基于单颗粒模型的航发叶片砂带磨削微观仿生锯齿状表面形成及实验

基于鲨鱼皮衍生出来的微观仿生表面被广泛应用于机翼等航空零部件的设计中，对于提高航空零部件的疲劳寿命、气流动力性等服役性能具有重要作用。砂带磨削能实现零部件表面的高完整性要求的加工，故常用于叶片、整体叶盘等复杂曲面的精密磨削，且能实现微观表面形状，但目前缺乏砂带磨削微观表面的系统研究从而难以实现其精确控制。首先，分析了微观仿生锯齿状表面的典型结构特征，基于单颗粒砂带磨削模型，研究了单颗粒砂带磨削去除机理；然后，建立了砂带磨削多颗粒参数化数学模型，提出了微观仿生锯齿状表面砂带磨削方法；最后，以钛合金叶片型面为对象，搭建以钛合金为典型材料的微观仿生锯齿状表面砂带磨削基础实验平台，进行仿生表面的实验验证。通过对磨削后叶片的表面微观形状参数进行检测，结果表明通过砂带磨削方法实现的微观仿生锯齿状表面以锯齿形沟槽为主，其中沟槽的宽度在2.5~8 μm之间、平均值为4.91 μm，沟槽的高度在3.5~9 μm之间、平均值为5.91 μm，沟槽的夹角在28°~68°之间、平均值为42.3°，验证了微观仿生锯齿状表面砂带磨削的可行性。     

低温度系数SmCo磁钢类精密零件加工技术

Sm Co磁钢属于稀土永磁材料,总体磁性能高,矫顽力大,抗干扰能力强;同时,温度系数低,磁性能更稳定。但这种材料零件脆性大,切削性能差,在加工或碰撞中容易掉渣、崩裂;加工中往往更难以装夹与定位。针对这些问题,本文从加工技术、工艺方法和加工参数等方面做了一定的分析与研究,并取得了较好的效果。     

Development of microstructural inhomogeneity in multi-pass flow forming of TA15 alloy cylindrical parts

Revealing the development of microstructural inhomogeneity in the multi-pass flow forming of titanium alloy components is of great significance to the microstructure control and property tailoring. To this end, the microstructural inhomogeneity of TA15 alloy spun cylindrical parts was analyzed based on the deformation history. The results indicate that the material underwent significant compressive strain in the normal direction (ND), tension strain in the rolling and circumferential directions (RD and CD), while tension strain in the CD is slightly small due to the limited material flow in this direction. These strain characteristics make the microstructure, especially the primary α (α_p), present different morphologies in the different planes of the part. Meanwhile, the combined effects of inhomogeneous deformation and temperature distribution in the ND also cause the inhomogeneity of microstructure morphology and parameters in this direction. Quantitative analyses show that with the forming pass increasing, the aspect ratio of α_p increases most in the normal-rolling plane, then in the normal-circumferential plane and least in the circumferential-rolling plane, whereas α_p content decreases in an opposite trend. Along the ND, the aspect ratio and content of α_p is relatively high in the outer and inner surface areas but lowest in the central area, and these inhomogeneous characteristics can be gradually diminished with the forming pass increasing. Furthermore, the variation of hardness inhomogeneity factor indicates that a four-pass forming with the total reduction ratio of 63% could obtain a homogenous microstructure along the ND of the TA15 alloy spun cylindrical part.     

构架式可展开抛物柱面网状天线结构设计

针对具有大尺度抛物柱状反射面需求的空间可展开天线,提出一种基于四棱柱折展模块的构架式可展开抛物柱面网状天线,依靠模块驱动组件实现天线联动展开。把抛物面天线工作表面的拟合方法拓展到抛物柱面天线,采用工作面拟合圆均等网格划分径向投影获取天线支撑桁架设计的关键节点。柔性网状反射面采用双层索网结构形式,提出与前索具有较好对称性的背索网悬链线设计,前、后索网节点由支撑立柱间拟合圆弧均等分径向分别投影到抛物线段和悬链线圆弧上获取,根据前后索网节点建立索网拓扑构型,基于非线性有限元法对索网预张力进行设计迭代,获得抛物线维索网预张力与其均值的最大误差率为12.3%及柱面维索网预张力与其均值的最大误差率为7.6%的优化结果。研制了机械口径12 m×12 m样机,多次展开获得2 mm RMS以内的形面精度,验证了构架式可展开抛物柱面网状天线较优的展开性能和形面精度保持性能。     

Robotic Instrument for Grinding Rocks Into Thin Sections (GRITS)

We have developed a rock grinding and polishing mechanism for in situ planetary exploration based on abrasive disks, called Grinding Rocks Into Thin Sections (GRITS). Performance characteristics and design considerations of GRITS are presented. GRITS was developed as part of a broader effort to develop an in situ automated rock thin section (ISARTS) instrument. The objective of IS-ARTS was to develop an instrument capable of producing petrographic rock thin sections on a planetary science spacecraft. GRITS may also be useful to other planetary science missions with in situ instruments in which rock surface preparation are necessary.     

基于四轴数控机床面齿轮磨削方法

为了制造出高精度硬齿面面齿轮,提高刀具的通用性并简化机床结构,提出一种基于四轴数控机床和盘形砂轮多线包络磨削面齿轮的加工方法。设计顶刃带有圆弧的盘形砂轮对插齿刀齿面进行仿形。建立盘形砂轮磨削面齿轮的数学模型,规划盘形砂轮的刀位轨迹。通过数值模拟方法探究刀具的顶刃圆弧半径和转矩角对齿面包络残差的影响规律。结合选用的四轴数控机床结构,推导盘形砂轮磨削面齿轮的数控运动规律,并在VERICUT软件中进行仿真加工。将仿真模型与理论齿面进行对比分析,得到齿面偏差的最大值为-4.3~4.7 μm,结果验证了所提出加工方法的正确性,也证明了根据齿面包络残差的影响规律选用合适的刀具加工参数,可以保证面齿轮齿面精度的同时提高加工效率。     

ELID成形磨削实验研究与表面粗糙度预测

为了探究ELID成型磨削中磨削参数和电解参数对表面粗糙度的影响规律,基于未变形切屑厚度模型,考虑砂轮上磨粒出刃高度的随机性以及ELID磨削中氧化膜的影响,建立了针对ELID磨削的表面粗糙度预测模型。单因素实验研究了ELID成形磨削电源参数对表面粗糙度的影响规律,并探讨了电解电流与氧化膜厚度之间的关系。全因子实验以工件转速、砂轮转速和进给切深为影响因素,研究了磨削参数对表面粗糙度的影响规律,并对预测模型进行了验证。结果表明:磨削参数中,其他条件一定时,表面粗糙度随砂轮转速的增大而减小,随工件转速和切深的增大而增大;同时对于粗糙度的预测误差达到了8.75%,预测模型有效可靠。     

航空发动机叶片叶缘随形磨抛刀路规划

航空发动机叶片是整机核心零件,其制造量占到30%以上。叶片叶缘具有大弯扭复杂曲面、薄壁圆角半径微小渐变、精度要求苛刻等特征,末端工序磨抛的精度和品质直接决定整机的性能与寿命。人工仍然是叶片叶缘磨抛的主要手段,然而粉尘危害健康、经验依赖性强、零件一致性差等不足决定了自动化磨抛是必然趋势。叶片叶缘自动化磨抛多采用砂轮横磨或纵磨的刀路规划方式,存在刀路不连续且分行密集、力控制困难等不足,易造成叶缘局部过切,难以保证圆角轮廓创成。为此,建立了砂带包络叶缘的螺旋进给力控磨抛工艺,提出了面族与复杂曲面高阶切触的随形磨抛路径规划方法,实现了叶片叶缘的宽行高效磨抛。首先对叶缘区域进行横磨刀路规划,然后依照圆弧拟合曲线原理进行高阶切触式包络段再规划,最后进行横纵混合磨抛路径规划实现螺旋式连续进给。针对航空发动机叶片开展仿真和实验验证,结果表明所提出的方法相比于传统的横磨或纵磨方法,可将刀触点减少78.8%,轮廓精度由-0.06~+0.07 mm提高到-0.015~+0.05 mm,表面粗糙度由R_a>3.2 μm提高到0.175 μm,并且有效保证了叶缘轮廓形状,避免了过切现象。     

Profile error compensation in precision grinding of ellipsoid optical surface

Optical glass elements with the ellipsoidal surface are used in many critical aerospace instruments, such as satellites, telescope and cameras. Their optical performance is mainly affected by profile accuracy and surface quality. In this paper, a rectangular ellipsoid surface is precisely ground on a BK7 optical glass blank by grating scanning grinding path with a three-axis CNC precision surface grinder. A profile error compensation procedure for ellipsoidal grinding is proposed based on the error analysis about the primary error sources in the XY and YZ projection planes during the grinding process. The mathematical prediction models of the wheel arc profile error, the measurement and wear error of the grinding wheel radiuses are established. By applying the proposed error compensation procedure, the profile accuracy of the ellipsoidal surface was improved from 4 μm to 2 μm in the XY plane, and improved from 15 μm to 5 μm in the YZ plane.     

Performance evaluation of creep feed grinding of γ-TiAl intermetallics with electroplated diamond wheels

This paper evaluates the performance of creep feed grinding γ-TiAl intermetallic (Ti-45Al-2Mn-2Nb) using electroplated diamond wheels. Firstly, a comparative analysis with the grinding results by using electroplated CBN wheels was conducted, mainly involving abrasive wheel wear behavior and maximum material removal rate below surface burn limit. It was found that the diamond wheel would produce much better grinding results including lower wheel wear rate and higher maximum material removal rate. Then the surface integrity obtained at different level of material removal rate was characterized with the utilization of the diamond wheel. The poor ductility of this γ-TiAl intermetallic material was found to have a marginal effect on the surface integrity, as no severe surface defects such as material pullout were generated during the stable wheel wear stage. For the involved operating parameters, a deformation layer was produced with ∼10 μm or more in thickness depending on the material removal rate used. Meanwhile, a work-hardened layer extending to more than 100 μm was produced with a maximum microhardness of above 520 HV_0.05 (bulk value 360 HV_0.05). The residual stress remained compressive, with a value of above −100 MPa and even up to −500 MPa for an elevated material removal rate. Shearing chip was the main chip type, indicating good wheel sharpness in the grinding process.