Surface Modification Process by Electrical Discharge Machining with Ti Powder Green Compact Electrode

This paper describes a new method of surface modification by Electrical Discharge Machining (EDM). By using ordinary EDM machine tool and kerosene fluid, a hard ceramic layer can be created on the workpiece surface with Ti or other compressed powder electrode in a certain condition. This new revolutionary 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 thermal and chemical reaction between the worn electrode material and the carbon particle decomposed from kerosene fluid under high temperature. The carbide is piled up on a workpiece quickly and becomes a hard layer of ceramic about 20 μm in several minutes. This paper studies the principle and process of EDC systemically by using Ti powder green compact electrode. In order to obtain a layer of compact ceramic film, it is very important to select proper electric pulse parameters, such as pulse width, pulse interval, peak current. Meantime, the electrode materials and its forming mode will effect the machining surface quality greatly. This paper presents a series of experiment results to study the EDC process by adopt different technology parameters. Experiments and analyses show that a compact TiC ceramic layer can be created on the surface of metal workpiece. The hardness of ceramic layer is more 3 times higher than the base body, and the hardness changes gradiently from surface to base body. The method will have a great future because many materials can be easily added to the electrode and then be coated on the workpiece surface. Gearing the parameters ceramic can be created with different thickness. The switch between deposition and removal process is carried out easily by changing the polarity, thus the gear to the thickness and shape of the composite ceramic layer is carried out easily. This kind of composite ceramic layer will be used to deal with the surface of the cutting tools or molds possibly, in order to lengthen their life. It also can be found wide application in the fields of surface repairing and strengthening of the ship or aircraft.

A special CAD/CAM software for electro-discharge machining of shrouded turbine blisks

In this paper, a special-purpose CAD/CAM software package, BliskCad/Cam, based on a commercial CAD/CAM software Unigraphics is developed to reduce difficulties in CNC-EDM of the shrouded turbine blisks. The software package consists of five modules such as electrode design, path searching, and machining simulation module. Functions of BliskCad/Cam include parametrical reconstruction of 3-D model of the blisk, intelligent design of complex shaped electrode, automatic generation of NC codes, search of interference-free tool path for multi-axis NC-EDM and machining simulation, etc. Experimental verification is conducted by using BliskCad/Cam and the results show that it satisfies the requirements, and can realize precision machining and reduce accessorial time remarkably.

RESEARCH OF MICRO ELECTRO DISCHARGE MACHINING EQUIPMENT AND PROCESS TECHNIQUES

Micro electro discharge machining (micro EDM) is a feasible way tomanufacture micro structures and has potential application in advanced industrial fields. For therealization of micro EDM, it is necessary to pay careful attention to its equipment design and thedevelopment of process techniques. The present status of research and development of micro EDMequipment and process techniques is overviewed. A micro electro discharge machine incorporated withan inchworm type of micro feed mechanism is introduced, and a micro electro discharge machine fordrilling micro holes suitable to industrial use is also introduced. Some of the machiningexperiments carried out on the micro EDM prototypes are shown and the feasibility of the micro EDMtechnology to practical use is discussed.

Experimental Research on Effects of Process Parameters on Servo Scanning 3D Micro Electrical Discharge Machining

Servo scanning 3D micro electrical discharge machining (3D SSMEDM) is a novel and effective method in fabricating complex 3D micro structures with high aspect ratio on conducting materials. In 3D SSMEDM process, the axial wear of tool electrode can be compensated automatically by servo-keeping discharge gap, instead of the traditional methods that depend on experiential models or intermittent compensation. However, the effects of process parameters on 3D SSMEDM have not been reported up until now. In this study, the emphasis is laid on the effects of pulse duration, peak current, machining polarity, track style, track overlap, and scanning velocity on the 3D SSMEDM performances of machining efficiency, processing status, and surface accuracy. A series of experiments were carried out by machining a micro-rectangle cavity (900 μm×600 μm) on doped silicon. The experimental results were obtained as follows. Peak current plays a main role in machining efficiency and surface accuracy. Pulse duration affects obviously the stability of discharge state. The material removal rate of cathode processing is about 3/5 of that of anode processing. Compared with direction-parallel path, contour-parallel path is better in counteracting the lateral wear of tool electrode end. Scanning velocity should be selected moderately to avoid electric arc and short. Track overlap should be slightly less than the radius of tool electrode. In addition, a typical 3D micro structure of eye shape was machined based on the optimized process parameters. These results are beneficial to improve machining stability, accuracy, and efficiency in 3D SSMEDM.

Machining performance on hybrid process of abrasive jet machining and electrical discharge machining

To develop a hybrid process of abrasive jet machining (AJM) and electrical discharge machining (EDM),the effects of the hybrid process parameters on machining performance were comprehensively investigated to confirm the benefits of this hybrid process.The appropriate abrasives delivered by high speed gas media were incorporated with an EDM in gas system to construct the hybrid process of AJM and EDM,and then the high speed abrasives could impinge on the machined surface to remove the recast layer caused by EDM process to increase the efficiency of material removal and reduce the surface roughness.In this study,the benefits of the hybrid process were determined as the machining performance of hybrid process was compared with that of the EDM in gas system.The main process parameters were varied to explore their effects on material removal rate,surface roughness and surface integrities.The experimental results show that the hybrid process of AJM and EDM can enhance the machining efficiency and improve the surface quality.Consequently,the developed hybrid process can fit the requirements of modern manufacturing applications.

Parameter optimization model in electrical discharge machining process

Electrical discharge machining (EDM) process, at present is still an experience process, wherein selected parameters are often far from the optimum, and at the same time selecting optimization parameters is costly and time consuming. In this paper, artificial neural network (ANN) and genetic algorithm (GA) are used together to establish the parameter optimization model. An ANN model which adapts Levenberg-Marquardt algorithm has been set up to represent the relationship between material removal rate (MRR) and input parameters, and GA is used to optimize parameters, so that optimization results are obtained. The model is shown to be effective, and MRR is improved using optimized machining parameters.

Scale Effects and a Method for Similarity Evaluation in Micro Electrical Discharge Machining

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

Electrical discharge machining of 6061 aluminium alloy

The wire electrical discharge machining（EDM） of 6061 aluminium alloy in terms of material removal rate,kerf/slit width,surface finish and wear of electrode wire for different pulse on time and wire tension was studied.Eight experiments were carried out in a wire EDM machine by varying pulse on time and wire tension.It is found that the material removal rate increases with the increase of pulse on time though the wire tension does not affect the material removal rate.It seems that the higher wire tension facilitates steady machining process,which generates low wear in wire electrode and better surface finish.The surface roughness does not change notably with the variation of pulse on time.The appearance of the machined surfaces is very similar under all the machining conditions.The machined surface contains solidified molten material,splash of materials and blisters.The increase of the pulse on time increases the wear of wire electrode due to the increase of heat input.The wear of wire electrode generates tapered slot which has higher kerf width at top side than that at bottom side.The higher electrode wear introduces higher taper.

Surface performance of workpieces processed by electrical discharge machining in gas

The surface performance of workpieces processed by electrical discharge machining in gas(dry EDM)was studied in this paper.Firstly,the composition,micro hardness and recast layer of electrical discharge machined(EDMed)surface of 45 carbon steels in air were investigated through different test analysis methods.The results show that the workpiece surface EDMed in air contains a certain quantity of oxide,and oxidation occurs on the workpiece surface.Compared with the surface of workpieces processed in kerosene,fewer cracks exist on the dry EDMed workpiece surface,and the surface recast layer is thinner than that obtained by conventional EDM.The micro hardness of workpieces machined by dry EDM method is lower than that machined in kerosene,and higher than that of the matrix.In addition,experiments were conducted on the surface wear resistance of workpieces processed in air and kerosene using copper electrode and titanium alloy electrode.The results indicate that the surface wear resistance of workpieces processed in air can be improved,and it is related with tool material and dielectric.

Comparative study on discharge conditions in micro-hole electrical discharge machining of tungsten carbide (WC-Co) material

WC-Co is used widely in die and mold industries due to its unique combination of hardness, strength and wear-resistance. For machining difficult-to-cut materials, such as tungsten carbide, micro-electrical discharge machining(EDM) is one of the most effective methods for making holes because the hardness is not a dominant parameter in EDM. This paper describes the characteristics of the discharge conditions for micro-hole EDM of tungsten carbide with a WC grain size of 0.5 μm and Co content of 12%. The EDM process was conducted by varying the condenser and resistance values. A R-C discharge EDM device using arc erosion for micro-hole machining was suggested. Furthermore, the characteristics of the developed micro-EDM were analyzed in terms of the electro-optical observation using an oscilloscope and field emission scanning electron microscope.

Integrated CAD/CAPP/CAM system for electric discharge machining

An integrated CAD/CAPP/CAM system modeling for Electric Discharge Machining (EDM) is constructed on the basis of an integrated engineering database. EDM feature objects are developed using the object oriented database provided by AutoCAD R14, and EDM feature modeling is realized in AutoCAD environments.

Modelling effect of magnetic field on material removal in dry electrical discharge machining

One of the reasons for increased material removal rate in magnetic field assisted dry electrical discharge machining （EDM） is confinement of plasma due to Lorentz forces. This paper presents a mathematical model to evaluate the effect of external magnetic field on crater depth and diameter in single- and multiple-discharge EDM process. The model incorporates three main effects of the magnetic field, which include plasma confinement, mean free path reduction and pulsating magnetic field effects. Upon the application of an external magnetic field, Lorentz forces that are developed across the plasma column confine the plasma column. Also, the magnetic field reduces the mean free path of electrons due to an increase in the plasma pressure and cycloidal path taken by the electrons between the electrodes. As the mean free path of electrons reduces, more ionization occurs in plasma column and eventually an increase in the current density at the inter-electrode gap occurs. The model results for crater depth and its diameter in single discharge dry EDM process show an error of 9%-10% over the respective experimental values.

A Study on Modelling Surface Finish in Electrical Discharge Machining Tablet Shape Punches Using Response Surface Methodology

This paper introduces a study on modelling surface finish in EDM （Electrical Discharge Machining） of tablet shape punches when using copper as electrode material. In this study, 27 experiments were performed based on BBD （Box-Behnken Design） and the work-piece material was 9CrSi steel. The input process parameters were the current, the pulse on time, the pulse off time and the voltage. The effects of the input parameters on the surface finish were evaluated by analysing variance. Besides, from the results of the experiments, a regression equation for determining the surface roughness is introduced. Also, the optimum input parameter values were found in order to get the minimum surface roughness.

Modeling and Optimization of Electrical Discharge Machining of SiC Parameters, Using Neural Network and Non-Dominating Sorting Genetic Algorithm (NSGA II)

Silicon Carbide (SiC) machining by traditional methods with regards to its high hardness is not possible. Electro Discharge Machining, among non-traditional machining methods, is used for machining of SiC. The present work is aimed to optimize the surface roughness and material removal rate of electro discharge machining of SiC parameters simultaneously. As the output parameters are conflicting in nature, so there is no single combination of machining parameters, which provides the best machining performance. Artificial neural network (ANN) with back propagation algorithm is used to model the process. A multi-objective optimization method, non-dominating sorting genetic algorithm-II is used to optimize the process. Affects of three important input parameters of process viz., discharge current, pulse on time (Ton), pulse off time (Toff) on electric discharge machining of SiC are considered. Experiments have been conducted over a wide range of considered input parameters for training and verification of the model. Testing results demonstrate that the model is suitable for predicting the response parameters. A pareto-optimal set has been predicted in this work.

Fabrication of Micro Structures by Ultrashort Voltage Pulse Electrical Discharge Machining

The machining of small holes and array holes has been a difficult problem in machining field. Tiny hole is widely used in mechanical field, for instance, fuel injection nozzles, spinneret holes for synthetic fibers and wire drawing dies. This paper investigated the application of EDM (electrical discharge machining) to the fabrication of micro structures. There are obvious limitations in the process of micro-electrical discharge machining, such as electrode wear, unstable discharge condition and low machining efficiency. The effects of EDM parameters were investigated, such as voltage, pulse frequency, and frequency of ultrasonic vibration applied to electrode. Micro holes were machined with Pt electrode made by focused-ion-beam chemical vapor deposition (FIB-CVD) and Cu electrode made by wire-electrode cutting. The comparison experiments between EDM and ECM (electrochemical machining) indicated that the processing of ECM has serious stray current corrosion and poor machining precision. Moreover, the workpiece vibration was firstly proposed to be utilized in the micro-electrical discharge machining. It can be concluded that maximum machine could be obtained under the amplitude ratio of 76%, which was an appropriate parameter.

Review on non-conventional machining of shape memory alloys

Shape memory alloys （SMAs） are the developing advanced materials due to their versatile specific properties such as pseudoelasticity, shape memory effect （SME）, biocompatibility, high specific strength, high corrosion resistance, high wear resistance and high anti-fatigue property. Therefore, the SMAs are used in many applications such as aerospace, medical and automobile. However, the conventional machining of SMAs causes serious tool wear, time consuming and less dimensional deformity due to severe strain hardening and pseudoelasticity. These materials can be machined using non-conventional methods such as laser machining, water jet machining （WJM） and electrochemical machining （ECM）, but these processes are limited to complexity and mechanical properties of the component. Electrical discharge machining （EDM） and wire EDM （WEDM） show high capability to machine SMAs of complex shapes with precise dimensions. The aim of this work is to present the consolidated references on the machining of SMAs using EDM and WEDM and subsequently identify the research gaps. In support to these research gaps, this work has also evolved the future research directions.

超声振动辅助电火花加工表面成形机理研究

以TC4钛合金作为工件材料,通过建立高斯热源在工件表面的分布模型,描述了单脉冲电火花加工凹坑的成形机理。为了验证模型的准确性,进行了仿真和实验验证。结果表明:通过分析仿真得到的温度场云图和实验测得的数据发现,高斯热源分布模型与两者一致。在引入超声振动后,表面粗糙度降低35%~46%,材料表面凹坑明显减少,表面形貌发生显著变化。随振幅增大,高斯热源分布曲线的最大值减小,温度场中心最高温度降低,深度变浅的表面凹坑数量增加,单个凹坑的面积增加,表面粗糙度变好。

Machining of a film-cooling hole in a single-crystal superalloy by high-speed electrochemical discharge drilling

Single-crystal superalloys are typical advanced materials used for manufacturing aero- engine turbine blades. Their unique characteristics of high hardness and strength make them exceedingly difficult to machine. However, a key structure of a turbine blade, the film-cooling hole, needs to be machined in a single-crystal superalloy; such machining is challenging, especially considering the increasing levels of machining efficiency and quality demanded by the aeroengine industry. Tube electrode high-speed electrochemical discharge drilling （TSECDD）, a hybrid technique of high-speed electrical discharge drilling and electrochemical machining, provides high machining efficiency and accuracy, as well as eliminating the recast layer. In this study, TSECDD is used to machine a film-cooling hole in a nickel-based single-crystal superalloy （DD6）. The Tagu- chi methods of experiment are used to optimise the machining parameters. Experimental results show that TSECDD can effectively drill the film-cooling hole; the optimum parameters that give the best performance are as follows： pulse duration： 12μs, pulse interval： 30 gs, peak current： 6 A, and salt solution conductivity： 3 mS/cm. Finally, a hole is machined by TSECDD, and the results are compared with those obtained by electrical discharge machining. TSECDD is found to be promising for improving the surface quality and eliminating the recast layer.

Electrode Wear Prediction in Milling Electrical Discharge Machining Based on Radial Basis Function Neural Network

Milling electrical discharge machining(EDM) enables the machining of complex cavities using cylindrical or tubular electrodes.To ensure acceptable machining accuracy the process requires some methods of compensating for electrode wear.Due to the complexity and random nature of the process,existing methods of compensating for such wear usually involve off-line prediction.This paper discusses an innovative model of electrode wear prediction for milling EDM based upon a radial basis function(RBF) network.Data gained from an orthogonal experiment were used to provide training samples for the RBF network.The model established was used to forecast the electrode wear,making it possible to calculate the real-time tool wear in the milling EDM process and,to lay the foundations for dynamic compensation of the electrode wear on-line.This paper demonstrates that by using this model prediction errors can be controlled within 8%.

金属钨小孔电火花–电解复合能场加工工艺研究

钨具有一系列优良的物理化学性能,可以满足航天材料的性能要求,已广泛应用于卫星、飞机及航空发动机等设备的一些关键部件。在使用传统加工技术制造零件时,加工过程通常受到零件和刀具界面处发热、弹性和塑性变形、高刀具磨损率及工件材料特性改变等问题的限制。电火花加工(EDM)技术是导电材料最有效的加工工艺之一,但对于金属钨小孔的制造,现有的电火花加工工艺可靠性和加工效率仍无法满足加工需求。提出在具有一定电导率的盐溶液下电火花–电解复合能场加工金属钨小孔的方法,分析加工时材料去除的机理,该方法利用电解作用在工具电极端产生氢气并形成气膜,促进两极之间等离子体放电通道的快速形成。开展了加工工艺优化试验,分析不同参数对加工特性的影响规律。在脉冲宽度3μs、脉冲间隙20μs、峰值电流14.17A、工作液浓度18 g/L的NaNO_(3)电解液下获得了高效率高质量的金属钨小孔。