五轴联动高速加工螺旋桨叶轮的关键技术研究

为提高整体叶轮的五轴高速加工精度和加工效率,利用B样条方法通过调整偏离权和光顺项权得到理想的二阶连续的桨叶曲面.把叶轮的CAD几何模型导入到CAM加工模块中,通过对五轴高速加工工艺规划的研究和加工参数的选择,计算出叶轮的加工刀轨路径,并通过后置处理得到符合MIKRONUCP800数控机床的NC代码并加工出叶轮产品.     

TC11合金热变形特性及变形参数对组织的影响

通过热模拟压缩试验,分析了TC11合金的高温变形特性及不同变形参数下的组织演化规律,用非线性回归方法建立了TC11合金Kumar型材料的本构关系,得出了TC11合金的高温流变曲线基本呈流变软化特征的结论;最后应用MSC,Autoforge软件对TC11合金某型号涡轮盘的等温锻造工艺进行了模拟式工艺设计,验证了TC11合金材料本构关系的工程适用性.     

基于主动轮廓方法提取雾化锥角

基于主动轮廓方法（ACM）原理,将ACM延伸开发应用到雾化锥角的测量领域.经过调试,ACM成功捕捉到了雾锥边界以及喷雾矩在喷口后一定位置处出现的收缩特征,准确地获得了雾化锥角.验证结果显示:ACM获得的雾化锥角数值与阴影法测量值之间的相对误差小于1.5%.基于ACM提取雾化锥角方法的应用可以在保证实验结果准确度的同时降低工程应用成本.      

基于LODTM的大口径太赫兹波束控元件确定性超精密加工

为解决大口径太赫兹波探测系统束控元件加工精度差、效率低的难题,本文提出了一种利用LODTM数控光学加工机床进行SPDT(单点金刚石车削)制备太赫兹波束控元件的方法。该方法属于确定性加工范畴,通过使用单晶金刚石刀具进行超精密切削加工,可直接得到适用于太赫兹波段的高面形精度的反射及透射类元件。针对铝基金属材料进行了加工工艺实验,得到了口径Φ300mm的太赫兹雷达主反射镜;并利用精密坐标测量技术对主反射镜的面形精度进行检测,其检测结果优于设计指标。实验表明,基于LODTM确定性超精密加工得到的太赫兹波束控元件具有面形精度高、表面光洁度好等优点,可实现太赫兹波探测系统的高精度和低成本目标。     

基于CATIA生成数控加工路径的机器人纤维铺放轨迹规划

纤维铺放轨迹规划是纤维铺放成型中控制加工路径的关键步骤,直接影响复合材料构件的成型精度和铺放效率。本文基于成熟的商业化CATIA数控加工编程软件进行纤维铺放轨迹计算,获取待处理的加工路径,利用矢量补充和格式转换算法解决了铺放轨迹信息与FANUC机器人兼容性差的问题;借助插值算法求出了输送点和剪断点,补充了铺放轨迹信息,进而得到了完整的铺放信息,缩短了开发周期。在基于FANUC机器人的铺放装备上对某飞机舱门进行铺放实验,验证了基于CATIA数控加工技术的纤维铺放轨迹生成方法具有可行性,铺放轨迹结束点位置误差及轨迹间距误差都在±0.5mm之内。     

飞机结构件内型转角一体加工刀轨生成方法

针对飞机结构件内型转角传统的分开加工易产生接刀痕以及转角处进给方向和刀具接触角急剧变化引起的切削力增大和刀具振动增强的问题,提出了飞机结构件内型转角一体加工工艺及其刀轨生成方法。该方法对内型和转角进行组合加工,首先计算满足接触角均匀变化的精加工所需余量和精加工刀轨,以及后续刀轨加工区域;其次在后续加工转角时通过采用最大和恒定接触角相结合的原则,循环分层加工转角,改善了加工状况。在刀轨连接处使用变螺旋曲线,保证了曲率的连续变化,减小了机床振动。切削实验表明:该刀轨改善了加工过程中的切削力和刀具振动,提高了工件表面的加工质量。     

航空整体结构件加工变形有限元数值仿真

加工变形是航空整体结构件数控加工领域普遍存在的问题.选取典型航空整体结构件,基于有限元法研究了毛坯初始残余应力对于加工变形的影响,仿真结果与试验结果一致;对残余应力引起的加工变形特点进行了分析,基于不同加工路径对航空结构件加工变形进行了有限元数值仿真,结果表明,对于单一残余应力引起的加工变形分析,可以忽略加工路径的影响.考虑铣削力与残余应力的耦合作用,建立了残余应力、铣削力的耦合力学模型,给出了具体仿真流程,针对不同加工路径进行有限元仿真,研究了铣削力对于残余应力分布及最终加工变形的影响.     

三维地形不变性特征描述及其在地形匹配中的应用

 针对实时地形图与基准地形图之间存在旋转、缩放和平移等相似变换的地形匹配问题,提出一种基于地形不变性特征描述的匹配方法。分析了地形的凹凸特征,根据三维地形表面的局部极值点相对位置分布稳定的特点,采用极值点相对位置归一化表示的方法构造了地形的不变性特征向量,基于二维地形特征向量间的距离比较,实现了适应相似变换的地形匹配。该地形描述与匹配方法不依赖于地形的绝对尺度值,仿真实验表明了方法具有较好的实用性,是解决导航定位中存在缩放变换的地形匹配的有效方法。     

Changes in the Structure of Comet Nuclei Due to Radioactive Heating

The initial structure of a comet nucleus is most probably a homogeneous, porous, fine-grained mixture of dust and ices, predominantly water. The water ice is presumably amorphous and includes considerable fractions of occluded gases. This structure undergoes significant changes during the early evolution of the nucleus at large heliocentric distances, due to internal radiogenic heating. Structural changes occur mainly as a result of gas flow through the porous medium: the gas pressure that builds up in the interior is capable of breaking the fragile structure and altering the pore sizes and porosity. These effects are modeled and followed numerically, testing a large number of parameters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modeling and Experimental Investigation of Laser Drilling with Jet Electrochemical Machining

As two kinds of defects, recast layers and spatters, commonly accompanied by laser-drilled holes always prevent the laser drilling technique from extending its applications in aerospace and aircraft industries, therefore, a novel hybrid process incorporating laser drilling with jet electrochemical machining (JECM-LD) has been developed to solve these problems as well as improve the overall quality of laser-drilled holes. It is executed by directing an electrolyte jet coaxially aligned with a laser beam onto the workpiece surface. During the process, the electrolyte jet produces electrochemical reaction with the surface material, effective cooling of it and carries away the process scraps. A two-dimensional mathematical model is proposed to describe the shape of the holes machined by JECM-LD. The model is verified through comparison between the results from simulation and those from experiments conducted on the test pieces made of 321 stainless steel 0.5 mm thick processed by the pulsed Nd:YAG laser at second harmonic wavelength. An examination of the experimental results under an optical microscope discovers that, by contrast with the laser drilling in air, the JECM-LD has effectively removed the recast layers and spatters, but its efficiency dropped by about 30%.