Modeling and fabrication of micro tools by pulsed electrochemical machining

Accurate and precise micro tools are essential for the micromachining of complex micro features in a wide range of engineering materials including metals and ceramics. Existing micro tool fabrication processes suffer from drawbacks such as surface cracks, residual stress and deformations. Electrochemical machining of micro tools is proposed in this work to overcome these limitations. In this research, a mathematical model has been developed to predict the diameter of the micro tool fabricated. Experimental verification of the model using an in-house built micro electrochemical machining system reveals good correlation with theoretical predictions. Using the procedure described in this paper, very high aspect ratio (280–450) tungsten micro tools have been produced.     

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.     

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.     

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.     

Micro fabrication by electrochemical process in citric acid electrolyte

This paper describes micro electrochemical machining of stainless steel in an environmentally friendly electrolyte of citric acid. Electrochemical dissolution region is minimized by applying a few hundred nanosecond duration pulses between the tungsten SPM tip and the work material. Electrochemical machining (ECM) characteristics according to citric acid concentration, feed speed and electric conditions such as pulse amplitude, pulse frequency, and tool electrode baseline potential are investigated through a series of experiments. Micro holes of 60 μm in diameter with the depth of 50 μm and 90 μm in diameter with the depth of 100 μm are perforated using citric acid electrolyte. Square and circular micro cavities are also fabricated by electrochemical milling. This research may contribute to the development of safe and eco-friendly micro manufacturing technology.     

Electrochemical micromachining using vibratile tungsten wire for high-aspect-ratio microstructures

Electrochemical micromachining can remove electrically conductive materials with the transferring of ions, so that high precision is achievable. A novel method for fabricating high-aspect-ratio microstructures by electrochemical micromachining using vibratile tungsten wire was proposed in this paper. The slight vibration of tungsten wire can improve the machining stability. The relations between the machining accuracy and machining parameters were experimentally studied. Micro groove with the width of 15 μm was machined, and micro sharp-angles structure with aspect ratio of 10 was obtained experimentally.     

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.     

Fabrication of deep micro-holes in reaction-bonded SiC by ultrasonic cavitation assisted micro-EDM

Ultrasonic vibration was applied to dielectric fluid by a probe-type vibrator to assist micro electrical discharge machining of deep micro-holes in ceramic materials. Changes of machined hole depth, hole geometry, surface topography, machining stability and tool material deposition under various machining conditions were investigated. Results show that ultrasonic vibration not only induces stirring effect, but also causes cloud cavitation effect which is helpful for removing debris and preventing tool material deposition on machined surface. The machining characteristics are strongly affected by the vibration amplitude, and the best machining performance is obtained when carbon nanofibers are added into the vibrated dielectric fluid. As test pieces, micro-holes having 10 μm level diameters and high aspect ratios (>20) were successfully fabricated on reaction-bonded silicon carbide in a few minutes. The hybrid EDM process combining ultrasonic cavitation and carbon nanofiber addition is demonstrated to be useful for fabricating microstructures on hard brittle ceramic materials.     

Design and development of a precision machine tool using counter motion mechanisms

In order to meet the increasing demand for high-quality miniature parts made of a wide variety of materials, the electronics, biomedical and optical industries are moving towards micro/nano-machining. Currently, mechanical micromachining can only be performed under very low feed rates and small depth of cut, which makes it very difficult to reach reasonable productivity. To cope with the low-productivity problem for micro/nano-machining of high-precision molds or miniature parts, a highly accurate and productive machining center has been designed and developed in this paper. The developed machine tool is equipped with counter balance axes, and each axis is driven at its center of gravity to achieve high acceleration/deceleration without causing any vibration. This paper describes the theoretical and practical background of the design of the machine tool and its control and measurement system. Then, experiments are carried out to evaluate the machining performance of this designed machine tool.     

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.     

某型航空发动机燃油喷嘴旋流室的微细电解加工研究

针对某型航空发动机燃油喷嘴结构尺寸微小、材料硬度较高、切削加工困难等问题,介绍了微细电解加工的原理和实验装置,制备了微细棒状工具电极和三角形钩状成形电极,利用分层电解铣削进行粗加工快速去除工件多余材料,再利用环形扫描电解铣削进行旋流室全锥面的精加工,实现了发动机喷嘴微小尺寸旋流室的微细电解加工成形,达到加工精度和表面质量要求。研究表明,微细电解铣削加工是加工金属材料微小结构的有效可行的方法。     

Fundamental investigation of ultra-precision ductile machining of tungsten carbide by applying elliptical vibration cutting with single crystal diamond

This paper presents essential investigations on the feasibility of ductile mode machining of sintered tungsten carbide assisted by ultrasonic elliptical vibration cutting technology. It lays out the foundations toward efficient application of elliptical vibration cutting technology on tungsten carbide. Tungsten carbide is a crucial material for glass molding in the optics manufacturing industry. Its grain size and binder material have significant influence not only on the mechanical and chemical properties but also on the machining performance of tungsten carbide. In order to investigate the influence of material composition on tungsten carbide machining, a series of grooving and planing experiments were conducted utilizing single crystal diamond tools. The experimental results indicated that as compared to ordinary cutting where finished surface deteriorates seriously, ductile mode machining can be attained successfully by applying the elliptical vibration cutting technique. It was also clarified that the binder material, the grain size, cutting/vibration conditions as well as crystal orientation of the diamond tool have significant influence on the tool life and the machined surface quality. Based on these fundamental results, feasibility of micro/nano-scale fabrication on tungsten carbide is investigated. By applying amplitude control sculpturing method, where depth of cut is arbitrary changed by controlling the vibration amplitude while machining, ultra-precision textured grooves and a dimple pattern were successfully sculptured on tungsten carbide in ductile mode.     

超声辅助电解磨削GH625微小孔工艺研究

超声振动辅助电解磨削加工技术是一种以超声振动作为辅助、电解磨削为主要加工方式实现零件精加工的新型加工技术.为获得更高表面质量的管电极微孔,首先利用单因素法对GH625材料进行管电极打孔,初步得到最小平均锥度0.043°的微小孔,然后通过正交试验研究脉冲电压、电解液浓度、主轴进给速度、阴极转速对加工微小孔锥度和表面质量的...     

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.     

激波辅助纯钛微细群孔光刻电解试验研究

随着微机电系统(MEMS)技术的发展,近年来钛及钛合金的微细群孔加工成为国内外研究的热点。虽然光刻电解加工结合了光刻技术和电解加工两者的优点,可实现高效、高精度金属微细群孔加工。但由于钛及钛合金表面极易钝化,常规电解加工难度很大。采用有机电解液有效地解决了加工过程中的表面钝化问题。此外,为克服电解加工过程中产物难以排出造成的腐蚀不均匀等难题,进行了激波辅助纯钛微细群孔光刻电解试验研究,在厚100μm纯钛薄板上进行了群孔加工,平均孔径为371μm,材料蚀除速率达到35μm/min。实验结果表明,通过激波产生的瞬时压力扰动,能显著改善极间状态,有效提高加工稳定性和表面质量,尺寸一致性好。     

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.     

Electrochemical micromachining of microstructures of micro hole and dimple array

This paper proposes a method of electrochemical micromachining of micro hole or dimple array, in which a patterned insulation plate coated with metal film as cathode is closely attached to workpiece plate. When voltage is applied across the workpiece and cathode film over which the electrolyte flows at high speed, hole or dimple array will be produced. The proposed technology offers unique advantages such as short lead time and low cost. The effect of process parameters on the microstructure shape was demonstrated numerically and experimentally. Arrays of holes or dimples of several hundred micrometers diameter have been produced.     

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.     

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.     

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.