基于动态Bayesian网络的叶片加工质量监控与溯源

 针对叶片加工过程中质量精度不高的问题,提出了基于动态Bayesian网络的叶片加工质量监控与溯源方法.利用动态Bayesian网络建立起叶片加工工序间的相互联系,实现对整个加工过程的控制.基于Bayesian网络对影响加工工序的因素集建立因果联系,采用多元统计过程控制中的T²控制图完成对各工序影响因素集的监控.进行误差溯源时,根据Bayesian网络建立的因果关系对失控样本的T²统计量依据原因变量进行误差分解,并构建各分解变量的控制限,将其作为误差源判定的条件.通过对某叶片加工过程的仿真,验证了所提方法的有效性.     

Phase Residual Estimations for PCVs of Spaceborne GPS Receiver Antenna and Their Impacts on Precise Orbit Determination of GRACE Satellites

In-flight phase center systematic errors of global positioning system(GPS) receiver antenna are the main restriction for improving the precision of precise orbit determination using dual-frequency GPS.Residual approach is one of the valid methods for in-flight calibration of GPS receiver antenna phase center variations(PCVs) from ground calibration.In this paper,followed by the correction model of spaceborne GPS receiver antenna phase center,ionosphere-free PCVs can be directly estimated by ionosphere-free carrier phase post-fit residuals of reduced dynamic orbit determination.By the data processing of gravity recovery and climate experiment(GRACE) satellites,the following conclusions are drawn.Firstly,the distributions of ionosphere-free carrier phase post-fit residuals from different periods have the similar systematic characteristics.Secondly,simulations show that the influence of phase residual estimations for ionosphere-free PCVs on orbit determination can reach the centimeter level.Finally,it is shown by in-flight data processing that phase residual estimations of current period could not only be used for the calibration for GPS receiver antenna phase center of foretime and current period,but also be used for the forecast of ionosphere-free PCVs in future period,and the accuracy of orbit determination can be well improved.     

柔性电极电火花强化钛合金表面性能

采用旋转的柔性铜电极与钛合金表面在高频脉冲电源的作用下进行电火花表面强化,使空气中的氧等元素在放电形成的高温高压条件下与钛合金表面发生反应。结果表明:该试验条件下可以使钛合金表面硬度相对基体提高237%～399%;强化层厚度达到21～157μm;通过能谱分析(Energy dispersive spectrometer,EDS)及X射线衍射(X-ray diffraction,XRD)分析表明,在钛合金表面生成了钛的氧化物等强化物质和钛与铜、锌等的合金;强化表面不存在明显的传统放电蚀除凹坑,但有明显机械刮磨涂覆痕迹,同时单脉冲放电能量被分散,使得表面粗糙度值的提高量较小且可控;在氢氟酸和硝酸混合溶液中,强化层具有较高的抗腐蚀能力,经过点面磨损测试表明,强化层表面耐磨性能相对于基体表面有显著提高。经强化,能够获得具有良好耐磨性、抗腐蚀性、表面良好的钛合金。     

Electrochemical machining on blisk channels with a variable feed rate mode

Electrochemical machining (ECM) is an economical and effective method for blisk manufacturing and includes two steps: channel machining and profile machining. The allowance distribution after the channel machining will directly affect the profile machining. Therefore, to improve the uniformity of allowance distribution in the machining of channels, a method that incorporates a variable feed rate mode is developed. During the machining process, the feed rates are dynamically changed according to the needs of the side gap at the different feed depths. As a result, the side gaps at the different feed depths vary, contributing to a decrease in the allowance difference. In this study, the dissolution processes of a blisk channel are simulated using different feed rates, and prediction profiles are obtained. Based on the prediction profiles, the relationship among the feed rate, feed depth, and side gap is established. Then, the feed rates at different feed depths are adjusted according to the relationship. In addition, contrast experiments are conducted. Compared with blisk channel ECM using a constant feed rate of 1 mm/min, using the variable feed rate decreases the allowance differences in the convex and concave parts by 62.2 % and 67.4 %, respectively. This indicates that using the variable feed rate in the ECM process for a blisk channel is feasible and efficient.     

Theoretical and Experimental Investigation of Laser Milling Assisted with Jet Electrochemical Machining

In laser milling assisted with jet electrochemical machining （LMAJECM）, the source of energy is a pulsed laser beam aligned coaxially with a jet of electrolyte, which focuses optical energy on the surface of work- piece. The impact of jet of electrolyte develops a state-of-art work to perform operations such as electrolytic etch- ing, effective cooling, and transportation of debris. Therefore, a special jet cell is designed to obtain stable jet as to be a kind of noneontact tool, i. e. , electrode. According to the theoretical model of on-off pulse time process, laser machining and electrolytic anodization are simulated by finite element analysis （FEA） method. Grooves on a 0.5 mm thick 321 stainless steel sheet produced by LMAJECM is performed with pulsed Nd：YAG laser at the second harmonic wavelength. Compared with laser milling under ambient atmosphere conditions, the recast layer and burrs are effectively diminished. And the accuracy of depth is dedicated to laser milling, whilst that of width is dominated by jet electrochemical machining. It is demonstrated that LMAJECM can be a highly potential approach for fabricating 3-D micro components.     

整体叶盘电解加工阴极修正方法与试验

电解加工是航空发动机整体叶盘制造的主要技术之一,阴极修正是该加工技术的重要环节。为了提升阴极修正精度,提出了恒采样点空间法向修正方法。该方法将阴极型面设计、加工误差分析、工具阴极修正统一至阳极采样点空间法向的一维坐标系中,将复杂的三维曲面修正简化为离散的一维修正,消除了加工误差与修正量的错位。以某整体叶盘为例,在自行研制的整体叶盘型面电解加工机床上开展工具阴极修正试验,采用三坐标测量机对修正前后的加工样件进行检测,经过一次修正,叶片电解加工精度由0.25mm提高至0.04mm,试验结果表明该阴极修正方法合理有效,具有较强的可行性。     

钛合金宽弦空心风扇叶片数控切削加工关键技术

数控切削加工是最终保证钛合金宽弦空心风扇叶片制造精度的重要技术手段。分析了采用超塑成形/扩散连接技术制作的钛合金宽弦空心风扇叶片结构特征以及毛坯状态,指出了后续的数控切削加工应突破复杂曲面结构测量、加工变形控制以及切削加工误差补偿等关键技术。提出了开发集测量、分析和加工为一体的数控切削加工集成系统的研究思路,可为实现钛合金宽弦空心风扇叶片加工精度的精确控制提供指导。     

改善机床运动的五轴刀轨光顺方法

建立了五轴数控加工刀轨光顺优化模型,改善了线性插补方式下拐角过渡运动中的机床加速度情况。考虑了5个轴加速能力的差异,以轴加速度比,即轴实际达到的最大加速度与其允许最大加速度的比值,来衡量轴的加速度情况,以5个轴加速度比的平方平均数在整体上衡量机床的加速度情况,降低该值可提高机床运动平稳性。采用最短距离线法在初始刀轨的各切触点处建立了刀轴偏航角和俯仰角的可行域,使光顺后的刀轨满足残高和无过切要求。实例表明:该方法可有效光顺五轴数控加工刀轨,改善机床加速度情况,提高机床运动平稳性。      

飞机结构件轮廓特征加工自动分区算法

作为飞机结构件重要组成部分,轮廓特征包含大量复杂曲面,且与工艺凸台等干涉物相连接,使得轮廓特征编程需综合考虑复杂曲面及干涉物信息,在自动编程模式下,轮廓特征编程仍严重依赖人工经验,其编程周期占结构件编程周期的40%以上,严重影响了结构件编程效率。针对该问题,提出了一种综合考虑复杂曲面及干涉物信息的轮廓特征加工自动分区方法,基于相邻轮廓面连接边属性及凸边约束原则对轮廓面进行初分区,依据干涉物信息构建虚拟边界,并基于虚拟边界对轮廓面初分区结果进行横向和纵向加工区域划分,通过对划分区域进行合并得到轮廓特征加工分区结果。根据提出的方法开发了飞机结构件轮廓特征加工自动分区系统,经过多项典型飞机结构件测试,该方法稳定可靠,可为轮廓特征加工程序编制提供支撑。     

基于经验学习的空间机器人精细抓捕方法

机器人在空间环境下完成对复杂形状物体的精细操作,要求其具有较强的自主操作规划能力.从学习人类经验出发,模仿人类经验生成来建立经验数据库,提出有效的物体分类方法,在物体类别基础上,识别同类物体的可抓取区域,并提出“单拇指”姿态规划方法,将对物体的操作经验泛化到同类物体的操作规划中.试验证明了算法的有效性.