数控机床轴承预紧对主轴刚度的影响

主轴系统的工作性能,对工件的加工质量和机床生产率均有重要影响,对轴承实行预紧,可提高主轴刚度和主轴旋转精度.文章运用ANSYS软件并结合实测研究了轴承预紧与机床主轴刚度的关系,结果表明:通过增加前端轴承预紧量在一定程度上可以改善主轴弯曲刚度,为设计主轴系统提供了一定的借鉴.     

主轴轴承预紧力的在线测量与控制及其对主轴系统特性的影响(上)

文中讨论了主轴轴承预紧力变化机理及预紧力的定量计算,分析了预紧力对主轴热特性和动力学特性的影响并做了试验验证,在介绍国外预紧力控制和补偿的方法的基础上,重点介绍了作者研制的“测力轴承”和“预紧力控制环”,前者用于预紧力的在线监测,后者用于预紧力的调整,后者由于具有较大的阻尼值,能大大地提高主轴系统的动态刚度和抗振能力,减少主轴系统的热变形,从而提高了主轴系统精度,可有效地实现预紧力的最佳适应控制。本文分两期刊完。     

非均匀预紧力对主轴系统回转性能的影响研究

为研究非均匀预紧力对轴承-主轴系统回转性能的影响,通过对轴承-主轴试验台施加可控预紧力,检测主轴轴心回转轨迹,并采用最小二乘圆法评定轴心轨迹,研究不同的转速及工况下轴承的非均匀预紧力对主轴轴心轨迹半径的影响。研究结果表明：即使在空载情况下,轴承外圈不同施力点导致的非均匀预紧会对轴心轨迹产生不同的影响;在径向载荷下,合适的非均匀预紧会逐渐改善主轴的回转性能。     

轴承预紧对机床主轴刚度的影响

阐明了用有限元法分析计算机床主轴组件刚度的步骤和方法,并对主轴刚度进行计算,讨论不同预紧条件下,轴承刚度对主轴性能的影响;并探讨轴承预紧后,增大预紧量对主轴刚度的影响。结果表明:支承轴承预紧的增大使主轴弯曲刚度增幅最大为22%,而对固有频率的影响不明显。     

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。     

滚动轴承预紧力对其转子系统特性影响的理论及试验研究

为了改善滚动轴承-高速电主轴系统特性分析中对轴承只取其刚度和阻尼元素参与计算的情况,引入滚动轴承预紧力参数,建立用于轴承转子系统特性分析的滚动轴承预紧力约束方程,从理论上计算预紧力对系统刚度、临界转速和轴承性能的影响.以角接触球轴承-高速(60 000 r/min)电主轴系统为对象,设计一种预紧力测量方法,通过实验研究轴承预紧力对轴承转子系统的影响,结果表明测量结果与理论计算基本一致.     

主轴轴承预紧力在数控维修中的解决方法研究

介绍了计算轴承预紧力需要考虑的因素,研究了轴承预紧力的计算方法及数控机床主轴轴承预紧的方法,详细阐述了以预紧力为依据的机床主轴预紧的方法。该方法用在机床主轴的安装及维修中,可以成功恢复高转速、高精度机床主轴的精度。     

精密高速磨床主轴支承轴最佳预紧力计算

研究了精密高速磨床主轴－轴承轴系动学力特性,在旋转轴振动理论和高速球轴承刚度理论的基础上,本文提出了一种新的计算精密高速磨床主轴轴在的最佳预紧力算法。     

风机主传动系统法兰连接摩擦性能与预紧力研究

传统风电法兰连接预紧力设计采用经验公式进行计算。本文以风电机组主传动系统法兰连接为研究对象,对含涂层法兰材料进行了摩擦特性对比试验,结果表明含涂层材料比普通材料的摩擦系数高40%;同时,建立了不同摩擦系数和不同预紧力下的轮毂-主轴法兰连接数值模型,分析了预紧力-应力动态响应特性,发现在保证设计安全系数前提下适当减小预紧力可提高法兰连接应力场分布均匀性。在一定程度上缓解热点区域应力集中现象,为风电机组法兰连接预紧力设计和主传动系统轴承选型提供一定的理论支撑和技术指导。     

弹性预紧轴承组件预紧力测试台的研制及试验

利用轴承组件轴向刚度的特性,采用精密力传感器开发了弹性预紧轴承组件预紧力测试台.利用该试验台可以实现对弹性预紧轴承组件预紧力的检测和弹性预紧限位行程的检测.加载组件采用精密螺旋弹簧实现了大载荷高分辨率的加载,并通过直线导轨保证加载力的加载方向.最后利用该试验平台对某弹性预紧电机轴承组件的预紧力进行了检测.     

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.     

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.     

Effect of preload of linear guides on dynamic characteristics of a vertical column–spindle system

Realization on the dynamic characteristics of the column–spindle system is of importance for enhancing the structural performance of a vertical milling machine. Generally, the spindle head is fed under linear guide mechanism through a ball-screw driver. To assess the dynamic characteristics of a vertical column–spindle system under the influence of a linear guide, this study developed a finite element model integrated with the modeling of linear components with the implementation of contact stiffness at the rolling interface. Both the finite element simulations and the vibration tests reveal that the preload of a linear guide greatly affects the vibration behavior associated with a spindle head, and the dynamic stiffness of the spindle head could be enhanced by increasing the preload of the linear guide. Current results clearly indicate that the simulations agree well with the experimental measurements. This also confirms that the proposed model can be successfully applied to evaluate the dynamics characteristics of machine tool systems of various configurations.     

微型钻头磨床砂轮轴振动的分析与消除

微型钻头磨床砂轮轴振动严重地影响了钻头加工精度。通过对砂轮轴的传递矩阵建模分析，发现砂轮轴轴承刚工和砂轮尺寸是影响其振动的固有频率与振型的两个主要因素。轴承刚度越高，砂轮尺寸越小，基各阶固有频率越高；由于砂轮小对称布置，砂轮尺寸越大，各阶振型的振幅也越大。在调整砂轮轴轴承预紧前，采用Machinery Analyzer model 2130振动分析仪的测试结果也显示该砂轮轴在低频部分的振动较为严重，预紧轴承和精修砂轮后，振动消除。     

An elastic deformation model of high speed spindles built into ball bearings

Kinematic characteristics and elastic deformation properties of ball bearings such as stiffness, axial, and radial deflections of the rings, speeds of balls, contact angles, and loads, all vary strongly with rotational speed, temperature, and axial preload. This paper presents an elastic deformation model of spindle units built into ball bearings, which are running on high rotational speed and axial preload. For this, software for simulation of the high speed spindle units was developed and introduced into a practical use. A computer aided analysis of the model was carried out and experiments were made, which showed a significant effect of high rotational speed, cutting load, bearing axial preload, and a new effect for which the criteria for a choice of bearing preload are given.     

Effect of preload on running accuracy of spindle

The rotational performance of a machine tool spindle has a direct influence upon both the surface finish and geometric shape of the finished workpiece. The variation of preload affects the stiffness of the spindle and the temperature of the bearing, which are also important factors in spindle motion. Although the large preload and stiffness will probably increase the stability of the spindle, the high temperature of the bearing will decrease the processing accuracy and damage the bearing. Contrarily, if the preload is not large enough, the error in the running spindle will increase, which represents lower precision. Therefore, the preload cannot be too large or too small, resulting in the compromising of these factors. In this study, the effect of the preload on the roundness accuracy has been examined at the different cutting conditions through the developments of measurement system of preload, temperature and roundness accuracy. The step-by-step data analysis procedure has also been developed to get the spindle radial error motions from the measured data. Through measurements of spindle running accuracy, the optimal preload was determined at the different cutting conditions.     

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.     

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.