坐标镗床主轴力学特性的有限元分析

建立了某坐标镗床主轴的实体模型,计算了在计算转速下的受力参数,依据实际载荷和边界条件,建立了有限元分析模型,分析了主轴在加工过程中的变形、应力和固有振动参数.分析结果表明,现有主轴力学性能满足要求.依据有限元分析结果,提出了减小机床加工误差的方法.     

HDBS-63高速立式加工中心主轴系统热分析

分析了主轴系统在机床中的重要性及机床误差的主要来源.设计一种立式加工中心的主轴系统,建立主轴系统三维实体模型,经简化导入有限元分析软件,利用有限元法对主轴系统进行热分析及"热--结构"耦合分析.通过不同工况的仿真结果分析,得到主轴系统的温度场分布状况和热变形状态的变化规律,为主轴系统设计提供了良好的参考依据.     

精密主轴热变形误差的实验研究

主轴是机床的关键部件,其热变形误差是影响精密机床工作精度的主要因素之一。文章对镗床主轴的不同热变形误差形式及对加工精度的影响进行了讨论。依据ISO和ASME标准建立某型号精密卧式坐标镗床热变形误差的测试环境,采用高精度测试系统对其主轴进行温度和热变形误差的实验测试与分析。结果表明,主轴热变形误差严重影响机床加工精度,主轴转速影响其达到热平衡的时间及热误差大小,需采取有效措施对热变形误差进行补偿,优化热结构,进一步提高机床加工精度。     

精密卧式加工中心主轴轴向热误差补偿方法

热误差是精密机床最主要的误差源之一。主轴是机床的关键部件,其热误差直接影响机床的加工精度。文章以某型号精密卧式加工中心主轴为对象,对其温度场和热变形进行了仿真分析。根据仿真结果发现主轴轴向热变形更严重,并结合机床结构确定温度传感器布置位置。在此基础上,对不同转速下主轴部分位置温度和轴向热误差进行现场测试。运用最小二乘法建立热误差补偿模型,直接结合机床FANUC数控系统实施主轴轴向热误差补偿。经实验验证,补偿后主轴轴向热误差减小了85%以上。     

基于运动控制器的CA6140车床数控改造

传统机床的数控化改造已成为各个工厂对传统机床应用的最佳选择,针对 CA6140普通车床,提出数控改造整体方案,做出了硬件选型。为了适应数控系统,对车床进行了结构设计分析,本方案应用在 CA6140车床上切实可行,具有一定的指导意义。     

龙门加工中心主轴滑枕结构有限元分析技术研究

龙门加工中心主轴滑枕结构是连接刀具和机床的一个重要部件,其受切削力和受热变形将直接影响刀具的加工精度.通过建立龙门加工中心主轴滑枕结构的有限元分析模型,在计算热源发热量以及主轴滑枕结构热边界条件的基础上,利用ANSYS有限元分析软件在其工作状态下进行切削力变形分析、稳态热变形分析以及热-结构耦合分析.得到了主轴不同转速条件下主轴滑枕结构热态性能及刀盘直径方向变形规律,为该型龙门加工中心主轴滑枕结构优化设计和热变形补偿提供了理论依据.     

数控机床导轨变形误差补偿技术研究

针对机床导轨变形特别是大型、重型机床的导轨变形降低加工精度的问题,提出了利用软件误差补偿技术来消除导轨变形对加工精度的影响.以数控车床为例,分析了导轨变形对加工零件的影响,提出了利用最小二乘法拟合导轨变形曲线,阐述了利用指令修正技术进行误差补偿的原理,为进行数控机床全局误差补偿提供了理论依据和技术参考.对CK6140型数控车床进行了补偿,有效地改善了加工精度.     

精密机床主轴弹簧夹头夹紧力计算方法研究

研究精密机床主轴弹簧夹头夹紧力计算方法,建立了弹簧夹头夹紧力的可靠性分析模型,并对某精密机床主轴弹簧夹头夹紧力可靠度进行了计算;建立了整个弹簧夹头夹紧机构的非线性有限元模型,通过与理论计算结果的对比验证了有限元模型的准确性;通过有限元分析得到了弹簧夹头夹紧状态下夹紧面接触变形规律,为精密机床主轴弹簧夹头的设计及性能分析提供了方法和依据。     

基于运动控制器的CA6140车床数控改造（英文）

传统机床的数控化改造已成为各个工厂对传统机床应用的最佳选择,针对CA6140普通车床,提出数控改造整体方案,做出了硬件选型。为了适应数控系统,对车床进行了结构设计分析,本方案应用在CA6140车床上切实可行,具有一定的指导意义。     

高速电主轴系统的热瞬态分析北大核心

以CX8075型车铣复合加工中心的电主轴为研究对象,对其进行三维建模,利用工程有限元分析软件ABAQUS进行瞬态的热—结构耦合分析,研究了主要热源附近的温升变化和主轴轴端的热变形的变化趋势。分析结果表明,电主轴温升最大的部位位于主轴电机的定子和前后轴承的滚动体;主轴的轴向和径向热误差主要在前3 000 s变化较大,因此在加工前对机床适当地预热能够一定程度上减少热误差对加工精度的影响,为进一步研究机床的热误差提供了理论依据。     

A study of pre-compensation for thermal errors of NC machine tools

Thermally-induced errors are major contributors to the overall accuracy of machine tools. In this paper, an error pre-compensation system is developed to correct the thermal errors of the spindle and lead screws. A simple gauge 1-D ball array is used to accelerate and simplify the error measurement. An auto-regressive model based on spindle rotation speed is then developed to describe the thermal errors. Using the model, the thermal errors can be predicted without measuring the temperature field of the machine tool as soon as the workpiece NC machining program is made. By correcting the program, the errors can be pre-compensated before machining. Thus the process of compensation is greatly simplified and the cost is reduced. The test results on a vertical machining center show that a 70% reduction of thermal errors has been gained after compensation.     

Particular behavior of spindle thermal deformation by thermal bending

Thermally induced errors reduce the accuracy in precision machining, and a great deal of research has been presented on compensation for these errors in machine tools. However, during the transition period after commencing or stopping spindle rotation, thermal deformation behavior is very complex. In particular, the y-directional movement of the vertical machining center cannot be explained by thermal expansion alone because of the relationship between deformation and temperature. Thermal bending that is generated from the thermal gradient in the structure causes this movement. In the research described in this paper, a theoretical explanation and an experimental verification is given for the particular behavior of spindle thermal deformation. As it is not easy to map the relationship of the compensation model, separation of the steady from the non-steady state in the mapping process is strongly recommended.     

Analysis of thermal errors in a high-speed micro-milling spindle

Thermally induced errors account for the majority of fabrication accuracy loss in an uncompensated machine tool. This issue is particularly relevant in the micro-machining arena due to the comparable size of thermal errors and the characteristic dimensions of the parts under fabrication. A spindle of a micro-milling machine tool is one of the main sources of thermal errors. Other sources of thermal errors include drive elements like linear motors and bearings, the machining process itself and external thermal influences such as variation in ambient temperature. The basic strategy for alleviating the magnitude of these thermal errors can be achieved by thermal desensitization, control and compensation within the machine tool.This paper describes a spindle growth compensation scheme that aims towards reducing its thermally-induced machining errors. The implementation of this scheme is simple in nature and it can be easily and quickly executed in an industrial environment with minimal investment of manpower and component modifications.Initially a finite element analysis (FEA) is conducted on the spindle assembly. This FEA correlates the temperature rise, due to heating from the spindle bearings and the motor, to the resulting structural deformation. Additionally, the structural deformation of the spindle along with temperature change at its various critical points is experimentally obtained by a system of thermocouples and capacitance gages.The experimental values of the temperature changes and the structural deformation of the spindle qualitatively agree well with the results obtained by FEA. Consequently, a thermal displacement model of the high-speed micro-milling spindle is formulated from the previously obtained experimental results that effectively predict the spindle displacement under varying spindle speeds. The implementation of this model in the machine tool under investigation is expected to reduce its thermally induced spindle displacement by 80%, from 6 microns to less than 1 micron in a randomly generated test with varying spindle speeds.     

Measurement of spindle thermal errors in machine tool using hemispherical ball bar test

The assurance of top-quality products in machining processes requires improved machine tool accuracy. Among the various errors related to machine tools, thermal errors of a spindle have a significant effect on machining accuracy and directly influence both the surface finish and the geometric shape of the finished workpiece. Accordingly, the current paper proposes a new measurement method for spindle thermal errors in a machine tool based on the use of a ball bar system instead of the conventional capacitance sensor system. The novel measurement method is more efficient and easier to use compared to conventional measurement systems. Furthermore, a single ball bar system is sufficient for the simultaneous measurement of both geometric and thermal errors.     

A machining test to calibrate rotary axis error motions of five-axis machine tools and its application to thermal deformation test

This paper proposes a machining test to parameterize error motions, or position-dependent geometric errors, of rotary axes in a five-axis machine tool. At the given set of angular positions of rotary axes, a square-shaped step is machined by a straight end mill. By measuring geometric errors of the finished test piece, the position and the orientation of rotary axis average lines (location errors), as well as position-dependent geometric errors of rotary axes, can be numerically identified based on the machine׳s kinematic model. Furthermore, by consequently performing the proposed machining test, one can quantitatively observe how error motions of rotary axes change due to thermal deformation induced mainly by spindle rotation. Experimental demonstration is presented.     

ICA based thermal source extraction and thermal distortion compensation method for a machine tool

Thermal distortion in machine tools is one of the most significant causes of machining errors. One of the difficult issues in developing a system to compensate for thermal distortion is to select the appropriate temperature variables and to obtain an accurate thermal distortion model. This paper presents a new thermal distortion compensation method based on the Independent Component Analysis (ICA) method. The ICA method was used to extract the thermal sources from the temperature variables. The Optimal Brain Surgeon (OBS) algorithm was used to reduce the temperature variables with insignificant information. Using the extracted sources, a new thermal distortion model and a compensation method is proposed and is implemented in real-time hardware. In these experiments, the proposed method was shown to be capable of compensating for thermal distortions to a few micrometers.     

Analysis of setting errors in precision ballscrew machining and the automatic adjustable center

Generally, in machining precision machine elements such as ballscrews, machining errors could occur for various reasons. In this research, the influence of improper setting errors in ballscrew machining, such as misalignment between centers, runout of spindle, and unsuitable contact conditions between the center and the center hole, was analyzed. From the analysis, among the setting errors, the misalignment between centers was found to be an important one. An automatic adjustable center for 2D arbitrary positioning was designed and manufactured to eliminate the alignment error in machining workpieces supported by two centers. This adjustment system could be practically applied to reduce machining errors.     

The improvement of thermal error modeling and compensation on machine tools by CMAC neural network

In this paper, a cerebellar model articulation controller (CMAC) neural network is proposed for thermal error modeling in machine tools. The CMAC is a systematic learning algorithm which can search for the nonlinear and interaction characteristics between the thermal errors and temperature field on the machine tools. The CMAC is investigated in terms of accuracy in prediction, robustness to sensor placement, speed of learning, and tolerance to sensor failures. Experimental measurements of the spindle drift errors for both a horizontal machining center and a CNC turning center were performed using capacitance sensors and thermal sensors. Results show that the CMAC model has better performance than other modeling methods in robustness to sensor placement and speed of learning. This makes determination of the sensor locations easier, and reduces calibration time. In addition, a sensor failure detection algorithm is developed to provide better reliability.     

一种航空铝合金铣削力模型的试验研究

基于航空铝合金材料7050-T7451的机械加工性能,理论上分析了航空薄壁件加工变形机理。通过四因素、四水平回归正交试验法确定铣削加工过程中切削力的力学性质和相关参数,根据铣削力形状特征建立了数控加工铣削力力学数值计算模型。采用合理的平均力试验验证了模型的有效性,为进一步研究航空铝合金数控加工变形提供了可靠的边界条件。     

Direct adaptive control of end milling process

A direct adaptive control algorithm, which is spindle speed and drive dynamics independent, has been developed for machining operations. The combined dynamics of feed motion and cutting process are modelled as a third order system whose parameters may vary with spindle speed and part geometry changes during machining. The algorithm does not use any specific time interval, thus sampling time dependent discrete transfer functions and pole assignments are avoided. The adaptive controller is designed to have a closed loop characteristic function which behaves like an open loop regular and stable machining operation. The proposed direct adaptive controller is practical, can be used in any multi-axes machining, and can be combined with chatter suppression techniques which require spindle speed regulation. The algorithm is applied to the adaptive control of milling. Satisfactory results are obtained in constraining the maximum cutting forces and dimensional surface errors in milling experiments.