Machining Characteristics of Inconel 718 by Sinking-EDM and Wire-EDM

Inconel 718 superalloy has wide applications in several industries due to its excellent mechanical properties. However, it is very difficult to machine using conventional cutting and grinding because of its high strength at elevated temperatures. Electrical discharge machining (EDM) is an alternative competitive process to machine Inconel alloys by electrical erosion. However, machinability and surface characteristics of EDMed Inconel surfaces are poorly understood. This study focuses on the machining characteristics of Inconel 718 by Wire-EDM and Sinking-EDM with a new Cu-SiC electrode, respectively. Material removal efficiency, surface roughness, surface topography, surface alloying, and electrode wear have been characterized. It is found that the high toughness of Inconel 718 would be the major contributing factor to the absence of microcracks on the EDMed surface. The new fabricated Cu-SiC electrode for Sinking-EDM has better performance in terms of material removal rate (MRR), surface roughness, and electrode wear. The higher melting temperature and fine microstructure of SiC contribute to the lower electrode wear of the new Cu-SiC electrode than the traditional Cu electrode.     

Multi-Material Inconel 718 Parts with Highly Conductive Copper Cooling Channels for Aerospace Applications

Multi-material parts can offer valuable solutions to engineering problems when compared to single materials. The conceptualization of a multifunctional Inconel 718 (IN718)–Copper (Cu) solution aims to improve the heat extraction capacity of an aerospace component. High-strength IN718 was used as the base material and highly thermal conductive Cu was employed for internal cooling channels. The cooling channels are produced by electrical discharge machining (EDM) and subsequently filled with Cu to be sintered by hot pressing (HP). The morphological, microstructural, hardness, and thermal properties of the hot-pressed multi-material IN718–Cu specimens are studied to evaluate the feasibility of HP processing as a viable manufacturing approach for these multi-material solutions. The multi-material IN718–Cu specimens presents a well-defined design with good metallurgical bonding between the two materials and a thin diffusion region is found, assuring the final properties of each individual material. The Vickers’ microhardness of IN178 and Cu are in accordance with the reported for conventional processes which indicates good densification. The thermal conductivity of the multi-material IN718–Cu specimen is 25% higher than mono-material IN718, which can be a significant improvement in the thermal efficiency of an aerospace component.     

Electrical Discharge Machining (EDM) Characteristics Associated with Electrical Discharge Energy on Machining of Cemented Tungsten Carbide

In this investigation, cemented tungsten carbides graded K10 and P10 were machined by electrical discharge machining (EDM) using an electrolytic copper electrode. The machining parameters of EDM were varied to explore the effects of electrical discharge energy on the machining characteristics, such as material removal rate (MRR), electrode wear rate (EWR), and surface roughness. Moreover, the effects of the electrical discharge energy on heat-affected layers, surface cracks and machining debris were also determined. The experimental results show that the MRR increased with the density of the electrical discharge energy; the EWR and diameter of the machining debris were also related to the density of the electrical discharge energy. When the amount of electrical discharge energy was set to a high level, serious surface cracks on the machined surface of the cemented tungsten carbides caused by EDM were evident.     

Optimization of cryo-treated EDM variables using TOPSIS-based TLBO algorithm

In order to machine hard and high-strength-to-weight ratio materials, electrical discharge machining (EDM) process is extensively used in aerospace, automobile and other industrial applications. However, high erosion of tool and improper selection of machining variables have emerged as a major obstruction to achieve productivity in this direction. High erosion of tool not only enhances the cost of machining but also increases the machining time by causing interruption during machining. Therefore, proper selection of machining variables and tool material life are the two vital aspects for the tool engineers working in EDM. In view of this, the present work proposes an extensive experimental investigation and optimization of machining variables of cryogenically treated brass tool materials on machining competences of Inconel 718 workpiece. The study primarily highlights the outcome of cryogenically treated soaking duration of tools along with other important process variables, viz. discharge current, open-circuit voltage, pulse-on time, duty factor and flushing pressure, on the performance measures such as electrode wear ratio (EWR), surface roughness and radial over-cut. The study revealed that soaking duration in deep cryo-treatment of the electrode is a significant variable to achieve improved machining characteristics. The performance measures are converted into equivalent single performance measure by calculating the relative closeness coefficient by the techniques for order preferences by similarity to ideal solution (TOPSIS) approach. Finally, a novel teaching–learning-based optimization (TLBO) algorithm has been proposed to find the optimal level of machining variables for the performance measures. The optimal levels of cutting variables obtained through the algorithm are validated through confirmation test, predicting an error of 2.171 percentages between the computational and experimental results. The predicted result suggests that the proposed model can be used to select the ideal process states to achieve productivity for the cryo-treated EDM.     

Improvement of Machinability using Laser-Aided Hybrid Machining for Inconel 718 Alloy

Hybrid machining is an emerging technique for difficult-to-cut materials to overcome the problems associated with conventional machining (CM). Inconel 718, a super alloy of nickel, is a high-temperature alloy commonly used in aircraft and thermal industries and categorized as one among the difficult-to-cut materials. In this study, the influence of cutting conditions of Inconel 718 alloy during laser-assisted hybrid machining (LAHM) is investigated and the results are compared with CM. During LAHM, the process parameters of cutting speed, feed rate, approach angle, and laser power are varied. The present work is carried out in two phases: (i) determination of effective heat-affected depth (HAD) during laser preheating (using central composite design (CCD) in response surface methodology); (ii) optimization of cutting conditions during machining (using Taguchi's method). Compared with CM, the LAHM shows the following reduction benefits: (i) 33% in feed force (Fx), 42% in thrust force (Fy), and 28% in cutting force; (ii) improved surface finish (surface roughness, Ra) of 28%; and (iii) reduction in tool wear by 50%. The chip morphology reveals the decrease in shear angle and increase in chip thickness during LAHM. No change in the hardness value of the machined surface after LAHM indicates the absence of subsurface damage.     

Parametric Optimization for Selective Surface Modification in EDM Using Taguchi Analysis

This paper introduces selective modification of surface by electric discharge machining process and its parametric optimization. A hard layer of tungsten and copper mixture is created at selected area of aluminum surface. The process is done using W–Cu powder metallurgical green compact tool and masking technique in die-sinking electric discharge machining (EDM). The modified surface is evaluated by the performance measures such as tool wear rate, material transfer rate, surface roughness, and edge deviation from the pre-defined boundary line of deposited layer by analysis of variance using Taguchi design of experiment. Minimum surface roughness of 4.5 µm and minimum edge deviation of 37.29 µm is achieved. The hardness of the surface layer is increased more than three times of base metal. Overall effects of parameters are also analyzed considering multiple performance criteria using overall evaluation criteria. The modified surface is characterized using scanning electron microscopy and energy dispersive spectroscopy analysis, which show the tool material transfer at the selected area of the surface.     

Examinations concerning the electric discharge machining of AZ91/5B4CP composites utilizing distinctive electrode materials

In this study, investigation has been conducted in the focus of obtaining better surface finish in the electro discharge machining (EDM) of AZ91/5B₄C_p magnesium composites using distinctive sort of anode viz. copper, tungsten–copper, brass, aluminum and 20Gr/AA6061 (GRAL-20) composites. The process parameters, pulse on time and current were performed to research the machining qualities through material removal rate (MRR) and tool wear rate (TWR). The machined composites were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The formation of black spots was observed on machining with copper–tungsten and these black spots were not found when GRAL-20 was used as electrode. Machined with GRAL-20 electrode leads to the increase in spark gap, hence adequate flushing occurs; it eliminates re-melted layers on machined surface results in better surface roughness value. The results revealed that GRAL-20 electrodes posses better MRR followed by copper electrode whereas tungsten–copper exhibits better TWR followed by GRAL-20 electrode.     

Machining Parameter Optimization in High-Speed Milling for Inconel 718 Curved Surface

Machining technology for nickel-based alloy Inconel 718 is a hotspot and difficult problem in industrial fields and the high-speed milling (HSM) shows obvious superiority in difficult-to-process material machining. As the machining parameters are crucial in processing of Inconel 718 and the study of chip is important in metal cutting, there is an urgent need for deep research into the machining parameter optimization based on chip variation in HSM for Inconel 718 curved surface, so as to further increase the productivity of Inconel 718 in aerospace field. Regarding Inconel 718 curved surface, an experimental study about the machining parameter optimization based on chip variation in HSM is conducted. The relationship between chip shape and machining parameters is studied, and the roughness is measured and discussed for the machined curved surface. Results indicate that the chip area relates to geometric feature of curved surface, the optimal range for spindle speed is from 9000 to 11000 rpm based on chip variation, the feed per tooth should be large in case that condition permitted, and the cutting depth can be selected according to other constraint conditions. This study is significant for improving the machining quality and efficiency of Inconel 718 curved surface.     

Experimental investigation of water-in-oil nanoemulsion in sinking electrical discharge machining

The most common dielectric in sinking electrical discharge machining (EDM) is kerosene. However, kerosene is inflammable; besides, it can be decomposed and release harmful gases during machining process. And, owing to its low viscosity, using kerosene in sinking EDM has low machining efficiency. Accordingly, conventional sinking EDM using kerosene as dielectric has poor safety, unfriendly environment impact, and low machining efficiency. A new water-in-oil (W/O) nanoemulsion is presented in this paper. This W/O nanoemulsion not only can eliminate the hazards from kerosene to operator and environment but also improve the machining performance of conventional sinking EDM. This research aims to experimentally investigate the machining performance of W/O nanoemulsion in comparison with kerosene in sinking EDM at relatively low discharge energy. The effects of electrode material, electrode polarity, peak current, and pulse duration on machining performance are studied. The machined surface and recast layer of workpiece are characterized as well. The experimental results demonstrate that compared with kerosene, using W/O nanoemulsion in sinking EDM can obtain a higher material removal rate (MRR), a lower relative electrode wear rate (REWR), and a machined workpiece with fewer defects and thinner recast layer.     

An experimental analysis of effective high speed turning of superalloy Inconel 718

Superalloy, Inconel 718 is widely used in the sophisticated applications due to its unique properties. However, machining of such superior material is difficult and costly due its peculiar characteristics. The present article is an attempt to suggest Taguchi optimization technique to study the machinability of Inconel 718 with respect to cutting force, cutting temperature, and tool life in high speed turning of Inconel 718 using cemented tungsten carbide (K20) cutting tool. Therefore, the objective of this work is divided into two phases: (i) to demonstrate a correlation between cutting speed, feed, and depth of cut with respect to cutting force, cutting temperature, and tool life in a process control of high speed turning of Inconel 718 in order to identify the optimum combination of cutting parameters; (ii) to show the effect of high speed cutting parameters on the tool wear mechanism and chip analysis. These correlations were obtained by multiple linear regressions. The confirmation tests were carried out to make a comparison between the experimental results and mathematical models proposed. The proposed models agree well with the experimental results.     

The Feasibility Analysis of Electrical-Discharge Machining of Carbon-Carbon Composites

The objective of this research is to investigate the feasibility of using Electrical-Discharge Machining (EDM) for carbon-carbon composite materials as well as the effects of major machining parameters. The material was machined by electrical-discharge sinker using copper electrode. The mechanism of material removal has been revealed by the morphology of debris. The material removal rate, the surface topography and the recast layer that remains on the workpiece surface were studied in terms of EDM processing variables (e.g., pulse current and pulse duration time). The machined surface showing resolidification was examined by Scanning Electron Microscopy (SEM). A qualitative energy dispersive spectroscopic analyzer was used to measure the amount of migrated alloy in the workpiece and the chemical composition of recast layer. The machining damage, the recast layer, and the mass transfer was proportional to the power input. The EDM process is a feasible method for machining of carbon-carbon composites.     

EDM performance of TiC/copper-based sintered electrodes

This paper presents a study of the effect of titanium carbide (TiC) on the performance of sintered copper-based materials as electrical discharge machining (EDM) electrodes. The aim of this study was to provide a preliminary evaluation of EDM electrodes fabricated by laser-based sintering using rapid prototyping technology (RP). Six batches of titanium carbide with content from 5% to 45% were fabricated by mixing, ball milling, pressing, and liquid phase sintering with copper-tungsten (Cu–W) and copper (Cu), respectively. The performance of the newly formed material is compared with commercial electrodes. The densification of TiC/Cu–W system was improved by the addition of nickel (Ni), as Ni shows good solubility in both Cu and W. The distribution of particle size becomes narrow as the proportion of TiC is increased. A uniform dispersion of small TiC particles in the Cu–W system and a narrow particle size distribution provide the possibility of obtaining dense electrodes. With increasing TiC, the relative density first increased and then decreased, whereas the electrical resistivity first decreased and then increased. EDM electrodes, with the addition of TiC, show good performance in surface finishing. This is an important characteristic as RP-sintered EDM electrodes are expected to be used as finishing electrodes. The surface roughness of most specimens is less than those machined using commercial electrodes. Electrodes with 15% TiC show the highest relative density, lowest electrical resistivity, and good EDM performance, i.e. lowest tool wear ratio (TWR) and highest material removal rate (MRR) at low current, and the best surface finish not only at low current, but also at high current.     

Constrained multi-objective optimization of EDM process parameters using kriging model and particle swarm algorithm

This paper investigates the highly nonlinear relationship between process parameters and machining responses, including material removal rate (MRR), surface roughness (SR), and electrode wear rate (EWR) of electric discharge machining (EDM) using Kriging model. Subsequently, an emerging multi-objective optimization algorithm called particle swarm is used to determine the best machining conditions that not only maximize the machining speed but also minimize the EWR with a constraint of the SR. The experiment was carried out with P20 steel on a CNC EDM machine using copper electrode. The research result shows that the MRR increases sharply when increasing the discharge current just like other researches pointed out. However, the relationship between EWR and current is complicated. EWR appears the minimum value when the current is around 30?A. The speed of change of MRR per unit of EWR is the highest when the SR is around 14.5?µm. The combination of Kriging regression model and particle swarm optimization is considered as an intelligent process modeling and optimization of EDM machining. The proper selection of process parameters helps the EDM operator to reduce the machining time and cost.     

Activated flux TIG welding of Inconel 718 super alloy in presence of tri-component flux

In this study, we have explored the influence of newly developed tri-component oxide flux (Cr₂O₃, FeO, and MoO₃) on weldability, bead geometry, weld pool temperature variation, and mechanical strength of Inconel 718 welded joints. Moreover, the influence of used flux on weld pool, the surface morphology of electrode and penetration capability of tungsten inert gas (TIG) welding on Inconel 718 plates have been well elucidated. Results indicate that the flux mixture significantly increases the penetration depth as well as aspect ratio almost 200% as compared to conventional TIG welding. The arc constriction caused by newly developed oxide flux upsurges the heat density and the weld pool temperature of joints. The alloying effect caused by entrapped oxide particles greatly improves the hardness as well as the tensile strength of joints. The reported reinforcement in the welding performance may increase potential utility of the developed methods for real-world applications.     

Parametric Evaluation on Near-Dry Electric Discharge Machining

Near-dry electric discharge machining (EDM) is an eco-friendly process. It does not produce toxic fumes and consequent health hazards. The near-dry EDM generally utilizes a mixture of two phase (liquid and air) dielectric for machining. This investigation reports the influence of four processing parameters, viz. current, flushing pressure, duty factor, and lift on three responses. The responses measured were material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). The work material chosen was high speed steel (HSS). Mathematical models have been proposed herein for evaluation of the effect of processing parameters in near-dry EDM. These models were developed using response surface methodology (RSM). The experimental results reveal that the process parameters taken into consideration were significant for MRR. The TWR was negligible in near-dry EDM. This process gives a finer surface finish with thinner recast layer even at higher discharge energies as compared to conventional EDM.     

Fabrication and characterization of vacuum plasma sprayed W/Cu-composites for extreme thermal conditions

The joining of tungsten to copper and the ongoing search for commercially viable production techniques is one of the challenging issues in the field of composite materials. The reason why this material combination is of essential importance is its ability to withstand erosion and high temperatures on the tungsten side and to remove big quantities of heat on the copper side. Due to the mismatch of thermal expansion and Young’s moduli, the direct joining of these two materials results in high residual and thermal stresses at the interface, ultimately reducing component lifetime. One potential answer to this problem is functionally graded structures of W and Cu, which smoothen the transition of material properties. The present study focuses on vacuum plasma spraying (120 mbar, Ar) of W/Cu-gradients and composites with defined mixing ratios. The influence of the fabrication process and the W:Cu ratio on the microstructure has been investigated and results from thermo-mechanical and thermo-physical results analyses are presented. Finite element modeling has been used to demonstrate the positive effect of gradients on the elastic and elastic–plastic response within two different model-geometries. Partial gradients, ranging from pure tungsten to 75 vol.% tungsten, exhibit the best results and improve the expected life-time performance significantly by reducing the stresses at both interfaces, W/FGM and FGM/Cu, compared to a reference interface between W and Cu.     

Microstructural Analysis and Multiresponse Optimization During ECM of Inconel 825 Using Hybrid Approach

In the current study, electrochemical machining of Inconel 825, a Ni-based super alloy, was carried out using tungsten as a tool electrode material and NaCl as electrolyte. The present investigation attaches particular emphasis on explaining the mechanism of material removal of Ni-based super alloys in the ECM process. The influence of various ECM parameters such as voltage (V), concentration (C), and tool feed (F) has been investigated on the evolution of the surface morphology of Inconel 825 after ECM. Different performance measures in ECM such as material removal rate (MRR), surface roughness (SR), and radial overcut (ROC) have been measured. Grey relational analysis that uses grey relational grade as performance index has been adopted to simultaneously optimize multiple performance characteristics and determine optimal combination of ECM parameters. Moreover, principal component analysis is utilized to determine the weighting values corresponding to various output responses so that their relative importance can be adequately expressed. Optimal condition was found to be V = 16 V, C = 45 g/L, and F = 0.3 mm/min. Confirmation test was further performed to authenticate the approach applied for determining the optimal conditions that resulted in MRR of 20.867 mm³/min, SR of 0.156 µm, and ROC of 0.0697 mm, which were superior to those corresponding to all previous experimental runs.     

Study of the Effect of Machining Parameters on the Machining Characteristics in Electrical Discharge Machining of Fe-Mn-Al Alloy

In this work we investigated the electrical discharge machining (EDM) of a Fe-Mn-Al alloy. The surface phenomena caused by EDM were studied in terms of machining parameters. An empirical model of the Fe-Mn-Al alloy was also proposed based on the experimental data. Experimental results indicate that the higher the discharge energy, the faster the machining time. This treatment introduces machining damage in the resolidified surface layer and worsens the surface roughness. The optimum pulse-on duration on the basis of the electrode wear ratio for the copper electrode was about 200 μs. The increase of crater depth with the applied pulsed current and pulse-on duration appears minimal under a small input energy.