Diffusion Bonded EDM Electrode with Micro Holes for Jetting Dielectric Liquid

This paper describes improvement of machining characteristics of electrical discharge machining of deep slots using a tool electrode which has micro holes for jetting dielectric liquid over the working surface. The tool electrode was made by the diffusion bonding of two copper plates, over an interface on which micro grooves for jetting the dielectric fluid were formed using electrolyte jet machining. In conventional machining, it is difficult to drill micro holes at the end of a slim electrode and circulate the dielectric fluid from the other end. Hence a solid tool electrode is used and periodically lifted up during machining to flush debris particles out of the discharge gap. Use of the newly developed tool electrode was found to shorten the processing time and improve machining accuracy significantly compared with the conventional solid tool electrode. Since the holes are micro, the outlet shapes are not replicated onto the bottom surface of the slot machined.     

Surface modification by electrical discharge machining: A review

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.     

硅电极电火花表面改性的研究

以工业纯硅为电极,通过电火花放电对试样进行表面改性处理.电火花设备型号为EDM7125,工作液为普通煤油,电极材料含硅99.6%,工件材料为45钢和球铁.采用扫描电镜及金相显微镜对试样表面形态进行了研究,对试样表面进行了能谱分析,对试样进行了耐蚀及表层结合强度等试验.结果表明:试样加工后表面形成一层含硅超过16%的合金层.电火花加工球铁石墨基本未脱落,但石墨周围易产生或扩展显微裂纹.高硅层结合强度非常高,进行永久变形时,无剥离和裂纹产生.而且,经电火花加工过的试样耐蚀性得到极大提高.另外,电火花加工,当参数合理时,可达到粉末混入加工的目的,试样可获得好的表面质量.     

Investigation of the effects of electrode orientation and fluid flow rate in near-dry EDM milling

This research investigates the effects of electrode lead and tilt angles and dielectric fluid flow rate on material removal rate, tool electrode wear ratio, and surface roughness in near-dry electrical discharge machining (EDM) milling process. Computational fluid dynamics (CFD) model is developed to predict the dielectric fluid flow rate and qualitatively compare with the experimentally measured EDM material removal rate. The optimum lead angle, which maximized material removal rate and minimized tool electrode wear ratio, was found. The decrease in the lead angle has a negative effect on the roughness of machined surface. The increase in tilt angle reduces the material removal rate and increases the tool electrode wear ratio. The change in tilt angle does not have a significant effect on the surface roughness and can be used to prevent gouging in finishing EDM milling. This study shows that the material removal rate is linearly proportional to the mass flow rate of air and kerosene mixture, the tool electrode wear ratio is inversely related to the mass flow rate of air and kerosene mixture, and the average surface roughness does not have a good correlation with the flow rate of the mixture.     

超声振动辅助气中放电加工实验分析

超声振动辅助气中放电加工技术避免了常用的煤油等工作液作为介质带来的环境污染问题，具有工作环境清洁、适用范围广、加工效率高、工具电极简单等优点。实验研究了电压、脉冲宽度、峰值电流、超声振幅及气体介质压力等参数对加工效率、工件表面粗糙度及电极损耗的影响．并对试验结果进行了分析。     

Development of a reversible machining method for fabrication of microstructures by using micro-EDM

A new micromachining method for the fabrication of micro-metal structures by using micro-reversible electrical discharge machining (EDM) was investigated. The reversible machining combines the micro-EDM deposition process with the selective removal process, which provides the ability of depositing or removing metal material using the same micro-EDM machining system. From the discharge mechanism of micro-EDM, the process conditions of micro-EDM deposition were analyzed firstly. Using the brass and steel materials as a tool electrode, the micro-cylinders with 200 μm in diameter and height-to-diameter ratio of more than 5 were deposited on a high-speed steel surface. Then the machining procedure was transformed easily from deposition to selective removal process by switching the process conditions. Different removal strategies including micro-EDM drilling and micro-EDM milling were used in the machining. Micro-holes with 80 μm in diameter are drilled successfully in the radial direction of the deposited micro-steel cylinder. Also, a brass square column with 70 μm in side length and 750 μm in height, and a micro-cylinder with 135 μm in diameter and 1445 μm in height are obtained by using micro-EDM milling. Finally, the characteristics of the deposited material were analyzed. The results show that the material components of a deposited micro-cylinder are almost the same as those of the tool electrode, and the metallurgical bonding has been formed on the interface. In addition, the Vickers-hardness of 454Hv of the steel deposited material is higher when compared to the hardness of 200Hv of the raw steel electrode.     

Improvement of Dry EDM Characteristics Using Piezoelectric Actuator

This paper describes improvement of the machining characteristics of dry electrical discharge machining (dry EDM) by controlling the discharge gap distance using a piezoelectric actuator. Dry EDM is a new process characterized by small tool electrode wear, negligible damage generated on the machined surface, and significantly high material removal rate especially when oxygen gas is used. However, the narrow discharge gap length compared with conventional EDM using oil as the dielectric working fluid results in frequent occurrence of short circuiting which lowers material removal rate. A piezoelectric actuator with high frequency response was thus introduced to help control gap length of the EDM machine. To elucidate the effects of the piezoelectric actuator, an EDM performance simulator was newly developed to evaluate the machining stability and material removal rate of dry EDM.     

Effect of surface roughness of tool electrode materials in ECDM performance

Electrochemical discharge machining (ECDM) is an emerging non-traditional machining process that involves high-temperature melting assisted by accelerated chemical etching. In this study, the tool electrode (200 μm in diameter) is fabricated by wire electrical discharge grinding (WEDG). After the tool electrode is machined, the surface roughness of tool electrode materials (stainless steel, tungsten carbide, and tungsten) is different because of the physical properties. However, the surface roughness affects the wettability on tool electrode, and also changed the coalesce status of gas film in ECDM. Hence, this study explores the wettability and machining characteristics of different tool electrode materials and their impact on gas film formation. Their machining performance and extent of wear under gravity-feed micro-hole drilling are also examined. Experimental results show that the optimal voltage of different tool electrode can shed light on the machining performance. Moreover, wettability of tool electrode is determined by surface roughness of tool material, which in turn affects the coalesce status of gas film, machining stability and micro-hole diameter achieved. In addition, differences in tool material also results in variations in machining speed. Significant tool wear is observed after repeated gravity-feed machining of 50 micro-holes.     

An investigation of ultrasonic-assisted electrical discharge machining in gas

This study focuses on using ultrasonic to improve the efficiency in electrical discharge machining (EDM) in gas medium. The new method is referred to as ultrasonic-assisted electrical discharge machining (UEDM). In the process of UEDM in gas, the tool electrode is a thin-walled pipe, the high-pressure gas medium is applied from inside, and the ultrasonic actuation is applied onto the workpiece. In our experiment, the workpiece material is AISI 1045 steel and the electrode material is copper. The experiment results indicate that (a) the Material Removal Rate (MRR) is increased with respect to the increase of the open voltage, the pulse duration, the amplitude of ultrasonic actuation, the discharge current, and the decrease of the wall thickness of electrode pipe; and (b) the surface roughness is increased with respect to the increase of the open voltage, the pulse duration, and the discharge current. Based on experimental results, a theoretical model to estimate the MRR and the surface roughness is developed.     

Probability of precision micro-machining of insulating Si3N4 ceramics by EDM

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.     

Study of the Diffusion of Carbon, Its Sources, and Effect on Finishing Micro-EDM Performance of Cemented Carbide

Apart from the necessity of surface modification based on different applications, in most of the cases, diffusion of carbon or foreign particles on the workpiece surface during micro-electrodischarge machining (micro-EDM) is avoidable, especially in finishing micro-EDM. This study aims to investigate different sources of materials that migrate to the machined surface during fine-finishing of micro-EDM of cemented tungsten carbide (WC-Co). The machined surfaces have been examined under scanning electron microscope and energy dispersive x-ray to investigate the changes in chemical composition. It has been observed that during finishing of micro-EDM, the major source of materials' transfer to both the workpiece and electrode is the diffusion of carbon that comes from the decomposition of the hydrocarbon dielectric. In addition, materials from both workpiece and electrode transfer to each other based on machining conditions and discharge energy. The migration occurs more frequently at lower gap voltages during die-sinking with micro-EDM because of low spark gap and stationary tool electrode. Milling micro-EDM results in lower amount of carbon migration and fewer surface defects that improve the overall surface finish significantly.     

Effect of micro-powder suspension and ultrasonic vibration of dielectric fluid in micro-EDM processes—Taguchi approach

Solutions are needed for increasing the material removal rate without degrading surface quality in micro-electrical discharge machining (μ-EDM). This paper presents a new method that consists of suspending micro-MoS₂ powder in dielectric fluid and using ultrasonic vibration during μ-EDM processes. The Taguchi method is adopted to ascertain the optimal process parameters to increase the material removal rate of dielectric fluid containing micro-powder in μ-EDM using a L₁₈ orthogonal array. Pareto analysis of variance is employed to analyze the four machining process parameters: ultrasonic vibration of the dielectric fluid, concentration of micro-powder, tool electrode materials, and workpiece materials. The results show that the introduction of MoS₂ micro-powder in dielectric fluid and using ultrasonic vibration significantly increase the material removal rate and improves surface quality by providing a flat surface free of black carbon spots.     

工作液超声振动辅助电火花小孔加工装置设计与试验

电火花加工小孔存在电蚀产物排出效率低导致加工效率低、电蚀产物排除导致二次放电现象影响加工精度等问题,而超声振动在工作液中产生空化效应和泵吸作用,能大幅提高电火花的排屑和消电离能力,进而在很大程度上减少上述问题的发生。设计一套工作液超声振动辅助电火花小孔加工装置,主要包括主轴系统、微三维运动平台、超声振动工作液槽和数据采集系统,其中主轴系统包括NSK电主轴、引电结构、工具电极装夹结构,可以实现工具电极的高速旋转;基于LabVIEW开发了电火花小孔加工控制系统,主要包括初始化模块、粗定位模块、恒电压对刀模块、实时电压分段控制加工模块和实时显示模块。开展了工作液超声振动辅助电火花小孔加工试验研究,试验结果表明：随电火花加工电压的增加,工件材料去除率和电极损耗率都趋于增大。     

Experimental characterization of material removal in dry electrical discharge drilling

Dry electrical discharge machining is one of the novel EDM variants, which uses gas as dielectric fluid. Experimental characterization of material removal in dry electrical discharge drilling technique is presented in this paper. It is based on six-factor, three-level experiment using L₂₇ orthogonal array. All the experiments were performed in a ‘quasi-explosion’ mode by controlling pulse ‘off-time’ so as to maximize the material removal rate (MRR). Furthermore, an enclosure was provided around the electrodes with the aim to create a back pressure thereby restricting expansion of the plasma in the dry EDM process. The main response variables analyzed in this work were MRR, tool wear rate (TWR), oversize and compositional variation across the machined cross-sections. Statistical analysis of the results show that discharge current (I), gap voltage (V) and rotational speed (N) significantly influence MRR. TWR was found close to zero in most of the experiments. A predominant deposition of melted and eroded work material on the electrode surface instead of tool wear was evident. Compositional variation in the machined surface has been analyzed using EDAX; it showed migration of tool and shielding material into the work material. The study also analyzed erosion characteristics of a single-discharge in the dry EDM process vis-á-vis the conventional liquid dielectric EDM. It was observed that at low discharge energies, single-discharge in dry EDM could give larger MRR and crater radius as compared to that of the conventional liquid dielectric EDM.     

Fabrication of deep micro-holes in reaction-bonded SiC by ultrasonic cavitation assisted micro-EDM

Ultrasonic vibration was applied to dielectric fluid by a probe-type vibrator to assist micro electrical discharge machining of deep micro-holes in ceramic materials. Changes of machined hole depth, hole geometry, surface topography, machining stability and tool material deposition under various machining conditions were investigated. Results show that ultrasonic vibration not only induces stirring effect, but also causes cloud cavitation effect which is helpful for removing debris and preventing tool material deposition on machined surface. The machining characteristics are strongly affected by the vibration amplitude, and the best machining performance is obtained when carbon nanofibers are added into the vibrated dielectric fluid. As test pieces, micro-holes having 10 μm level diameters and high aspect ratios (>20) were successfully fabricated on reaction-bonded silicon carbide in a few minutes. The hybrid EDM process combining ultrasonic cavitation and carbon nanofiber addition is demonstrated to be useful for fabricating microstructures on hard brittle ceramic materials.     

High-speed EDM milling with moving electric arcs

A novel high-speed electrical discharge machining (EDM) milling method using moving electric arcs has been proposed in this study. We connected a copper electrode rotating rapidly around its axis and a work piece to a DC power supply to generate a moving electric arc. To ensure high relative speed of any point on the electrode with respect to the work piece, the electrode was shaped like a pipe. It was observed that the electric arcs move rapidly within the discharge gap due to the revolution of the tool electrode, removing the materials on the electrode along the track of the arc roots. To explore the characteristics of machining with moving electric arcs, an EDM milling apparatus was devised. Two planes with approximately the same roughness were machined separately by this equipment and a traditional EDM machine for comparison. It was found that a much higher material removal rate can be easily achieved by EDM milling with moving electric arcs. In the meanwhile, wear of the tool electrode in this new method is negligible, which is greatly favorable for machining accuracy. The microstructures of these surfaces were also investigated for further information.     

Machining performance of silicon carbide ceramic in end electric discharge milling

A new process of machining silicon carbide (SiC) ceramic using end electrical discharge milling is proposed in this paper. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and low cost. The effects of machining conditions on the material removal rate, electrode wear ratio, and surface roughness have been investigated. The surface microstructures machined by the new process are examined with a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and an X-ray diffraction (XRD). The results show that the SiC ceramic is removed by melting, evaporation and thermal spalling, the material from the tool electrode can transfer to the workpiece, and a combination reaction takes place during end electric discharge milling of the SiC ceramic.     

The effect in EDM of a dielectric of a urea solution in water on modifying the surface of titanium

This study investigates the influence of the machining characteristics on pure titanium metals using an electrical discharge machining (EDM) with the addition of urea into distilled water. Additionally, the effects of urea addition on surface modification are also discussed. In the experiments, machining parameters such as the dielectric type, peak current and pulse duration were changed to explore their effects on machining performance, including the material removal rate, electrode wear rate and surface roughness. Moreover, the elemental distribution of nitrogen on the machined surface was qualitatively determined by EPMA to assess the effects on surface modification. Micro hardness and wear resistance tests were performed to evaluate the effects of the reinforced surface.Experimental results indicate that the nitrogen element decomposed from the dielectric that contained urea, migrated to the work piece, forming a TiN hard layer, resulting in good wear resistance of the machined surface after EDM.     

Effect of machining fluid on the process performance of electric discharge milling of insulating Al2O3 ceramic

Wire electric discharge machining (WEDM) and electrical discharge machining (EDM) promise to be effective and economical techniques for the production of tools and parts from conducting ceramic blanks. However, the manufacturing of insulating ceramic blanks with these processes is a long and costly process. This paper presents a new process of machining insulating ceramics using electrical discharge (ED) milling. ED milling uses a thin copper sheet fed to the tool electrode along the surface of the workpiece as the assisting electrode and uses a water-based emulsion as the machining fluid. This process is able to effectively machine a large surface area on insulating ceramics. Machining fluid is a primary factor that affects the material removal rate and surface quality of the ED milling. The effects of emulsion concentration, NaNO₃ concentration, polyvinyl alcohol concentration and flow velocity of the machining fluid on the process performance have been investigated.     

A new method for monitoring micro-electric discharge machining processes

Micro-electric discharge machining (μ-EDM) is a very complex phenomenon in terms of its material removal characteristics since it is affected by many complications such as adhesion, short-circuiting and cavitations. This paper presents a new method for monitoring μ-EDM processes by counting discharge pulses and it presents a fundamental study of a prognosis approach for calculating the total energy of discharge pulses. For different machining types (shape-up and flat-head) and machining conditions (mandrel rotation and tool electrode vibration), the results obtained using this new monitoring method with the prognosis approach show good agreement between the discharge pulses number and the total energy of discharge pulses to the material removal and tool electrode wear characteristic in μ-EDM processes. On applying tool electrode vibration, the machining time becomes shorter, because it removes adhesion. The effect of tool electrode vibration in order to remove adhesion can be monitored with good results. In order to achieve high accuracy, the tool wear compensation factor has been successfully calculated, since the amount of tool electrode wear is different in each machining type and condition. Consequently, a deeper understanding of the μ-EDM process has been achieved.