油气润滑条件下电主轴轴承腔内多相流特性分析

基于油气润滑气液两相流理论,采用COMSOL Multiphysics仿真软件建立B7003CY/P4角接触球轴承腔内的油气两相流模型,分析轴承腔内气相流速、压力以及润滑油的分布。通过计算轴承的摩擦生热量以及腔内关键点的换热系数,分析轴承腔内温度场的分布。试验与仿真结果表明:润滑油沿着进油管道进入轴承腔内,大量的润滑油聚集在轴承腔内的前端,少许润滑油会随着空气进入轴承腔内,而进气速度影响润滑油的分布;轴承腔内的温度受电主轴的转速和进气压力影响,随着电主轴转速提高,摩擦产生的热量增多,轴承腔内的温度升高;进气压力越大,空气流速越大,轴承腔内的温度越低,且轴承腔内换热系数细化后得出的温度场更接近真实值。     

高速电主轴用球轴承油气润滑温度场仿真与实验研究

基于局部热源计算轴承内部生热,考虑不同转速计算油气润滑下轴承滚道表面对流换热系数,采用Mixture多相流模型结合RNG k-ε湍流模型和Fluent软件动网格技术,建立球轴承两相流场模型,求解得到电主轴球轴承油气润滑温度场,分析轴承内部温度分布,给出最佳供油量的确定方法。对某高速电主轴用球轴承进行了油气润滑两相计算,结果表明:随着转速增大,轴承总摩擦生热率急剧增大,且转速越大,增长幅度越大;给定工况存在最佳供油量,且最佳供油量随转速增大而增大。最后通过电主轴轴承实验证明了该模型对油气润滑模拟的可靠性。     

Thermo-mechanical model of spindles

This paper presents a Finite-Element-method-based thermo-mechanical model of spindles with rolling bearings. The heat generated in the bearings and the motor is transferred to the ambient air, the motor coolant and the spindle structure, and causes thermal expansion of spindle parts. The experimentally validated thermo-mechanical spindle model predicts temperature distribution and thermal growth, as well as bearing stiffness and contact loads, under specified operating conditions. Transient changes in temperatures, deformations, viscosity of the lubricant, and bearing stiffness are considered in the solution. The predicted bearing properties are used to estimate the changes in the dynamic behavior of spindles.     

Thermal characteristics of the spindle bearing system with a gear located on the bearing span

High cutting speeds and feeds are essential requirements of a machine tool structure to accomplish its basic function which is to produce a workpiece of the required geometric form with an acceptable surface finish at as high a rate of production as is economically possible. Since bearings in high speed spindle units are the main heat source of total cutting system, in this work, the thermal characteristics of the spindle bearing system with a tilting axis were investigated using finite element method to improve the performance of the spindle bearing system. Based on the numerical results, a specially designed prototype spindle bearing system was manufactured. Using the manufactured spindle bearing system, the thermal characteristics were measured and compared to the numerical results. From the comparison of the numerical results with the experimental results, it was found that the finite element method predicted well the thermal characteristics of the spindle bearing system.     

An improved thermal model for machine tool bearings

Thermal model for machine tool spindle is of great importance to machine tool design. Traditionally, the thermal contact resistance between solid joints and the change of the heat generation power with the bearing temperature are often ignored when thermal characteristics of a machine tool spindle are analyzed. This has caused inaccuracies in the thermal model. With the heat source models and the heat transfer models from Bossmanns and Tu [Journal of Manufacturing Science and Engineering 123 (2001) 495–501, International Journal of Machine Tools & Manufacture 39 (1995) 1345–1366], a model including the thermal contact resistance at solid joints based on a fractal model and the change of the heat generation power, viz. the amount of the heat generation per second, with the bearing temperature increases is developed. The complete thermal model is used to simulate the temperature distribution in grinding machine housing with a conventional spindle bearing. Compared with experiment, it is shown that the completed model is much more accurate than the traditional model which ignores the two important factors above. The thermal expansion of the housing system is analyzed.     

Simulation of thermal behavior of a CNC machine tool spindle

The thermal deformations of a CNC machine tool spindle are the major contributor of thermal error. It is very significant both theoretically and practically to study how to accurately simulate the thermal error of the spindle. Firstly, this paper proposes a method for computing the coefficient of convection heat transfer of the spindle surface by referencing the theory on computing the coefficient of convection heat transfer of a flat plate when air flows along it. Secondly, the temperature field and thermal errors of the spindle are dynamically simulated under the actions of thermal loads using the finite element method. Thirdly, the characteristics of heat flow and thermal deformation within the spindle are analyzed according to the simulation results. Fourthly, the selection principle of thermal key points, which are indispensable for building a robust thermal error model, is provided based on the thermal error sensitivity technology. At last, a verification experiment is implemented on a CNC turning center, and the results show the simulation results are satisfying to replace the experiment results for further studies.     

大型空冷发电机转子的锻热工艺分析

对空冷转子的锻造、热处理工艺进行了分析,并制定出合理的工艺方案。选用短粗锭,并采用两次高温加一次回火工艺实现了该类产品的批量化生产。     

Microstructure characterization and charpy toughness of P91 weldment for as-welded,post-weld heat treatment and normalizing & tempering heat treatment

The effect of weld groove design and heat treatment on microstructure evolution and Charpy toughness of P91 pipe weldments was studied. The P91 pipe weldments were subjected to subcritical post weld heat treatment (760 °C-2 h) and normalizing/tempering conditions (normalized-1040 °C/40 min, air cooled; tempered 760 °C/2 h, air cooled) were employed. The influence of subsequent PWHT and N&T treatment on the microstructure of various zone of P91 pipe weldments were also investigated. The present investigation also described the effect of PWHT and N&T treatment on hardness, grain size, precipitate size, inter-particle spacing and fraction area of precipitates present in each zone of P91 pipe weldments. The result indicated great impact of heat treatment on the Charpy toughness and microstructure evolution of P91 weldments. The N&T treatment was found to be more effective heat treatment compared to subsequent PWHT. Charpy toughness value was found to be higher for narrow-groove design as compared to conventional V-groove design.     

小模数滚齿机用电主轴的设计与研究

小模数数控滚齿机去掉了传动用的齿轮副、蜗轮蜗杆副等传动元件,刀具轴和工件轴直接与电机轴相联。几何误差和热误差是小模数滚齿机的主要误差来源,为此,设计了一种新型的电主轴。该电主轴采用了主轴电机置于主轴后轴承之后的形式,缩小了主轴轴承位置的径向尺寸,使轴承摩擦产生的热量的散发,减少了电机发热对轴承变形产生的影响;主轴轴承采用了静压轴承的形式,提高了主轴轴承的耐磨性和回转精度。该电主轴的设计能够提高小模数滚齿机的生产效率和加工精度。     

Evaluation of an internally spring preloaded four contact-points bearing for spindle units

In this paper, the concept of an internally spring preloaded four contact-points bearing for the use in high precision and high speed applications is investigated. It is designed as a compact self-contained fixed bearing unit that is free of play, easy to mount and resistant against temperature differences between the inner and outer ring. The concept of the bearing, its functionality and properties are introduced and the results of an experimental analysis of a first prototype are presented. The prototype bearing, which is based on a hybrid 7014 spindle bearing with an additional spring preload unit, was manufactured by hard turning. Its properties are compared to those of similar two and three contact-points spindle bearings. Typical requirements in modern high precision applications, e.g. machine tool spindle units, and limiting characteristics of bearings, such as displacement, stiffness, friction torque and operating temperature, are considered. Finally, the potential of the new bearing concept is discussed.     

空气静压主轴有限元建模及动态特性研究

为提高空气静压轴承支撑的空气静压主轴的动态工作性能,文章利用Fluent计算出了空气静压轴承在不同供气压力下气膜刚度,利用Ansys Workbench中的轴承单元和弹簧—阻尼单元模拟轴承支承,对主轴系统进行了模态分析和动态响应分析,得到不同供气压力下主轴系统的固有频率、振型以及激振力作用下的位移幅频动态响应曲线。结果表明,随着供气压力的增加,轴承气膜刚度增加,且对主轴系统的低阶模态和高阶模态影响不同。另外随着气膜刚度增加,谐振频率逐渐增大、振幅减小,系统抵抗受迫振动能力逐渐增强。研究结果为提高空气静压主轴的动态性能提供了一定的理论依据。     

扁平沟槽烧结吸液芯热管的设计与制造

随着电子芯片热流密度的急剧增加及有效散热空间的日益狭小,具有高热导率、高可靠性、快热响应、无需额外动力等特点的扁平热管已成为电子领域使用的理想导热元件。提出了沟槽烧结吸液芯扁平热管的加热相变压扁制造方法;理论分析了加热相变压扁制造过程中热管几何形状变化和热管弹塑性大变形的成形过程,并进行了实验测试。结果发现：相变压扁过程作用机制为热管内部的饱和蒸汽压方程;相变压扁过程中,热管几何形状变化很大,最大等效塑性应变主要发生在扁平段吸液芯/蒸汽界面上;当压扁温度为480 K时,压扁热管的屈曲率微小,可忽略不计;相变压扁力随着压扁温度的升高和压扁位移的增大而增大。     

主动磁悬浮电主轴系统建模与控制参数分析

为实现磁悬浮电主轴的稳定悬浮运行并满足加工精度要求,通过对某型号主动磁悬浮电主轴的结构和控制原理进行研究,在忽略主轴转子磁化和磁漏等非线性因素影响的前提条件下,通过对主轴转子在磁悬浮轴承中的受力分析,建立了磁悬浮轴承的电磁支承力与轴承气隙偏移量及控制电流的表达式,对基于不完全微分PID控制的磁悬浮电主轴系统的临界转速与磁悬浮轴承的电磁刚度进行了定量研究,得到不同PID控制参数下,磁悬浮轴承支承刚度随涡动频率的变化曲线及固有频率随PID控制参数的变化曲线图。研究结果为磁悬浮电主轴控制系统进一步设计使用和分析优化提供了依据。     

采用导波杆方式超声检测高高压管道壁厚的方法

为了测量高温高压的管道壁厚,将与管道材料相同的导波杆以全焊透的形式垂直地焊接在管道的监测部位。导波杆端部采用风冷或水冷,使端部温度降低,直到可以使用常规的超声波探头及耦合剂进行测厚。讨论了测厚系统温度与声速的关系及测量数据的修正方法,以不锈钢材料为例;对焊接导波杆的圆平板、直管及弯管试件进行了测量和修正,测量结果与壁厚实际值能较好地吻合。     

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.     

主轴传动部件的热平衡技术研究与应用

分析主轴箱的主要热源以及发热量对整个主轴箱部组精度的影响,采用大流量的恒温油对主轴箱进行冷却与润滑以及优化主轴轴承安装工艺,以保证主轴高速运行的过程中其轴向变形量达到最小。通过试验验证,主轴达到热平衡时其伸长量为0.035 mm。通过对温升与热伸长量的函数进行研究,对轴向热变形进行补偿,以保证机机床在达到热平衡过程中,对工件加工精度的影响最小。     

热管砂轮干磨削温度场数值模拟

基于一种利用热管技术对磨削弧区进行强化换热的构想,采用FLUENT软件建立了环形热管砂轮干磨削温度场的仿真模型,得到了热管换热能力与热流密度、转速和砂轮壁厚的关系,并在相同热流密度下对比了热管砂轮与热管砂轮弧区的温度。仿真结果表明:弧区温度会随着热流密度的增大相应升高,随着转速的增大而降低,热管的启动时间会随着砂轮壁厚的增大减慢;相同热流密度下,热管砂轮的弧区温度明显低于无热管砂轮。最后通过干磨削钛合金TC4试验,对仿真结果进行了验证。     

管内空气流动对大口径厚壁P92管道局部焊后热处理温度场的影响

使用Ansys CFX软件建立了P92管道与管内空气的共轭传热模型，并进行了试验验证.使用该模型计算了不同管内空气流速时，局部焊后热处理的温度场分布.结果表明，管内空气流动对恒温后管道外壁温度影响较小，但会显著降低内壁温度，并增加内、外壁的轴向温度梯度.随着管内空气流速的增加，焊缝中心内外壁温差和轴向温度梯度近似线性增加，空气流速每增加1 m/s，内外壁温差将增大约5.0℃，内、外壁轴向温度梯度分别增加约0.03和0.02.对热处理温度要求很高的P92管道，局部焊后热处理时应限制管道内空气流动，或在选取热处理参数时考虑空气流速的影响.     

两种不同材料的电主轴磁-热耦合有限元仿真分析

电主轴热态稳定性影响电主轴整体工作性能,作为电主轴主要热源的内置电机对电主轴热态性能的影响是设计过程中优先考虑的问题之一。电主轴生热小,散热快是保证其优良热态性能的前提。基于电主轴电磁损耗生热机制和电主轴传热散热机制,建立电主轴有限元模型。提出一种电主轴磁-热耦合分析方法,分析电主轴额定转速下内置电机的磁场和温度场,监测电主轴内置电机各部分温度场以及瞬态温度。以170SD30陶瓷电主轴与金属电主轴作为分析对象,分析了采用新型陶瓷主轴材料对改善电主轴内置电机温度场分布的影响。结果表明:陶瓷电主轴电磁损耗小于金属电主轴电磁损耗,在电机损耗热的影响下,陶瓷电主轴温度低于金属电主轴温度。     

锂离子动力电池包液冷散热分析与优化

为满足动力电池的最佳工作性能要求,保障电池系统的安全运行,大部分电池系统都需要进行有效的热管理设计。利用CFD仿真技术分析自然散热、单层水冷板散热、双层水冷板散热3种整包模组散热方式;研究了双层水冷板散热时进口水流量大小对整包散热效果的影响。结果表明:双层水冷散热的温升及温差相对较小,散热效果较为明显;当水流量小于5 L/min时,随水流量的增大,模组的整体温度下降较为明显;当水流量大于5 L/min时,模组整体温度下降较慢,散热效果不明显。