Micro-electrical Discharge Milling Research Articles

To investigate the effect of discharge energy and addition of nano-powder on processing of micro slots using EDM assisted µ-milling operation

ABSTRACT Micro-electric Discharge-Milling (µ-ED-M) is a non-contact process that uses an electrical spark to remove the material from a submerged workpiece with an electrode in a dielectric. The present paper focuses on optimizing process energizing (Capacitor, Voltage) and process stabilizing (Tool Travel Speed, Nano-Powder) parameters for controlling the size and surface characteristics of micro-crater. The present work focuses on the effect of nano-powder concerning dimensional aspects and surface characteristics at high and low capacitance levels. A µ-slot has been generated on the copper material by a tungsten carbide electrode. The experimentation is performed with two capacitor levels and three voltage and tool travel speed levels using full factorial design technique using with and without mixing of nano-powder in dielectric. The desirability functional multi-objective optimization approach is used to analyze the MRR, TWR, Width, and Depth. Field emission scanning electron microscopy (FESEM), non-contact optical profilometer, and x-ray diffraction (XRD) techniques are used to analyze the surface morphology of machined surfaces. The ANOVA is used to optimize the results; at low discharge energy, tool travel speed contributes 41% and promotes a higher thickness of recast layer 12.7 µm, whereas high discharge energy and nano-powder concentration contribute approx.—36% with 8.56 µm of recast layer.

Powder mixed micro-electric discharge milling of Ni-rich NiTi SMA: an investigation on machining performance and biocompatibility

ABSTRACT Nickel and titanium (NiTi) based shape memory alloys (SMAs) are novel materials endowed with exceptional super-elasticity, corrosion resistance, and shape memory capabilities, making them well-suited for biomedical and industrial applications. The current study explores the impact of process parameters in powder mixed micro-electrical discharge milling (µ-EDM) on NiTi SMA, focusing on pulse on time (TON), voltage, pulse off time (TOFF), and RPM individually, employing a one factor at a time (OFAT) methodology to analyze surface characteristics, surface roughness (Ra), and material removal rate (MRR). The impact of black phosphorus powder combined with sesame oil (dielectric) on the surface of fabricated channels in commonly used biomaterials was investigated. The cytotoxicity test for biocompatibility was carried out to enhance the cell viability up to 79.89% after machining, which showed enhanced cell viability. The highest MRR the lowest Ra were obtained at the best input factors combination of 24 µs (TON), 6 µs (TOFF), 240 V, and 50 RPM tool rotation. Improved micro-channel quality was observed with lower TON, voltage, and RPM.

Experimental investigation during nano powder added µ-ED milling on nickel-titanium shape memory alloy

Nickel-titanium (NiTi) shape memory alloy (SMA) is one of the smart materials which has a vast application in the aerospace and biomedical industry due to its shape memory effect (SME), strong corrosion and wear resistance. Thus, the present study investigates the influence of process variables like gap voltage (V), powder concentration (PC) and pulse on time (ton) towards the material removal rate (MRR), surface roughness (SR) and micro-hardness (MH) amid graphene nano powder added micro-electrical discharge milling (µ-ED milling) of NiTi SMA. ANOVA analysis has been carried out to determine the % distribution of individual machining parameters towards all responses. The addition of graphene nano particles to the dielectric oil considerably enhanced the MRR, MH, and decreased the SR of the milled micro-channel. Taguchi’s grey relational analysis (GRA) and grey-desirability approach have been applied for multi-response optimisation to find the maximum MRR, MH, and minimum SR. It is discovered that the grey-desirability method improves all the responses. The Field emission scanning electron microscopy (FESEM) micro-graphs confirm defect-free mirror-like surface finish at the optimal grey-desirability setting. The X-ray diffraction (XRD) analysis discovered the formation of oxides and hardened phases in the machined surface. The application of graphene enhanced the recast layer thickness and reduced the indentation depth at subsurface region. The nano indentation test validates the rise in nano hardness and elastic modulus at the grey desirability optimal setting compared to the initial machining condition.

Simulation of flow-field and debris temperature analysis in micro-electrical discharge milling using slotted tools

In micro-electrical discharge milling (μED-milling), the rotation and forward feed motion of the tool is the key element responsible for evacuation of the debris particles. The inability to eliminate debris from the interelectrode gap (IEG) causes secondary discharge, short-circuit, and hampers removal rate. This problem is predominant in electrical discharge machining (EDM) where the tool is stationary. Various methods have been devised in the literature to boost debris removal from the IEG. In this paper, the use of a slotted tool with different cross-sections is proposed. The dielectric flow-field, debris trajectory, and cooling rate are calculated using computational fluid dynamics (CFD). Effect of different parameters such as tool rotation, gap size, jet velocity, the shape of slots on the dielectric flow is determined. The slots on the tool create turbulence which enhances the debris removal from the IEG. It also provides the space to accumulate the debris particles, thereby increasing the removal rate. The variation in the dielectric flow-field greatly affects the debris flushing from the IEG. The trajectory of the debris particles depends on their initial position in the IEG and they cool rapidly, which is validated using simulation and mathematical approach.

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.

Dimensional accuracy and surface quality of micro-channels with low-frequency vibration assistance in micro-electro-discharge milling

ABSTRACT Micro-electric discharge milling (µ-ED milling) process has attracted interests of researchers in the area of fabrication of three-dimensional miniaturised features specifically in difficult-to-cut materials. However, significant electrode wear during machining degenerates the accuracy fabricated micro-features. Therefore, in this work, low-frequency workpiece vibration is introduced to assist µ-ED milling to improve the dimensional accuracy of fabricated micro-channels. Difficult-to-cut Inconel 718 superalloy was selected as a workpiece for fabricating straight micro-channels. Initially, the effect of vibration assistance on the µ-ED milling process performance was evaluated in terms of material removal rate and tool wear. Then, the effect of low-frequency workpiece vibrations on dimensional accuracy and surface quality of fabricated micro-channels was investigated using microscopic images. Overall, the low-frequency workpiece vibration assistance found to be effective in enhancing the process performance of µ-ED milling process.

Correlation of Three-Dimensional Roughness Parameters With the Crater Dimensions in μED-Milling of Cryogenic-Treated Tool and Workpiece

Abstract Microfluidics is one of the rapidly growing markets in the present era of miniaturization. Microchannels have wide applications in various fields such as biomedical, mechanical, electrical, and chemical sciences. Machining microfeatures with high aspect ratio in metals is difficult by mechanical and lithography-based processes. Micro-electric discharge milling is a suitable process to machine microcavities and microchannels in all electrically conductive materials. The main disadvantage of this process is its very low material removal rate. Improving the machining performance of micro-electric discharge machining (μEDM) is a research area that attracts researchers and remains as an unfulfilled agenda. The aim of this study is to improve the machining performance of micro-electric discharge milling process by investigating the performance of cryogenically treated tool and workpiece materials. Since surface roughness determines the minimum feature size machinable by any micromachining process and also it is an important factor in determining the flow characteristics of microchannels, a detailed comparative study was conducted on the three-dimensional (3D) surface quality parameters along with machining performance while using all four different combinations of untreated and cryogenically treated tool and workpiece, and the roughness parameters are correlated with the erosion behavior. The study revealed significant change in material removal rate and erosion pattern due to cryogenic treatment.

Improving the performance of µED-milling using assisting electrode for fabricating micro-channels in CFRP composites

Micro-electrical discharge milling (µED-milling) is an emerging non-traditional material removal process used to fabricate micron-size features in the materials which are difficult to machine by the traditional machining process. Carbon fiber-reinforced polymer (CFRP) is one such material which is not compatible with the traditional micro-machining process due to excessive damage to the machined surface in terms of fiber breakage, delamination, fiber pull-out, etc. These types of damages mostly occur due to the mechanical interaction between the tool and workpiece. Also, fabricating features of micron size in CFRP using µED-milling is a challenging task due to its low electrical conductivity. In this research endeavor, an attempt was made to improve the performance of µED-milling with the aid of a conductive copper foil as assisting electrode to initiate the sparking between the tool and work surface. Taguchi’s L9 experimental design was applied considering three input parameters namely input energy (1.805, 18.05, and 180.5 µJ), tool speed (300, 400, and 500 RPM), and EDM feed (2, 3, and 4 µm/s). The regression analysis was performed to understand the effect of the input factors on the deviation in channel width (DCW). The profiles of the fabricated microchannels were studied under an optical microscope. The detailed morphology of the machined surface was analyzed using field emission scanning electron microscope (FESEM).

Evaluation of the sustainability of the micro-electrical discharge milling process

The sustainability evaluation of an industrial process is an actual issue: a process should not only grant part quality and high production rates at the lowest cost, but it should minimize its impact on the environment as well. Micro‐EDM (Electrical Discharge Machining) is widely used in micro machining for its small force and high precision and environmental aspects related this technology are taken into account. In this paper, an evaluation of the micro‐ED milling process concerning the sustainability manufacturing was made. For this purpose, a method to assess the sustainability process was developed, taking into account the energetic consumption, the environmental impact, the dielectric consumption, the wear of the electrode and the machining performance. This method was applied for the execution of micro‐pockets using two workpiece materials, two types of electrode and five types of dielectric, both liquid and gaseous. This analysis permits the identification of the critical aspects of the micro‐ED milling process form the point of view of the sustainability. The comparison between the different solutions in terms of electrode material and dielectric underlines interesting considerations about the usage of non‐traditional dielectrics. As regards electrode material, the environmental impact process when brass electrode is adopted is lower than tungsten carbide electrode. As concerns dielectric, water reveals to be the most sustainable dielectric; vegetable oil and oxygen, proved to be valid substitutes to traditional dielectrics under several viewpoints, including sustainability.

Experimental Investigation of Machinability and Surface Characteristics in Microelectrical Discharge Milling of Titanium, Stainless Steel and Copper

Microelectrical discharge milling (µED-milling) possesses good processing capability to fabricate intricate shapes in any electrically conductive material. In the present work, an experimental study is carried out to investigate machinability and surface characteristics of titanium (Ti) grade 2 alloy, stainless steel 304 (SS304) and copper (Cu) undergoing microelectrical discharge milling (µED-milling) process. Voltage, feed rate (FR) and tool rotation speed (TRS) are the process parameters that are varied during machining. The response measures chosen for evaluating machinability performance are material removal rate (MRR) and tool wear rate (TWR). After performing µED-milling, topography of the fabricated microslots is characterized by optical microscopy, scanning electron microscopy and surface roughness (Ra) analysis, whereas material composition analysis is carried out by X-ray diffraction and energy-dispersive X-ray techniques. It is found that Cu exhibits higher MRR than Ti and SS304, whereas SS304 exhibits higher TWR than Ti and Cu at all the chosen parametric conditions. The most significant parameter affecting MRR and TWR as ascertained by analysis of variance is FR, followed by voltage and TRS. Surface morphology of the microchannels fabricated by µED-milling reveals that globule formation and redeposition phenomenon is profound in case of Cu and SS304. In contrast, Ti grade 2 exhibits better surface morphology in terms of less globule formation, microvoids, redeposition layer and lower Ra as compared to Cu and SS304.

μED milling of Ti-6Al-4V using cryogenic-treated Wc tool and nano-graphene powder-mixed dielectricat different discharge energy regimes

Micro-electric discharge milling (μED milling) has the potential to create micro-channels in metals. Since μED milling is a slow machining process, the requirement of strategies that can enhance the material removal rate (MRR) is always crucial in the field of micro-machining. Nano-powder-mixed micro-electric discharge milling (NPMμED milling) is least explored by researchers. Also, the behaviour of μED milling at various discharge energy regime (D.E.R) was not analysed extensively. The present study investigates the combined effects of nano-powder-mixed dielectric at three different regimes of discharge energies with respect to MRR and tool wear rate (TWR) while micro-machining of Ti-6Al-4V using cryogenically treated electrodes. There is significant difference in the machining behaviour at low, medium and high D.E.Rs. Also, the effects of transformation in cathodic streamers due to addition of nano-graphene powders in the dielectric fluid were extensively analysed. Cryogenic treatment of the tool electrodes gave better MRR. The addition of nano-powders in the dielectric has reduced the crater diameter significantly however increased the overall 3D roughness of the machined surface.

Effect of reverse current on tool wear in micro-electrical discharge milling

An RC-type pulse generator is useful in micro-electrical discharge milling due to its small discharge energy. However, when using this kind of generator, the current between the tool and the workpiece oscillates because of the stray inductance of the circuit. This causes current to flow from the tool to the workpiece in reverse direction to the main discharge current. When the reverse current flows, tool polarity is changed which intensifies tool wear. In this research, the reverse current is eliminated by connecting a MOSFET to a normal RC-type pulse generator. As a result, tool wear was reduced and geometrical accuracy was increased during machining of stainless steel using cemented carbide tool. Tool wear was further reduced through the use of deionized water with low resistivity. However, the use of low resistivity water decreases tool wear but can also reduce geometrical accuracy. The combination of using a MOSFET with low resistivity water therefore reduces tool wear while maintaining geometrical accuracy. The addition of the MOSFET to the RC circuit reduced the relative wear ratio by up to 67%. Thus, removing the reverse current is effective in reducing tool wear in various machining conditions.

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.

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.

Effects of Different Cavity Geometries on Machining Performance in Micro-Electrical Discharge Milling

Abstract Low energy-short pulsed electric discharge coupled with precise movement of circular electrode in micro-electrical discharge-milling (μ-EDM-milling) enables generation of three-dimensional (3D) cavities in the order of few tens of microns. Use of unshaped rotating electrode alters the spark discharge pattern that is primarily driven by the shape and size of the cavities being machined. In this paper, effects of five different cavities: circular, triangular, square, channel, and cross channel (square pillars) on the machining performance have been studied. These cavities having a nominal dimension of 1000 μm were machined on steel sample using 200 μm tungsten carbide electrode. The machining performance has been evaluated by analyzing dimensional accuracy, surface integrity, profile error, and formation of recast layers. The results highlight significant shape effect on machining performance in μ-EDM-milling. Circular holes machined by die sinking (tool advancement in Z-axis) are found to be more accurate, and square shaped pillars machined in two settings by generating cross channels at 90 deg have poor dimensional control. On the other hand, triangular cavities have the highest surface finish and profile uniformity compared to other shapes. The microscopic study in scanning electron microscopy (SEM) reveals significant variations in globule formation, recast layer deposition, flow of eroded molten metal, and final shape of cavities, which are found to be dependent of tool rotation.

Effects of Ultrasonic Vibration and Magnetic Field in Micro-EDM Milling of Nonmagnetic Material

Micro-electric discharge milling (μ-EDM milling) is one of the micromachining processes which draw the attention of researchers in fabricating microcavities and microchannels. Improving the efficiency of this process remains challenging. There are publications that report the benefits of applying ultrasonic vibration to tool or workpiece and using magnetic fields to enhance debris removal. In almost all the literature, magnetic field and/or ultrasonic vibration were applied separately in micro-/macro-EDM. The aim of this study is to apply ultrasonic vibration and magnetic field simultaneously/separately, and compare the machining performance by analyzing material removal rate and tool wear rate (TWR) while fabricating microchannels on nonmagnetic materials using μ-EDM milling. From the results, it is recommended to use magnetic field or ultrasonic vibrations separately for achieving high MRR, but the combination of both gave poor results.

Innovative process chain for the development of wear resistant 3D metal microsystems

This paper presents an innovative process chain, that is based on microelectrical discharge machining for the fabrication of 3D microsystems made of stainless steel. The fabrication process cluster consists of three technologies: microelectrical discharge milling, die-sinking microelectrical discharge machining and a subsequent electrochemical polishing step. The described fabrication processes are applied to design a microsystem for the integrated generation and loading of drug carrier systems. @mED-milling orifices with a minimum width of 50@mm and a surface roughness of Ra,@mEDM=(94.9+/-1.0)nm are fabricated. The application of a subsequent electrochemical polishing step improves the surface quality to Ra,ECP=(22.1+/-1.3)nm. Solid lipid nanoparticles were efficiently produced with a mean particle size of 135nm within one emulsification cycle.

Research on the Process of High Silicon Aluminum Alloy in MEDM

Because of the high content of Si, traditional machining can hardly machine micro and small structures. While there is almost no microscopic force in the process of micro-electrical discharge milling (MEDM), so it has great advantages. In the process of MEDM for high silicon aluminum (Si-Al) alloy, the impacts of electrical parameters on processing time, the trend and degree of electrode wear are researched. The Al-50wt%Si alloy made by spray forming (SF) and casting forming (CF) and electrode of copper and tungsten are adopted to do the research. Related processing laws are summarized. A micro-3D structure was made by using appropriate parameters based on the experiment and research.

Towards the effective tool wear control in micro-EDM milling

The electrode wear in micro-electrical discharge milling (micro-EDM milling) is one of the main problems to be solved in order to improve machining accuracy. This paper presents an investigation on wear and material removal in micro-EDM milling for selected process parameter combinations typical of rough and finish machining of micro-features in steel. The experiments were performed on state-of-the-art micro-EDM equipment. Based on discharge counting and volume measurements, electrode wear per discharge and material removal per discharge were measured for several energy levels. The influence of the accuracy of volume measurements on the electrode wear per discharge and on the material removal per discharge are discussed, and the issues limiting the applicability of real time wear sensing in micro-EDM milling are presented.