高精度角度加工技术研究

激光陀螺不仅对合光棱镜角度精度有极高的要求,而且对角度和尺寸的一致性有严格的限制。为了加工这种高精度角度光学元件,提出通过手修工装母体复制出成盘加工工装,再复制出光学零件的加工方法,并分析了测角仪的测量精度、面形之间的匹配误差和平行的测量误差所引入的角度加工误差情况,提高了面形加工的平面度,避免了局部不规则现象,控制了温差对面形变化的影响。另外通过降低平行测量的误差以及减小闭合角度之间的叠加误差等具体措施也可以提高光学元件加工效率和角度加工精度。     

Electrical discharge machining of titanium alloy (Ti-6Al-4V)

In this study, the electrical discharge machining (EDM) of titanium alloy (Ti-6Al-4V) with different electrode materials namely, graphite, electrolytic copper and aluminium and process parameters such as, pulse current and pulse duration were performed to explore the influence of EDM parameters on various aspects of the surface integrity of Ti6Al4V. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and hardness analysis were performed. The experimental results reveal that the value of material removal rate, surface roughness, electrode wear and average white layer thickness are tendency of increase with increasing current density and pulse duration. However, extremely long-pulse durations such as 200 μs led to decrease MRR and surface roughness. Furthermore, the surface hardness is increasing due to the Ti₂₄C₁₅ carbides formed on the surface and obvious cracks are always evident in re-solidified layer when machining copper electrode. The surface crack densities and critical crack lines were determined for the tested material. The graphite electrode is beneficial on material removal rate, electrode wear and surface crack density but relatively poorer surface finish.     

Residual stresses and white layer in electric discharge machining (EDM)

The effect of dielectric liquid and electrode type on white layer structure in electric discharge machined surfaces has been studied in terms of retained austenite and residual stresses using X-ray diffraction method. The machining tests were conducted by using two different tool electrodes (copper and graphite) and dielectric liquid (kerosene and de-ionized water) under same operational conditions. The present work suggests that the surface is saturated with carbon irrespective of the tool electrode material when machining with kerosene dielectric liquid. But, retained austenite is formed on the surface due to carbon uptake from graphite tool electrode when machining with de-ionized water dielectric liquid. On the other hand, even though surface residual stresses increase with structural non-homogeneities in the white layer, no clear consequences have been observed in residual stress distribution beneath the white layer.     

On the dependence of circular Bragg phenomenon of noble metals helicoidally periodic sculptured thin films on visible and IR wavelengths

The concept of local homogenization in the visible and infra-red frequencies is used by estimating the permittivity dyadics of noble metals (Cu, Ag, and Au) in the form of thin film helicoidal bianisotroptic media (TFHBM). Despite the fact that the absorption transitions of dielectric to metal (percolation threshold) in metallic TFHBMs occur at long wavelengths at lower volumetric fraction of metallic particles, at these wavelengths the transition from dielectric to metal in composite relative permittivity scalar occurs at higher volumetric fraction of metallic particles. The latter is responsible for the increase of circular Bragg phenomenon.     

高速切削刀具磨损表面形态研究

对立方氮化硼刀具、陶瓷刀具、涂层刀具及超细晶粒硬质合金刀具高速铣削灰铸铁、调质45#钢和淬硬45#钢时的刀具磨损形态及其磨损机理进行观察和分析.结果表明:在高速切削条件下,不同刀具材料与工件材料匹配时的刀具磨损形态主要表现为前刀面磨损、后刀面磨损、微崩刃、剥落和破损等;高速切削时刀具的前刀面磨损形态不同于常速切削时的磨损形态,即磨损不表现为月牙洼的形式,而是表现为切削刃处磨损最大的斜面磨损形式,前刀面磨损区域随切削速度提高而减小,但磨损深度增大.研究结果可用于指导高速切削刀具材料的设计、合理选用及刀具磨损控制.     

Surface Formation of Single Silicon Wafer Polished with Nano-sized Al2O3 Powders

"Ice polishing single silicon wafers with nano-sized Al2O3 abrasives can be known as ice fixed abrasives chemical mechanical polishing (IFA-CMP). TAn abrasive slurry was made of nano-sized Al2O3 particles dispersed in de-ionized water with a surfactant and the slurry was frozen to form an ice polishing pad. Then polishing tests of blanket silicon wafers with the above ice polishing pad were carried out. The morphologies and surface roughness of the polished silicon wafers were observed and examined on an atomic force microscope. The subsurface damage was assessed by means of cross-section transmission electron microscopy. The surface chemical constituents of the polished silicon wafers were characterized using X-ray photoelectron spectroscopy in order to gain insight into the chemical mechanisms in the process. Scratch resistance of the single silicon wafer was measured by nanoscratching using a nanoindenter to explore the mechanical removal mechanism. The results show that a super smooth surface with an average roughness of 0.367 nm is obtained within 1000 nm￡1000 nm and there is a perfect silicon diamond structure without any microcracks in the subsurface. The removal of material is dominated by the coactions of ductile regime machining and chemical corrosion. In the end, a model of material removal of IFA-CMP is built."     

高速车削钛合金的硬质合金刀具磨损机理研究

使用硬质合金刀具材料进行钛合金(Ti-6Al-4V)的高速干车削试验.采用电子扫描显微镜(SEM)观察刀具的磨损形貌,通过能谱分析(EDS)分析磨损表面的元素分布,并对刀具的主要磨损机理进行了分析.研究结果表明,使用硬质合金刀具材料高速干车削Ti-6Al-4V时,刀具的磨损机理主要为粘结磨损、氧化磨损和扩散磨损.硬质合金刀具的氧化磨损主要发生在刀具前刀具和后刀面的磨损边缘区.由于车削过程中刀具前刀面的切削温度比后刀面的切削温度高,导致刀具前刀面的氧化磨损、粘结磨损和扩散磨损较后刀面严重.     

Vibration suppression in multi-tool ultrasonic machining to multi-external and parametric excitations

Ultrasonic machining （USM） is of particular interest for the machining of non-conductive, brittle materials such as engineering ceramics. In this paper, a multi-tool technique is used in USM to reduce the vibration in the tool holder and have reasonable amplitude for the tools. This can be done via dynamic absorbers. The coupling of four nonlinear oscillators of the tool holder and tools representing ultrasonic cutting process are investigated. This leads to a four-degree-of-freedom system subjected to multi-external and multi-parametric excitation forces. The aim of this work is to control the tool holder behavior at simultaneous primary, sub-harmonic and internal resonance condition. Multiple scale perturbation method is used to obtain the solution up to the second order approximations. The different resonance cases are reported and studied numerically. The stability of the system is investigated by using both phase-plane and frequency response techniques. The effects of the different parameters of the tools on the system behavior are studied numerically. Comparison with the available published work is reported.     

Accuracy control of three-dimensional Nd:YAG laser shaping by ablation

Improving the dimensional accuracy along the optical axis without decreasing the materials removing rate is a key issue in three-dimensional laser shaping. This paper presents a concept for performing three-dimensional laser shaping by directly using machining laser as the photo source of the non-contacting measuring device. Due to the high power measuring photo source and a 1.06 μm bandpass filter, the interference caused by the emission light of ablated surface can be effectively avoided, the delay time is not needed to be inserted between the laser pulse and the measurement. So the measurement will not decrease the material removal rate and productivity. By using this system, the shaping accuracy of 30 μm can be achieved at the removing rate of about 4.0×10⁻² mm³/sec for Si₃N₄ ceramic, both are much better than the results obtained before.     

振动辅助磁力研磨超硬精密Al2O3陶瓷管内表面试验研究

针对普通磁力研磨超硬精密Al2O3陶瓷管内表面加工效率低且纹理不均匀的问题,提出了一种振动辅助磁力研磨的技术.采用曲柄滑块振动机构和超声振动机构辅助磁力研磨,通过改变磁粒刷的运动轨迹,实现对陶瓷管内表面的高效精密加工.对比施加振动前后表面加工质量和加工效率的变化,利用单因素试验分析了振幅和振动频率对表面加工质量和加工效率的影响规律.试验结果表明:振动辅助磁力研磨技术实现了对超硬精密Al2O3陶瓷管内表面的高效精密加工,相比普通磁力研磨,经过50 min的加工,超声振动辅助磁力研磨效果最好,加工效率提高70%,表面粗糙度Ra由平均1.1μm降至0.03μm以下;采用高频率小振幅的振动更有利于加工效率和表面加工质量的同时提高.