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Micro electrical discharge drilling (ED-drilling) is a machining method used to make micro holes in hard-to-cut materials. The RC-discharge generator is often used because it creates a short and strong discharge spark. However, this method has issues such as current oscillation between tool electrode and workpiece, causing polarity changes that increase tool wear, and a low material removal rate due to long spark delay time. Furthermore, micro ED-drilling results in a large taper angle due to second discharge sparks created by debris in the narrow gap. To address these issues, the effect of adding graphite powder to the working fluid was studied. The graphite powder in kerosene created a bridge effect that reduced tool wear and taper angle, while improving MRR and surface roughness. The electrical conditions were not changed, and the machining process was improved by only altering the working fluid without modifying the existing system. [ABSTRACT FROM AUTHOR]

In comparison to conventional EDM, micro EDM distinguishes itself through its brief discharge duration, narrow discharge channel radius, and concentrated energy density. However, there remains a paucity of comprehensive research on the surface formation characteristics in this domain. This paper delves into the formation mechanism of the recast layer in micro EDM workpieces, scrutinizing the primary factors that influence the formation process and the morphological attributes of the recast layer. We conducted a series of single-pulse experiments and micro EDM trials. Utilizing surface fitting tools, our experimental findings facilitated the derivation of a relational expression between the recast layer thickness of high-speed steel and the discharge parameters in micro EDM. Notably, when the energy is below 100 μJ, the recast layer thickness remains under 10 μm. Specifically, at an energy level of 16 μJ, opting for a smaller capacitance of 2200 pf and a higher voltage of 120 V in micro EDM results in a thinner recast layer. This study serves as a cornerstone for future efforts aimed at controlling and assessing the surface morphology of micro EDM. [ABSTRACT FROM AUTHOR]

Micro-tools comprising difficult-to-machine materials have seen widespread application in micro-manufacturing to satisfy the demands of micro-part processing and micro-device development. Taking micro-shafts as an example, the related developmental technology, based on wire electric discharge grinding (WEDG) as the core method, is one of the key technologies used to prepare high-precision micro-shafts. To enable efficient and high-precision machining of micro-shafts with target diameters, instead of performing multiple repeated on-machine measurements and reprocessing, a geometric constraint strategy is proposed based on the previously introduced twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG). This strategy encompasses the tool setting method, tangential feed distance compensation, and an equation that establishes the relationship between tangential distance and diameter variation. These components are derived from a key points analysis of the geometric constraints. The micro-shafts with diameters of 50 µm and consistencies of ±1.5 µm are repeatedly processed. A series of micro-shafts with diameters ranging from 30 µm to 120 µm achieve geometric constraints with a diameter accuracy of ±2 µm, accompanied by the complete continuous automation of the entire process. Accordingly, it can be concluded that the geometric constraint strategy is flexible and stable and can be controlled with high precision in the TMTF-WEDG process. [ABSTRACT FROM AUTHOR]

Micro-electrical discharge machining (μEDM) is severely affected by tool wear and its process variants, which can lead to compromised precision and dimensional disruptions in micro-part production. Several attempts have been made to address this problem by suggesting offline and online (real-time) tool wear compensation strategies. Research efforts in this area have intensified over the last 20 years. However, most methods proposed were applicable only for a few work-tool combinations and in limited input process parametric settings. Instead of tool wear compensation, several research articles have focused on strategies to reduce the negative impact of tool wear on the quality of fabricated parts. The present study systematically reviews various investigations conducted in this area and aims to add cutting-edge compensation for tool wear to future inquiries. The articles reviewed here are explored in detail. Critical findings/innovations are classified into four categories: tool wear in μEDM, tool wear compensation techniques, and offline and online compensation methods.

Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The electrostatic field-induced electrolyte jet (E-Jet) electric discharge machining (EDM) is a newly developed micro machining method. However, the strong coupling of the electrolyte jet liquid electrode and the electrostatic induced energy prohibited it from utilization in conventional EDM process. In this study, the method with two discharge devices connecting in serials is proposed to decouple pulse energy from the E-Jet EDM process. By automatic breakdown between the E-Jet tip and the auxiliary electrode in the first device, the pulsed discharge between the solid electrode and the solid workpiece in the second device can be generated. With this method, the induced charges on the E-Jet tip can indirectly regulate the discharge between the solid electrodes, giving a new pulse discharge energy generation method for traditional micro EDM. The pulsed variation of current and voltage generated during the discharge process in conventional EDM process verified the feasibility of this decoupling approach. The influence of the distance between the jet tip and the electrode, as well as the gap between the solid electrode and the work-piece, on the pulsed energy, demonstrates that the gap servo control method is applicable. Experiments with single points and grooves indicate the machining ability of this new energy generation method. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of machining accuracy indexes such as the entry, exit and shape of micro-hole, a multi-objective parameter optimization weigh method for micro electrical discharge machining（EDM） based on grey relational analysis（GRA） and entropy weight method is proposed.By designing orthogonal experiment and processing test for H62 brass, the grey relational coefficient of each index of the experiment result sequence is calculated.The entropy weight method and grey relational analysis method are used to comprehensively evaluate the model, and the grey relational degree of each experiment sequence is obtained, and the mean value analysis is carried out to realize the transformation from multi-objective optimization to single objective optimization.The research results show that the entry Overcut（EnOV）, exit Overcut（ExOV） and taper（TA） of the optimized process parameters are reduced by 8.97%, 4.11% and 8.33% respectively compared with those of the H-22 group with the largest grey relational degree, and the machining accuracy of micropores is improved.

In comparison to conventional EDM, micro EDM distinguishes itself through its brief discharge duration, narrow discharge channel radius, and concentrated energy density. However, there remains a paucity of comprehensive research on the surface formation characteristics in this domain. This paper delves into the formation mechanism of the recast layer in micro EDM workpieces, scrutinizing the primary factors that influence the formation process and the morphological attributes of the recast layer. We conducted a series of single-pulse experiments and micro EDM trials. Utilizing surface fitting tools, our experimental findings facilitated the derivation of a relational expression between the recast layer thickness of high-speed steel and the discharge parameters in micro EDM. Notably, when the energy is below 100 μJ, the recast layer thickness remains under 10 μm. Specifically, at an energy level of 16 μJ, opting for a smaller capacitance of 2200 pf and a higher voltage of 120 V in micro EDM results in a thinner recast layer. This study serves as a cornerstone for future efforts aimed at controlling and assessing the surface morphology of micro EDM.

Micro-tools comprising difficult-to-machine materials have seen widespread application in micro-manufacturing to satisfy the demands of micro-part processing and micro-device development. Taking micro-shafts as an example, the related developmental technology, based on wire electric discharge grinding (WEDG) as the core method, is one of the key technologies used to prepare high-precision micro-shafts. To enable efficient and high-precision machining of micro-shafts with target diameters, instead of performing multiple repeated on-machine measurements and reprocessing, a geometric constraint strategy is proposed based on the previously introduced twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG). This strategy encompasses the tool setting method, tangential feed distance compensation, and an equation that establishes the relationship between tangential distance and diameter variation. These components are derived from a key points analysis of the geometric constraints. The micro-shafts with diameters of 50 µm and consistencies of ±1.5 µm are repeatedly processed. A series of micro-shafts with diameters ranging from 30 µm to 120 µm achieve geometric constraints with a diameter accuracy of ±2 µm, accompanied by the complete continuous automation of the entire process. Accordingly, it can be concluded that the geometric constraint strategy is flexible and stable and can be controlled with high precision in the TMTF-WEDG process.

Titanium alloy (Ti-6Al-4 V) is widely used in a number of fields such as medical, aeronautical, and nuclear fields. Since the surface finish should be enhanced as much possible in efficient way, the micro EDM process can be used for machining such materials. The process mechanism can be enhanced by utilizing the coated electrode in the process. In the present study, an effort was made to investigate the effects of process parameters on drilling titanium alloy with aluminum chromium nitride (AlCrNi)-coated aluminum electrode in micro EDM process. An optimization approach was also implemented using Taguchi-DEAR approach. From the experimental interpretation, the conclusions were made as follows. The AlCrNi-coated aluminum electrode can enhance the machinability of micro EDM process. The optimal combination of voltage (140 V), capacitance (10000pF), and spindle rotation (200 rpm) could provide better quality measures among the chosen variables. The moderate voltage and capacitance can remove the material effectively with lower overcut, since the electrical conductivity can effectively enhance the conductivity of the plasma energy column. The coated electrode can create the tiny craters with uniform energy distribution. [ABSTRACT FROM AUTHOR]

The titanium alloy specimens are generally utilized in many manufacturing applications due to their higher corrosion resistance and lower density. Since it is highly tedious to machine such materials using conventional machining processes, it can be easily machined using micro Electrical Discharge Machining (EDM). In the present study, an attempt was made to optimize the process parameters on machining titanium alloy specimens with tungsten carbide in micro EDM process. Taguchi-Topsis method was used to derive better process factors such as voltage, capacitance and Electrode rotational speed. Depth of machining, Overcut and tool wear were considered as quality measures to evaluate the machining characteristics. It was found that 160 V of voltage could produce better machinability with the capacitance of 10 nF and electrode speed of 400 rpm. It was also found that the parameters can produce a better surface finish with better machining accuracy. The only fewer agglomeration of tool electrodes was observed over the machined titanium specimen. [ABSTRACT FROM AUTHOR]

The electrostatic field-induced electrolyte jet (E-Jet) electric discharge machining (EDM) is a newly developed micro machining method. However, the strong coupling of the electrolyte jet liquid electrode and the electrostatic induced energy prohibited it from utilization in conventional EDM process. In this study, the method with two discharge devices connecting in serials is proposed to decouple pulse energy from the E-Jet EDM process. By automatic breakdown between the E-Jet tip and the auxiliary electrode in the first device, the pulsed discharge between the solid electrode and the solid workpiece in the second device can be generated. With this method, the induced charges on the E-Jet tip can indirectly regulate the discharge between the solid electrodes, giving a new pulse discharge energy generation method for traditional micro EDM. The pulsed variation of current and voltage generated during the discharge process in conventional EDM process verified the feasibility of this decoupling approach. The influence of the distance between the jet tip and the electrode, as well as the gap between the solid electrode and the work-piece, on the pulsed energy, demonstrates that the gap servo control method is applicable. Experiments with single points and grooves indicate the machining ability of this new energy generation method.

This study investigates the tool-wear-reduction mechanism of graphite-powder mixed kerosene (GPMK) in micro electric-discharge machining (EDM). RC discharge circuits produce small, short discharge pulses and are therefore widely used in micro-EDM, rather than transistor circuits. In this case, given that an anode has higher energy proportion than a cathode by the massive electron collision to the positively charged workpiece, a tool electrode is negatively charged for a high material-removal rate (MRR) and low tool-wear length (TWL). In the discharge phase, however, the stray inductance of the RC discharge circuit reverses the direction of the current before the discharge plasma channel disappears; a reverse current increases the TWL and reduces processing efficiency. In this study, the TWL was decreased with GPMK by creating a circumstance that facilitates the early extinction of discharge plasma channel before the generation of the reverse current in two ways. The widening of the discharge gap by GPMK reduces the intensity of the discharge energy and enables the plasma channel to be extinguished before the reverse current generation. Furthermore, as the tool electrode approaches the workpiece, a small amount of energy discharges before the capacitor is fully charged, and these initial discharges quickly disappear before the reverse current flows. The machining performance and the quality of micro ED milling with GPMK were evaluated and compared with those of pure kerosene. With optimal machining conditions, MRR was increased by 61%, and GPMK decreased the TWL and surface roughness by 61% and 23%, respectively. This technique was also successfully applied to micro-molding fabrication. [ABSTRACT FROM AUTHOR]

This paper introduces an experimental investigation of micro hole drilling on two different categories of material such as silicon and german silver using micro electrical discharge machining (μEDM) process. The conductivities of the two materials are of different levels; silicon being a semiconductor has relatively much lower electrical conductivity as compared to german silver which is an alloy of copper, nickel and zinc. The tool electrode used is tungsten rod of 518 μm diameter. Responses like material removal rate (MRR), taper angle (TA), circularity error (CE) and overcut (OC) have been calculated and their variation with respect to the process parameters such as capacitance and voltage are evaluated. In both the materials, the values of all the responses increases with an increase in both voltage and capacitance. German silver is observed to have a higher MRR and OC than that of silicon while silicon has a higher TA for the same values of process parameters. The CE of silicon is higher at lower capacitance while it is higher for german silver at higher capacitance. From the analysis of variance (ANOVA), it is observed that both the voltage and capacitance played a significant role in all the responses. An optimum condition of micro hole drilling of both the materials is achieved by formulating overall evaluation criteria (OEC), which combines all the response parameters into a single index. In most of the cases, OEC of german silver is found to be higher than silicon, thus justifying the superior machinability performance of german silver. From the ANOVA of OEC, the role of capacitance is found to be more significant as compared to the voltage. [ABSTRACT FROM AUTHOR]

Copyright of Duzce University Journal of Science & Technology is the property of Duzce University Journal of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In micro electro discharge machining (EDM), single pulse energy of pulsed power supply needs to be limited to a micro order of magnitude. One developing direction is to reduce the discharge pulse width for increasing discharging frequency. In order to research on micro EDM with nanometer gaps and nanometer removing units, a novel pulsed power supply with nanosecond pulse width was developed based on triode avalanche principle. The basic electric circuit with a steepening electric circuit was designed for the nanosecond pulse width. The test results show that the discharge pulses with an adjustable peak voltage and a pulse width down to 18 ns can be obtained. The developed pulsed power supply can output a single pulse and continuous pulses under high frequency. [ABSTRACT FROM AUTHOR]

Due to the non-isoenergetic nature of discharge pulses in resistance-capacitance (RC) based micro electrical discharge machining (μEDM), the volume of produced micro-crater by each pulse varies significantly. This fact has driven the researchers in this work to propose an electrothermal principle–based analytical model to approximate dimensional accuracies of such micro-craters. A finite element (FE) simulation considering Gaussian heat flux distribution of single discharge μEDM has been performed at significant input parameters such as discharge energy, capacitance, and open-circuit voltage and compared with analytical simulation results. Upon validation of these simulated results with experimental results, nominal dimensional inaccuracies of 2–11% for a wide range of input parameters have been noticed. This effectively predicted crater dimension from the workpiece can be incorporated in the proposed thermal modeling–based real-time tool wear monitoring and compensation system through a unique strategy, which is discussed at the end. [ABSTRACT FROM AUTHOR]

3D scanning (or milling) micro electrical discharge machining (EDM) can machine 3D microstructures with free-form surfaces on metal/alloy materials. The novel process of servo scanning 3D micro EDM (SS-3D micro EDM) provides a practical solution for the real-time online compensation of micro tool-electrode wear. However, the key parameters of servo scanning are difficult to be optimized by a large number of trial-and-error experiments. This causes the unstable and destructive process of frequent short circuit, less cutting, and collision of tool electrode and workpiece because the optimization still lacks theoretical basis. In this research, considering the actual influence of delay response time of a machining system, we analyzed the process of servo control of machining gap according to threshold control method and the matching effect with scanning speed. Boundary models were established for providing the theoretical basis of the servo control speed and its reasonable matching with the scanning speed. Furthermore, the optimization procedures with the proposed boundary models for the reasonable matching of these parameters were proposed and verified by machining experiments. [ABSTRACT FROM AUTHOR]

Micro electrical discharge machining (micro EDM) is able to remove conductive material by non-contact instantaneous high temperature, which is more suitable for machining titanium and its alloys compared with traditional machining methods. To further improve the machining efficiency and machined surface quality of micro EDM, the nano particle surfactant mixed micro EDM method is put forward in this paper. Experiments were conducted to explore the effect of nano particle surfactant on the micro EDM performance of titanium alloy. The results show that the material removal rate of micro EDM in dielectric mixed with TiO2 is the highest when open-circuit voltage is 100 V, followed by Al2O3 and ZrO2. Lower tool wear rate can be produced by using dielectric mixed with nano particle surfactant. The taper ratio of micro EDM in dielectric mixed with nano particle surfactant is higher than that in deionized water. The surface roughness Ra of micro EDM in dielectric mixed with TiO2 can be 50% lower than that in deionized water. It is helpful to improve the machining performance by adding surface surfactant in the dielectric of micro EDM.

Micro-electrical discharge machining (μEDM) is severely affected by tool wear and its process variants, which can lead to compromised precision and dimensional disruptions in micro-part production. Several attempts have been made to address this problem by suggesting offline and online (real-time) tool wear compensation strategies. Research efforts in this area have intensified over the last 20 years. However, most methods proposed were applicable only for a few work-tool combinations and in limited input process parametric settings. Instead of tool wear compensation, several research articles have focused on strategies to reduce the negative impact of tool wear on the quality of fabricated parts. The present study systematically reviews various investigations conducted in this area and aims to add cutting-edge compensation for tool wear to future inquiries. The articles reviewed here are explored in detail. Critical findings/innovations are classified into four categories: tool wear in μEDM, tool wear compensation techniques, and offline and online compensation methods., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Micro electrical discharge machining (micro EDM) provides an alternative in generating complex 3-D micro features in difficult-to-machine materials. The micro EDM performance depends not only on machining parameters but also on the microstructures and micro-characteristics of materials. The effect of free surface layer of austenitic stainless steel on the micro EDM performance is investigated in this paper. Experiments are carried out by machining multilayer stainless steel workpieces without and with surface treatment (acid pickling and oxidation treatment). Surface layer model is built to demonstrate the increasing influence of surface layer on micro EDM performance when the size of workpiece is decreased. The surface free energies of AISI 304 workpieces are estimated by measuring the contact angles. The results show that the steel workpiece with oxidation treatment has the highest surface free energy and the highest material removal rate compared with those without treatment and with acid pickling treatment. The influence of surface layer of steel workpiece on micro EDM performance is more significant when the discharge energy is lower due to size effects. Taper ratio of machined holes on steel workpiece without treatment is much higher than those of holes on steel workpieces with acid pickling and oxidation treatment. As a conclusion, surface treatment of steel workpiece before machining is an effective method to improve the machining efficiency and machining precision of micro EDM, especially when involving the sub-micro or nano-machining where machining is conducted on the workpiece surface. • Surface layer model in micro EDM has been developed to demonstrate the increasing influence of surface layer with decreasing size of workpiece. • The higher the surface free energy, the higher the MRR, the less the taper ratio of machined hole. • The influence of surface layer of workpiece becomes more significant when the discharge energy is lower. [ABSTRACT FROM AUTHOR]

Abstract This study describes a TR-iso-pulse generator which has better machining performance than an RC-pulse generator in micro-electrical discharge drilling (micro ED-drilling). Although machining with a TR-pulse generator is more efficient compared to when using a RC-pulse generator in macro-scale EDM, an RC-pulse generator is often used in micro EDM because it can generate the short discharge pulse necessary to minimize the discharge energy. However, to increase the machining efficiency, it is necessary to develop a TR-iso-pulse generator capable of generating a small amount of uniform discharge energy. In this research, a TR-iso-pulse generator was constructed for micro ED-drilling. For an accurate performance comparison between an RC-pulse generator and a TR-iso-pulse generator, each pulse generator was set up to generate the same discharge energy for a single discharge. Through micro ED-drilling, material removal rate (MRR) and relative wear ratio (RWR) were measured with respect to feed rate, and then the periphery of the machined hole, longitudinal section, lateral overcut, and surface roughness were compared for machining accuracy analyses. As a result, MRR was increased by 121% and RWR was decreased by 39% in the TR-iso-pulse generator compared with the RC-pulse generator. In addition, while lateral overcut was increased by 4.63%, less amounts of re-solidified material were deposited at the periphery of the machined hole and surface roughness was also reduced by 22% in the TR-iso-pulse generator. Highlights • A TR-iso-pulse generator outperformed an RC-pulse generator in micro ED-drilling. • Material removal rate increased by 121% due to the quick voltage recovery time. • Relative wear ratio decreased by 39% owing to the absence of reverse current. • Surface roughness decreased by 22% because of short and uniform discharges. • Less amounts of re-solidified material were deposited at the periphery of holes. [ABSTRACT FROM AUTHOR]

In this work, micro-EDM ( μ EDM) characteristics of conductive SiC have been evaluated using the knowledge of existing coupled thermo-structural model. A simplified thermo-structural model of μ EDM process on conductive SiC has been used to simulate the μ EDM process on conductive SiC. So far, the studies have used traditional melting and evaporation removal mechanism during EDM simulation which is suitable for metals. In case of ceramics, material removal occurs by various phenomenon such as spalling, melting, evaporation and it depends on μ EDM energy and type of ceramic. Thus, we aim here to evaluate the characteristics of a SiC ceramic using the thermo-structural model. To make the model more realistic, Gaussian heat flux distribution has been used and transient study has been performed. The model uses process parameters (voltage, capacitance and time) and material properties as input to predict the transient temperature distribution, crater dimensions, volume of material removed and thermal residual stresses. To simulate the material removal, element death has been performed. The element death is purely based on attainment of certain temperature suitable for material removal irrespective of material removal mechanism. The transient thermal analysis was carried out in heating phase and the structural analysis was carried out in cooling phase. Observatory experiments were performed to add value to the model predictions. [ABSTRACT FROM AUTHOR]

Micro electrical discharge machining (micro EDM) is a proven technology for the manufacturing of miniaturized parts and components. This study uses the Taguchi method with an L9 orthogonal array, a signal-to-noise (S/N) ratio, and an analysis of variance (ANOVA) to determine the performance characteristics for micro EDM milling operations. The micro EDM milling parameters (pulse duration, pulse off, discharge current, and working period) are optimized using multiple performance characteristics (electrode wear rate (EWR), material removal rate (MRR), and overcut). Grey relational Taguchi analysis is used to optimize the process parameters for micro EDM ofTi-6Al-4V alloy, using tungsten carbide (WC) tool electrodes. The results demonstrate that using a grey-based Taguchi analysis, the EWR decreases from 1.694 × 10−5 to 1.671 × 10−5 mm3/min, the MRR increases from 6.44 × 10−4 to 7.23 × 10−4 mm3/min, and the overcut decreases from 0.092 × 10−1 to 0.088 × 10−1 mm. There is also a comparative study of the performance of WC, WC-coated Ag (high electrical and thermal properties), WC-coated TiN, and ZrN electrodes (excellent electrical insulation, high melting points, and superior hardness) used for micro EDM milling. A confirmation run shows that the WC electrode-coated Ag thin film yields the highest EWR, MRR, and overcut values. The WC electrodes that are coated with TiN thin film give the lowest EWR and overcut value, which would improve the micro EDM stability and enhance microscale component machining quality. [ABSTRACT FROM AUTHOR]

Conical surfaces can be applied in the valves of liquid seal. In the fuel injection unit of a diesel engine, an outer conical surface at the tip of a slender needle works with an inner conical surface as injector-body seat to realize the switching and sealing of a fuel passage. So far, the conical surfaces are usually machined by mechanical grinding. The small grinding wheels < φ3 mm and its rotation speed >100,000 RPM have to be utilized for achieving enough circumferential speed. The inner conical surface is located in a small and deep bore, so the insufficient stiffness of the grinding tool is easy to cause machining errors. In this research, the process of wire electro discharge grinding (WEDG) by using a line-segment wire discharge (called line-segment WEDG in this paper) was explored for machining such conical surfaces. The emphasis was focused on the effect of wire alignment error on the accuracy of the conical surfaces. By the line-segment WEDG, an outer conical surface, or a conical tool electrode, can be machined directly and whereby an inner conical surface can be machined by die-sinking electro discharge machining (EDM). Machining experiments achieved some promising results including the outer conical surfaces with a total height of waviness profile Wt <2.5 μm and surface roughness of Ra0.4μm, the inner conical surfaces with Wt <1.5 μm and Ra0.2 μm, and all cone-angle errors are less than 0.1?. [ABSTRACT FROM AUTHOR]

This study proposes a new explanation of how tool wear is reduced during powder-mixed micro electrical discharge machining. Owing to its lower discharge energy than a transistor discharge circuit, an RC discharge circuit outperforms in micro EDM. Given that the energy distribution of a cathode is lower than that of an anode during discharge, a tool is negatively charged to reduce tool wear and increase the material removal rate. However, due to the stray inductance of an RC discharge circuit, the tool polarity and direction of the current fluctuate before the discharge plasma channel is extinguished, which increases the tool wear. In this study, it was found that graphite powder in a dielectric fluid disperses the charged energy into several small discharge plasma channels. These small channels were extinguished quickly before the tool polarity and direction of the current fluctuate; which decreases the amount of tool wear. The machining time and tool wear length in powder-mixed micro ED-drilling were evaluated with various particle diameters and concentrations of powder-mixed dielectric fluid. With the optimal tool feeding conditions, the machining time and tool wear length of graphite-powder-mixed kerosene were reduced by 30.9% and 28.3%, respectively, as compared to those in non-powder-mixed EDM. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

As one of the micro-forming technologies, micro punching process produces workpieces in high efficiency and low cost. It has attracted the attention of researchers from all over the world in recent years. The current micro punching mold is prepared on-line by micro electrical discharge machining (EDM) with simple cross-sectional shape. During punching, the punching load is small due to the soft material and small circumference of workpiece. To form micro part with complex cross sectional shape using micro punching technology, three-dimensional micro-EDM milling and reversed micro EDM are used to generate micro die and punch on-line to provide a solution to alignment of die and punch on machine. In order to obtain high dimensional accuracy of micro punching mold, in this paper, dimensional errors including electrode, reversed electrode, micro die and micro punch caused during machining process are identified. The correlation between dimensional errors and the clearance of micro die and micro punch are analyzed. Based on preliminary experimental results and dimensional error control strategy, the final punching clearance of micro punch molds was machined within the required range. [ABSTRACT FROM AUTHOR]

This paper investigates the characteristics of micro electrical discharge machining (EDM) in cold plasma jet using transistor pulse generator. In order to improve the processing efficiency and quality in stable process conditions, oxygen-assisted nitrogen plasma jet, nitrogen-oxygen mixed plasma jet and external compressed air assisted nitrogen plasma jet are used in micro-EDM experiments. It was found that the material removal rate and surface roughness increases with the increase of oxygen flow rate in oxygen-assisted nitrogen plasma jet experiment. In addition, it was found that micro-EDM with a compressed air-assisted plasma jet is superior to oxygen-assisted nitrogen plasma jet in surface quality and edge quality. Nitrogen element is not found on the machined surface in micro-EDM based in NPJ or NJ. The content of oxygen element has an increasing trend when compressed air is used as an auxiliary gas. [ABSTRACT FROM AUTHOR]

An RC-type generator circuit is suitable for micro-electrical discharge machining (micro EDM) owing to its low single discharge energy. In micro EDM, negative tool polarity has the advantage of reducing the tool wear rate and the relative ratio. However, when using an RC-type generator circuit in micro EDM, the direction of the current fluctuates at the plasma channel between the tool and the workpiece due to stray inductance. Because the current flowing from the tool to the workpiece can intensify the tool wear rate, it is preferable to prevent the fluctuation of the current direction. In this study, we propose the RC-type generator circuit using an n-channel MOSFET to prevent the fluctuation of the current direction and to increase duty ratio to enhance the material removal rate. Using a micro ED drilling process, the material removal rate, relative ratio, and surface roughness were measured with respect to the feeding control conditions and electrical conditions. As a result, by using the RC-type generator circuit with a MOSFET, the relative ratio is reduced by up to 40%, with the same material removal rate and surface roughness, compared with the results without a MOSFET. [ABSTRACT FROM AUTHOR]

Micro electric discharge machining (μ-EDM) is a widely used process for machining of difficult to machine materials. The occurrence of arcing and short circuiting in micro electric discharge drilling (EDD) is a common problem which limits the aspect ratio achieved during the process. The present study is focused on the improvement in response characteristics by eliminating the occurrence of arcing and short circuiting. These problems can be addressed by modifying the tool electrode geometry. Although, EDD using shaped tool electrodes improve response characteristics as proven by the previous studies, but time spent in electrode fabrication must also be considered as it affects the overall productivity. Considering the literature related to EDD using shaped tool electrodes, the proposed electrode has been found to have minimum electrode fabrication time i.e. 9 min for an electrode length of 3.2 mm. Therefore, the proposed electrode is capable of producing holes of high aspect ratio with minimum electrode fabrication time. The proposed electrode was also found to be effective in eliminating the accumulation of debris in the machining zone. Moreover, the need of flushing during the process has been totally eliminated making it a self-flushing electrode. The mechanism of removal of debris is well explained based on the images captured using a high speed camera. The performance of the proposed electrode was evaluated with respect to response characteristics such as material removal rate, tool wear rate, aspect ratio, taper angle and corner radius of the drilled hole. A substantial increase of 300% in aspect ratio was recorded using the designed electrode as compared to the solid cylindrical electrode for the hole diameter of 0.8 mm. [ABSTRACT FROM AUTHOR]

In electrical discharge machining (EDM), material is heated to an extremely high temperature then moved by melting and vaporization. Understanding the energy distribution and heat transfer during the process is conducive to knowing more about the machining mechanism of EDM. Many researches have been conducted to explore the energy distribution in micro EDM. Almost all of these efforts did not consider the difference in material removal mechanism between conventional and micro EDM, which has severe effects on the accuracy of their research. This paper proposes a method in regard to micro EDM for estimating plasma radius and energy distribution through comparing the results of experiment and theoretical calculation. In this method, the differences in the material removal mechanism between conventional and micro EDM are properly considered. The results of single discharge experiment were analyzed by this method. The plasma radius and fraction of energy transferred into workpiece are determined by the discharge current and discharge duration. The increase of discharge current and discharge duration led to the increase of plasma radius, while low discharge current and high discharge duration is helpful for improving the fraction of energy transferred into workpiece. [ABSTRACT FROM AUTHOR]

Micro-electrodes are used for micro holes EDM drilling in miniaturized products. This study represents novel fabricating and measuring processes of high aspect ratio micro-electrodes based on horizontal moving block electrical discharge grinding (horizontal moving BEDG [HM-BEDG]) and gage block with a typical EDM machine, as well as solving the problems that occur during micro-electrode fabrication. The EDM machine has been used as a coordinate measuring machine (CMM) for measuring micro-electrode diameter, where the gage block acts as a probe and the micro-electrode as a workpiece. As a result, a micro-electrode with the highest aspect ratio (over 60.25) was fabricated successfully with 78.19 μm diameter and 4.70 mm length after producing a through micro hole with 134.5 μm diameter on WC Co. As these processes are simple and do not require high investment for special equipment, micro-electrodes can be fabricated and measured for micro EDM drilling and milling in conventional workshops equipped with EDM machines. [ABSTRACT FROM AUTHOR]

This paper describes the machining characteristics of electrolysis-free micro EDM in water using the electrostatic induction feeding method. With the electrostatic induction feeding method, if deionized water is used for the working liquid, electrolysis can be prevented because bipolar voltage is applied to the working gap. Results of micro-holes drilling showed that the material removal rate with deionized water is higher than that with oil, and the oversize of holes machined in deionized water is smaller. Moreover, micro-holes could be drilled successfully even in a tap water with the oversize of several micrometers using this method.

This study aims at developing a machine center consisting of high-speed micro-milling machine, micro-EDM and coordinate measuring machine. The machine center uses a commercially available PC-Based CNC controller and micro-EDM power supply. The structure design is based on an open L-shaped granite base, where a Z-axis platform is mounted on the top of an L-type base, while X and Y-axis platforms are assembled by stacking. Additionally, a fuel tank, WEDG winding mechanism and a work piece holder were fixed to the X-axis work platform. Three-axis positioning stages use servomotors to drive lead screws for motion control. Equipped with a commercially available PC-Based CNC controller, any processing path and precision motion control can be achieved. In addition, the Z-axis platform includes a commercially available rapid adapter for the rapid assembly of C-axis rotation, high-speed micro-milling spindle and three-dimensional measuring probe. This means that the machine can quickly switch between micro-EDM, high-speed micro-milling and three-dimensional measurement. The machine center successfully produced micro probes with a front-end sphere with a diameter of less than 100 μm. Combined with a self-developed trigger circuit, it also completed a three-dimensional touch trigger probe. The measurement software was developed with Borland C++ Builder. Integrating the three-dimensional touch trigger probe with the three-axis linear scale, the three-dimensional coordinates of the measured values were calculated and processed. It has been successfully applied to the measurement of point, line, circle and angle.

Energy distribution ratio into micro EDM electrodes was determined based on the summation between the ratio of energy loss due to heat conduction within electrodes and ratio of energy carried away by debris. Ratio of energy loss due to heat conduction was obtained by comparing the measured and calculated temperature rise on electrode after igniting plural pulses discharges. On the other hand, the ratio of energy carried away by debris was calculated based on the measured removal volume. Energy distribution ratio into micro EDM anode and cathode was between 10% and 15% in total which was comparatively lower than that of macro EDM. This is because much larger fraction of the total discharge energy is consumed for the generation and enthalphy increase of the plasma in the early stage of discharge. Besides, unlike macro EDM the energy carried away by debris in micro EDM cannot be ignored compared with the energy lost due to heat conduction. This means, the energy consumption by material removal in micro EDM with regard to the energy distributed into the electrodes is more efficient compared to that of macro EDM.

Electrical discharge machining(EDM) is a promising non-traditional micro machining technology that offers a vast array of applications in the manufacturing industry. However, scale effects occur when machining at the micro-scale, which can make it difficult to predict and optimize the machining performances of micro EDM. A new concept of 'scale effects' in micro EDM is proposed, the scale effects can reveal the difference in machining performances between micro EDM and conventional macro EDM. Similarity theory is presented to evaluate the scale effects in micro EDM. Single factor experiments are conducted and the experimental results are analyzed by discussing the similarity difference and similarity precision. The results show that the output results of scale effects in micro EDM do not change linearly with discharge parameters. The values of similarity precision of machining time significantly increase when scaling-down the capacitance or open-circuit voltage. It is indicated that the lower the scale of the discharge parameter, the greater the deviation of non-geometrical similarity degree over geometrical similarity degree, which means that the micro EDM system with lower discharge energy experiences more scale effects. The largest similarity difference is 5.34 while the largest similarity precision can be as high as 114.03. It is suggested that the similarity precision is more effective in reflecting the scale effects and their fluctuation than similarity difference. Consequently, similarity theory is suitable for evaluating the scale effects in micro EDM. This proposed research offers engineering values for optimizing the machining parameters and improving the machining performances of micro EDM. [ABSTRACT FROM AUTHOR]

Porous metals are widely used in acoustic or heat absorbing material, heat exchanger, catalysis and biochemical products. Porous metals are available to be processed by electrical discharge machining (EDM). However, the relationship between machining parameters and performance is unclear. In this investigation, extensive experiments are conducted on solid stainless steel 304 and porous stainless steel 304 with different pore sizes. Material removal rate (MRR) and tool wear ratio (TWR) are used to evaluate the machining performance of micro EDM. It was found that the machining of porous metal has a higher MRR and lower TWR than those of solid one. It was also found that the machining performance is significantly affected when the size of porous metal is close to the discharge gap. The abilities of debris removal and machining in porous metal machining by EDM are proposed to analyze this phenomenon. Experimental results match the calculated values well. It is helpful to select proper machining parameters of micro EDM to process porous metals. [ABSTRACT FROM AUTHOR]

Electrical discharge machining (EDM) is one of the most promising non-traditional micro-scale machining methods. Because several operating parameters that are insignificant in macro EDM cannot be neglected during micro EDM process, models derived from the macro EDM process may be inappropriate at the micro scale. This paper contains a comprehensive review of size effects in traditional micro-machining and characteristics specific to micro EDM compared to macro EDM techniques. The very concept of size effects in micro EDM is thoroughly defined and three categories of effects are presented: material microstructure, processing parameter and thermal conduction size effects. Future potential research directions on the subject are also summarized. We assert that careful research and precise attention must be given to size effects in micro EDM. Size effect information especially benefits the machining speed and machining precision of micro EDM. [ABSTRACT FROM AUTHOR]

As an important manufacturing technology, micro EDM is widely applied in many industry fields. However, the slow response speed of servo system often leads to short circuit and arc discharge. To deal this problem, a magnetic suspension spindle system is used to improve the response frequency. This paper introduces the structure and principle of the magnetic suspension spindle device used for micro EDM, hardware and software solutions of the control system are illuminated by schematic diagram or flow chart. Using incremental PID algorithm, the axial (Z) response frequency reaches 150 Hz, the radial and axial position accuracy is achieved with 5 μm and 2 μm. And the micro EDM is realized through the magnetic suspension spindle in 1.3 mm stroke. [ABSTRACT FROM AUTHOR]

SiC is an important industrial ceramic and also the fourth hardest ceramic after diamond, boron nitride and boron carbide. Due to very low fracture toughness, it is very difficult to machine SiC using conventional machining methods. EDM can machine such materials irrespective of their hardness. Micro electrical discharge machining (micro-EDM) is an adaptation of conventional EDM process that has similar electro-thermal methods of material removal for manufacturing miniature or micro parts. Micro EDM is used for obtaining burr-free micro dimensional apertures in difficult-to-cut materials. For improved understanding of the micro EDM process and achieve high quality machining on conductive SiC, it is necessary to characterize the machined surface and understand the material removal and material migration mechanism. In this work, micro depth holes were machined in SiC workpiece. The experimentation was planned using Taguchi's L9 theory. A combination of scanning electron microscopy (SEM), white light interferometry (WLI), energy dispersive x-ray spectroscopy (EDX), atomic force microscopy (AFM) and X-ray diffraction (XRD) was used to characterize the machined surface and study the material removal and material migration mechanism. It was found that improved characterization and understanding of μEDM can lead to better micro-machining of conductive SiC. [ABSTRACT FROM AUTHOR]

The importance of Electrical Discharge Machining (EDM) process is increasing, especially for the machining of electric conductive ceramic materials within the field of micro production technology. Due to its thermal working principle, EDM is particularly suitable because it allows almost force free machining independent of the material's mechanical properties [1] . High aspect ratios and precise micro holes with diameters D ≤ 0.3 mm leads manufactures to more complex processes, which reduce the flushing in the working gap and therefore the stability of the process. Enabling the increase of flushing by gaseous dielectrics, dry-EDM technology represents an alternative solution. This paper presents a comparative analysis of dry-EDM with two different gases as dielectric (oxygen and argon) and conventional EDM (deionized water) to manufacture micro holes in Si 3 N 4 -TiN ceramic. The results show that the axis displacement y, voltage u 0 , and current i L differ for the processes. It can be observed that dry-EDM has higher effective pulse frequency f e and shorter relative motions between workpiece and tool electrode than the conventional EDM process [2] . The differences observed in the discharge flow and relative motions between workpiece and tool electrode are related to the dielectric fluid properties. As for example, deionized water as a dielectric has a higher viscosity η wa = 89·10 -5 Pa·s than oxygen η o2 = 2,1·10 -5 Pa·s and argon η ar = 2,3·10 -5 Pa·s. Thus, with the same flushing pressure of p = 80 bar it is possible to achieve higher flow speed for faster removal of particles in dry-EDM. Furthermore, deionized water has a higher breakdown resistance E D_wa = 650 kV/cm than oxygen E D_o2 = 29 kV/cm and argon E D_ar = 6,5 kV/cm. The better flushing condition enables the increase of the effective pulse frequency f e for oxygen and a decrease of the electrode relative wear ϑ. [ABSTRACT FROM AUTHOR]

This work describes deformation of fin machined by micro electrical discharge machining (EDM). First, temperature distribution in a workpiece due to micro EDM single discharge was calculated using finite element method, and the result was used to calculate residual stress. It was found that the residual stress in the radial direction, σ r ( z ) along the centre axis of the single discharge crater was distributed non-linearly in thickness direction from top surface of the workpiece. Then, in structural analysis, the result of σ r ( z ) was imposed within micro fin model. Here, thermal stress field due to series of sequential discharges was considered. The summation of calculated deflections after three sequential discharges was almost equal to the measurement result. To explain the deformation of fin, additional models of uniform rectangular beam were built. As a result, the non-linear distribution of σ r ( z ) was found to be the main reason that causes the non-uniform curvature of micro fin. [ABSTRACT FROM AUTHOR]

Considering the traditional power amplifier has the disadvantage of poor reliability and flexibility, a three-level pulse-width modulation (PWM) power amplifier which is based on a novel field-programmable logic gate array (FPGA) algorithm and hardware solution is proposed. The power amplifier can provide various signals flexibly and realize rapid response of the magnetic suspension spindle in micro-electrical discharge machining (EDM). In this paper, the principle of three-level PWM amplifier with half bridge and full bridge power circuit is introduced. According to different functions, the amplifier is divided into four function modules which include PWM signal generator module, voltage signal convert module, bootstrap drive module, and power bridge module. PWM signal generator module is also divided into four sub-modules in term of a new FPGA algorithm. Voltage signals are converted by high-speed photo coupler HCPL-2630. IR2110S chips are applied to drive the half bridge and full bridge power circuits. According to Kirchhoff voltage law, when the period of PWM signals is 50 μs and the duty cycles are larger than 0.76 and 0.665, the average current of half bridge and full bridge are more than 3 and 4 A; however, the ripple of the half bridge and full bridge are still less than 0.25 and 0.2 A, this advantage is suitable for the control system of magnetic suspension spindle. Test results of the average current and ripple are close to theoretical value. The axial response frequency of the spindle can reach 125 Hz, using this power amplifier and the magnetic suspension spindle, micro EDM can be achieved in Z axis with 1.2 mm stroke. [ABSTRACT FROM AUTHOR]

This paper demonstrates the process of micro electro-discharge machining (micro EDM) assisted with high-frequency vibration machining micro holes and linear grooves which are straight or inclined on WC/8 % Co (MA) and WC/15 % TiC/6 %Co (MB) cemented carbide cutting tool rake face or scrap reeling slot. Low-voltage sensing contact is introduced to determine the exact position of holes and grooves. Morphology of textured regions is examined and the elemental chemical composition of close proximity region to a straight hole is identified. Results show that micro holes and linear grooves with high dimension accuracy and exact position are machined as expected by micro EDM assisted with high-frequency vibration. There is no debris accumulating around the cavities. Materials of MA cutting tool adhere on the micro tool electrode slightly, while the dimension of adhesion position becomes constant after 3 μ holes are finished. However, the adhesion does not occur during machining MB cutting tools. The distance of edges of grain refinement regions and areas where elemental chemical composition varies to the contour of the hole is no more than 15 μm. [ABSTRACT FROM AUTHOR]

A micro hole is a basic feature in micro manufacturing. Micro electrical discharge machining (EDM) is one of the key techniques for machining micro holes in metallic materials. Since debris is accumulated in the discharging gap between the tool electrode and the workpiece, it becomes increasingly very difficult to machine a micro hole as the chosen diameter is progressively decreased or the depth increased. The use of vibration in micro EDM drilling can improve machining efficiency by refreshing dielectric fluids and flushing out the debris from the gap. Although ultrasonic vibration over a few kHz has been introduced in many applications of micro EDM, it is difficult to apply to a workpiece of a very large size or mass. In this study, the effect of very-low-frequency vibration was investigated to improve the efficiency of micro EDM. Low-frequency vibration in the range of 10 to 70 Hz was applied to single-hole machining, to reverse EDM, and to multiple-hole machining. The machining efficiency was investigated while varying the vibration frequency and amplitude. [ABSTRACT FROM AUTHOR]