Showing papers on "Electrical discharge machining published in 2013"

Multiple process parameter optimization of wire electrical discharge machining on Inconel 825 using Taguchi grey relational analysis

Abstract: In this paper, an effective approach, Taguchi grey relational analysis, has been applied to experimental results of wire cut electrical discharge machining (WEDM) on Inconel 825 with consideration of multiple response measures. The approach combines the orthogonal array design of experiment with grey relational analysis. The main objective of this study is to obtain improved material removal rate, surface roughness, and spark gap. Grey relational theory is adopted to determine the best process parameters that optimize the response measures. The experiment has been done by using Taguchi’s orthogonal array L36 (21 × 37). Each experiment was conducted under different conditions of input parameters. The response table and the grey relational grade for each level of the machining parameters have been established. From 36 experiments, the best combination of parameters was found. The experimental results confirm that the proposed method in this study effectively improves the machining performance of WEDM process.

Mathematical and numerical modeling of the effect of input-parameters on the flushing efficiency of plasma channel in EDM process

Abstract: In the present study, the temperature distribution on the surface of workpiece and tool during a single discharge in the electrical discharge machining process has been simulated using ABAQUS code finite element software. The temperature dependency of material properties and the expanding of plasma channel radius with time have been employed in the simulation stage. The profile of temperature distribution has been utilized to calculate the dimensions of discharge crater. Based on the results of FEM and the experimental observations, a numerical analysis has been developed assessing the contribution of input-parameters on the efficiency of plasma channel in removing the molten material from molten puddles on the surfaces of workpiece and tool at the end of each discharge. The results show that the increase in the pulse current and pulse on-time have converse effects on the plasma flushing efficiency, as it increases by the prior one and decreases by the latter one. Later, the introduced formulas for plasma flushing efficiency based on regression model were utilized to predict the cardinal parameter of recast layer thickness on the electrodes which demands expensive empirical tests to be obtained.

Parametric optimization for surface roughness, kerf and MRR in wire electrical discharge machining (WEDM) using Taguchi design of experiment

Abstract: This paper reports the effect and optimization of eight control factors on material removal rate (MRR), surface roughness and kerf in wire electrical discharge machining (WEDM) process for tool steel D2. The experimentation is performed under different cutting conditions of wire feed velocity, dielectric pressure, pulse on-time, pulse off-time, open voltage, wire tension and servo voltage by varying the material thickness. Taguchi’s L18 orthogonal array is employed for experimental design. Analysis of variance (ANOVA) and signal-tonoise (S/N) ratio are used as statistical analyses to identify the significant control factors and to achieve optimum levels respectively. Additionally, linear regression and additive models are developed for surface roughness, kerf and material removal rate (MRR). Results of the confirmatory experiments are found to be in good agreement with those predicted. It has been found that pulse on-time is the most significant factor affecting the surface roughness, kerf and material removal rate.

Surface characterization and material migration during surface modification of die steels with silicon, graphite and tungsten powder in EDM process

Abstract: The present study reports the results of an experimental work carried out to evaluate the improvement in machined surface properties of die steels machined using powder mixed electric discharge machining (PMEDM) process. Two surface responses, surface finish and microhardness were analyzed for changes when machined with Si, W and graphite powders mixed in dielectric fluid. The machined surfaces were subsequently analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to study the element migration from powder, dielectric and the tool. The powder mixed with dielectric and its concentration, current and pulse on time were identified as the significant factors affecting surface finish. Brass electrode and tungsten powder resulted in good surface finish. Amongst the dielectrics used, kerosene provided a better cooling effect whereas EDM oil resulted in better surface finish. The microhardness of the machined surface was also affected by powder and its concentration, current, pulse on time and electrode material. W-Cu electrode and W powder resulted in a higher microhardness. The SEM and EDS analysis showed significant migration of material from the suspended powder, electrode and dielectric to the machined surface.

Estimating the effect of process parameters on MRR, TWR and radial overcut of EDMed AISI D2 tool steel by RSM and GRA coupled with PCA

Abstract: This paper investigates an optimisation design of the various machining parameters for the electrical discharge machining (EDM) processes on AISI D2 tool steel using a hybrid optimisation method. A new combination of response surface methodology (RSM) and grey relational analysis coupled with principal component analysis (PCA) has been proposed to evaluate and estimate the effect of machining parameters on the responses. The major responses selected for this analysis are material removal rate, tool wear rate and radial overcut or gap, and the corresponding machining parameters considered for this study were pulse current (Ip), pulse duration (Ton), duty cycle (Tau) and discharge voltage (V). Thirty experiments were conducted on AISI D2 steel workpiece materials based on a face-centred central composite design. The experimental results obtained were used in grey relational analysis, and the weights of the responses were determined by the PCA and further evaluated using RSM. The results indicate that the grey relational grade (GRG) was significantly affected by the machining parameters considered and some of their interactions. The $R^2$ value for the GRG model was found to be 0.83, and the optimal parameter setting was determined for the grey relational grades. The analysis of variance results reveal that Tau is the most influencing parameter having 28.57 of percentage contribution followed by Ip, V and Ton with 11.52, 5.89 and 5.83 %, respectively. The interaction of the parameters contributes 31.19 % of percentage contribution. These results provide useful information on how to control the machining parameters and thereby responses and ensure high productivity and accuracy of the EDMed component. This method is simple with easy operability, and the results have also been verified by running confirmation tests.

Effect of Wire-EDM Machining Parameters on Surface Roughness and Material Removal Rate of High Strength Armor Steel

Abstract: This work presents the influence of machining parameters on surface roughness (SR) and material removal rate (MRR) of high strength armor steel using wire cut electrical discharge machining (WEDM). Tests have been carried out with six process parameters: pulse-on time, pulse-off time, wire feed, flushing pressure, spark voltage, and wire tension. Taguchi's technique has been employed for experimental investigation. Results show that pulse-on time, pulse-off time, and spark voltage are significant variables to MRR and surface roughness (SR). The confirmation experiments have also been conducted to validate the results obtained by the Taguchi technique.

A dual response surface-desirability approach to process modeling and optimization of Al2O3 powder-mixed electrical discharge machining (PMEDM) parameters

Abstract: This paper presents an effort to model and optimize the process parameters involved in powder-mixed electrical discharge machining (PMEDM). Aluminum oxide (Al2O3) fine abrasive powders with particle concentration and size of 2.5–2.8 g/L and 45–50 μm, respectively, were added into the kerosene dielectric liquid of a die-sinking electrical discharge machine. The experiments were carried out in planing mode on a specially designed experimental set up developed in laboratory. The CK45 heat-treated die steel and commercial copper was used as work piece and tool electrode materials, respectively. Response surface methodology, employing a face-centered central composite design scheme, has been used to plan and analyze the experiments. Based on the preliminary and screening tests as well as the working characteristics of selected EDM machine, discharge current (I), pulse-on time (Ton), and source voltage (V) were designated as the independent input variables to assess the process performance in terms of material removal rate (MRR) and surface roughness (Ra). Suitable mathematical models for the response outputs were obtained using the analysis of variance technique, in which significant terms (main effects, two factor interactions, and pure quadratic terms) were chosen according to their p values less than 0.05 (95 % of confidence interval). Having established the suitable regression equations, a search optimization procedure, based on the use of desirability functions, optimizes the process performance in each machining regime of finishing (Ra ≤ 3 μm), semifinishing (3 μm ≤ Ra ≤ 4.5 μm), and roughing (Ra ≥ 4.5 μm). The results are sets of optimum points which make the MRR as high as possible and keep the Ra and all machining parameters in their specified ranges simultaneously. Finally, the modeling and obtained optimization results were also discussed and verified experimentally. It was shown that the error between experimental and anticipated values at the optimal combination settings of input variables are all less than 11 %, confirming the feasibility and effectiveness of the adopted approach.

Modeling and multiresponse optimization on WEDM for HSLA by RSM

Abstract: Wire electric discharge machining (WEDM) is a nonconventional machining method to cut hard and conductive material with the help of a moving electrode. High-strength low-alloy steel (HSLA) is a hard alloy with high hardness and wear-resisting property. The purpose of this study is to investigate the effect of parameters on cutting speed and dimensional deviation for WEDM using HSLA as workpiece. It is seen that the most prominent factor for cutting speed and dimensional deviation is pulse-on time, while two-factor interactions play an important role in this analysis. Response surface methodology was used to optimize the process parameter for cutting speed and dimensional deviation. The central composite rotatable design was used to conduct the experiments. The analysis of variance was used for the investigation of significant factors.

Influence of Discharge Current Pulse on Machinability in Electrical Discharge Machining

Abstract: In this study, the machining characteristics of AISI 202 stainless steel have been investigated in thermal erosion process. Taguchi method based experiments have been conducted with conventional and modified pulse generators using electric discharge machining. Material removal rate (MRR) and surface roughness were taken to evaluate performance of process. Gap voltage, discharge current, and duty factor have been chosen as input parameters to access the machinability. The efficacy of pulse generators in thermal erosion process is determined by high material removing property and better surface finish. Since this machining process has stochastic nature, conventional RC relaxation pulse generator and transistor pulse train generator could not satisfy both the two requirements. It is proved that modified ISO current pulse generator could produce better surface finish with high MRR than conventional pulse generators in thermal erosion process.

Experimental study of rotary magnetic field-assisted dry EDM with ultrasonic vibration of workpiece

Abstract: Dry electrical discharge machining (EDM) is a green machining method which replaces the gas instead of liquid as dielectric medium. Due to the environmentally friendly nature of this method, recently, researchers focused on characterization of this process. In this work, effects of rotary magnetic field and also ultrasonic vibration of work- piece were studied on dry EDM process performance. Con- ducted experiments were divided in two main stages. At first stage, preliminary experiments were carried out to deter- mine the best tool design in material and geometry points of view by considering the material removal rate (MRR). Also, effect of magnetic field was studied in the first stage. Results of the first stage of experiments indicated that the brass tool with two eccentric holes has the highest MRR rather than the other existing tool. In the second stage of experiments, parametric study on dry EDM process were implemented by using a brass tool with two eccentric holes and by applying rotary magnetic field for all experiments of the second stage. Influences of parameters such as pulse current, pulse on-time, pulse off-time, tool rotational speed, air injection inlet pressure, and especially power of ultra- sonic table were studied on MRR, surface roughness (SR), electrode wear rate (EWR), and overcut (OC). Results showed that magnetic field has positive effects on MRR and SR. Also, by application of ultrasonic vibration achiev- ing to superior MRR is feasible. At the end of the work, mathematical models were developed to correlate a relation- ship between process inputs and main outputs.

Technological and economical comparison of roughing strategies via milling, sinking-EDM, wire-EDM and ECM for titanium- and nickel-based blisks

Abstract: Due to their particular mechanical and thermal properties titanium- and nickel-based alloys such as Ti–6Al–4V or Inconel 718 are in common use as blisk materials. Besides conventional milling in this paper two alternative technologies for roughing operations in blisk manufacture – electro discharge machining (EDM) and electrochemical machining (ECM) – are presented. Therefore material removal rates in sinking-EDM (SEDM) and ECM as well as cutting rates in wire-EDM (WEDM) are determined for the above mentioned materials and class of geometries. With these results, an extensive cost-analysis is made where different production technologies are compared for analogical blisk geometries. It is demonstrated that for distinct geometries, materials and batch sizes unconventional manufacturing technologies are economic alternatives to existing milling strategies.

Influence of parameters and optimization of EDM performance measures on MDN 300 steel using Taguchi method

Abstract: Maraging steel (MDN 300) exhibits high levels of strength and hardness. Optimization of performance measures is essential for effective machining. In this paper, Taguchi method, used to determine the influence of process parameters and optimization of electrical discharge machining (EDM) performance measures on MDN 300 steel, has been discussed. The process performance criteria such as material removal rate (MRR), tool wear rate (TWR), relative wear ratio (RWR), and surface roughness (SR) were evaluated. Discharge current, pulse on time, and pulse off time have been considered the main factors affecting EDM performance. The results of the present work reveal that the optimal level of the factors for SR and TWR are same but differs from the optimum levels of the factors for MRR and RWR. Further, discharge current, pulse on time, and pulse off time have been found to play a significant role in EDM operations. Detailed analysis of structural features of machined surface was done by using scanning electron microscope (SEM) to understand the influence of parameters. SEM of electrical discharge machining surface indicates that at higher discharge current and longer pulse on duration give rougher surface with more craters, globules of debris, pockmarks or chimneys, and microcracks than that of lower discharge current and lower pulse on duration.

Micro-cutting characteristics of EDM fabricated high-precision polycrystalline diamond tools

Abstract: To fabricate three-dimensional microstructures, such as micro dimples, micro grooves and micro channels, on ceramic mold materials, tool fabrication with super hard materials is an essential step. In this work, micro electro discharge machining (EDM) was used to fabricate high-precision polycrystalline diamond end mills. Form accuracy and edge sharpness in one micron level were achieved by utilizing electro discharge induced graphitization of diamond grains under extremely low discharge energy conditions. The cutting performance of the fabricated tools was examined by machining micro dimples and micro grooves on tungsten carbide mold substrates. Results showed that using the EDM-fabricated tools, ductile mode machining of tungsten carbide was realized with a surface finish of 2 nm R-a, which is comparable to that produced by polishing. (C) 2012 Elsevier Ltd. All rights reserved.

Multiobjective Optimization of Electrical Discharge Machining Process Using a Hybrid Method

Abstract: Electrical discharge machining (EDM) is a widely used process in manufacturing industries for high-precision machining of all types of conductive materials. Material of any hardness can be machined as long as material can conduct electricity. Proper selection of input parameters is one of the most important aspects in the die sinking EDM, as these conditions determine important characteristics such as surface roughness and material removal rate (MRR). In the present work, empirical models have been developed for relating the surface roughness and MRR to machining parameters like pulse-on time, pulse-off time, and discharge current. Response surface methodology (RSM) has been applied for developing the models using the technique of design of experiments (DOE) and multilinear regression analysis. The developed empirical models are used for optimization. Since the influence of machining parameters on surface roughness and MRR are conflicting in nature, there is no single combination of machining parameters, ...

Electrical discharge machining of ceramic matrix composites with ceramic fiber reinforcements

Abstract: Ceramic matrix composites (CMC) are considered the next generation of advanced materials used in space and aviation due to their high-temperature strength, creep resistance, chemical resistance, low porosity, and low density. However, these materials are difficult to process owing to the large cutting force and high cost on tool consumption. electrical discharge machining (EDM), featured by the negligible machining force and acceptable tooling cost, is a potential nontraditional machining technique for CMC. In this paper, EDM was used to process a new class of advanced CMC, that is, those with continuous ceramic fiber reinforcements. The challenge is its low material removal rate (MRR) due to the low workpiece conductivity and debris evacuation efficiency. Electrode vibration and dielectric deep flushing were used to promote debris evacuation, and an increase of MRR and surface quality without sacrificing tool wear ratio was observed. Gap voltage, peak current, pulse duration, and duty ratio were studied using design of experiments for deeper understanding of the process. The effect of these parameters was investigated, and an analysis of variance was conducted. The optimal condition was also predicted and experimentally validated. It was found that a high gap voltage or low duty ratio leads to a high machining rate due to improved debris evacuation efficiency. The material removal mechanism was found to be cracking due to thermal expansion of the matrix and breakage of the nonconductive fibers.