Micro-wire Electrical Discharge Machining Research Articles

Demonstration of an integrated-heating load frame for quantitatively assessing microscale tensile properties of copper and Zircaloy-2

Small-scale mechanical testing (SSMT) is of great interest in the nuclear materials community as it permits the use of surrogate irradiation techniques, such as ion beam irradiation when investigating the impact of irradiation damage on mechanical properties. The design of a micro-electro-mechanical-system (MEMS) micro-tensile stage is demonstrated to enable micron-sized specimen testing up to failure under ambient and reactor-relevant temperatures. Copper and Zircaloy-2 microscale specimens, having gauge lengths of 200 μm, gauge widths of 48 μm, and specimen-dependent constant gauge thicknesses of 10 μm to 26 μm, are fabricated using micro-wire electrical discharge machining and focused ion beam milling. From each gauge section, microstructure data is captured prior to testing using electron backscatter diffraction analysis, and an optimized digital image correlation speckle pattern is deposited on the specimen surface. The speckle pattern is tracked during deformation and post-processed to obtain strain-field evolution maps throughout deformation. Strain maps provide a means to account for and explain microstructure-dependent features observed in the captured stress-strain curves. The combination of using micro-wire electrical discharge machining, focused ion beam cleaning, and ion beam induced platinum deposition for micron-sized specimen preparation as well as utilizing microfabrication techniques to fabricate an integrated heating microtensile load frame reported herein serve as a demonstration of SSMT approaches that can be adopted to tackle challenging problems in nuclear materials research, including but not limited to the effects of ion beam irradiation on mechanical performance and providing experimental data to support small-scale modeling efforts of embrittling precipitates or radiation-induced segregation.

Simulation and Optimization of Surface Roughness and Process Performance during Machining of HSS by Micro-WEDM Technology.

When machining high-speed steels (HSS) with micro-wire electrical discharge machining (micro-WEDM), high surface quality is achieved as standard. The value of the roughness parameter Ra is less than 0.2 μm. However, the problem is the performance of the electroerosion process (MRR), which is low. This problem is related to the mechanical and physical properties of the HSS in combination with the setting of the main technological parameters (MTP). The proposed solution to eliminate this problem relies on the selection of proper procedures for the determination of optimization criteria in relation to Ra and MTP, with the inclusion of properties of the machined material. The solution consisted in the identification of four significant physical (ρ, κ) and mechanical (Rm, HRC) indicators of HSS properties, on the basis of which a suitable combination of the process output parameters Ra and MRR can be determined through established mathematical regression models using simulation and optimization. In the next step, the proper values of the MTP output process parameter settings, which correspond to the optimized output parameters Ra and MRR during machining of HSS by micro-WEDM technology, were then obtained by the same approach.

A multi-length-scale investigation of the applicability of ductility laws for annealed and work-hardened copper

Small-scale mechanical testing provides unique advantages over conventional testing in investigating the mechanical response of nuclear materials. While small-scale testing enables accelerated materials research, it raises the question of comparability to large-scale properties for engineering design considerations. Among different mechanical properties for structural design considerations such as yield and ultimate tensile stress, ductility is of critical importance with respect to structural component health. The effectiveness of using small-scale mechanical testing for probing these mechanical properties is dictated by understanding how the mechanical responses translate from the microscale to the engineering scale. Therefore, a better understanding of size scaling effects via gathering and analysis of experimental data is required to bridge length-scales. This work builds upon previous reports to provide statistical data on how mechanical response changes as the size of the specimens are reduced from conventional sizes. One hundred twenty mesoscale tensile coupons of oxygen-free high thermal conductivity (OFHC) copper in work-hardened and annealed state have been manufactured using micro-wire electrical discharge machining (EDM) and tested under uniaxial tension. The mesoscale specimens have dimensions dictated by pre-selected geometric ratios (i.e., gauge section length over the square root of the cross-section area) with gauge length dimensions of 3 mm (or less) and sub-millimeter gauge widths and thicknesses. The mesoscale responses were compared to bulkscale properties to reveal the effect of specimen size on the mechanical response as a function of grain size and material state for a single phase face-centered cubic metal.

Implementation and experimental validation of nonlocal damage in a large-strain elasto-viscoplastic FFT-based framework for predicting ductile fracture in 3D polycrystalline materials

Ductile materials, such as metal alloys, can undergo substantial deformation before failure. Additionally, these materials are usually of polycrystalline composition and exhibit strongly anisotropic behavior at small length scales. Previously developed fast Fourier transform (FFT)-based models can model ductile fracture of isotropic materials or the elastic–plastic behavior of anisotropic polycrystalline materials; however, there remains a need to couple both capabilities. This work extends a large-strain FFT-based crystal plasticity model to simulate ductile fracture of polycrystalline materials. A triaxiality-based continuum damage mechanics (CDM) formulation is incorporated into a large-strain elasto-viscoplastic FFT (LS-EVPFFT) framework. The CDM formulation is augmented with an integral-based nonlocal regularization approach that correctly handles gas-phase material necessary to model unconstrained surfaces. To validate the damage-enabled LS-EVPFFT framework, mesoscale copper tensile coupons were machined using microwire electrical discharge machining and experimentally characterized using electron backscatter diffraction. In-situ optical digital image correlation was performed during uniaxial testing to provide a side-by-side comparison of the experimental and computational strain fields and stress–strain responses. The damage-enabled LS-EVPFFT framework can simulate the complete macroscopic stress–strain response of ductile polycrystals to failure. The model reproduces necking behavior that qualitatively agrees with experimental observations. By leveraging the relatively low computational cost of the damage-enabled LS-EVPFFT framework, the framework presented here allows the ductile fracture response of 3D polycrystalline materials to be tractably predicted.

A novel electromagnetic microactuator with a stainless steel mas-spring structure

Microactuators are one of the main components of the microelectromechanical and microfluidic systems and play a key role in their development. Many such systems, e.g. micropumps and microvalves, utilize an electromagnetic microactuator with a displacement range of a few micrometers traversed within a few seconds. Most of the electromagnetic microactuators have low lifetime and fracture toughness or low recovery speed. Microactuators with metallic mass-spring structure can overcome the mentioned disadvantages or limitations. This paper presents the design and fabrication of a novel stainless steel electromagnetic microactuator fabricated using micro-wire electrical discharge machining. The microactuator in question consists of a mass-and-spring structure made of 304 stainless steel, a permanent magnet made of NdFeB, and a microcoil. The impacts of the number of turns, distance, and electric current on the magnetic field of the microcoil and the displacement of the microactuator membrane with time have been investigated to determine the microactuator characteristics. The results indicated a displacement of about ±10 (20) μm within 7 s for an electric current of 1100 mA. This microactuator exhibits a faster response compared to the similar microactuators. Consequently, it can be used at higher operating frequencies and, thus, improves the fluid flow in micropumps.

Analysis of kerf accuracy in dry micro-wire EDM

Mineral oil–based liquids are normally used as the dielectric fluid in electrical discharge machining (EDM) where it has the ability in improving the efficiency of the machining process. Nevertheless, these dielectric fluids have the tendency to cause environmental problems. Therefore, as an alternative, gas has been introduced as the dielectric fluid also known as dry EDM (DEDM) process. However, kerf variation in dry micro-wire EDM (DμWEDM) process remains a critical issue. Thus, the objective of this research is to investigate kerf accuracy in DμWEDM. Experimental investigation was carried out on a stainless steel (SS304) with a tungsten wire as the electrode and compressed air as the dielectric fluid using integrated multi-process machine tool, DT 110 (Mikrotools Inc., Singapore). Central composite design (CCD) was used to design the experiment using two controlled parameters: capacitance and gap voltage. Analysis of variance (ANOVA) was used to analyse the results and to evaluate the adequacy of the developed model. The results were obtained by measuring the kerf using a scanning electron microscope (SEM) (JEOL JSM-5600, Japan). The investigation of kerf was divided into two responses which were upper kerf and bottom kerf. Empirical models were developed, and it was found that both parameters (capacitance and gap voltage) have high influence on both responses. The optimum parameters for both minimum upper and bottom kerf were found to be 0.1 nF capacitance and 91 V gap voltage. The developed models were found to be adequate since the percentage error is relatively small (< 3%).

A novel single axis capacitive MEMS accelerometer with double-sided suspension beams fabricated using μWEDM

Design and fabrication of the first micromachined accelerometer made from steel and the first MEMS accelerometer fabricated using micro-wire electrical discharge machining (μWEDM) process is presented in this paper. By utilizing this fabrication method, it is possible to achieve a huge proof mass that has a prominent effect on reducing noise. The proof mass in this design has a mass of 7.85 mg which leads to the Brownian noise of 0.8 μg/Hz that is comparable to low noise MEMS accelerometers. Another advantage is the higher density of the steel relative to the silicon, so a heavier proof mass can be achieved in a smaller size, providing a better control over the damping. The finite element analysis of the accelerometer shows that this sensor is able to measure high-amplitude accelerations up to 131 g without the risk of failure and fatigue because of the high yield stress and fracture toughness of the steel. Consequently, due to its low noise, resulting from its heavy mass, and also the ability to measure high amplitude acceleration, resulting from the high yield stress, the fabricated accelerometer has a dynamic range of more than 100 dB. Experimental tests showed that the accelerometer has the sensitivity, nonlinearity and range of 18 mV/g, 3% and 100 g respectively. This sensor provides the ability to operate in the air, which makes the packaging process easier. Also, the accelerometer shows the cross axis sensitivity of 0.44% accruing from the symmetrical arrangement of suspension beams used to suspend the proof mass.

Surface characteristics of nano powder mixed micro-wire electrical discharge machining on inconel alloy

Micro electric discharge machining (Micro-EDM) is an established machining process used in modern manufacturing industries to make miniaturized and precision parts/components with superior surface finish. This present work, investigates the effect of graphite nanoparticle suspended dielectric on machining Inconel 718-alloy with zinc coated copper electrode using Micro-Wire Electric Discharge Machining (Micro-WEDM) process. Micro-WEDM process input variables are voltage 80 V, 100 V and 120 V, capacitance 0.0001μF, 0.01μF and 0.1μF, and concentration of powder 0 g/l, 0.25 g/l, and 0.5 g/l. Experimental work was carried out on inconel alloy using Taguchi Design of Experiments. Surface roughness was taken as response parameter. Analysis of Variance (ANOVA) was used to assess model significance. All three process parameters have been significant influences on surface roughness.

Thin-wall micromachining of Ti–6Al–4V using micro-wire electrical discharge machining process

Machining of delicate thin members having extremely small thickness as compared to the other two dimensions is a precarious task when performed using conventional fabrication techniques. Non-contact machining process, such as micro-wire electrical discharge machining (micro-WEDM) process, an advanced means of machining, offers an appropriate way to machine thin-wall structures in an utmost precise manner. In the present work, thin-wall micromachining of Ti–6Al–4V is performed while utilizing the contactless, negligible thermal damage, and deformation-free nature of micro-WEDM process energized through the resistance–capacitance generator. The objective is to explore the feasibility of a minimum possible wall thickness. Performing the thin-wall micromachining using wire step-over approach, it is established that a wall of average thickness 8.47 µm with an end deflection and a wall of thickness about 15 µm free from end deflection is possible to fabricate using micro-WEDM process. It achieves a high aspect ratio of 70 corresponding to the minimum thickness of the wall. What’s more, a theoretical analysis is carried out to illustrate the functional relationship between wall-end deflection with workpieces’ thermophysical properties, discharge parameters, and the geometric parameters of the wall. Finally, the comparative assessment of wall-end deflection and volumetric material removal rate attained with three different materials, namely Ti–6Al–4V, mild steel, and SS-304, reveal that thermophysical properties of workpiece material play a critical role in determining the wall-end deflection and the resultant volumetric material removal rate.

Experimental investigation and multi-objective optimization of micro-wire electrical discharge machining of a titanium alloy using Jaya algorithm

Experimental investigation and multi-objective optimization of micro-wire electrical discharge machining of a titanium alloy using Jaya algorithm

Micro-Abrasive Water Jet and Micro-WEDM Process Chain Assessment for Fabricating Microcomponents

The capability to manufacture high-precision components with microscale features is enhanced by the combination of different micromanufacturing processes in a single process chain. This study explores an effective process chain that combines micro-abrasive water jet (μ-AWJ) and microwire electrical discharge machining (μ-WEDM) technologies. An experimental spring component is chosen as a leading test case, since fine geometric features machining and low roughness on the cut walls are required. The advantages deriving from the two technologies combination are discussed in terms of machining time, surface roughness, and feature accuracy. First, the performances of both processes are assessed by experimentation and discussed. Successively, different process chains are conceived for fabricating two test cases with different sizes, displaying some useful indications that can be drawn from this experience.

Modeling and analysis of surface roughness of microchannels produced by μ-WEDM using an ANN and Taguchi method

Microchannel heat exchangers are used to remove the high heat fluxes generated in compact electronic devices. The roughness of the microchannels has a significant effect on the heat transfer characteristics, especially the nucleate boiling and pumping power. Therefore, development of predictive models of surface texture is of significant importance in controlling heat transfer characteristics of these devices. In this study, micro-Wire electrical discharge machining (μ-WEDM) was employed to fabricate metal-based microchannel heat sinks with different surface textures. First, experiments were conducted to achieve the desired surface roughness values. Oxygen-free copper is a common material in the cooling systems of electronic devices because of its high thermal conductivity and low cost. Design of experiment approach based on the Taguchi technique was used to find the optimum set of process parameters. An analysis of variance is also performed to determine the significance of process parameters on the surface texture. An artificial neural network model is utilized to assess the variation of the surface roughness with process parameters. The predictions are in very good agreement with results yielding a coefficient of determination of 99.5 %. The results enable to determine μ-WEDM parameters which can result in the desired surface roughness, to have a well-controlled flow and heat transfer characteristics for the microchannels.

Micro-wire electric discharge machining of Mg alloy used in biodegradable orthopaedic implants

In current day practice, orthopaedic implants generate tremendous functional features due to their superior material properties and the use of filigree 3D microstructures. Magnesium is an important material which is especially used in such types of biodegradable orthopaedic implants applications etc. Micro-Wire Electric Discharge Machining (micro-WEDM) is an advanced machining process (AMP) which can be effectively used for its fabrication into different micro size intricate shapes. It can produce accurate matte finish of the order of 0.1 µm and more. However, the effect of process parameters viz. voltage, capacitance, wire tension, wire feed in context with micro-WEDM is yet to be established. In this work, biodegradable Mg alloy (AZ31) was selected for experimentation. The voltage and capacitance were taken as variable process parameters while wire tension and speed were kept as constant at 10%. Material removal rate (MRR) and kerf width were taken as machining performance parameters. After analysis it was found that, for optimum MRR, medium voltage and high capacitance is desirable, while for optimum kerf width, low voltage and capacitance is required.

Development of a novel micro w-EDM power source with a multiple Resistor-Capacitor (mRC) relaxation circuit for machining high-melting point, -hardness and -resistance materials

This study presents the development of a novel micro-wire electric discharge machining (w-EDM) power source for machining high-melting point, -hardness and -resistance materials. The relaxation circuit power devised with a multiple Resistor-Capacitor (mRC) is triggered by a Programmable Logic Device (PLD) to generate a high-peak, short-pulse-time current train. The mRC relaxation circuit is characterized by high density discharge-spots per unit of time for swiftly removing material and creating fine discharge craters. Three microstructures made of tungsten carbide, WC-based cermet, and Boron-Doped Polycrystalline Composite Diamond (BD-PCD), respectively, are machined to validate the novel relaxation circuit. Experimental results demonstrate the 3RC relaxation circuit reduces machining times by 25%–35%, resulting in a more time efficient micro w-EDM process. Compared with a transistorized power source, the heat-affected zone is smaller and surface finish is better when using the 3RC relaxation circuit. A set of metrics for helping measure important electro-thermal machining related properties during micro w-EDM is proposed in this study. These are the ‘Spark Erosion Rate (SER)’, ‘Electro-Thermal Machinability (ETM)’, and ‘Cutting Performance (CP)’. An extensive examination of the quantitative and qualitative properties of material erosion mechanisms, material removal rates (MRR), and cobalt deposition for machining of difficult-to-machine materials is undertaken and the results discussed in detail.

Experimental investigation on low-frequency vibration assisted micro-WEDM of Inconel 718

The micro-wire electric discharge machining (micro-WEDM) has emerged as the popular micromachining processes for fabrication of micro-features. However, the low machining rate and poor surface finish are restricting wide applications of this process. Therefore, in this study, an attempt was made to improve machining rate of micro-WEDM with low-frequency workpiece vibration assistance. The gap voltage, capacitance, feed rate and vibrational frequency were chosen as control factors, whereas, the material removal rate (MRR) and kerf width were selected as performance measures while fabricating microchannels in Inconel 718. It was observed that in micro-WEDM, the capacitance is the most significant factor affecting both MRR and kerf width. It was witnessed that the low-frequency workpiece vibration improves the performance of micro-WEDM by improving the MRR due to enhanced flushing conditions and reduced electrode-workpiece adhesion.

Kerf analysis and control in dry micro-wire electrical discharge machining

This paper describes the analysis and control method for the kerf of cut slots in dry micro-wire electrical discharge machining (μ-WEDM). First, the influence of the controllable parameters such as the air injection pressure, relative electrode feedrate, open voltage, and input capacitance were investigated based on the Taguchi methodology. The behavior of the kerf with respect to the workpiece height was also considered. Second, to improve the machining accuracy of the dry μ-WEDM, a control method was developed to compensate for the kerf based on real-time estimation of the material removal rate and by controlling the air injection pressure. In this research, all the experiments were performed in a constant-feedrate mode and with various high-pressure air injection. The experimental results show that the kerf in dry μ-WEDM was significantly affected by the air injection pressure, electrode relative feedrate, and cut height of the workpiece. Moreover, by monitoring the material removal rate of the process, the kerf in dry μ-WEDM was efficiently controlled.

Modeling and analysis of micro-WEDM process of titanium alloy (Ti–6Al–4V) using response surface approach

Micro-machining technology is effectively used in modern manufacturing industries. This paper investigates the influence of three different input parameters such as voltage, capacitance and feed rate of micro-wire electrical discharge machining (micro-WEDM) performances of material removal rate (MRR), Kerf width (KW) and surface roughness (SR) using response surface methodology with central composite design (CCD). The experiments are carried out on titanium alloy (Ti–6Al–4V). The machining characteristics are significantly influenced by the electrical and non-electrical parameters in micro-WEDM process. Analysis of variance (ANOVA) was performed to find out the significant influence of each factor. The model developed can use a genetic algorithm (GA) to determine the optimal machining conditions using multi-objective optimization technique. The optimal machining performance of material removal rate, Kerf width and surface roughness are 0.01802 mm3/min, 101.5 μm and 0.789 μm, respectively, using this optimal machining conditions viz. voltage 100 V, capacitance 10 nF and feed rate 15 μm/s.

Multiresponse optimization of micro-wire electrical discharge machining process

In recent years, micro-wire electric discharge machining (micro-WEDM) has become one of the most popular micromachining processes used for creating complex microfeatures on electrically conductive materials. However, it suffers from few limitations such as low machining efficiency and poor surface finish. To overcome these limitations, an attempt has been made to model the performance of micro-WEDM process. The effect of various process parameters such as gap voltage, capacitance, feed rate, and wire tension on the performance characteristics of micro-WEDM is studied on titanium alloy (Ti-6AL-4V). Analysis of variance (ANOVA) is performed to identify the significant factors. From the study, it is revealed that capacitance is the predominant factor that influences the machining characteristics. In order to correlate relationship between process parameters and responses, a fuzzy logic model has been employed to predict the process characteristics based on experimental observations. Traditional fuzzy logic system is unable to directly handle uncertainties and its simple information processing method will lead to low accuracy and poor dynamic quality of the system. The feasible way for solving this is to use particle swarm optimization (PSO) algorithm to enhance the performance of micro-WEDM process. Experimental results confirm the feasibility of proposed fuzzy logic strategy and the developed particle swarm optimization (PSO) algorithm. The adequacy of the model is tested and validates the results by conducting the experiments with optimum parameter settings.

Surface Integrity Associated with SiC/Al Particulate Composite by Micro-Wire Electrical Discharge Machining

It is difficult to have high accuracy and low surface roughness in processing of metal matrix composites (MMCs). Micro-wire electrical discharge machining (micro-WEDM) has no obvious cutting force in processing because there is no direct action between tool electrode and workpiece, which makes micro-WEDM complete the machining of MMCs with high hardness and high strength. However, the recast layer can be formed with damages on machining surface in micro-WEDM process. Therefore, to resolve these problems, this paper highlights analysis of the surface characteristics of SiC/Al particulate MMC in micro-WEDM process. In addition, the characteristics of recast layer with different discharge energy are analyzed. And the removal process of ceramic particles in the composite is thermal spalling process, which is proved using surface morphology of SiCp/Al MMC by micro-WEDM. Finally, to reduce the thickness of recast layer and improve surface integrity of SiCp/Al2024 MMC by micro-WEDM, a multicutting experimental is performed and the machined surface with 0.774 µm in surface roughness and 3 µm in recast layer thickness are obtained.

Design of endoscopic micro-robotic end effectors: safety and performance evaluation based on physical intestinal tissue damage characteristics

During the last several years, legged locomotive mechanism has been considered as one of the main self-propelling mechanisms for future endoscopic microrobots due to its superior propulsion efficiency of an endoscopic microrobot inside the intestinal track. Nevertheless, its clinical application has been largely limited since the legged locomotive mechanism utilizes an end effector which has a sharp tip to generate sufficient traction by physically penetrating and interlocking with the intestinal tissue. This can cause excessive physical tissue damage or even complete perforation of the intestinal wall that can lead to abdominal inflammation. Hence, in this work two types of new end effectors, penetration-limited end effector (PLEE) and bi-material structured end effector (BMEE) were specially designed to acquire high medical safety as well as effective traction generation performance. The microscopic end effector specimens were fabricated with micro-wire electric discharge machining process. Traction generation performance of the end effectors was evaluated by direct measurement of resistance forces during contact-sliding tests using a custom-built contact-sliding tester. The safety of the end effector design was evaluated by examination of microscopic intestinal tissue damage using a scanning electron microscope (SEM). Physical damage characteristics of the intestinal tissue and related contact physics of the end effectors were discussed. From the results, the end effectors were evaluated with respect to their prospects in future medical applications as safe end effectors as well as micro-surgical tools.