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Electrochemical jet machining (EJM) has attracted considerable attention in alloy manufacturing due to its versatility and flexibility. However, for EJM of titanium alloys, the Material Removal Rate (MRR) is low due to the formation of the refractory oxide layer and the non-participation of end face of tool electrode. In order to improve the MRR in this study, a novel hybrid method called gas electrical discharge and electrolyte jet simultaneous machining, which combines electrical discharge machining (EDM) and electrochemical jet machining (EJM), is proposed to effectively reduce the oxide layer and promote the participation of the end of electrode tool in machining process. In the hybrid EDM-EJM method, an instantaneous high voltage spark discharge breaks down the air between two electrodes to remove instantaneously the oxide layer, and then the workpiece is machined to a smooth surface by subsequent and highly efficient EJM. Each point on the workpiece surface is treated successively via EDM and EJM, so the entire surface is machined by the two separate machining modes. The EDM and EJM act simultaneously on the workpiece and in synchronization throughout the machining process. Also, the end face of the workpiece contributes to material removal, hence the MRR is improved. Due to the periodic change of the machining voltage at the EDM stage, the reflection angle of the flowing electrolyte also changes periodically, and this is conducive to increasing fluctuations in the flow of electrolyte and hence accelerating the removal of the electrolysis products. Our studies shows that this new combined approach improves not only the MRR, but also greatly reduces erroneous corrosion effects and reduced the surface roughness Ra from 0.800 µm to 0.177 µm. [Display omitted] • A novel hybrid method is proposed to effectively promote the participation of the end of the tool in machining. • EDM and EJM act simultaneously on the workpiece and in synchronization throughout the processing. • The flow of the deflected electrolyte was periodic in line with the periodic change in voltage. [ABSTRACT FROM AUTHOR]

In previous studies, the electrical discharge machining (EDM) ablation technology was developed, which removed materials by using the chemical energy released from the combustion of metal instead of the energy of pulse power supply used in EDM. Although the machining efficiency was greatly improved, the problem of recast layer that generated on the machined surface during EDM ablation process had not been solved. In this study, the combined process of EDM ablation and electrochemical machining (ECM) in aerosol dielectric was investigated, which aims to solve the recast layer problem of deep hole machining by using the aerosol dielectric EDM ablation technology. The mechanism was analyzed based on numerous experiments. Mechanism analysis indicated that the combined process includes the cycle machining state of micro-electrolysis and EDM ablation. Five microcosmic stages were included in the typical combined process: metal activation at discharge point, surface metal oxidation, blocking of surface metal oxidation, rapid oxidation of internal substrate metal, and micro-electrolysis of recast layer. Contrast experiments were performed to compare conventional electrical discharge machining, aerosol dielectric EDM ablation, and combined process of EDM ablation and ECM in aerosol dielectric. Results showed that the material removal rate of the combined process was 40% less than that of the EDM ablation but was still 3.7 times more than that of EDM. Moreover, the relative tool wear ratio decreased by 53.3%, the value of corner arc radius decreased by 44.3%, and the thickness of the recast layer decreased by 42.9%. [ABSTRACT FROM AUTHOR]

In powder-mixed electrical discharge machining (PMEDM), a suspension of powder particles is added to the dielectric to achieve a high surface quality and to improve the material removal rate (MRR). However, for biomedical applications, the machined surface must be nontoxic and also contain bioactive species; these constraints limit the choice of powder material. This study focuses on machining orthopedic-implant materials based on titanium and titanium–tantalum alloys using bioactive hydroxyapatite (HA)-powder suspension as the dielectric. The influence of the powder particles and the work-piece composition on the machining performance was investigated. Employing a suspension dielectric with 5 g/L HA caused a smoother surface (Ra 2.1 μm) with a thinner recast layer (∼9 μm) as compared to using water to machine titanium which has surface roughness of Ra 2.4 μm with a recast layer close to 10 μm. In addition, the MRR of titanium machined in the HA-powder-suspension dielectric (6.4 × 10 −4 g min −1 ) was greatly lower than that in water (28.6 × 10 −4 g min −1 ). However, increasing the HA concentration led to a gradual increase in the MRR, electrode wear rate (EWR), surface roughness, and recast-layer thickness. The MRR, EWR, and the surface roughness of titanium and titanium–tantalum alloys under PMEDM exhibited an inverse relation with respect to the melting temperature and thermal conductivity of the alloy. Furthermore, calcium and phosphorus were incorporated into the recast layer, and their amounts decreased when the discharge current was increased. [ABSTRACT FROM AUTHOR]

In this study, electrical discharge machining (EDM), a non-contact thermal machining process, is proposed for machining single crystal silicon carbide (SiC) which exhibits extreme mechanical hardness. However, as a semiconductor, SiC demonstrates significantly different EDM characteristics compared with those of metallic materials. This research clarifies the EDM characteristics of SiC from thermal, mechanical and chemical aspects through experimental and analytical approaches. The heat transfer analysis of a single discharge of SiC taking into account Joule heating effect revealed that Joule heating effect can increase the surface temperature of SiC near the discharge spot considerably. On the other hand, experimental investigations on the EDM of SiC found that brittle fractures along crystal orientations occur in the EDM of SiC due to thermal shock. However, the influence of the crystal anisotropy of SiC on the EDM characteristics was not significant. Finally, the EDM mechanism of SiC was investigated from chemical aspects. Oxidation reaction was confirmed in the EDM of SiC in deionized water. All of these factors helped improve the machining rate of SiC to a certain extent. [ABSTRACT FROM AUTHOR]

Film cooling holes are required in many crucial and widely used structures. The creation of good film cooling holes requires machining at high speeds with high accuracy and good surface quality. For this purpose, a promising hybrid machining method combining electrical discharge machining and electrochemical machining, called tube-electrode high-speed electrochemical discharge drilling (TEHECDD), has been proposed, which can be used for machining difficult-to-machine superalloys. In TEHECDD, the flushing condition is considered as an important element. To improve the flushing condition and further enhance the machining performance, improved tube-electrode structures, obtained by varying the inner diameter and inner shape, are introduced. In this study, different inner structures are designed for the tube electrodes, whereby the mechanism of the enhanced TEHECDD performance for different tube-electrode inner shapes are analysed and the effects of different tube-electrode inner structures on the machining performance are investigated. The results show that an increase in the tube-electrode inner diameter results in a higher material removal rate, smaller average bore diameter, and smaller taper angle. However, for the single-hole tube electrode, a larger inner hole results in the formation of a residual cylinder. Thus, the double-hole and multi-hole tube electrodes are proposed and found to be effective in removing the residual cylinder. Finally, it is verified that the tube electrodes with improved inner shapes can be used to further enhance the machining performance. The double-hole tube electrode is confirmed to have the optimal structure. [ABSTRACT FROM AUTHOR]

Many electro-arc machining (EAM) processes have been put forward in recent years. Theories of electrical discharge machining (EDM) are utilized to study EAM processes frequently. Though EDM and EAM are different in their ranges of discharge current and pulse duration, there is no specific discrimination between EDM and EAM. To find different characters of EDM and EAM, experiments adopting a single pulse discharge were designed and carried out. Fundamental phenomena of EDM and EAM including the plasma tunnel and crater geometry were researched and discussed. Results show that the discharge current and pulse duration influence the diameter and temperature of the plasma tunnel, and then determine the crater geometry, causing a short circuit of the discharge gap finally. Whether a short circuit appeared after a single pulse discharge was researched and adopted for the discrimination between EDM and EAM. A discriminatory line was proposed based on the theoretical analysis and experiments. An experimental verification was conducted and the results were coincident with the deduction. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new compound machining process is proposed by combining EDM milling and arc machining. [•] The power supply contained a pulse generator and a DC power. [•] The machining could achieve high MRR and low REWE. [•] Flushing played an important role in deionizing the arc plasma channel. [ABSTRACT FROM AUTHOR]

To fabricate small holes in a nickel-based single crystal superalloy without formation of recast layer and stray corrosion, electrochemical discharge drilling utilising a compound flow field of different fluids (DF-ECDD), is investigated in this study. DF-ECDD is a compound machining method that electrical discharge machining (EDM) and electrochemical machining (ECM) can occur simultaneously in the process. In this method, the internal flushing of a low-concentration salt solution and external flushing of a deionized water occur simultaneously. By means of the internal flushing, EDM and ECM occur synchronously in the process. Owing to the external flushing, the conductivity of the solution on the surface of the workpiece is significantly reduced, thus reducing the stray electric field distribution. In this study, the influence of the conductivity of the external flushing liquid in the DF-ECDD process was analysed. The simulation results showed that when deionized water with a conductivity of 2 μS/cm was used as the external flushing liquid, the stray current on the workpiece surface was almost completely eliminated. Furthermore, the expression is theoretically derived for the relationship between the radii of the stray corrosion areas and the conductivity of solution domain. The experiments verified that the radii of the stray corrosion areas decrease with the decreasing of external flushing liquid conductivity. Finally, the stray corrosion could also be almost eliminated with the DF-ECDD process, and the machined holes were free of recast layer. [ABSTRACT FROM AUTHOR]

Abstract: Silicon carbide (SiC) is an extremely hard and difficult-to-shape engineering ceramic material used extensively in industry because of its superior mechanical properties, wear and corrosion resistance even at elevated temperature. Conventional ceramic processing and structuring techniques such as injection molding and grinding are costly and difficult to obtain flawless complex shaped components. By infiltrating free Si into the SiC, the electrical conductivity of the matrix is largely improved. Thus it can be machined by electrical discharge machining (EDM). In this paper, a die-sinking EDM technology for manufacturing components in a commercial available silicon infiltrated silicon carbide (SiSiC) is developed. The influences of the major operating EDM parameters (discharge current , open gap voltage , discharge duration and pulse interval ) of the iso energetic generator on the machining performances like Material Removal Rate (MRR), Tool Wear Ratio (TWR) and surface roughness (Ra) are examined. Relaxation pulses which have lower energy input are also considered to improve the surface quality. Furthermore, the topography and surface integrity of the material after the EDM process are analysed to determine the corresponding material removal mechanism. With the developed machining strategy, a sample piece with designed features such as ribs, a deep cavity and chamfers are manufactured to examine the machining performances. [Copyright &y& Elsevier]

Abstract: When using the electrical discharge machining (EDM) hole-drilling strain gage method to measure the residual stress within a component, the metallurgical transformation layer formed on the wall of the EDMed hole induces an extra stress, which can lead to significant measurement errors. Accordingly, the objective of the present work was to explore and determine the optimal EDM parameters which reduce the thickness of the metallurgical transformation layer and therefore minimize the magnitude of the hole-drilling induced stress. The experimental results demonstrated that by maintaining the relative stability coefficient of the discharge duty ratio at a value greater than 0.99, the induced stress emerged in EDM hole-drilling measurement can be reduced substantially and becomes insensitive to the parameters of the pulse current and pulse-on duration. Further investigations revealed that when the residual stress is to be measured accurately, using a hollow electrode instead of the usual solid electrode and the following parameters are recommended. The pulse current and pulse-on duration are in the ranges of 4–12A and 9–23μs, respectively, and the pulse-off duration needs to be longer than the value required to ensure that the relative stability coefficient of the discharge duty ratio exceeds 0.99. [Copyright &y& Elsevier]

Abstract: This study explores the feasibility of removing the recast layer (RCL) using etching and mechanical grinding for Ni-based superalloy materials by means of electrical discharge machining (EDM). The EDM process is widely used for machining hard metals and performing specific tasks that cannot be achieved using conventional techniques. The sparks produced during the EDM process melt the metal''s surface, which then undergo ultra rapid quenching. A layer forms on the workpiece surface defined as a recast layer after solidification. Molds and dies desire to remove the RCL even though it is hard and has good matrix adherence. This experiment is divided into three stages. The first stage acquires a thick recast layer by using EDM with a larger discharging energy. A thick recast layer is essential for verification of the EDM technique for observing the recast process. Thus, this work applies the Taguchi L18 analytical method to acquire the thick recast layer. The second stage optimizes the recast layer removal technique. Therefore, the thick recast layer is intentionally made in the first stage. This work determines the second stage setting using Taguchi''s recommendation. Thus, the L9 orthogonal array sets up the etching and mechanical grinding parameters and observes the recast layer removal quantity analysis. Finally, an experiment studies the surface characteristics of Ni-based superalloys, such as composition and micro-hardness after removing the recast layer. [Copyright &y& Elsevier]

Abstract: The last decade has seen an increasing interest in the novel applications of electrical discharge machining (EDM) process, with particular emphasis on the potential of this process for surface modification. Besides erosion of work material during machining, the intrinsic nature of the process results in removal of some tool material also. Formation of the plasma channel consisting of material vapours from the eroding work material and tool electrode; and pyrolysis of the dielectric affect the surface composition after machining and consequently, its properties. Deliberate material transfer may be carried out under specific machining conditions by using either composite electrodes or by dispersing metallic powders in the dielectric or both. This paper presents a review on the phenomenon of surface modification by electric discharge machining and future trends of its applications. [Copyright &y& Elsevier]

• Electrical discharge texturing is utilized to enhance pool boiling over aluminum surfaces. • Effects of process parameters viz. discharge current and discharge duration are investigated. • A ∼500 % increase in the heat transfer coefficient relative to a polished surface is achieved. • Crater geometry computed from textured surface profiles correlate well with boiling performance. This research pertains to pool boiling heat transfer characteristics of Aluminum 6061 alloy surfaces that were textured using sink electrical discharge machining (EDM). Prior related work elsewhere utilized EDM as an essential means to roughen a surface or fabricate geometric features such as microchannels and micropillars to investigate boiling. As opposed to this, the present work systematically examined the effect of EDM process parameters viz., the discharge current and the discharge duration to enhance/benchmark boiling performance in the natural convection and nucleate boiling regimes, and comprehend underlying mechanisms. A process-related factor that limits boiling was found to be the growth of a superficial layer on the machined surface, the formation of which is facilitated by the hydrocarbon dielectric fluid used in EDM. This notwithstanding, the highest heat transfer coefficient obtained in this work was roughly five times as that of a reference polished surface. The Data Dependent Systems methodology was adopted to mathematically extract characteristic crater geometry from EDM-textured surface profiles, which highlighted the significance of parameters that are physically relevant such as the crater diameter and the crater volume in correlating boiling performance. [ABSTRACT FROM AUTHOR]

Abstract: A new mechanism of cutting pipe combined with electrical discharge machining (EDM) is designed. The mechanism is set up on the working table of electrical discharge machine and used to investigate the effects of machining parameters such as material removal rate (MRR), relative electrode wear rate (REWR) on machining characteristics. The machining variables including machining polarity, peak current, pulse duration and the rotary speed of electrode have been chosen to explore the machining efficiency. The purpose of this study is to confirm the mechanism could not only increase material removal rates but also decrease the electrode wear rates in the EDM process. [Copyright &y& Elsevier]

Abstract: The method of electrical discharge machining (EDM), one of the processing methods based on non-traditional manufacturing procedures, is gaining increased popularity, since it does not require cutting tools and allows machining involving hard, brittle, thin and complex geometry. By using different EDM parameters (current, pulse on-time, pulse off-time, arc voltage), the R a (μm) roughness value as a result of application of a number of copper electrode-hardened powder metals (cold work tool steel) to a work piece has been investigated, in this study. At the same time, roughness values obtained from the experiments that have been modeled by using the genetic expression programming (GEP) method and a mathematical relationship has been suggested between the GEP model and surface roughness and parameters affecting it. Moreover, EDM has been used by applying copper, copper–tungsten (W–Cu) and graphite electrodes to the same material with experimental parameters designed in accordance with the Taguchi method. Results obtained from this study have been compared among each other and similar studies in the literature. [Copyright &y& Elsevier]

Abstract: Electrical discharge machining (EDM) is one of the most widely disseminated manufacturing technologies, in particular as regards the generation of accurate and complex geometrical shapes on hard metallic components. Nevertheless current EDM technologies have major limitations when dealing with fine surface finish over large process area. Indeed this is one reason that explains the need of final manual polishing of mould cavities performed by EDM. Recently EDM with powder-mixed dielectric (PMD-EDM) has been a focus of an intense research work in order to overcome these technological performance barriers. This paper presents a research work within the objective to acquire deep knowledge on EDM technology with powder mixed dielectric and to compare its performance to the conventional EDM when dealing with the generation of high-quality surfaces. In particular the analysis of the effect of the electrode area in the surface quality measured by the surface roughness and craters morphology was carried out for both technologies. The results achieved evidenced a linear relationship between the electrode area and the surface quality measures as well as a significant performance improvement when the powder mixed dielectric is used. [Copyright &y& Elsevier]

Abstract: This paper investigates the electrical discharge machining of gallium-doped p-type germanium with a relaxation type pulse generator. A series of experiments were performed to establish the slicing rate for different types and sizes of electrode wires. The cut samples were analyzed using a 3D optical profiler and a scanning electron microscope (SEM) for surface roughness and subsurface damage. The samples were etched and analyzed for any contamination using an X-ray energy dispersive spectrometer (EDS). This paper also investigates the use of small wire diameters (50–200μm) to enhance slicing rate and surface characteristics. The maximum discharge energy at which germanium can be machined without any subsurface damage was determined using the experiments. The phenomenon of increase in slicing rate with decrease in wire diameter is explained using the concept of discharge energy density (E d). [Copyright &y& Elsevier]

Abstract: Following a brief summary of the electrical discharge surface alloying process and key publications, the paper details experimental results when alloying α–β titanium Ti–6Al–4V, using both solid and powder compacted copper electrodes with a commercial water-based dielectric fluid. At the discharge energies employed, recast layer thickness varied from ∼4 to 11μm with thicker and rougher layers evident when using positive tool electrode polarity. All layers were in general discontinuous, however those produced with negative polarity were more uniform, especially when using solid electrodes. The hardness of the recast varied between ∼200 and 1100HK0.025 compared to the bulk material ∼365HK0.025. Glow discharge optical emission spectroscopy showed that the percentage of copper transferred from the solid electrodes to the workpiece was up to ∼29at%, while for the powder compact electrodes the level was significantly higher, with the 32MPa pressed pellets giving ∼78at% at the surface. [Copyright &y& Elsevier]

The electrical discharge machining of cylindrical components is decisively influenced by the process conditions resulting from the rotational movement of at least one of the two electrodes. This paper analyses the machining effects developing at high peripheral speeds. Focus of investigation is especially placed on the evaluation of the effects on process behaviour and surface topography. The process variants electrical discharge turning (EDT), electrical discharge grinding (EDG), and wire electrical discharge grinding (WEDG) are compared with respect to the influence by the above-mentioned effects and the resulting process planning. [Copyright &y& Elsevier]

The paper reviews the manufacture, physical/mechanical properties and cutting tool applications of chemical vapour deposited (CVD) diamond and makes comparisons with polycrystalline diamond (PCD). The morphology of CVD diamond is significantly different from that of PCD, the former exhibiting continuous columnar grains extending from nucleation sites, whereas the latter involves an agglomeration of intergrown diamond crystals with a minor secondary phase of cobalt.Experimental work is detailed involving the electrical discharge wire machining (EDWM) and electrical discharge grinding (EDG) of boron doped CVD diamond (CVDITE CDE). Results from Taguchi experiments are presented which were carried out to assess the effect of generator operating parameters on sparked surface/edge quality and productivity. Typically when EDWM (roughing) CVDITE CDE surface roughness values were ∼0.7–2.78 μm Ra while cutting speeds were ∼0.87–2.14 mm/min. Sparked PCD surfaces were generally of lower quality, even when using fine diamond (2 μm) products, however, cutting speeds were substantially increased by as much as 100%. When EDG, CVDITE CDE cutting speeds of ∼0.11–0.26 mm/min were obtained. Visual examination of machined surfaces in general showed that the CVD diamond was cleanly cut, with no obvious surface degradation, however, in a minority of cases which were not operating parameter specific, there was wholesale loss of the columnar diamond crystals. [Copyright &y& Elsevier]

As previously reported, several insulating ceramics such as Si3N4, SiC and ZrO2 have successfully been machined by sinking electrical discharge machining using the surface discharge modification phenomenon. As unstable discharges occur during the machining of Al2O3 ceramics, inferior machining properties have been obtained as compared to other ceramics. It seems that the formation process of the electrically conductive layer on the workpiece during discharge is much different compared with that of other dissociated ceramics at high temperature. In this study new methods are devised and the electrical discharge machining mechanism of insulating Al2O3 ceramics is researched using high purity alumina and single crystal Al2O3 of sapphire. Machining properties are dependent on the purity and structure of the workpiece, and correlated to its thermal properties. [Copyright &y& Elsevier]

Electrical discharge machining became a commercial process after the discovery of the importance of the dielectric fluid, which affects factors such as productivity and quality. Health, safety and environment are also important factors, particularly when oil-based fluids are used. This paper presents a literature survey on the use of dielectric fluids that provide an alternative to hydrocarbon oil. It has been reported that water-based dielectrics may replace oil-based fluids in die sink applications. Gaseous dielectrics such as oxygen may also be the alternative. Nonetheless, these need further research in order to be commercially viable. [Copyright &y& Elsevier]

This paper details the electrical discharge surface alloying/modification of γ-TiAl (Ti–46.5Al–4(Cr, Nb, Ta, B)) and α/β Ti alloy (Ti–6Al–4V) sheet (1 mm thick) during wire cutting using deionised water dielectric with nickel and copper wires. In addition, topography, microstructure and wear test data are given for a 2% Cr steel mill roll material textured/alloyed using partially sintered powder metallurgy (PM) hardmetal tool electrodes. Wire cutting produced surfaces with porous discontinuous recast layers up to 136 μm thick and in some cases, a surface hardness lower than the bulk was obtained. In contrast, some textured and alloyed layers on the roll material were over 900 HK0.025 when using WC/Co electrodes as compared to surfaces produced with standard Cu/graphite tools of 500–740 HK0.025. Scratch wear test data on the alloyed 2% Cr steel surfaces showed that a significantly reduced coefficient of friction (∼50%) was obtained when using the carbide electrodes as compared with similar surfaces machined with standard tools. Chromium-plated surfaces however gave a 30% reduction in friction force over the hardmetal alloyed surface. [Copyright &y& Elsevier]

In order to achieve high removal rate and low electrode wear in sinking electrical discharge machining (EDM) a stable machining process is required. The process stability is partly influenced by the contamination of the gap between the workpiece and the electrode. Additionally, it also depends on the size of the eroding surface at the given machining regime. When the eroding surface size varies with the depth of machining, the roughing regime has to be selected on-line. The work presented in this paper shows that the average discharge voltage depends on the eroding surface size. Through sets of experiments at constant machining parameters, varying size of the eroding surface and varying geometry of engaged surface were investigated. The average discharge voltages were calculated on the acquired electric voltage signals in the gap. The average discharge voltage is simple for on-line monitoring and it enables on-line detection of the eroding surface size as well as the on-line selection of the rough machining parameters. Thus the average discharge voltage depends on the geometry of the engaged surface, the prototype of the engaged surface has to be presented to the model for successful selection of the roughing regime as well. [Copyright &y& Elsevier]

In this paper, the machining phenomena in the electrical discharge machining (EDM) process are investigated through a new method of in-process measurement of gap distance. The aim of this study is to understand the cause of short-circuiting and to improve the machining rate. A pipe electrode is used and the working fluid is supplied to the gap space though a fixed restrictor and the pipe electrode. Since the pressure between the fixed restrictor and the tip of the pipe electrode (fluid pressure) depends on the gap distance, the absolute value of the gap distance can be determined in-process by measuring the fluid pressure. It is found that the gap distance at the moment when the short-circuiting occurs is more than several micrometers. This result indicates that the cause of the short-circuiting is the bridging of the gap space by collected debris. Based on these results, a new gap control method in which the gap distance is kept constant even when short-circuiting occurs is examined. [Copyright &y& Elsevier]

Electrical discharge machining (EDM) is widely used for manufacturing various kinds of dies and molds. However, EDM has numerous problems such as low material removal rate and generation of heat-affected zones, in which there are numerous cracks and microcraters. Recently, many new machining technologies utilizing EDM have been developed. However, the mechanism of material removal in EDM has not yet been sufficiently explained. In this study, to clarify the mechanism of material removal, first, the impulsive force transitions in an impulse discharge were measured. Second, how the mechanism by which the impulsive forces affect the crater formation by impulse discharge was examined. The following results were obtained: (1) a typical waveform obtained from an impulse discharge in kerosene consists of primary, secondary, tertiary and quaternary waves, and the intervals between the peaks of the waves gradually become smaller; (2) because the shape of the crater is strongly dependent on the polarities under the same conditions in EDM, the effect of the impulsive force acting between the workpiece and the electrode on the crater formation by impulse discharge may be insignificant. [Copyright &y& Elsevier]

A new EDM impulse generator based on a HF-switched dc to dc series–parallel resonant converter is presented. The converter generates the necessary voltage, first to ionize the dielectric and then to maintain the discharge and, provided that it operates in constant current mode, the impulse generator has inherent short-circuit protection. As the switches turn on at zero voltage the converter presents minimum switching losses. The characteristics of this power electronic system are high speed control of the quality of each pulse, small size and light weight suitable for on-site machining.The EDM power supply has been validated to perform operations in a nuclear power plant application. The design and results are described in this paper. [Copyright &y& Elsevier]

In this paper, it is shown that dynamic optimization problems of first-order systems can be transformed into a static parametric programming problem, where the state plays the role of the parameter. Thus, an optimal feedback law is obtained. This concept is applied to the die-sinking electrical discharge machining, a highly time varying industrial process which necessitates adaptation of machining settings during operation. It is shown that the minimum-time operation of this process is equivalent to choosing the manipulated variables that maximizes the speed of machining at every position. [Copyright &y& Elsevier]

Electrical discharge machining (EDM) is used as a precision machining method for the electrically conductive hard materials with a soft electrode material. But recently we succeeded to machine on insulating material by EDM. The technology is named as an assisting electrode method. The EDMed surface is covered with the electrical conductive layer during discharge. The layer holds the electrical conductivity during discharge. For micro-EDM, the wear of tool electrode becomes lager ratio than the normal machining. So the micro-machining is extremely difficult to get the precision sample.In this paper to obtain a fine and precise ceramics sample, some trials were carried out considering the EDM conditions, tool electrodes material and assisting electrode materials. Insulating Si3N4 ceramics were used for workpiece. The machining properties were estimated by the removal rate and tool wear ratio. To confirm the change of micro-machining process, the discharge waveforms were observed. The micro-machining of the Ø0.05 mm hole could be machined with the commercial sinking electrical discharge machine. [Copyright &y& Elsevier]

A comprehensive study of the surface integrity of the machined workpiece in the electrical discharge machining (EDM) of tungsten carbide is presented in this paper. EDM tests on a tungsten carbide workpiece were conducted on a Charmilles Technologies Roboform 40 EDM Die-Sinking Machine, with the peak current and pulse duration varied. The EDMed surface morphology was examined with a scanning electron microscope (SEM) (JEOL JSM-5600LV) with energy dispersive spectrometers. Surface hardness was determined with a macro-hardness tester. It is found that there is no difference between the hardness of the EDMed surface and the original hardness of the workpiece for all EDM conditions. It is observed from the SEM micrographs that there is a clear EDM damaged layer on the workpiece, distinguished by the amount of WC grains and micro-cracks. The amount or concentration of WC grains decreases from the internal structure of the workpiece to the top surface layer. Another feature on EDMed surfaces is the abundance of cracks, especially at high peak current and pulse duration. It is also observed that the EDM conditions have no effect on the microstructures of the bulk workpiece material. This means that damage caused by EDM on the EDMed surface is limited to a certain depth only. However, it is observed that the depth of the damaged layer and the average length, width and number of micro-cracks increase with the peak current and pulse duration. The damaged layer and micro-cracks seem to disappear when the peak current and pulse duration were set at very low values. [Copyright &y& Elsevier]

This paper describes a new method of surface modification by electrical discharge machining (EDM). By using an ordinary EDM machine tool and kerosene fluid, a hard ceramic layer can be created on the workpiece surface with a Ti or other compressed powder electrode in a certain condition. This revolutionary new method is called electrical discharge coating (EDC). The process of EDC begins with electrode wear during EDM, then a kind of hard carbide is created through the chemical reaction between the worn electrode material and the carbon particles decomposed from kerosene fluid under high temperature. The carbide is piled up on a workpiece quickly and becomes a hard layer of ceramic of about 20 μm thickness in several minutes. This paper studies the principle and process of EDC systemically by using a Ti powder green compact electrode. Experiments and analyses show that a compact TiC ceramic layer can be created on the surface of the metal workpiece. The hardness of the ceramic layer is more than three times higher than that of the base body, and the hardness changes gradually from the surface to the base body. This method can find wide application in the fields of surface modification, such as the surface repairing and strengthening of cutting tools and molds. [Copyright &y& Elsevier]

Introducing small-sized functional features such as anti-drag and anti-icing micro structures on Carbon Fibre Reinforced Plastics (CFRPs) is challenging but a still unmet demand. Existing contact CFRP machining solutions may bring unavoidable tool wear and surface defects. Non-contact approaches may introduce significant thermal damage (laser), inconsistent features (waterjet), and limited achievable micro structure shapes and sizes (die sinking Electrical Discharge Machining). Wire Electrical Discharge Machining (WEDM) has the potential to overcome the mentioned limitations. Both theoretical thermal calculation and experimental demonstration in our work, however, showed that conventional WEDM was not working well. Here we propose and implement a Preheating Assisted Wire EDM (PAWEDM) to cut CFRPs. Machining anisotropy in terms of kerf geometry and morphology at the cut entries, ends, and edges was studied carefully. Discussions on the anisotropy principle, the influence of carbon fibre and epoxy resin, and the minimum achievable feature were also provided. PAWEDM is an entirely new CFRP cutting method and effective to enhance CFRP performances by creating micro functional and structural features on CFRP products. [ABSTRACT FROM AUTHOR]