Showing papers on "Electrical discharge machining published in 2006"

Multi response optimization of wire EDM operations using robust design of experiments

Abstract: In this present study a multi response optimization method using Taguchi’s robust design approach is proposed for wire electrical discharge machining (WEDM) operations. Experimentation was planned as per Taguchi’s L16 orthogonal array. Each experiment has been performed under different cutting conditions of pulse on time, wire tension, delay time, wire feed speed, and ignition current intensity. Three responses namely material removal rate, surface roughness, and wire wear ratio have been considered for each experiment. The machining parameters are optimized with the multi response characteristics of the material removal rate, surface roughness, and wire wear ratio. Multi response S/N (MRSN) ratio was applied to measure the performance characteristics deviating from the actual value. Analysis of variance (ANOVA) is employed to identify the level of importance of the machining parameters on the multiple performance characteristics considered. Finally experimental confirmation was carried out to identify the effectiveness of this proposed method. A good improvement was obtained.

A finite element model of EDM based on the Joule effect

Abstract: A thermal–electrical model was developed for sparks generated by electrical discharge in a liquid media. A cylindrical shape has been used for the discharge channel created between the electrodes. The discharge channel being an electrical conductor will dissipate heat, which can be explained by the Joule heating effect. The amount of heat dissipated varies with the thermal–physical properties of the conductor; as a result, the maximum temperature reached is different. In the present model, the radii value of the conductor is a function of the current intensity and pulse duration. The thermal–physical values used in the model are the average of both the ambient and melting value. Copper and iron are the materials used for anode and cathode, respectively. The Finite Element Analysis (FEA) results were compared with the experimental values of the table of AGIE SIT used by other researchers [D.D. DiBitonto, P.T. Eubank, M.R. Patel, M.A. Barrufet, Theoretical models of the electrical discharge machining process—I: a simple cathode erosion model, Journal of Applied Physics, 66(9) (1989) 4095–4103; M.R. Patel, M.A. Barrufet, P.T. Eubank, D.D. DiBitonto, Theoretical models of the electrical discharge machining process—II: the anode erosion model, Journal of Applied Physics, 66(9) (1989) 4104–4111; P.T. Eubank, M.R. Patel, M.A. Barrufet, B. Bozkurt, Theoretical models of the electrical discharge machining process—III: the variable mass, cylindrical plasma model, Journal of Applied Physics, 73(11) (1993) 7900–7909]. In order to show the universality of the model it was obtained results for all current intensity values of the table. The Tool Wear Ratio (TWR) and Material Removal Rate (MRR) as well as surface roughness results agree reasonably well with the researcher's values found for that table and itself.

Taguchi and Gauss elimination method: A dual response approach for parametric optimization of CNC wire cut EDM of PRAlSiCMMC

Abstract: Machining parameters tables provided by the machine tool manufacturers often do not meet the operator requirements and sometimes even do not provide efficient guidelines to manufacturing engineers. Hence, a suitable selection of machining parameters of CNC wire cut electrical discharge machining (EDM) process is necessary. This paper present a reliable set of parameters that demonstrate versatility, and numerous and diverse range based on experience and technology. We offer an experimental investigation to determine the parameters setting during the machining of aluminium-reinforced silicon carbide metal matrix composite (Al/SiC-MMC). The Taguchi method, a powerful tool for experimental design, is used to optimize the CNC-wire cut-EDM parameters. According to the Taguchi quality design Concept, a L18 (21×37) mixed orthogonal array was used to determine the S/N ratio, and an analysis of variance (ANOVA) and the F-test values were used to indicate the significant machining parameters affecting the machining performance. From experimental results and through ANOVA and F-test values, the significant factors are determined for each machining performance criteria, such as the metal removal rate, surface roughness, gap current and spark gap (gap width). Considering these significant CNC wire cut-EDM parameters, verification of the improvement in the quality characteristics for machining Al/SiC-MMC was made with a confirmation test with respect to the chosen initial or reference parameter setting. Mathematical models relating to the machining performance are established using the Gauss elimination method for the effective machining of Al/SiC-MMC. Yet again, confirmation test results also show that the developed mathematical models are appropriate for the effective machining of Al/SiC-MMC. The determined optimal combination of CNC-wire cut-EDM parameters obtained from the study satisfy the real requirement of quality machining of Al/SiC MMC in practice.

An investigation of ultrasonic-assisted electrical discharge machining in gas

Abstract: 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.

Parametric optimisation of wire electrical discharge machining of γ titanium aluminide alloy through an artificial neural network model

Abstract: In the present research, wire electrical discharge machining (WEDM) of γ titanium aluminide is studied. Selection of optimum machining parameter combinations for obtaining higher cutting efficiency and accuracy is a challenging task in WEDM due to the presence of a large number of process variables and complicated stochastic process mechanisms. In general, no perfect combination exists that can simultaneously result in both the best cutting speed and the best surface finish quality. This paper presents an attempt to develop an appropriate machining strategy for a maximum process criteria yield. A feed-forward back-propagation neural network is developed to model the machining process. The three most important parameters – cutting speed, surface roughness and wire offset – have been considered as measures of the process performance. The model is capable of predicting the response parameters as a function of six different control parameters, i.e. pulse on time, pulse off time, peak current, wire tension, dielectric flow rate and servo reference voltage. Experimental results demonstrate that the machining model is suitable and the optimisation strategy satisfies practical requirements.

The gas film in Spark Assisted Chemical Engraving (SACE) - A key element for micro-machining applications

Abstract: Machining of various electrically non-conductive materials is possible with Spark Assisted Chemical Engraving (SACE) Even though this technology presents several interesting properties like simplicity, flexibility and the possibility to obtain very smooth machined surfaces, it has one severe weakness: reproducible machining can hardly be achieved One of the main limiting factors is the unstable gas film around the tool electrode in which the necessary electrical discharges for machining take place The known facts about this gas film are reviewed and a theoretical model allowing an estimation of its thickness is derived An experimental method for measuring this thickness using the inspection of the current-voltage characteristics of the process is presented Several methods to obtain more reproducible machining are proposed It is demonstrated that decreasing the gas film thickness by changing the wettability of the tool electrode can result in significantly higher machining repeatability

Parametric optimization of wire electrical discharge machining (WEDM) process using taguchi method

Abstract: Wire electrical discharge machining (WEDM) is a specialized thermal machining process capable of accurately machining parts of hard materials with complex shapes. Parts having sharp edges that pose difficulties to be machined by the main stream machining processes can be easily machined by WEDM process. Technology of the WEDM process is based on the conventional EDM sparking phenomenon utilizing the widely accepted non-contact technique of material removal with a difference that spark is generated at wire and work piece gap. Since the introduction of the process, WEDM has evolved as a simple means of making tools and dies to the best alternative of producing micro-scale parts with the highest degree of dimensional accuracy and surface finish. This paper outlines the development of a model and its application to optimize WEDM machining parameters. Experiments are conducted to test the model and satisfactory results are obtained. The methodology described here is expected to be highly beneficial to manufacturing industries, and also other areas such as aerospace, automobile and tool making industries.

An experimental study for determination of the effects of machining parameters on surface roughness in electrical discharge machining (EDM)

Abstract: Electrical discharge machining (EDM) is a non-traditional production method that has been widely used in the production of dies throughout the world in recent years. The most important performance measure in EDM is the surface roughness; among other measures material removal and tool wear rates could be listed. In this study, experiments were performed to determine parameters effecting surface roughness. The data obtained for performance measures have been analyzed using the design of experiments methods. A considerably profound equation is obtained for the surface roughness using power, pulse time, and spark time parameters. The results are discussed.

Machining Characteristics and Optimization of Machining Parameters of SKH 57 High-Speed Steel Using Electrical-Discharge Machining Based on Taguchi Method

Abstract: The effects of the machining parameters in electrical-discharge machining (EDM) on the machining characteristics of SKH 57 high-speed steel were investigated. A well-designed experimental scheme was used to reduce the total number of experiments. Parts of the experiment were conducted with the L18 orthogonal array based on the Taguchi method. Moreover, the signal-to-noise ratios associated with the observed values in the experiments were determined by ANOVA and F-test. The significant parameters that critically influenced the machining characteristics were examined, and the optimal combination levels of machining parameters for material removal rate, electrode wear rate, and surface roughness were determined.

An experimental investigation of tool wear in electric discharge machining

Abstract: In this study, the variations of geometrical tool wear characteristics – namely, edge and front wear – and machining performance outputs – namely, workpiece removal rate, tool wear rate, relative wear and workpiece surface roughness – were investigated with varying machining parameters. Experiments were conducted using steel workpieces and round copper tools with a kerosene dielectric under different dielectric flushing conditions (injection, suction and static), discharge currents and pulse durations. The experiments have shown that machining parameters and dielectric flushing conditions had a large effect on geometric tool wear characteristics and machining performance outputs. Additionally, published research on tool wear is presented in detail in this study.

Finite element prediction of material removal rate due to electro-chemical spark machining

Abstract: Electro-chemical spark machining (ECSM) is an innovative hybrid machining process, which combines the features of the electro-chemical machining (ECM) and electrodischarge machining (EDM). Unlike ECM and EDM, ECSM is capable of machining electrically non-conducting materials. This paper attempts to develop a thermal model for the calculation of material removal rate (MRR) during ECSM. First, temperature distribution within zone of influence of single spark is obtained with the application of finite element method (FEM). The nodal temperatures are further post processed for estimating MRR. The developed FEM based thermal model is found to be in the range of accuracy with the experimental results. Further the parametric studies are carried out for different parameters like electrolyte concentration, duty factor and energy partition. The increase in MRR is found to increase with increase in electrolyte concentration due to ECSM of soda lime glass workpiece material. Also, the change in the value of MRR for soda lime glass with concentration is found to be more than that of alumina. MRR is found to increase with increase in duty factor and energy partition for both soda lime glass and alumina workpiece material.

Fabrication of multiple electrodes by reverse EDM and their application in micro ECM

Abstract: Micro electrodes of various shapes were fabricated by reverse electrical discharge machining (REDM). The machining characteristics of REDM were investigated under varying capacitances and applied voltages, and optimal conditions for stable machining were suggested. Multiple-tipped micro electrodes fabricated by REDM were then introduced for micro electrochemical machining in order to increase productivity over single micro electrodes. By using various multiple electrodes, micro hole arrays, grooves and channels were machined on stainless steel.

Characterization of electrical discharge machining plasmas

Abstract: Electrical Discharge Machining (EDM) is a well-known machining technique since more than fifty years. Its principle is to use the eroding effect on the electrodes of successive electric spark discharges created in a dielectric liquid. EDM is nowadays widely-used in a large number of industrial areas. Nevertheless, few studies have been done on the discharge itself and on the plasma created during this process. Further improvements of EDM, especially for micro-machining, require a better control and understanding of the discharge and of its interaction with the electrodes. In this work, the different phases of the EDM process and the properties of the EDM plasma have been systematically investigated with electrical measurements, with imaging and with time- and spatially-resolved optical emission spectroscopy. The pre-breakdown phase in water is characterized by the generation of numerous small hydrogen bubbles, created by electrolysis. Since streamers propagate more easily in a gaseous medium, these bubbles can facilitate the breakdown process. In oil, no bubbles are observed. Therefore, the breakdown mechanism in oil could be rather enhanced by particles present in the electrode gap. Fast pulses of current and light are simultaneously measured during the pre-breakdown. These pulses are characteristic of the propagation of streamers in the dielectric liquid. The pre-breakdown duration is not constant for given discharge parameters, but distributed following a Weibull distribution. This shows that the breakdown is of stochastic nature. After the breakdown, the plasma develops very rapidly ( 2·1018 cm-3 during the first microsecond). Then it decreases with time, remaining nevertheless above 1016 cm-3 after 50 μs. During the whole discharge, the density is slightly higher in the plasma center. The EDM plasma has such a high density because it is formed from a liquid, and because it is constantly submitted to the pressure imposed by the surrounding liquid. This extreme density produces spectra with strongly-broadened spectral lines, especially the Hα line, and with an important continuum. During the first microsecond when the density is at its maximum, spectral lines are so broadened that they are all merged into a continuum. The low temperature and the high density of the EDM plasma make it weakly non-ideal. Its typical coupling parameter Γ is indeed around 0.3, reaching 0.45 during the first microsecond. In this plasma, the Coulomb interactions between the charged particles are thus of the same order as the mean thermal energy of the particles, which produces coupling phenomena. Spectroscopic results confirm the non-ideality of the EDM plasma. The strong broadening and shift of the Hα line and its asymmetric shape and complex structure, the absence of the Hβ line, and the merging of spectral lines are typical of nonideal plasmas. The EDM plasma has thus extreme physical properties, and the physics involved is astonishingly complex.

Surface and Sub-Surface Quality of Steel after EDM†

Abstract: This paper deals with the influence of electrical discharge machining (EDM) on surface and sub-surface quality in the manufacturing of mould and tool steel. The thermal nature of material removal by EDM yields a thermally affected zone at the surface of the manufactured part. This zone consists of a molten and resolidified layer, and a heat affected zone, showing properties that differ considerably from the base material. Based on experimental investigations with three types of EDM processes (sinking EDM, wire EDM and milling EDM), the influence of process parameters on surface and sub-surface properties is discussed. These include surface roughness, sub-surface micro-structure and composition, micro-hardness and residual stresses. Attention goes to the dangers of surface degradation, yet also to the opportunities to use the EDM process for surface improvement.

Numerical study of thermal aspects of electric discharge machining process

Abstract: This paper presents numerical results concerning the temperature distribution due to electric discharge machining process. From these thermal results, the material removal rate and the total roughness are deduced and compared with experimental observations. It is shown that taking into account the temperature variation of conductivity is of crucial importance and gives the better correlations with experimental data.

Electrical Discharge Machining of Functionally Graded 15–35 Vol% SiCp/Al Composites

Abstract: A functionally Graded 15–35 volume% silicon carbide particulate (SiCp) reinforced Al359 metal matrix composite (SiCp/Al MMC) was drilled by electrical discharge machining (EDM) to assess the machinability and workpiece quality. The machining conditions were identified for both the machining performance and workpiece quality of the EDM process, including some aspects of material removal mechanisms, material removal rate (MRR), electrode tool wear, and subsequent drilled hole quality including surface texture and roundness by using surface profilometry, coordinate measuring machine (CMM), and scanning electron microscopy (SEM). It was observed that the material removal rate increases with increasing peak current and pulse-on-time up to the optimal points and drops drastically thereafter. Higher peak current and/or pulse-on-time result in both the greater tool wear and the larger average diameter error. As the percentage of the SiC particles increases, MRR was increased and electrode wear was found to be dec...

A semi-empirical approach for residual stresses in electric discharge machining (EDM)

Abstract: High residual stresses are developed on the surfaces of electric discharge machined parts. In this study, layer removal method is used to measure the residual stress profile as a function of depth beneath the surface caused by die sinking type EDM. Cracking and its consequences on residual stresses are also studied on samples machined at long pulse durations. A modified empirical equation is developed for scaling residual stresses in machined surfaces with respect to operating conditions. In this model, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found to be a special form of a Gauss Distribution. It is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location. The form can be represented by three constant coefficients. These coefficients depend on the released energy by a power function.

Electrical discharge machining with ultralow discharge energy

Abstract: The possibility of electrical discharge machining (EDM) with ultralow discharge energy has been investigated. EDM using an RC discharge circuit was performed at low open-circuit voltages and a capacitance of approximately 30 pF. Workpieces were ultrasonically vibrated to remove debris and bubbles from the discharge gap, thus preventing short-circuiting. The machining proceeded at voltages lower than 15 V at a vibration amplitude of 0.4 μm. The maximum discharge energy per pulse is as small as approximately 3 nJ under these conditions. The volumetric electrode wear ratio can be 0.2% at voltages lower than 40 V, while it is normally more than 1% for EDM using an RC discharge circuit. Workpiece surfaces processed at voltages of 20 V or lower are smooth and free of observable discharge craters, and show no typical features of surfaces machined by EDM.

An experimental investigation on the effect of powder mixed dielectric on machining performance in electric discharge machining

Abstract: In this study, the variations of machining performance outputs, namely workpiece surface roughness, surface profile power spectral density, workpiece removal rate, electrode wear rate, relative wear, workpiece surface hardness, and workpiece surface microstructure were experimentally investigated with the varying machining parameters for metal powder mixed dielectric liquid in electrical discharge machining (EDM). The machining tests were conducted by using a prismatic steel workpiece and copper electrodes with graphite and boric acid powders (H3BO3) mixed kerosene dielectric at different powder concentrations and pulse time settings. The experiments have shown that the type and concentration of the powders mixed into the dielectric and the pulse time were effective on machining performance outputs in EDM.

Performance parameters optimization (multi-characteristics) of powder mixed electric discharge machining (PMEDM) through Taguchi's method and utility concept

Abstract: Electrical discharge machining (EDM) is widely used in the production of dies. This paper describes an investigation into the optimization of the EDM process when silicon powder is suspended into the dielectric fluid of EDM. Taguchi’s method with multiple performance characteristics has been adopted to obtain an overall utility value that represents the overall performance of powder mixed EDM (PMEDM). The four input process parameters, viz., concentration of silicon powder added into the dielectric fluid, peak current, pulse duration and duty cycle, are optimized with consideration of multiple performance characteristics including machining rate (MR), surface roughness (SR) and tool wear rate (TWR). A modified powder mixed dielectric circulation system has been developed. Experiments have been performed on the newly designed experimental set-up developed in the laboratory. The obtained experimental results indicate that the peak current and concentration of the silicon powder suspended into dielectric fluid are most significant parameters. Moreover, the performance of PMEDM has improved over EDM. The predicted optimal values for MR, SR and TWR obtained for PMEDM are 1.22 mm 3 /min, 0.51 μm and 0.005 mm 3 /min respectively. The results are further verified by conducting confirmation experiments. IPC Code: B05C, B23H1/00

Computer simulation of wire-EDM taper-cutting

Abstract: Wire electro discharge machining (WEDM) has become one of the most popular processes for producing precise geometries in hard materials, such as those used in the tooling industry. Since it is recognized as a precision process, optimization of different aspects related to dimensional accuracy is a classic research topic. The so-called taper-cutting involves the generation of inclined ruled surfaces, and it is especially important in the manufacturing of tooling requiring draft angles. In this paper a computer simulation software for the analysis of error in wire EDM taper-cutting is presented. The software is based on previous research work, but it includes the effect of friction to model adequately the cutting of large angles. Experimental tests have been carried out to establish the limits of application of the software, and the results compared with those obtained by the classical trial-and-error method. Although this latter approach is more precise, computer simulation dramatically reduces experimenta...

Experimental attempts of sub-micrometer order size machining using micro-EDM

Abstract: So far, parts larger than several micrometers can be machined by micro-electrical discharge machining (micro-EDM). However, with the growing demands for even smaller parts, sub-micrometer order machining or even nanometer order machining are increasingly required in various industrial areas. In order to meet these requirements, the study on sub-micrometer order manufacturing has become considerably important. In the present study, experimental attempts of sub-micrometer order size machining using micro-EDM was performed, in which the smallest possible size that can be achieved for machined parts was examined, and the factors affecting the manufacturing of sub-micrometer parts were investigated. The results showed that insufficient positioning accuracy, smallest discharge energy and the machined shape error due to the influence of gap control and thermal deformation are not suitable for sub-micrometer machining. Disregarding positioning accuracy and machined shape error, cemented tungsten carbide (WC) and cemented tungsten carbide made of super fine particles (SWC) are relatively better than tungsten (W) from the viewpoint of material structure and influence of residual stress. In particular, SWC is more suitable than WC because both crystal grains size and size of defects among grains are smaller. Setting the polarity of workpiece negative was found to contribute to achieving sub-micrometer machining if the material removal rate is disregarded. Based on these investigation results, sub-micrometer machining using SWC was attempted. The minimum diameter obtained was about 2.8 μm.

Micro-machining and micro-grinding with tools fabricated by micro electro-discharge machining

Abstract: This paper provides an overview of several approaches to micro-machining by mechanical and electro-discharge means of material removal. Two steps are required in machining micro features. Firstly, a custom-shaped tool is created from suitable stock. In many cases, this is carried out using a small-scale version of wire Electro-Discharge Machining (EDM) in tool materials such as sintered PolyCrystalline Diamond (PCD) or tungsten carbide. Then the micro-tool can be used as a miniature end mill, drill or abrasive wheel. Each of these mechanical machining methods can be combined with EDM to achieve a customisable surface finish and feature accuracy. Trade-offs such as tool wear, Material Removal Rate (MRR) and machining time are discussed in this paper within the context of several examples.

Optimization of wire electrical discharge machining (WEDM) process parameters using genetic algorithm

Abstract: Wire electrical discharge machining (WEDM) is a special form of traditional electrical discharge machining in which the electrode is a continuously moving conducting wire. The mechanism of metal removal in wire electrical discharge machining involves the complex erosion effect from electric sparks generated by a pulsating direct current power supply. The sparks generated between two closely spaced electrodes are immersed in dielectric liquid. However, dimensional accuracy and surface finish largely depend on process parameters such as discharge current, pulse duration, pulse frequency, wire speed, wire tension and dielectric flow rate. An experimental study has been carried out on a Robofil 100 WEDM machine to identify various significant control factors and their interactions that affect the machining performance such as metal removal rate (MRR) and surface finish (SF) based on Taguchi method. The relationship between control factors and responses like MRR and SF are established by means of non-linear regression analysis resulting in a valid mathematical model. Finally, genetic algorithm, a popular evolutionary approach, is used to optimize the wire electrical discharge machining process with multiple objectives. The study demonstrates that the WEDM process parameters can be adjusted to achieve better metal removal rate and surface finish simultaneously. IPC Code: B23H 1/00 Wire electrical discharge machining (WEDM) is a special form of the traditional electrical discharge machining process in which the electrode is a continuously moving electrically conductive wire. Sparks are generated between two closely spaced electrodes immersed in dielectric liquid which is continuously forced fed to the machining zone to flush away the eroded particles. The movement of wire is controlled numerically to achieve the desired three-dimensional shape and accuracy of the workpiece. In most cases, horizontal movement of the work table (controlled by computer numerical controlled on modern machines) determines the path of the cut. However, WEDM allows intricate cutting and shaping of materials to nearly any threedimensional size and shape. Past works indicates that extensive research has been carried out to study the effect of various machining parameters on metal removal rate (MRR), surface roughness, cutting speed, wire rupture and wire craters. Rajurkar and Wang 1 extensively experimentally investigated the effect of machining parameters on machining performance outputs, viz.,

An experimental study of the machining parameters in powder mixed electric discharge machining of Al–10%SiCP metal matrix composites

Abstract: The aim of this present research is to establish optimum process conditions for Powder Mixed Electric Discharge Machining (PMEDM) of Al–10%SiCP Metal Matrix Composites (MMC) by an experimental investigation using Response Surface Methodology (RSM) Aluminium powder was suspended into the dielectric fluid of Electric Discharge Machining (EDM) A modified powder mixed dielectric circulation system was developed in the laboratory for experimentation Relationships are developed between various input process parameters (concentration of the added aluminium powder, peak current and pulse duration) and output characteristics (Machining Rate (MR), Surface Roughness (SR)) The obtained result allowed how to find the most important parameters and determine the optimal values that maximise the MR and minimise the SR The recommended optimal process conditions have been verified by conducting confirmation experiments