基于主动磁轴承的切削颤振稳定性分析及控制

提出了基于主动磁轴承的铣削颤振主动控制技术。用有限元法分析了主动磁轴承等效刚度与等效阻尼对铣削稳定性区域的影响,并对铣削过程中的颤振进行了主动控制。结果表明:主动磁轴承的等效刚度能够改变电主轴转子的临界转速,但对铣削的临界切削宽度影响很小;相反,主动磁轴承的等效阻尼能够较大幅度地增大铣削的临界切削宽度,但对电主轴转子的临界转速影响不大。颤振的控制效果表明,调节主动磁轴承的等效刚度和等效阻尼能够减小铣削过程中颤振的振幅。     

基于阻尼减振器的铣削过程稳定性研究

针对薄壁件铣削加工中出现的颤振现象采用外置式阻尼减振器。该减振器与刀杆过盈配合联接为一体,铣削过程中可以吸收刀杆受到的振动,通过安装阻尼减振器和未安装阻尼减振器两个铣削对比试验,以阻尼材料、阻尼减振器安装位置为变量,探究该阻尼减振器对铣削抑振和加工稳定性的影响程度及变化规律。试验结果表明,安装该阻尼减振器后系统铣削稳定性得到提高,切削深度平均提高2.5倍。     

机床切削系统摩擦颤振影响因素分析

建立舍干摩擦的单自由度机床一刀具系统的动力学模型,列写运动方程,确定系统发生颤振的临界驱动速度,给出计算临界驱动速度的计算流程图,采用理论分析和数值仿真方法讨论驱动速度、动摩擦因数、系统阻尼比对系统颤振的影响。结果表明,发生颤振后,驱动速度对于颤振的影响较为显著,动摩擦因数主要影响颤振的平衡位置,系统阻尼比对颤振的影响较为微弱,最后给出降低颤振的几项措施。     

动态切削力对切削颤振的影响

以外圆车削实验为依据,建立加工过程中刀具振动的非线性动力学模型,并采用数值分析方法,研究切削力中的动态分量对切削颤振的影响.结果表明,随速度变化的切削力分量对颤振幅值影响较小,而且会在短时间内被系统内的结构阻尼所衰减.而与加速度成非线性关系的切削力分量对颤振的影响却很显著,而且加速度系数有临界值存在,当超过这个临界值后,颤振的理论幅度将急剧增大.     

四辊冷带轧机再生颤振稳定性的统一理论

研究了四辊冷带轧机三倍频和五倍频颤振的产生机理，分析了由于负阻尼效应所导致的轧机再生颤振现象，提出了再生颤振稳定性分析的统一模型，并对其进行了理论探讨。在此基础上，通过轧机颤振的现场测试数据论证了再生颤振理论模型的正确性及其工业价值，并用数值仿真方法给出了再生颤振统一模型的稳定性图。     

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.     

一种新的临界稳定公式及其绝对稳定切削判据

1. The transfer function of .chatter and its extend results. Experiments show that when chatter is excited, the dynamic cutting forces in cross directions are linearly related, i. e. Fc (S) = aFd (S). Here Fc (S) and Fd (S) are individualy the cross force and direct force, a is the linear factor. So the transfer function of the structure is Gd(S)+aGc(S), Gd(S) and Gc(S) are individually direct dynamic compliance and cross one. Therefore, the transfer fuction of the cutting chatter loop should be A system which can be calculated as a single degree of freedom has been designed by the authors for the test. Its damping ratio can be adjusted from 0.03 to 0.8. When chatter is just excited, μ = 0 and the natural damping ratio of the structure just offset by the cutting damping ratio. The results of measuring shows the latter ratio is-0.18. According to the for-mula (3), we can get critical cutting width 21.9mm, and the test value is 20.5mm. But the value of Tlusty formula is 26.97mm.The confirming test has proved the theory and the formulas in this paper are correct. They show that the absolutly stability criterion is not only related to the maxmum dynamic negative part of the real compliance of the structure but also to the maxmum negative coefficient of cutting damping force and the frequency of the chatter. The test show the formula (3) can be used for forecasting the cutting clatter.     

Dynamic analysis on the closing resistors of Gas Insulated Switchgear

GIS (Gas Insulated Switchgear) is used in electric power system to insure non conductivity, breaking capacity and operating reliability. In the present study, dynamic analysis on the closing resistors of the GIS has bees carried out by the commercial dynamic analysis code COSMOS MOTION and 3-D modeling program SOLID WORKS. In order to find the minimum value of chatter vibration of closing resistors, the motion of moving and fixed resistor parts of closing resistors were simulated by varying the spring constant, the damping coefficient and the mass of moving and fixed resistor parts. The simulated results were compared with experimental results. The application of the results could reduce chatter vibration of closing resistors of the GIS. These data are also useful on the development of future model GIS with minimum chatter vibration for the determinations of the spring constant, the damping coefficient and mass of a moving part.     

高速铣削时颤振的诊断和稳定加工区域的预报

给出一种通过测量加工过程中的噪声来诊断高速铣削时颤振的方法.先测量环境噪声,然后测量加工噪声.理论分析和试验结果表明,如果加工噪声的主谐振频率接近其中一个环境噪声主谐振频率或者是齿频的整数倍,那么系统无颤振,否则有颤振.建立系统结构和铣削过程动力学特征参数的数学模型.根据测出的颤振频率,通过所建模型可解出系统的固有频率、阻尼比和过程参数,并计算出稳定极限曲线.试验证明,该方法能较好地预报高速铣削时的稳定加工区域.     

Time domain coupled simulation of machine tool dynamics and cutting forces considering the influences of nonlinear friction characteristics and process damping

A higher machining ability is always required for NC machine tools to achieve higher productivity. The self-oscillated vibration called “chatter” is a well-known and significant problem that increases the metal removal rate. The generation process of the chatter vibration can be described as a relationship between cutting force and machine tool dynamics. The characteristics of machine tool feed drives are influenced by the nonlinear friction characteristics of the linear guides. Hence, the nonlinear friction characteristics are expected to affect the machining ability of machines. The influence of the contact between the cutting edge and the workpiece (i.e., process damping) on to the machining ability has also been investigated. This study tries to clarify the influence of the nonlinear friction characteristics of linear guides and ball screws and process damping onto milling operations. A vertical-type machining center is modeled by a multi-body dynamics model with nonlinear friction models. The influence of process damping onto the machine tool dynamics is modeled as stiffness and damping between the tool and the workpiece based on the evaluated frequency response during the milling operation. A time domain-coupled simulation approach between the machine tool behavior and the cutting forces is performed by using the machine tool dynamics model. The simulation results confirm that the nonlinear frictions influence the cutting forces with an effect to suppress the chatter vibration. Furthermore, the influence of process damping can be evaluated by the proposed measurement method and estimated by a time domain simulation.     

STUDY ON ELECTRORHEOLOGICAL FLUID DAMPER FOR APPLICATION IN MACHINING CHATTER CONTROL

The electrorheological fluid(ERF)is a kind of intelligent material with bright prospects for industry applications, which has viscoelastic characteristic: under the applied electric field. The dynamic model of a milling system with an ERF damper is established, and the chatter suppression mechanism of the ER effect is discussed theoretically. Both the theoretical study and the experimental investigation show that the additional damping and additioaal stiffness produced by the ERF increase with the rise in the strength of electric field E, but their influence on the cutting stability is different. Only when both additional damping and additional stiffress cooperate, the milling chatter can be suppressed quickly and effectively. In additional, an ERF dumper used on the arbor of horizontal spindle milling machine is developed, and a series of milling shatter control experiments are performed. The experimental results show that the milling chatter can be suppressed effectively by using the ER damper.     

四辊冷带轧机三倍频颤振机理的研究

研究了四辊冷带轧机三倍频颤振的产生机理,发展了轧件振动模型,分析了由于轧件失稳所导致的轧机颤振现象,提出了轧机三倍频再生颤振模型,并对其进行了理论研究,仿真结果和现场测试进一步论证了三倍频再生颤振理论模型的正确性及其工业价值。     

Chatter stability of micro end milling by considering process nonlinearities and process damping

The micro end milling uses the miniature tools to fabricate complexity microstructures at high rotational speeds. The regenerative chatter, which causes tool wear and poor machining quality, is one of the challenges needed to be solved in the micro end milling process. In order to predict the chatter stability of micro end milling, this paper proposes a cutting forces model taking into account the process nonlinearities caused by tool run-out, trajectory of tool tip and intermittency of chip formation, and the process damping effect in the ploughing-dominant and shearing-dominant regimes. Since the elasto-plastic deformation of micro end milling leads to large process damping which will affect the process stability, the process damping is also included in the cutting forces model. The micro end milling process is modeled as a two degrees of freedom system with the dynamic parameters of tool-machine system obtained by the receptance coupling method. According to the calculated cutting forces, the time-domain simulation method is extended to predict the chatter stability lobes diagrams. Finally, the micro end milling experiments of cutting forces and machined surface quality have been investigated to validate the accuracy of the proposed model.     

Improvement of chatter stability in boring operations with passive vibration absorbers

This paper is focused on the behavior of boring bars with a passive dynamic vibration absorber (DVA) for chatter suppression. The boring bar was modeled as a cantilever Euler-Bernoulli beam and only its first mode of vibration was considered. The stability of the two-degree-of-freedom model was analyzed constructing the stability diagram, dependent on the bar characteristics and on the absorber parameters (mass, stiffness, damping, and position). Two analytical approaches for tuning the absorber parameters were compared. The selection criterion consisted on the maximization of the minimum values of the stability-lobes diagram. Subsequent analysis performed in this work, allowed formulating of new analytical expressions for the tuning frequency improving the behavior of the system against chatter.     

Optimization of the Tuned Mass Damper for Chatter Suppression in Turning

The tuned mass damper(TMD) has been successfully applied to the vibration control in machining,while the most widely adopted tuning is equal peaks,which splits the magnitude of the frequency response function(FRF) into equal peaks.However,chatter is a special self-excited problem and a chatter-free machining is determined by FRF at the cutting zone.A TMD tuning aiming at achieving the maximum chatter stability is studied,and it is formulated as an optimization problem of maximizing the minimum negative real part of FRF.By employing the steepest descend method,the optimum frequency and damping ratio of TMD are obtained,and they are compared against the equal peaks tuning.The advantage of the proposed tuning is demonstrated numerically by comparing the minimum point of the negative real part,and is further verified by damping a flexible mode from the fixture of a turning machine.A TMD is designed and placed on the fixture along the vibration of the target mode after performing modal analysis and mode shape visualization.Both of the above two tunings are applied to modify the tool point FRF by tuning TMD respectively.Chatter stability chart of the turning shows that the proposed tuning can increase the critical depth of cut 37% more than the equal peaks.Cutting tests with an increasing depth of cut are conducted on the turning machine in order to distinguish the stability limit.The tool vibrations during the machining are compared to validate the simulation results.The proposed damping design and optimization routine are able to further increase the chatter suppression effect.     

A simple approach to analyze process damping in chatter vibration

This paper investigates how changes in chatter amplitude and frequency depend on process damping effect in dynamic turning process. For this purpose, the two degrees of freedom (TDOF) cutting system was modeled, and for an orthogonal turning system, the process damping model with a new simple approach was developed. To further explore the nature of the TDOF cutting model, a numerical simulation of the process was developed by this model. This simulation was able to overcome some of the weaknesses of the analytical model. The equations of motion for this cutting system were written as linear and nonlinear in the τ-decomposition form. The variation in the process damping ratios for different work materials was simply obtained by solving the nonlinear differential equations. A series of orthogonal chatter stability tests were performed for the identification of dynamic cutting force coefficients, using AISI-1040, Al-7075, and Al-6061 work materials, at a constant spindle speed. Finally, the experimental results were analyzed and compared with the simulation model, and it was observed that the results obtained through the experiments comply with the simulation model results.     

Chatter stability prediction in milling using time-varying uncertainties

The chatter stability in milling severely affects productivity and quality of machining. Tool wear causes both the cutting coefficient and the process damping coefficient, but also other parameters to change with cutting time. This variation greatly reduces the accuracy of chatter prediction using conventional methods. To solve this problem, we consider the cutting coefficients of the milling system to be both random and time-varying variables and we use the gamma process to predict cutting coefficients for different cutting times. In this paper, a time-varying reliability analysis is introduced to predict chatter stability and chatter reliability in milling. The relationship between stability and reliability is investigated for given depths and spindle speeds in the milling process. We also study the time-varying chatter stability and time-varying chatter reliability methods theoretically and with experiments. The results of this study show that the proposed method can be used to predict chatter with high accuracy for different cutting times.     

CSP轧机扭振中“伪拍振”的研究

某厂CSP轧机出现了严重的扭振.扭振具有拍振的特征.为摸清轧机振动规律进而解决轧机振动问题.对栽CSP轧机拍振进行了研究.测试分析和理论研究发现这是一种"伪拍振"现象,"伪拍振"的形成是由于工作辊辊面局部区域有振纹存在.振纹区域与轧件接触时,轧机以振纹频率做强迫振动;没有振纹的辊面区域与轧件接触时,因负阻尼作用,系统表现为固有频率下的自激振动.两种振动形式交替出现,且振动强度大小不同,使扭振表现出"拍振"的形态.上述发现对轧机的振动机理及其抑制措施的研究有重要价值.试验证明,据此提出的使用高速钢轧辊等抑制振动措施有很好的效果.     

刀具颤振抑制用机械阻尼器的理论分析及数值模拟

为了抑制高速铣削中的颤振影响,提出在刀具中心插入一个分层梁结构机械阻尼器,依靠刀具与阻尼器间的相对运动产生的摩擦阻尼,以耗散振动能量.通过理论分析和数值模拟的方法分别计算了接触压力和阻尼耗散功率,并对两种结果比较分析,找出了造成结果差异的主要原因.     

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.