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.     

Nanocrystaline Electroforming Process

This study focuses on nanocrystalline electroforming for the improvement of the properties of deposited parts in precision and micro fabrications. Experiments were conducted to refine the grain size and understand the effects of the grain size on properties of deposited metals. It has been found that high frequency pulse current, strong electrolyte flushing and some additive significantly refined the crystal grain and reduced average sizes of grains down to 20nm. The reduction of grain sizes has been found to offer substantial gains in the properties of the deposited metal such as the hardness and the corrosion resistance.     

In‐situ investigation of the surface‐topography during anodic dissolution of copper under near‐ECM conditions

Electrochemical machining is characterized by deliberate high speed anodic dissolution. The distance between anode and cathode are only a few hundred microns. Additionally, the electrolyte flow rate is in the range of approximately meter/second. A special electrochemical cell design was developed to investigate the surface topography during the anodic dissolution simultaneously and in‐situ under near‐ECM conditions. The anode was directly placed under the cathode with a gap of 350 µm. We carried out pulse experiments at 15 A/cm² and 25 A/cm² with an electrolyte flow rate of 4m/s. First‐time it was possible to observe the surface changing of the anode directly during current pulses by using a video camera. Different stages e.g. roughening, film formation or gas evolution could be distinguished.     

综合改善微细电解加工精度的工艺研究

电解加工的阳极电化学溶解原理使其在微细加工领域具有巨大的发展潜力,但杂散腐蚀和流场条件恶劣制约加工精度的提高.分析了影响微细电解加工的主要因素,提出综合改善微细电解加工精度的工艺途径.理论分析和实验研究均表明:将LIGA工艺制备高质量微细阵列电极、电极侧壁绝缘、高频脉冲电流及非线性电解液加工、电极间歇回退伺服控制等方法有机结合,能有效约束电场、改善流场,提高微细电解加工的精度.     

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.     

新型高频窄脉冲电解电源的研制

针对精微电解加工工艺的要求,提出了一种新的电源设计方案,并研制了一台样机,解决了当前电解电源输出频率低、脉宽较大不能满足微精加工要求的问题.该电源具有调压精度高、损耗低、效率高以及体积、质量小等特点,输出频率最高可达100 kHz,最小脉宽1 μs.经初步的加工实验,证明了此方案的可行性.     

微细电解加工技术的概况与展望

概括总结了微细电解加工的典型技术,综合分析了近几年微细电解加工技术的研究成果和最新进展,包括脉冲电源、新型电解液、复合加工、微器件加工以及基础理论等方面,展望了其未来的研究重点和发展趋势.     

TC4钛合金异形型腔电解加工实验研究

通过分析钛合金电解加工时金属基体表面点蚀、钝化过程,研究了NaNO_3电解液、NaCl电解液及其混合电解液对TC4钛合金的电化学溶解特性的影响。对比分析不同成分电解液中的工件表面质量和加工效率,最终选用质量分数为10%NaNO_3和20%NaCl的混合电解液进行TC4钛合金异形型腔电解加工工艺实验。结果表明:采用混合电解液可实现TC4钛合金异形型腔的高效加工,稳定加工速度可达2.8 mm/min;当阴极进给速度为2.4 mm/min时,型腔一致性较好。     

Study of the electrolyte flow at narrow openings during electrochemical machining

Modelling of ECM is a powerful tool to improve the cost- and time intensive tool-development process. However, for certain combinations of process and geometric parameters, the simulation results include non-physical negative pressure values inside the electrolyte flow. These phenomena occur near the narrow opening into the machining gap. According to Bernoulli's law, it is plausible that low-pressure values are present in this region possibly leading to evaporation. Based on these facts, it was hypothesized that cavitation could occur during ECM. In order to successfully validate this hypothesis, the electrolyte flow is analysed both in experimental as well as simulation-based studies.     

GCr15轴承钢脉冲电化学光整加工实验研究

对GCrl5轴承钢的脉冲电化学光整加工进行了实验研究，重点讨论了加工间隙、电流密度、脉冲参数、电解液浓度、加工温度等主要工艺参数对加工表面质量的影响规律。研究结果表明：用脉冲电化学光整加工技术加工GCrl5轴承钢能取得很好的效果，在轴承滚道光整加工中具有良好的应用前景。     

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。     

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.     

脉冲电沉积超细晶粒Ni-Mn合金的显微硬度

利用冲液装置和高频窄脉宽脉冲电流,开展了Ni-Mn合金的电沉积试验,得到的沉积层具有接近或达到纳米级的超细晶粒.对电沉积所得到的试片进行了显微硬度测试,研究与分析了电沉积工艺条件对沉积层显微硬度的影响.结果表明,电沉积工艺条件通过影响沉积层的锰含量和晶粒大小而影响沉积层的显微硬度.     

Micro electrochemical machining using electrostatic induction feeding method

This paper describes a micro ECM system using the electrostatic induction feeding method. With this method, since the pulse voltage is coupled to the tool electrode by capacitance, the pulse duration of the electrolytic current is determined by the rise and fall time of the voltage pulse and is thus significantly short, realizing short gap width. A servo feed system was also developed based on the measurement of the gap voltage. Wear of the tungsten tool was negligibly small because of the oxide layer formed on the tool, allowing micro-holes with sharp edges and straight walls to be drilled.     

Analysis of the electrochemical behaviors of WC–Co alloy for micro ECM

Micro electrochemical machining (ECM) of tungsten carbide with cobalt binder (WC–Co) was studied using ultrashort pulses. In ECM, the machining characteristics were investigated according to machining conditions such as electrolyte, workpiece potential, and applied voltage pulse. Using a mixture of sulfuric acid and nitric acid, microstructures with a sharp edge and good surface quality were machined on tungsten carbide alloy. The potentials of workpiece electrode and tool electrode were determined by considering the machining rate, machining stability, and surface quality of products. With the negative potential of the workpiece electrode, oxide formation was successfully prevented and shape with good surface quality in the range from R_a 0.069 μm to 0.075 μm were obtained by electrochemical machining. Moreover, the performance of ECM, which includes machining gap, tapering, surface roughness, and machining time, without tool wear was compared with that of electrical discharge machining (EDM). Microstructures of WC–Co with a sharp edge and good surface quality were obtained by electrochemical milling and electrochemical drilling. Micro electrochemical turning was also introduced to fabricate micro shafts.     

Crevice Corrosion of Titanium in High Temperature-Concentrated Chloride Environments

Crevice corrosion of titanium is activated in concentrated chloride media at 100 °C. This was possible only with the tightest gap (0.005 cm) between Ti-Ti surfaces. No crevice corrosion was observed with greater gap dimensions. The design of the crevice led to the occurrence of two concentric circular rings of corroded areas, with many pits on them. After potentiostating in the passive region for 5 h in 25% NaCl (pH = 4.7)—where hydrogen evolution is thermodynamically prohibited—hydrogen gas bubbles were observed to egress out of the crevice mouth during ongoing crevice corrosion. This indicates that hydrogen evolution occurs within the crevice. The results are compatible with the occurrence of gradually increasing ohmic potential shift and localized acidification in the crevice electrolyte as judged by the measured gradual increase of the crevice corrosion current. The high acidity of the bulk electrolyte does not seem to be sufficient or even a necessary condition for crevice corrosion to occur.     

Experimental investigation on the influence of electrochemical machining parameters on machining rate and accuracy in micromachining domain

Non-conventional machining is increasing in importance due to some of the specific advantages which can be exploited during micromachining operation. Electrochemical micromachining (EMM) appears to be a promising technique, since in many areas of application, it offers several special advantages that include higher machining rate, better precision and control, and a wider range of materials that can be machined. A better understanding of high rate anodic dissolution is urgently required for EMM to become a widely employed manufacturing process in the micro-manufacturing domain. An attempt has been made to develop an EMM experimental set-up for carrying out in depth research for achieving a satisfactory control of the EMM process parameters to meet the micromachining requirements. Keeping in view these requirements, sets of experiments have been carried out to investigate the influence of some of the predominant electrochemical process parameters such as machining voltage, electrolyte concentration, pulse on time and frequency of pulsed power supply on the material removal rate (MRR) and accuracy to fulfil the effective utilization of electrochemical machining system for micromachining. A machining voltage range of 6 to 10 V gives an appreciable amount of MRR at moderate accuracy. According to the present investigation, the most effective zone of pulse on time and electrolyte concentration can be considered as 10–15 ms and 15–20 g/l, respectively, which gives an appreciable amount of MRR as well as lesser overcut. From the SEM micrographs of the machined jobs, it may be observed that a lower value of electrolyte concentration with higher machining voltage and moderate value of pulse on time will produce a more accurate shape with less overcut at moderate MRR. Micro-sparks occurring during micromachining operation causes uncontrolled material removal which results in improper shape and low accuracy. The present experimental investigation and analysis fulfils various requirements of micromachining and the effective utilization of ECM in the micromachining domain will be further strengthened.     

Enhancement of mass transport in micro wire electrochemical machining

In micro wire electrochemical machining, the machining gap between the cathode wire and anode workpiece is so tiny that it is difficult to remove electrolysis products and renew electrolyte, leading to frequent electric short circuits and quite low processing speed. Three approaches of enhancing mass transport, electrolyte flushing along the wire, wire traveling in one direction and micro-vibration of cathode wire have been studied theoretically and experimentally in this paper. The results demonstrate that the proposed methods significantly enhance the mass transport and thus improve the machining stability, the productivity and the surface quality for micro wire electrochemical machining.     

Mechanical Properties of Electrodeposited Nanocrystalline Nickel

In this paper, dense bulk nanocrystalline (nc) nickel electrodeposits with various grain sizes were produced by using high frequency pulse current and strong electrolyte flushing. The effects of the grain sizes on the mechanical properties were discussed for room and a medium temperature. It was found that the properties of the deposited nickel such as microhardness, corrosion resistance and yield stress (at room temperature and 473 K) were improved substantially with the decrease in the grain size. A deviation of yield stress from the Hall-Petch relationship for nc nickel was observed when the grain sizes were decreased to less than 70 nm at room temperature. A low yield stress value of nc nickel was obtained at a temperature of 673 K as a result of its thermodynamic instability.     

On Electro Discharge Machining of Inconel 718 with Hollow Tool

Inconel 718 is a nickel-based alloy designed for high yield, tensile, and creep-rupture properties. This alloy has been widely used in jet engines and high-speed airframe parts in aeronautic application. In this study, electric discharge machining (EDM) process was used for machining commercially available Inconel 718. A copper electrode with 99.9% purity having tubular cross section was employed to machine holes of 20?mm height and 12?mm diameter on Inconel 718 workpieces. Experiments were planned using response surface methodology (RSM). Effects of five major process parameters??pulse current, duty factor, sensitivity control, gap control, and flushing pressure on the process responses??material removal rate (MRR) and surface roughness (SR) have been discussed. Mathematical models for MRR and SR have been developed using analysis of variance. Influences of process parameters on tool wear and tool geometry have been presented with the help of scanning electron microscope (SEM) micrographs. Analysis shows significant interaction effect of pulse current and duty factor on MRR yielding a wide range from 14.4 to 22.6?mm³/min, while pulse current remains the most contributing factor with approximate changes in the MRR and SR of 48 and 37%, respectively, corresponding to the extreme values considered. Interactions of duty factor and flushing pressure yield a minimum surface roughness of 6.2???m. The thickness of the sputtered layer and the crack length were found to be functions of pulse current. The hollow tool gets worn out on both the outer and the inner edges owing to spark erosion as well as abrasion due to flow of debris.