Overcut Research Articles

Machinability of Silicon and German Silver in Micro Electrical Discharge Machining: a Comparative Study

This paper introduces an experimental investigation of micro hole drilling on two different categories of material such as silicon and german silver using micro electrical discharge machining (μEDM) process. The conductivities of the two materials are of different levels; silicon being a semiconductor has relatively much lower electrical conductivity as compared to german silver which is an alloy of copper, nickel and zinc. The tool electrode used is tungsten rod of 518 μm diameter. Responses like material removal rate (MRR), taper angle (TA), circularity error (CE) and overcut (OC) have been calculated and their variation with respect to the process parameters such as capacitance and voltage are evaluated. In both the materials, the values of all the responses increases with an increase in both voltage and capacitance. German silver is observed to have a higher MRR and OC than that of silicon while silicon has a higher TA for the same values of process parameters. The CE of silicon is higher at lower capacitance while it is higher for german silver at higher capacitance. From the analysis of variance (ANOVA), it is observed that both the voltage and capacitance played a significant role in all the responses. An optimum condition of micro hole drilling of both the materials is achieved by formulating overall evaluation criteria (OEC), which combines all the response parameters into a single index. In most of the cases, OEC of german silver is found to be higher than silicon, thus justifying the superior machinability performance of german silver. From the ANOVA of OEC, the role of capacitance is found to be more significant as compared to the voltage.

Multi-response optimization of magnetic field assisted EDM through desirability function using response surface methodology

Abstract Magnetic field assisted electrical discharge machining (MFAEDM) is the modification of in conventional EDM process by use of magnetic field on EN-31. This article explain the application of response surface methodology to analyzes the effect of various process parameters such as Ton, Toff and Ip on performance measures such as material removal rate (MRR), electrode wear rate (EWR) and overcut (OC). Analysis of variance was used to check the adequacy of response surface model and significance of process parameters on performance measures. Multi-objective desirability function has been applied to obtain the optimal process parameter settings. Thereafter, machined surface of EN-31 characterized through SEM and EDX. The novelty of this paper is to improve the strategies for flushing the debris which remain clogged in standard EDM in-between machining gap that will interrupts the regular discharge conditions and reduces cutting rate as well as deteriorate the surface characteristics.

Electrical discharge turning by assistance of external magnetic field, part I: Study of MRR and dimensional accuracy

Hybrid machining process is increasing its importance toward processing of advanced materials with complex geometries. Electrical discharge machining is a type of non-conventional machining process that is extensively used for creating micro and macro features in hard material. The process has capability to be used for flat samples and round bars that former application is more common. In the present study an experimental work has been made to produce sharp edge grooves in round bard made of AISI D2 by electrical discharge turning process. To do so, an external magnetic flux density has been applied around machining gap to enhance the performance measures. Series of experiments have been carried out in order to find effect of magnetic flux density (0, 0.2 and 0.4T), discharge current (5, 10, 15A), pulse on time (600, 800 and 1000μs), and work rotational speed (50, 150 and 250RPM) on material removal rate (MRR) and overcut (OC). Finally optimization has been carried out in different machining modes to find how the optimum value of magnetic field is varied in roughing and finishing. Results indicated that irrespective to the machining regime, application of high intensity magnetic field (i.e. 0.4T) is dominant in increasing the machining rate as well as enhancing the dimensional accuracy. Therefore, the method can be useful for performing the electrical discharge turning process.

Effect of coated and geometrically modified tools on performance of electrochemical micromachining

ABSTRACT Micro-holes are the basic features which are found in various components of medical devices, electronics, and biotechnology devices. The existing machining methods in ECMM for making micro-holes are generally accompanied with higher overcut (OC). Therefore, it is important to suppress OC and improve the machining rate (MR) which predominantly depend on electrode size, electrical parameters, tool electrode insulation, and electrolyte type. Hence, in this research, the suitable tool geometry and coating for the tool electrode is proposed, namely, ceramic, hot melt adhesive (HMA), and hollow wedge, short solid tools, respectively. The effect of electrolyte concentration in g/L, machining voltage in V and duty cycle in % on the OC and MR was studied. The results show that the ceramic tool produces 43.1% lesser OC than normal tool at the parameter combination of 23 g/L, 15 V, and 85% and short solid tool produces 74.3% higher MR for former with same parametric combination. The scanning electron microscope pictures of micro-holes were analyzed to study the effect of tool geometry and its coating. The ceramic and HMA coated tools control the leakages of current and shape modified tools to enhance the flow of current in the inter-electrode gap.

Analysis of high aspect ratio small holes in rapid electrical discharge machining of superalloys using Taguchi and TOPSIS

The main aim of this paper is to perform high aspect ratio small holes using rapid electrical discharge machining (rapid-EDM) of superalloys, namely Ti–6Al–4V and Inconel 718 with the tool materials like brass tubes and copper tubes. For employing the above-said materials, the performance characteristics such as material removal rate (MRR), tool wear rate (TWR) and overcut (OC) have been studied. In these investigations, DOE-Taguchi’s L9 orthogonal array has been utilized to build an experimental layout with the machining parameters such as current, on-time, off-time and capacitance. From the analysis, it is confirmed that there was a 40% increase in MRR, 282% decrease in TWR and 56% decrease in OC for rapid-EDM of Ti–6Al–4V material using the brass tubes than the copper tubes. Further, it is also validated that there is a 61% increase in MRR, 6% drop of TWR and 33% increase in OC for rapid-EDM of Inconel 718 material using brass tubes than the copper tubes. So, this comparative study has concluded that the machining of Ti–6Al–4V using brass tube has produced a maximum of MRR and minimum of TWR and OC. In Taguchi analysis, the individual effect of machining parameters on MRR, TWR and OC was studied. In addition, optimum combinations of machining parameters for MRR, TWR and OC were also discussed. Furthermore, multi-objective optimization was executed using TOPSIS to find good combination of machining parameters.

Analysis of surface integrity and dimensional accuracy in EDM of P91 steels

For any type of machining process, surface integrity and dimensional accuracy is a critical examination for machined material. Electro-discharge machining (EDM) process is the most effective method for surface integrity and dimensional accuracy evaluation of the machined surface. The present research work focused to investigate the influencing of machining parameters (pulse current, pulse on time and duty cycle) on machining of P91 tool steel. During the machining process, quantitively measurement of surface roughness (SR) and surface crack density (SCD) has been considered as surface integrity. Dimensional accuracy is characterized by over cut (OC) in this process of machining. In this study EDM parameters arranged using RSM-based design of experiment, on SCD, SR, and OC and study their individual impact on these response parameters. Pulse current is the most significant factor as compared to other parameters for the machining in EDM. The current work also recommends an optimum setting of system parameters for obtained good dimensional accuracy and surface integrity after P91 tool steel machining with EDM.

Optimization of Micro-EDM drilling parameters of Ti–6Al–4V alloy

The present work, analysis of parametric optimization of Micro-electrical discharge machining (µEDM) process of Ti–6Al–4V alloy. The important EDM parameters selected as capacitance, voltage, pulse on time and tool rotation. The Surface morphology and Material removal rate (MRR) of the Ti–6Al–4V alloy have been analyzed. Further, the machining parameters were optimized using Fuzzy-TOPSIS approach. The results showed that, MRR is directly proportional to capacitance and is inversely proportional to over-cut (OC). By using multi criteria decision making approach (MCDM) of micro-hole machining with Ti–6Al–4V alloy, the optimum conditions of machining parameters were obtained. It is noted that, capacitance is the most influencing factor of µEDM process for both MRR and OC. The results of this research work can therefore be used to improve the geometric accuracy and precision of the micro-hole for various micro-manufacturing medical and industrial applications.

Investigation on surface Integrity, Machining and Form tolerance characteristics using TOPSIS approach for Electrical Discharge Machining of Biocompatible material

Abstract Magnesium alloy (AZ91D) is a biocompatible material used for manufacturing critical degradable orthopaedic implants. One of the significant manufacturing processes used for machining these orthopaedic implants is Electric Discharge Machining (EDM). EDM is a non-traditional machining process where electric energy is used for removal of material from the work piece. The focus of this work is to optimize and investigate the contribution of process parameters such as discharge current (I), pule on time (TON), pulse off time (TOFF) on response variables such as surface roughness (Ra), material removal rate (MRR), tool wear rate (TWR), overcut (OC), tapercut (TC), circularity (CIR) and cylindricity (CYL). The experiments are carried out based on Taguchi’s L16 orthogonal array. The discharge current is found to contribute significantly on response variables when compared with other experimented process parameters. The performance measures are converted into equivalent single performance measure for achieving the required level of responses by calculating the relative closeness coefficient using the Techniques for Order Preferences by Similarity to Ideal Solution (TOPSIS) approach

Analysis of EDM Process Parameters on Inconel 718 Using the Grey-Taguchi and Topsis Method

Nickel-based superalloys are gaining importance for their growing usage in aerospace industries. Amidst the various advanced machining processes, electro discharge machining (EDM) is considered to be an important one for its ability to machine materials irrespective of its intrinsic properties. In this study, Inconel 718 is considered as a work material, and an L18 orthogonal array (OA) experimental plan is utilized to machine the work material. The influential factors, which affect the EDM performance characteristics, are identified using analysis of variance (ANOVA). Not much work has been done regarding using grey-Taguchi technique for order of preference by similarity to ideal solution (TOPSIS) methods, although these methods can be easily applied for multi-objective optimization. These methods provide the best results with the available sparse data. The best combination of machining factors is determined using grey-Taguchi and TOPSIS methods. Based on the conducted experiments, voltage (V) and pulse off-time (t_off) show a notable contribution on output performance. The optimal combination of input parameter through grey-Taguchi is found to be 10 A, 30 V, 200 μs, and 20 μs respectively, for the EDM parameters: current (I), V, pulse on-time (t_on) and t_off for improved response. Moreover, the best parameter setting (I = 10 A, V = 30 V, t_on =100 μs and t_off = 20 μs) is identified using the TOPSIS method for the performance measures machining rate (MR), tool wear rate (TWR), overcut (OC), and taper overcut (TOC). Further tool wear behaviour is also studied through scanning electron microscope (SEM) images by varying the voltage.

Analysis of Dimensional Accuracy (Over Cut) and Surface Quality (Roughness) in Electrical Discharge Machining of Inconel-718 Alloy

Inconel-718 is a nickel based super alloy (difficult-to-cut material) used in aerospace industry. Analysis of machining performances viz. Over Cut (OC) & Surface Roughness (SR) for Inconel-718 through rotary Cu-pin tool electrode have been carried out. Peak current (Ip), pulse-on time (Ton), tool rotation (Nt) & hole depth (h) were used as input factors in Electrical Discharge Drilling (EDD) of Inconel-718 work-piece. Effect of input parameters on performance characteristics like OC & SR were found by Taguchi’s L9 (34) orthogonal array. It is reveals that Ip & h are most affecting factors that affects OC & SR. The Scanning Electron Microscope image was used to measure diameter of hole on work-piece after machining.

Effect of deep cryogenic treatment on copper electrode for non-traditional electric discharge machining (EDM)

Abstract. In the last few decades, non-traditional machining made the machining process easier than the traditional machining method. Electric discharge machining (EDM) is one of the most prominent methods of non-traditional machining processes. By the use of EDM, a complex profile and high hardness materials can be easily machined, which cannot easily be machined by the traditional machining method. EDM is widely used by the industries. This paper investigates an experiment with the cryogenically treated copper electrode and an ordinary copper electrode with various input parameters like the electrode rotation, gap voltage and discharge current for an EN24 (a high-strength and wear-resistant steel) material. An experiment was performed with electric discharge machining. Designs of an experiment are carried out using the Taguchi approach. An orthogonal L16 array prepared and used the different combination of the three input parameters (current, electrode rotation and gap voltage) to find an optimum value of the factors. The output factors are the overcut (OC), the tool wear rate (TWR) and surface roughness (Ra). The optimal level and importance levels of each of these parameters are obtained statically using an analysis-of-variance (ANOVA) table through the analysis of the S∕N ratio. The study also compares the theoretical and experimental values of the overcut, tool wear rate and surface roughness for traditional and non-traditional EDM. The following research finds optimal or dominating factors (current and rotational speed) for the TWR and Ra in both traditional and non-traditional electric discharge machining; moreover there was a reduction of approximately 9 % in overcut, 13.25 % in the tool wear rate and 15.75 % in surface roughness for the deep cryogenic and non-traditional machining process.

Influence of various metal powder mixed dielectric on micro-EDM characteristics of Ti-6Al-4V

ABSTRACTTi-6Al-4V, an advanced engineering material is difficult-to-machine using conventional machining process due to its high strength. It has properties like low weight ratio, outstanding corrosion resistance along with high level of reliable performance in micro components. Micro-electro-discharge machining (Micro-EDM), a popular nontraditional machining process has been identified as the most appropriate machining process for such material. In this paper, the effect of various conducting powders such as copper, nickel and cobalt with different concentrations are mixed with deionized water dielectric, on various responses such as material removal rate (MRR), tool wear rate (TWR), overcut (OC) and taper has been presented. Also, principal component analysis (PCA) has been applied to select the optimal parametric combination of micro-EDM process to achieve optimal values of MRR, TWR, OC and taper during micro-through hole machining. The optimal process parametric setting obtained from the proposed approach is peak current (Ip) of 1.5 A and cobalt (Co) powder concentration of 4 g/L so as to obtain the desired responses. It is also observed from the SEM image that the machined profile and surface topography obtained through the multi-objective optimal parametric combination based on PCA is quite satisfactory and can be applied to achieve geometrically more accurate micro-through holes on Ti-6Al-4V.

EDM of Ti-6Al-4V: Electrode and polarity selection for minimum tool wear rate and overcut

ABSTRACTTitanium and its alloys especially Ti-6Al-4V are being widely used numerous application areas. In addition to have iconic properties, Ti-6Al-4V is considered as challenging material in machining perspective that is why it has captured global research focus. In this research, electric discharge machining of Ti-6Al-4V has been carried out by employing four different types of electrode materials (graphite, aluminum, copper, and brass) assigned with two alternate polarities (positive and negative). Selection of the most appropriate tool material and electrode polarity is the important aspect needed to be explored for this alloy. In addition to polarity, discharge current, and pulse time ratio have been considered as process variables owing to have their direct influence in electric discharge machining. Taguchi L9 array has been employed for each of the four electrodes with positive polarity and similarly L9 with negative polarity. Thus, a total number of 72 experiments have been conducted. Tool wear rate and overcut (OC) around the machined surfaces are the response characteristics to be investigated in order to achieve minimum amounts of both of these two responses. Selection of the most suitable tool with common tool polarity has been carried out meeting the decision criteria of minimum tool wear and minimum OC.

Evaluation of scale effect of micro electrical discharge machining system

Micro electrical discharge machining (EDM) is generally regarded as the application of conventional EDM in micro scale. The energy transfer characteristic and material removal mechanism of micro EDM are differ from that of macro EDM due to the miniaturization of tool electrode and discharge energy. The unexpected machining performance can be attributed to the so-called scale effect. In this study, the similarity theory was used to quantitatively evaluate the scale effect and the effectiveness of this evaluation method was established. In this method, greater similarity precision means more significant scale effect. Tool electrode diameter, capacitance, and open circuit voltage were adopted as factors in orthogonal experiment to explore the scale effect caused by the miniaturization of tool electrode and discharge energy. The single factor scale effect and system scale effect of EDM are evaluated based on orthogonal experiment. Scale effect with different degree is presented in terms of material removal rate (MRR), relative tool wear ratio (RTWR), and overcut (OC). The machining type is transferred from macro EDM to micro EDM as a result of the decrease of machining parameters. A positive scale effect is produced and open circuit voltage is the most important factor for the scale effect of EDM.

Experimental Investigation of High Speed Tool Rotation on Heat Affected Zone and Over Cut in ECDM

Abstract Micro-channeling and micro-engraving processes on the glass material are difficult using the conventional machining methods. Channeled parts of glass material are widely used in the micro electromechanical system (MEMS), biomedical applications, aerospace etc. Electrochemical discharge machining (ECDM) shows the potential of machining of non-conducting materials like glass, ceramics and composites. Formation of heat affected zone (HAZ) and over cut (OC) are the weakness in the ECDM engraving process. These weaknesses can be overcome with high speed electrochemical discharge machining (HSECDM) which has the ability to reduce the heat affected zone and over cut because of the higher tool rotation speed at different feed rate. This paper mainly concentrated on the engraving with high speed tool rotation and different feed rate, the experimental setup has been developed for the experimentation. In this study, engraving on the soda lime glass material is studied and tungsten carbide tool electrode of diameter 500 µm is used. The experimental result shows that with tool rotation speed and feed rate width of heat affected zone (HAZ) and over cut (OC) changes.

Analysis on the effect of ECDM process parameters during micro-machining of glass using genetic algorithm

Electro chemical discharge hybrid machining process involves in micro-machining to cut micro- channel, micro-profile as well as micro-slot, blind hole on hard materials like ceramic, quartz and glass. Experimentation has been performed using an indigenously developed micro-ECDM set up in which pressurized automated spring feeding mechanism and cam follower system is used to control the working gap. This paper emphasis to the influences of different process parameters like applied voltage (V), electrolyte concentrations (wt%), pulse frequency (Hz) and duty ratio (%) on different machining performance characteristics such as Material Removal Rate (MRR), Overcut (OC), Surface Roughness (Ra) and Heat Affected Zone (HAZ) during micro-channel cutting on glass. The empirical mathematical model has been validated by the analysis of variances. This research paper rendered the suitable optimal parametric condition during single as well as multi objective optimization using genetic algorithm (GA). Applied voltage and duty ratio has dominating role to increase MRR, OC, HAZ and surface roughness. Machining Depth increased using automated spring feeding with Cam-follower mechanism and achieved machining depth of 1.35mm. This research paper also presented the SEM analysis of micro-channel to find out the debris and other particles.

On performance enhancement of electrochemical discharge trepanning (ECDT) process by sonication of tool electrode

In the present work, an attempt has been made to use ultrasonic energy to augment the performance of electrochemical discharge trepanning (ECDT) process. The effect of various process parameters such as applied voltage, pulse on time, tool rotation rate and power rating on quality characteristics (over cut (OC) and depth of penetration (DOP)) of machined work materials has been experimentally investigated. The underlying process mechanism for ultrasonic assisted ECDT (UA-ECDT) process is proposed by considering the high speed images of gas film, mathematical formulations and electrical signals as evidences. A comparative analysis between ECDT and UA-ECDT has also been performed. The experimental results reveal that the integration of ultrasonic vibrations in ECDT process facilitates evacuation of the sludge/debris from the machining zone. Also, it generates thin and stable gas film over the tool electrode. Therefore, the use of UA-ECDT improves the energy channelization index (ECI), and exhibits 10 times more ECI than the ECDT process. The second-order mathematical models have been developed to determine the relationship between input process parameters and quality characteristics (OC and DOP). The developed models are in good agreement with the experimental results and exhibit an average error of less than 3%. Additionally, a desirability approach has been employed to conduct the multiobjective optimization for the minimization of OC and maximization of DOP. The parametric combination of applied voltage of 60 V, pulse on time of 3 ms, tool rotation rate of 42 rpm and power rating of 17% is recommended to perform the UA-ECDT process.

Metaheuristic Approach of Multi-Objective Optimization during EDM Process

In modern-day manufacturing Electric Discharge Machining (EDM) process has successfully placed itself in the domain of precision machining and generating complex geometries where secondary machining processes are eliminated. In this research paper, a die sinking EDM is applied to machine mild steel in order to measure the different multi-objective results like Material Removal Rate (MRR) and Over Cut (OC). This contradictory objective is accomplished by using the control parameters like a pulse on time, duty factor, gap current and spark gap employing copper tool with lateral flushing. Here the individual objective function of the responses is created through regression analysis. Primarily the contradictory objectives are optimized by employing Taguchi Methodology, then Regression analysis is done on the test results. Additionally, the experimental results are optimized using Response Surface Methodology (RSM). It is followed by a multi-objective optimization through Overlaid contour plots and Desirability functions to ascertain the best parametric combination amongst the set of feasible alternatives.

Parametric Optimization of Micro-EDM Process during Micro-hole Machining on Ti-6Al-4V using WASPAS Method

Micromachining of Ti-6Al-4V is extremely difficult using conventional machining processes, especially during machining of micro-cavities and micro- through holes as it exhibits poor machinability. Amongst various non-conventional machining processes, micro-electro discharge machining (micro-EDM) has been recognized to be most suitable machining method for micromachining of Ti-6Al-4V. However, micro-EDM is an extremely complicated micromachining process, influenced by several process parameters. In present research investigation, an attempt has been made to select the optimal combination of micro-EDM process parameters such as pulse on time (Ton), peak current (Ip), flushing pressure (Fp) and type of dielectric, which greatly influence the micro-EDM process during machining of Ti- 6Al-4V using WASPAS (Weighted Aggregated Sum Product ASsessment) method. In a series of planned experimental runs, micro-through hole machining has been carried out during experimental investigation and a model for multi-criteria decision making (MCDM) has been successfully developed in order to identify the optimum process parameters in micro-EDM process, which influence several machining criterion such as material removal rate (MRR), tool wear rate (TWR), overcut (OC) and taper. WASPAS method has been applied to obtain the optimal process parameters from the sets of various combinations of process parameters in order to achieve maximum MRR and minimum TWR, OC and taper during machining of Ti-6Al-4V. The obtained optimal process parametric combination has been experimentally validated and a significant improvement of 30.87% is observed.

Experimental Investigation of the PMEDM of Nickel Free Austenitic Stainless Steel: A Promising Coronary Stent Material

A new composition of Taguchi and the technique for order preference by similarity to ideal solution (TOPSIS) in combination with principal component analysis (PCA) has been explored. A series of experiments were performed in order to acquire an optimal parametric combination during powder mixed electro-discharge machining (PMEDM) of nickel free austenitic stainless steel. Peak current, pulse on time and powder concentration were selected as three process variables, whereas the material removal rate (MRR), tool wear rate (TWR) and over cut (OC) were the major attention. Domain of the investigation was adopted from Taguchi based L16 orthogonal array. The outcomes of the experiment were optimized using TOPSIS method whereas PCA technique was employed to determine the weightage of each response. Response table for S/N ratio was drawn to identify the most influencing machining parameter. Results of the investigation indicated that, peak current was the most effective machining variable followed by pulse on time and powder concentration. The proposed amalgamation of PCA-TOPSIS method was observed to be robust, easily understandable, time saving and modest approach which can help the decision maker to identify an optimal parametric combination with desirable accuracy.