How to diamond turn an elliptic half-shell?

In this research note we are introducing a new slow slide servo (SSS) turning technique which enables fast diamond machining of deep aspheric surfaces which otherwise can only be machined by ball-end milling, if at all. The key idea is to execute the servo motion not only parallel to the axis of rotation, which is the standard mode implemented in commercial SSS software, but in a plane incorporating both directions parallel and perpendicular to the rotational axis. In this way the risk of collisions in non-circular turning between the tool shaft and the machined surface can be reduced significantly. Moreover, when a 180° contour is machined, the acceleration of the servo slide will not increase indefinitely. After a review of the standard SSS turning technique we will outline the generalized SSS concept and demonstrate its applicability by diamond turning of an elliptic half-shell on a commercial diamond turning lathe.     

SURFACE ROUGHNESS PREDICTION MODEL FOR ULTRAPRECISION TURNING ALUMINIUM ALLOYWITH A SINGLE CRYSTAL DIAMOND TOOL

A surface roughness model utilizing regression analysis method is developed for predicting roughness of ultra-precision machined surface with a single crystal diamond tool. The effects of the main variables, such as cutting speed, feed, and depth of cut on surface roughness are also analyzed in diamond turning aluminum alloy. In order to predict and control the surface roughness before ultraprecision machining, constrained variable metric method is used to select the optimum cutting conditions during process planning. A lot of experimental results show that the model can predict the surface roughness effectively under a certain cutting conditions .     

An empirical survey on the influence of machining parameters on tool wear in diamond turning of large single-crystal silicon optics

We conducted a series of screening experiments to survey the influence of machining parameters on tool wear during ductile regime diamond turning of large single-crystal silicon optics. The machining parameters under investigation were depth-of-cut, feed rate, surface cutting speed, tool radius, tool rake angle and side rake angle, and cutting fluid. Using an experimental design technique, we selected twenty-two screening experiments. For each experiment we measured tool wear by tracing the tool edge with an air bearing linear variable differential transformer before and after cutting and recording the amount of tool edge recession. Using statistical tools, we determined the significance of each cutting parameter within the parameter space investigated. We found that track length, chip size, tool rake angle and surface cutting speed significantly affect tool wear, while cutting fluid and side rake angle do not significantly affect tool wear within the ranges tested. The track length, or machining distance, is the single most influential characteristic that causes tool wear. For a fixed part area, a decrease in track length corresponds to an increase in feed rate. Less tool wear occurred on experiments with negative rake angle tools, larger chip sizes and higher surface velocities. The next step in this research is to perform more experiments in this region to develop a predictive model that can be used to select cutting parameters that minimize tool wear.     

A loop shaping perspective for tuning controllers with adaptive feedforward cancellation

This paper presents a loop-shaping perspective on the tuning of systems using adaptive feedforward cancellation (AFC). The AFC technique is very useful for reducing/eliminating errors in a controlled system at a selected set of harmonics. Such a technique has applicability for hard disk and optical disk track following, vibration rejection in spindle systems and helicopters, camshaft and piston machining, as well as in fast tool servos for diamond turning. This last application provides the motivation for the work described herein. The paper shows how an AFC loop with N resonators results in 2N parameters, a gain and phase advance parameter for each resonator, which must be adjusted to maximize closed-loop performance. This paper details a frequency shaping method of selecting the AFC phase advance parameters and resonator gains in multiple AFC resonator systems. We have applied these techniques to our prototype diamond turning machine with a fast tool servo for cutting ophthalmic lenses. Experimental results comparing the performance of this machine with and without AFC control are presented.     

TOOL FORCE MODEL FOR DIAMOND TURNING

A new tool force model to be presented is based upon process geometry and the characteristics of the force system, in which the forces acting on the tool rake face, the cutting edge rounding and the clearance face have been considered, and the size effect is accountable for the new model. It is desired that the model can be well applicable to conventional diamond turning and the model may be employed as a tool in the design of diamond tools. This approach is quite different from traditional investigations primarily based on empirical studies. As the depth of cut becomes the same order as the rounded cutting edge radius, sliding along the clearance face due to elastic recovery of workpiece material and plowing due to the rounded cutting edge may become important in micro-machining, the forces acting on the cutting edge rounding and the clearance face can not be neglected. For this reason, it is very important to understand the influence of some parameters on tool forces and develop a model of the relatio     

基于仿形测量和误差补偿处理的模具逆工程曲面重构

阐述了逆工程的概念、组成及实施的关键技术 ,重点讨论了逆工程仿形测量技术、误差补偿处理、以及基于测量数据的曲面重构技术 ,包括测量数据预处理、曲线拟合及曲线的光顺处理、曲面的拟合以及结果的检测与评估。以变矩器叶轮叶片芯模具为实例 ,就逆工程技术在模具快速设计与制造方面的应用做了初步的探讨。     

Miniaturized TIR Fresnel lens for miniature optical LED applications

Light-emitting diodes (LEDs) have been investigated to expand their application to very thin electronic devices, including various optical components in a single device. In such applications, the collimation of light produced by LEDs using a conventional Fresnel lens can be bent at angles greater than 45°, whereas most LEDs radiate at solid angles greater than 60°. This paper describes a miniaturized total internal reflection (TIR) Fresnel lens for such miniature optical LED applications. The proposed lens reduces the solid angle of a LED from 60° to 12°, and was designed to have a thickness of less than 1 mm with eleven facets on a single side. The overall geometry of the TIR lens was calculated numerically using Matlab, and the central hyperboloid was designed using Code V.     

金刚石刀具刃口轮廓新型检测方法与技术

研究了原子力显微镜扫描方式及原子力微探针坐标方式的刃口轮廓测量技术。原子力探针新型检测方法与技术可以在亚微米尺度内很好地克服传统测量方法精确度低的缺点，而且操作简便，为目前超精密加工领域中金刚石刀具研磨技术水平的提高提供了有利的技术手段。     

Modeling and machining evaluation of microstructure fabrication by fast tool servo-based diamond machining

A fast-tool servo-machining process is typically utilized to generate sinusoidal microstructures for optical components only when the clearance angle of the cutting tool is greater than the critical value. This paper focuses on the generation characteristics of microstructures for surface texturing applications when the clearance angle of the cutting tool is smaller than this critical angle. A method for calculating the microstructure profile amplitude and wavelength is introduced for the prediction of microstructure generation. Cutting tests were conducted, and the measured results were quite close to the corresponding calculated results, further verifying the capability of the proposed analytical model.     

菲涅耳透镜的通光分析及设计方法探讨

研究了菲涅耳透镜成像质量差的原因,提出一种改进的方法,即改善轴外点的成像质量以增大菲涅耳透镜的视场。分析了三种常用的设计菲涅耳透镜的方法,用光学设计软件Zem ax模拟设计结果,对三种设计方法进行比较。得出结论:像面为曲面时可校正场曲;基面和底面为曲面的菲涅耳透镜与平面型菲涅尔透镜相比彗差较小。     

Diamond Turning of Soft Semiconductors to Obtain Nanometric Mirror Surfaces

Diamond cutting is a viable alternative to grinding and polishing in the fabrication of high-quality soft semiconductors. Investigation of indentation provides useful information for understanding the practical diamond cutting process of brittle materials. Cutting forces and temperatures were analysed using a Kistler dynamometer and an infrared technique. A zero rake angle cutting tool was found to be most efficient, partly because the effective rake is really a strong negative rake brought about by the peculiar configuration of very low feeds and depths of cut. This is explained by means of the comparison of the force distribution between conventional turning and ultraprecision machining. Atomic force microscopy and scanning electron microscopy were used to study the surfaces. Zinc sulfide gave subnanometric surfaces (0.88 m) and zinc selenide gave Ra values of 2.91 nm.     

ACHIEVING THRESHOLD BARRIER OF 1 nm ROUGHNESS VALUE OF SILICON SURFACE BY DIAMOND TURNING

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基于菲涅尔透镜的室内LED射灯配光设计

为了将LED发出的光均匀投射到3m远直径为1m的圆形区域内,设计了一种LED(发光二极管)射灯。采用菲涅尔透镜对射灯进行二次光学配光设计,并通过调整菲涅尔透镜的各个独立环带的倾角来优化投射光的分布。文中对菲涅尔透镜的投光效果、安全性和加工误差等方面进行了考察,结果表明设计是安全的、可靠的并具有良好的投光效果。     

菲涅耳透镜对平行光的成像特性分析

利用光线追迹与实验的方法 ,对菲涅耳透镜在平行光照明时的成像特性进行了分析。给出了在各种角度入射情况下的最佳像点位置及像点弥散斑大小 ,通过对结果进行分析 ,得出了最佳像面曲线及其特征与参数。并讨论了它们与菲涅耳透镜参数的关系。     

Microscopic topographical analysis of tool vibration effects on diamond turned optical surfaces

In diamond turning for the manufacture of optical surfaces, a certain degree of relative vibration is inevitably encountered between the tool and work, deteriorating the surface quality. In this paper we first describe how the tool vibration affects the surface profiles in microscopic level, and then propose a metrological scheme to identify any existence of tool vibration with a minimum effort of surface measurement and analysis.     

Annealing treatment of amorphous silicon generated by single point diamond turning

Mechanical material removal during ultraprecision machining of semiconductor crystals normally induces surface damage. In this article, Raman micro-spectroscopy has been used to probe structural alteration as well as residual stresses in the machined surface generated by single point diamond turning. The damage found is characterized by an amorphous phase in the outmost surface layer. In addition, the results of in-situ re-crystallization annealing of micromachined silicon monitored by micro-Raman spectroscopy are reported for the first time. It is also shown that the annealing heat treatment influenced surface roughness, whereby R_max was equal to 24.3 nm and 47.5 nm for the non-treated and annealed surfaces, respectively.     

On the effect of crystallographic orientation on ductile material removal in silicon

In this work the critical chip thickness for ductile regime machining of monocrystalline, electronic-grade silicon is measured as a function of crystallographic orientation on the (0 0 1) cubic face. A single-point diamond flycutting setup allows sub-micrometer, non-overlapping cuts in any direction while minimizing tool track length and sensitivity to workpiece flatness. Cutting tests are performed using chemically faceted, −45° rake angle diamond tools at cutting speeds of 1400 and 5600 mm/s. Inspection of the machined silicon workpiece using optical microscopy allows calculation of the critical chip thickness as a function of crystallographic orientation for different cutting conditions and workpiece orientations. Results show that the critical chip thickness in silicon for ductile material removal reaches a maximum of 120 nm in the [1 0 0] direction and a minimum of 40 nm in the [1 1 0] direction. These results agree with the more qualitative results of many previous efforts.     

Investigation and prediction of chip geometry in diamond turning

Management of the chips generated in diamond turning is often critical, because contact between chips and the workpiece can result in superficial damage to the finished surface. Controlling chip motion is not a trivial process as the proper positioning of an oil or air stream requires an understanding of the dynamics of a diamond turned chip and the machining parameters that affect it. Work has been performed to investigate the effects of cutting speed, depth of cut, tool geometry, tool wear, and workpiece material properties on chip motion and geometry. Utilizing radius of curvature data from cutting experiments, a parameter has been proposed that can be used to predict chip radius of curvature for a wide range of machining conditions. This chip curvature parameter, χ, exhibits a power law relationship with chip radius of curvature as a function of tool geometry, depth of cut, cutting speed, and both elastic and plastic properties of the workpiece material.