Electrochemical Micromachining Research Articles

Effect of micro tool-tips in electrochemical micromachining

Electrochemical micromachining (EMM) is an anodic dissolution process which governs by Faraday’s laws of electrolysis. The accuracy of the machining de-pends on the tool design as the streamline of current density formed in between the tool and the workpiece (electrodes) depends on it. In the present paper, two different tool-tips namely flat and ball end are considered for investigation. The complete set-up is modeled in the COMSOL Multiphysics® software coupling electrochemistry and fluid flow. The current density develops during EMM for both the tool-tips are used for analysis. The tool material is tungsten and work-piece material is stainless steel. Keeping parametric conditions constant for the two, simulation was performed. It was observed that more uniform current developed for ball end compared to flat end. It leads to a decrease in overcut of 120 µm in ball tip than the flat end. The fluid flow shows flushing of debris particles from the interelectrode gap is more effective in ball end than the flat end tooltip.

Profile deviation and surface roughness during electrochemical micromachining of low-clearances

The mechanism of the formation of deviations in the relative position of the bottom of the low-clearance and the base end of the part, the shape of the bottom is investigated. A method is proposed for calculating the parameters of the electrolysis mode, which ensures the specified accuracy and roughness of the processed surface. Keywords: electrochemical micromachining, surface low-clearance, deviation of relative position, shape deviation, mode parameters. morgunov56@mail.ru

Evaluation of surface integrity in electrochemical micromachining of A286 super alloy

Surface integrity of micro components is a major concern particularly in manufacturing industries as most geometry of the products must meet out necessary surface quality requirements. Advanced machining process like electrochemical micro machining possess the capabilities to machine micro parts with best surface properties exempting them from secondary operations. In this research work, different electrolytes have been employed for producing micro holes in A286 super alloy material to achieve the best surface quality and the measurement of surface roughness and surface integrity to evaluate the machined surface are carried out. The machined micro hole provides detailed information on the geometrical features. A study of parametric analysis meant for controlling surface roughness and improvement of surface integrity has been made to find out the suitable parameters for machining. The suitability of various electrolytes with their dissolution mechanism and the influence of various electrolytes have been thoroughly studied. Among the utilized electrolytes, EG + NaNO3 electrolyte provided the best results in terms of overcut and average surface roughness.

Micro-Shaping of Pure Aluminum by Intermittent Ultrasonic Oscillation Assisted Wire Electrochemical Micromachining with an Ultra-Low-Concentration Mixed Electrolyte

Sacrificial mandrels and micro-components made from pure aluminum have considerable application potential for fabricating terahertz micro-cavity components and for MEMS. Although WECMM has significant advantages in micro-shaping micro-components from difficult-to-machine materials, high-quality micro-shaping of pure aluminum has always been very challenging due to its extremely high chemical activity in an aqueous solution. This study analyzes the electrochemical characteristics of pure aluminum and the corresponding machining experiments by traditional WECMM in various electrolytes, and manufactures a high-quality micro-slit with a short machining path in the obtained ultra-low-concentration mixed electrolyte. However, in a continuous long-term WECMM with a long machining path, poor mass transport leads to the accumulation of bubbles around the machining area and the deposition of insoluble products on the wire surface that reduce the machining stability and machining accuracy. Therefore, a mass transport method of using intermittent ultrasonic oscillation is proposed. The principle was expounded, systematic comparative experiments demonstrated the effectiveness of this method in continuous long-time WECMM in improving the machining stability and machining accuracy. Finally, a rectangular mandrel of pure aluminum with a path length greater than 10,000 μm was fabricated. After dissolving the rectangular mandrel, a terahertz hollow-core rectangular waveguide micro-cavity was produced.

Reducing micro-sparks using reusable and low-cost pencil graphite cathode in electrochemical micromachining of SS304

Reducing micro-sparks using reusable and low-cost pencil graphite cathode in electrochemical micromachining of SS304

Evaluation of 3D surface roughness in electrochemical micromachining of Nitinol

Equiatomic nickel-titanium (NiTi) composed of Nickel and Titanium (i.e. 50:50% of Ni and Ti) or Nitinol, an expensive, very smart shape memory alloy material of choice for biomedical applications because of its bio compatibility. Machining Nitinol is challenging by means of non- traditional techniques. Experiments are carried out to produce a precise geometrical micro hole in Shape memory alloy Nitinol, using Electrochemical Micromachining (Abbreviated as ECMM). In ECMM process, micro holes are produced with 500 μm tool electrode in a shape memory alloy (SMA)—Nitinol of 0.25 mm thickness using the Non-passivating electrolyte (NPE), Passivating electrolyte (PE) and the Composite electrolyte (CPE) to study the machining characteristics. A tedious effort is made to produce such a micro hole using a noval mixed electrolyte to improve machining process. Polarization studies are also carried out for all the chosen electrolytes. The process is clearly analyzed thoroughly with the help of polarization and SEM. Expected results with good precision and surface characteristics are obtained when the nitinol is machined with the composite electrolyte. The results proved that the compatibility of machining nitinol is composite type of electrolyte. Composite electrolyte provides the combined advantages of both the passivated and non-passivated electrolytes. This study resulted in finding the suitable and optimized parameters for machining Nitinol with PE, NPE and CPE with better precision and good surface integrity.

Micro-machining: An overview (Part II)

This article on ‘Micro-machining: An Overview (Part II)’ is in continuation to ‘Micro-machining: An Overview (Part I)’ published in this journal ( Journal of Micromanufacturing). It consists of four parts, namely, electrochemical micro-texturing, electrochemical spark micro-machining, molecular dynamics simulation and sustainability issues of micro-machining processes. Electrochemical micro-texturing (ECMTex) deals with various techniques developed for micro-texturing on different types of workpiece-surfaces, namely, flat, curved and free-form surfaces. Here, basically two categories of techniques have been reviewed, namely, with mask and without mask. It also deals with ‘single point tool micro-texturing’ which turns out to be a single-step technique requiring minimum time, but the accuracy and repeatability obtained after micro-texturing need to be critically analysed. For mass production, one needs to go for sinking kind of ECMTex processes. Electrochemical spark micro-machining (ECSMM) is an interesting hybrid (ECM+EDM) process which can be applied for electrically conducting as well as electrically non-conducting materials. However, the work reported in this article deals only with the electrically non-conducting materials for which this process was initially developed. This process has a lot of potential for theoretical work to be done. In this article, two theories of sparking/discharging have been briefly mentioned: single bubble discharging/sparking and single surface discharging. It also dicusses its applications for different types of electrically non-conducting materials. Molecular dynamics simulation (MDS) of micro-/nano-machining processes is very important, but it is very cumbersome to understand at atomic/molecular scale. In these processes, the material behaviour at micro-/nano-level machining is completely different as compared to bulk-machining (macro-machining) processes. Hence, some fundamentals of MDS have been discussed. It just gives the idea of available techniques, softwares and models for different types of processes. However, there is the need of further research work to be done for clearly understanding the MDS of micro-/nano-machining. In the end, the sustainability of micro-machining issues have been discussed, mainly based on the energy consumption per unit mass of production. It is concluded that the advanced micro-manufacturing processes are highly energy-intensive processes, and they need further studies to be done for making them more suitable from sustainability point of view. At the end of each section, some potential areas of research for enhancing the accuracy and repeatability, and minimising the production time of each process have been discussed.

Electrochemical micromachining of actuator-grade Nitinol shape memory alloy with and without laser assistance

The growing demand of Nitinol shape memory alloys (SMAs) in medical and actuator applications has necessitated research in developing micromachining technologies which do not induce mechanical or thermal load induced microstructural transformations in the alloy. This work presents electrochemical micromachining as a potential technology for machining Nitinol SMAs without deteriorating their functional property. A further hybridization of ECM with a ns pulsed laser has been presented to enhance machining in terms of uniform dissolution of surface and processing speed. Insights into dissolution mechanisms have been presented. The results indicate successful machining of Nitinol SMAs with electrochemical machining with added benefits using laser assistance. The shape memory property (transformation temperatures) is not largely affected post-machining. The Differential Scale Calorimetry (DSC) results show only slight variations (±3 °C) of the transformation peaks, but there is no correlation between peak shifts and process energies (electrochemical and laser). Post-machining, the material remains well-suited for thermal cycling in an actuator application.

Electrochemical Microslot Machining by Ultrasonic-Vibration-Aided Electrolyte on Nitinol Wire

In this research, the main purpose was to study the applicability of a machining method on microscale medical-equipment manufacturing. The characteristics of wire electrochemical micromachining (WECMM) against NiTi 50-50 wire was investigated. The study utilized a tungsten wire 0.03 mm in diameter as an electrode to cut a fine slot into the nickel–titanium wire. In order to reach a high-precision WECMM finish, an ultrashort pulse power generator was used as a power source to minimize the stray current effect, thus improving the machining accuracy. During the process, various machining parameters were tested for their effects on machining characteristics. In addition, ultrasonic-vibration-aided WECMM was investigated to determine whether it benefited the machining characteristics. The experiment’s results showed that under such an experiment setting, microslots can be successfully manufactured. Furthermore, with the advance adjustment of experimental parameters, the machining accuracy was improved. Finally, a fine slot was manufactured under the optimum experiment parameters and aided by ultrasonic vibration.

A study of air/ultrasonic co-assisted electrochemical micromachining

A study of air/ultrasonic co-assisted electrochemical micromachining

Anodic Dissolution Behavior of Passive Layer During Hybrid Electrochemical Micromachining of Ti6Al4V in NaNO3 Solution

AbstractTitanium and its alloys are considered as difficult to cut material classes, and their processing through the traditional machining methods is a painful task. These materials have an outstanding combination of properties like high specific strength, excellent corrosive resistance, and exceptional biocompatibility; therefore, they have broad fields of application like aerospace, micro-electromechanical system, and biomedical. Electrochemical micromachining (ECMM) is a vital process for the production of microdomain features in difficult-to-machine materials. The machining issue with ECMM for titanium and their alloys is the passive layer formation, which hinders the dissolution and causes stray removal. To overcome these issues, a hybrid ECMM approach has been proposed by using a diamond abrasive tool combined with ECMM. This study focuses on the detailed characterization of the passive layer formed using the hybrid approach. Through the use of abrasive tool, the abrasive grits scoop the passive layer by the mechanical grinding action, formed in microdrilling on the Ti6Al4V alloy to expose a new surface for further dissolution. The microholes were produced incorporating the abrasive tool and then compared by the holes created using a cylindrical tool (tool without abrasive). The taper and the stray dissolution of the microholes were also compared, produced at different applied potentials. The minimum average entry overcut and exit overcut of the hole were obtained as 29 μm and 3 μm, respectively, also a microhole with the lowest taper of 2.7 deg, achieved by the use of the abrasive microtool.

Investigation on Bidirectional Pulse Electrochemical Micromachining of Micro Dimples.

Through-mask electrochemical micromachining (TMEMM) is a promising method to prepare micro dimples on the surface of metallic parts. However, the workpiece is machined one by one in traditional TMEMM. This paper introduced bidirectional pulse to TMEMM to improve the machining efficiency. Two masked workpieces were placed face to face, and connected to the ends of the bidirectional pulse power supply. Along with the change of the pulse direction, the polarities of the two workpieces were interchanged periodically, and micro dimples could be prepared on both workpieces at one time. The simulation and experiment results indicated that with bidirectional pulse mode, micro dimples with same the profile can be prepared on two workpieces at one time, and the dimension of micro dimple was smaller than that with unidirectional pulse mode. In bidirectional pulse current, the pulse frequency and pulse duty cycle played an important role on the preparation of micro dimple. With high pulse frequency and low pulse duty cycle, it is useful to reduce the undercut of micro dimple and improve the machining localization. With the pulse duty cycle of 20% and pulse frequency of 10 kHz, micro dimples with etch factor (EF) of 3 were well prepared on both workpieces surface.

On altering the wetting behaviour and corrosion resistance of a large metallic surface area by wire electrochemical texturing

This paper presents a novel and practically applicable method for a quick fabrication of uniform surface patterns (periodic micro-pillars with rectangular and square cross-section) on a large surface area of any conducting or semi-conducting material using Wire Electrochemical Micromachining (Wire-ECMM). Micro pillars with a rectangular cross-section are generated by machining mutually perpendicular micro channels. The depth, spacing, and cross-sectional area of pillars are controlled by varying the process parameters and tool travel distance. Primary pillars (level-1 texture) are machined with a constant Direct Current (DC) voltage and secondary pillars (level-2 texture) are machined with a pulsed DC voltage using a tungsten wire of diameter 100 μm. An aqueous solution of sodium nitrate (NaNO 3 ) is selected as an electrolyte having a pH of about 7.01. A good repeatability in the geometrical parameters of a pillar profile is observed on analysing 3D profilometer micrographs of the textured surfaces. Wetting behaviour of textured surfaces with different geometrical parameters is observed using drop shape analyser. A surface with two levels of textures offers highest contact angle of 147.3° with deionized water. Corrosion current and resistance of the textured surfaces are obtained using Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS), respectively. Results suggest that corrosion resistance depends upon the area of texture and is highest for the sample with the largest textured area. Also, a sample with the smallest value of area factor (ratio of total area of the top surface of all the pillars in a region to the total projected area of a region) offers highest resistance to corrosion. • A novel approach for large area texturing on any conducting and semi-conducting surface using Wire Electrochemical Micromachining (Wire-ECMM). • A study of the influence of different process parameters on various geometrical features of a textured surface. • A detailed characterization of different textured surfaces using SEM imaging and surface topography. • In depth analysis of the wetting and corrosion behaviour of the textured surfaces using drop shape analyser and Electrochemical Impedance Spectroscopy (EIS).

Micro-electrochemical jet machining of large area microtexturing with tool movement strategy

ABSTRACT Microtextured surfaces, particularly circular micropattern, significantly enhance the function and performance of microfabricated devices and engineering parts. A distinctive and inventive concept of maskless microelectrochemical jet machining (EJM) is utilized for producing the microcircular pattern over large area. In this research work, an advanced concept, i.e. maskless micro-EJM is presented to produce the microtextures on large area using the reusable masked tool movement strategy on stainless steel. One masked patterned tool can fabricate many high-quality micropatterned samples over large area using the tool movement strategy. High-pressure electrolyte flow through textured tool is developed to acquire the high-quality microtextures with controlled dimensions. The machining consequence of substantial input parameters, i.e. IEG, flow rate and frequency on microdimpled characteristics such as MRR, overcut, depth, and R a is explored. Microdimples of 5.3 mg/min MRR, 20.07 µm overcut, 13.5 µm depth, and 0.0601 µm surface roughness and 5.29 cm2 machining area are successfully fabricated using the reusable masked tool. The present study confirms that it is achievable to acquire the large area microtexturing using this innovative technique.

Electrochemical Micromachining Using Real Pulse Signals

The machining resolution of pulse electrochemical micromachining technology can be increased by shorting the pulse duration and changing the voltage signal waveform. With a triangular pulse, the energy per pulse was reduced by about two-thirds, and the machining gap was decreased by about eleven times compared to one with a rectangular pulse. Here, we put forward a real pulse waveform for electrochemical micro-machining. The pulse waveform is obtained by rectangular pulse plus differential circuits. The waveform can greatly reduce energy per pulse and surprisingly improve the precision of micro-electrochemical machining. The basic principle of the micromachining is analyzed. The equations of the machining accuracy and energy per pulse are deduced. Using the equations, the machining accuracy and energy per pulse as a function of the differential times of the differential circuits are calculated and compared with simulated and experimental results. Compared to the rectangular pulse, the energy per pulse for the waveform can be reduced by about six times and the machining gap was decreased can be improved by about 11 times. Using this method, some micro structures are produced and nanometer lever machining accuracy is realized which illustrates the proposed machining method.

Effect of tool rotation on the fabrication of micro-tool by electrochemical micromachining

Electrochemical micromachining (EMM) uses anodic dissolution in the range of microns to remove material. Complex shapes that are difficult to machine on hard materials can be fabricated easily with the help of EMM without any stresses on the workpiece surface and no tool wear. Fabrication of microfeatures on microdevices is a critical issue in modern technologies. For the fabrication of microfeatures, precise micro-tools have to be fabricated. In this present study, EMM milling is used for the fabrication of micro-tools. For this, an EMM setup has been designed. Tungsten carbide tools with an initial diameter of 520 µm have been selected and are electrochemically machined to reduce their diameter. The tool and workpiece are connected as anode and cathode, respectively. The electrolyte solution used for this investigation is sodium nitrate. A comparative analysis of the effect of tool rotation over both machining accuracy and surface finish has been performed.

Confining invasion directions of Li+ to achieve efficient Si anode material for lithium-ion batteries

Tremendous volume expansion of silicon anode during cycling limits its further application. Here, a novel silicon nano-ribbon (SiNR) with (110) crystal plane is proposed as anode for the Lithium-ion batteries. The SiNRs with (110) crystal plane have been synthesized by a simple electrochemical micromachining method. Both invasion direction of the lithium-ions and expansion directions of the lithiated silicon are limited to the <110> crystal direction. Recrystallization of SiNR induced by the retention of silicon atomic chains after delithiation is verified experimentally and theoretically. Such SiNR, without necessary surface coating treatment, exhibits high ionic conductivity, high stable solid electrolyte interphase (SEI) and long cycling stability, retaining a specific capacity of 1721.3 mAh g−1 (∼80% capacity retention) after 2000 cycles with an initial coulombic efficiency (CE) of 83%. The rational design of nanostructured battery materials and electrodes in this work also opens a new dimension in material design for other batteries.

Generation of Microtextured Characteristics using Maskless Electrochemical Micromachining

To minimize and control friction and wear, the manufacture of microtextured characteristics on circular micropatterns is an innovative approach to extend the life of mechanical systems and components and enhance their reliability and performance. The form, size, and surface quality of circular micropatterns developed on stainless steel surfaces using maskless electrochemical micromachining directly affect the service life and function of textured surface. This article presents the experimental study on the generation by electrochemical micromachining of circular micropatterns on stainless steel. The effect of process variables such as inter-electrode gap (IEG), flow velocity and machining time on current density, current efficiency, material removal rate (MRR), surface roughness, and diametric taper angle are examined during the generation of circular micropatterns. The best parameters obtained from the experimental results are 100μm IEG, 4.4 m/s flow velocity and 3 minutes machining time for producing this micropattern. An attempt is also made to analyze the optical and 3D images of circular micropattern from the experimental results.

Generation of square micropattern using electrochemical micromachining

Surface microtexturing accomplishes a substantial role in enhancing the interfacial functional performance of machine-driven components. For producing good-quality square micropatterns, maskless electrochemical micromachining (EMM) is a viable option. Maskless EMM is employed for producing micropatterns, wherein the workpiece remains close by interaction with the mask tightly enclosed to the coated tool surface, and the electrolysis of job involves in the enclosed cell. The special micropatterning setup is developed to produce the good quality square micropatterns including micropatterning cell, pulsed electrical unit and perpendicular cross flow electrolyte system. The developed flow method on the job surface in this unit produces better good quality micropatterns. A reused textured tool and developed flow method is applied in maskless EMM in an enclosed unit, which eradicates the sludges and fabricate micropatterns with higher depth. This unique method is an efficient approach for improving the dimensional accuracy of micropatterns. The influences of input criteria, viz. voltage, duty ratio and frequency are studied on surface roughness, current efficiency, length overcut, and textured depth using this technique. The experimental outcomes show that the best parametric combination, viz. 30% duty ratio, 5 kHz frequency and 8 V voltage, enhances the micropatterned quality. A study has been approached based on micrographs for attaining the best input criteria combination.

Electrodissolution Processes and Their Application in Manufacturing for Shaping and Finishing of Advanced Materials

Controlled material removal by anodic dissolution at high rates forms the basis of non-conventional metal shaping and finishing processes such as Electrochemical Machining (ECM), Electrochemical Micromachining (EMM), and Electropolishing (EP). These processes are employed in the manufacturing and processing industries for a variety of applications ranging from the machining of complex shaped components for heavy industries to the fabrication of microstructures in thin films and foils and microfinishing of superconducting radiofrequency cavities (1-3). Application of these processes for the production of reliable, reproducible, and high-yielding components require an understanding of the parameters that influence the anodic dissolution processes.ECM, EMM, and EP can be understood and theoretically modeled based on the same principles provided the scaling effects related to each process are considered (2). In the first part of this presentation, the high rate anodic dissolution behavior of different materials including refractory materials are described which helps in establishing the basic concepts that govern ECM/EMM/EP processes. Electrochemical reactions taking place at high anodic potentials depend on the metal-electrolyte combination and the operating conditions. These reactions include active metal dissolution, passivity, oxygen evolution, and the phenomena of passive film breakdown leading to the transpassive metal dissolution. In passivating electrolytes (containing oxidizing anions), oxygen evolution and metal dissolution take place simultaneously. The current density dependence of meat dissolution efficiency in such electrolytes provides minimized stray cutting in ECM. Mass-transport, current distribution, and surface film properties play a significant role in the metal removal rate and surface finish. Whereas the formation of a salt film on the dissolving anode in ECM electrolytes is well established, the identification of the rate-controlling species during electropolishing of metals in concentrated acid solutions remains a controversial issue.The second part of the presentation deals with the applications of these processes in the manufacturing of advanced products for the aerospace, biomedical, electronics, and photovoltaics industries. Different ECM techniques such as die-sinking, combined tool machining, EC drilling, and EC deburring are described that are used in the manufacturing of complicated shaped parts such as turbine blades. Maskless EMM methods such as Jet EMM, micro-drilling, and wire EMM are applied to fabricate precision microstructures. For process enhancement, assisted techniques such as laser, abrasive, vibration, and ultrasonic are incorporated with maskless EMM. For through mask electrochemical micromachining (TMEMM), an understanding of mass transport in a cavity and shape evolution modeling is critical. The use of laser patterned oxide film mask for Ti patterning is presented as an interesting application of TMEMM (4). A few case-studies on electropolishing are described which include the fabrication of STM probes and Nitinol stents, and microfinishing of print bands. In the microprocessor industry, a significant effort was invested in the development of EP and electrochemical mechanical planarization (ECMP) approaches as a no-contact or low-contact planarization processes for the integration of ULK/copper interconnects. The development work, including processing details and planarization efficiency of EP and ECMP, are reviewed. A critical evaluation of the current status of EP/ECMP vis a vis the chemical mechanical planarization (CMP) process is presented.References J. McGeough, Principles of Electrochemical Machining, Chapman and Hall, Wiley, London, 1974.M. Datta, Electrodissolution Processes: Fundamentals and Applications, CRC Press/Taylor and Francis, Boca Raton, 2020.E. J. Taylor and M. Inman, Electrochemical Surface Finishing, The Electrochemical Society Interface, Fall 2014, p47.P.-F. Chauvy, P. Hoffmann, D. Landolt, Electrochemical Micromachining of Titanium Through a Laser Patterned Oxide Film, Electrochem. Solid-State Lett., 4(5), C31 (2001).