确定性光学加工中抑制边缘效应的一种方法(英文)

在确定性光学抛光过程中,当加工到工件边缘时由于工艺条件发生变化会产生边缘效应,导致加工效率降低和面形误差增大.针对这种情况,提出了一种可修正边缘现象的球形工具抛光技术,其去除函数稳定性较好,形状趋于高斯分布且束径也较小,对修正边缘现象以及局部面形误差具有较好的效果.同时规划了其抛光路径,采用一种伪ρ-θ光栅扫描运动方式的加工路径,简化了球形抛光工具的结构,并且由于使加工纹路有了变化,可使加工后的表面纹理呈现无序性和均匀性特征,相应可提高加工后工件的表面质量.最后通过对一块微晶球面镜的加工(面形误差峰谷值PV由加工前1.607λ(λ=632.8 nm)收敛到加工后0.365λ,均方根值RMS由0.195λ收敛到0.024λ),验证了球形抛光工具具有修正边缘翘边现象的能力.     

一种SiC非回转对称非球面的加工与检测

针对一种SiC材质的非回转对称非球面元件,本文介绍了该元件的加工和检测方法.该实验件的理想面形方程为z=3λ(X3-y3)(x,y为归一化坐标,λ=0.632 8μm),镜胚材料为Φ150 mm的SiC,加工方式为数控机床和手工研抛相结合.在加工过程中为提高加工效率缩短加工时间,选择平面作为最接近表面并认为去除了面形中的倾斜项.去倾斜之前最低点的材料去除量为3.8μm,而去倾斜后则为2.06μm.本文提出了一种新的基于数字模板的非零位检测方法.直接采用Zygo平面干涉仅检测工件,检测结果可以分为三部分:工件实际面形与理想面形的误差,工件理想面形与平面波前的误差和非共路误差.其中第二部分可以事先计算出来并转换为系统误差文件在检测过程中自动去除.通过在相同条件下检测一个已知的球面样板验证了非共路误差对于检测结果的影响可以忽略不计.由此在一次测量中可直接得到面形误差.实验结果表明,基于这种检测手段最后测得实验件的面形精度PV达到0.327λ,RMS优于0.025λ,达到设计要求.     

光学元件聚氨酯抛光特性研究

本文研究了应用于平面光学元件的快速抛光技术,从材料去除率、元件面形和表面粗糙度出发,对快速抛光技术应用于平面大口径元件的加工效果进行了探讨。研究了在快速抛光技术中压力和主轴转速对材料去除率的影响,验证了Preston公式在快速抛光中的适用性,快速抛光技术的去除效率可达10μm/h;其次,研究了聚氨酯抛光元件面形的精度,对于330mm×330mm元件可达～1.0λ（λ=632.8nm）;最后,对快速抛光系统中抛光粉颗粒大小及形态随使用时间的变化进行了观测,并测量了使用300目和500目抛光粉时快速抛光元件表面粗糙度以及其随抛光粉使用时间的变化。     

磁流变抛光驻留时间算法

针对磁流变抛光去除量与驻留时间呈线性关系特点,本文以Preston方程为依据,根据磁流变抛光专用机床的运动形式,提出了基于矩阵的磁流变抛光驻留时间算法,该算法通过调整各点驻留时间控制光学器件表面的去除量,达到面形误差修正的目的,适用于非球面等可用通用光学方程表示的回转对称曲面.仿真实验结果表明,采用该算法仿真加工可以使球形表面面形误差收敛至十几个纳米.通过对K9光学玻璃球面进行的磁流变抛光实验,获得了表面粗糙度Ra0.636 nm的球形表面,面形精度P-V值由抛光前的158.219nm减小到52.14 nm,验证了驻留时间算法的合理性.     

高表面粗糙度6061铝合金的两酸抛光工艺研究

目的 为了降低6061铝合金的表面粗糙度,提出了一种环保型的两酸化学抛光工艺,并探究了抛光工艺条件对6061铝合金表面粗糙度和表面形貌的影响。方法 采用正交实验设计,确定6061铝合金两酸抛光添加剂的浓度,在此基础上通过单因素实验进一步对抛光液配方、温度和时间进行参数优化。通过粗糙度仪测量抛光前后的粗糙度和表面轮廓曲线,利用金相显微镜观察抛光前后的微观表面和断面金相,并且计算最佳工艺下的失重率。结果 在温度100 ℃、抛光10 min条件下,当抛光液的成分为H3PO4+H2SO4(质量比为2︰1)、10 g/L硫酸铝、2 g/L硫酸铜、1.6 g/L金属盐A、3 g/L氧化剂B、15 g/L过硫酸铵、1.5 g/L钼酸铵时,抛光效果最好。在最佳工艺下进行抛光,使铝合金表面粗糙度从6~8 µm降低至2 µm左右,粗糙度的标准差从2 µm左右降低至1 µm以下,失重率在0.002~0.004 g/(cm².min)范围内波动,并且得到了光亮的表面。结论 该抛光体系在处理高表面粗糙度的6061铝合金时表现出良好的抛光效果,研究结果对提高3D打印的6061铝合金零件表面质量提供了较好的借鉴与理论分析基础。     

计算机控制抛光机的论证

最近的工作进行了论证计算机控制抛光机(CCP)加工的效率。写入的计算机算法预测每个抛光周期的面形进展。用CCP的四个周期抛光了一块直径1.8米的轻质玻璃反射镜。采用预测程序对每个周期提供所期望的面形修整值。把均方根误差为0.16波长(λ=0.633微米)的反射镜面修整到0.04波长,抛光时间仅用了72小时。由于计量不精确,虽然这次面形修整比预计的修整时间拖长,但这样快速的误差校正还是证明了CCP是非常重要的加工工具。     

磁流变抛光高精度光学表面中的工艺参数

对磁流变抛光进行高精度光学表面加工中必须考虑和控制的7类参数,即磁流变液黏度、磁场强度、磁流变液流量、抛光轮转速、锻带厚度、切深以及抛光斑点特性进行分析和优化,得出单因素条件下材料的去除量总是同这7类参数的变化存在一定的内在联系．在分析和优化磁流变抛光过程中这些参数的基础上,采用自研的KDMRF-1000机床对一块K4材料口径100mm的平面镜进行了抛光加工实验．经过两次循环大约200min的抛光后．面形误差值由最初的峰谷值（PV）为262nm,均方根值（RMS）为49nm收敛到最终的PV为55nm,RMS为5．7nm实验中面形误差的收敛表明：只要掌握了磁流变抛光过程中的这7种参数的变化规律,就能充分利用磁流变抛光技术,为高精度光学表面的加工提供可靠的保障．     

Ni-Ti形状记忆合金电化学抛光工艺研究

为提高Ni-Ti形状记忆合金的表面质量,以Ti50.8Ni(原子分数,%)为基材进行纳米级电化学抛光加工试验。基于自行研制的电化学抛光加工系统及抛光液,通过正交试验和单因素试验,分析了电流密度、抛光时间、抛光温度、电极间距等因素对电化学抛光的影响程度及影响机理。采用Micro XAM-100白光干涉仪对抛光试样进行检测。结果表明:最佳抛光工艺为电流密度J=1.0 A/cm2、电极间距d=15 mm、抛光时间t=140 s、抛光温度θ=15℃。在最佳工艺参数下抛光质量良好,试件表面粗糙度值显著降低至27.8 nm,表面平整均匀、光亮如镜。     

超薄件加工变形误差补偿的研究（英文）

超薄件可广泛应用于高精度微型器件、光子系统等领域.针对加工后超薄件的较大变形,采用基于超精密车削的误差补偿方法进行研究.提出补偿理论与补偿方法,对原位面形误差与离线面形误差进行测量,利用补偿理论计算得到补偿面形,最后采用三轴伺服控制技术对超薄件变形误差进行车削补偿.补偿加工的超薄铝几何尺寸为Φ20×0.1 mm,一次补偿加工后,工件面形峰谷值由变形产生的误差从15μm降到10μm,具有较好的补偿效果.对补偿中原位测量误差与位置偏移误差进行讨论,提出提高补偿加工精度的方法.     

超声振动辅助固结磨粒抛光硅片表面形貌及粗糙度研究

高面型精度和高表面质量的硅片表面加工是目前研究的难点和热点问题之一,基于超声加工所具有的加工效率和加工表面质量高的特性,以及固结磨粒的加工质量易控制和对环境污染小的特点,开展超声椭圆振动辅助固结磨粒抛光硅片的材料去除、抛光表面面型精度及粗糙度的加工机理及实验研究。研究认为抛光工具运动轨迹是影响上述问题的主要因素,为此在对抛光实验系统描述基础上,分析并建立了抛光工具运动轨迹及轨迹密度模型,进而完成硅片材料去除,抛光表面形貌和表面粗糙度的建模仿真。开展相应的实验研究,发现理论分析与实验的结果相一致,基于抛光工具运动轨迹建模的可行性。该研究方法和得出结论为今后开展固结磨粒抛光硅片表面实验的工艺参数的选择和优化,提供了可供借鉴的研究成果,为实际生产提供了可供参考的理论依据。     

Surface integrity and removal mechanism in grinding sapphire wafers with novel vitrified bond diamond plates

In order to improve machining efficiency of sapphire wafer machining using the conventional loose abrasive process, fixed-abrasive diamond plates are investigated in this study for sapphire wafer grinding. Four vitrified bond diamond plates of different grain sizes (40?µm, 20?µm, 7?µm, and 2.5?µm) are developed and evaluated for grinding performance including surface roughness, surface topography, surface and subsurface damage, and material removal rate (MRR) of sapphire wafers. The material removal mechanisms, wafer surface finish, and quality of the diamond plates are also compared and discussed. The experiment results demonstrate that the surface material is removed in brittle mode when sapphire wafers are ground by the diamond plates with a grain size of 40?µm and 20?µm, and in ductile mode when that are ground by the diamond plates of grain sizes of 7?µm and 2.5?µm. The highest MRR value of 145.7?µm/min is acquired with the diamond plate with an abrasive size of 40?µm and the lowest surface roughness values of 3.5?nm in Ra is achieved with the 2.5?µm size.     

Laser polishing of aluminum by remelting with high energy pulses

Laser polishing is a contact‐free, quick and automated method to smooth surfaces. The method has been applied to different forging and casting aluminum alloys. The surfaces of the samples were belt‐grinded with a grain size of mesh 240. The samples are protected from ambient air in a gas shield chamber. The used laser system is an Nd : YAG Laser with maximum pulse energy of 65 J. The initial and the laser polished surfaces have been analyzed by microscopy, roughness spectroscopy, white light interferometry and cross‐section polishes. The surfaces of the laser polished forging alloys are covered by multiple lateral and horizontal cracks. Unlike the forging alloys, the casting alloys could be processed well by laser polishing. The initial surface roughness of Ra₂₄₀ = 1.37 µm was reduced up to Ra_LP ≈ 0.47 µm. This represents a roughness reduction of 66%. The roughness spectroscopy of the laser polished surface shows for structural wavelengths from 2.5 µm to 500 µm a Ra‐value close to 0.1 µm and from 500 µm to 800 µm higher values. The remelted area extends up to100 µm into the material.     

Experimental investigation on carbon steel micro-rod machining by LS-WEDT

This article proposed for the first time the method of the low-speed wire electrical discharge turning (LS-WEDT) combined with the multiple cutting strategy to fabricate carbon steel micro-rods. First, the rotating apparatus submerged in working fluid is designed and manufactured to enable the low-speed wire electrical discharge machine to generate cylindrical geometries. Besides, material removal rate, surface roughness, and machining precision of the micro-rod manufactured by the LS-WEDT are, respectively, investigated. Moreover, the surface microstructure and surface chemical reaction of micro-rods are characterized using scanning electron microscopy and energy-dispersive spectroscopy analysis. Experimental results display that the micro-rod of 70?µm diameter and 1000?µm length can be successfully fabricated. More importantly, the mean absolute diameter deviation of the micro-rod fabricated by LS-WEDT is 0.65?µm and the surface roughness is 0.53?µm, which identified the high machining precision and good surface quality of the micro-rod.     

Combining physical shell mapping and reverse-compensation optimisation for spiral machining of free-form surfaces

Machining of free-form surfaces has an important role in industrial manufacturing, but conventional tool-path generation strategies for free-form surfaces machining have the drawbacks of serious flattening distortion and poor tool-path continuity. Therefore, a novel method is developed to generate a spiral tool path for the machining of free-form surfaces by improving surface-flattening distortion and tool-path continuity. First, physical shell mapping is presented to flatten a free-form surface into a plane, which takes stretching energy, bending energy, and global energy into account. Then, the spatial spiral polyline is rounded to generate a spiral path by proposing reverse-compensation optimisation. Therefore, the free-form surfaces can be quickly flattened with less distortion, remaining free of overlap, and can in addition be machined at high speed along a C² continuous spiral tool path. Further, the flattening error, tool-path length, mean curvature, mean scallop-height error of the spiral path, machining time and surface roughness are obviously reduced. Finally, simulation results are given to show the effectiveness and feasibility of the presented strategy.     

Experimental investigations of ceramic machining using µ-grinding and µ-rotary ultrasonic machining processes: A comparative study

Comparative experimental investigations of µ-grinding and µ-rotary ultrasonic machining (µ-RUM) were made on borosilicate and Zerodur materials to know the efficacy of the processes for micro electro mechanical system (MEMS) application. The electroplated diamond tool of Ø 300 µm for drilling operation and Ø 300 µm to Ø 6 mm for milling operation has been tried in the computer numerical control (CNC) machine with an HSK63 ultrasonic actuator. A suitable interface has been developed to hold the micro tool with the ER11 taper in the existing ER20 collet ultrasonic tool holder. Cutting force, edge-chipping area, and taper in drilling operation; and surface finish, material removal mode, specific energy and un-deformed chip thickness in milling operation were evaluated for both processes under the same material removal rate conditions. The experimental results showed that µ-RUM could perform in a less spindle speed machine as compared to µ-grinding. It was inferred that the maximum and minimum amount of reduction in cutting force, edge chipping, and taper were found to be (49.3%, 10.8%), (87%, 40%), and (95.56%, 4.76%), respectively, in µ-RUM compared to µ-grinding for drilling operation. It was also concluded that surface finish and ductile mode of fracture were higher in µ-RUM compared to µ-grinding for the milling operations. These effects were more pronounced as tool size decreased.     

Optimization of photochemical machining process parameters for manufacturing microfluidic channel

In the present study, the investigation on photochemical machining (PCM) of stainless steel (SS-304) by ferric chloride as etchant is reported. SS-304 is machined by PCM process to obtain accurate dimensions and better geometrical features. Weighted grey relational analysis (WGRA) technique is used in optimization of PCM process parameters. DoE (L₂₇) orthogonal array is applied to evaluate machining parameters, such as concentration of etchant, etching time, and temperature of etchant. The multiobjective optimization technique is used to optimize material removal rate (MRR), surface roughness (R_a), undercut (U_c) and etch factor (EF). Weighted grey relational grade is calculated to minimize U_c and surface roughness and to maximize MRR and EF. The quality characteristics MRR, EF, U_c, and R_a are reporting the improvement after the confirmatory test. The optimum machining parameters are processed to manufacture the microfluidic channel used in biomedical applications. The microfluidic channels and its assembly with Y-type for mixing of fluid with a size of 100 µm, 200 µm, and 300 µm are developed and investigated.     

Experimental investigations in powder mixed electric discharge machining of Ti–35Nb–7Ta–5Zrβ-titanium alloy

The present research is the first type of study in which the application of powder mixed electrical discharge machining (PMEDM) for the machining of β-phase titanium (β-Ti) alloy has been proposed. β-Ti alloys are new range of titanium alloys, which has a wide-spread application in dental, orthopedics, shape memory, and stents. The aim of the present study is to fabricate submicro- and nanoscale topography by PMEDM process to enhance the biocompatibility without affecting machining efficiency. The effect of Si powder concentration along with pulse current and duration on the surface and machining characteristics has been investigated. A significant decrease in surface crack density on the machined surface with 4 g/l Si powder concentration was observed. When β-Ti alloy was modified at 15 A pulse current, longer pulse interval with 8 g/l concentration of Si powder particles, the interconnected surface porosities with pore size 200–500 nm was observed. Moreover, at Si powder concentrations of 2 g/l and 4 g/l, the recast layer thickness is 8 µm and 2–3 µm, respectively. Elemental mapping analysis confirmed that PMEDM also generated carbides and oxides enriched surface, a favorable surface chemistry to enhance the biocompatibility of β-Ti alloy. Furthermore, PMEDM also enhances the machining performance by improving material removal rate and reducing tool wear rate.     

Controlling the material removal and roughness of Inconel 718 in laser machining

Nickel alloys including Inconel 718 are considered as challenging materials for machining. Laser beam machining could be a promising choice to deal with such materials for simple to complex machining features. The machining accuracy is mainly dependent on the rate of material removal per laser scan. Because of the involvement of many laser parameters and complexity of the machining mechanism it is not always simple to achieve machining with desired accuracy. Actual machining depth extremely varies from very low to aggressively high values with reference to the designed depth. Thus, a research is needed to be carried out to control the process parameters to get actual material removal rate (MRR_act) equals to the theoretical material removal rate (MRR_th) with minimum surface roughness (SR) of the machined surfaces. In this study, five important laser parameters have been used to investigate their effects on MRR and SR. Statistical analysis are performed to identify the significant parameters with their strength of effects. Mathematical models have been developed and validated to predict the machining responses. Optimal set of laser parameters have also been proposed and confirmed to achieve the actual MRR close to the designed MRR (MRR_% = 100.1%) with minimum surface roughness (R_a = 2.67 µm).     

Parametric Optimization for Selective Surface Modification in EDM Using Taguchi Analysis

This paper introduces selective modification of surface by electric discharge machining process and its parametric optimization. A hard layer of tungsten and copper mixture is created at selected area of aluminum surface. The process is done using W–Cu powder metallurgical green compact tool and masking technique in die-sinking electric discharge machining (EDM). The modified surface is evaluated by the performance measures such as tool wear rate, material transfer rate, surface roughness, and edge deviation from the pre-defined boundary line of deposited layer by analysis of variance using Taguchi design of experiment. Minimum surface roughness of 4.5 µm and minimum edge deviation of 37.29 µm is achieved. The hardness of the surface layer is increased more than three times of base metal. Overall effects of parameters are also analyzed considering multiple performance criteria using overall evaluation criteria. The modified surface is characterized using scanning electron microscopy and energy dispersive spectroscopy analysis, which show the tool material transfer at the selected area of the surface.