【作者】 王昆；

【导师】 朱荻；

【作者基本信息】 南京航空航天大学 ， 机械工程， 2007， 博士

【摘要】 电解加工是利用金属在电解液中可以发生阳极溶解的原理将零件加工成形的,其材料的减少过程以离子的形式进行。由于金属离子的尺寸非常微小,因此这种微溶解去除方式使得电解加工技术在微细制造领域有着很大的发展潜力。电火花线切割加工是用线电极靠电火花放电对工件进行切割加工,因为电极丝的损耗,必须采用30微米以上直径的线电极,而且为了补偿金属丝损耗必须使电极丝进行快速的运动,不可避免地带来了一定程度的运动误差。因此,它的微细加工能力得到很大的限制。本文结合微细电解加工技术和线切割的基本思想,提出一种新的微细加工方法:微细电解线切割加工。原理上阴极电极丝不会损耗,采用微米级直径的电极丝,可加工出微米至数十微米尺度的复杂微结构件。提出的技术主要面向航空航天、精密仪器、生物医疗等领域。本文的主要内容包括以下几个方面:1.建立了微细电解线切割加工的基本理论。分析了微细电解线切割加工的特点,利用法拉第定律和巴特勒-伏尔摩方程,建立了微细电解线切割加工的理论模型,得出线电极进给速度具有理论上限。将微流体边界层理论引入到微细电解线切割加工间隙流场特性的分析中,分析了微细电解线切割加工中微尺度间隙流场下物质的输运机理,提出了加快微尺度间隙中产物排出的技术方案。2.设计了微细电解线切割加工系统。分别对运动系统、加工检测系统、线电极系统、超短脉宽电源、电解液系统进行设计。提出了加工间隙中短路的两种类型:加工产物堵塞性短路、加工机理性短路,研究了通过统计发生短路位置的分散程度来判别短路类型的方法,实现加工间隙状态的在线检测与辨识。在加工中采用罚函数法优化线电极的进给速度,并依此设计了伺服进给控制策略。最后,基于虚拟仪器技术设计了微细电解加工控制系统及其软件。3.提出了在线制备微米尺度线电极的新方法。用实时测量金属丝自身电阻变化的方法来控制其腐蚀到所需的尺寸,并基于有限元电场分析优化设计了电化学腐蚀装置,保证线电极的腐蚀均匀性。基于虚拟仪器技术建立了线电极电化学腐蚀法制备监控系统。微细电解线切割的线电极制作和后续加工在同一工艺系统中连续完成,工艺兼容性好,对于提高微细加工精度十分有利。通过实验制备出直径为5μm的线电极。4.进行了微细电解线切割加工工艺的实验研究。对影响加工精度、加工稳定性和表面质量的因素进行分析。通过微缝的加工实验,全面分析了进给速度、进给频率、电参数、电解液浓度和线电极直径等工艺参数对加工的影响规律。此外,还通过实验验证了线电极相对微幅振动法改善加工稳定性的可行性。5.进行了微细结构电解线切割加工的实验研究。提出了两种微细电解线切割的加工模式:缝槽切割和结构加工。在缝槽切割模式中,将参数曲线分割为众多直线段,使线电极始终以恒定的线速度沿参数曲线轮廓运动,获得了各种形状缝宽为15μm、深宽比为10的微细缝槽结构;在结构加工模式中,对理论轮廓进行等距偏移,加工出切缝宽度为20μm左右的微型桨叶结构和曲率半径在1μm以下的微细尖角结构。本文对微细电解线切割加工这一微细加工新技术进行了基础研究,为特殊性能材料的微细加工提供了新的加工途径,必将对微机电系统的进一步发展起到有力的推动作用。更多还原

【Abstract】 Electrochemical machining (ECM) is an anodic dissolution process to machine workpiece in a flowing electrolyte where the shape of the cathode (as tool) is copied onto the workpiece (as anode) with the removal of the anode in ions. Due to the tiny size of metal ion, this micro-dissolution process brings ECM tremendous potential in the micro-manufacturing field. As for wire electrical discharge machining (WEDM), because of tool wear, the metal wire with the diameter of more than 30μm must be used as the wire electrode of WEDM, and the wire must be move quickly for the compensation of the tool wear. Therefore, WEDM has great limitations for its applications in micro machining in the future.Wire electrochemical micro machining (WEMM), which is the combination of electrochemical micro machining and the idea of wire cutting, was proposed as a new method of micro machining in this dissertation. Because of no electrode wear in this process the micrometer scale metal wire can be used as the wire electrode in WEMM, and the micrometer or tens micrometer structure can be fabricated. The proposed technology can be used in the field of aviation & aerospace industry, precision instrument, biological and medicinal instrument. The dissertation consists of five sections, including:1. The fundamental theory of WEMM was investigated. Firstly, the characteristics of WEMM were summarized. Secondly, the theoretical model of WEMM was founded based on the Bulter-Volmer equation and Faraday’laws, and the top limit of the feed speed was studied. At last, the boundary layer theory of micro fluid was introduced into the analysis of the transport mechanism of materials in the micro scale gap of WEMM, and the solution to improving the discharge of materials from the micro gap.2. The machining system of WEMM was developed. The movement system, measuring system, wire electrode system, high-frequency short-pulse power supply and electrolyte system were designed. The two types of short-circuit: clogging short-circuit and unavoidable short-circuit was proposed, and the type of short-circuit can be determined by the locality distributing of short-circuit, then the state of the micro gap in WEMM was online measured and distinguished. The method of punitive function was used to optimize the velocity of feed forward, and the strategy of servo-control system were designed. Finally, the control system was founded using devices of virtual instruments, and the software of the system was designed based on Labwindows/CVI.3. The new method of the online fabrication of the micrometer scale wire electrode used in WEMM was investigated. A model about the process of electrochemical etching was developed, the diameter of wire electrode was real-time monitored by precisely measuring the variation in resistance of the electrode. Based on electric field analysis, the device of electrochemical etching was designed to ensure the uniform wear of the wire electrode, and a monitoring system used for fabricating the wire electrodes was developed based on virtual instrument technology. The online fabrication of wire electrode and the following process of WEMM were integrated into one system. Because of the compatibility of the technology, the machining accuracy can be improved. Finally, a tungsten wire electrode of 5μm in diameter was experimentally fabricated.4. The laws of machining process were experimentally investigated. The effects of various parameters on the machining accuracy, stability and surface quality were analyzed, and the impacts of feed speed, frequency of feed, electrical parameter, electrolyte and the diameter of wire electrode on the machining process were experimentally investigated. Besides, the slight vibration of workpiece took place along the direction of the wire electrode length for effectively refreshing electrolyte in the machining area. A slight vibration of workpiece taking place along the length direction of the wire electrode for effectively refreshing the electrolyte was experimentally proved to be able to improve the stability of WEMM.5. The micro metal structures were obtained. Two models of machining process: cutting slits and fabricating structures were proposed. In model of cutting slits, parameter curve was divided into micro line segments, the wire electrode fed forward following the profile at constant speed, and the various micro grooves in width of 15μm and aspect-ratio of 10 were obtained; In model of fabricating structures, the profile was deviated from the same distance, micro blades with the slit width of 20μm and micro sharp-angles structure with the radius of 1μm were machined.The proposed technique can provide a new manufacturing method for machining high-performance materials. Applying this technique to the fabrication of micro products would speed up the development of MEMS.更多还原