A study on the machining of high-aspect ratio micro-structures using micro-EDM

Micro-electro-discharge machining (micro-EDM or μ-EDM) has been gaining popularity as a new alternative method to fabricate micro-structures. The main advantages of the micro-EDM method are its low set-up cost, high accuracy and large design freedom. Compared to etching or deposition techniques, micro-EDM has the advantage of being able to fabricate complex three-dimensional shapes with high-aspect ratio. However, there are many operating parameters that affect the micro-EDM process. The fabrication of micro-electrodes on the machine is also an important process to remove the clamping error to maintain high accuracy in the machined micro-structures.

In this paper, the machining of micro-structures is divided into two basic processes. One is the on-machine fabrication of the micro-electrodes with high-aspect ratio, and the other is the EDM of the workpiece in micrometer range. An optical sensor has been developed to measure and control the dimension of the thin electrode during the tool fabrication process. Different methods have been investigated to fabricate a thin electrode into the desired dimension without deflection. The performance of the micro-EDM process is evaluated in terms of the material removal rate (MRR), tool wear ratio (TWR), and the stability of the machining. Influences of the various operating parameters of the micro-EDM process, such as the operating voltage, gap control algorithm, and resistance and capacitance values in the R–C spark control circuit, are discussed.     

Ultra-precision machining of Fresnel microstructure on die steel using single crystal diamond tool

With the increasing demand for the replication of structured optical elements such as Fresnel lenses and prism arrays, more attention is being paid to the development of ultra-precision diamond machining technology for the fabrication of die steel molds. However, the machining process would be a catastrophic failure because of rapid and excessive tool wear if a diamond tool is used to machine die steel. In the present paper, a micromachining method for fabricating microstructures on die steel using single crystal diamond tool is presented. The presented technology is based on a thermochemical technique that uses plasma nitriding treatment to suppress the rapid and excessive tool wear in the diamond machining of steel. Experimental findings revealed that severe chemical tool wear, which is the main wear mechanism in the diamond machining of steel, was reduced significantly after plasma nitriding treatment, and a mirror-quality surface with an average surface roughness of 20 nm root-mean-square (RMS) was achieved over a cutting distance of approximately 5.4 km. Furthermore, a Fresnel microstructure with surface roughness RMS better than 40 nm was precisely fabricated on AISI 4140 die steel using single crystal diamond tool.     

UMAC时基控制原理及其在非轴对称微结构表面切削中的应用

针对非轴对称微结构表面加工的实时性要求,采用压电陶瓷驱动的快速伺服刀架(FTS)作为微进给机构,实现刀具沿z向高频响、短行程的快速精密进刀运动,并构建了基于UMAC多轴运动控制器的微结构车削数控系统。应用UMAC的时基控制功能实现快速伺服刀架(FTS)进给与主轴转角θ的同步,来完成非轴对称微结构表面的加工。     

等离子-MIG焊接设备的设计与研制

采用双电源供电和双电弧共枪体等技术，成功地完成了等离子-MIG焊接设备的研制。在设计中还采用了焊接参数专家库管理和等离子枪体计算机辅助优化设计等技术，并将该焊接方法应用于三峡电站大型开关断路器的制造过程。     

水下自动套料切割定位系统

介绍了数控等离子切割机在完成钢板套料后,切割机z,y,z三轴驱动系统协调工作;割炬在水下工作时,等离子发生器起弧后,霍尔传感器采集到变化的弧压信号,将其反馈到自动高低调节器,完成割炬的定位和高低调节,使割炬在水下沿着套料轨迹对钢板进行自动切割。     

Fabrication of free-form surfaces using a long-stroke fast tool servo and corrective figuring with on-machine measurement

Fabrication of free-form surfaces that are frequently demanded for the construction of optical imaging systems is described. To obtain a tool motion with large amplitude and high bandwidth, a novel long-stroke fast tool servo is proposed and installed on the Z-axis of a diamond turning machine as an additional synchronized axis. In addition, a special on-machine measurement device is used to measure the optical parameters of the machined surface and to compensate for the residual form of errors that are commonly produced in the diamond turning process. Actual machining test results show that the proposed procedures are capable of generating the copper free-form mirrors of 50 mm diameter to a form accuracy of 0.15 μm in peak-to-valley value error.     

Experimental determination of optimum parameters for nano-grinding of optical fibre end faces

This study presents detailed experimental results that help to determine the optimal grit size, speed and in-feed rate for grinding end faces of optical fibres on a nano-grinding machine. The determination of these parameters was based on surface roughness, material removal rate and the surface and sub-surface damage investigations. The observations consisted of qualitative as well as quantitative evaluations. Qualitative assessment of surface quality was carried out using an optical microscope. The quantitative measurement of surface roughness was carried out using atomic force microscopy (AFM). The material removal rates were determined using feed rates of the nano-grinding machine. Using a focussed ion beam (FIB), the ground surfaces were milled to expose their cross sections. The ground surfaces and the cross sections were examined using scanning electron microscopy (SEM) for surface or sub-surface damage.     

Development of monitoring system on the diamond tool wear

Recently, ultra-precision machining using a single crystal diamond tool has been developing very rapidly, especially in the fields of production processes for optical or magnetic parts such as magnetic discs, laser mirrors, polygon mirrors and copier drums. As a result, it has been successfully extended to machine various soft materials, generating mirror-like surfaces to sub-micron geometric accuracy with the ultra-precision CNC machine and the single crystal diamond tool. With the real cutting operation, the geometric accuracy and the surface finish attainable in machined surfaces are mainly determined by both of the sharpness of a cutting tool and stability of the machine vibration. In this study, for monitoring the progress of machining state for assuring the machining accuracy and the surface quality, a new monitoring method of machining states in face-cutting with diamond tool is proposed, using the frequency response of multi-sensors signal, which includes wear state of tool in terms of the energy within the specific frequency band. A magnetic disc is machined on the ultra-precision lathe.     

Characteristics of a Plasma Torch Designed for Very Low Pressure Plasma Spraying

Unlike atmosphere plasma spraying (APS), very low pressure plasma spraying (VLPPS) can only weakly heat the feed materials at the plasma-free region exit of the nozzle. Most current VLPPS methods have adopted a high power plasma gun, which operates at high arc currents up to 2500?A to remedy the lower heating ability, causing a series of problems for both the plasma torch and the associated facility. According to the Kundsen number and pressures distribution inside of the nozzle in a low-pressure environment, a plasma torch was designed with a separated anode and nozzle, and with the powder feed to the plasma jets inside the nozzle intake. In this study, the pressures in the plasma gas intake, in the nozzle intake and outside the plasma torch were measured using an enthalpy probe. For practice, SUS 316 stainless steel coatings were prepared at the plasma currents of 500-600?A, an arc voltage of 50?V and a chamber pressure of 1000?Pa; the results indicated that coatings with an equiaxed microstructure could be deposited?in proper conditions.     

A multiprocess machine tool for compound micromachining

Compound micromachining is the most promising technology for the production of miniaturized parts and this technology is becoming increasingly more important and popular because of a growing demand for industrial products, with an increased number not only of functions but also of reduced dimensions, higher dimensional accuracy and better surface finish. Compound micromachining processes that combine multiple conventional and non-conventional micromachining processes have the capability to fabricate high aspect ratio microstructures with paramount dimensional accuracy. Such machining should be carried out on the same machine with minimum change of setups. At the same time, on-machine tool fabrication along with on-machine tool and workpiece measurement facilities should also be available for further enhancement of the functionality of the machine and higher productivity. In order to achieve effective implementation of compound micromachining techniques, this research seeks to address four important areas, namely (a) development of a machine tool capable of both conventional micromachining including microturning, micromilling, etc., and non-conventional micromachining including microelectrical discharge machining (micro-EDM), wire-cut electrical discharge machining (WEDM), etc.; (b) process control; (c) process development to achieve the necessary accuracy and quality and (d) on-machine measurement and inspection. An integrated effort into these areas has resulted in successful fabrication of microstructures that are able to meet the miniaturization demands of the industry. This paper presents a few tool-based approaches that integrate micro-EDM, micro-EDG, microturning and microgrinding to produce miniature components on the same machine tool platform in order to demonstrate the capabilities of compound micromachining.     

基于PC的数控火焰切管机床研制

在对数控火焰切管机床的加工原理和割炬路径的运动学分析基础上,研制了一种功能强大的火焰切管数控机床.设计了相应的计算机程序,能够根据切割类型和参数直接定义加工程序;构建了开放式、模块化的数控系统平台,实现了高质、高效、自动切管.     

Electric Characteristics of Plasma Arc Produced by Bi-Anode Torch

In order to improve the voltage control and stability of a plasma arc, a new-type plasma torch was designed and constructed. The torch, called bi-anode torch, has two anodes that were inter-insulated and have different distances from the cathode tip. The position of the arc root can be controlled to attach to either anode surface during operation to obtain a low-voltage and high-fluctuation arc or a high-voltage and low-fluctuation arc. The paper discussed the occurrence of the double-arc phenomenon and its prevention. Experimental work has been carried out to compare voltage-current (U-I) characteristic of the arc when using different plasma gases and anode arc root attaching to different anode surfaces. The results show that the U-I characteristic of the plasma arc is affected by the position of the anode arc root attachment and the composition of the plasma gas, which was explained by a simplified arc model.     

Fabrication of off-axis aspheric surfaces using a slow tool servo

Off-axis aspheric surfaces have been widely applied in optical systems, but it is difficult to fabricate this kind of optical surface with high quality. Slow tool servo is one of the methods for turning off-axis aspheric surfaces on-axis, which have a large travel range without an additional device. This paper presents a theoretical and experimental investigation on the 3D surface generation in single point diamond tuning using slow tool servo. The form error of off-axis paraboloid caused by tool centering error is analyzed and verified by cutting experiment.     

Effect of atmospheric microwave plasma treatment on organic lubricant on a metallic surface

Coaxial injection microwave excited plasma torch, operating at atmospheric pressure has been tested to treat greased metallic surfaces. The treatment conditions were controlled using optical emission spectroscopy. The plasma treatment was carried out using argon plasma, with argon or oxygen in the periphery. The effect of plasma treatment on the grease was evaluated, using gravimetric analysis by weighing the sample before and after treatment, surface energy and X-ray photoelectron spectroscopic measurements. Initial period of treatment yielded etching of the grease, but, later on, the grease stabilized forming polymeric films, independent of the gas present in the periphery. The etching behavior was explained by different mechanisms involved in the plasma grease surface and sub-surface interactions.     

焊接与切割设备的使用和维修(六十五)——空气等离子弧切割机的使用与维修

分析了LGK系列空气等离子弧切割机的使用方法,例举了其引弧故障、主电路故障、气路故障、割枪故障产生的原因和解决方法.同时也讲述了晶闸管式等离子弧切割机的操作原理和使用方法.     

Investigations of a high volume atmospheric plasma torch at 915 MHz

An atmospheric pressure microwave plasma torch at a frequency of 915 MHz was developed and investigated. The development was accompanied by simulations of the electromagnetic field distribution in the plasma device with the programme CST Microwave Studio®. Optical emission spectroscopy (OES) was carried out in order to determine the gas temperature of the plasma. The measured temperature of an argon/hydrogen-plasma was up to 7000 K which is high enough to evaporate all materials. As an application we used the plasma torch for reactive evaporation of silicon powder and subsequent deposition of silicon coatings with different morphologies which were investigated mainly by scanning electron microscopy.     

焊接与切割设备的使用和维修(六十七)——空气等离子弧切割机的使用与维修

介绍了空气等离子弧切割机切割前的准备、手工切割程序、自动切割程序、注意事项、割炬的安装维护及零件的更换、故障原因及其排除方法.同时列举了日本A-70等离子弧焊机的故障实例和解决方法.     

强电流直流扩展弧金刚石沉积技术的研究

采用自行研制的Q-500金刚石涂层沉积设备,同时采用两种不同结构的等离子体炬对经酸碱二步法处理后的硬质合金钻杆(YF06)分别进行了金刚石涂层的沉积,并对沉积后的样品表面进行了分析和研究.初步的研究结果表明:等离子体炬的结构对金刚石涂层的沉积影响很大,改进前的等离子体炬所产生的弧柱不稳,导致沉积温度波动幅度大,而改进后的等离子体炬能产生稳定的弧柱,沉积温度变化不大并且沉积的金刚石涂层具有大面积、均匀性好和高质量的特点.     

Synchronization of Suspension Plasma Spray Injection with the Arc Fluctuations

Poorly controlled heat and momentum transfers between plasma and material, plasma instabilities are some of the difficulties encountered in suspension plasma spraying. The improvement of this method is usually attempted by means of the reduction of arc fluctuations. This paper presents a new approach to the injection of reactive material in an arc jet. The principle is to produce a pulsed laminar plasma jet combined with phased injection of liquid droplets. This is achieved by the particular design of the plasma torch that works at moderate power and following a resonant mode. The droplets are injected using a piezoelectric device, based on drop-on-demand method, triggered by the voltage signal sampled at the torch connections. The results are evaluated by time-resolved imaging technique that shows how the trajectories are influenced by the moment at which the droplets penetrate the plasma jet.     

反应等离子喷涂 TiN 涂层的研究进展

TiN具有硬度高、韧性好、摩擦系数小、化学性能稳定等优点,广泛应用于刀具、装饰、表面防护等领域。目前制备TiN涂层的方法有很多,如气相沉积、热喷涂、电镀等,反应等离子喷涂则是最常用的金属-陶瓷复合涂层制备方法。概述了反应等离子喷涂技术的基本原理和分类,包括反应等离子喷涂涂层的形成过程及工艺的优缺点。综述了反应等离子喷涂TiN涂层的喷涂工艺及性能的研究进展,包括涂层的制备方法(原位合成法、烧结破碎法)和性能特点,重点分析了涂层的力学性能、耐磨损性能、耐腐蚀性能,并提出了可以依靠热处理工艺或封孔技术来提高涂层的耐腐蚀性能。依据实验和查阅的文献,反应等离子喷涂结合了自蔓延高温合成技术和等离子喷涂技术,可以制备质量优良的厚TiN涂层(500μm),是一种新型的低成本涂层制备技术,但是反应等离子喷涂制备TiN涂层存在孔隙率较高(5%~10%)、结合强度较低(50 MPa)的问题。分别从技术、设备、工艺、后处理四个方面总结了改善涂层质量的相应措施,展望了今后的研究发展方向。