超精密机床减振分析

良好的减振措施是提高机床,特别是超精密机床加工精度的重要技术之一.本文以亚微米超精密车床为研究对象,论述了该机床从结构到材料选取上的减振特点,并重点进行了空气弹簧和空气静压轴承主轴减振分析,由理论分析和实验表明:减振措施合理,减振效果良好.     

整体叶盘铣削数控编程与加工技术

整体叶盘有良好的结构完整性、轻质化、装配环节少、装配精度高等优点,已被广泛应用于航空发动机中。根据整体叶盘的切削加工特征,将其简化为整体叶盘基准件,从数控编程和加工技术两方面实现整体叶盘的高质量加工。首先,利用Hyper MILL软件对整体叶盘基准件进行数控编程,优化获得理想的刀具路径,保证高效高质量的零件加工。然后,利用DMU-70V五轴加工中心对钛合金TC4整体叶盘基准件进行切削加工,在整体叶盘基准件叶片和流道几何特征的精加工时,选用不同型号的立铣刀,并监测加工过程中的切削力。最后,对加工后叶片和流道加工表面形貌进行测试分析,并结合切削力对比分析国产刀具和进口刀具对钛合金整体叶盘的切削加工性能。     

国内外深空探测器精密定轨软件研究综述及WUDOGS简介

深空探测器精密定轨软件系统的研制在深空探测活动中是一个非常重要的环节,一直受到各大航天机构的重视。针对国内外深空探测器精密定轨软件平台的研究现状,重点介绍了具有代表性的美国JPL(Jet Propulsion Laboratory,喷气推进实验室)的DPTRAJ/ODP(Double Precision TRAJectory program/Orbit Determination Program,双精度轨道程序/定轨程序)和MONTE(Mission analysis,Operations,and Navigation Toolkit Environment,任务分析、操作和导航工具箱环境),GSFC(Goddard Space Flight Center,戈达德航天飞行中心)的GEODYN-II以及法国CNES(Centre National dEtudes Spatiales,国家空间研究中心)的GINS(Géodésie par Intégrations Numériques Simultanées,同步数值积分大地测量)软件系统,对这些软件的结构与功能进行了总结。之后对武汉大学自主研制的深空探测器精密定轨软件系统WUDOGS(Wuhan University Deep space Orbit determination and Gravity recovery System,武汉大学深空探测器精密定轨与重力场解算软件系统)的主要模块与功能进行了介绍,通过与GEODYN-II的交叉对比验证,表明:对于探测器的轨道预报,WUDOGS与GEODYN-II的1个月位置差异小于0.3mm,2d位置差值小于5×10~(-3) mm;双程测距、双程测速的理论计算值和GEODYN-II的差值RMS(Root Mean Square,均方根)分别在0.06mm,0.002mm/s的水平;WUDOGS目前已初步具备了月球和火星探测器精密定轨能力。最后对WUDOGS的下一步发展方向进行了展望。     

方坯叶片电解加工过程的模糊控制方法

采集方料毛坯叶片电解加工整个过程的电流信号,用小波变换法对信号进行降噪处理,得到一条电流随间隙减小而呈增大趋势的光滑曲线。设计了一种二维M andan i型模糊控制器,以所得光滑电流曲线作为标准曲线,以加工电压的增量为模糊控制器输出,控制实际加工电流,使其在多种扰动下跟踪标准电流曲线。在M atlab的S im u link模块中,通过对由模糊控制器和电解加工系统组成的联合模型进行仿真试验,整定模糊控制器的3个增益参数。仿真试验表明,该方法可使电解加工系统较好地重现预设的加工过程,实现对电解加工全过程的控制。该方法也可以应用于其他类型的电解加工过程控制。     

非接触供电旋转超声加工系统负载特性研究

在旋转超声波加工过程中负载的变化会引起振幅衰减,进而造成加工精度和加工效率降低。本文针对非接触供电旋转超声加工系统在加工过程中振幅衰减的问题,首先,通过静态加载实验,获得了负载对超声振子电学参数的影响规律;其后,在此基础上进行了超声振子的非接触能量传输系统的加载实验,得到负载对能量传输特性的影响规律。实验结果表明,超声振子的电学参数受负载力大小、负载力方向和被加工材料特性的共同影响而发生改变,超声振子电参数改变引起了非接触供电超声系统输出功率的改变,进而导致了振幅衰减的问题;本文采用了串联谐振下主边串联电容、副边并联电容的电路补偿方式来减小振幅的衰减。本文的研究成果为解决振幅衰减问题提供了实验依据。     

高速端面铣削加工引入残余压应力场的试验研究

为研究高速铣削加工表面残余应力分布,在统计试验设计指导下,使用X射线衍射/电解抛光方法对试样表层、次表层残余应力分布进行测量,得出残余应力分布曲线经验预报公式,探讨切削参数对残余压应力场特征指标的影响规律。研究结果表明,合理的高速切削工艺将在加工表面内引入类似喷丸强化效果的残余压应力场;(3,1)有理式模型与三阶多项式模型是描述高速铣削引入残余应力分布曲线的有效拟合公式;高速切削工艺参数对加工表面残余应力场的产生有直接影响,每齿进给量是决定残余压应力分布的关键因素,每齿进给量的变化将引起残余应力场形成机理的改变。     

钣金件快速精确加工中的激光切割工艺分析

针对δ0．5mm～δ6mm钣金件的结构特点,通过比较常用加工工艺和激光切割过程工艺．选出适合实际的优化方案。验证了不同切割参数对切割质量的影响。在工艺参数为：脉冲功率2．4kW、脉冲宽度约10ms、功率密度10^7W/cm^2的情况下,激光切割δ0．5mm～δ6mm钣金件获得了良好的切割质量,尺寸精度控制在误差（±100μm）范围内。工艺方案合理,生产率高。     

Analysis of GNSS clock prediction performance with different interrupt intervals and application to real-time kinematic precise point positioning

Continuous and timely real-time satellite orbit and clock products are mandatory for real-time precise point positioning (RT-PPP). Real-time high-precision satellite orbit and clock products should be predicted within a short time in case of communication delay or connection breakdown in practical applications. For prediction, historical data describing the characteristics of the real-time orbit and clock can be used as the basis for performing the prediction. When historical data are scarce, it is difficult for many existing models to perform precise predictions. In this paper, a linear regression model is used to predict clock products. Seven-day GeoForschungsZentrum (GFZ) final clock products sampled at 30 s are used to analyze the characteristics of GNSS clocks. It is shown that the linear regression model can be used as the prediction model for the satellite clock products. In addition, the accuracy of the clock prediction for different satellites are analyzed using historical data with different periods (such as 2 and 10 epochs). Experimental results show that the accuracy of the clock with the linear regression prediction model using historical data with 10 epochs is 1.0 ns within 900 s. This is higher accuracy than that achieved using historical data of 2 epochs. Finally, the performance analysis for real-time kinematic precise point positioning (PPP) is provided using GFZ final clock prediction results and state space representation (SSR) clock prediction results when communication delay or connection breakdown occur. Experimental results show that the positioning accuracy without prediction is better than that with prediction in general, whether using the final clock product or the SSR clock product. For the final clock product, the positioning accuracy in the north (N), east (E), and up (U) directions is better than 10.0 cm with all visible GNSS satellites with prediction. In comparison, the 3D positioning accuracy of N, E, and U directions with visible GNSS satellites whose prediction accuracy is better than 0.1 ns using historical data of 10 epochs is improved from 15.0 cm to 7.0 cm. For the SSR clock product, the positioning accuracy of N, E, and U directions is better than 12.0 cm with visible GNSS satellites with prediction. In comparison, the 3D positioning accuracy of N, E, and U directions with visible GNSS satellites whose prediction accuracy is better than 0.1 ns using historical data of 10 epochs is improved from 12.0 cm to 9.0 cm.     

Chatter stability and precision during high-speed ultrasonic vibration cutting of a thin-walled titanium cylinder

Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties. Specifically, thin-walled titanium (Ti) cylinders have received increasing attention for their applications as rocket engine casings, aircraft landing gear, and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio. However, the conventional cutting (CC) process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity, high strength, and low stiffness. Instead, high-speed ultrasonic vibration cutting (HUVC) assisted processing has recently proved highly effective for Ti-alloy machining. In this study, HUVC technology is employed to perform external turning of a thin-walled Ti cylinder, which represents a new application of HUVC. First, the kinematics, tool path, and dynamic cutting thickness of HUVC are evaluated. Second, the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model. HUVC can increase the critical cutting thickness and effectively reduce the average cutting force, thus reducing the energy intake of the system. Finally, comparison experiments are conducted between HUVC and CC processes. The results indicate that the diameter error rate is 10% or less for HUVC and 51% for the CC method due to a 40% reduction in the cutting force. In addition, higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC.     

纳米胶体射流抛光技术综述

纳米胶体射流抛光技术是一种超光滑表面加工方法,加工范围广,具有广泛的应用前景。本文回顾了纳米胶体射流抛光技术的提出以及目前的研究现状,最后对其今后的发展进行了简单展望。