【作者】 罗红平；

【导师】 张璧； 周志雄；

【作者基本信息】 湖南大学 ， 机械工程， 2009， 博士

【摘要】 电化学微加工技术(Electrochemical Micromachining,ECMM)由于具有加工单位小(0.1nm以下)、无宏观加工作用力、加工的表面质量好(无残余应力、表面变质层和热影响层)、工具无损耗、可实现多样化的工艺、具备三维加工的能力等众多突出优点而成为微细制造领域当中很有发展前途的热点研究课题。为了实现电化学微加工,需要采取有效措施克服传统电解加工所特有的杂散腐蚀现象,增强电化学反应的定域性;同时还要使加工系统的运动部件具有很高的运动精度,以满足微加工的要求。鉴于超短脉宽脉冲电源在保证加工精度和稳定性方面的特殊作用,本文以设计一套实现纳秒脉宽脉冲电化学微加工的机床为主要目标,对该机床的关键技术开展了相关研究。从电化学的基本原理出发,概括总结了纳秒脉宽脉冲电化学微加工的基本理论,阐释了纳秒脉宽脉冲电化学微加工能够实现微米/亚微米级精度加工的根本原因,建立了描述电化学微加工成形规律的理论模型,对其进行了数值仿真;实际构建了电化学微加工机床系统,介绍了电化学微加工机床的运动平台、加工电源、电解液槽、显微观测等各部分的硬件组成,控制系统硬件,控制流程及控制软件设计等方面的具体内容;针对纳秒脉宽脉冲电化学微加工加工状态的监测与控制中对于高频/甚高频信号高速采集的困难,提出了将极间的超短脉宽电压信号转化为近直流信号再进行采集的解决方法,设计了极间电压的转换调理电路,实现了对加工状态的自动识别与监控。首次提出一种新型柔性回转轴承及其主轴单元的设计方案。由于这种轴承利用柔性元件的弹性变形实现运动导向,因此其重复运动精度极高,理论上可以实现零误差的回转运动,而且其回转运动平稳、无机械摩擦磨损和运动间隙、无需润滑、可靠性高、结构适宜微小型化。从柔性回转轴承的设计理念和总体设计原则出发,提出了一系列的相关设计准则,对材料的选择、应力的分析与计算(如非线性有限元分析、静强度分析与抗疲劳设计)、回转误差,结构参数等进行了分析,给出了柔性回转轴承的设计实例;提出了轴承扭转管的制造工艺路线,并采取选用慢走丝电火花线切割加工方法(Low speed Wire EDM, LSWEDM)、减小加工过程中工件内部的残余应力、加强轴承扭转管的刚度(尤其是扭转刚度)等措施,实际加工出了柔性回转轴承扭转管结构,加工所得柔性片的厚度尺寸精度为±5μm,而处于相对分布角度的柔性片厚度之差则小至3μm,表面粗糙度可低至Ra0.3μm。提出了一种在内扭转管的两端配合限制同心度的装配方法,可有效防止因配合面垂直度误差所造成偏摆角度的“误差放大”现象。介绍了主轴单元各组成部分的选用或设计原则;对柔性回转轴承的振动特性和固有频率进行了理论分析和实际测试;针对微小型主轴系统回转精度测试的现实困难,探讨了几种可能的测试方法并分析了它们的特点和不足,为将来进一步精确评定回转误差或对误差进行补偿时正确选用测试方法提供了有益的参考。全面概述了微细工具电极的在线制作方法,并采用电化学腐蚀的方法,获得了直径φ20μm以下的微细圆柱状工具电极;讨论了在不锈钢工件上实现纳秒脉宽脉冲电化学微加工的试验思路,为进一步深入研究电化学微加工的机理和机床的实际应用奠定基础。更多还原

【Abstract】 Electrochemical micromachining (ECMM) is a promising micromachining technology, since it offers several advantages which include absence of machining forces and residual stresses, no tool wear, good surface finish, adaptability to various processes, and ability to machine complex 3D micro features with the material removal/addition unit at the atomic scale (0.1nm or even smaller).To realize ECMM, the foremost thing is to prevent the stray erosion caused by the distributing electric field in the conventional ECM, which means the localization of electrochemical reaction should be improved. Motion platforms (linear stages and rotation stages) with high accuracy and resolution in an ECMM machine tool are needed as well to meet the requirements for micromachining. Based on the application of ultrashort voltage pulses to the localized electrochemical reactions, this study is aimed at developing an ECMM setup to achieve nanosecond voltage pulses ECMM and focuses on several key issues of electrochemical micromachine.the theory of ultrashort voltage pulses ECMM are summarized from the basic principle of electrochemistry and the related literature, which explains the principles for the micrometer and submicrometer machining by using ultrashort voltage pulses in ECMM. The equivalent electric circuit of electrochemical polarization is formed, and mathematical models describing the forming laws of ECMM are established. Simulations on the ECMM are carried out.An electrochemical machining system is developed. The elements of the machine setup are descirbed in detail, which includes the drive of the nanometer accuracy and resolution, power supply, machining chamber, microscope, etc. The control strategy and hardware and software for the control system are presented as well. A circuit enabling the transformation of the voltages between the cathode and anode is specially designed to solve the problems encountered in direct sampling of the ultrashort voltage pulses because of their very high equivalent frequencies. Thus autoidentification and controlling of machining is achieved.This dissertation proposes a novel concept of rotary flexural bearing that is based on the motion principles of elastic flexures to provide rotational oscillations of one complete revolution, therefore the repeatablility of the rotary motions guided by this type of bearing is expected to be very high (atomic scale), thus the error motions with extremely high accuracy (nanometer or less) can be obtained. The bearing is also characterized by smooth motions, no mechanical wear and no lubrication requirements, no gaps or interfaces, in addition to its compactness. The overall conceptual design of the bearing is presented. A design analysis on the various aspects of the bearing is provided, including material selection, stress analysis and calculations (such as nonlinear finite element analysis, static and fatigue strength designs), motion error analysis and error reduction strategy, parametric design, etc. A prototype bearing is presented. The machining route of the bearing tube is proposed from the analysis of the fabrication characteristics. Low speed Wire EDM (LSWEDM) is chosen as the machining method of the flexural bearing. Technical measures to reduce the residual stresses and strengthen the stiffness (especially the torsional stiffness) of the bearing tube are adopted. Dimensional accuracy of±5μm is obtained over the 150μm thickness for the bearing flexures and a variation of less than 3μm is achieved for the flexures of opposing sides, and surface roughness Ra of 0.3μm is obtained for the flexures of the entire bearing. The assembly methodology focuses on the reduction of radial motion error caused by the tilt angle between axes of the inner bearing tube and the outer bearing tube due to the“error enlargement effect”. A special assembly measure is suggested to confine the location of the both ends of the inner bearing tube, thus preventing the“error enlargement effect”from happening. The basic principle for component selection or designing of the spindle system is presented. The vibration characteristics of the bearing is theoretically analysed and experimentally measured. Several techniques concerning the micro spindle motion error measurements are discussed and compared to provide useful references for future use of motion error estimation or motion error compensation.On-the-machine tool-making methods are overviewed. Micro cylindrical electrodes with diameterφ20μm or less are obtained by using the electrochemical fabrication method with constant current density; The basic methods and key operating steps towards successful ECMM machining of micro features in stainless steel (SS) using nanometer voltage pulses are discussed, which is important to further unveil the machining mechanisms of ECMM and to lay foundation for future practical application of ECMM machine tool.更多还原