Micro-electrical Discharge Machining Process Research Articles

A review of experimental investigations to attain productive and sustainable micro-electrical discharge machining process on metals and superalloys

Purpose This study aims to understand the current production scenario emphasizing the significance of green manufacturing in achieving economic and environmental sustainability goals to fulfil future needs; to determine the viability of particular strategies and actions performed to increase the process efficiency of electrical discharge machining; and to uphold the values of sustainability in the nonconventional manufacturing sector and to identify future works in this regard. Design/methodology/approach A thorough analysis of numerous experimental studies and findings is conducted. This prominent nontraditional machining process’s potential machinability and sustainability challenges are discussed, along with the current research to alleviate them. The focus is placed on modifications to the dielectric fluid, choosing affordable substitutes and treating consumable tool electrodes. Findings Trans-esterified vegetable oils, which are biodegradable and can be used as a substitute for conventional dielectric fluids, provide pollution-free machining with enhanced surface finish and material removal rates. Modifying the dielectric fluid with specific nanomaterials could increase the machining rate and demonstrate a decrease in machining flaws such as micropores, globules and microcracks. Tool electrodes subjected to cryogenic treatment have shown reduced tool metal consumption and downtime for the setup. Practical implications The findings suggested eco-friendly machining techniques and optimized control settings that reduce energy consumption, lowering operating expenses and carbon footprints. Using eco-friendly dielectrics, including vegetable oils or biodegradable dielectric fluids, might lessen the adverse effects of the electrical discharge machine operations on the environment. Adopting sustainable practices might enhance a business’s reputation with the public, shareholders and clients because sustainability is becoming increasingly significant across various industries. Originality/value A detailed general review of green nontraditional electrical discharge machining process is provided, from high-quality indexed journals. The findings and results contemplated in this review paper can lead the research community to collectively apply it in sustainable techniques to enhance machinability and reduce environmental effects.

Experimental Investigation on Micro-Electrical Discharge Machining process for heat treated Nickel-based Nimonic 80A

ABSTRACT Nimonic 80 A is a nickel-based alloy having diverse applications in aerospace, automotive, biomedical, and military sectors owing to its immense strength to weight proportion and resistance to corrosion at raised temperatures. As a result of the problems associated with its conventional machining, unconventional machining, in particular, EDM is preferred. Micro-machining has become a key attraction point for manufacturing organizations. This requires to have an understanding of the process in terms of the impact of control factors on the performance characteristics. In the prevailing experimentation, micro holes were drilled on a heat-treated Nimonic 80A plate. Current, pulse-on time and pulse-off time are considered as the control factors, whereas tool wear ratio and drilling rate are considered as the performance variables. The experiments were designed using RSM. ANOVA has been carried out and the SEM analysis of the drilled hole was performed for examining the quality of the holes. The measurement of the thickness of recast layer was performed. Copper and zinc, diffused around the micro-drilled area, were identified through the elemental composition of the drilled sample using EDX. Minimum tool wear ratio and the maximum drilling rate were obtained to be 0.78 and 0.77 mm/sec, respectively.

Pulsed Power Supply Superposed With Radio Frequency Oscillating Wave for the Improvement of Micro-Electrical Discharge Machining Process

Abstract During the micro-electrical discharge machining (micro-EDM) process, the dielectric property of narrow interelectrode gap is transiently changing. With the hysteretic servomotion of spindle, the effective discharge ratio (EDR) between electrodes is low. In this research, a pulsed power supply superposed with the radio frequency (RF) oscillating wave of controllable frequency and amplitude is proposed in order to induce interelectrode continuous discharge, so that, the machining efficiency and accuracy are improved simultaneously. The experimental results of microhole machining show that under the oscillating frequency of 160 MHz and amplitude of ±10 V, the machining efficiency is increased by 35%, the tool electrode wear rate (TWR) remains almost unchanged, and the taper error of microhole is reduced by 43%. Furthermore, the process of relatively enlarging discharge gap range and increasing number of discharges after superposition is discussed, and the proper superposed oscillating amplitude is identified.

Machinability of copper-based metallic glass in micro EDM and its optimisation by grey fuzzy logic

The present study investigates the machinability of metallic glass by drilling micro holes using the micro-electrical discharge machining process. The variation of microhole features such as material removal rate (MRR), overcut (OC), circularity error (CE), recast layer thickness (RLT) and edge deviation (ED) with respect to variable process parameters such as voltage, capacitance and tool rotation speed has been investigated by Taguchi method and analysis of variance. Multi-objective optimisation approaches such as grey relational analysis (GRA) and grey-based fuzzy logic (GFL) are implemented to optimise the process parameters to attain microholes having quality features. The studies exhibit that microholes of higher MRR and lower OC, CE, RLT, and ED can be machined by controlling the process parameters. GFL exhibits a lower error of 7.16% as compared to GRA's 11.40% in between the experimental and predicted results.

Optimization of μEDM process assisted with rotating magnetic pulling force and ultrasonic vibration

The micro-electrical discharge machining process is hindered by low material removal rate and low surface quality, which bound its capability. The assistance of ultrasonic vibration and magnetic pulling force in micro-electrical discharge machining helps to overcome this limitation and increase the stability of the machining process. In the present research, an attempt has been made on Taguchi based GRA optimization for µEDM assisted with ultrasonic vibration and magnetic pulling force while µEDM of SKD-5 die steel with the tubular copper electrode. The process parameters such as ultrasonic vibration, magnetic pulling force, tool rotation, energy and feed rate have been chosen as process variables. Material removal rate and taper of the feature have been selected as response measures. From the experimental study, it has been found that response output measures have been significantly improved by 18% as compared to non assisted µEDM. The best optimal combination of input parameters for improved performance measures were recorded as machining with ultrasonic vibration (U1), 0.25 kgf of magnetic pulling force (M1), 600 rpm of tool rotation (R2), 3.38 mJ of energy (E3) and 1.5 mm/min of Tool feed rate (F3). The confirmation trail was also carried out for the validation of the results attained by Grey Relational Analysis and confirmed that there is a substantial improvement with both assistance applied simultaneously.

In situ drilling and milling of thin sheet using microelectrical discharge machining

The present study investigates fabrication of microrod using block electrical discharge grinding process and performs in situ drilling and milling of thin sheets using the fabricated rods by the microelectrical discharge machining process. The microrods are fabricated at a wide range of discharge energy (DE) by varying voltage and capacitance, and their effect on machining time (MT), material removal rate, average diameter and standard deviation in diameter (SDD) are evaluated. To get the benefit of both higher efficiency as well as dimensional accuracy, a technique of variable energy setting is coined, wherein higher DE is applied initially to increase efficiency followed by lower DE to improve dimensional accuracy and precision. The fabricated microrods are then used as tools for in situ microelectrical discharge drilling (µED-drilling) and microelectrical discharge milling (µED-milling) on brass and titanium sheet. In µED-drilling, MT and tool wear (TW) of brass is lower as compared to titanium, whereas overcut of brass is higher than titanium. ‘To and fro’ technique is used to compensate the TW in µED-milling and to achieve dimensional accuracy. The technique is successful in achieving fairly straight microslot in brass with SDD of 17 µm as compared to titanium with SDD of 113.50 µm.

Monitoring of material-removal mechanism in micro-electrical discharge machining by pulse classification and acoustic emission signals

Micro-electrical discharge machining is a stochastic process where the interaction between the materials and the process parameters are difficult to understand. Monitoring of the process becomes necessary to achieve the dimensional accuracy of the micro-featured components. Although thermo-mechanical erosion is the most accepted material-removal mechanism, it fails to explain the material removal with very short pulse duration. Alternative postulate like electrostatic force-induced stress yielding provides a stronger argument, rising ambiguity over the material-removal process in the micro-electrical discharge machining regime. In this work, it was found that the stress waves released from the material during micro-electrical discharge-machining process indicate material removal by mechanical deformation and fracture mechanism. These stress waves were captured using the acoustic emission sensor. The discharge pulses were captured by voltage measurement and classified using voltage gradient and machining time duration into three major categories, open pulse, normal pulse and arc pulse. The acoustic emission signal features were extracted and identified by time–frequency–energy distribution analysis. A feed-forward back-propagation neural network mapping of the pulse instances was performed with the obtained acoustic emission signature. The time–frequency–energy distribution analysis of the acoustic emission and the scanning electron microscope images of the craters provide conclusive evidence that the material is removed by mechanical stress and fracture. The feed-forward back-propagation network model was trained to predict the discharge categories of the pulse instances with AE signal inputs which can be used for monitoring the material-removal mechanism in micro-electrical discharge machining operation.

Pulse Generator for Obtaining Surfaces of Small Dimensions by Electrical Discharge Machining

The last decades highlighted the necessity of obtaining surfaces of small dimensions in case of some complex parts or workpieces made of materials difficult to be cut by classical machining methods. In such cases, one of the machining methods able to facilitate the obtaining of surfaces of small dimensions is the electrical discharge machining. The purpose followed by research whose results are presented in this paper was to identify a solution for a pulse generator which could be incorporated and used in equipment for electrical discharge machining of surfaces of small dimensions. The analysis of microelectrical discharge machining process showed the conditions necessary to be fulfilled by the pulse generator. The experience of researchers who built electrical discharge equipment was taken into consideration. In order to limit the heat dissipation and energy waste on resistors and semiconductors, a subsystem based on the use of transistors characterized by high speed switching was applied within an independent pulse generator. In order to obtain a high quality of the small dimensions machined surfaces, a relaxation-type pulse generator was included in equipment for electrical discharge machining. An intelligent control unit was used, in order to ensure possibilities of changing the characteristics of machining pulses, in accordance with the conditions from work gap. The preliminary experiments proved the good functioning of the pulse generator and the possibilities to obtain surfaces of small dimensions on the proposed equipment.

Design and Fabrication of a Polymeric Microfilter for Medical Applications

This paper reports on design, fabrication, and characterization of a microfilter to be used in biomedical applications. The microfilter, with mesh of 80 μm, is fabricated by micro-injection molding process in polymeric material (polyoxymethylene (POM)) using a steel mold manufactured by micro-electrical discharge machining process. The characteristics of the filter are investigated by numerical simulation in order to define a suitable geometry for micro-injection molding. Then, different process configurations of parameters (melt temperature, injection velocity, mold temperature, holding pressure and time, cooling time, pressure limit) are tested in order to obtain the complete part filling via micro-injection molding process preventing any defects. Finally, the component is dimensionally characterized and the process parameters optimized to obtain the maximum filtration capacity.

Effect of non-electrical parameters in μED milling: an experimental investigation

Machining of high aspect ratio micro-channels and cavities in metals is a challenging task. Micro-electrical discharge milling is a version of micro-electrical discharge machining process which is capable of micro-machining of all electrically conductive materials. The aim of this study is to analyze the effects of non-electrical parameters such as layer thickness (LT), horizontal tool feed rate (HTF), and tool rotational speed (TRS) on material removal rate (MRR) and relative electrode wear (REW) while micro-electrical discharge (μED) milling of stainless steel using tungsten electrode. The study revealed that layer thickness along with tool rotational speed and horizontal feed rate of the tool significantly influences the performance of μED milling.

Modeling Debris Motion in Vibration Assisted Reverse Micro Electrical Discharge Machining Process (R-MEDM)

Reverse microelectrical discharge machining (R-MEDM) process is a recent variant of microelectrical discharge machining process capable of fabricating high aspect ratio arrayed microfeatures and textured surfaces. Efficient flushing of the debris particles from the interelectrode gap is essential for process stability, but extremely small interelectrode gaps ( $\sim 5~\mu $ m) make the dispelling of debris difficult, rendering the R-MEDM process infeasible for machining difficult-to-erode materials and creation of engineered/textured surfaces. It has been experimentally observed that the electrode vibrations facilitate the flushing of debris particles and improve the erosion rate, surface morphology, and dimensional accuracy of the machined features. Despite the obvious advantages, the vibration-assisted R-MEDM process, specifically the debris motion and dielectric flow under the effect of vibration, is not very well understood. Consequently, this paper is focused on computational modeling of the debris motion and its interaction with the dielectric fluid under low-amplitude vibrations imparted via a magnetorestrictive actuator. The effects of frequency and amplitude of the electrode vibration on the debris motion have been quantified. The higher local debris velocities and oscillatory motion due to flow reversal potentially reduce the debris agglomeration. As a result, the normal discharge duration, which is responsible for the material erosion, is increased and fabrication of arrayed features on difficult-to-erode materials and creation of surface texture over large areas become feasible. [2013-0394]

Effect of Powder Mixed Dielectric on Material Removal and Surface Modification in Microelectric Discharge Machining of Ti-6Al-4V

Microelectric discharge milling is one of the variants of microelectric discharge machining process which acquire the attention of researchers due to its unique ability to produce microchannels and three-dimensional structures in difficult-to-machine materials like titanium. In the present work, an experimental investigation has been performed in order to study the effect of SiC microparticle suspended dielectric on machining Ti-6Al-4V with tungsten carbide electrode. The effects of major electric discharge milling process parameters—voltage, capacitance, and powder concentration in dielectric—on responses—viz., material removal rate (MRR) and tool wear rate (TWR)—were studied. Experiments were designed and performed based on response surface methodology (RSM)-Box–Behnken statistical design and the significance of in put parameters were identified with the help of analysis of variance. From the results, it is recommended to use powder concentration of 5 g/L, capacitance of 0.1 µF, and voltage of 115 V for achieving high material removal and low tool wear rate. Finally, the studies were conducted to analyze the surface modification and the quality of machined surface.

Evaluation of the characteristics of the microelectrical discharge machining process using response surface methodology based on the central composite design

Evaluation of the characteristics of a microelectrical discharge machining (Micro-EDM) process is challenging, because it involves complex, interrelated relationships so a proper modeling approach is necessary to clearly identify the crucial machining variables and their interrelationships in order to initiate more effective strategies to improve Micro-EDM qualities (electrode wear (EW), material removal rate (MRR) and overcut). This paper uses a response surface method (RSM) based on the central composite design (CCD) for Micro-EDM problems with four EDM variables (peak current, pulse on-time, pulse off-time and electrode rotation speed). Experimental results indicate that peak current is the EDM variable that most affects the Micro-EDM qualities for SK3 carbon tool steel while pulse off-time had a significant interaction with that. The results show that RSM based on the CCD could efficiently be applied for the modeling of Micro-EDM qualities (EW, MRR, and overcut), and it is an economical way to obtain the performance characteristics of Micro-EDM process parameters with the fewest experimental data.

Study of precision micro-holes in borosilicate glass using micro EDM combined with micro ultrasonic vibration machining

Because of its excellent anodic bonding property and surface integrity, borosilicate glass is usually used as the substrate for micro-electro mechanical systems (MEMS). For building the communication interface, micro-holes need to be drilled on this substrate. However, a micro-hole with diameter below 200 μm is difficult to manufacture using traditional machining processes. To solve this problem, a machining method that combines micro electrical-discharge machining (MEDM) and micro ultrasonic vibration machining (MUSM) is proposed herein for producing precise micro-holes with high aspect ratios in borosilicate glass. In the investigations described in this paper, a circular micro-tool was produced using the MEDM process. This tool was then used to drill a hole in glass using the MUSM process. The experiments showed that using appropriate machining parameters; the diameter variations between the entrances and exits (DVEE) could reach a value of about 2 μm in micro-holes with diameters of about 150 μm and depths of 500 μm. DVEE could be improved if an appropriate slurry concentration; ultrasonic amplitude or rotational speed was utilized. In the roundness investigations, the machining tool rotation speed had a close relationship to the degree of micro-hole roundness. Micro-holes with a roundness value of about 2 μm (the max. radius minus the min. radius) could be obtained if the appropriate rotational speed was employed.