Design and implementation of nonlinear TMD for chatter suppression: An application in turning processes

A new-type nonlinear tuned mass damper (TMD) containing an additional element of elastic support dry friction compared with the common linear TMD is proposed to suppress machining chatter. The design and tuning process of this nonlinear TMD have used a combination of analytical modeling with experimentally measured frequency response function (FRF) of the machining system. Theoretical studies and experimental results show that the proposed nonlinear TMD can remarkably improve the machining stability by effectively suppressing the magnitude of the real part of the FRF of the damped machining system.     

Optimization of multiple tuned mass dampers to suppress machine tool chatter

Chatter is more detrimental to machining due to its instability than forced vibrations. This paper presents design and optimal tuning of multiple tuned mass dampers (TMDs) to increase chatter resistance of machine tool structures. Chatter free critical depth of cut of a machine is inversely proportional to the negative real part of frequency response function (FRF) at the tool–workpiece interface. Instead of targeting reduction of magnitude, the negative real part of FRF of the machine is reduced by designing single and multiple TMD systems. The TMDs are designed to have equal masses, and their damping and stiffness values are optimized to improve chatter resistance using minimax numerical optimization algorithm. It is shown that multiple TMDs need more accurate tuning of stiffness and natural frequency of each TMD, but are more robust to uncertainties in damping and input dynamic parameters in comparison with single TMD applications. The proposed tuned damper design and optimization strategy is experimentally illustrated to increase chatter free depth of cuts.     

Vibration suppression of boring bar by piezoelectric actuators and LR circuit

This paper presents the vibration suppression of a boring bar using piezoelectric actuators installed in the boring bar, and an inductor-resister (LR) circuit, which acts as a mechanical dynamic absorber. The frequency response function of the compliance was designed so that its real part is constrained to suppress regenerative chatter. The designed boring bar with an optimally tuned LR circuit was set on a lathe to evaluate its dynamic characteristic, and it was found that the chatter vibration was successfully suppressed in the cutting test.     

A study of cutting process stability of a boring bar with active dynamic absorber

In this paper, the use of an active dynamic absorber to suppress machine tool chatter in a boring bar is studied. The vibrations of the system are reduced by moving an absorber mass using an active device such as an piezoelectric actuator, to generate an inertial force that counteracts the disturbance acting on the main system.An equivalent lumped mass model of a boring bar with active dynamic absorber is considered. A cutting process model that considers the dynamic variation of shear and friction angle, that causes self-excited chatter during the cutting process, is applied to the lumped mass model. The theory of regenerative chatter is also applied to the model. Stability boundaries have been calculated for maximum permissible width of cut as a function of cutting speed. A comparison of the boundaries for chatter-free cutting operation of a plain boring bar, a boring bar with passive tuned dynamic absorber and a boring bar with active dynamic absorber is provided in this paper. The comparison shows that a substantial increase in the maximum permissible width of cut for stable cutting operation, over a range of cutting speeds, is obtained for a boring bar equipped with an active dynamic absorber.     

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.     

Magnetorheological fluid-controlled boring bar for chatter suppression

An innovative chatter suppression method based on a magnetorheological (MR) fluid-controlled boring bar for chatter suppression is developed. The MR fluid, which changes stiffness and undergoes a phase transformation when subjected to an external magnetic field, is applied to adjust the stiffness of the boring bar and suppress chatter. The stiffness and energy dissipation properties of the MR fluid-controlled boring bar can be adjusted by varying the strength of the applied magnetic field. A dynamic model of a MR fluid-controlled boring bar is established based on an Euler–Bernoulli beam model. The stability of the MR fluid-controlled boring system is analyzed, and the simulation results show that regenerative chatter can be suppressed effectively by adjusting the natural frequency of the system. Experiments in different spindle speeds utilizing a MR fluid-controlled boring bar are conducted. Under a 1 Hz square wave current, chatter can be suppressed, as evidenced by the elimination of chatter marks on the machined surfaces and the reduction in the vibration acceleration at the tip of the boring bar.     

内置式减振镗杆温升的分析与研究

深孔加工中镗杆的颤振严重影响孔的加工质量,而振动的抑制与镗杆的内部工作温度有很大关系.文章主要研究镗杆在工作中,温度升高以后对镗杆减振性能的影响.通过对镗杆的结构设计和三维模型的简化,根据热力学第一定律,对镗杆内置减振器振动产生的热量进行分析,运用有限元分析软件ANSYS Workbench,对镗杆进行稳态热分析和瞬态热分析,最后得出镗杆减振效果和阻尼液的温度变化情况.     

Theoretical and experimental study on rifling mark generating phenomena in BTA deep hole drilling process (generating mechanism and countermeasure)

Boring and Trepanning Association (BTA) deep hole drilling is used for producing holes with high aspect ratios. In this process, chatter vibration sometimes occurs, and a rifling mark is formed on the bore surface. The rifling mark generating phenomenon is considered to be a result of self-excited vibration caused by time delay. An analytical model is proposed considering the supporting condition of the boring bar in detail. In a real machine for BTA drilling, the boring bar is supported at the oil pressure head and the supporting pad, as well as at the base. The stability of the self-excited vibration is analyzed numerically, and the result is compared with the experiment. The theoretical and experimental results agree well with each other. Furthermore, the effect of an additional guide pad proposed by the authors as a countermeasure is evaluated theoretically and experimentally.     

WD12气缸体三轴孔精镗机床的设计

为保证缸体曲轴孔、凸轮轴孔和惰轮孔的加工精度,设计了WD12气缸体三轴孔精镗机床,确定了单面卧式总体方案、加工示意图和电气动作循环表.曲轴孔和凸轮轴孔均是多档间断的长孔,其精度要求高.为提高镗杆的刚度,除尽量加粗镗杆、设置中间支承外,选择德国玛帕生产的直线镗杆和浮动接头及美国GATCO生产的滚动导向套保证精度.采用"一面两销"的定位方案和液压夹紧机构.并对镗模安装提出了具体的要求.设备经十个月的研制,得到用户的认可.     

Design and implementation of tuned viscoelastic dampers for vibration control in milling

Passive means of vibration attenuation have been employed successfully and efficiently in machining systems such as turning and milling. Traditional approach to controlling vibration in a milling system is to develop control mechanisms for cutting tools or machine spindles. However, due to the nature of milling operations where the cutting tools rotate at high speed, the passive vibration control methods find very limited application with the traditional approach. In order to utilise the potential of the passive vibration control methodology in milling applications, the milling operation should be viewed as a system comprising an elastic structure and operation parameters. Dynamics of this closed-loop system should improve with improvement in dynamics of any of the system components, especially within the elastic structure that comprises the cutting tool, the machine tool, the workholding system and the workpiece. Although the level of improvement will vary depending on which component of the elastic chain is targeted for this purpose. This paper presents the development and testing of tuned viscoelastic dampers (TVDs) for vibration control through their application on a workpiece in milling operations. This work targets workpiece held on a palletised workholding system for the control of unwanted vibration and thus deviates from the traditional approach where cutting tool and/or machine spindles are targeted for vibration control strategies. Palletised workholding systems, due to their compact design, offer an opportunity to design passive damping mechanisms that are easier to implement in the case of a milling system. The TVD developed through this research is based on a commercially available viscoelastic damping polymer. Advantage of such materials is their high damping performance over a wide range of excitation frequencies. The TVD design process has used a unique combination of analytical modelling with experimental FRF data. Modal impact testing showed that the application of the TVD reduced the amplitude of vibration acceleration by 20 dB for the target mode. Since the target mode corresponded to torsional vibration, the TVD was effective in two planar coordinates, i.e. X and Y. In addition, the TVD also significantly reduced the amplitude of a vibration mode far from the mode it was designed for. The system has been tested experimentally to demonstrate significant reduction in vibration amplitudes during a milling process. The milling tests with different combinations of cutting parameters show that multi-TVD approach is always valid regardless of the parameters being used. The only requirement for TVDs to function effectively is that the natural frequency of the system, for which the TVDs are designed, is excited during the milling process.     

基于ANSYS的内置式双减振镗杆参数优化

内置式双减振镗杆通过动力学模型分析得出设计参数后,在Pro/engineer中建立镗杆的实体模型,导入Ansys Workbench中进行参数优化.由于双减振镗杆的两个减振块之间的距离及前后两减振橡胶的弹性模量这三个参数,在镗杆动力学模型分析中不能得出最优值,因此在Ansys中把这三个变量设为参数进行优化.得到这三个参数的最优值后,对减振镗杆进行谐响应分析,得出优化后的镗杆径向振幅和切向振幅均比优化前减小,证明优化后的镗杆具有更好的减振性能,为双减振镗杆制造提供了依据.     

Enhancement of dynamic stability of cantilever tooling structures

The least rigid components of machining systems are cantilever tools and cantilever structural units of machine tools (rams, spindle sleeves, etc.). These components limit machining regimes due to the development of chatter vibrations, limit tool life due to extensive wear of cutting inserts, and limit geometric accuracy due to large deflections under cutting forces. Use of high Young's modulus materials (such as sintered carbides) to enhance the dynamic quality of cantilever components has only a limited effect and is very expensive. This paper describes a systems approach to the development of cantilever tooling structures (using the example of boring bars) which combine exceptionally high dynamic stability and performance characteristics with cost effectiveness. Resultant success was due to: (1) a thorough survey of the state of the art; (2) creating a “combination structure” concept with rigid (e.g. sintered carbide) root segments combined with light (e.g. aluminum) overhang segments, thus retaining high stiffness and at the same time achieving low effective mass (thus, high mass ratios for dynamic vibration absorbers, or DVAs) and high natural frequencies; (3) using the concept of “saturation of contact deformations” for efficient joining of constituent parts with minimum processing requirements; (4) suggesting optimized tuning of DVAs for machining process requirements; (5) development of DVAs with the possibility of broad-range tuning; (6) structural optimization of the system; and (7) using a novel concept of a “Torsional Compliant Head”, or TCH, which enhances dynamic stability at high cutting speeds and is suitable for high rev/min applications since it does not disturb balancing conditions. The optimal performance and interaction of these concepts were determined analytically, and then the analytical results were validated by extensive cutting tests with both stationary and rotating boring bars, machining steel and aluminum parts. Stable performance with length-to-diameter ratios up to L/D = 15 was demonstrated, with surface finish 20–30 μm with both steel and aluminum at L/D = 7–11. Comparative tests with commercially available bars demonstrated the advantages of our system.     

卧式镗铣床电气控制系统的PLC改造

采用PLC作为主控制器，选择SSD590数字式直流调速装置作为拖动电源，研制了一种新型的通用镗铣床电气控制系统，用于大型高精度卧式镗铣床的电气控制。应用实践表明，该系统设计先进、性能价格比高、调速范围大、运行可靠、可移植性强，可以广泛应用于各种类型卧式镗铣床的电气控制系统改造。     

A novel approach to machining condition monitoring of deep hole boring

In the optimization of deep hole boring processes, machining condition monitoring (MCM) plays an important role for efficient tool change policies, product quality control and lower tool costs. This paper proposes a novel approach to the MCM of deep hole boring on the basis of the pseudo non-dyadic second generation wavelet transform (PNSGWT). This approach is developed via constructing a valuable indicator, i.e., the wavelet energy ratio around the natural frequency of boring bar. Self-excited vibration occurs at the frequency of the most dominant mode of the machine tool structure. Via modeling dynamic cutting process and performing its simulation analysis during deep hole boring, it is found that the vibration amplitudes at the nature frequency of the machine tool rise with the tool wear. The PNSGWT that has relative adjustable dyadic time-frequency partition grids, good time-frequency localizability and exact shift-invariance is used to extract the wavelet energy in the specified frequency band. Accordingly, the MCM of deep hole boring can be implemented by means of normalizing the wavelet energy. Finally, a field experiment on deep hole boring machine tool is conducted, and the result shows that the proposed method is effective in the process of monitoring tool wear and surface finish quality for deep hole boring.     

Blast Erosion Properties of Overlay Weld Metal

Summary

Solid horns for power ultrasonics usually magnify the vibration amplitude by reducing the cross-sectional area along their axis. However, these horns are usually too heavy to handle easily, and their fatigue strength is reduced by the stress concentration induced by their profile. The authors have therefore attempted to develop a new type of horn based on a different magnification principle by connecting two simple round bars with different specific acoustic impedances. Vibration of the round bar horn has been analysed by longitudinal wave theory and FEM to achieve a practical design. New types of horn were fabricated and tested to confirm their displacement amplitude magnification capabilities. The analytical and experimental results showed that the simple round bar horn is satisfactory for practical use. On this basis, an attempt was made to fabricate a simple round bar horn using a friction-welded joint consisting of SUS304 stainless steel and 6061 aluminium alloy dissimilar metals. The vibration characteristics of the input-output displacement amplitude, frequency, elevated temperature, and fatigue fracture were respectively investigated for friction-welded simple round bar, step, and exponential horns consisting of SUS304 and A6061. The results obtained suggest that the simple round bar horn has better vibration characteristics than the others.     

Dynamic simulation of boring process

This article presents a model to simulate the dynamics of boring process. In boring operations the boring bar should be long and slender; therefore it is easily subjected to vibrations. Tool vibrations result in reduced tool life, poor surface finish and may also introduce chatter. Hence, predicting the vibrational behavior of boring process for certain cutting conditions and tool work-piece properties is of great importance. The proposed method models the cutting tool geometry by B-spline parametric curves. By using B-spline curves it is possible to simulate different tool geometries with a single approach. B-spline curves also enable the modeling of the kinematics of chip formation for different tool work-piece engagement conditions with a single formulation. The boring bar has been modeled by the Euler–Bernoulli beam theory. The simulation process has been implemented with MATLAB. The algorithm consists of different computational modules that are interconnected by a main program. Experimental machining tests have been conducted to verify the validity of the proposed model. Proposed dynamic models have been able to predict the dynamic cutting force components and vibration frequencies with less than 15% deviation. The proposed model has been also able to predict the chatter onset correctly.     

Towards improved design of boring bars part 1: Dynamic cutting force model with continuous system analysis for the boring bar performance

The vibrational amplitude is generally large in the case of a boring bar due to its slenderness. A dynamic cutting force model has been presented to take this large amplitude into account. The boring bar is then modelled as a cantilever with this dynamic force acting at the free end and a generalized continuous system model is obtained. This model is solved for the specific case of boring with a zero side cutting edge angle for which published results are available. A reasonably close agreement is found between the proposed model and the experimental results.     

发动机缸体曲轴孔精加工专用夹具设计与研究

曲轴孔精加工工序的精度将直接影响发动机的寿命与品质,而先进合理的夹具系统是加工精度的重要保障。针对某企业对缸体曲轴孔精加工精度要求,确定了工艺参数及定位基准,在此基础上,对夹具系统的定位机构、让刀机构、夹紧机构及镗模等主要结构进行了设计与分析。最后,分析了镗杆的动态特性,并研究了轴承刚度对镗杆动态特性的影响,适当提高轴承预紧力即轴承刚度,能有效提高镗杆系统的刚度。经实际加工检验,验证了设计的正确性。     

超声波椭圆振动加工技术的研究进展

超声波椭圆振动加工是功率超声加工技术的重要分支之一,在硬脆性材料加工方面具有非常广阔的应用前景。综述了超声波椭圆振动加工系统的研究进展和超声波椭圆振动加工技术在车削、镗削、钻削、铣削、磨削、化学机械抛光、砂轮修整、表面滚压与焊接等方面的最新应用,最后对超声波椭圆振动加工技术的发展方向提出了一些建议。     

基于连续小波的螺杆压缩机气阀状态监测方法研究

针对实测螺杆压缩机气阀在不同状态下振动信号的特点,采用连续小波变换的方法得到信号在尺度上的平均能量分布,即信号的平均尺度-小波能量谱.根据气阀不同状态下振动信号在尺度上的能量分布差异,提出了基于平均尺度-小波能量的标准特征向量判断压缩机气阀状态的方法,能够很好地识别出螺杆压缩机气阀的状态类型.该方法为螺杆压缩机状态监测及故障诊断提供了一种新的有效途径.