micro-EDM Characteristics Research Articles

Material removal mechanisms, processing characteristics and surface analysis of Cf-ZrB2-SiC in micro-EDM

Cf-ZrB2-SiC is a new composite material with excellent properties for making the next-generation aerospace component. This material is extremely difficult to removal by mechanical machining, and there is a lack of research on feasible secondary processing methods of this composite at present. Micro-EDM is not limited by material hardness, so it is very suitable for machining this material. In this paper, the Material removal mechanisms and processing characteristics of Cf-ZrB2-SiC by micro-EDM is analyzed. The removal mechanism of composite materials is explored though the discharge crater morphology, and the single-discharge experiments of each phase materials with different medium and different energies are also carried out as a reference. Electrical discharge milling experiments of Cf-ZrB2-SiC are performed to explore the medium on processing index, and found that the best surface quality and maximum processing efficiency can be realized in kerosene. An experiment with four factors (pulse width, voltage, peak current, capacitance) and three indexes (surface roughness, MRR, TWR) is designed to analyze the Cf-ZrB2-SiC process characteristics of micro-EDM and the response surface diagram and second-order regression equation are obtained. Milling the Cf-ZrB2-SiC by electrical discharge according to the optimal combination of surface roughness parameters deduced above, the as-machined surface is analyzed including the surface morphology by SEM, element content by EDS and the surface phase by XRD. The feasibility and advantages of micro-EDM on machining Cf-ZrB2-SiC are prove.

Investigation on performance characteristics of micro-EDM dressing for the fabrication of micro-rod(s) on Ti-6Al-7Nb biomedical material

The performance characteristics of micro-EDM dressing were investigated based on some real-time and offline responses for the fabrication of micro-rod(s) on a novel Ti-6Al-7Nb biomedical material. These characteristics evaluated along the micro-rod length at three different discharge energy settings were analyzed by monitoring the discharge gap condition captured through an in house developed pulse-discriminating system (PD). The experimental results show that the normal pulse was more (∼90%) in the low energy setting (E 1). In contrast, arcing was more (∼28%) in the high energy setting (E 3). Pulse frequency was found more (∼60 ) in E 1. However, due to an increase in the ‘idle’ time, it significantly decreased (∼25) along the machining length. however, was found more (∼5.7 × 103, µm3/s) in E 3. The specific energy was found very high (∼9 MJ/mm3) in E 1 since the process spent additional energy to remove the re-solidified molten metal. The was, on the other hand, found very high (∼2.1) in E 1 due to prolonged exposure to discharges and experiencing higher total discharge energy by the work-tool interface. E 3 was found more suitable for fabricating dimensionally accurate micro-rod(s) on this material because of less tool wear.

Effect of coated and treated electrodes on Micro-EDM characteristics of Ti-6Al-4V

This research work was carried out to find a suitably treated electrode for the required machining output response like MRR and TWR. The experimental design was formed using Box–Behnken design. Experiments were conducted to machine 500 µm holes on titanium (Ti-6Al-4V) alloy using copper electrodes. Input parameters selected were input current (Ip), pulse-on time (Ton), and pulse-off time (Toff). Material removal rate and tool wear rate were analyzed using contour plots. Based on these experimental data, the grey relational analysis technique was applied to find the optimal parameters for achieving maximum MRR and minimum TWR. Optimal parametric values obtained were input current (Ip) 4.0 A, pulse on time (Ton) 2.0 µs and pulse off time (Toff) 6.4 µs. The achieved optimized parameters were further used to conduct experiments with cryogenic treated and coated electrodes. Electrodes were coated with conductive materials (silver, nickel, and zinc) and non-conductive material (epoxy). The experimental results showed each type of electrode enhances a particular machining characteristic such as silver-coated electrode produced a higher value of MRR, epoxy-coated electrode achieved minimum TWR. It is observed from the results that this work can be applied to identify the suitable electrode for producing the desired machining output characteristics.

Influence of various metal powder mixed dielectric on micro-EDM characteristics of Ti-6Al-4V

ABSTRACTTi-6Al-4V, an advanced engineering material is difficult-to-machine using conventional machining process due to its high strength. It has properties like low weight ratio, outstanding corrosion resistance along with high level of reliable performance in micro components. Micro-electro-discharge machining (Micro-EDM), a popular nontraditional machining process has been identified as the most appropriate machining process for such material. In this paper, the effect of various conducting powders such as copper, nickel and cobalt with different concentrations are mixed with deionized water dielectric, on various responses such as material removal rate (MRR), tool wear rate (TWR), overcut (OC) and taper has been presented. Also, principal component analysis (PCA) has been applied to select the optimal parametric combination of micro-EDM process to achieve optimal values of MRR, TWR, OC and taper during micro-through hole machining. The optimal process parametric setting obtained from the proposed approach is peak current (Ip) of 1.5 A and cobalt (Co) powder concentration of 4 g/L so as to obtain the desired responses. It is also observed from the SEM image that the machined profile and surface topography obtained through the multi-objective optimal parametric combination based on PCA is quite satisfactory and can be applied to achieve geometrically more accurate micro-through holes on Ti-6Al-4V.

Comparison of Micro-EDM Characteristics of Inconel 706 between EDM Oil and an Al Powder-Mixed Dielectric

Inconel 706 is a newly developed aeronautical material that has corrosion resistance along with high mechanical strength. Conventional machining of Inconel 706 results in a poor surface finish and a low-dimensional accuracy. Hence, micro-EDM (electrical discharge machining) is utilized to machine Inconel 706. This work proposes a comparison of micro-EDM characteristics of Inconel 706 between EDM oil and an Al powder mixture. The effects of input parameters on the surface roughness, material removal rate, tool removal rate, and microstructures of the machined surfaces between EDM oil and EDM oil mixed with Al were investigated. It was clarified that micro-EDM with a certain amount of Al powder added to the EDM oil can attain a high MRR and better surface integrity. However, the TWR discharge gap was larger than that in the EDM oil. Furthermore, it was observed that more attachment of the workpiece was adhered to the top surface of the electrode in the EDM oil due to its unstable machining. It was explained that the MRR increases with an increase in the Al concentration and then tends to decline.

Study of Machining Characteristics of Micro EDM in Nitrogen Plasma Jet

Micro electrical discharge machining (EDM) has been used to drill micro-holes and to generate micro-features for applications in automotive, aerospace and biomedical industries. The tool electrode wear ratio in micro-EDM usually is larger than that in conventional EDM process. It has been reported that the electrode wear ratio is almost zero in gas. However, its narrow discharge gap leads to frequent occurrence of abnormal discharges. In order to enlarge the discharge gap in micro-EDM, Nitrogen plasma jet (NPJ) has been used as the working media for micro-EDM in this study. NPJ is generated by using a needle-cylinder type corona discharge with an AC power supply in pure nitrogen gas. A RC-type pulse generator is used to realize micro electrical discharges in this investigation. It is expected that the electrons and ions in NPJ increase the electrical conductivity in the discharge gap. Thus, a large discharge gap can be obtained.To investigate the machining characteristics of micro-EDM in NPJ, series of experiments in NPJ, nitrogen jet (NJ) and deionized water (DIW) have been carried out. The discharge distance, machining time, electrode wear and surface roughness under different conditions have been recorded. The measured data has been analyzed together with the discharge signals. It was found that the discharge distance in NPJ is larger than that in NJ. The machining process in NPJ is much more stable than in NJ. The observed volumetric difference of electrode wear is very small, probably due to the small total material removal. The machining efficiency in DIW is the highest. However, the surface roughness in DIW is worse than that in NPJ.

Influence of Tool Size on Machining Characteristics of Micro-EDM

Electrical discharge machining (EDM) is an alternative processing method of conductive materials. Stray capacitance exists between the electric feeders, between the tool electrode holder and work table, between the tool electrode and workpiece. The energy stored in the stray capacitance cannot be neglected similarly to that in macro EDM due to the low discharge energy. It is necessary to research the capacitive effect to better apply micro-EDM. In this study, the influence of the tool electrode scale on micro-EDM performances was analyzed from the perspective of capacitive effect. The stray capacitance was calculated by using the charging waveforms. Experimental results elucidate that material removal rate (MRR), tool wear rate (TWR), and diametrical overcut (DOC) increased with the enlargement of tool size. When the tool diameter was greater than 500μm, the rate of increase in MRR was apparently higher than that of TWR, and the relative tool wear ratio (RTWR) exhibited a downward trend. This study benefits to better understand the capacitive effect and provides a reference for building the machining performance prediction model of micro-EDM.

Study on machining characteristics of micro EDM with high spindle speed using non-contact electric feeding method

In order to improve the efficiency of micro electrical discharge machining (micro EDM), the rotational spindle is widely used at present. Since the EDM technology is invented, the relaxation-type pulse generator, transistor-type pulse generator, or their combinations have been generally used. However, with these pulse generators, it is difficult to supply electrical power to the tool electrode rotating at extremely high speed without causing the vibration and spindle wear due to the contact electric feeding using a brush. So the tool electrode rotating speed is less than thousands of revolutions per minute (rpm) usually. Based on the principle of electrostatic induction, the non-contact electric feeding can be realized in micro EDM. So the rotating speed of the tool electrode can reach high rotating speed. This paper studied the machining characteristics of micro EDM under the high spindle speed up to 60,000 rpm by the machining of micro rods and the micro holes. As a result, the minimum electrode of Φ 2 μm in diameter and 10 μm in length, and the micro rod of Φ 5 μm in diameter and 80 μm in length with a high aspect ratio of 16 were obtained by block electrical discharge grinding (BEDG) method. From the micro hole machining results, it was found that with the increase of the spindle speed, the material removal rate increases, while the electrode wear ratio decreases. Meanwhile, the higher aspect ratio and machining accuracy were realized and the surface roughness was also improved significantly.

Experimental investigation into the micro-EDM characteristics of conductive SiC

SiC is an advanced ceramic which finds wide range of industrial applications. Cutting of SiC is difficult using conventional machining methods due to its low fracture toughness. In the past few years, researchers have claimed successful machining of SiC using EDM process. Furthermore, increasing trend for miniaturization in MEMS and semiconductor industry has necessitated the development of micro-machining methods for advanced ceramics. Therefore, this research was focused on micro-EDM of SiC. In this work, the effect of voltage, capacitance and threshold on surface roughness, MRR, TWR, radial overcut (ROC) and residual stresses was studied through experiments. Signal to noise ratio analysis was used to determine the optimum machining parameters in conjunction with ANOVA. The surface condition of the machined surface was studied using SEM and EDX. The experimental observations revealed that during µEDM operation, all the process parameters (Voltage, Capacitance and Threshold) affect the Surface Roughness, MRR, TWR and ROC significantly. The process input parameters are directly related to micro discharge energy which affects the process performance. Experimental results and optimization attempts show that in micro-EDM of SiC, optimum machining conditions for good surface finish are 150V, 0.1µF and 60% threshold. For high MRR, the optimum conditions are 150V, 0.4µF and 80% threshold. Optimum parameters for low TWR are 110V, 0.4µF and 40% threshold and those for low ROC are 110V, 0.4µF and 60% threshold. Surface characterization revealed the presence of debris, resolidified material and craters on the µEDMed surface that were responsible for high surface roughness. XRD analysis revealed the presence of compressive residual stresses of the order of 1200N/mm2 on the µEDM surface and their magnitude varied slightly with the input parameters. EDX analysis revealed the bidirectional material migration phenomenon in µEDM of SiC.

Influence of Grain Size and Grain Boundary of Workpiece on Micro EDM

Micro EDM is used to machine micro features which are of the same size order as material microstructure of workpiece. Due to the difference of the thermal properties between the crystal grain and grain boundary, the machining performance of micro EDM varies with the crystal grain sizes of workpiece. This paper investigated on the influence of grain size and grain boundary on the machining performance of micro EDM. By drilling micro holes on two pieces of stainless steel 304 (SUS 304) which are different in grain sizes, test results revealed that the characteristics of micro EDM is influenced by grain sizes of workpiece materials significantly.

Experimentation and Analysis into Micro-Hole Machining of Ti-6Al-4V by Micro-EDM Using Boron Carbide Powder Mixed De-Ionized Water

In micro-electrical discharge machining (micro-EDM), dielectric plays a significant role during the machining process as different types of dielectrics encounters different chemical compositions, cooling rates and dielectric strengths. Therefore, while employing these different dielectrics, dissimilar process responses are accounted when machining in EDM at micron level. The present paper investigates micro-EDM characteristics such as material removal rate (MRR), tool wear rate (TWR), overcut (OC), taperness and machining time (MT) during micro-machining of through holes on Ti-6Al-4V superalloy employing de-ionized water based dielectric other than conventional hydro-carbon oil i.e. kerosene. The paper also includes the comparative study of the micro-EDM machining characteristics employing boron carbide (B4C) powder as additive in de-ionized water dielectric at different discharge energies. The results show that MRR and taper of micro-hole are better and TWR is less employing B4C additive in the dielectric than pure one, i.e. the productivity is improved and same micro-tool can be used for machining an array of micro-holes. Surface topography and recast layer formed during micro-hole machining by micro-EDM has also been investigated based on optical and SEM micrographs. Energy dispersive spectroscopy (EDS) analysis of machined surface as well as tool electrode surface has been done and the results show that there is significant amount of infusion of tungsten element onto the machined surface. A significant amount of carbon element is found onto the tool electrode surface.

Investigation of Machining Characteristics of Micro-EDM with Ultrasonically Vibrated Machining Fluid under Ultra-small Discharge Energy

Micro-EDM has its potential in micro tools and parts manufacturing. However, the machining speed is quite low due to short-circuits and abnormal discharges, because of the difficult debris removal from the narrow gap-width. Especially, hole drilling process becomes impossible under an ultra-small discharge energy condition, such as a low open voltage and the stray capacitor in the RC discharge circuit. In this study, the effect of applying ultrasonic vibration to the machining fluid in micro-EDM was experimentally investigated, in order to realize a higher machining speed in the deep hole drilling process. Furthermore, the effect of vibration on the machining characteristics of micro-hole drilling under the ultra-small discharge energy condition was investigated. It was found that a significant increase in the machining speed was realized by applying ultrasonic vibration to the machining fluid. Also, with the vibration to the machining fluid, micro-hole drilling with ultra-small discharge energy became possible. Additionally, the experimental results show that the lateral gap-width between the tool electrode and workpiece was shortened, and the tool wear ratio became smaller.

Characteristics of Micro EDM for Insulating Aluminum Nitride Ceramics

Aluminum Nitride (AlN) ceramic materials have high thermal conductivity and electrical insulation, prompting consideration of their use as a semiconducting material. Although AlN should be machined with a high accuracy of form and dimension to achieve products and components with requisite precision, mechanical and other machining methods such as the laser method cannot be used because of the brittleness and high thermal conductivity of AIN. Recently, we have succeeded in machining many insulating ceramics by sinking (SEDM) and Wire-Electrical Discharge Machining (WEDM) with the assisting electrode method. We have already machined many insulating ceramic materials such as Si3N4, ZrO2 and Al2O3. However, inferior machining characteristics were obtained with AlN than with other materials. In this study, the effects of several electrical discharge conditions were examined to obtain better machining properties, such as high material removal rate and a low electrode wear ratio. It was found that machining time decreased with an increase in capacitance, while the electrode wear ratio increased. The electrode wear ratio of the W electrode was low, suggesting that it is suited for accurate machining of AlN. Additionally, the electrically conductive layer was analyzed using Energy Dispersive X-ray Spectrometry (EDS) and X-ray Diffraction (XRD). As a result, the architectural component of the EDMed AlN surface is considered mostly Al that is resolution of the workpiece. Therefore, in the EDM of AlN using the assisting electrode method, machinability using deionized water may be superior to dielectric oil. To investigate the effect of the dielectric working fluid, AlN was machined using deionized water and dielectric oil. In the case of machining with deionized water, the removal rate was faster and electrode wear ratio was lower, compared to dielectric oil.

Machining characteristics of micro EDM in water using high frequency bipolar pulse

Micro EDM using conventional pulse generators such as the RC type or transistor type with water as the dielectric fluid suffers from poor accuracy of machined structures due to electrolytic corrosion. In this study, a new high frequency bipolar pulse generator for micro EDM in water was developed in order to prevent electrolytic corrosion. The new pulse generator produced a high frequency bipolar pulse possessing a positive pulse duration of several hundred nanoseconds with a high repetition rate provided to the machining gap. Discharge characteristics of micro EDM using the new pulse generator were investigated. Machining characteristics were also investigated according to machining conditions such as the repetition rate, positive voltage, capacitance and resistivity. Using the new pulse generator, micro holes without electrolytic corrosion were successfully fabricated in deionized water and tap water. Machining time, tool wear and clearance using the new pulse generator in deionized water decreased compared with those using the RC circuit in kerosene.

Study on Discharge Characteristics of Piezoelectric Self-Adaptive Micro-EDM System

A new technology of piezoelectric self-adaptive micro electrical discharge machining has been developed in this paper according to the characteristics of micro-EDM. Its working principle and the discharge characteristics are introduced, and it has been proved that the new technology can achieve micro machining. Using piezoelectric actuator as micro-feed mechanism, this new technology is simple in structure and can improve the discharging gap effectively. The discharge frequency and effective pulse utilization rate of the power supply is enhanced in machining. Experimental results show that this new technology can achieve good results.

Process capabilities of Micro-EDM and its applications

The micro-electrical discharge machining (micro-EDM) process has proved to be an appropriate nonconventional machining method for manufacturing accurate and complex three-dimensional structural micro-features which are difficult to be produced by conventional processes. However, the miniaturisation of the EDM process requests special requirements on the machining equipment. Pulse generators which can produce small input energy pulses and high precision systems are the two major requirements. In this paper, newly developed technologies regarding these aspects are explored with the aid of a commercial micro-EDM machine. By examining the pulses, innovative strategies implemented in the pulse generator are studied. Pulse measurements reveal the correlation between the discharge pulses and the machine parameters in order to provide an overview of process capability. Conclusions are applied on machining of a ceramic composite Si3N4-TiN and optimised machining settings for different machining conditions are achieved. Accordingly, applications of two- and three-dimensional micro-structures on different types of materials such as a stainless steel micro-compressor and a ceramic miniature gas turbine are demonstrated. By inspecting the machining geometry and surface integrity, process characteristics of micro-EDM are discussed.

Modelling of micro-electrodischarge machining during machining of titanium alloy Ti—6Al—4V using response surface methodology and artificial neural network algorithm

Micro-electrodischarge machining (EDM) can produce microhole and other complex three-dimensional features on a wide range of conductive engineering materials such as titanium super alloy, inconel, etc. The micromachining of titanium super alloy (Ti—6Al—4V) is in very high demand because of its various applications in aerospace, automotive, biomedical, and electronics industries, owing to its good strength-to-weight ratio and excellent corrosion-resistant properties. The present research study deals with the response surface methodology (RSM) and artificial neural network (ANN) with back-propagation-algorithm-based mathematical modelling. Furthermore, optimization of the machining characteristics of micro-EDM during the microhole machining operation on Ti—6Al—4V has been carried out. The matrix experiments have been designed based on rotatable central composite design. Peak-current (Ip), pulse-on time (Ton), and dielectric flushing pressure have been considered as process parameters during the microhole machining operation and these parameters were utilized for developing the ANN predicting model. The performance measures for optimization were material removal rate (MRR), tool wear rate (TWR), and overcut (OC). The ANN model was developed using a back-propagation neural network algorithm, which was trained with response values obtained from the experimental results. The Levenberg—Marquardt training algorithm has been used for a multilayer feed-forward network. The developed model was validated using data obtained by conducting a set of test experiments. The optimal combination of process parametric settings obtained are pulse-on-time of 14.2093 μs, peak current of 0.8363 A, and flushing pressure of 0.10 kg/cm2 for achieving the desired MRR, TWR, and OC. The output of RSM optimal data was validated through experimentation and the ANN predicted model. A close agreement was observed among the actual experimental, RSM, and ANN predictive results.

Micro-EDM of sintered diamond

Abstract This paper concerns with an experimental research on the machining of sintered diamond (SD) by electrical discharge machining (EDM). Experiments were carried out with four types of SD, composed of 1-, 3-, 10-, and 20 μm-diameter diamond particles. Tungsten carbide alloy was also tested for comparison. Basic characteristics of micro-EDM were investigated by machining through-holes and trenches in SD plates. Although in some cases unstable machining status was observed, it was found that SD has machining characteristics basically similar to those of tungsten carbide alloy. Machined surfaces were observed in the experiment of machining trenches. The surface roughness of SDs was found to be sufficiently good for micromold applications and the surface property of SDs with large diamond particles was quite different from that of metals.

Improvement of machining characteristics of micro-EDM using transistor type isopulse generator and servo feed control

This paper describes the improvement of machining characteristics of micro electrical discharge machining (micro-EDM) using a newly developed transistor type isopulse generator and servo feed control. The RC generator is mainly applied in conventional micro-EDM even though the transistor type isopulse generator is generally more effective for obtaining higher removal rate, because the transistor type generator is unable to generate iso-duration discharge current pulses with small pulse duration (several dozen nano-seconds), which is the normal level for micro-EDM. A new transistor type isopulse generator was therefore developed using a current sensor with high frequency response. With the new transistor type isopulse generator developed, the pulse duration can be reduced to about 30 ns, which is equivalent to the pulse duration used in finishing by the conventional RC pulse generator for micro-EDM. In order to achieve stable machining and improve machining characteristics, a new servo feed control system for micro-EDM using average ignition delay time to monitor the gap distance was also developed. By integrating the transistor type isopulse generator with this new servo feed control system, we were able to obtain a removal rate of about 24 times higher than that of the conventional RC pulse generator with a constant feed rate in both semifinishing and finishing. The effectiveness of the servo feed control proved higher in finishing than in semifinishing, whereas the transistor type isopulse generator was more effective in semifinishing than in finishing.