GMC2550u桥式加工中心样机综合精度测评研究

数控机床的精度、切削能力、稳定性是机床用户关注的三个主要指标,研究机床样机的综合精度对于掌握机床现有性能,并相应改进和提升具有重要意义。依据国内外标准,建立包含检测项目和评价指标的桥式数控加工中心精度评价体系。应用试验测试方法对首台套机床样机进行精度检测,重点关注机床的静态、动态和工作精度。测试位置精度、最小设定单位误差、圆运动精度、主轴动态回转精度、进给轴动态响应性能,以及典型验收零件的切削精度等。同时,关注机床主轴径向振动、静刚度以及热态性能等动态性能对机床精度的影响,并分别开展三种三轴联动和五轴联动零件的工作精度检验。研究发现,机床静态精度指标满足设计要求,而加速度和主轴热态精度等指标与设计指标存在差距,并会对机床的最终工作精度产生影响。综合各项精度指标的测试结果,获得机床的实际精度表现和分布规律,可以对样机在各项精度指标上所反映出的精度问题进行评价,为有针对性地进行机床后期优化改进给出方向。     

基于粒子群优化灰色神经网络的机床主轴热误差建模

主轴热误差是影响机床精度的主要因素,建立准确的主轴热误差模型是进行机床误差补偿的关键。研究了温度测点优化和神经网络建模的方法,给出了粒子群优化灰色神经网络建模的流程。开展了主轴热误差热特性试验,得到了主轴热变形随主轴转速的变化规律。基于粒子群优化灰色神经网络建立了主轴轴向伸长和俯仰角热误差模型,并与灰色神经网络和BP网络的预测性能进行了对比,结果表明该模型可有效提高网络模型的收敛性和预测精度。     

小型数控车床热态性能的分析优化与实验辨识

针对CMK系列小型数控车床运行过程中普遍存在的主轴"翘头"问题,试图通过热变形分析与实验辨识相结合的方法找出上述问题的成因,并给出相应的优化方案,因此,建立了基于有限元法的机床热态特性分析模型来解析整机温度场,同时,通过热应力耦合分析预测了机床各部分的热变形以及主轴的热倾斜,随后,利用红外热成像仪测量、验证了整机温度分布,通过特别设计的六个测点三个方向的热变形实验辨识了主轴系统的热倾斜特性,最后,以降低主轴热倾斜角为目标,给出了提升机床热态性能的两种方案,热优化设计和采用人造花岗岩床身。     

数控机床主轴-立柱系统热态特性分析与测试

针对数控机床主轴-立柱系统因受热变形而影响机床加工精度的问题,本文基于能量守恒定律建立了主轴-立柱系统耦合分析模型来获取其热态特性。该模型综合考虑了热源计算、传热系数计算、结构约束以及散热面放置情况等因素,并采用风速法来获取主轴与空气间的传热系数。为了验证主轴-立柱系统耦合分析模型的有效性,本文设计并搭建了数控机床热态特性试验平台,以具体数控机床为研究对象获得了其主轴-立柱系统的温度场分布、热变形以及热平衡时间等热态特性。试验结果表明:各测点数据中温度的最长绝对误差和最大相对误差分别为0.71℃,2.94%,出现在主轴体的测点处,热变形的绝对误差和相对误差分别为1.49μm,8.71%,采用风速法建立的主轴-立柱系统耦合分析模型所获得的热态特性与试验获得的结果基本一致。本文的研究成果为数控机床减少热误差,提高精度保持性提供了参考。     

龙门加工中心主轴系统的热态性能分析技术研究

龙门加工中心主轴系统热态特性是提升机床性能的一个关键问题。针对龙门加工中心主轴系统热态特性分析的需要,建立有限元分析模型,计算主轴轴承的发热量以及主轴系统各个表面的对流换热系数,利用ANSYS WORKBENCH对其温度场、热变形状况以及热-结构耦合问题进行了分析计算,得到了不同位置轴承对总热变形的影响以及不同转速条件下主轴系统的稳态热态性能。实验测试数据表明分析计算结果的准确性较高,可用于指导该型龙门加工中心主轴系统结构优化设计和热变形补偿。     

车磨复合机床主轴系统的温度场建模与仿真

影响现代高速机床加工精度的主要因素是热误差。机床主轴系统的热特性直接影响到机床的精度进而影响零部件精度,因此有必要对主轴系统进行热分析,了解其热特性,以便进一步分析和改进。车磨复合机床主轴回转系统结构设计及性能要求很高,应具有足够的强度、刚度、抗振性、韧性和抗疲劳性能。分析主轴热源,计算发热量,确定边界条件,利用有限元软件ANSYS建立了主轴系统的温度场模型并进行了数字模拟仿真,为类似主轴系统的热应力及热变形设计提供了参考。     

接触热阻效应下的数控机床主轴系统热态特性

为了更为精确地获取数控机床主轴系统的热态特性,基于W-M分形函数与赫兹接触理论获取主轴系统的接触热阻,并在综合考虑机床热源、传热系数计算等因素影响的情况下,建立了主轴系统热态特性分析模型。通过有、无加载接触热阻的主轴系统模型仿真分析与实验研究可知:有接触热阻的主轴系统热态特性模型相较于无热阻的有更高的精度。有接触热阻的主轴系统热态特性模型仿真结果与实验测点获得的温度结果最大绝对误差和相对误差分别1.25℃、4.74%,而热变形结果的绝对误差和相对误差分别为0.73μm、4.27%。该研究为数控机床的热设计与分析提供了参考。     

数控螺杆转子磨床主轴热特性实验及分析

主轴热误差是影响机床加工精度的一个主要因素。针对数控螺杆转子磨床主轴开展了热特性实验分析,通过测量阶段转速条件下主轴各部分的温升和热变形,获得了主轴的热特性,并提出了改善主轴热特性的措施。     

TK6920DA重型数控落地铣镗床主轴-滑枕系统热态特性结构优化研究

针对TK6920DA重型数控落地铣镗床主轴-滑枕系统的热态特性展开研究,首先采用有限元法(FEM)建立了主轴-滑枕系统的热态特性有限元模型,通过分析该系统的热源并确定热边界条件,利用ANSYS软件对系统温度场与热变形场进行了数值仿真,获得了影响机床精度的关键部位。其次,分析了主轴前端轴承冷却套流量对系统热态特性的影响规律。最后,通过改进液压冷却方式和优化滑枕结构提高了主轴-滑枕系统的热态特性。为重型落地铣镗床结构优化设计和热变形误差补偿提供参考依据。     

龙门数控机床主轴热误差及其改善措施

依据ISO和ASME标准建立龙门数控(Numerical control,NC)机床热误差测试条件,通过主轴恒转速和变转速热误差试验分析主轴箱温度场分布及其对主轴热误差的影响趋势。建立龙门机床误差元素模型,分析影响机床各坐标轴加工精度的主轴热误差分量。研究发现,主轴热误差和主轴箱温度存在单调对应关系,温度对主轴轴向的热伸长误差的影响要远大于主轴径向的热漂移误差,但温度变化相对各坐标变形存在热延迟和热惯性等特性。对主轴径向精度影响最大的热误差分量是由机床生热产生的同方向的偏移误差和与之垂直的偏转误差;对轴向精度影响最大的则是轴向的偏移误差。针对热误差特点和分布规律,提出结构优化、热平衡、误差补偿建模等3种减小热误差的措施,并对其各自优点进行了分析。     

Spindle thermal drift measurement using the laser ball bar

Thermally induced errors are major contributors to the overall accuracy of machine tools. An important component of thermally induced errors is the error associated with spindle thermal drifts. In this paper, a novel method is developed to measure spindle thermal drifts in machine tools using a laser ball bar (LBB) as the calibration instrument. The method is implemented on a two-axis CNC turning center. The LBB is used to measure the coordinates of the spindle center and the direction cosines of the spindle axis at various thermal states. The axial, radial, and tilt thermal drifts of the spindle are then computed from the changes in these coordinates. The new method is verified by comparing the spindle drifts measured with the LBB to those measured by capacitance gauges. The results obtained by the new method show good agreement with the capacitance gauge technique. The primary advantage of the new method is the ability to measure the spatial coordinates of the spindle center and direction cosines of the spindle axis with the same instrument used for measurement of the geometric errors of the machine axes.     

Analysis of CNC machining based on characteristics of thermal errors and optimal design of experimental programs during actual cutting process

The compensation of thermal errors plays a critical role in developing the machine tools of intelligent computer numerically controlled (CNC). According to the international standards, the testing, modeling, and compensation of thermal error of CNC machine tools are carried out only in a so-called idling state where the spindle is free running without any workload. However, in practical applications, machine tools are often applied in the actual cutting state with more influence factors, such as cutting parameters, cooling liquid, and cutting force. Subsequently, the thermal characteristics at idling state and actual cutting state are compared and analyzed in this paper. It was found that the thermal error compensation model under idling state is not precise enough to be applied in actual cutting state. Also, further research finds that different combinations of cutting parameters, such as spindle speed and feed rate, also have influences on the accuracy of prediction and robustness of thermal error model under actual cutting state. Therefore, the cutting parameters of spindle speed, feed rate, depth of cut, and ambient temperature are studied with the usage of the Taguchi method. Through calculating signal-to-noise ratio (SN) of each combination through residual standard deviation of thermal error model, the combination of optimal cutting parameters can be obtained. The resultant analysis shows that the thermal error model under the combination of optimal cutting parameters demonstrates higher accuracy of prediction and better robustness.     

Thermal influence of the Couette flow in a hydrostatic spindle on the machining precision

Hydrostatic spindles are increasingly used in precision machine tools. Thermal error is the key factor affecting the machining accuracy of the spindle, and research has focused on spindle thermal errors through examination of the influence of the temperature distribution, thermal deformation and spindle mode. However, seldom has any research investigated the thermal effects of the associated Couette flow. To study the heat transfer mechanism in spindle systems, the criterion of the heat transfer direction according to the temperature distribution of the Couette flow at different temperatures is deduced. The method is able to deal accurately with the significant phenomena occurring at every place where thermal energy flowed in such a spindle system. The variation of the motion error induced by thermal effects on a machine work-table during machining is predicated by establishing the thermo-mechanical error model of the hydrostatic spindle for a high precision machine tool. The flow state and thermal behavior of a hydrostatic spindle is analyzed with the evaluated heat power and the coefficients of the convective heat transfer over outer surface of the spindle are calculated, and the thermal influence on the oil film stiffness is evaluated. Thermal drift of the spindle nose is measured with an inductance micrometer, the thermal deformation data 1.35 μm after running for 4 h is consistent with the value predicted by the finite element analysis's simulated result 1.28 μm, and this demonstrates that the simulation method is feasible. The thermal effects on the processing accuracy from the flow characteristics of the fluid inside the spindle are analyzed for the first time.     

150MD24Z7.5型电主轴动态误差和热变形实验研究

电主轴的动态误差和热变形是影响数控机床精度的重要指标,其对定位精度和工件表面加工质量的影响尤为显著。采用主轴误差分析仪,对150MD24Z7.5型主轴的各项动态误差及各方向的热变形量进行实验研究。通过试验结果数据分析,获得了主轴系统在不同转速下的同异步误差、热平衡时间及不同方向的热变形量等,为主轴动态误差补偿和热变形智能预测提供了准确的数据支撑。     

机床的主轴单元（下）

通过回顾机床主轴发展历程,指出电主轴在高端数控机床的应用日益广泛。继而详尽地阐述了机床主轴单元的设计要点,包括轴承、润滑和冷却以及刀具接口等。接着对主轴的静动态和热性能分析以及建模仿真进行了全面介绍。最后指出主轴的工况监控、智能化和自适应控制是新一代电主轴的重要特征和未来发展趋势。     

Thermal error reduction based on thermodynamics structure optimization method for an ultra-precision machine tool

Thermal error is one of the main errors in ultra-precision machine tools. This paper presents a thermodynamics-based structure optimization method to reduce the thermal displacements of machine tools during operation. The method makes use of the thermal–structure coupled model to analyze the thermal behavior considering the thermal contact resistance and the temperature rise of the oil film in hydrostatic spindle. The structure of the motor link, spindle, and headstock of grinder are optimized by setting appropriate gaps in the contact region of two neighboring parts to change the heat transfer distribution and minimize the thermal displacement of the spindle center position. The proposed method is validated by an equivalent thermal conductivity-based simulation method and experiment on an ultra-precision grinding machine tool. Experimental results show that the proposed method can provide an important instruction on how to reduce the thermal error for the design of the precision machine tools, especially for those with key parts placed near the heat sources.     

Automated measurement and compensation of thermally induced error maps in machine tools

In this paper, a direct method of machine tool calibration is adopted to model and predict thermally induced errors in machine tools. This method uses a laser ball bar (LBB) as the calibration instrument and is implemented on a two-axis computerized numerical control turning center (CNC). Rather than individually measuring the parametric errors to build the error model of the machine, the total positioning errors at the cutting tool and spindle thermal drifts are rapidly measured using the LBB within the same experimental setup. Unlike conventional approaches, the spindle thermal drifts are derived from the true spindle position and orientation measured by the LBB. A neural network is used to build a machine model in an incremental fashion by correlating the measured errors with temperature gradients of the various heat sources during a regular thermal duty cycle. The machine model developed by the neural network is further tested using random thermal duty cycles. The performance of the system is also evaluated through cutting tests under various thermal conditions. A substantial improvement in the overall accuracy was obtained.     

卧式HMC500主轴系统热特性分析及结构优化

以HMC500主轴系统的特有结构为研究对象,建立主轴系统的温度场模型。实验结果表明,主轴系统热变形与温度有较好的对应关系,主轴发热量增大引起主轴变形增大,而主轴轴承的摩擦生热是主轴系统热量产生的重要原因,主轴系统的最高温升位于前轴承内圈处。进一步仿真计算主轴系统的热变形,通过对主轴箱体散热凹面的优化设计,可有效降低主轴系统温升,使主轴系统的热变形达到最小,从而使关键部位变形小于10 μm,满足机床的设计要求。在优化后的主轴箱系统上布置温度传感器和位移传感器,在8 000 r/min转速下进行实时测量,将实验结果与ANSYS的模拟结果进行对比,验证了优化结构的可行性与可靠性。