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With the increasing application of three-dimensional pure aluminum microstructures in micro-electromechanical systems (MEMS) and for fabricating terahertz components, high-quality micro-shaping of pure aluminum has gradually attracted attention. Recently, high-quality three-dimensional microstructures of pure aluminum with a short machining path have been obtained through wire electrochemical micromachining (WECMM), owing to its sub-micrometer-scale machining precision. However, machining accuracy and stability decrease owing to the adhesion of insoluble products on the surface of the wire electrode in long-duration WECMM, which limits the application of pure aluminum microstructures with a long machining path. In this study, the bipolar nanosecond pulses are used to improve the machining accuracy and stability in long-duration WECMM of pure aluminum. A negative voltage of −0.5 V was considered appropriate based on experimental results. Compared with the traditional WECMM using unipolar pulses, the machining accuracy of the machined micro-slit and the duration of stable machining were significantly improved in long-duration WECMM using bipolar nanosecond pulses. [ABSTRACT FROM AUTHOR]

With the development of fabrication technology for terahertz rectangular cavity devices, the fabrication process of integral terahertz waveguide cavities has received much attention because of its beneficial effect on improving the transmission of terahertz signals. However, smaller feature sizes, higher dimensional accuracy, and more stringent requirements for cavity surface roughness and edge radius make it difficult to manufacture terahertz waveguide cavities with a high operating frequency by using existing micro-manufacturing technology. At the same time, the smaller feature size also makes it more difficult to realize uniform metallization on the inner surface of a terahertz waveguide cavity. In this paper, a new and improved combined manufacturing process based on wire electrochemical micromachining and electrochemical deposition is proposed to realize the integral fabrication and uniform metallization of the inner surface of a high-frequency terahertz metal rectangular waveguide cavity. A detailed description and analysis of this combined process are carried out, together with corresponding experimental investigations. An integral 1.7 THz hollow-core metal rectangular waveguide cavity with an end-face size of 165.9 μm × 88.3 μm, an edge radius of less than 10 μm, an internal bottom surface roughness of less than 0.10 μm, and an internal side surface roughness of less than 0.40 μm was manufactured, and high-quality metallization of its inner surface was also achieved. [ABSTRACT FROM AUTHOR]

With the increasing application of three-dimensional pure aluminum microstructures in micro-electromechanical systems (MEMS) and for fabricating terahertz components, high-quality micro-shaping of pure aluminum has gradually attracted attention. Recently, high-quality three-dimensional microstructures of pure aluminum with a short machining path have been obtained through wire electrochemical micromachining (WECMM), owing to its sub-micrometer-scale machining precision. However, machining accuracy and stability decrease owing to the adhesion of insoluble products on the surface of the wire electrode in long-duration WECMM, which limits the application of pure aluminum microstructures with a long machining path. In this study, the bipolar nanosecond pulses are used to improve the machining accuracy and stability in long-duration WECMM of pure aluminum. A negative voltage of −0.5 V was considered appropriate based on experimental results. Compared with the traditional WECMM using unipolar pulses, the machining accuracy of the machined micro-slit and the duration of stable machining were significantly improved in long-duration WECMM using bipolar nanosecond pulses.

The development and application of wire electrochemical micromachining (WECMM) technology have become a research hotspot of non-traditional machining. However, a series of problems cannot be eliminated due to the machining products of micromachining gap, which leads to poor machining performance. This paper proposed a new method named ultrasonic vibration–added wire electrochemical micromachining (UA-WECMM) technology, which can solve the mass transfer problem in WECMM with extremely narrow gap. Firstly, the flow field of machining gap was simulated. The results showed that the pressure range of machining gap was larger and was more conducive to the renewal of electrolyte when ultrasonic vibration was added. Secondly, the effects of ultrasonic amplitude and ultrasonic vibration object on machining accuracy and surface quality were compared by experiments, which illustrated that the machining performance was greatly improved with the increase of ultrasonic amplitude of the workpiece. The slit width can be reduced from 196.2 to 151.2 μm, and the surface roughness can be reduced from Ra 0.863 to Ra 0.259 μm. Finally, the micro-gear structure with surface roughness of Ra 0.263 μm and depth-to-width ratio of 6.7:1 was fabricated, which proved that UA-WECMM technology is an effective technology for fabricating metal microstructures with high aspect ratio and good machining quality. [ABSTRACT FROM AUTHOR]

With the development of fabrication technology for terahertz rectangular cavity devices, the fabrication process of integral terahertz waveguide cavities has received much attention because of its beneficial effect on improving the transmission of terahertz signals. However, smaller feature sizes, higher dimensional accuracy, and more stringent requirements for cavity surface roughness and edge radius make it difficult to manufacture terahertz waveguide cavities with a high operating frequency by using existing micro-manufacturing technology. At the same time, the smaller feature size also makes it more difficult to realize uniform metallization on the inner surface of a terahertz waveguide cavity. In this paper, a new and improved combined manufacturing process based on wire electrochemical micromachining and electrochemical deposition is proposed to realize the integral fabrication and uniform metallization of the inner surface of a high-frequency terahertz metal rectangular waveguide cavity. A detailed description and analysis of this combined process are carried out, together with corresponding experimental investigations. An integral 1.7 THz hollow-core metal rectangular waveguide cavity with an end-face size of 165.9 μm × 88.3 μm, an edge radius of less than 10 μm, an internal bottom surface roughness of less than 0.10 μm, and an internal side surface roughness of less than 0.40 μm was manufactured, and high-quality metallization of its inner surface was also achieved.

Microstructures with superior surface quality have been becoming more and more important in many fields. Various methods have been exploited to fabricate high quality microstructures. Among those approaches, wire electrochemical micromachining (WEMM) is an effective and efficient way to manufacture micro components. Generating passive film on the workpiece is an alternative to improve surface quality in WEMM, which necessitates a delicate selection of electrolyte. NaNO3 solution as a passive electrolyte is beneficial to obtain good surface quality, but it barely takes effect in WEMM. Herein, an attempt is made to combine ethylene glycol (solvent) and NaNO3 (solute) to investigate its influences on surface quality in WEMM of stainless steel (304 SS). Electrochemical measurements reveal that 304 SS is subjected to secondary passivation in 1 mol/L NaNO3-ethylene glycol. X-ray photoelectron spectroscopy analysis indicates that the compositions of the passive films formed at various potentials are not exactly the same. Both the secondary passivation and the passive films make dramatic contributions to the improvement of the machined surface quality. Experimental results demonstrate that surface roughness achieved with ethylene glycol is Ra = 0.034 μm, noticeably smaller than that with traditional acid solutions. Finally, microstructures with ultra-smooth surfaces are fabricated on the 304 SS plate. [ABSTRACT FROM AUTHOR]

The application requirements of terahertz hollow-core metal rectangular waveguides with a high-working frequency have become increasingly urgent with the rapid development of terahertz technology. Integral fabrication of terahertz hollow-core metal rectangular waveguides can improve considerably the transmission performance of terahertz signals. However, with current manufacturing techniques, the high-precision integral fabrication of high-working-frequency terahertz hollow-core metal rectangular waveguides is difficult owing to their characteristically small end face size and the need for strict dimensional accuracy and high internal surface quality. In this paper, an innovative combined process of wire electrochemical micromachining, electrochemical deposition, and selective chemical dissolution is proposed firstly to overcome this puzzle. Taking the fabrication of an integral 1-THz hollow-core metal rectangular waveguide as an example, the manufacturing methods involved in each step are described particularly, together with the corresponding experimental investigations. With the end face size of 127 μm × 254 μm, edge radius less than 5 μm, and internal surface roughness less than 0.08 μm, the experimental results satisfy the design requirements for a 1-THz hollow-core metal rectangular waveguide. This study demonstrates that the proposed combined process is flexible, controllable, and suitable for the high-precision integral fabrication of high-working-frequency terahertz hollow-core metal rectangular waveguides. [ABSTRACT FROM AUTHOR]

Abstract In wire electrochemical micromachining, insoluble products are still generated in spite of the use of acidic electrolyte and adhere onto the wire cathode. In this work, the compositions of the adhered products and their influences on the electrochemical characteristics of the wire cathode were studied. The XRD results suggest that the insoluble products are mainly composed of γ-Fe 2 O 3 and α-FeOOH and that reduction of Fe ions occurs on the wire cathode to form metallic Fe (α-Fe). In addition, the electrochemical impedance spectroscopy measurement results indicate that the electrochemical characteristics of the wire cathode are significantly affected by the insoluble products. These insoluble products together with the deposited iron on the wire pose negative effects on the machining results. Finally, qualitative models for the cathodic reactions are proposed. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining is a promising micromachining method of fabricating micro metal parts. Before conducting wire electrochemical micromachining, microwire electrode should be prepared. Existing microwire electrode preparation processes suffer from drawbacks such as inconvenience in remounting the fabricated electrode and losses of accuracy and efficiency as the electrode is moved for the subsequent wire electrochemical micromachining. Dynamic liquid membrane electrochemical etching of a microwire electrode is proposed here as a way to overcome these limitations by in situ fabrication of the electrode. A mathematical model is constructed to predict the diameter of the fabricated microwire electrode and experimental results are in good agreement with the model. An experimental setup is developed combining the functions of electrode fabrication and wire electrochemical micromachining. Microwire electrodes with the diameter of 14 μm have been prepared, and microslits with the width of 34 μm have been fabricated without the need to remount the electrode. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WECMM) technology is regarded a promising method to fabricate high aspect ratio microstructures on hard-to-machining materials, however, the by-product accumulation in the machining gap limits its application. In this paper, a new method called ultrasonic-assisted wire electrochemical micromachining (UA-WECMM) is proposed to improve the machining performance of WECMM. Firstly, a flow-field simulation in the machining gap was carried out; the results showed that the ultrasonic vibration of electrode can remarkably enhance the mass transport in the machining gap and improve the machining condition. Secondly, experiments were performed to confirm the effect of ultrasonic vibration, which illustrated that the vibration with proper amplitude can reduce the slit width and improve the morphology of machined surface. Moreover, the influence of other machining parameters were also discussed. Finally, a T-type micro connector with good surface roughness (Ra 0.286 μm) was fabricated on a 300-μm-thick 304 stainless steel workpiece and a micro gear (diameter: 3.362 mm; Ra: 0.271 μm) with an aspect ratio of 7 was fabricated on a 2-mm-thick workpiece. It is proved that the proposed ultrasonic-assisted wire electrochemical micromachining method has considerable potential and broad application prospects.

The micron-level machining gap of wire electrochemical micromachining (WECMM) makes it difficult to remove the electrolytic products, which always get deposited on the surface of the wire cathode. Usually, an acidic or alkaline solution is chosen as the electrolyte to reduce the insoluble electrolytic products during machining, but they are not environmentally friendly. To solve the problem, this paper proposed adding B4C particles to a neutral NaNO3 electrolyte and machining microgrooves by vibration-assisted WECMM. The effects of the B4C particles on the deposition occurring on a wire cathode surface during machining and their role in reducing bubbles accumulation were discussed. Additionally, the effects of the amplitude, frequency of the wire cathode vibration, and particle concentration on the maximum feed rate and profiles of the microgrooves were examined. The experimental results show that adding B4C particles not only significantly reduced the electrolytic products deposited on the surface of the wire cathode and prevented bubbles from accumulating in the machining gap but also improved the surface quality of the microgrooves. Based on the optimized parameters, to machine a 3-mm-thick stainless steel workpiece could have 3.5 μm/s of feed rate. Simultaneously, the typical array microgroove structures were formed on stainless steel. [ABSTRACT FROM AUTHOR]

Titanium and its alloys are widely used in the aerospace and biomedical industries owing to their outstanding corrosion resistance and good biocompatibility. Wire electrochemical micromachining (Wire-ECMM) is a promising method for fabricating titanium microstructures because of the absence of residual stress and tool wear. The electrochemical dissolution characteristics and polarization curves of titanium in aqueous and ethylene glycol-based electrolytes are obtained and analyzed. The effects of electrolyte anion species on electrochemical machining of pure titanium are experimentally evaluated. An NaCl--ethylene glycol electrolyte is selected to explore the influences of various process parameters on machining accuracy in ECMM. A rotary helical electrode is utilized to accelerate the removal of electrolysis products and thereby improve the refreshment of the electrolyte. Finally, titanium microstructures of high surface quality are fabricated with high precision using ECMM at a voltage of 11 V, a spindle rotation speed of 4000 rpm, a pulse frequency of 200 kHz, a duty ratio of 30%, and an electrode feed rate of 0.3 µm/s. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WECMM) is very useful for fabricating micro-structures without causing tool wear. In WECMM, the accumulation of products can lead to a change in electrolyte conductivity in the small inter-electrode gap, which significantly affects the machining accuracy and efficiency. In this paper, a rotary cutting edge electrode of stainless steel 304 is used as the tool to promote the renewal of electrolyte in the inter-electrode gap and to eliminate dissolution products in machining workpiece of stainless steel 304. The electric field simulation results show that current density distribution changes dynamically as the cutting edge tool rotates. The average current on the side wall is far smaller than when a cylindrical tool is used. The flow field simulation results reveal that only electrolyte in the vicinity of the surface of the tool can be recycled when the cylindrical tool is used, whereas most of the electrolyte in the front gap is involved in the circulation when a cutting edge tool is used. Experiments suggest that the maximum electrode feed rate is improved and the slit width is reduced when a cutting edge tool is used. The cutting edge is helpful to decrease the average current density and accelerate the mass transport process. Finally, a fir tree slot of 5 mm thickness is fabricated by WECMM using a cutting edge electrode at a spindle speed of 15,000 rpm and an electrode feed rate of 2.4 μm/s. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WECMM) is becoming more important in fabricating complex microstructures. The machining accuracy of WECMM is usually evaluated by the interelectrode gap width. Faster electrolyte refreshment increases the uniformity of the electrolyte electrical conductivity distribution in the machining gap, the machining stability and the machining accuracy. We propose a method of WECMM using a rotary helical electrode that improves the machining accuracy by increasing the electrolyte refreshment and achieving a faster electrode feed rate and consequently decreasing the machining gap. Simulations of the electric field indicated that the current density was localized for the rotary helical electrode. Experiments verified that the rotary helical electrode decreased the machining gap from 94 to 19 μm compared with a cylindrical electrode of the same diameter. In addition, the effects of the process parameters on the interelectrode gap width were experimentally investigated. Finally, using optimal parameters, two precision microstructures with clean-cut edges were fabricated. [ABSTRACT FROM AUTHOR]

Micromachining, using microelectrodes, is a key technology for manufacturing three-dimensional (3D) microstructures. However, 3D microelectrodes are difficult to fabricate, 3D microstructures are fabricated mainly using simple-shaped tools microelectrode with a layer by layer scanning strategy. Based on micro double-staged laminated object manufacture (micro-DLOM), 3D microelectrodes can be obtained by combining closed loop middle-speed wire (Ø100∼180 μm) electrical discharge machining (WEDM) and thermal diffusion welding. But it is difficult to obtain 3D microelectrodes with an edge length of end face less than 100 μm, though by low speed wire electrical discharge machining (LS-WEDM) or femtosecond laser cutting, the dimension of 3D microelectrodes can be further miniaturized, they are both very expensive. To solve the problem above, this paper proposed a low-cost method combining wire (Ø8 μm) electrochemical micromachining (WECMM) and micro-electric resistance slip welding to fabricate 3D microelectrodes. Firstly, with WECMM combining low frequency micro-vibration and travelling of wire electrode, 30-μm-thick 0Cr18Ni9 stainless steel foils were cut to obtain multi-layer two-dimensional (2D) microstructures. Secondly, through micro-electric resistance slip welding, the multi-layer 2D microstructures were laminated and bonded to fit 3D microelectrodes. Moreover, this paper investigated the influences of applied voltage, feed speed, wire electrode travelling and micro-vibration on machining surface quality and dimensional accuracy. Based on the studies above, two typical 3D microelectrodes with a dimension less than 100 μm were successfully fabricated. Finally, applying the fabricated 3D microelectrodes to micro-electrochemical machining (micro-ECM), 3D micro-cavities were obtained. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WECMM) with ultra-short voltage pulses has presented its great potential in the fabrication of micro structures in difficult to cut materials because of its tiny etch resolution and good surface integrity. However, this micromachining method has not been well applied as its current machining efficiency is unsuitable for mass production. In this paper, multiple wires electrochemical micromachining (MWECMM) is proposed to increase the productivity in machining arrayed micro structures. The principle of MWECMM has been analyzed to study the influence of ultrashort voltage pulse and the wire electrode amount on the machining process. Results indicated that the charging potential is significantly influenced by voltage pulse on time and the wire electrode amount. As the wire electrode amount increased, the maximum charged potential and the potential charging rate was obviously decreased. Besides, the actual applied voltage between the electrodes decreased because of the pulse generator's output characteristics. Thus, larger voltage amplitude and pulse on time are demanded to obtain a stable MWECMM process with more wire electrodes. In this paper, the optimal wire electrode amount was three when the voltage pulse on time was 80 ns and the voltage amplitude was 8 V. And the machining efficiency using three wire electrodes was enhanced to be twice that using a wire electrode. Finally, an arrayed tree-like microstructure was successfully fabricated by MWECMM using three wire electrodes simultaneously. [ABSTRACT FROM AUTHOR]

The inherent characteristics of wire electrochemical micromachining (WECMM) enable it to be a feasible alternative to machining micro structures with good surface integrity in difficult-to-machine materials. Efficient electrolyte renewal has been proven to be important to the process stability and material removal rate in the machining of high aspect ratio micro structures. This paper proposes a method of WECMM using a rotary helical electrode to enhance electrolyte refreshment in the machining depth direction gap. Simulations of the flow field indicate that when a helical electrode revolves at a high speed, the electrolyte in the machining gap is stirred drastically, and the helical groove on the electrode surface is conducive to electrolytic flow in the axial direction. In addition, a series of experiments verifies that the maximum electrode feedrate and the slit width uniformity in the depth direction are enhanced by using a rotary helical electrode. Finally, two complex micro structures are successfully produced using a rotary helical electrode at a spindle speed of 20000 rpm. [ABSTRACT FROM AUTHOR]

Wire electrochemical micro machining (WEMM) has many advantages in machining metal structures. Even though surface roughness is one of the important indicators for measuring processing quality, it has not been paid enough attention to when using WEMM. In this paper, cathode travelling and anode vibration were used to enhance mass transport and to improve the machining surface roughness, because electrolytic products accumulate easily in the machining gap, which causes a rough surface. Moreover, changes in the surface roughness under cathode travelling, anode vibration and pulse conditions were experimentally investigated, and surfaces with R a = 0.058 μm and R max = 0.670 μm were obtained. Micro cams with smooth faces were fabricated using optimal machining conditions. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WEMM) is a promising method to fabricate microstructures, but the gas bubbles generated make it more difficult to discharge electrolytic products out of the tiny machining gap, posing a significant challenge in the fabrication of microstructures using WEMM. Hence, gas bubbles are generally considered to be removed from the machining region as soon as possible. Herein, gas bubbles are taken advantaged of as a positive role to get rid of electrolytic products from the machining region. In this paper, the ethylene glycol solution is employed as electrolyte in WEMM to generate a gas bubble chain. Simulation and experiments were carried out to verify the feasibility of the method. It is demonstrated that the electrolytic products can be removed by gas bubble chains, which makes a significant contribution to the dramatic improvement of surface processing quality. The surface roughness achieved using the method is Ra = 0.032 μm on 3J21 alloy sheet and Ra = 0.025 μm on 304 stainless steel sheet. Complex microstructures with smooth surfaces are successfully fabricated. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WECMM) technology is regarded a promising method to fabricate high aspect ratio microstructures on hard-to-machining materials, however, the by-product accumulation in the machining gap limits its application. In this paper, a new method called ultrasonic-assisted wire electrochemical micromachining (UA-WECMM) is proposed to improve the machining performance of WECMM. Firstly, a flow-field simulation in the machining gap was carried out; the results showed that the ultrasonic vibration of electrode can remarkably enhance the mass transport in the machining gap and improve the machining condition. Secondly, experiments were performed to confirm the effect of ultrasonic vibration, which illustrated that the vibration with proper amplitude can reduce the slit width and improve the morphology of machined surface. Moreover, the influence of other machining parameters were also discussed. Finally, a T-type micro connector with good surface roughness (Ra 0.286 μm) was fabricated on a 300-μm-thick 304 stainless steel workpiece and a micro gear (diameter: 3.362 mm; Ra: 0.271 μm) with an aspect ratio of 7 was fabricated on a 2-mm-thick workpiece. It is proved that the proposed ultrasonic-assisted wire electrochemical micromachining method has considerable potential and broad application prospects. [ABSTRACT FROM AUTHOR]

Carbon nanotube fibers (CNFs) are a promising material for use as lightweight, high-strength, electrically conducting tool cathodes in wire electrochemical micromachining (WECMM) in which a high-performance tool cathode is crucial for optimal processing performance. However, the outstanding advantages of pristine CNFs, such as fiber strength, electrical conductivity, and hydrophilic surface, have so far remained underutilized as tool cathodes in WECMM. Herein, electrochemical modification using a dynamic liquid membrane is proposed as an effective online method for functionalizing CNFs prior to WECMM. The proposed method not only improves the assembly accuracy and efficiency but also avoids unnecessary damage to the modified CNF during installation. The introduced functional groups (-OH and -COOH) effectively improved the electrical conductivity and hydrophilicity of CNFs. The influences of H 2 O 2 concentration, applied voltage, and anodization time on the surface modification process were examined experimentally. The use of a pulsed voltage was further proposed to prevent the loss of fiber strength due to over-anodization. Finally, the use of modified CNF electrodes with good surface morphology, strength, and conductivity in WECMM was demonstrated to afford superior machining stability, efficiency, and accuracy as well as improved surface quality compared with the conventional tool cathodes.