A speed-dependent variable preload system for high speed spindles

High speed machine tools are required to operate in a wide range of spindle rotational speeds with high stiffness and high accuracy. The stiffness of the spindle is largely dependent on the axial preload of the angular contact bearings. A large preload is required at lower range of speeds to provide sufficient stiffness for vibration-free heavy cutting. However, at higher speeds, it results in rapid temperature rise and reduces the life of the bearing. For optimum performance, it is essential that the bearing preload is reduced as the rotational speed increases. In this paper, an automatic variable preload system is proposed that changes the preload on the bearings as a function of rotational speed. This system is based on the use of centrifugal forces and requires little space inside the spindle. The performance of this mechanical system is determined using finite element modeling. A prototype of the system is fabricated and its performance is investigated using a specially devised test stand for direct measurement of the preload. The effectiveness of the proposed system in reducing the preload at higher speeds is demonstrated.     

高速主轴轴承系统热机耦合动力学的研究

从轴承热动态特性,以及主轴-轴承系统的热动力学动态特性等角度,综述相关理论的研究进展以及影响电主轴工作性能的若干关键因素.     

高速加工的切削动力学

高速加工（HSM）的有效应用，需要了解工艺系统的动态特性，本文介绍了HSM的颤振，这将有助于用户来选择最佳的主轴速度。[编者按]     

A general method of kineto-elastodynamic design of high speed mechanisms

Kineto-elastodynamics is the kinematic and dynamic study of mechanisms including the effects of elastic deformation and mass distribution of the links. A new method of kineto-elastodynamic design is developed and illustrated with examples. With this method mechanisms with elastic links can be designed in a systematic way for a desired performance at high speeds. This is achieved by first performing the kinematic synthesis of the mechanism considering its links to be rigid and then proportioning the areas of cross-section of the links optimally to account for the kineto-elastodynamic effects.

In optimization of the design, the objective function to be minimized is taken to be the mass of the mechanism and constraints are imposed on deflections and stresses. The optimization problem is formulated in terms of stepwise linear programming. Using the simplex method, a design with minimum mass is obtained subject to linearized constraints on deflections and stresses. The design is used as an initial design for the next iteration, thus leading to an optimum design in a finite number of steps. Move limits in the form of side constraints are introduced to reduce the error incurred due to linearization of the constraint equations.     

Engine wear and used oil analysis—A comparative study in high speed diesel engines

The operational life and reliability of I.C. engines are limited to a certain extent by the break down of the engine components due to wear. It is advantageous to know the condition of an engine and its components without disassembling for detailed measurements. This paper describes the possibility of employing chemical analysis of the used crank case oil to predict the wear of engine components. It is concluded that the acidity and carbon contents of the crank case oil play a significant role in assessing the wear of copper-lead bearings used for the big end of the connecting rod.     

A comparative study of conventional and high speed grinding characteristics of a thin film multilayer structure

High speed and conventional speed grinding characteristics of a thin film multilayer solar panel were investigated. The grinding force and surface roughness were measured and the interface integrity of the ground workpieces was examined. The results indicated that when applying a high wheel speed of up to 120 m/s, the ground surfaces predominantly exhibited ductile flow and the interface integrity was significantly improved. The maximum undeformed chip thickness was found to be an important parameter to measure grinding performance and interfacial failure. Delamination was observed at interfaces when the maximum undeformed chip thickness exceeded a threshold value and the finite element method (FEM) analysis revealed that the interfacial failure was mainly induced by shear stress.     

高速精密平面定位机构的设计与应用

面向先进电子封装等领域对高速精密定位机构的需求，结合两种新型平面定位机构，对直接驱动并联机构的运动弹性动力学建模与仿真、基于扰动观测器的控制策略进行了研究。     

高速齿轮齿部修形技术研究

分析了高速齿轮传动的特点和齿部修形原因,进一步研究了直,斜齿高速齿轮齿部（齿形与齿向）修形的设计原则与计算修形量的经验公式。经生产实践验证,齿部修形有利于解决高速齿轮传动的振动和噪声问题,研究结论具有普遍的指导意义。     

A comparative study of the wear behaviour of sintered and laser surface melted AISI M42 high speed steel diluted with iron

Powders of AISI M42 high-speed steel (HSS) were blended with different proportions of water-atomised iron powders. The powders were subsequently submitted to uniaxial pressing and then divided in three lots. The first was submitted to sintering, the second was submitted to sintering plus laser surface melting (LSM) and the third was submitted to sintering plus LSM plus double tempering at the secondary hardening peak temperature of M42 HSS. The objective of this procedure was to evaluate the processing route that leads to reduced porosity in AISI M42 HSS and to higher abrasive wear resistance. Therefore the samples, with different chemical compositions and microstructures, were submitted to a detailed microstructural characterisation followed by microscale hardness and abrasive wear tests. It was observed that LSM leads to almost complete elimination of residual porosity and to the dissolution of large brittle carbides that are present in the as-sintered samples, leading to a homogeneous and extremely fine microstructure. This microstructure is formed of saturated plate martensite and a small proportion of retained austenite. The double tempering treatment, carried out in the laser surface melted samples samples, leads to the elimination of retained austenite and to a decrease of the lattice parameters of martensite due to the precipitation of thin carbides within martensite. As a result, while the hardness of the material in the sintered condition is between 245 and 625 HV (depending on the proportion of dilution with iron), after LSM the hardness is higher than 820 HV in all the samples. Surprisingly, the abrasive wear resistance of the laser melted and of the laser melted and tempered samples is lower than that of the as-sintered ones. Observation of the wear craters by scanning electron microscopy shows that this result is due to the different wear mechanisms acting on the samples processed by different routes.     

A study on the measurement of contact force of pantograph on high speed train

Appropriate contact force is required for the pantograph on the high speed train to collect current from the catenery system without separation. However, at high speed, large aerodynamic lifting force is generated by the contact plate and the body of pantograph, which may cause wear of the contact wire. In this study, to confirm the interface performance of the pantograph on Korea High Speed Train, a method to measure the contact force of the pantograph was proposed and the related measuring system was developed. The forces acting on the pantograph were clarified and a practical procedure to estimate the forces was proposed. A special device was invented and applied to measure the aerodynamic lifting force. Measured contact forces were displayed by the developed system and evaluated based on the criteria.     

高速止推轴承结构的研究

润滑剂的惯性离心力影响高速止推轴承的承载能力,根据修正雷诺数Ｒ＾＊ｅ的大小可这种影响。本文提出了两种结构改进措施,以克服惯性离心力 朱良影响,并指出在高速轻载条件下可采用浮环式止推轴承。     

On the breakup mechanisms of air-assisted drops in a high speed air

An experimental study was performed to investigate break-up mechanisms of liquid drops injected into a transverse high velocity air jet. The range of conditions included the three drop breakup regimes previously referred to as bag, shear or boundary layer stripping, and ‘catastrophic’ breakup regimes. The results show that the break-up mechanism consists of a series of processes in which dynamic pressure effects deform the drop into a thin liquid sheet. The flattened drop subsequently breaks up into small droplets. At high relative velocity, in the ‘catastrophic’ breakup regime, drops are flattened and fragmented by relatively large wavelength waves whose wavelengths and growth rates are consistent with estimates from Rayleigh-Taylor instability theory. The minute drops that are also produced at this high relative velocity appear to originate from short wave length of Kelvin-Helmholtz waves growing on the larger liquid fragments.     

A study on fluctuating pressure load on high speed train passing through tunnels

The carbody structure of a high speed train passing through a tunnel is subjected to pressure fluctuation. Fatigue strength of the carbody structure against the fluctuating pressure loading should be proved in the design stage for safety. In this study, to get the useful information on the pressure fluctuation in the tunnel, measurement has been conducted during test running of KHST on the high speed line for two years. The measured results were analyzed and arranged to be used for carbody design. A prediction method for the magnitude and frequency of pressure change was proposed and the propagating characteristics of pressure wave was investigated. By statistical analysis for the measured results, a pressure loading spectrum for the high speed train was given. The proposed method can also be used to estimate the pressure loading spectrum for new high speed line at design stage combined with the results of train performance simulation.     

A molecular dynamics study on atomistic mechanisms of nano-scale cutting process of sapphire

Journal of Mechanical Science and Technology - Sapphire is a promising material for various optical, electronic, and mechanical applications, but is very difficult to machine due to its high...     

基于不同井道模型的超高速电梯气动特性研究

针对超高速电梯气动特性研究问题,对比研究了电梯运行10 m/s时二维井道模型、三维井道模型及带层门地坎的三维井道模型。利用ANSYS有限元软件对各模型下的井道气动特性进行了分析,研究得到了各井道模型中不同截面上的气流分布情况,并进行了比较研究;建立了井道对称截面上各直线位置处气流的速度特性曲线,对井道前后侧速度大小进行了研究;建立了对称截面各直线上气流最大值,并进行了比较分析;在两种不同的三维井道模型中,针对层门地坎对轿厢的气动力影响大小进行了分析。研究结果表明,二维井道模型中整体井道流速大,最大流速相比增大近25%,且无法捕捉井道左右侧气流影响;三维井道模型中,层门地坎导致井道后侧流速增大,井道前侧流速减少,同时增加轿厢上下气动阻力93.2%及轿厢前后倾覆力566.7%。     

挤压铸造高速钢轧辊的研制和应用

挤压铸造的压力、保压时间和压下速度是影响高速钢轧辊缩孔的重要因素。采用浇注温度 14 0 0 14 5 0℃、压力15 0MPa、保压时间 12 0 15 0s ,压下速度 14 16mm/s ,可获得组织致密、无偏析、加工量少的高速钢轧辊。     

高速铣削中控制残留高度的实验研究

针对球头铣刀高速铣削表面残留高度的数学模型,提出了减小残留高度控制表面粗糙度的主要途径,通过实验研究获得了行间距、进给速度、切削速度对高速铣削铝合金表面粗糙度的影响规律,对优化切削参数,改善零件表面质量具有重要意义.     

Effect of different heat treatments on the wear of high speed steel cutting tools

High speed steel tool tips were given different heat treatments to vary the microstructure, and the nature of the wear produced in turning tests was examined under the scanning electron microscope. Wear was mainly confined to either the rake face or clearance face, the form of wear being dependent on the particular heat treatment of the tool steel. The forms and mechanisms of tool wear are discussed in terms of the changes in microstructure produced by the different heat treatments.