超精密定位工作台静压导轨静态特性及流场仿真分析

研究超精密液体静压定位工作台中的液体静压导轨静态特性问题。根据流体润滑理论及雷诺方程,构建了导轨油膜压力的数学物理模型,运用有限元方法求解静压导轨的各项静态特性参数,如导轨的承载能力、静刚度、流量等。运用三维造型软件Solid Works和CFD软件FLUENT,从结构三维造型设计和内部三维流动综合分析液体静压导轨,获得油膜压力的分布云图、曲线和油腔液压油流速分布云图,并分析不同结构设计参数和环境参数对液体静压导轨静态特性的影响。本文研究将对实际的静压导轨系统设计具有指导意义。     

Investigation of accuracy of aerostatic guideways

Aerostatic guideways are often used in machines requiring very high motion accuracy such as coordinate measuring machines. Currently, positioning error analysis for such machines focuses on the relationship between volumetric errors on one hand and axes’ motion errors and axes’ relative location errors on the other. The internal mechanisms causing motion errors are rarely considered. In order to gain a deeper understanding of aerostatic guideways, this paper investigates the relationship between the motion errors of the axis’ carriage and the guideways’ geometric errors both mathematically and experimentally. The analytical model uses bearings location and stiffness, guideway geometry and static equilibrium to produce a model in matrix form. Validation experiments are conducted on a machine axis moving on aerostatic guideways with and without preload.     

大型车铣磨复合机床静压转台油膜热特性分析及其优化研究

以重型立式磨床静压工作台为研究对象,通过ANSYS Workbench建立油膜-转台这一流固耦合模型,探讨在不同黏度、转速以及入口流量条件下的油膜热特性规律。分析结果表明:封油边出口温升随油液温度降低而逐渐增大;低转速时封油边右侧处有最高温升;在转速为20 r/min时,缝隙处油膜的温度随着流量的增大而增大的,随着入口流量增大油腔压力也逐渐增大。最后再对油垫结构参数进行优化,得出封油边宽度增加会产生更高的油膜温升。研究结果为进一步分析大型车铣磨复合机床运行过程中的热误差控制及结构设计优化提供了参考。     

XK2125床身工作台导轨副采用恒流供油式静压导轨的探讨

介绍了XK2125数控龙门镗铣床床身工作台导轨副的特点;阐述了定压供油式与恒流供油式静压导轨工作原理,对它们进行了对比分析,给出了选择方法;并对数控龙门镗铣床床身工作台导轨副采用开式或闭式静压导轨的理由分别进行了论述。     

基于Fluent的液压密封流体膜压力精确化研究

针对液压密封,密封区域流体膜压力不等于密封压力而导致对油液泄漏量研究有误差和对密封圈密封性能的研究因素考虑不足的情况,从密封圈的密封机制出发研究流体膜压力。基于Fluent中的层流模型Laminar,建立密封圈受到油液压力时的流体膜模型,对密封圈在静密封和动密封2种密封形式下进行有限元分析,得出密封区域的精确压力分布。对比分析了泄漏量的理论计算结果以及用流体膜压力代替密封压力后的修正数值计算结果。结果表明:用流体膜压力代替密封压力计算得到的泄漏量更加准确,误差更小;流体膜压力受密封压力和活塞杆运动速度影响,泄漏量与密封件所受密封压力、活塞杆运动速度成正比,活塞杆运动速度对流体膜压力和泄漏量的影响更大。流体膜精确压力的获得为密封圈密封性能的研究提供了参考,为获得其准确的密封机制奠定了一定基础。     

机床导轨表面淬火处理技术

研究了淬火工艺参数，特别是淬火移动速度对导轨表面硬度、淬火层深度、变形量以及产生裂纹的倾向的影响，以及铸件的化学成分对表面硬度、淬硬层深度的影响。通过对床身加压处理，使机床导轨在精刨后凸起，减小淬火后导轨的变形量，可以保证导轨磨削处理后，仍有有效的硬化层深度。同时，介绍了导轨表面缺陷的各种修补方法以及优缺点。     

导轨速度对静压导轨承载性能的影响

竖直液体静压导轨是纳米数控精密加工机床关键装备,机床静压导轨的运动速度不仅对零件加工精度有影响,也对导轨油膜承载性能有影响。因此确定机床导轨最佳工作速度就十分有必要。以纳米曲面磨床静压导轨油膜为例,通过Fluent流体仿真,对导轨运动速度与油膜最高压力、最低压力、油膜承载力定量的研究得到:在相对静止状态下,油腔压力场呈对称分布;导轨的运动速度增加,会产生油膜承载的不平衡性;验证了油膜负压对导轨承载性能影响很小,可以忽略;提出了纳米数控磨床的最佳静压导轨运动速度范围为0~0.1 m/s及0.3~0.5 m/s;在该工作速度范围内导轨的承载性能较好。研究结果为精密机床闭式静压导轨的工作参数选定提供了一定的依据。     

Single setup estimation of a five-axis machine tool eight link errors by programmed end point constraint and on the fly measurement with Capball sensor

Five-axis machine tools can be programmed to keep a constant nominal tool end point position while exercising all five axes simultaneously. This kinematic capability allows the use of a 3D proximity sensing head mounted at the spindle to track the position changes of a precision steel ball mounted on the machine table effectively measuring the 3D Cartesian volumetric errors of the machine. The new sensing head uses capacitive sensors to gather data on the fly during a synchronized five-axis motion which lasts less than 2 min. Because the measured volumetric errors are strongly affected by the link geometric errors, they can be used to estimate the link errors through an iterative procedure based on an identification Jacobian matrix. The paper presents the new sensor, the identification model and the experimental validation. The approach allows all eight link errors i.e. the three squarenesses of linear axes and the four orientations and center lines offset of the rotary axes to be estimated with the proposed single setup test. The estimation approach is performed on a horizontal five-axis machine tool. Then, using the estimated link errors, the volumetric errors are predicted for axes combinations different from those used for the identification process. The estimated machine model correctly predicts 52–84% of the volumetric errors for the tested trajectories.     

气压自动卸荷导轨的导轨面特性分析

通过试验对可能影响气压自动卸荷导轨性能的因素进行分析，从而得出：这种导轨具有很高的接触静刚度；进给速度和支撑导轨的几何精度对这种导轨的导轨面间的摩擦力不会产生影响。     

正弦微沟槽织构对柱塞密封副摩擦学性能的影响

目的 研究不同工况下正弦沟槽织构对柱塞密封副摩擦性能的影响,以降低压裂泵柱塞密封副的摩擦磨损.方法 基于压裂泵柱塞密封副几何模型和流体润滑理论,建立了正弦微沟槽织构化柱塞-橡胶密封副动压润滑数值理论模型,通过仿真模拟研究了不同柱塞密封压力、运动速度对正弦织构减磨性能的影响.结果 不同密封压力下,从40 MPa增至140...     

Effect of pressurizing speed on filling behavior of gradual expansion structure in low pressure casting of ZL205A alloy

The mold filling behavior of gradual expansion structure in low pressure casting was studied by two phase flow model using the Volume of Fluid method, and was verified by water simulation with a Plexiglas mold. To get smooth mold filling process and provide a guide for the pressurizing speed design in the producing practice, the mathematical model with the pressurizing speed, expansion angle and height of the gradual expansion structure was established. For validation experiments, ZL205 A alloy castings were produced under two different pressurizing speeds. Weibull probability plots were used to assess the fracture mechanisms under different pressurizing speeds. Mechanical properties of ZL205 A alloy were applied to assess the entrainment of oxide film. The results show that the filling process of a gradual expansion structure in a low pressure casting can be divided into the spreading stage and filling stage by gate velocity. The gate velocity continues to increase in the gradual expansion structure, and increases with the increase of pressurizing speed or expansion angle. Under the effect of the falling fluid raised by the jet flow along the sidewall, the fluid velocity decreases in the jet zone from ingate to free surface. As such, oxide film entrainment does not occur when the gate velocity is greater than the critical velocity, andthe gate velocity no longer reflects the real state of the free surface. The scatter of the mechanical properties is strongly affected by the entrainment of oxide films.     

不同工作参数下水轴承的空化程度及微形貌特征对减阻效果的影响

目的为了提高水轴承高速下的减阻效果以及预测水轴承的空蚀区域,研究了高速水静压轴承的空化与减阻性能。方法基于低雷诺数Launder-Sharma模型和空化气泡的动力学模型,分析了不同工作参数下水轴承的空化程度研究及微形貌特征对减阻效果的影响。结果空化气泡主要出现在静压轴承水腔之间的负压封水面及小孔节流器附近,空化气泡溃灭时容易造成轴承材料的空蚀破坏。高速小偏心率时,相比流向和展向微形貌,凸柱微形貌特征表面具有较好的减阻效果,且减阻效果受轴颈线速度的影响较大。结论转速、供水压力和偏心率等物理参数影响水静压轴承空化气泡分布和静态性能,微形貌界面的速度滑移有利于提高减阻效果。     

基于ANSYS-FLUENT的高精密液体静压径向轴承动静态特性研究

以液体静压轴承为支撑的电主轴是高精密数控机床的一个最为关键的组成部件。静压轴承润滑油膜的压力分布、刚度和温度场的分布直接影响数控机床的加工精度。基于液体静压技术理论,对轴承的流量、静压腔压力和刚度进行数值计算。基于ANSYS-FLUENT联合仿真平台,以液体静压径向轴承的润滑油膜为研究对象,对其压力场、流场和温度场分布等进行了静态和瞬态的研究,仿真结果与数值计算结果取得了很好的一致性。分析表明,静压腔内的润滑油的压力和温度分布不会因为主轴的转速变化而发生明显的变化,而周向封油边和轴向封油边是压力和温度变化的敏感位置。     

纳米单峰粗糙壁面润滑模型的分子动力学模拟

为研究角鲨烷润滑油膜在固定压强、不同温度和不同剪切速度下的边界润滑行为,建立了具有单峰粗糙面的边界润滑模型。分析润滑油膜的密度分布,以及在剪切运动过程中固体壁面的力学响应和应力变化,以及不同剪切速度条件下润滑剂和凸峰的状态变化。结果表明:温度对角鲨烷润滑油膜的分层现象影响较小,对凸峰之间的粘着现象影响显著;较高的相对运动速度有利于减小磨损;混合摩擦状态时,两凸峰接触界面中有少量角鲨烷分子存在,且分子长链方向与剪切方向一致。     

重型数控龙门机床静压导轨承载能力研究

静压导轨是重型数控龙门机床的关键组成部分,用于支持整个机床的重量,并沿工作台平稳地移动。因此,导轨油膜对机床的承载能力和加工精度起着重要作用。通过三维CFD仿真对无摩擦条件下的重型数控龙门机床静压导轨油膜的承载能力、流场压力和速度特性进行了分析,并通过对比实验数据对仿真结果进行验证。为满足工程设计要求,采用简化的理论模型分析油膜的承载能力。通过实验数据,验证了简化模型的准确度及可靠性,从而为重型龙门数控机床滑动导轨的油垫设计的理论计算提供了方法。     

表面织构及供油量对润滑性能影响的建模分析

目的研究不同供油条件下织构表面的润滑性能。方法首先,建立考虑表面织构的乏油润滑模型,求解修正雷诺方程获得乏油工况下考虑织构表面的润滑油膜厚度以及压力分布。然后,依据求得的润滑油膜厚度判断计算域内各点润滑状态,通过接触压力及油膜厚度分别计算边界润滑、混合润滑以及流体润滑状态下的切应力,并积分求得摩擦力进而得到摩擦系数。结果模拟了供油层厚度为50~500 nm以及充分供油条件下三种织构的润滑行为,获得了不同润滑状态下表面织构的摩擦系数。速度为0.1 m/s时,供油量对接触区油膜厚度的影响较小,不同润滑状态下织构表现出不同的润滑性能。速度为0.2 m/s时,供油层厚度对油膜厚度的影响较大,随着供油层厚度的增大,膜厚明显增加,摩擦系数在供油层厚度为200 nm时最小。结论接触副处于流体润滑状态时,织构表面不具有减摩效果。接触副处于边界润滑状态时,织构表面具有减摩效果,并且织构较密时,摩擦系数较小。接触副处于混合润滑状态时,织构过于稀疏或密集时均不具有减摩效果,但是合理分布的织构具有减摩效果。     

基于热混合润滑的钢/橡胶接触表面水润滑增强调控

目的 增强钢/橡胶摩擦副的润滑性能,为提高混合润滑状态下水润滑轴承的性能提供参考。方法 建立水润滑条件下钢/橡胶摩擦副的热混合润滑模型,讨论热效应对润滑性能的影响,并在此基础上进一步研究表面粗糙度、水基润滑剂黏度和供水压力对水润滑增强调控的作用。结果 与等温解相比,热效应使Stribeck曲线发生了右移,摩擦因数和载荷比增大,膜厚比降低。最高水膜温度随着转速的增加而升高,热效应对混合润滑性能的影响显著。减小摩擦副表面粗糙度,Stribeck曲线向左移动。在相同转速下,载荷比随着表面粗糙度的减小而降低,膜厚比反之。表面粗糙度越大,水膜温度越高,最高温度位于出口区,且钢的表面温度低于水膜和橡胶的表面温度。当水基润滑剂的黏度增大时,膜厚比增大,载荷比和最高水膜温度降低,Stribeck曲线发生左移。增加供水压力可以改善水膜压力分布,使水膜承载区增大、压力减小,粗糙峰接触压力和承载区减小,导致载荷比减小、膜厚比增加,Stribeck曲线向左偏移,水膜最高温度降低。当接触区由边界润滑向混合润滑过渡时,水膜最高温度出现拐点,且水膜最高温度拐点随着供水压力的增加而左移。结论 热效应会降低摩擦副的混合润滑性能,因此在混合润滑中不能忽略。考虑热效应时,通过减小表面粗糙度,或增加水基润滑剂黏度和供水压力,均有利于增强钢/橡胶接触表面水润滑的混合润滑性能。     

Accuracy enhancement of five-axis machine tool based on differential motion matrix: Geometric error modeling,identification and compensation

This paper presents the precision enhancement of five-axis machine tools according to differential motion matrix, including geometric error modeling, identification and compensation. Differential motion matrix describes the relationship between transforming differential changes of coordinate frames. Firstly, differential motion matrix of each axis relative to tool is established based on homogenous transformation matrix of tool relative to each axis. Secondly, the influences of errors of each axis on accuracy of tool are calculated with error vector of each axis. The sum of these influences is integration of error components of machine tool in coordinate system of tool. It endows the error modeling clear physical meaning. Moreover, integrated error components are transformed to coordinate frame of working table for integrated error transformation matrix of machine tools. Thirdly, constructed Jacobian is established using differential motion matrix of each axis without extra calculation to compensate the integrated error components of tool. It makes compensation easy and convenient with reuse of intermediate. Fourthly, six-circle method of ballbar is developed based on differential motion matrix to identify all ten error components of each rotary axis. Finally, the experiments are carried out on SmartCNC500 five-axis machine tool to testify the effectiveness of proposed accuracy enhancement with differential motion matrix.     

大型机床静压导轨油膜厚度反馈补偿装置的设计

详细阐述了大型机床静压导轨油膜厚度反馈补偿装置的设计原理与补偿程序,通过光栅尺测量油膜厚度的变化,运用油膜厚度与流量的数学模型,结合具体机床参数,由PLC程序计算出油量的差异,输出相应的电信号,计算出恢复预设油膜厚度所需的油量,修正变频电机的频率,调整转速与供油量。实践证明,该方案是可行的。     

Analysis of solid-liquid fluid dynamics about the characteristics of electrotyping diamond-nickel composite film

In this paper,super-thin free-standing diamond grains-nickel composite film in large area were prepared by using electrotyping method,which were used to make super-thin cutting blades.Scanning electron microscope(SEM) were used to analyse the characteristics of the film.It was found that the agitation velocity and the place of impeller strongly affected the content and uniformity of diamond grains in deposited composite film when the other parameters were the same.The best film was deposited when agitation velocity was 180-220 r/m and the impeller was placed in the lower part of the solution.The obliquity of cathode strongly affected the content of diamond grains in the film,and the content reached maximum when the obliquity was kept at 45 degree.The hanging orientation of cathode strongly affected the uniformity of the thickness of the film,and uniform films were deposited when cathode was intermissively circumrotated by 90 degree in the plane itself during deposition.The fluid field in solid-liquid stirred electrolytic solution was analysed by using Computational Fluid Dynamics(CFD).And the influences of agitation velocity, the place of impeller and the obliquity of cathode on the content of diamond grains in the film were explained.With Euler-Lagrange model,the just-suspended speed of impeller in solid-liquid stirred electrolytic tank was predicted by using Zwietering formula,the predicted speed was and it was consistent with experimental result.