Showing papers on "Electrical discharge machining published in 2009"

Investigation of the effect of process parameters on the formation and characteristics of recast layer in wire-EDM of Inconel 718

Abstract: Inconel 718 is a high nickel content superalloy possessing high strength at elevated temperatures and resistance to oxidation and corrosion. The non-traditional manufacturing process of wire-electrical discharge machining (EDM) possesses many advantages over traditional machining during the manufacture of Inconel 718 parts. However, certain detrimental effects are also present and are due in large part to the formation of the recast layer. An experimental investigation was conducted to determine the main EDM parameters which contribute to recast layer formation in Inconel 718. It was found that average recast layer thickness increased primarily with energy per spark, peak discharge current, and current pulse duration. Over the range of parameters tested, the recast layer was observed to be between 5 and 9 μm in average thickness, although highly variable in nature. The recast material was found to possess in-plane tensile residual stresses, as well as lower hardness and elastic modulus than the bulk material.

Material removal rate and electrode wear ratio study on the powder mixed electrical discharge machining of cobalt-bonded tungsten carbide

Abstract: In this article, a material removal rate (MRR) and electrode wear ratio (EWR) study on the powder mixed electrical discharge machining (PMEDM) of cobalt-bonded tungsten carbide (WC-Co) has been carried out. This type of cemented tungsten carbide was widely used as moulding material of metal forming, forging, squeeze casting, and high pressure die casting. In the PMEDM process, the aluminum powder particle suspended in the dielectric fluid disperses and makes the discharging energy dispersion uniform; it displays multiple discharging effects within a single input pulse. This study was made only for the finishing stages and has been carried out taking into account the four processing parameters: discharge current, pulse on time, grain size, and concentration of aluminum powder particle for the machinability evaluation of MRR and EWR. The response surface methodology (RSM) has been used to plan and analyze the experiments. The experimental plan adopts the face-centered central composite design (CCD). This study highlights the development of mathematical models for investigating the influence of processing parameters on performance characteristics.

Thermal modeling of the material removal rate and surface roughness for die-sinking EDM

Abstract: The die-sinking electrical discharge machining (EDM) process is characterized by slow processing speeds. Research effort has been focused on optimizing the process parameters so as for the productivity of the process to be increased. In this paper a simple, thermal based model has been developed for the determination of the material removal rate and the average surface roughness achieved as a function of the process parameters. The model predicts that the increase of the discharge current, the arc voltage or the spark duration results in higher material removal rates and coarser workpiece surfaces. On the other hand the decrease of the idling time increases the material removal rate with the additional advantage of achieving slightly better surface roughness values. The model’s predictions are compared with experimental results for verifying the approach and present good agreement with them.

A numerical model of the EDM process considering the effect of multiple discharges

Abstract: The electrical discharge machining (EDM) process is, by far, the most popular amongst the non-conventional machining processes. The technology is optimum for accurate machining of complex geometries in hard materials, as those required in the tooling industry. However, although a large number of EDM machines are sold every year, scientific knowledge of the process is still limited. The complex nature of the process involves simultaneous interaction of thermal, mechanical, chemical and electrical phenomena, which makes process modelling very difficult. In this paper a new contribution to the simulation and modelling of the EDM process is presented. Temperature fields within the workpiece generated by the superposition of multiple discharges, as it happens during an actual EDM operation, are numerically calculated using a finite difference schema. The characteristics of the discharge for a given operation, namely energy transferred onto the workpiece, diameter of the discharge channel and material removal efficiency can be estimated using inverse identification from the results of the numerical model. The model has been validated through industrial EDM tests, showing that it can efficiently predict material removal rate and surface roughness with errors below 6%.

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

Abstract: 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-MoS 2 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 L 18 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 MoS 2 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.

Multi-response optimization of EDM with Al-Cu-Si-TiC P/M composite electrode

Abstract: The present study investigates the relationship of process parameters in electro-discharge of CK45 steel with novel tool electrode material such as Al–Cu–Si–TiC composite produced using powder metallurgy (P/M) technique. The central composite second-order rotatable design had been utilized to plan the experiments, and response surface methodology (RSM) was employed for developing experimental models. Analysis on machining characteristics of electrical discharge machining (EDM) die sinking was made based on the developed models. In this study, titanium carbide percent (TiC%), peak current, dielectric flushing pressure, and pulse on-time are considered as input process parameters. The process performances such as material removal rate (MRR) and tool wear rate (TWR) were evaluated. Analysis of variance test had also been carried out to check the adequacy of the developed regression models. Al–Cu–Si–TiC P/M electrodes are found to be more sensitive to peak current and pulse on-time than conventional electrodes. The observed optimal process parameter settings based on composite desirability are TiC percent of 18%, peak current of 6 A, flushing pressure of 1.2 MPa, and pulse on-time of 182 μs for achieving maximum MRR and minimum TWR; finally, the results were experimentally verified. A good agreement is observed between the results based on the RSM model and the actual experimental observations. The error between experimental and predicted values at the optimal combination of parameter settings for MRR and TWR lie within 7.2% and 4.74%, respectively.

Micro-structuring of glass with features less than 100 μm by electrochemical discharge machining

Abstract: Micro-electrochemical discharge machining (ECDM) was studied in order to improve the machining of 3D micro-structures of glass. To minimize structures and obtain good surface microstructures, the effects of the electrolyte, the pulse on/off-time ratio, the voltage, the feedrate, the rotational speed, and the electrolyte concentration in the drilling and milling processes were studied.In ECDM, voltage is applied to generate a gas film and sparks on a tool electrode; however, high voltage produces poor machining resolution. To obtain a stable gas film over the whole surface of the tool at a low voltage, a new mechanical contact detector, based on a loadcell, was used; the immersion depth of the tool electrode in the electrolyte was reduced as much as possible. In this study, various micro-structures less than 100 μm in size, such as O 60 μm micro-holes, a 10 μm-thin wall, and a 3D micro-structure were fabricated to demonstrate the potential for micro-machining of glass by ECDM.

Experimental investigation and empirical modeling of the dry electric discharge machining process

Abstract: Dry electric discharge machining (EDM) is an environment-friendly modification of the oil EDM process in which liquid dielectric is replaced by a gaseous medium. In the current work, parametric analysis of the process has been performed with tubular copper tool electrode and mild steel workpiece. Experiments have been conducted using air as the dielectric medium to study the effect of gap voltage, discharge current, pulse-on time, duty factor, air pressure and spindle speed on material removal rate (MRR), surface roughness (Ra) and tool wear rate (TWR). First, a set of exploratory experiments has been performed to identify the optimum tool design and to select input parameters and their levels for later stage experiments. Empirical models for MRR, Ra and TWR have then been developed by performing a designed experiment based on the central composite design of experiments. Response surface analysis has been done using the developed models. Analysis of variance (ANOVA) tests were performed to identify the significant parameters. Current, duty factor, air pressure and spindle speed were found to have significant effects on MRR and Ra. However, TWR was found to be very small and independent of the input parameters.

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

Abstract: 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.

Reducing electrode wear ratio using cryogenic cooling during electrical discharge machining

Abstract: In this study, cooling effect of copper electrode on the die-sinking of electrical discharge machining of titanium alloy (Ti-6Al-4V) has been carried out. Investigation on the effect of cooling on electrode wear and surface roughness of the workpiece has been carried out. Design of experiment plan for rotatable central composite design of second order with four variables at five levels each has been employed to carry out the investigation. Current intensity (I), pulse on-time (ton), pulse off-time (toff), and gap voltage (v) were considered as the machining parameters, while electrode wear and surface roughness are the responses. Analysis of the influence of cooling on the responses has been carried out and presented in this study. It was possible to reduce electrode wear ratio up to 27% by electrode cooling. Surface roughness was also reduced while machining with electrode cooling.

Machining Performance and Optimizing Machining Parameters of Al2O3–TiC Ceramics Using EDM Based on the Taguchi Method

Abstract: Investigating machining performance of conductive ceramics (Al2O3 + 30 vol% TiC) using electrical discharge machining (EDM) is the aim of this work. The EDM machining parameters such as machining polarity, peak current, auxiliary current with high voltage, pulse duration, no load voltage, and servo reference voltage were chosen to explore the effects on material removal rate (MRR), electrode wear rate (EWR), and surface roughness (SR). The L18 orthogonal array based on the Taguchi experimental method was adopted to determine EDM machining characteristics systemically, and the experimental data were statistically analyzed by analysis of variance (ANOVA). Experimental results showed EDM is a feasible process to shape conductive ceramics, and relationships between machining characteristics and parameters were examined. Moreover, machining parameter optimal combination levels in machining conductive ceramics via EDM were also determined.

Effects of process parameters on material removal rate in WEDM

Abstract: Purpose: In this paper, the effects of various process parameters of WEDM like pulse on time (TON), pulse off time (TOFF), gap voltage (SV), peak current (IP), wire feed (WF) and wire tension (WT) have been investigated to reveal their impact on material removal rate of hot die steel (H-11) using one variable at a time approach. The optimal set of process parameters has also been predicted to maximize the material removal rate. Design/methodology/approach: The experimental studies were performed on ELECTRONICA SPRINTCUT WEDM machine. Findings: The material removal rate (MRR) directly increases with increase in pulse on time (TON) and peak current (IP) while decreases with increase in pulse off time (TOFF) and servo voltage (SV). Practical implications: Wire electrical discharge machining (WEDM) is a specialized thermal machining process capable of accurately machining parts which have varying hardness, complex shapes and sharp edges that are very difficult to be machined by the traditional machining processes. The practical technology of the WEDM process is based on the conventional EDM sparking phenomenon utilizing the widely accepted noncontact technique of material removal. Originality/value: We can say that the wire feed and wire tension are neutral input parameters.

Determination of an Optimum Parametric Combination Using a Surface Roughness Prediction Model for EDM of Al2O3/SiCw/TiC Ceramic Composite

Abstract: Alumina has become one of the most popular ceramic materials used in wear-resistant and structural applications due to its attractive physical characteristics together with chemical inertness at elevated temperature. Its inherent brittleness and low fracture toughness make its machining difficult and consequently limit its utilization. Considerable improvement in mechanical properties of the single-phase alumina ceramic has been achieved by incorporating SiC whisker, TiC particles into Al2O3, which also allow electrical discharge machining (EDM) to fabricate components with complex geometry and widen the applications. This article presents an experimental investigation of the influence of parametric setting on machining performance during EDM of Al2O3/SiCw/TiC ceramic composite. In EDM, machining parameters determine the quality of surface produced. Second order regression model has been developed for predicting surface roughness (SR) in terms of machining parameters using the response surface methodology...

Development of an intelligent process model for EDM

Abstract: This paper reports the development of an intelligent model for the electric discharge machining (EDM) process using finite-element method (FEM) and artificial neural network (ANN). A two-dimensional axisymmetric thermal (FEM) model of single-spark EDM process has been developed based on more realistic assumptions such as Gaussian distribution of heat flux, time- and energy-dependent spark radius, etc. to predict the shape of crater cavity, material removal rate, and tool wear rate. The model is validated using the reported analytical and experimental results. A neural-network-based process model is proposed to establish relation between input process conditions (discharge power, spark on time, and duty factor) and the process responses (crater geometry, material removal rate, and tool wear rate) for various work—tool work materials. The ANN model was trained, tested, and tuned using the data generated from the numerical (FEM) simulations. The ANN model was found to accurately predict EDM process responses for chosen process conditions. It can be used for the selection of optimum process conditions for EDM process.

Investigations into the effect of tool shapes with size factor consideration in sink electrical discharge machining (EDM) process

Abstract: In sink electric discharge machining (EDM) process, the tool shape and size along with wear are of great importance because they adversely affect the accuracy of machined features. This paper presents the application of response surface methodology (RSM) for investigating the effect of tool shapes such as triangular, square, rectangular, and circular with size factor consideration along with other process parameters like discharge current, pulse on-time, pulse off-time, and tool area. The RSM-based mathematical models of material removal rate (MRR) and tool wear rate (TWR) have been developed using the data obtained through central composite design. The analysis of variance was applied to verify the lack of fit and adequacy of the developed models. Further, the confirmation tests were performed to ascertain the accuracy of the developed models. The investigations revealed that the best tool shape for higher MRR and lower TWR is circular, followed by triangular, rectangular, and square cross sections. From the parametric analysis, it is also observed that the interaction effect of discharge current and pulse on-time is highly significant on MRR and TWR, whereas the main factors such as pulse off-time and tool area are statistically significant on MRR and TWR.

Optimization of machining parameters using magnetic-force-assisted EDM based on gray relational analysis

Abstract: This work developed a novel process of magnetic-force-assisted electrical discharge machining (EDM) and conducted an experimental investigation to optimize the machining parameters associated with multiple performance characteristics using gray relational analysis. The main machining parameters such as machining polarity (P), peak current (IP), pulse duration (τP), high-voltage auxiliary current (IH), no-load voltage (V), and servo reference voltage (SV) were selected to explore the effects of multiple performance characteristics on the material removal rate, electrode wear rate, and surface roughness. The experiments were conducted according to an orthogonal array L18 based on Taguchi method, and the significant process parameters that affected the multiple performance characteristics of magnetic-force-assisted EDM were also determined form the analysis of variance. Moreover, the optimal combination levels of machining parameters were also determined from the response graph and then verified experimentally. The multiple performance characteristics of the magnetic-force-assisted EDM were improved, and the EDM technique with high efficiency, high precision, and high-quality surface were established to meet the demand of modern industrial applications.

Geometric improvement of electrochemical discharge micro-drilling using an ultrasonic-vibrated electrolyte

Abstract: Electrochemical discharge machining (ECDM) is a spark-based micromachining method especially suitable for the fabrication of various microstructures on nonconductive materials, such as glass and some engineering ceramics. However, since the spark discharge frequency is drastically reduced as the machining depth increases ECDM microhole drilling has confronted difficulty in achieving uniform geometry for machined holes. One of the primary reasons for this is the difficulty of sustaining an adequate electrolyte flow in the narrow gap between the tool and the workpiece, which results in a widened taper at the hole entrance, as well as a significant reduction of the machining depth. In this paper, ultrasonic electrolyte vibration was used to enhance the machining depth of the ECDM drilling process by assuring an adequate electrolyte flow, thus helping to maintain consistent spark generation. Moreover, the stability of the gas film formation, as well as the surface quality of the hole entrance, was improved with the aid of a side-insulated electrode and a pulse-power generator. The side-insulated electrode prevented stray electrolysis and concentrated the spark discharge at the tool tip, while the pulse voltage reduced thermal damage to the workpiece surface by introducing a periodic pulse-off time. Microholes were fabricated in order to investigate the effects of ultrasonic assistance on the overcut and machining depth of the holes. The experimental results demonstrated that the possibility of consistent spark generation and the machinability of microholes were simultaneously enhanced.

Modelling and optimization of process parameters of wire electrical discharge machining

Abstract: The optimum selection of process parameters is essential for advanced machining processes as these processes incur high initial investment, tooling cost, operating cost, and maintenance cos...

The machining characteristics and shape recovery ability of Ti-Ni-X (X = Zr, Cr) ternary shape memory alloys using the wire electro-discharge machining

Abstract: The wire electro-discharge machining (WEDM) characteristics of TiNiX ternary shape memory alloys (SMAs) have been investigated in this study. Experimental results show that the maximum feeding rate without breakage of wire electrode of Ti35.5Ni49.5Zr15 and Ti50Ni49.5Cr0.5 alloys in the WEDM process exhibits a reverse relationship with the product of the alloy's melting temperature and thermal conductivity. The surface roughness (Ra) of the machined TiNiX alloys increases with growing pulse duration. Having a larger λΘKΤ value, Ti35.5Ni49.5Zr15 alloy has a lesser Ra value and feeding rate of wire electrode than those of Ti50Ni49.5Cr0.5 alloy after WEDM. Electro-discharge craters and recast materials are observed on the wire electro-discharge machined (WEDMed) surface of TiNiX alloys. The thickness of the recast layer varies with pulse duration. The hardening effect near the outer surface for WEDMed TiNiX alloys arises from the recast layer. The WEDMed TiNiX alloys still exhibit a good shape recovery, but a slight degradation of shape recovery occurs due to the depression of the recast layer.

Surface integrity and material removal mechanisms associated with the EDM of Al2O3 ceramic composite

Abstract: Electric discharge machining (EDM) has been proven as an alternate process for machining complex and intricate shapes from the conductive ceramic composites The performance and reliability of electrical discharge machined ceramic composite components are influenced by strength degradation due to EDM-induced damage The success of electric discharge machined components in real applications relies on the understanding of material removal mechanisms and the relationship between the EDM parameters and formation of surface and subsurface damages This paper presents a detailed investigation of machining characteristics, surface integrity and material removal mechanisms of advanced ceramic composite Al 2 O 3 –SiC w –TiC with EDM The surface and subsurface damages have also been assessed and characterized using scanning electron microscopy (SEM) The results provide valuable insight into the dependence of damage and the mechanisms of material removal on EDM conditions

Influence of electrical conditions on performance of electrical discharge machining with powder suspended in working oil for titanium carbide deposition process

Abstract: This paper describes the influence of the discharge current and the pulse duration on the titanium carbide (TiC) deposition process by electrical discharge machining (EDM) with titanium (Ti) powder suspended in working oil. Although the influence of the electrical conditions for removal EDM has been investigated, the criteria for deposition have not been discussed. In the experiments, a 1-mm copper rod was used for an electrode to prevent the flushing of working oil from the gap between the electrode and a workpiece. Ti powder reacted with the cracked carbon from the working oil, then depositing a TiC layer on a workpiece surface. A major criterion of the deposition or removal was the discharge energy over a pulse duration of 10 μs. A thickness of the TiC layer became the maximum at a certain discharge current and pulse duration. Larger discharge energy and power promoted the removal by heat and pressure caused by the discharge. The removal was classified further into two patterns; cracks were observed on the Ti-rich surface in removal pattern 1 and a workpiece was simply removed in removal pattern 2. The maximum hardness of the deposition was 2000 Hv. The workpiece about 10 μm beneath its surface was also hardened because of the dispersion of TiC. The machining conditions for the hardest deposition did not coincide with those for the highest one. Therefore, the discharge current and pulse duration should be optimized for the deposition.