Stabilization of high frequency chatter vibration in fine boring by friction damper

Friction damper has been found successful to prevent high frequency chatter occurring at more than 10,000Hz, and causing problem of reduced tool life in fine boring operation. The new damper is characterized by simple structure that consists of an additional mass attached to the main vibrating structure with small piece of permanent magnet. The principle is straightforward in which Coulomb and viscous frictions dissipate vibration energy at the interface between the damper and main vibrating structure. The damper needs no tuning, and is effective at high frequency. The paper first introduces a typical design of the friction damper with experimental proof by cutting tests of its effectiveness in eliminating the high frequency chatter in fine boring, and assuring normal tool life of the cutting edge. Theoretical and experimental analyses are introduced for understanding the fundamental principle and characteristics of the new damper. The new damper is effective for boring tools, which vibrate at frequency more than 5,000Hz.     

高频群脉冲电源在微细孔电化学加工中的应用

针对电化学加工的特殊需要所设计的一种新型电源———高频群脉冲电源的设计原理和特征,从理论上分析其对 于传统的直流电源和脉冲电源在微小型零件加工中的优越性;通过微细孔加工对这种新型的电源进行了分析和说明。 结果表明,在微小型加工领域,采用高频群脉冲电源在改善加工精度,提高加工质量方面优于直流电源和脉冲电源。     

一种基于振动信号处理的颤振预报方案研究

针对切削过程中产生的颤振现象,通过对机床的在线监测,将采样出的振动加速度信号进行数据处理,提出一种以方差和互相关系数作为综合判据的方法来判别颤振是否发生,并在MATLAB环境下仿真证明该方法的可行性。     

Theoretical and experimental study of the chatter vibration in wet and MQL machining conditions in turning process

Turning is one of the most commonly used cutting processes for manufacturing components in production engineering. The turning process, in some cases, is accompanied by intense relative movements between tool and workpiece, which is called chatter vibrations. Chatter has been identified as a detrimental problem that adversely impacts surface finish, tool life, process productivity, and dimensional accuracy of the machined part. Cooling/Lubrication in the turning process is normally done for some reasons, including friction and force reduction, temperature decrement, and surface finish improvement. Wet cooling is a traditional cooling/lubrication process that has been used in machining since the past. Besides, a variety of new cooling and lubricating approaches have been developed in recent years, such as the minimum quantity lubrication (MQL), cryogenic cooling, nanolubrication, etc., due to ecological issues. Despite the importance of cooling/lubrication in machining, there is a lack of research on chatter stability in the presence of cutting fluid in cutting processes. In this study, the chatter vibration in turning process for two cooling/lubrication conditions of conventional wet and MQL is investigated. An integrated theoretical model is used to predict both the metal cutting force and the chatter stability lobe diagram (SLD) in turning process. This model involves deriving a math equation for predicting metal cutting force for both wet and MQL conditions using experimental training force data and a Genetic Expression Programming (GEP)-based regression model. Also, the traditional single degree of freedom chatter model is used here for predicting the SLDs. The chatter model is discussed and verified with experimental tests. Then, the experimental results of the tool's acceleration signal, work surface texture, surface roughness, chip shape, and tool wear are presented and compared for wet and MQL conditions. The results of this study show that the cooling/lubrication systems such as wet or MQL have a considerable effect on the SLDs. Also, the predicted results of metal cutting force and SLD for both wet and MQL techniques are in good agreement with the experimental data. Therefore, it is recommended that for each lubrication condition including wet, or MQL, the SLD be determined to achieve higher machinability.     

Simultaneous double-sided milling of flexible plates with high accuracy and high efficiency—Suppression of forced chatter vibration with synchronized single-tooth cutters

This paper presents a new method to finish flexible plates with high accuracy and high productivity. Precision steel plates are finished conventionally by face milling with electro-magnetic chucks. It is difficult to improve flatness of the flexible plates, because they deform to fit the chuck surfaces while clamped. The authors have applied simultaneous double-sided milling to solve this problem, but it causes forced chatter vibration which is not allowed in precision finishing. Thus, the new method is proposed and verified to suppress the forced chatter vibration, in which the both surfaces are finished simultaneously with single tooth milling cutters with synchronization so that the thrust forces are cancelled out on the both sides.     

制动摩擦高频振动及其防治

在低速制动工况下一些机车车辆转向架有高频振动现象出现,有的还非常大。制动高频振动对车体、转向架和系统产生较大的破坏作用,恶化了车辆的运行平稳性,对铁道沿线的噪音污染加重。制动高频振动是一种自激振动,如何避免对制动系统十分重要。对制动工况下一些机车车辆转向架发生的高频振动现象的机理进行了分析,并提出了解决方法。仿真结果表明制动高频振动与转向架构架结构和悬挂系统有关,可通过改进构架设计或调整转向架参数予以避免。     

一种新型高低频复合振动装置的研究

针对金属材料疲劳断裂研究的现状以及实际应用中应力比r的变化情况,分析了应力比r对金属疲劳裂纹萌生和扩展的影响.运用Pro/E设计了一种新型高低频复合振动装置,对其空载运动状态下的动力学特性做了理论分析.建立了振动装置加栽金属材料时的动力学模型,以加载7A09高强度铝合金为算例,运用ANSYS对模型进行谐波分析,得到了此种情况下的幅频特性曲线图,并由此获得了在该状态下最易发生疲劳断裂的变频区间.     

Analysis of regenerative chatter suppression with adding the ultrasonic elliptical vibration on the cutting tool

A method is proposed to suppress regenerative chatter in turning operation, in which the ultrasonic elliptical vibration is added on the cutting tool. It results in the fact that the cutting tool is separated periodically from the chip and the workpiece, and the direction of the frictional force between the rake face of the cutting tool and the chip is reversed in each cycle of the ultrasonic elliptical vibration. The experimental investigations show that the regenerative chatter occurring in ordinary turning operation can be suppressed effectively by applying the ultrasonic elliptical vibration on the cutting tool. In order to clearify the reason of the regenerative chatter suppression, theoretical analysis and computer simulation are performed on turning with ultrasonic vibration. There is a good agreement among the experimental investigations, theoretical analysis and the computer simulation.     

高频群脉冲电化学加工中频率对极间间隙的影响

给出了脉冲电化学加工极间平衡间隙的数学模型,并据此讨论了高频群脉冲电化学加工中,电源主脉冲频率与平衡加工间隙的关系.在模拟结果中,极间平衡间隙与主脉冲频率则呈严格的线性关系,即随频率增加平衡间隙线性减小.并根据设计的硬币花纹工艺试验表明,选择较高的主脉冲频率,可获得较小的加工间隙,进而获得良好的表面质量.由此可得出结论：良好的加工质量来源于高频所带来的较小极间间隙.     

Rotary ultrasonic machining: effects of tool natural frequency on ultrasonic vibration amplitude

Rotary ultrasonic machining (RUM) is a hybrid machining process that combines the material removal mechanisms of grinding and ultrasonic machining. RUM has been applied to hole-making for a wide range of materials. It is known that ultrasonic vibration amplitude has significant effects on cutting force, torque, and surface finish in RUM. One experimental observation that has been reported in the literature multiple times states that different tools show different vibration amplitudes on the same ultrasonic power level. However, no analyses can be found in the literature to explain this observation. The existence of this knowledge gap makes it difficult to explain some experimentally obtained trends or to conduct more realistic physics-based modeling work. The objectives of this research are to understand the effects of tool natural frequency on ultrasonic vibration amplitude in RUM, to provide an explanation to the observation and verification of measurement methods, and also to guide tool design and selection in RUM. Ultrasonic vibration amplitudes of tools are measured by three methods and compared. It is found that tool natural frequency significantly affects ultrasonic vibration amplitude. The tool with its natural frequency closest to that of the ultrasonic power supply (20?kHz) generates the highest ultrasonic vibration amplitude on every ultrasonic power level tested.     

Proposal of novel spindle speed variation profile with constant acceleration rate for improvement of chatter stability

Spindle speed variation (SSV) is one of the effective methods which suppresses regenerative chatter. However, regenerative chatter can grow even if SSV is applied. In the previous work, the chatter growth characteristics in SSV were clarified. The chatter frequency changes proportionally to the varying spindle speed, and it causes the change of the magnitude of the dynamic compliance. Hence, chatter can be suppressed through SSV since the dynamic compliance usually reduces as the chatter frequency changes. A greater compliance reduction can be obtained by a higher rate of spindle speeds in two consecutive revolutions at the same angular position, i.e., acceleration rate. From the investigations in the previous work, limitation of the conventionally utilized SSV profiles is found as follows: the acceleration rate always fluctuates with speed variation and the chatter vibration grows where the acceleration rate is insufficient for suppression, and hence suppressing chatter in all sections of SSV is difficult. In this paper, a new SSV profile with a constant acceleration rate, namely CAR-SSV, is proposed to overcome the limitation of chatter stability improvement by utilizing conventional SSV profiles. The magnitude of the acceleration rate is kept constant to realize the chatter suppression effect throughout the cutting process. Through time-domain simulation and cutting experiments, the chatter stability of CAR-SSV is investigated based on the previously introduced chatter stability evaluation indices. Influence of the parameters of CAR-SSV on the stability is investigated, and an appropriate strategy for setting SSV parameters to achieve higher stability is discussed. In addition, in order to verify the effectiveness of the proposed profile, the stabilities of conventional SSV profiles and CAR-SSV are compared through time-domain simulations and cutting experiments.     

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.     

枪钻低频振动钻削振动问题的研究

概述了枪钻低频振动钻削的加工原理,介绍了国内外的研究和发展状况,指出了该项技术研究所存在的问题,并对今后的研究方向作了展望。     

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.     

高频热合机电磁辐射抑制技术的研究

根据国家电磁兼容标准(GB4824-2004-2A),针对传统高热合机在主频、二倍频和三倍频处的辐射强度严重超标的问题,结合高频热合机的工作原理对其电磁兼容性进行深入的研究,通过采取三种措施:1)在热合机机头部位设计制作谐振电路衰减器,通过建立陷波槽和反作用场的方法,削弱和吸收热合机机头强辐射电磁场,使电磁泄漏辐射场强得到衰减;2)采用电磁辐射屏蔽衰减技术,对高频功率的铜片馈线进行屏蔽;3)重新设计高频振荡电路,减少振荡输出的谐波分量.试验结果证明:采取对电磁辐射抑制措施后高频热合机的输出频率符合国家规定的频率标准,解决了目前高频热合机工作时的电磁泄露辐射污染问题,带来了很好的社会、环境和经济效益.     

Identification and characterisation of steel corrosion using passive high frequency RFID sensors

High frequency RFID sensors are attractive in diverse applications where sensor performance is required at a low cost and dimension restriction. An approach adapting commercial passive 13.56 MHz RFID tags has been developed for sensing corrosion stage. This investigation includes balance of sensing and positioning of RFID sensors for corrosion detection by analysing real and imaginary parts of the complex impedance. With passive HF RFID sensors, real part and imaginary part of complex impedance have been extracted from the reader coil with VNA (vector network analyser) and delivering a unique capability for corrosion sensing with different atmospheric exposure time steel samples (1 month, 6 months, 10 months and 12 months). With different positioning (5–25 mm), features extraction based on the complex impedance with PCA (principal component analysis) has been designed for position-independent corrosion evaluation.     

Slug frequency in high viscosity oil-gas two-phase flow: Experiment and prediction

The number of slug units that traverses a particular point at a given time within a defined pipe cross-section is known as slug frequency. The behaviour of this critical parameter for two-phase flow in high viscosity oils is significantly different from those of conventional oils (of less than 1 Pa s). In this experimental investigation, new data on slugging frequency in high viscosity oil-gas flow are reported. Scaled experiments were carried out using a mixture of air and mineral oil in a 17 m long horizontal pipe of 0.0762 m ID. A high-speed Gamma Densitometer of frequency of 250 Hz was used for data acquisition over a time interval of 30 s. For the range of flow conditions investigated, increase in oil viscosity was observed to strongly influence the slug frequency. Comparison of the present data with prediction models available in the literature revealed discrepancies. A new correlation incorporating the effect of viscosity on slug frequency has been proposed for horizontal flow. The proposed correlation will improve the prediction of slug frequency in high viscosity oils.     

高锰钢切削刀具的设计

高锰钢切削极易产生硬化层,很难加工。在生产实践中,通过合理地选择刀具材料、刀具结构、切削用量等,可以很好解决高锰钢难加工的问题,保证了高锰钢的加工质量。     

高速加工技术在模具制造中的应用

阐述了在模具加工中实现高速加工所必需的一些关键技术,及高速加工技术在模具制造中的意义,并通过与常规的加工方式EDM的对比,描述了高速加工的优越性和局限性。同时以加工实例说明高速切削是现代模具加工的发展方向之一。     

Identification of bearing dynamics under operational conditions for chatter stability prediction in high speed machining operations

Chatter is a major problem causing poor surface finish, low material removal rate, machine tool failure, increased tool wear, excessive noise and thus increased cost for machining applications. Chatter vibrations can be avoided using stability diagrams for which tool point frequency response function (FRF) must be determined accurately. During cutting operations, due to gyroscopic moments, centrifugal forces and thermal expansions bearing dynamics change resulting in tool point FRF variations. In addition, gyroscopic moments on spindle–holder–tool assembly cause separation of modes in tool point FRF into backward and forward modes which will lead to variations in tool point FRF. Therefore, for accurate stability predictions of machining operations, effects of operational conditions on machine tool dynamics should be considered in calculations. In this study, spindle bearing dynamics are identified for various spindle rotational speeds and cutting forces. Then, for a real machining center, tool point FRFs under operating conditions are determined using the identified speed dependent bearing dynamics and the mathematical model proposed. Moreover, effects of gyroscopic moments and bearing dynamics variations on tool point FRF are examined separately. Finally, computationally determined tool point FRFs using revised bearing parameters are verified through chatter tests.