Electrical discharge machining of submicron holes using ultrasmall-diameter electrodes

We have carried out the electrical discharge machining (EDM) of submicron holes using ultrasmall-diameter electrodes. Two types of electrode were used: tungsten electrodes fabricated by the combination of wire electrodischarge grinding and electrochemical machining, and silicon electrodes originally designed as probes for scanning probe microscopes. The diameters of the former and latter were 1 μm or less, and less than 0.15 μm, respectively. Holes were drilled using a relaxation-type pulse generator at an open-circuit voltage of less than or equal to 20 V with the machine's stray capacitance as the only capacitance. Using tungsten electrodes, holes of less than 1 μm in diameter and more than 1 μm in depth were successfully drilled. A 1.3-μm-wide slot was also fabricated by drilling many holes with a small pitch. It was possible to drill holes of approximately 0.5 μm diameter using silicon electrodes because the electrode diameter was less than those of the tungsten electrodes. These holes have the smallest reported diameter for holes drilled by EDM, indicating the possibility of submicron- and nanoscale machining by EDM.     

The development of an electrodischarge machine for micro-hole boring

This paper describes an electrodischarge machine^† for micro-hole boring capable of improved accuracy and performance in boring precision small diameter holes in components such as ink jet nozzles for printers, electron gun apertures for graphic displays, micro-connectors for high-speed computers, and optical components for telecommunications. Micro-energy discharging permits machining of 15–300 μm diameter micro-holes with a roundness accuracy of 0.5 μm or better and a surface roughness less than 0.1 μm. No bending stress is applied to the tool electrode, therefore high precision machining of cylindrical surfaces, machining with very thin side-walls, and machining of overlapping multiple-holes are all possible, regardless of the hardness of any electrically conductive material. Tool electrodes of any diameter are machinable using reversed-polarity electric discharge and are replaceable in the same way as conventional drills. Travel of the tool electrode is controlled automatically by microprocessor, thus eliminating the need for a skilled operator.     

Study of the Batch Production of Micro Parts Using the EDM Process

The micro machining of copper plates by the electrical discharge machining (EDM) process is described. Tungsten carbide was selected as the material for the electrode. Experiments were carried out on a conventional CNC-EDM machine to investigate machining of micro holes, and micro slots. The results show that micro holes, and micro slots can be successfully processed on a conventional CNC-EDM machine. To improve the productivity of micro parts using the EDM process, a batch production method of micro EDM using multi-electrodes has been studied. A new technique for preparing multi-electrodes has been developed. Results also show that the batch production of micro parts using EDM is feasible and that the batch production of micro parts using EDM process with multi-electrodes is very effective.     

On the temperature and specific energy during electrodischarge diamond grinding (EDDG)

Electrodischarge diamond grinding (EDDG) is a hybrid machining process comprising conventional grinding and electrodischarge machining (EDM) as its constituent processes. It has the potential of shaping advanced engineering materials. Temperature of the workpiece and material removal rate are chosen as responses in full factorial (3³) design with current, pulse-on time, and wheel speed as process parameters. Specific energy is a vital consideration for any machining process. EDM is known for its inefficiency. Experiments were conducted with a specially fabricated bronze disk as tool electrode to evaluate specific energy in EDM, and the results were compared with that of EDDG. It has been found that specific energy required in EDDG is less than that in EDM with a rotating disk electrode.     

Experimental study on micro EDM-drilling of Ti6Al4V using helical electrode

There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helical-shaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 μm) when using electrode helix angle of 45° and flute-depth of 50 μm, and an additional 19% with flute-depth of 150 μm. Holes of 661 μm diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V.     

Development and application of copper–nickel zirconium diboride as EDM electrodes manufactured by selective laser sintering

The production of electrical discharge machining (EDM) electrodes by conventional machining processes can account for over 50 % of the total EDM process costs. The emerging additive manufacturing (AM) technologies provide the possibility of direct fabrication of EDM electrodes. Selective laser sintering (SLS) is an alternative AM technique because it has the possibility to reduce the tool-room lead time and total EDM costs. The main difficulty of manufacturing an EDM electrode using SLS is the selection of an appropriate material. This work investigated the direct production of EDM electrodes by means of the SLS using a newly developed non-conventional metal–matrix composite material composed of a metallic matrix (CuNi) and an advanced ceramic (ZrB₂). The influence of important SLS parameters and material content on the densification behavior and porosity of the electrodes was investigated. EDM experiments were conducted to observe the electrodes behavior and performance. It was found that the ZrB₂-CuNi electrodes could be successfully manufactured by SLS. Interlayer bonding and porosity are directly influenced by the layer thickness. Smaller layer thicknesses improved bonding between layers and decreased the porosity of the parts. The laser scan speed has a significant effect on the densification behavior. The scan line spacing affects the pore structure by means of overlapping. The surface morphology of the samples was not affected by varying the scan line spacing. The ZrB₂-CuNi electrodes presented a much superior performance than SLS copper powder electrodes, but inferior to solid copper electrodes.     

Determining the energy distribution during electric discharge machining of Ti–6Al–4V

The titanium (Ti) alloys are the notoriously “difficult-to-machine” aerospace materials. Compared with the traditional mechanical cutting methods which are costly because of high tooling costs, electrodischarge machining (EDM) is an effective machining method for the Ti alloys. The energy distribution during the EDM process of Ti alloys was rarely reported, though it is a very important factor that can affect the machining performance. In this work, the energy distribution during EDM of Ti–6Al–4V has been investigated by a novel method, at different EDM parameters including interelectrode distance, pulse duration, polarity, and electrode shape. The results of this work show that energy distribution characteristics are greatly affected by the power density applied on the electrodes and more energy is distributed into the anode than into the cathode, which are in good concurrence with the results obtained by other authors. The results of this work will be helpful for further improving the technological performance of this process.     

Optimization of EDM process for multiple performance characteristics using Taguchi method and Grey relational analysis

Electrical discharge machining (EDM) is one of the most extensively used non-conventional material removal processes. The Taguchi method has been utilized to determine the optimal EDM conditions in several industrial fields. The method, however, was designed to optimize only a single performance characteristic. To remove that limitation, the Grey relational analysis theory has been used to resolve the complicated interrelationships among the multiple performance characteristics. In the present study, we attempted to find the optimal machining conditions under which the micro-hole can be formed to a minimum diameter and a maximum aspect ratio. The Taguchi method was used to determine the relations between machining parameters and process characteristics. It was found that electrode wear and the entrance and exit clearances had a significant effect on the diameter of the micro-hole when the diameter of the electrode was identical. Grey relational analysis was used to determine the optimal machining parameters, among which the input voltage and the capacitance were found to be the most significant. The obtained optimal machining conditions were an input voltage of 60V, a capacitance of 680pF, a resistance of 500Ω, the feed rate of 1.5μm/s and a spindle speed of 1500rpm. Under these conditions, a micro-hole of 40μm average diameter and 10 aspect ratio could be machined.     

超声振动辅助电火花微小孔加工中超声参数对加工效率的影响

利用研制的超声振动辅助电火花微小孔加工系统进行加工试验,研究了超声波激励电压的频率、幅值、脉宽与脉间对复合加工微孔的影响。为了考察加工效果,与传统电火花微孔加工试验进行了对比。试验结果表明,超声能显著改善极间工作液的循环,占空比为1/2时加工效率最高,超声激励电压、激励频率与加工时间成浴盆曲线关系,合理选择超声波参数可以有效提高加工效率。     

Investigation of electro-discharge micro-machining of titanium super alloy

Being a difficult-to-cut material, titanium alloy suffers poor machinability for most cutting processes, especially the drilling of micro-holes using traditional machining methods. Although electrical discharge machining (EDM) is suitable for machining titanium alloys, selection of machining parameters for higher machining rate and accuracy is a challenging task in machining micro-holes. The present research attempts to optimize micro-EDM process parameters for machining Ti-6Al-4V super alloy. To verify the optimal micro-EDM process parameters settings, metal removal rate (MRR), tool-wear rate (TWR), over cut (OC) and taper were chosen as observed performance criteria. In addition, four independent parameters such as peak current, pulse-on time, flushing pressure, and duty ratio were adopted for evaluation by the Taguchi method. From the ANOVA and S/N ratio graph, the significant process parameters and the optimal combination level of machining parameters were obtained. It is seen that machining performances are affected mostly by the peak current and pulse-on time during micro-electro-discharge machining of titanium alloy. Mathematical models have been developed to establish the relationship between various significant process parameters and micro-EDM performance criteria. In-depth studies have also been made to examine the influence of various process parameters on the white layer and surface topography through SEM micrographs of machined micro-hole.     

Micro-hole Maching of Copper Using the Electro-discharge Machining Process with a Tungsten Carbide Electrode Compared with a Copper Electrode

This paper describes micro-hole machining of a copper plate using the electro-discharge machining (EDM) process. Tungsten carbide was selected as the material for the electrode and compared with a copper-electrode. A precision centreless grinding process was employed to grind the electrode down to the desired diameter. A series of experiments were performed on a traditional EDM machine to investigate the effects of electrode material polarity setting and of a rotating electrode. Results have shown that electrode wear and hole enlargement are both smaller when positive polarity machining is selected; whereas electrode wear is larger and machining speed is higher when negative polarity machining is selected. High-quality micro-hole machining in copper can be achieved by the proposed method.     

Fabrication of multiple electrodes and their application for micro-holes array in ECM

In this study, a two-step composite processing technology combining the EDM process and electrochemical etching is introduced to fabricate a micro-electrodes array. Firstly, rectangular columns measuring 0.2×0.2 mm are machined by the wire-EDM (electrical discharge machining) machine tool, then electrochemical etching is used to erode the microelectrodes array into cylindrical columns. Results show that microelectrodes ranging from hundreds of micrometers to several millimeters could be prepared. Then the machined microelectrodes are used as a cathode tool for electrochemical drilling of micro-hole arrays in electrochemical micromachining (EMM). Furthermore, various parameters affecting the performance of EMM are discussed in detail. Results indicate that the production of EMM improves by using multiple microelectrodes. The pulse current shows strong localization in micro-hole drilling and improves the machining accuracy.     

Experimental study and parameter design of electro-discharge diamond grinding

Electrical discharge diamond grinding (EDDG), which integrates diamond grinding and electro-discharge machining (EDM), is a new hybrid machining process for shaping electrically conductive very hard materials. The process employs synergetic interactive effect of electro-discharge action and abrasion action to increase machining performance. This paper presents an investigation on the experimental study and machining parameter design of electro-discharge diamond grinding (EDDG). The EDDG setup was designed and fabricated, and experiments were conducted on high speed steel (HSS) workpiece under varying current, pulse-ontime, duty factor and wheel speed. The settings of machining parameters were determined by using the Taguchi experimental design method. The level of the machining parameters on the MRR is determined by using analysis of variance (ANOVA). The optimum machining parameter combination was obtained by using the evaluated S/N ratio.     

A method to predict possibility of arcing in EDM of TiB2p reinforced ferrous matrix composite

Electrical Discharge Machining (EDM) is very popular for machining conductive metal matrix composites (MMCs) because the hardness rendered by the ceramic reinforcements to these composites causes very high tool wear and cutting forces in conventional machining processes. EDM requires selection of a number of parameters for desirable results. Inappropriate parameter selection can lead to high overcuts, tool wear, excessive roughness, and arcing during machining and adversely affect machining quality. Arcing leads to short circuit gap conditions resulting in large energy discharges and uncontrolled machining. Arcing is a detrimental phenomenon in EDM which causes spoiling of workpiece and tool electrode and tends to damage the power supply of EDM machine. Parameter combinations that lead to arcing during machining have to be identified and avoided for every tool, work material, and dielectric combination. Proper selection of parameter combinations to avoid arcing is essential in EDM. In the work, experiments were conducted using L27 design of experiment to determine the parameter settings which cause arcing in EDM machining of TiB₂p reinforced ferrous matrix composite. Important EDM process parameters were selected in roughing, intermediate, and finishing range so as to study the occurrence of arcing. Using the experimental data, an artificial neural network (ANN) model was developed as a tool to predict the possibility of arcing for selected parameter combinations. This model can help avoid the parameter combinations which can lead to arcing during actual machining using EDM. The ANN model was validated by conducting validation experiments to ensure that it can work accurately as a predicting tool to know beforehand whether the selected parameters will lead to arcing during actual machining using EDM. Validation results show that the ANN model developed can predict arcing possibility accurately when the depth of machining is included as input variable for the model.     

Effects of Powder Characteristics on Electrodischarge Machining Efficiency

This paper presents the effects of various powder characteristics on the efficiency of electrodischarge machining (EDM) SKD-11. The additives examined include aluminium (Al), chromium (Cr), copper (Cu), and silicon carbide (SiC) powders that have significant differences in their thermophysical properties. The machining mechanism with the addition of the foreign particles, the tool wear rate (TWR), and the material removal rate (MRR) have been investigated. It was found experimentally that the particle concentration, the particle size, the particle density, the electrical resistivity, and the thermal conductivity of powders were important characteristics that significantly affected the machining performance in the EDM process. Proper addition of powders to the dielectric fluid increased the MRR and, thus, decreased the TWR. Under the same particle concentration experiments, the smallest suspended particle size led to the greatest MRR and, thus, the lowest TWR. Of the additives investigated, chromium powder produced the greatest MRR and the lowest TWR, whereas the process without foreign particles has the converse effects. The addition of copper powder to the dielectric fluid was found to make almost no difference to the pure kerosene EDM system.     

一种微小孔电火花加工模糊控制策略研究

针对微小孔电火花加工(EDM)放电环境恶劣、放电间隙状态复杂多变,以及采用传统的PID控制策略难于达到预期效果等问题,提出了一种基于多层压电陶瓷叠加驱动下的控制策略,并对其进行了控制算法研究,设计了一种微小孔电加工微进给模糊PID自适应控制系统,并进行了仿真试验来验证其控制效果。研究结果表明,采用模糊自适应控制策略能加快微进给系统的响应速度,具有稳定性好、精度高等优点,并得到了良好的控制效果,为微小孔电加工机床的实际应用打下了良好的理论基础。     

Development and application of new composite materials as EDM electrodes manufactured via selective laser sintering

The cost of a part manufactured by electrical dischargeEDM machining (EDM) is mainly determined by electrode cost. The production of electrodes by conventional machining processes is complex, time consuming, and can account for over 50 % of the total EDM process costs. The emerging additive manufacturing (AM) technologies provide the possibility of direct fabrication of EDM electrodes. Selective laser sintering (SLS) is an alternative AM technique because it has the possibility to directly produce functional components, reducing the tool-room lead time and total EDM costs. The main difficulty of manufacturing an EDM electrode using SLS is the selection of an appropriate material, once both processes require different material properties. The current work focused on the investigation of appropriate materials that fulfill EDM and SLS process demands. Three new metal-matrix materials composed of Mo–CuNi, TiB₂–CuNi, and ZrB₂–CuNi were developed and characterized. Electrodes under adequate SLS conditions were manufactured through a systematic methodology. EDM experiments using different discharge energies were carried out, and the performance evaluated in terms of material removal rate and volumetric relative wear. The results showed that the powder systems composed of Mo–CuNi, TiB₂–CuNi, and ZrB₂–CuNi revealed to be successfully processed by SLS, and the EDM experiments demonstrated that the new composite electrodes are promising materials. The work also suggests important topics for future research work on this field.     

Improvement of EDM efficiency of silicon single crystal through ohmic contact

This paper describes the improvement of the machining rate of electrical discharge machining (EDM) for silicon single crystals by reducing the contact resistance between the silicon single crystal and metal electric feeder. To decrease the resistance of the rectifying contact between a p-type silicon wafer and the metal feeder, attempts to achieve ohmic contact were made by plating the contact surface of the silicon wafer with aluminum by vacuum evaporation, followed by the diffusion process. To accomplish an ohmic contact between n-type silicon and metal, gold–antimony alloy was used in place of aluminum. The influence of polarity on the machining rate is also discussed from the viewpoint of the rectifying nature of the interface between the arc plasma and silicon single crystal.     

High efficiency fine boring of monocrystalline silicon ingot by electrical discharge machining

This article deals with high efficiency and high accuracy fine boring in a monocrystalline silicon ingot by electrical discharge machining (EDM). In manufacturing process of integrated circuits, a plasma-etching process is used for removing oxidation films. This process has recently been examined for use of monocrystalline silicon as the electrode to minimize the contamination. However, it is difficult to machine silicon accurately by the conventional diamond drilling method, because the material removal is due to brittle fracture. The machining force in the EDM process is very small compared with that in conventional machining, therefore, the possibility of high efficiency and high accuracy boring holes in silicon ingot by EDM is experimentally investigated. The removal rate of monocrystalline silicon by EDM is much higher than that of steel, while the electrode wear is extremely small. The improvement method leads to a better hole without chipping at the exit of hole or sticking of the insulator on the wall of hole. Furthermore, it is proved that even a high aspect ratio of about 200 boring is possible.     

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

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