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.     

Effect of laser-discrete-quenching on bonding properties of electroplated grinding wheel with AISI 1045 steel substrate and nickel bond

To improve the bonding strength between the nickel bond and the hub of the electroplated diamond grinding wheel, a hybrid technique was proposed to combine laser pre-quenching steel substrate and post-electroplating nickel. To validate the effectiveness of the proposed technique, AISI 1045 substrate was nickel-coated. The bonding properties between the electroplated nickel coating and substrate with or without laser-discrete-quenching were discussed comparatively by scratch, indentation, and thermal shock tests. The results show that the pre-quenching treatment leads to phase transformation of AISI 1045 microstructure from the mixed pearlite and ferrite phases into the martensitic phase. Since the martensitic phase is characterized as a high corrosion resistance, the interface of substrate/coating is smooth and flat in the pre-quenched zone, and the coating is bonded well with the steel substrate. In contrast to the steel substrate without pre-quenching treatment, the proposed technique significantly enhanced the bonding strengths of the electroplated nickel-coating. On one hand, the average hardness of electroplated nickel-coating on the laser pre-quenched zone is increased by 18.7%, and the scratch depth with the same load become narrower and shallower. On the other hand, the coefficient of friction (CoF) and the vibration amplitude are reduced, and the coating is bonded effectively with the substrate to inhibit the crack initialization at the interface. This prevents effectively the coating from peeling off and improves significantly the thermal shock resistance property.     

ELID超精密镜面磨削过程中磨削力变化规律的试验分析

通过对ＥＬＩＤ磨削过程中磨削力变化规律的试验分析,并对试验结果进行了讨论,得出ＥＬＩＤ磨削力与磨削深度、磨粒粒度、磨削时间等之间的变化规律。     

磨粒磨损对砂带磨削TC17表面完整性的影响研究

砂带磨粒磨损直接影响磨削表面质量进而影响构件综合服役性能.以表面完整性为评估指标,对砂带磨损前后钛合金的表面加工质量进行了试验研究,揭示了砂带磨粒磨损对磨削TC17表面粗糙度、残余应力和表面硬度的影响规律及机制.结果表明,磨粒磨损后由于高度均匀化、单位面积切削磨粒数增加、磨削深度减小,使得表面粗糙度减小、纹理均匀细腻,...     

K417合金缓进磨削烧伤表面形貌及形成机理

本文在严格控制的实验条件下,建立了磨削弧区温度同试件表面烧伤色之间的对应关系;并以扫描电镜(SEM)、电子探针(EPA)等较为先进的测试仪器为手段详细研究了K417镍基铸造高温合金缓进磨削中表面为正常、淡黄、黄褐、紫褐以及紫黑等深浅不同的色斑时诸试件表面形貌特征和对应的砂轮表面形貌特征,揭示了K417材料缓磨中表面形貌的变化特征及其形成机理。测试结果表明,K417材料缓磨表面出现烧伤色斑时,磨粒与试件材料之间存在粘结现象;试件表面出现粘结滞留的涂覆物。随表面烧伤色层次的加深,磨粒与试件材料之间的粘结越普遍、越严重,试件表面涂覆程度亦越强烈。当出现紫黑色斑时,表面还伴有微裂纹出现。