Development of a newly structured variable preload control device for a spindle rolling bearing by using an electromagnet

For high speed and high efficiency machining, the spindle of modern machine tools simultaneously requires high speed and high stiffness characteristics, and its range of use rotation is becoming wider. Both heavy cutting at low speed and light cutting at high speed must be carried out successively in series with a single machine tool spindle. As such, many studies are being carried out on variable preload control methods that apply a preload to a spindle rolling bearing, as an alternative to the existing fixed position preload and constant pressure preload methods. This paper introduces a newly structured variable preload control device that can arbitrarily adjust the preload applied to spindles employing a rolling bearing. The device controls the coil current on an electromagnet and thereby uses the magnetic force between the electromagnet and a magnetic substance to arbitrarily control the preload applied to the rolling bearing during operation. A prototype for the variable preload control device of the proposed structure was created and a functionality test was then carried out with a test bench prepared using a load cell. The operating principle of the proposed device was verified and the interrelationships between the coil current on the electromagnet and the preload applied to rolling bearing were analyzed through the functionality test. Lastly, the fabricated variable preload control device was applied to a prototype of a spindle system, and a rigidity test was carried out. The test results confirmed that the variable preload control device operates properly and smoothly.     

机床主轴的仿生设计

基于对稻麦秸秆空心结构的仿生,提出了主轴的仿生空心结构设计.计算结果表明,当空心轴的壁厚约为其外径的2/7时,其主轴的抗扭、抗弯性能最好,而且使用的材料最少;对于阶梯轴或圆锥轴,可按其当量光轴直径来设计空心轴壁厚.另外,计算分析了滚动轴承的刚度,认为一定预紧力与定压预紧方式有益于提高主轴刚度.     

Bearing load analysis and control of a motorized high speed spindle

Angular contact ball bearings are the most popular bearing type used in the high speed spindle for machining centers. Because the bearing load is increased rapidly with the raised spindle speed due to the centrifugal force and temperature raise, proper initial preload and especially operating-induced load control of the angular ball bearing is important to the rigidity, accuracy and life of the spindle. The bearing layout, preload mechanism an on-line load bearing control are discussed in this paper. The management of the centrifugal force and thermally-induced bearing loads is especially emphasized. An active bearing load monitoring and control mechanism that consists of an integrated strain-gage load cells and piezoelectric actuators has been developed and tested. This active control and monitoring mechanism on-line adjusts the bearing load according the cutting conditions. Experiments were conducted to identify the proper initial bearing preload range. Optimal preload for the lowest bearing temperature raise existed for a specified spindle speed. The optimum preload, however, should be raised when the operational speed is increased.     

角接触球轴承组合轴向预紧力分析

在赫兹接触理论和滚动轴承拟静力学分析理论的基础上,建立了角接触球轴承串联组合时计算轴向预紧力的方程.采用Matlab编程求解了动态条件下的轴向预紧力,分析了轴承内外圈宽度尺寸偏差、隔套长度尺寸偏差、滚动体直径尺寸偏差、转速及轴承沟曲率半径系数对轴承组合轴向预紧力的影响规律.结果表明:尺寸偏差越大两个轴承轴向预紧力的差别越大,内外圈沟曲率半径系数越大轴向预紧力的差别越小;外圈沟曲率半径系数比内圈沟曲率半径系数对轴向预紧力分配的影响更明显;转速增大时两个轴承轴向预紧力的差别先减小后增大.     

An integrated thermo-mechanical-dynamic model to characterize motorized machine tool spindles during very high speed rotation

High speed machining (HSM) is a promising technology for drastically increasing productivity and reducing production costs. Development of high-speed spindle technology is strategically critical to the implementation of HSM. Compared to conventional spindles, motorized spindles are equipped with built-in motors for better power transmission and balancing to achieve high-speed operation. However, the built-in motor introduces a great amount of heat into the spindle system as well as additional mass to the spindle shaft, thus complicating its thermo-mechanical-dynamic behaviors. This paper presents an integrated model with experimental validation and sensitivity analysis for studying various thermo-mechanical-dynamic spindle behaviors at high speeds. Specifically, the following effects are investigated: the bearing preload effects on bearing stiffness, and subsequently on overall spindle dynamics; high-speed rotational effects, including centrifugal forces and gyroscopic moments on the spindle shaft and, subsequently, on overall spindle dynamics; and the spindle dynamics on the cutting point receptance. The proposed integrated model is a useful tool for differentiating quantitatively different effects on the spindle behaviors. The results show that a motorized spindle softens at high speeds mainly due to the centrifugal effect on the spindle shaft.     

短应力线轧机带载压下装置设计计算

为了适应长材轧制技术中无头轧制的工艺要求，短应力线轧机需具备带载压下功能。实现带载压下功能则要求压下装置具有较高的强度。通过对短应力线轧机压下装置的压下力矩、零部件承载能力、传递效率的计算和分析，得到了带载压下装置的力能参数，为带载压下技术的实现提供了理论支撑。采用该方法设计出合理的带载压下装置结构，实际应用表明效果较好。     

短应力线轧机带载压下装置设计计算

为了适应长材轧制技术中无头轧制的工艺要求，短应力线轧机需具备带载压下功能。实现带载压下功能则要求压下装置具有较高的强度。通过对短应力线轧机压下装置的压下力矩、零部件承载能力、传递效率的计算和分析，得到了带载压下装置的力能参数，为带载压下技术的实现提供了理论支撑。采用该方法设计出合理的带载压下装置结构，实际应用表明效果较好。     

Vibration based preload estimation in machine tool spindles

Prevention of catastrophic bearing failures caused by excessive thermally induced preload is one of the key issues in the design and operation of high speed spindles. Temperature monitoring and shutting the spindle off in hazardous conditions is at present the most common method of avoiding bearing seizure. However, due to a rapid heat built-up and measurement delay, this solution in not reliable. An improved protection can be achieved either by custom systems with springs or hydraulic actuators that maintain a steady preload, or by monitoring the instantaneous preload and appropriate, predictive adjustment of machining conditions. While the former approach increases the cost of spindles and degrades their potential reliability, monitoring and proactive control of the actual preload eliminates these disadvantages. Its feasibility is predicated upon fast, reliable and accurate in-process preload estimation. A suitable estimation algorithm proposed in this paper employs vibrations of the spindle housing measured by means of accelerometer(s) and analyzed in the context of mechanical multi-degree-of-freedom model of the spindle assembly treated as a component of the entire machine tool. Representative experimental results are presented.     

Development of a modular dynamometer for triaxial cutting force measurement in turning

Accurate and reliable measurement of cutting forces in turning is essential for tool geometry, tool trajectory and cutting parameters optimization, as well as for tool condition monitoring and machinabilty testing. In this work, an innovative dynamometer for triaxial cutting force measurement in turning, specifically designed to be applied at a milling-turning CNC machine tool endowed with an indexable head, is presented. The device is based on a piezoelectric force ring integrated into a commercial toolshank, and its modular design allows the easy change of the cutting insert without altering sensor preload. The prototype device was assembled and experimentally tested by means of static calibration and dynamic identification, which evidenced good static and dynamic characteristics. Eventually, the sensor was tested in operating conditions by machining a benchmark workpiece.     

Development of a micro/meso-tool clamp using a shape memory alloy for applications in micro-spindle units

In developing micro-spindle units, a critical problem is miniaturization of the tool clamp. Approaches for scaling down conventional tool clamps, such as the collet-chuck, hydraulic chuck, and shrink-fit methods may be limited by their inherently complicated mechanisms. This study developed a novel tool clamp based on shape memory alloy (SMA), which allows further miniaturization. The tool clamp can be simplified by using an SMA ring, which is all that is needed for clamping. The SMA-based tool clamp does not require any collet, and its structural configuration is axisymmetric. Furthermore, the SMA makes it possible to switch between the clamped and unclamped states by using a simple device to regulate small changes in temperature. This paper first describes the operating principle of the SMA-based tool clamp. Second, it presents the finite element method (FEM) analyses that were conducted to investigate the characteristics of the clamping/unclamping operations and the effect of centrifugal force. Third, it describes a prototype of the SMA-based tool clamp, which was designed and built for applications in micro-spindle units. Fourth, it presents an evaluation of the time needed for the clamping/unclamping operations and the tool-clamping force, which were both evaluated experimentally. Finally, it describes a mill-machining test conducted with the prototype, which confirmed that the tool clamp is little affected by centrifugal force at high rotational speeds. The experimental results confirm that the proposed SMA-based tool clamp can be successfully applied to micro-machining.     

热镀锌机组光整机工作辊清洁技术

结合某钢厂热镀锌机组光整机工作辊清洁装置的改造项目,分析了刷辊和高压水清洗装置的特点,并对高压水清洗装置从设备组成、技术说明、自动控制等几方面进行了详细说明。通过实际生产数据,验证了高压水清洗装置的实用性、可靠性及先进性。     

Modeling of spindle-bearing and machine tool systems for virtual simulation of milling operations

This paper presents a general, integrated model of the spindle bearing and machine tool system, consisting of a rotating shaft, tool holder, angular contact ball bearings, housing, and the machine tool mounting. The model allows virtual cutting of a work material with the numerical model of the spindle during the design stage. The proposed model predicts bearing stiffness, mode shapes, frequency response function (FRF), static and dynamic deflections along the cutter and spindle shaft, as well as contact forces on the bearings with simulated cutting forces before physically building and testing the spindles. The proposed models are verified experimentally by conducting comprehensive tests on an instrumented-industrial spindle. The study shows that the accuracy of predicting the performance of the spindles require integrated modeling of all spindle elements and mounting on the machine tool. The operating conditions of the spindle, such as bearing preload, spindle speeds, cutting conditions and work material properties affect the frequency and amplitude of vibrations during machining.     

部分式滑动轴承整体离心铸造的研制

采用离心浇注的工艺方法制造轧机用滑动轴承;通过理论分析实验研究,重点探讨锡基轴承合金剖分式瓦体整体离心浇注工艺应用的可行性;同时给出能减轻密度偏析的最优浇注工艺参数组合。     

滚动轴承疲劳失效故障的数字孪生虚拟实体建模

针对目前基于数据驱动和机制建模的滚动轴承故障诊断方法的不足,提出一种针对疲劳故障的滚动轴承数字孪生虚拟实体模型。基于L-P疲劳失效理论,对滚动轴承全寿命周期的振动响应进行建模。在轴承五自由度非线性滚动振动模型的基础上,考虑滚动体-滚道冲击力的影响,对滚动轴承内、外圈局部缺陷模型进行改进,并提出一种滚动轴承次表面裂纹早期故障模型,从而建立了疲劳失效下的滚动轴承全寿命数字孪生虚拟实体模型。该模型可表征轴承疲劳故障的产生、发展到严重的全过程。对不同类型的轴承疲劳故障虚拟实体数据进行了分析,验证了所建模型的正确性和有效性。     

混合陶瓷球轴承振动特性仿真分析

为研究混合陶瓷角接触球轴承剥落故障振动特性,在ANSYS Workbench中建立了角接触球轴承的动力学有限元模型,通过在外圈滚道、内圈滚道及滚动体上设置剥落故障,分析特定工况下正常与剥落故障时轴承各零件受力变化。在此基础上,研究正常与不同零件故障对接触力的影响,并分析剥落故障对轴承零件运动特性的影响。结果表明：轴承各元件中应力最大的是滚动体,剥落故障使轴承最大应力增加,且最大应力大都出现在滚动体上;外圈剥落对经过剥落处的滚动体造成冲击,增大滚动体公转和自转周期,使滚动体速度降低,接触力明显增大;外圈剥落对内圈振动加速度的变化影响较小。     

基于CWT-CNN的离心泵轴承故障识别方法

针对传统的轴承故障诊断方法在面对强噪声和非平稳信号识别时特征提取过度依赖先验知识和专家经验等问题,结合传统的信号处理方法和深度学习算法提出一种基于CWT-CNN的离心泵轴承故障识别方法。连续小波变换(CWT)将原始的1D振动信号转化为故障特征信息更丰富的2D时频图,2D时频图再输入到卷积层完成特征的自动提取,最后SoftMax层完成故障识别。经过西储大学公开轴承数据集和实验室搭建的离心泵振动轴承采集实验台验证,该方法的故障识别准确率均能达到90%以上。     

大型轧辊轴承座拆装机液压系统设计

介绍了一套大型轧辊轴承座拆装机的液压系统,分析了系统设计过程中的技术难点,确定了系统的主要性能参数.该液压系统已在轧钢生产、有色金属加工的大型企业投入使用.在实际应用中,该系统运行平稳、可靠,实现了轧辊轴承座的高效、可靠、安全的拆卸和安装.     

Virtual Design and Optimization of Machine Tool Spindles

An integrated digital model of spindle, tool holder, tool and cutting process is presented. The spindle is modeled using an in-house developed Finite Element system. The preload on the bearings and the influence of gyroscopic and centrifugal forces from all rotating parts due to speed are considered. The bearing stiffness, mode shapes, Frequency Response Function at any point on the spindle can be predicted. The static and dynamic deflections along the spindle shaft as well as contact forces on the bearings can be predicted with simulated cutting forces before physically building and testing the spindles. The spacing of the bearings are optimized to achieve either maximum dynamics stiffness or maximum chatter free depth of cut at the desired speed region for a given cutter geometry and work-piece material. It is possible to add constraints to model mounting of the spindle on the machine tool, as well as defining local springs and damping elements at any nodal point on the spindle. The model is verified experimentally.     

Modeling of dynamic characteristic of the aerostatic bearing spindle in an ultra-precision fly cutting machine

Axis orientation stability of aerostatic bearing spindles has great influence on machining precision of ultra-precision fly cutting machines used for processing ultra-precision optical components of large diameter. Mid-spatial frequency errors (amplitude<0.1 μm, wavelength about 100 nm) always existed on the machined surfaces along feeding direction. Generally, the waviness errors on processed surfaces will impact the performance of workpiece used as optical components greatly, and the tilting motions of spindles were believed to be the main source which produced the waviness errors. In this paper, to study the tilting motions of spindles, the Euler dynamic equations of angular displacements of spindles were proposed, and analytic solutions of the equations were also presented. At the same time, the 3D surface profile simulations of workpieces based on analytic solutions of Euler equations were achieved. The simulation results have been verified by lots of experiments on an ultra-precision fly cutting machine. At last, the inertia tensor criterion which can decrease the waviness errors of machining surface was represented, and it can be applied to instruct the structure design of aerostatic bearing spindles.     

高速电主轴辐射噪声特性分析

研究了3种电主轴的辐射噪声特性。通过实验测量了电主轴辐射噪声,分析了全陶瓷轴承电主轴、钢轴承电主轴和无内圈式陶瓷轴电主轴辐射噪声的时频特性。实验结果表明:提高旋转速度,全陶瓷轴承电主轴与钢轴承电主轴辐射噪声均呈增大趋势,且辐射噪声中含有旋转频率和2倍转频特征,而无内圈式陶瓷轴电主轴的辐射噪声呈现波动式变化,其声压级高于其他2种电主轴,且频谱较为杂乱;在高转速时全陶瓷轴承电主轴声波具有明显的周期性;3种电主轴辐射噪声中均具有较高的摩擦与冲击噪声。