Experimental investigation into electrochemical micromachining (EMM) process

Due to several advantages and wider range of applications, electrochemical micromachining (EMM) is considered to be one of the most effective advanced future micromachining techniques. A suitable EMM setup mainly consists of various components and sub-systems, e.g. mechanical machining unit, micro-tooling system, electrical power and controlling system and controlled electrolyte flow system etc. have been developed successfully to control electrochemical machining (ECM) parameters to meet the micromachining requirements. Investigation indicates most effective zone of predominant process parameters such as machining voltage and electrolyte concentration, which give the appreciable amount of material removal rate (MRR) with less overcut. The experimental results and analysis on EMM will open up more application possibilities for EMM.     

Influence of tool vibration on machining performance in electrochemical micro-machining of copper

Electrochemical micro-machining (EMM) appears to be promising as a future micro-machining technique since in many areas of applications, it offers several advantages, including biomedical and MEMS applications. A suitable micro-tool vibration system has been developed, which consists of tool-holding unit, micro-tool vibrating unit, etc. The developed system was used successfully to control material removal rate (MRR) and machining accuracy to meet the micro-machining requirements. Micro-holes have been produced on thin copper workpiece by EMM with stainless-steel micro-tool. Experiments have been carried out to investigate the most effective values of process parameters such as micro-tool vibration frequency, amplitude and electrolyte concentration for producing micro-hole with high accuracy and appreciable amount of MRR. From the experimental results and SEM micrographs, it is evident that the introduction of micro-tool vibration improves EMM performance characteristics. Lower electrolyte concentration in the range of 15–20 g/l reduces stray current effects. Hertz (Hz) range of tool vibration frequency improves the removal of sludge and precipitates from very small interelectrode gap. The 150–200 Hz range of tool vibration frequency can be recommended for EMM, which provides a better electrochemical machining in the narrow end gap. Compared to kHz range, Hz range micro-tool's vibration improves the MRR and accuracy in EMM.     

Impact of the shape of electrode-tool on radical overcut of micro-hole in electrochemical micromachining

To make use of the full capability of electrochemical micro-machining (EMM), a meticulous research is needed to improve the material removal, surface quality and accuracy by optimizing various EMM process parameters. Keeping this in view, an indigenous development of an EMM machine set-up has been considered to carry out a systematic research for achieving a satisfactory control on the EMM process parameters to meet the micromachining requirements. In this study an EMM machine has been developed and experiments were conducted to study the influence of some of the major process parameters such as the machining voltage, electrolyte concentrations, the pulse-on-time and the machining current on the machining rate and accuracy. The effect of the shape of the tool electrode tips on EMM has been investigated experimentally with 304 stainless steel sheets. The machining rate and the overcut are significantly influenced by the shape of the tool electrode tip.     

A study of three-dimensional shape machining with an ECμM system

This paper presents an electrochemical micromachining (ECμM) system developed with a machining gap control system. As a preliminary, electrochemical machining (ECM) experiments are carried out. The optimum machining condition of ECM is determined in terms of machining voltage, machining pulse length, amplitude of the electrode for flushing out contamination, and electrolyte concentration. After the preliminary ECM experiments, three-dimensional shape micromachining is carried out under the optimum condition. First, a prismatic electrode with a 200-μm square as the base shape is machined by ECM. Next, three-dimensional shape micromachining is carried out by scanning the prismatic electrode. A three-dimensional shape with sub-millimeter range is successfully machined.     

Influence of vibration on micro-tool fabrication by electrochemical machining

Recent trend in societies is to have micro products in limited space. Efficient micromachining technologies are essential to fabricate micro products which in turn will be helpful in saving material, energy and enhancing functionality. For micromachining, micro tool is very much essential. This paper is aimed at finding the most suitable and quickest method of micro tool fabrication by electrochemical machining. Tungsten micro tools were fabricated at different machining conditions to know the influences of voltage, frequency of tool vibration, amplitude of vibration of tungsten tool, concentrations of electrolyte and dipping length of tool inside the electrolyte. Fabrication of uniform diameter of micro tool is possible at each applied voltage starting at 2 V to higher volt utilizing vibration with appropriate amplitude. Good quality micro tools with different shapes can be fabricated by controlling a proper diffusion layer thickness within a very short time introducing the vibrations of micro tool. Finally, the fabricated micro tools were applied for machining precise micro holes and micro channel using electrochemical micromachining (EMM).     

微小孔的电解加工工艺研究

为了研究微小孔的电解加工工艺,采用在线加工的微细电极和超短脉冲电压,以及复合电解液电解加工微小孔.通过在线加工电极,避免了电极的二次装夹,提高了加工孔时的定位精度.实验中,分析了不同种类的电解液及其浓度、加工电压以及脉冲宽度对微小孔加工精度的影响.实验结果表明,添加络合剂的钝化电解液既能溶解阳极的电解产物,避免发生短路,提高了加工的稳定性,又不会增大加工间隙.而超短脉冲电压能明显减小微小孔加工的侧面间隙,并保证孔直径的一致性.     

Electrochemical drilling with vacuum extraction of electrolyte

Forward flow pattern of electrolyte is widely used in electrochemical drilling (ECD) process. But electrolyte in the machining gap presents a sharp divergent flow which causes an abnormal dissolution and even harmful sparking. Reverse flow of electrolyte leads to a stable machining process but is rarely used due to the poor application feasibility. In this paper, an electrochemical drilling method with vacuum extraction of electrolyte has been proposed. Vacuum extraction of electrolyte greatly facilitates the application of reverse flow in electrochemical drilling. Flow distributions along the machining gap with different electrolyte flow pattern are compared numerically and experimentally. Reverse flow using vacuum extraction is shown to improve the process stability while diminishing sparking and formation of striations. Machining characteristics of vacuum extraction are investigated experimentally. To minimize the radial overcut of machined hole by electrochemical machining with vacuum extraction of electrolyte, the orthogonal design is used to optimize process parameters such as initial machining gap, applied voltage, tool feed rate, and electrolyte concentration. Good results have been obtained in the experiments with optimized parameters.     

Improving machining performance of wire electrochemical discharge machining by adding SiC abrasive to electrolyte

The use of wire electrochemical discharge machining (WECDM) to slice hard brittle materials has recently been studied because its effectiveness is independent of the mechanical characteristics of the machined materials. Therefore, materials with high hardness, brittleness, strength and electrical insulation, which are difficult-to-cut, can be machined. In ECDM, the electrochemical reaction produces hydrogen bubbles, which accumulate around the cathode. A thin gas layer forms on the surface of the electrode and isolates the electrode from the electrolyte. When a voltage that exceeds the critical voltage is applied, continuous discharge occurs. The material near the electrode is removed by the discharge erosion and chemical etching. The use of WECDM to cut electrically insulating materials has only recently been investigated. However, the breakdown of the gas in the bubbles and the vibration of the wire in WECDM strongly affect the shape accuracy. This work aims to improve the over cut quality by adding SiC abrasive to the electrolyte. A mechanism that combines discharge, chemical etching and abrasive cutting is studied. The effects on expansion, roughness and material removal rate (MRR) are discussed. The experimental results reveal that adding abrasive reduces the slit expansion because it increases the critical voltage. The particles disrupt the bubble accumulation to form an isolating layer around the wire, increasing the critical voltage and reducing the discharge energy. The surface roughness is improved because the abrasive helps to refine the micro-cracks and melted zone that is formed by discharge heat erosion. Meanwhile, smaller grit produces lower roughness. The quality of the slit can be controlled; its expansion and roughness of the slit are 0.024 mm and 0.84 um Ra, respectively.     

Compound machining of titanium alloy by super high speed EDM milling and arc machining

A novel compound machining of titanium alloy (Ti6Al4V) by super high speed electrical discharge machining (EDM) milling and arc machining was proposed in this paper. The power supply consisted of a pulse generator and a DC power source which were isolated from each other. A rotating pipe graphite electrode was connected to the negative pole of the power supply. The plasma channel was able to deionize, and maximum material removal rate (MRR) reached 21,494 mm³/min with a relative electrode wear ratio (REWR) of 1.7% because of high current and efficient flushing. Compared with traditional EDM, the compound machining achieved a significantly higher MRR but a similar REWR. To investigate the characteristics of the compound machining, the effects of electrode polarity, peak voltage, peak current, and flushing pressure on the performance of the process, including its MRR, REWR, and radius of overcut (ROC), were determined. In addition, scanning electron microscopy, X-ray diffraction, and microhardness analysis were conducted. Result shows that the proposed method can machine difficult-to-machine materials efficiently.     

Electrochemical micromachining of a Zr-based bulk metallic glass using a micro-tool electrode technique

For the first time the possibility of electrochemical micromachining (ECMM) of a Zr-based bulk metallic glass (BMG) using a micro-tool electrode technique is reported. It is demonstrated that the choice of the electrolyte chemistry is substantial for a successful ECMM processing. For the bulk glassy Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ alloy a concentrated aqueous NaNO₃ standard machining solution is not suitable due to formation of thick and dense corrosion product layers which hinder the machining of structures with high aspect ratio. On the other hand, a commercial methanolic HClO₄ solution is shown to be very promising. In the first experiments with this electrolyte micro-hole structures were machined with aspect ratios of about 1 at depths of ～40 μm. The effect of process parameters such as pulse voltage and pulse length was investigated and their influence on the machined structure morphology is established. In a first approach the potential and challenges of this electrochemical micromachining technique for microforming of multi-component bulk metallic glass surfaces will be discussed.     

光刻胶掩膜微细电化学加工参数的试验研究

对光刻胶掩膜微细电化学加工参数进行了试验分析研究，发现光刻胶厚度、开口角度、咏冲电源频率、脉宽及电解液配方对加工质量都有影响，在此基础上提出改善加工质量的可行性方案。     

Finite element prediction of material removal rate due to electro-chemical spark machining

Electro-chemical spark machining (ECSM) is an innovative hybrid machining process, which combines the features of the electro-chemical machining (ECM) and electrodischarge machining (EDM). Unlike ECM and EDM, ECSM is capable of machining electrically non-conducting materials. This paper attempts to develop a thermal model for the calculation of material removal rate (MRR) during ECSM. First, temperature distribution within zone of influence of single spark is obtained with the application of finite element method (FEM). The nodal temperatures are further post processed for estimating MRR. The developed FEM based thermal model is found to be in the range of accuracy with the experimental results. Further the parametric studies are carried out for different parameters like electrolyte concentration, duty factor and energy partition. The increase in MRR is found to increase with increase in electrolyte concentration due to ECSM of soda lime glass workpiece material. Also, the change in the value of MRR for soda lime glass with concentration is found to be more than that of alumina. MRR is found to increase with increase in duty factor and energy partition for both soda lime glass and alumina workpiece material.     

Micropatterning of Ni-based metallic glass by pulsed wire electrochemical micro machining

The technique of wire electrochemical micro machining (WECMM) is proposed firstly for the micropatterning of Ni-based metallic glass in this paper. Metallic glass (MG) exhibits many outstanding properties such as high hardness and strength, which enable it to be used as functional and structural materials in micro electromechanical systems (MEMS). A significant limitation to the application of MGs is the challenge of shaping them on micro scale. WECMM is a non-traditional machining technique to fabricate microstructures that has some unique advantages over other methods, which will be a promising technique for micro shaping of metallic glass structures. Taking the example of a Ni-based glassy alloy, Ni₇₂Cr₁₉Si₇B₂, the polarization and fabrication characteristic in dilute hydrochloric acid electrolyte were investigated. Changes in the machined slit width in terms of several experimental parameters were investigated to find the optimal ones. Finally, the optimal machining parameters: HCl electrolyte concentration of 0.1 M, applied voltage of 4.5 V, pulse duration of 80 ns, pulse period of 3 μs and feed rate of 0.3 μm s⁻¹ were employed for the fabrication of microstructures. Such as a micro square helix with a slit width of 14.0 μm, standard deviation of 0.2 μm and total length up to 2000 μm, along with a micro pentagram structure with side length of 90 μm and sharp corner of 36°, were machined with a high level of stability and accuracy.     

Advancement in electrochemical micro-machining

Electrochemical micro-machining (EMM) appears to be very promising as a future micro-machining technique, since in many areas of applications it offers several advantages, which include higher machining rate, better precision and control, and a wide range of materials that can be machined. In this paper, a review is presented on current research, development and industrial practice in micro-ECM. This paper highlights the influence of various predominant factors of EMM such as controlled material removal, machining accuracy, power supply, design and development of microtool, role of inter-electrode gap and electrolyte, etc. EMM can be effectively used for high precision machining operations, that is, for accuracies of the order of ±1 μm on 50 μm. Some industrial applications of EMM have also been reported. Further research into EMM will open up many challenging opportunities of improvement towards greater machining accuracy, new materials machining and generation of complex shapes for effective utilization of ECM in the micro-machining domain.     

微细电化学加工研究新进展

结合国内外微细电化学加工技术的最新进展，系统地综述了微细电化学加工在多个方面的研究情况和工艺特点，例如LIGA工艺、用电化学隧道显微镜(electmchemical STM)的针尖进行纳米级尺寸的电化学加工、用超短脉宽脉冲电压微细电化学加工等。微细电化学在未来的微纳加工中必将大有作为。     

MA956高温合金活动模板电解加工小孔技术研究

对采用活动模板电解加工技术在MA956铁基高温合金薄板上加工小孔的工艺方法进行了讨论。研究了电解液温度、加工电压、电源占空比和脉冲频率等参数对小孔加工结果的影响。研究表明:采用10%w.t.NaNO_3电解液,在电解液温度为30℃、加工电压为40 V、电源占空比为30%、电源脉冲频率为400 Hz时,能在MA956高温合金薄板上加工获得锥度小的小孔。     

Micro electrochemical machining for complex internal micro features

In this paper, the application of micro electrochemical machining (ECM) for the micromachining of internal features is investigated. By controlling pulse conditions and machining time, micro features are machined on the side wall of a micro hole. These methods can easily machine a micro hole with larger internal diameters than the entrance diameter, which is very difficult to do by the conventional processes. A micro disk-shaped electrode with an insulating layer on its surface is also introduced to machine microgrooves inside the hole. This method is similar to the turning lathe process. The purpose of this study was to confirm the various possibilities of making complex internal structures in a micro hole by micro ECM.     

A material removal analysis of electrochemical machining using flat-end cathode

Electrochemical machining (ECM) has been increasingly recognized for the potential for machining, while the precision of the machined profile is a concern of its application. A process to erode a hole of hundreds of micrometers on the metal surface is analyzed in the current paper. A theoretical and computational model is presented to illustrate how the machined profile evolves as the time elapses. The analysis is based on the fundamental law of electrolysis and the integral of a finite-width tool. The paper also discusses the influence of experimental variables including time of electrolysis, voltage, molar concentration of electrolyte and electrode gap upon the amount of material removal and diameter of machined hole. The results of experiment show the material removal increases with increasing electrical voltage, molar concentration of electrolyte, time of electrolysis and reduced initial gap. The time of electrolysis is the most influential factor on the produced diameter of hole.     

Study of gas film quality in electrochemical discharge machining

Electrochemical Discharge Machining (ECDM) has been demonstrated to be an alternative spark-based micromachining method for fabricating microholes and microchannels in non-conductive brittle materials. However, the mechanism for attaining accurate control of the contour shape and dimensions remains to be explored. In ECDM process, the gas film on the electrode surface is used as the dielectric medium required for discharge generation. Quality of gas film is the dominant factor that determines the machining qualities such as geometric accuracy, surface roughness and repeatability. Nevertheless, it is difficult to assess the gas film quality of ECDM. In this study, current signals and machined contours were taken as indexes of gas film quality. Experimental results showed that a stable and dense gas film could be obtained when the applied voltage exceeded the critical voltage and reached a specific level, which is called the “transition voltage” in this study. At the transition voltage, a stable electrochemical discharge activity could be generated, thus producing the smallest deviation of contour dimensions. Moreover, when the drilling process reached a certain critical depth, bubbles inside the hole could not easily escape. In order to reduce the interface energy between bubbles, a thicker gas film is formed at the hole entrance, resulting in unstable discharge performance that undermined machining results. In summary, information provided by current signals can shed light on the changes in gas film structure, which serve as useful reference for varying process parameters to achieve better efficiency and accuracy.     

微细组合电加工样机研制及实验研究

基于新研发的一套微细组合电加工样机μEM-200CDS2,介绍了研发过程中探索出的最小脉宽可以达纳秒级的双功能微能脉冲电源以及样机中的若干关键技术,包括放电状态的双参数检测技术、工具电极在位多功能磨削技术、工作液稳定供给控制技术等。其中,双功能微能脉冲电源具备主动消电离环节,可以减少脉间的残余电荷放电,有利于提高加工表面质量;组合电加工样机床身设计有利于提高系统的加工精度和效率。最后,结合小孔的加工试验研究了典型的组合电加工工艺过程,结果表明:该过程中,可以并行完成工具电极在位修整与零件加工,有利于提高微小特征的加工效率。