超声振动辅助气中放电加工的研究

介绍了超声振动辅助气中放电加工技术，试验研究了电压、脉冲宽度、峰值电流、超声振幅及气体介质压力等参数对加工效率、工件表面粗糙度及电极损耗的影响，并对试验结果进行了分析。     

超声振动辅助气体介质电火花加工机理研究

简述了超声振动辅助气体介质电火花加工原理，分析了超声振动辅助气体介质电火花加工电极材料抛出的物理过程，探讨了工件材料抛出机理以及气体介质、超声振动对材料蚀除的影响机理。     

介质氧化特性对钛合金电火花加工电极损耗的影响研究

研究了工作介质的氧化特性对钛合金电火花加工电极绝对损耗、相对损耗率及电极表面微观形貌的影响规律。结果表明,具有氧化特性的工作介质可在加工过程中使电极氧化,并在电极表面形成一层氧化保护膜,减小带电粒子对基体的轰击,从而降低电极绝对损耗;介质的氧化特性也会对钛合金电火花加工效率和排屑产生影响,使电极相对损耗率呈先减小、后增长、再趋于稳定的趋势;极间氧气增多能增大放电爆炸力,使电极表面微裂纹和气孔数量增多;工作介质存在一个最佳氧化性能,可使钛合金加工的电极损耗达到最佳状态。     

电极结构对短电弧-电化学复合加工深窄槽影响研究

深窄槽结构具有尺寸小、深宽比较大的特点,狭小的加工区域存在排屑不畅、散热效果差等问题。为解决深窄槽加工过程中排屑困难的问题,提出通过优化电极结构来提升深窄槽短电弧-电化学复合加工的稳定性。分别设计单孔、多孔及螺旋3种管状电极结构,对不同电极结构加工时的间隙流场状态进行仿真研究。对比不同电极结构极间介质流速与压力的分布状态,并对仿真结果进行实验验证,探究电极结构对短电弧-电化学复合加工性能包括加工效率、尺寸精度、表面质量等指标的影响。实验结果表明：螺旋电极结构相比于单孔电极和多孔电极更能改善极间的流场状态,在保证深窄槽尺寸精度的情况下提高了加工效率与表面质量。     

电极丝超声振动的低速走丝电火花线切割加工研究

研究了低速走丝电火花线切割加工中附加超声振动后电极丝的高频振动对加工性能的影响。建立了描述超声振动下的电极丝振动的数学模型，并进行了计算机模拟分析。实验表明，电极丝附加超声振动可以改善极间放电状态，提高加工效率，减少断丝率，降低加工表面粗糙度值。     

丙三醇水溶液电火花加工硅晶体特性研究

为了提高硅晶体电火花成形加工效率、降低电极损耗,采用丙三醇水溶液作为工作介质。分析了介质中的碳、氢、氧元素对加工效果的影响,以及电导率、粘度、介质成分对加工特性的影响,研究表明:击穿放电间隙受电导率与粘度的影响,丙三醇水溶液可提高放电间隙,增强加工稳定性;丙三醇分子会在放电高温下分解出碳分子,其自身的微观爆炸力可促使碳分子和极间蚀除产物向两极移动,增强了电极的涂覆效应,降低了电极损耗。工艺实验结果表明:丙三醇水溶液的加工特性优于去离子水,采用质量分数为30%的丙三醇溶液加工时的最佳占空比为1∶7,加工效率为11.88 mm~3/min,电极损耗比为3.7%。     

电极侧壁绝缘微细孔电解加工工艺研究

将超声振动技术应用于微细孔的电解加工中,以排除间隙内的加工产物,然而,超声空化现象产生的冲击力会影响电极表面的绝缘层,并加速其破坏。为提高侧壁绝缘电极的使用寿命,采用微弧氧化和阴极电泳工艺在微细钛电极表面形成由陶瓷膜和电泳漆膜组成的双绝缘层。通过超声振动辅助微细孔电解加工实验,对电极侧壁双绝缘层的耐久性进行验证,并分析了超声振动功率、电解液浓度和加工电压对双膜侧壁绝缘电极微细孔加工精度的影响。实验表明:双绝缘层电极在超声辅助微细孔电解加工中显示了很强的绝缘耐久性;当超声振动功率超过一定值后,微细孔电解加工能稳定进行,之后,随着功率的增加,孔的精度改善很小。在稳定加工中,需降低电解液浓度和加工电压,从而减小杂散腐蚀,保证加工孔的形状精度。     

液包丝供给方式的电火花线切割实验研究

在大气介质中对Cr12MoV模具钢进行电火花线切割精加工,较工作液介质中加工可获得更高的加工表面质量,但也存在表面碳化、电极丝热疲劳损伤等问题。为解决上述问题,采用液包丝(双介质)供给代替传统供给方式进行电火花线切割精加工。结果表明:在液包丝(双介质)中加工的表面质量比大气介质中的略高,且电极丝损耗明显降低。研究结果可为Cr12MoV模具钢的高质量、稳定、低损切割提供参考。     

钛合金深小孔精微电火花加工工艺研究

对钛合金深小孔的电火花加工工艺进行了深入的研究。优选了电火花加工放电参数;应用了超声复合和削边电极等工艺手段。通过研究,极大地提高了加工速度和加工质量。     

Study on the Combined Machining Technology of Ultrasonic Vibration Assisted EDM in Gas Medium

介绍一种新兴的加工技术——超声振动-气体介质电火花复合加工技术,并通过机制分析和加工实验比较超声振动-气体介质电火花复合加工与普通气体介质电火花加工各项数据的差异,得出超声振动-气体介质电火花复合加工技术优于普通气体介质电火花加工的结论.     

微细电火花加工实现条件的研究

介绍了微细电火花加工的原理和特点,从加工表面质量、脉冲电源、微细工具电极的制造和安装、放电面积效应的影响、伺服控制系统等方面对微细电火花加工的实现条件进行了研究,并给出了微细轴的电火花加工等具体加工实例.研究结果对微细电火花加工技术的具体应用具有重要的参考价值和指导意义.     

Workpiece debris deposition on tool electrodes and secondary discharge phenomena in micro-EDM

During electrical discharge machining (EDM), ablated workpiece material is rapidly solidified upon ejection into the dielectric and thought not to become reattached to the electrode surfaces. This work furthers the understanding of the little understood discharge gap phenomena by investigating the attachment of machined material back onto the tool electrode surface and explains the mechanism of this attachment. After the machining of high-aspect ratio slots, SEM and EDS techniques along with single discharge and cross-sectional analysis were used to explain that debris reattachment onto the tool electrode does not occur randomly but is dependent on its remelting in the dielectric by the secondary discharge process. The subsequently bonded material is present mainly in the centre of the discharge crater, with no attachment occurring outside of discharge affected regions. The surfaces of electrodes subject to intense secondary sparking are therefore liable to transient surface properties dependent on the composition of the deposited material. It is also observed that the deposited material on the tool electrode can offer a protective effect against wear from further secondary discharges and so potentially enhancing tool life.     

Effect of machining fluid on the process performance of electric discharge milling of insulating Al2O3 ceramic

Wire electric discharge machining (WEDM) and electrical discharge machining (EDM) promise to be effective and economical techniques for the production of tools and parts from conducting ceramic blanks. However, the manufacturing of insulating ceramic blanks with these processes is a long and costly process. This paper presents a new process of machining insulating ceramics using electrical discharge (ED) milling. ED milling uses a thin copper sheet fed to the tool electrode along the surface of the workpiece as the assisting electrode and uses a water-based emulsion as the machining fluid. This process is able to effectively machine a large surface area on insulating ceramics. Machining fluid is a primary factor that affects the material removal rate and surface quality of the ED milling. The effects of emulsion concentration, NaNO₃ concentration, polyvinyl alcohol concentration and flow velocity of the machining fluid on the process performance have been investigated.     

Effect of surface roughness of tool electrode materials in ECDM performance

Electrochemical discharge machining (ECDM) is an emerging non-traditional machining process that involves high-temperature melting assisted by accelerated chemical etching. In this study, the tool electrode (200 μm in diameter) is fabricated by wire electrical discharge grinding (WEDG). After the tool electrode is machined, the surface roughness of tool electrode materials (stainless steel, tungsten carbide, and tungsten) is different because of the physical properties. However, the surface roughness affects the wettability on tool electrode, and also changed the coalesce status of gas film in ECDM. Hence, this study explores the wettability and machining characteristics of different tool electrode materials and their impact on gas film formation. Their machining performance and extent of wear under gravity-feed micro-hole drilling are also examined. Experimental results show that the optimal voltage of different tool electrode can shed light on the machining performance. Moreover, wettability of tool electrode is determined by surface roughness of tool material, which in turn affects the coalesce status of gas film, machining stability and micro-hole diameter achieved. In addition, differences in tool material also results in variations in machining speed. Significant tool wear is observed after repeated gravity-feed machining of 50 micro-holes.     

Machining performance of silicon carbide ceramic in end electric discharge milling

A new process of machining silicon carbide (SiC) ceramic using end electrical discharge milling is proposed in this paper. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and low cost. The effects of machining conditions on the material removal rate, electrode wear ratio, and surface roughness have been investigated. The surface microstructures machined by the new process are examined with a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and an X-ray diffraction (XRD). The results show that the SiC ceramic is removed by melting, evaporation and thermal spalling, the material from the tool electrode can transfer to the workpiece, and a combination reaction takes place during end electric discharge milling of the SiC ceramic.     

Surface modification by electrical discharge machining: A review

The last decade has seen an increasing interest in the novel applications of electrical discharge machining (EDM) process, with particular emphasis on the potential of this process for surface modification. Besides erosion of work material during machining, the intrinsic nature of the process results in removal of some tool material also. Formation of the plasma channel consisting of material vapours from the eroding work material and tool electrode; and pyrolysis of the dielectric affect the surface composition after machining and consequently, its properties. Deliberate material transfer may be carried out under specific machining conditions by using either composite electrodes or by dispersing metallic powders in the dielectric or both. This paper presents a review on the phenomenon of surface modification by electric discharge machining and future trends of its applications.     

CuW90微小孔电火花加工实验研究

利用单因素实验和正交试验法探究了电源电容、电流、伺服参考电压、伺服速度及占空比对CuW90微小孔电火花加工效率和电极损耗的影响。结果表明:伺服参考电压和占空比对加工效率和电极损耗的影响都较大,而电容、电流对其影响较小,最终得到了CuW90电火花微小孔加工的最优参数组合。     

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.     

Probability of precision micro-machining of insulating Si3N4 ceramics by EDM

Electrical discharge machining (EDM) is used as a precision machining method for the electrically conductive hard materials with a soft electrode material. But recently we succeeded to machine on insulating material by EDM. The technology is named as an assisting electrode method. The EDMed surface is covered with the electrical conductive layer during discharge. The layer holds the electrical conductivity during discharge. For micro-EDM, the wear of tool electrode becomes lager ratio than the normal machining. So the micro-machining is extremely difficult to get the precision sample.

In this paper to obtain a fine and precise ceramics sample, some trials were carried out considering the EDM conditions, tool electrodes material and assisting electrode materials. Insulating Si₃N₄ ceramics were used for workpiece. The machining properties were estimated by the removal rate and tool wear ratio. To confirm the change of micro-machining process, the discharge waveforms were observed. The micro-machining of the Ø0.05 mm hole could be machined with the commercial sinking electrical discharge machine.     

Experimental characterization of material removal in dry electrical discharge drilling

Dry electrical discharge machining is one of the novel EDM variants, which uses gas as dielectric fluid. Experimental characterization of material removal in dry electrical discharge drilling technique is presented in this paper. It is based on six-factor, three-level experiment using L₂₇ orthogonal array. All the experiments were performed in a ‘quasi-explosion’ mode by controlling pulse ‘off-time’ so as to maximize the material removal rate (MRR). Furthermore, an enclosure was provided around the electrodes with the aim to create a back pressure thereby restricting expansion of the plasma in the dry EDM process. The main response variables analyzed in this work were MRR, tool wear rate (TWR), oversize and compositional variation across the machined cross-sections. Statistical analysis of the results show that discharge current (I), gap voltage (V) and rotational speed (N) significantly influence MRR. TWR was found close to zero in most of the experiments. A predominant deposition of melted and eroded work material on the electrode surface instead of tool wear was evident. Compositional variation in the machined surface has been analyzed using EDAX; it showed migration of tool and shielding material into the work material. The study also analyzed erosion characteristics of a single-discharge in the dry EDM process vis-á-vis the conventional liquid dielectric EDM. It was observed that at low discharge energies, single-discharge in dry EDM could give larger MRR and crater radius as compared to that of the conventional liquid dielectric EDM.