Optimal design of thrust bearing for high-speed composite air spindles

High-speed air spindles are appropriate for high-speed and high-precision machining such as small hole drilling of printed circuit board (PCB) or wafer cutting for manufacturing semiconductors. The axial load capability and stiffness of the air spindles for drilling operation are dependent on the thrust bearings. The thrust bearings are composed of an air supply part in the housing and a rotating part. Since stresses induced in the rotating part of thrust bearing by centrifugal force are very high at high-rotational speed, the axial stiffness and load capability of an air spindle should be designed considering stresses due to centrifugal force as well as the natural frequency of the rotating shaft to avoid the resonant whip vibration of the spindle. In this work, the air supply part and the rotating part of a thin thrust bearing were designed for a high-speed carbon fibre composite air spindle using the stiffness map to maximize the stiffness of the thrust bearing under axial and centrifugal forces.     

高转速对电主轴系统动力学特性的影响分析

高速切削的加工质量、加工效率与高速主轴系统的动力学特性密切相关,而转速对主轴系统的动力学特性有着明显的影响。该文首先确定了由高转速所诱发的主轴系统动力学特性影响因素,包括离心力、陀螺力矩以及轴承刚度软化等,并列举了围绕上述影响因素的相关研究成果。在此基础上,基于有限元法构建了考虑转速的主轴-轴承的通用有限元模型。以某电主轴为例,分别定性或定量分析了离心力、陀螺效应、轴承的径向刚度以及上述因素的耦合对高速主轴动力学特性的影响。该文的研究表明,主轴在高速运转状态下,轴承径向刚度、离心力和陀螺效应对主轴系统动力学特性都有较显著的影响,在对高速运转状态下的主轴系统动力学建模时,必须考虑上述影响因素。     

基于离心力和陀螺力矩效应的“主轴-轴承”系统动力学特性研究

研究“主轴-轴承”系统在高转速场中受离心力和陀螺力矩影响的动力学特性对于提高主轴系统运行稳定性有重要的作用。在扩展Harris滚动轴承非线性分析模型、建立滚动轴承耦合刚度矩阵的基础上,建立了一种综合考虑主轴离心力效应和陀螺力矩效应的“主轴-轴承”系统动力学数字模型,并借助锤击模态实验验证了其准确性;分析论述了主轴离心力效应、主轴陀螺力矩效应及滚动轴承运行刚度对“主轴-轴承”系统在高转速场中的动力学特性的影响规律。通过模型分析计算表明：当轴承处于超轻预紧（EL）工况时,主轴的高速效应比轴承运行刚度对“主轴-轴承”系统动力学特性的影响更大,尤以主轴陀螺力矩效应的影响最为突出。     

高速电主轴多场耦合动力学特性研究

建立了一种新型的高速电主轴多场耦合动力学模型,讨论了轴承模型、热态模型、芯轴动力学模型和电机电磁模型之间的耦合关系,提出热膨胀、轴承内圈离心膨胀、轴承内外圈接触膨胀、电磁不平衡拉力载荷和离心力载荷5种耦合因素,并且设计出多场耦合动力学模型的计算流程,分析耦合因素对高速电主轴系统运行状态的影响。以2ZDG60型高速电主轴为研究对象,计算结果表明：考虑耦合因素与不考虑耦合因素相比较,轴承动态支承刚度、轴承损耗功率以及芯轴动力学行为差别较大;实验结果表明：考虑耦合因素时的高速电主轴温升分布和芯轴固有特性与实验结果的吻合度较高。     

基于空气弹簧的振动离心机顺臂隔振技术研究

振动离心机是地震研究和飞行器离心振动复合环境试验研究的重要工具,顺臂振动是其重要的运行工况,而顺臂隔振是振动离心机在该工况下稳定运行的关键。在分析振动离心机顺臂振动工况的基础上,利用空气弹簧的动刚度小而轴向承载力大等特点,设计了一种安装于振动离心机转臂上可测不平衡力的顺臂隔振系统。基于隔振系统的力学模型,通过解析简化获得该系统的力传递率解析方程,并分析了影响该系统隔振能力的主要因素。针对某振动离心机,利用解析方程计算了其隔振系统的力传递率,并通过隔振系统力学模型对其传递力进行了仿真分析,理论计算及仿真所得的力传递率基本一致且均较小。结果表明：以空气弹簧为主体的顺臂隔振系统可有效隔离振动离心机的顺臂振动冲击,力传递率解析方程可用于隔振系统隔振能力评估计算。     

计及套圈变形的电主轴角接触球轴承动刚度分析

针对高速电主轴结构特点,应用弹性力学和滚动轴承动力学理论,建立考虑内圈弯曲变形影响的角接触球轴承动刚度分析模型,探讨不同工况下内圈的径向挠度及其对轴承动刚度的影响,最后在12MD60Y6型号电主轴上进行轴承动刚度测试。理论和实验结果表明,内圈径向挠度和轴承的轴向载荷成正比、与转速成反比,在重载条件下其值不容忽视。考虑内圈径向挠度的轴承动刚度计算结果更接近实验结果。     

高速主轴动力学建模及速度效应分析

考虑高速旋转部件的离心力和陀螺力矩效应,利用Timoshenko梁单元和转盘单元建立主轴转子、转盘、主轴箱等部件有限元模型,并对Jones轴承模型进行扩展建立高速滚动轴承非线性模型。将各子部件模型进行集成,得到整个高速主轴系统的非线性动力学方程,并进行试验验证。分别从转子陀螺力矩、转子离心力和轴承软化这三个角度,系统地研究高速旋转状态下主轴-轴承系统内部的速度效应及其对整个系统动态特性的影响规律。结果表明:当系统存在较大的阻尼比(1%~5%)时,陀螺力矩对系统的直接频率响应函数影响不明显,但是对交叉传递函数的影响显著;随着主轴转速的升高,主轴转子的离心力效应会逐渐削弱主轴系统的刚度,最终使整个高速主轴系统的固有频率降低;必须综合考虑主轴转子的离心力效应和轴承的软化效应,才能比较准确地仿真高速主轴系统的动力学特性。     

Magnetic Bearing Configurations: Theoretical and Experimental Studies

A radial magnetic bearing, consisting of two permanent magnets, is an attractive choice because of its zero wear, negligible friction, and low cost, but it suffers from low load capacity, low radial stiffness, lack of damping, and high axial instability. To enhance the radial load and radial stiffness, and reduce the axial thrust, we have made a theoretical and experimental study of various radial configurations, including hydrodynamic lubrication to improve dynamic performance of the magnetic bearing. We developed an experimental setup to investigate the performance of bearing configurations under different operating conditions. The motion of a rotating shaft is mapped by two displacement sensors with a data acquisition system and personal computer. The first critical speed of each configuration is determined experimentally and verified through frequency analysis. We present a polar plot of displacement data.     

Investigation on Axial Displacement Fault Mechanism Based on Dynamic Characteristic Coefficients Identification of Tilting-Pad Thrust Bearing

To prevent the thrust bearing damage faults, the thrust bearing pad temperature and the static axial displacement variation are usually monitored and cared about, but axial vibration caused by axial dynamic excitation can also result in the severe rubbing. An electric oil pump system with overflow valve is designed on a similar industrial centrifugal compressor test-rig to apply the axial low-frequency excitation from 3 to 7 Hz, and the axial and radial vibration response amplitudes are analyzed. Then, the stiffness and damping coefficients of tilting-pad thrust bearing (TPTB) are identified by instrumental variable filter (IVF) algorithm to reveal the mechanism of TPTB dynamic characteristics affecting axial vibration. Finally, a fault case about surge and the rubbing of thrust bearing is studied. Compared with axial vibration, radial vibration does not directly correlate to axial excitation, and the axial frequency spectrum is an effective method to diagnose axial displacement faults; the static axial load, the dynamic excitation amplitude and the excitation frequency all exert influence on thrust bearing dynamic characteristics and axial vibration response. The research results can guide the design of thrust bearings and help to diagnose the axial displacement faults, while the test device and method can be used to measure the static and dynamic characteristics of thrust bearings.     

考虑刀具磨损影响的CFRP复合材料钻削轴向力预测

在碳纤维增强树脂(CFRP)复合材料钻削过程中,随着刀具磨损量的累积,轴向力会逐渐增加,轴向力过大会导致CFRP复合材料一系列的加工缺陷。为实现在CFRP复合材料钻削过程中随刀具磨损量的累积轴向力变化的有限元分析及预测,建立了CFRP复合材料钻削仿真模型,通过对ABAQUS仿真软件二次开发,利用Python语言开发子程序,将考虑磨损量累积的轴向力预测模型导入仿真软件,运用ABAQUS软件对CFRP复合材料钻削中轴向力进行研究,实现了随着刀具磨损量累积轴向力变化的预测功能。随后通过CFRP复合材料钻削试验,分析了轴向力随钻削孔数的变化规律,以验证轴向力的预测结果。结果表明:3D钻削有限元模型能够良好地预测实际加工过程中刀具未磨损时轴向力的大小,其误差为9.10%;在考虑磨损量累积后,轴向力预测模型能够较准确地预测实际加工过程轴向力的大小,其最大误差不超过10%。      

Mechanical effects in a vortex device with a rotating core

The process of the appearance of forced rotation of an axial core mounted in a modified vortex tube in the direction opposite to the rotation of the air vortex and the precession of its axis have been studied. It has been established that dynamical bending of a metal axial core arises in the process of rotation which causes mechanical wear of its end part and fracture in the fastening area of the bearing without residual curvature of the core axis. The excitation of rotation and observed force effects are not related to the mechanical action of rotating air flow on the axial core.     

硬质合金台阶钻结构参数及钻削工艺参数对CFRP开孔性能的影响

基于VMC850B立式加工中心和UltraPAC超声C-扫描仪,搭建了碳纤维增强树脂基复合材料(CFRP)钻削试验平台,探讨了台阶钻结构参数及钻削工艺参数对CFRP钻削过程中的钻削轴向力和分层因子的影响。结果表明,钻削工艺参数对第一段钻削轴向力影响较大,台阶钻结构参数对第二段钻削轴向力的影响较大;分层因子的大小与第一段钻削轴向力和第二段钻削轴向力有关,当第一段和第二段直径比d/D0.5时,分层因子主要与第一段钻削轴向力有关;减小分层的优水平组合为第一段直径2.8mm,第二段锋角95°,主轴转速7000r/min,进给速度2.5mm/s。     

Ferrohydrodynamic thrust bearings

This paper treats thrust bearings in which the lubricant is a ferroliquid confined by an applied magnetic field to the gap between two plates, one fixed and one mounted on a rotating shaft carrying an axial load. For plates with plane, parallel surfaces, the lubricant extends beyond the edges of the plates and axially along their sides. Since this is undesirable, other plate geometries are considered, for which the ferroliquid is confined to the gap between the plates. Plate surfaces which are considered are cones, paraboloids and frustrums, i.e. plane, parallel surfaces out to some radius and conical, diverging surfaces beyond. Results indicate that paraboloids and frustrums are suitable, but cones are not. FHD thrust bearings with magnetic plates are stiff, i.e. large changes in axial load produce relatively small changes in gap width. With currently available ferroliquids, FHD thrust bearings are limited to relatively small axial loads.     

计电磁不平衡拉力的高速电主轴转子偏心特性研究

针对高速电主轴转子偏心状态产生的两种载荷-电磁不平衡拉力与离心力,据电磁理论建立电磁不平衡拉力载荷模型,理论分析两种偏心载荷幅值及频率特性;应用Timoshenko梁理论,建立耦合入轴承动态支撑刚度矩阵并以两种偏心载荷为外力的转子有限元模型;据动力学方程计算转子系统固有频率、振型,研究电磁不平衡拉力载荷与离心力载荷对转子系统动态特性影响;通过实验验证两种偏心载荷为引起高速电主轴转子振动的主要因素及转子系统一阶固有频率随转速升高而升高,实验结果与理论计算误差较小。     

风电齿轮箱高速轴圆锥滚子轴承动态特性分析

齿轮箱是风电机组故障率最高的部件之一,其中高达50%的故障停机源于高速轴轴承的过早失效。外部变风载激励和齿轮箱内部激励下,高速轴轴承动载增大,将加速高速轴轴承破坏失效。论文以某750kW风电齿轮箱高速轴圆锥滚子轴承为分析对象,采用ADAMS软件建立圆锥滚子轴承的多体动力学仿真分析模型,研究轴向载荷和径向载荷变化对轴承动态响应特性的影响,基于美国Spectra Quest转子实验台开展了圆锥滚子轴承振动响应特性实验,掌握了圆锥滚子轴承的动态接触力与振动响应变化规律,将为风电齿轮箱高速轴圆锥滚子轴承选型与齿轮箱设计提供理论依据。     

Centrifugal inertia effects in high-speed hydrostatic air thrust bearings

A modified Reynolds equation for compressible flow is used to model the dynamics of pressurised air bearings in a simplified axisymmetric geometry. The formulation incorporates the effect of centrifugal inertia for high-speed operation. A steady-state analysis is presented with a fixed rotor–stator clearance. The load-carrying capacity of the bearing is assessed for both inward and outward pressurisation and the air-flow characteristics are seen to depend on the level and direction of pressurisation. A critical shaft speed is identified that maintains no-net flow by balancing inertia and pressurisation effects. The nonlinear air–rotor–stator dynamics are investigated by modelling the axial stator position using a spring–mass–damper system coupled to the air-film dynamics. Solutions are presented to illustrate the effect of various frequencies and amplitudes of forcing for a range of rotation speeds. The time-averaged axial force and mass flow of air are used as characteristic measures of bearing performance, and further numerical results are presented as part of a parameter space analysis. Using the method of arc-length continuation key measures of the numerical solutions are tracked for changing values of the physical parameters. The minimum rotor–stator clearance is used to evaluate the limit of stable periodic operation without resonant stator dynamics and incorporating high operating speeds.     

Vibration analysis of rotating cantilever plates

A finite element technique is used to determine the natural frequencies and the mode shapes of a cantilever plate mounted on the periphery of a rotating disc. The plane of the plate is assumed to make any arbitrary angle with the plane of rotation of the disc. The distributed centrifugal force is resolved into two components—one acting in the plane of the plate and the other normal to the plate. The stresses produced in the middle surface of the plate due to the in-plane forces are first determined. The increase in the bending stiffness of the plate elements due to these in-plane stresses is obtained in a manner similar to that used in the stability analysis of plates. The component of the distributed centrifugal force normal to the plate surface is added to the inertia force. From the results of computations carried out for various values of the aspect ratio, the speed of rotation, the disc radius and the setting angle, empirical formulae are derived giving the effect of these parameters on the natural frequencies. These empirical formulae are observed to be in agreement with the corresponding known formulae for rotating cantilever beams, when the aspect ratio is high.     

Machinability analysis in drilling woven GFR/epoxy composites: Part I – Effect of machining parameters

The present paper deals with the effect of machining parameters (feed, speed and drill diameter) on the thrust force and machinability of woven glass fiber-reinforced epoxy (GFRE) composites. The selected machinability parameters were delamination size, surface roughness, and bearing strength. The results show that, delamination-free in drilling GFRE composites was not observed, in the range of the investigated cutting parameters. Surface roughness instrument can be used as an indication for the position of the internal delamination damage in drilling GFRE composites. The high values of correlation coefficients between thrust force and the machinability parameters confirm the importance of reducing the thrust force to improve the load carrying capacity of composite structure assembled by rivets or bolted joints.     

Manufacture of one-piece automotive drive shafts with aluminum and composite materials

The natural bending frequency of a torque transmission shaft can be increased without reducing the torque transmission capability if the shaft is made using both carbon fiber composite and aluminum: the former increases the natural bending frequency and the latter sustains the applied torque. The high natural bending frequency of a shaft makes it possible to manufacture the drive shaft of passenger cars in one piece.

In this work, a hybrid one-piece drive shaft composed of carbon fiberepoxy composite and aluminum tube was manufactured by co-curing the carbon fiber on the aluminum tube.

The fabricational thermal residual stresses due to the coefficient difference of thermal expansions of aluminum and carbon fiber composite were eliminated by applying a compressive preload to the aluminum tube before the co-curing operation.

From the dynamic tests, it was found that the first natural bending frequency and the minimum static torque transmission capability of the hybrid shaft were 9000 rpm and 3550 Nm, respectively, and the shaft did not fail until 10⁷ cycles under a dynamic load of ± 500 Nm.     

The stability behavior of rotating composite shafts under axial compressive loads

This paper studies the stability behavior of a rotating composite shaft subjected to axial compressive loads using finite element method. The laminated composite shaft is modeled as a Timoshenko shaft by applying the equivalent modulus beam theory. Numerical results correlate well with the reported beam models. The critical speed of the thin-walled composite shaft is dependent on the stacking sequency, the length-radius ratio (L/R) and the boundary conditions. In addition, the effects of the rotational speeds and the disk location on the rotating shafts' stability are examined as well. The critical load of the rotating thin-walled composite shaft can be nearly assessed from the conventional buckling formulation.