基于Marangoni界面效应的数控化学抛光去除函数的研究

 利用基于Marangoni界面效应对化学抛光去除函数的理论及实验进行研究,提出采用湿法化学抛光（刻蚀）方法为大口径高精度光学元件的加工提供新的解决途径。介绍了Marangoni界面效应及其验证实验,运用WYKO轮廓仪对熔石英基片局域刻蚀前后的粗糙度进行检测,结果表明,粗糙度基本无变化,刻蚀前后粗糙度分别为0.72 nm和0.71 nm。基于Preston假设, 建立了数控化学抛光理论模型,运用WYKO干涉仪观察实验现象可知,化学抛光刻蚀曲线基本上成平底陡峭的去除函数曲线,小磨头抛光是倒置的仿高斯函数曲线。     

避免核函数导数的二阶导数核近似方法的修正

采用核近似光滑粒子流体力学SPH（Smooth Particle Hydrodynamics）方法计算一元函数二阶导数和多元函数二阶偏导数,对避免核函数导数算法进行了改进,提出了对核函数光滑长度处处具有o（h）精度的算法,并分别推导出一元和多元函数的修正公式。用不同的粒子间距和不同的光滑长度进行了二阶导数的计算和热传导问题的模拟,进行了修正方法与原方法的误差分析。结果表明,本文提出的修正措施在提高精度、减少误差及加快收敛速度等方面起到很大的作用。     

射流抛光多相紊流流场的数值模拟

 理论分析了射流抛光的紊动冲击射流特点,构建了射流抛光的垂直冲击射流模型和斜冲击射流模型。根据射流抛光冲击射流的特点,比较各种流体模型后,采用RNG k-e 模型应用于射流抛光模型的计算。利用计算流体力学理论的二阶迎风格式对抛光模型方程离散,用SIMPLEC数值计算方法对射流抛光过程的紊动冲击射流和离散相磨粒分布进行数值模拟,得到了射流抛光过程的连续流场和离散相磨粒与水溶液的耦合流场,同时计算出了抛光液射流在工件壁面上的压力、速度、紊动强度、剪切力分布和磨粒体积质量分布,分析了垂直射流抛光模型和斜冲击射流抛光模型紊流流场的特点。     

气囊抛光工艺参数的正交实验分析

针对平面光学零件,以抛光去除率和表面粗糙度为考核指标,应用正交试验法分析了气囊抛光过程中的主要工艺参数,包括抛光工具气囊的压缩量、气囊转速、气囊内部充气压力、抛光液的浓度对抛光去除效率和表面粗糙度的影响规律。结合气囊抛光的抛光机理对其进行了分析,根据实验结果对工艺参数进行了优化,并进行了综合参数的气囊抛光加工实验,获得了超精密光滑的表面。     

中小口径双非球面数控抛光技术研究

针对口径Φ62 mm双凸非球面透镜,进行了数控研磨和抛光技术研究.提出了规范性的加工工艺流程,实现了中小口径双非球面元件的高效、快速抛光.根据计算机控制光学表面成型技术,采用全口径抛光和小抛头修抛的两步抛光法,在抛光中对其面形误差进行多次反馈补偿,使被加工零件表面的面形精度逐步收敛.最终两面的面形精度均小于0.5 μm,中心偏差小于0.01 mm,满足了光学系统中对非球面元件的精度要求,并且在保证有较高面形精度和较好表面光洁度的同时,解决了双非球面中心偏差和中心厚度难以控制的加工技术难题.     

基于MHD的磁射流抛光中流场的分析与模拟

从理论上分析了磁射流抛光中的磁场与流场的相互作用,构建了磁射流抛光的冲击射流模型,基于磁流体动力学对磁射流抛光过程的紊动冲击射流进行数值模拟,得到了磁射流抛光过程的连续流场和射流在工件壁面上的压力、速度、紊动强度分布。通过比较射流抛光和磁射流抛光的数值计算结果,分析了磁流变效应对射流稳定性的影响,从射流的流场、速度、紊动强度等方面分析射流在磁场中稳定的原因。     

永磁流变抛光纳米精度非球面技术研究

利用永磁流变抛光技术制造高精度光学元件是一项极具前景的超精密制造技术。对一台五轴联动磁流变数控抛光系统的结构特点、功能特色及关键部件的设计进行了阐述。在此基础上,结合装置开展基础试验,对磁流变抛光过程中的主要控制参量如抛光轮下压量、抛光轮速度等对材料去除特性的影响进行了研究。开展了磁流变抛光对提高工件(K9玻璃)表面粗糙度效果的抛光试验,结果证明该套系统具有良好的磁流变抛光特性,抛光23min后工件表面粗糙度降低到0 6739nm。     

抛光对光纤连接器回波损耗的影响

分别选用氧化铝和氧化硅材料的抛光砂纸,在施加不同抛光压力、抛光时间,以及抛光助剂等工艺条件下,实验研究了抛光对连接器回波损耗的影响规律。通过实验发现:氧化铝砂纸干式抛光使光纤连接器的回波损耗仅保持在32～38dB之间;氧化硅砂纸干式抛光会造成光纤端面污损,使得连接器的回波损耗降低到20dB以下;氧化铝与氧化硅砂纸湿式抛光均可使光纤连接器的回波损耗提高到45～50dB,但氧化铝砂纸湿式抛光会造成80nm以上的光纤凹陷。因此,制作高回波损耗的光纤连接器应优先选用氧化硅砂纸湿式抛光工艺,抛光时间应控制在20～30s。     

Stabilization of gamma alumina slurry for chemical-mechanical polishing of copper

Stabilization of gamma-alumina suspension for chemical-mechanical polishing (CMP) of copper was investigated. Citric acid and poly(acrylic acid) (PAA) (M(w)=5000) were used as dispersant. The stability of suspension was evaluated from the changes in viscosity, particle size and zeta potential. It appears that metastable gamma-alumina mainly due to its high specific surface area and to the presence of aluminol groups on its surface is progressively transformed to bayerite (beta-Al(OH)(3)) by hydration procedure. Citric acid molecules were adsorbed onto gamma-alumina surface effectively and exhibited the excellent hydration inhibition effect. Although citrate-alumina surface complexes give barrier to the flocculation, the repulsion potential is based mainly on the electrostatic repulsion, thereby steric hindrance caused by the adsorption of these small molecules is very weak. The electrosteric repulsion, which provides more effective dispersion stability than electrostatic repulsion force, can be expected by using polyelectrolyte such as PAA; however, adsorbed layers of PAA onto solid/liquid interface are loosely formed. Therefore, a large amount of PAA was required to inhibit the surface hydration of gamma-alumina suspension, thereby the excess addition of PAA decreased the electrosteric repulsion and re-bridging of the dispersant between particles caused an increase in suspension viscosity. Therefore, synergistic effect can be expected in mixed dispersant system of citric acid and PAA, since small citric acid molecules are adsorbed faster than PAA, inhibiting the progress of surface hydration, and then adsorbed PAA layers exhibit the effective electrosteric repulsion interaction between particles with a small amount compared with PAA alone. It was revealed that the gamma-alumina slurry dispersed by mixed dispersant exhibited the improved removal rate of Cu layer by CMP polishing test.     

Laser polishing of additive manufactured Ti alloys

Laser-based additive manufacturing has attracted much attention as a promising 3D printing method for metallic components in recent years. However, surface roughness of additive manufactured components has been considered as a challenge to achieve high performance. In this work, we demonstrate the capability of fiber laser in polishing rough surface of additive manufactured Ti-based alloys as Ti-6Al-4V and TC11. Both as-received surface and laser-polished surfaces as well as cross-section subsurfaces were analyzed carefully by White-Light Interference, Confocal Microscope, Focus Ion Beam, Scanning Electron Microscopy, Energy Dispersive Spectrometer, and X-ray Diffraction. Results revealed that as-received Ti-based alloys with surface roughness more than 5 µm could be reduce to less than 1 µm through laser polishing process. Moreover, microstructure, microhardness and wear resistance of laser-polished zone was investigated in order to examine the thermal effect of laser polishing processing on the substrate of additive manufactured Ti alloys. This proof-of-concept process has the potential to effectively improve the surface roughness of additive manufactured metallic alloy by local polishing method without damage to the substrate.