Timoshenko beam model and receptance coupling for the prediction of tool point FRF

Regenerative chatter is a well-known machining problem that results in unstable cutting process, poor surface quality and reduced material removal rate. This undesired self-excited vibration problem is one of the main obstacles in utilizing the total capacity of a machine tool in production. In order to obtain a chatter-free process on a machining center, stability diagrams can be used. Numerically or analytically, constructing the stability lobe diagram for a certain spindle–holder–tool combination implies knowing the system dynamics at the tool tip; i.e., the point frequency response function (FRF) that relates the dynamic displacement and force at that point. This study presents an analytical method that uses Timoshenko beam theory for calculating the tool point FRF of a given combination by using the receptance coupling and structural modification methods. The objective of the study is two fold. Firstly, it is aimed to develop a reliable mathematical model to predict tool point FRF in a machining center so that chatter stability analysis can be done, and secondly to make use of this model in studying the effects of individual bearing and contact parameters on tool point FRF so that better approaches can be found in predicting contact parameters from experimental measurements. The model can also be used to study the effects of several spindle, holder and tool parameters on chatter stability. In this paper, the mathematical model, as well as the details of obtaining the system component (spindle, holder and tool) dynamics and coupling them to obtain the tool point FRF are given. The model suggested is verified by comparing the natural frequencies of an example spindle–holder–tool assembly obtained from the model with those obtained from a finite element software.     

A new perspective on the stability study of centerless grinding process

Regenerative chatter is one of the most complex dynamic processes in machine tools. It is characterized by the presence of self-excited vibrations during machining, limiting the achievable tolerances in the workpieces. In order to predict the set-up conditions that produce these vibrations, it is necessary to model the regenerative mechanism responsible of their appearance accurately, so that the system stability can be studied solving the characteristic equation of the chatter loop. Although the dynamic behavior of machining processes like milling, turning or drilling is governed by a time delayed differential equation with one time delay term, a very particular problem is presented in centerless grinding. In this process, in addition to the dynamic instabilities, geometric instabilities must be analyzed, which are another important factors limiting the workpiece tolerances and lead to three time delay terms in the modeling procedure. This fact complicates its study remarkably, and the resolution of the characteristic roots of the dynamic process of these kinds of machines has not been tackled in the specialized literature as extensively as in other machining processes, being this field a challenging research line. According to this, in this paper an original and efficient method is presented to solve the roots of the characteristic equation of the centerless grinding process, based on the application of the root locus method. The main features of the proposed procedure are its ability to obtain the solutions accurately and that it is capable of determining the origin of the instabilities, so it constitutes a powerful tool to predict machine response for different set-up conditions. These interesting properties are demonstrated through the simulation results presented in this paper.     

Analysis of compliance between the cutting tool and the workpiece on the stability of a turning process

Chatter is a common vibration problem that limits productivity of machining processes, since its large amplitude vibrations causes poor surface finishing, premature damage and breakage of cutting tools, as well as mechanical system deterioration. This phenomenon is a condition of instability that has been classified as a self-excited vibration problem, which shows a nonlinear behavior characterized by the presence of limit cycles and jump phenomenon. In addition, subcritical Hopf and flip bifurcations are mathematical interpretations for loss of stability. Regeneration theory and linear time delay models are the most widely accepted explanations for the onset of chatter vibrations. On the other hand, models based on nonlinearities from structure and cutting process have been also proposed and studied under nonlinear dynamics and chaos theory. However, on both linear and nonlinear formulations usually the compliance between the workpiece and cutting tool has been ignored. In this work, a multiple degree of freedom model for chatter prediction in turning, based on compliance between the cutting tool and the workpiece, is presented. Hence, a better approach to the physical phenomenon is expected, since the effect of the dynamic characteristics of the cutting tool is also taken into account. In this study, a linear stability analysis of the model in the frequency domain is performed and a method to construct typical stability charts is obtained. The effect of the dynamics of the cutting tool on the stability of the process is analyzed as well.     

高速切削稳定性研究综述

介绍国内外学者在高速切削稳定性方面的研究成果,着重总结和分析以下几方面的研究工作:颤振的发生机理及数学模型、颤振的监测及预测以及抑制颤振提高切削稳定性的方法.     

Chatter Stability of Metal Cutting and Grinding

This paper reviews fundamental modeling of chatter vibrations in metal cutting and grinding processes. The avoidance of chatter vibrations in industry is also presented. The fundamentals of orthogonal chatter stability law and lobes are reviewed for single point machining operations where the process is one dimensional and time invariant. The application of orthogonal stability to turning and boring operations is presented while discussing the process nonlinearities that make the solution difficult in frequency domain. Modeling of drilling vibrations is discussed. The dynamic modeling and chatter stability of milling is presented. Various stability models are compared against experimentally validated time domain simulation model results. The dynamic time domain model of transverse and plunge grinding operations is presented with experimental results. Off-line and real-time chatter suppression techniques are summarized along with their practical applications and limitations in industry. The paper presents a series of research topics, which have yet to be studied for effective use of chatter prediction and suppression techniques in industry.     

Chatter suppression based on nonlinear vibration characteristic of electrorheological fluids

Self-excited chatter is a serious problem in machining shops and its frequency is always near the resonant frequency of the machining system. This paper proposes a novel design method for a tunable-stiffness boring bar containing an electrorheological (ER) fluid to suppress chatter in boring. The ER fluid undergoes a phase change when subjected to an external electrical field and serves as a complex spring behaving nonlinearly in the structure. The deformation modes of the ER fluid are dependent on the applied electric field and the strain amplitude. As a result, the global stiffness and energy dissipation properties of the boring bar under an electric field change drastically at different amplitudes of vibration. It is found that the amplitude of chatter can be prevented from increasing by using the nonlinear vibration characteristic of the ER fluid. It is shown experimentally that the chatter can be suppressed under a certain range of the electric field related to the cutting conditions.     

基于小波包和倒频谱分析的颤振特征提取方法

立铣加工过程中的颤振会严重影响工件表面质量和材料去除率,加剧刀具磨损和恶化工作环境。虽然大部分颤振监测系统可以监测到颤振发生,但颤振发生时已经对工件和刀具产生了严重的损伤,因此,需要提前监测到颤振特征。由于加工过程的非线性导致振动信号频率成分复杂,单一的时频分析方法难于得到可靠的颤振特征。通过小波包分解确定颤振发生频段并重构该频段信号,通过颤振发生频段的倒频谱辨识稳定、过渡和颤振状态。研究结果表明,该方法可以有效识别立铣加工过程的稳定、过渡和颤振状态。     

Gripping by controllable wet adhesion using a magnetorheological fluid

The magnetorheological properties of ferrofluids (or smart, or active fluids) are well known, and are currently exploited in shear in advanced damping systems in the automotive industry, robotics (prosthesis), and machine tools (chatter reduction, positioning). This paper proposes an end effector for gripping by a novel form of controllable wet adhesion inspired by gastropod pedal mucus. The design of a gripper has been proposed, along with performance analysis based on experiments on various parameters, materials and surfaces, exhibiting robustness in unknown and dirty environment, typical of disassembly. Benefits over competing handling technologies and future research directions in this new area have been addressed.     

以方差和互相关系数判别切削颤振的仿真研究

文章采用仿真研究方法，对方差和互相关系数绝对值对机床切削颤振是否发生的判别能力进行了系统的研究，发现它们都不宜单独作为判别函数，提出了以方差和互相关系数绝对值作为综合判据判别切削颤振是否发生的观点。采用实验实际测得的机床切削颤振信号进行仿真验证，发现综合判据对于颤振有很好的判别能力。