Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. A pulse discharge occurs in a small gap between the work piece and the electrode and removes the unwanted material from the parent metal through melting and vaporising. The electrode and the work piece must have electrical conductivity in order to generate the spark. There are various types of products which can be produced using EDM such as dies and moulds. Parts of aerospace, automotive industry and surgical components can be finished by EDM. This paper reviews the research trends in EDM on ultrasonic vibration, dry EDM machining, EDM with powder additives, EDM in water and modeling technique in predicting EDM performances.

A review on current research trends in electrical discharge machining (EDM)

Surface modification by electrical discharge machining: A review

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Micro total analysis systems: latest achievements.

Parametric optimization of powder mixed electrical discharge machining by response surface methodology

Micro and Nano Machining by Electro-Physical and Chemical Processes

Electrochemical discharge machining (ECDM) is found to be a potential process for the microdrilling of glass wafers. However, some degree of heat-affected zone resulting from the thermal energy during ECDM produces several inherent problems that might be major issues, such as over cut and taper hole. To improve the quality of the ECDM microhole, a flat sidewall–flat front tool electrode is designed to reduce taper phenomena due to the sidewall discharge. In addition, a pulse voltage is applied to improve the heat-affected zone in the rectified dc voltage. The experimental results show that the combination of flat sidewall–flat front tool and pulse voltage conspicuously increases the machining accuracy while retaining the machining rate. This experimental investigation provides a new method that overcomes the disadvantages of conventional ECDM.

https://iopscience.iop.org/article/10.1088/0960-1317/17/2/012/pdf

The tool geometrical shape and pulse-off time of pulse voltage effects in a Pyrex glass electrochemical discharge microdrilling process

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.

Effect of surface roughness of tool electrode materials in ECDM performance

This paper presents a novel process using micro-electro-discharge- machining (micro-EDM) combined with ultrasonic vibration by a helical micro-tool electrode to drill and finish micro-holes. During the machining processes, a micro-tool is directly fabricated by wire electro-discharge grinding (WEDG) using micro-EDM combined with various methods for machining the micro-hole and by ultrasonic vibration to finish the hole wall. In this work, circular micro-holes are machined in a high nickel alloy by cylindrical and helical electrodes. Using a helical micro-tool electrode for micro-EDM combined with ultrasonic vibration (HE-MEDM-UV) can substantially reduce the EDM gap, taper and machining time for deep micro-hole drilling. In addition, using a helical micro-tool with micro ultrasonic vibration finishing (HE-MUVF), good surface quality and less taper of the hole wall can be obtained by applying a suitable electrode step variation, rotational speed and ultrasonic amplitude with a machining time of approximately 25 min. According to scanning electron microscopy (SEM) micrographs and atomic force microscopy (AFM) measurement, HE-MUVF can indeed improve the surface roughness from 1.345 µm Rmax before finishing to 0.58 µm Rmax after HE-MUVF. This result demonstrates that using HE-MEDM-UV combined with MUVF can yield micro-holes of precise shape and smooth surface.

https://iopscience.iop.org/article/10.1088/0960-1317/16/12/025/pdf

Using a helical micro-tool in micro-EDM combined with ultrasonic vibration for micro-hole machining

Electrochemical discharge machining (ECDM) is an effective unconventional method for micromachining in non-conducting materials, such as glass, quartz and some ceramics. However, since the spark discharge performance becomes unpredictable as the machining depth increases, it is hard to achieve precision geometry and efficient machining rate in ECDM drilling. One of the main factors for this is the lack of sufficient electrolyte flow in the narrow gap between the tool and the workpiece. In this study a magnetohydrodynamic (MHD) convection, which enhances electrolyte circulation has been applied to the ECDM process in order to upgrade the machining accuracy and efficiency. During electrolysis in the presence of a magnetic field, the Lorenz force induces the charged ions to form a MHD convection. The MHD convection then forces the electrolyte into movement, thus enhancing circulation of electrolyte. Experimental results show that the MHD convection induced by the magnetic field can effectively enhance electrolyte circulation in the micro-hole, which contributes to higher machining efficiency. Micro-holes in glass with a depth of 450 µm are drilled in less than 20 s. At the same time, better electrolyte circulation can prevent deterioration of gas film quality with increasing machining depth, while ensuring stable electrochemical discharge. The improvement in the entrance diameter thus achieved was 23.8% while that in machining time reached 57.4%. The magnetic field-assisted approach proposed in the research does not require changes in the machining setup or electrolyte but has proved to achieve significant enhancement in both accuracy and efficiency of ECDM.

https://iopscience.iop.org/article/10.1088/0960-1317/20/7/075019/pdf

Magnetic field-assisted electrochemical discharge machining

This study investigates the influence of process parameters of electrical discharge machining (EDM) on machining performances with the addition of Al and Cr powder into kerosene. In addition, the effects of powder addition on surface fine-finish and modification are also discussed. The machining process parameters of this empirical investigation included peak current, pulse duration, as well as the type of powder added, its grain size, and mixing ratio. The machining performance, characterized by material removal rate (MRR), electrode wear rate (EWR) and surface roughness, was monitored as a function of process variables. Moreover, surface modifications were also explored thoroughly. The experimental results demonstrate that addition of Al and Cr powders into the dielectric enlarges the gap distance and divides discharge current, which promotes better EDM performance. Restated, adding a mixture of Al and Cr powders into dielectric yields the best results. Moreover, during EDM, the added powder migrates and penetrates the machined surface. Test results reveal that the corrosion resistance and surface hardness was improved by adding the proper powder into dielectric.

Biing Hwa Yan

Papers

The tool geometrical shape and pulse-off time of pulse voltage effects in a Pyrex glass electrochemical discharge microdrilling process

Effect of surface roughness of tool electrode materials in ECDM performance

Using a helical micro-tool in micro-EDM combined with ultrasonic vibration for micro-hole machining

Magnetic field-assisted electrochemical discharge machining

Surface modification of SKD 61 during EDM with metal powder in the dielectric