Electrochemical Microdrilling Research Articles

Multi-objective optimization in electrochemical micro-drilling of Ti6Al4V using nature-inspired techniques

ABSTRACT Current study investigates the efficacy of electrochemical micro-drilling (ECMD) process during micro-hole fabrication on a Ti6Al4V alloy sheet of 1.2 mm thickness using a cylindrical-shaped micro-tool. Ethylene glycol-based electrolyte was selected to overcome excessive passivation. Experiments were conducted by altering voltage, feed rate (FR), and electrolyte concentration (EC) using a central-composite-design to observe their effects on the output parameters. The desired response parameters, such as radial overcut (ROC), and taper were examined while fabricating dimensionally accurate micro-holes including the volume removal rate (VRR) that occurred during the process. ANOVA results established voltage as the major significant input parameter that affects all the responses, followed by FR. In addition, different nature-inspired optimization techniques, namely Multi-Objective Grey-Wolf Optimizer (MOGWO), Multi-Objective Bonobo Optimizer (MOBO), and Multi-Objective Particle Swarm Optimization (MOPSO), were employed. MOBO reported the best Pareto-surface in terms of uniformity and spread measures and suggested a FR of 0.3 μm/s for optimal micro-drilling operations.

Experimental Investigations and Statistical Modeling of Ultrasonic Assisted Jet Electrochemical Micro-Drilling Process with Pulsed DC

This article presents an experimental study of a recently developed process, namely, ultrasonic assisted jet electrochemical micro-drilling (UAJet-ECMD) using pulsed DC voltage power supply. The goal of the work was to examine the effect of pulsed DC voltage on the performance of UAJet-ECMD process. In the previous work carried out by the authors, the process has been studied using the continuous DC voltage. The pulse “on” time (pulsed DC voltage), electrolyte pressure and pulse “on” time (ultrasonic vibrations) were selected as the process parameters, whereas material removal rate (MRR) and hole taper were chosen as process responses. It was found that the pulse “on” time (pulsed DC voltage) had crucial effect on the MRR as well as on the hole taper. MRR and hole taper were both found to increase with rise in pulse “on” time (pulsed DC voltage). Optimization of process responses of UAJet-ECMD process was done. The responses obtained for optimized set of process parameters were verified and found in good conformity with the experimental results.

Modelling of MRR and hole taper for ultrasonic assisted jet electrochemical micro-drilling process using Buckingham's <i>π</i> theorem

Ultrasonic assisted jet-electrochemical micro-drilling (UAJet-ECMD) process integrates ultrasonic vibrations and jet electrochemical micro drilling process. In the present study, Buckingham's π theorem has been employed to model the process responses namely material removal rate (MRR) and hole taper of the UAJet-ECMD process with continuous DC voltage. The model has been formulated taking into account the experimental parameters namely voltage, electrolyte concentration, electrolyte pressure, inter electrode gap, pulse on time of ultrasonic vibrations and other physical properties related to ultrasonic vibrations such as speed of ultrasonic waves in the electrolyte, amplitude and frequency of ultrasonic vibrations. Electrochemical properties of work piece material namely chemical equivalent of copper and Faraday's constant were also taken into considerations. The use of regression analysis has been done to model the process responses. From the resultant π terms contained in the developed models, insignificant terms based on their percentage contributions were reduced and the models for both MRR and hole taper were modified. The formulated models for MRR and hole taper were validated with the statistical models obtained from experimental results.

Investigation of pulsed electrochemical micro-drilling on titanium alloy in the presence of complexing agent in electrolyte

Titanium and its alloys have excellent mechanical and chemical properties; however, these properties make the processing of titanium alloys more challenging compared with other engineering materials. Electrochemical micromachining (ECMM) is a non-conventional machining process, which removes material through anodic dissolution regardless of the material’s hardness. However, during the electrochemical machining of titanium, the formation of a passive oxide layer inhibits further material removal and deteriorates the machined surface quality. In addition, the accuracy of micromachining of titanium alloys is especially affected by the formation of electrolysis precipitates such as TiO2 and stray current dissolution. In this study, the effect of the addition of the complexing agent to different electrolytic solutions on the radial overcut during micro-drilling of titanium alloy grade 5 (Ti6Al4V) has been experimentally studied using the in-house developed ECMM set-up. The influence of parameters such as applied voltage and different electrolytic concentration with and without the complexing agent on overcut during ECMM on Ti6Al4V of micro-holes has been studied. It has been safely concluded that the quality of micro-holes fabricated in the presence of EDTA in the electrolyte while machining is responsible for better dimensional characteristics.

Comparative studies in electro-physical processes (ECM & EDM) for circular micro-holes drilling

Day by day interest is growing in drilling of high quality and high aspect-ratio micro-holes in various difficult-to-cut materials for many applications. Electrochemical micro-drilling (ECMD) and electrodischarge micro-drilling (EDMD) are the two major electro-physical process (ECM and EDM) based cost-effective techniques, provide a better alternatives in drilling micro-holes with reasonably accurate dimensions and good surface finish in difficult-to-cut materials for various industrial applications especially in computer, electronic, and aerospace industries. This paper presents a review of comparative studies in electro-physical processes on the developments of circular micro-holes drilling. It highlights the studies on aspect-ratio, over-cut and diameter-error (difference between inlet diameter and exit diameter) of circular micro-holes obtained by various experiments of ECMD and EDMD. For further research, it will open up various challenging opportunities in the field of (i) development of micro-tools and micro-electrodes, and (ii) development in innovative techniques for the purpose of drilling high quality and high aspect ratio micro-holes into hard-to-machine materials using ECMD and EDMD..

Effect of electrolyte temperature on Faradaic effect in electrochemical microdrilling

Electrochemical micromachining (ECµM) is an emerging non-conventional manufacturing technology suitable for the fabrication of micro-sized components on a wide range of electrically conductive materials. This study emphasises on the effects of electrolyte temperature on the Faradaic effect during electrochemical microdrilling on nickel plates by a cylindrical microtool made of tungsten. A short cylindrical microtool of 43 µm in diameter near to the tool tip and 53 µm mean diameter was selected, and allowed to machine on nickel plate. During machining, only the electrolyte temperature was varied keeping all the other parameters constant. The shape and size of the fabricated microholes, machining time, actual material removal rate, non-Faradaic non-transient effect and the number of short circuits are considered as response factors. Experimental results confirm that the material removal rate and machining time, respectively, increases and decreases with an increase in the electrolyte temperature. It is also observed that both the side gap ratio and the taper angle increase with the electrolyte temperature.

Fabrication of helical micro pins by electrochemical machining

Helical tools have been proven to enhance the circulation of electrolyte between electrodes in electrochemical micro-drilling. However, the fabrication of micro helical tools is difficult by traditional machining methods. The aim of the present article is to fabricate a helical tungsten micro pin by electrochemical machining. Experimental results show that a helical pin can only be fabricated in the limiting current conditions, and the length of threaded region is proportional to the anode rotating rate. Under the conditions of applied voltage equal to 2.6 V, machining time of two minutes, and the anode rotating rate of 4,000 rpm, an optimal micro helical electrode with thread depth around 17 micro-metre can be obtained. The mechanism for the formation of helical groove is well explained.

Fabrication of helical micro pins by electrochemical machining

Helical tools have been proven to enhance the circulation of electrolyte between electrodes in electrochemical micro-drilling. However, the fabrication of micro helical tools is difficult by traditional machining methods. The aim of the present article is to fabricate a helical tungsten micro pin by electrochemical machining. Experimental results show that a helical pin can only be fabricated in the limiting current conditions, and the length of threaded region is proportional to the anode rotating rate. Under the conditions of applied voltage equal to 2.6 V, machining time of two minutes, and the anode rotating rate of 4,000 rpm, an optimal micro helical electrode with thread depth around 17 micro-metre can be obtained. The mechanism for the formation of helical groove is well explained.

Effect of electrolyte temperature on Faradaic effect in electrochemical microdrilling

Effect of electrolyte temperature on Faradaic effect in electrochemical microdrilling

Performance evaluation of different variants of jet electrochemical micro-drilling process

The article describes fabrication of an experimental setup which could be used for electrochemical drilling process to produce micro-holes in a copper workpiece with its different variants, namely, jet electrochemical micro-drilling, air-assisted jet electrochemical micro-drilling, ultrasonic-assisted jet electrochemical micro-drilling, and pulsed direct current–jet electrochemical micro-drilling process. Process parameters like voltage, electrolyte concentration, interelectrode gap, and electrolyte pressure have been selected to find out their effects on the process responses, namely, hole taper and material removal rate in all the above process. Attachments for air assistance and ultrasonic vibration application have been fabricated and incorporated in the setup. The effects of ultrasonic vibrations and the pulsed direct current voltage on the process responses like material removal rate and hole taper have been investigated. The effect of application of ultrasonic vibrations on the electrolyte jet has been studied. The experimental findings of ultrasonic-assisted jet electrochemical micro-drilling were compared with the findings of jet electrochemical micro-drilling. Similarly, the findings of pulsed direct current–jet electrochemical micro-drilling were also compared with the results of pulsed direct current ultrasonic-assisted jet electrochemical micro-drilling experiments. It has been found that the ultrasonic vibrations have significant effect on the two process responses. From the results, it was observed that with the use of ultrasonic vibrations, the material removal rate has increased to significant level and the hole taper has been decreased than in jet electrochemical micro-drilling. Effects of the pulsed direct current voltage supply on jet electrochemical micro-drilling and (ultrasonic-assisted jet electrochemical micro-drilling) were also analyzed. Application of pulsed direct current voltage has improved the material removal rate and reduced the hole taper in jet electrochemical micro-drilling as well as in ultrasonic-assisted jet electrochemical micro-drilling. The experimental results concluded that ultrasonic assistance have generated the holes with greater material removal rate and lower hole taper and with continuous direct current and pulsed direct current voltage.

Electro-Chemical Micro Drilling by Micro-Spherical Electrode

Manufacture of micro holes in difficult-to-machine material is very difficult, electro-chemical machining (ECM) is one of the more appropriate approach. However, micro holes fabricated using ECM can have different diameters at the entrances and exits and such tapering effect is not localized. In this work, a new ECM method named electro-chemical micro drilling (ECMD) for machining high quality straight micro holes in difficult-to-machine material was introduced, and the micro-spherical electrode fabricated by a hybrid technique combining micro-ECM with one pulse electro discharge (OPED) was used in ECMD process. Micro-spherical electrode and ultra short pulses (tens of nanosecond scale) were used to locally dissolve the area with the effect of voltage, pulse width and pulse frequency on the localization distance being studied. High quality micro holes with a diameter of 42 µm in a 70 µm thick nickel foil were drilled using micro-spherical electrode with a sphere diameter of 30 µm.

Development of Electrode Insulation Layer by Using Oxygen Plasma Surface Treatment for Electrochemical Microdrilling

In electrochemical microdrilling (ECMD), the machining accuracy will be affected by stray current. The most effective improvement is to coat the insulation layer on the electrode sidewall so that current can only be accurately released from the bottom end. In this he electrode is coated by using the sol-gel dipping method. The innovative oxygen plasma surface treatment is used to improve film adhesion on the helical edge. The electrode has voltage resistance up to 19.4V by oxygen pressure of 400 mtorr and plasma power of 40W. Finally, the coated electrode is tested to know the ECMD performance. The objective of this paper is to enhance the machining accuracy for ECMD process. The process parameter P44C01E could obtain effective improvement on difference between inlet and outlet from 157μm to 10μm.

How microtool dimension influences electrochemical micromachining

Recent innovations in the area of electrochemical micromachining (μECM) have created a unique opportunity for fabricating microproducts in the micron scale. A significant constraint in attaining improved machining effectiveness in μECM applications is that of achieving the correct microtool geometry for a specified workpiece profile. This study focuses on the influences of microtool dimension on machining characteristics of electrochemical microdrilling on nickel plate. During microtool fabrication, tungsten microshafts are electrochemically etched to make desired cylindrical microtools of different lengths and diameters to investigate the effects of tool dimension on electrochemical micromachining. The shape and size of the fabricated microholes, material removal rate, machining time, and taper angle formed in the fabricated microholes are considered as response factors. After machining, the shape and size of microdrilled holes are measured and compared to tool geometry. From the experiment, it is found that the material removal rate, machining time, and the size of fabricated microhole are significantly influenced by the microtool dimension.

Development of Helical Electrode Insulation Layer for Electrochemical Microdrilling

The microhole is an important basic element in microparts and devices. When ECM is used in electrochemical microdrilling (ECMD), the tool electrode is very small and the flow channel cannot be provided for electrolyte in electrode, so the electrolyte cannot be renewed rapidly. Therefore, the electrolyte cannot rapidly carry away the reaction products, such as gas bubbles, sludge and Joule heat, from the machining zone. The ions that are depleted during pulse-on period cannot easily be replenished by convection and diffusion of the electrolyte. These phenomena cause the resistance to be changed in the inter-electrode gaps. Variation in the resistance affects the machining accuracy and surface quality of microholes. It may sometimes cause short- circuiting, damaging the tool and workpiece during ECMD process because the inter-electrode gaps are small. However, the machining accuracy will be affected by stray current in ECM. The most effective way to improve is to coat the insulation layer on the electrode sidewall, so that current can only be accurately released from the bottom end. The life of the electrode would be reduced by thin-film cracks if the bonding force between the film and the electrode is too weak to machine a precious microhole. Therefore, this study proposed to use the helical electrode in order to promote the processing of product exclusions. The electrode is made by using the sol-gel method and dip coating method. The innovative ceramic and epoxy double layer films is used to avoid side machining. The study results found that the electrode surface corrosion and adding the surfactants into sol-gel can be used to improve film adhesion on the helical edge. The electrode has voltage resistance up to 19.4V by indirectly etching of 10seconds. Finally, the coated electrode is tested to know the ECMD performance. The process parameter EB10C01E could obtain effective improvement on average hole diameter from 426.5μm to 232.0μm. The objective of this paper is to develop a low price and high quality of the helical electrodes to achieve high shape accuracy for ECMD process.

Experimental investigation on the influence of electrochemical micro-drilling by short pulsed voltage

In this work, a tungsten carbide (WC) pin 50 μm in diameter was used to drill throughout nickel plates of 200 μm in thickness by electrochemical micro-machining. A novel pulsed power generator was used to support pulses of nanosecond duration in drilling. The influences of working parameters, such as pulsed duration, applied voltage, pulse frequency, electrolyte concentration, tool feed rates, and hole depth, on the hole overcut and conicity are investigated. A high-quality micro-hole with 11.1-μm overcut was drilled on a nickel plate of 200 μm in thickness.

A step towards the in-process monitoring for electrochemical microdrilling

The electrochemical micromachining appears to be a promising candidate as a future micromachining technique that utilizes high frequency pulses for micron- to nanoscale material dissolution. This article presents a step towards the in-process monitoring based on waveforms generated during electrochemical micromachining. An attempt has been taken to correlate between the waveforms generated during machining and experimental outcomes such as material removal rate, machining time, and the dimensions of the microholes fabricated on commercially available nickel plate with prefabricated tungsten microtools. An electrical function generator is used as a signal source and a digital storage oscilloscope is provided for observing the nature of electrical pulses used and recording the waveforms generated during machining. The waveforms are subgrouped depending on the parameters used and analyzed to correlate the waveform shape and the machining outcomes. The digital storage oscilloscope also facilitates for observing the short-circuit condition which may occur during microdrilling. These results show that the shape of the waveforms and their corresponding values are in good agreement with the material removal rate, machining time, and on the dimension of fabricated microholes. Therefore, the proposed monitoring technique can be employed as a predictive tool in electrochemical micromachining.

Fabrication of a Microtool in Electrophoretic Deposition for Electrochemical Microdrilling and in Situ Micropolishing

This work describes a microtool fabrication procedure that incorporates the electrophoretic deposition method and an in situ process. The microtool was used in electrochemical micro drilling combined with micropolishing to drill and finish a microhole. Exactly how electrophoretic deposition parameters affect the tool diameter was also addressed. A microtool with an improved shape was obtained when using an appropriate electrophoretic deposition parameter. Following electrochemical microdrilling combined with in situ micropolishing, the inlet and outlet diameters and wall surface roughness of the machined microhole were improved.

Electrochemical Micro-Drilling with Ultra-Short Pulses

Electrochemical micro-machining (EMM) has a high removal rate, leaves no residual stress on the surfaces of machined products, and generates a low level of roughness on the surface of machined products. In this work, a novel pulsed power generator is used to support tens of nanosecond duration to drilling. The influences of working parameters, such as pulsed duration, applied voltage, electrolyte concentration, pulse frequency, tool feed rates, and hole depth, on the hole over-cut and conicity in electrochemical micro-drilling are investigated. A high-quality micro hole with a 13.75 μm overcut is drilled into a nickel plate 300 μm thick.

The effect of high frequency and duty cycle in electrochemical microdrilling

Pulse electrochemical micromachining possesses attractive features compared to conventional electrochemical machining processes based on a continuous current because it allows instantaneous electrochemical reaction by applying ultrashort voltage pulses. This study focuses on effects of applied frequency and duty cycle in electrochemical microdrilling on nickel plate. During microtool fabrication, tungsten micro-shafts are electrochemically etched to make two desired cylindrical microtools of different lengths and diameters to investigate the effects of pulsed frequency and duty cycle on electrochemical micromachining. The shape and size of the fabricated microholes, machining time, actual material removal rate (MRRact) and the number of short circuits are considered as response factors. Shapes of micro-drilled holes are measured and compared to tool geometry. As for both short and long microtools, MRRact and machining time respectively decreased and increased with an increase in applied frequency. But the MRRact and machining time respectively increased and decreases with an increase in duty cycles. Experimental data reveals that there is a strong correlation among the shape and size of the microhole fabricated with applied frequency and duty cycle during microdrilling. However, MRRact was found to be much higher for short tool than a long tool.

Electrochemical micro-drilling of deep holes by rotational cathode tools

In numerous non-conventional micro-machining, electrochemical micro-machining has merits such as high removal rate, leaving no residual stress and lower roughness on surfaces of machined products. It has been considered as a highly promising technology in micro-machining. Little research has been done on the deep-hole micro-drilling by electrochemical methods. This work utilizes a rotational system to extract insoluble sludge from a deep hole and reduce the difficulty of filling deep hole with electrolyte. As well as a rotational tool cathode, a pulsed power generator is used to support the intermittence machining to increase the precision of the workpiece. The influence of working parameters, such as pulsed on-times, applied voltages, electrolyte concentrations, pulsed frequencies, tool feeding rates, tool diameters, tool rotational rates, and hole depth, on the hole overcut and conicity in a electrochemical micro-drilling is investigated. A high quality micro-hole with a 33.35-µm overcut is drilled by a tungsten carbide pin of diameter 50 µm on a 304 stainless steel plate of thickness 1,000 µm. The hole aspect ratio (depth/diameter) reaches 8.6. It shows that a rotational tool can be utilized in the deep-hole electrochemical micro-drilling.