Electrical Discharge Drilling Process Research Articles

Abrasive water flow polishing of superalloy microholes drilled by electrical discharge machining

Superalloy microholes resulting from electrical discharge drilling (EDD) can have recast layers and microcracks on the machined surfaces. In this study, the abrasive water flow polishing (AWFP) of superalloy microholes machined by EDD was investigated. The recast layer and surface roughness resulting from the EDD process were evaluated through orthogonal experiments. The machining mechanism of AWFP was analyzed. The effects of AWFP parameters were investigated experimentally. The results show that the material removal rate and surface roughness at the hole exit were better than those at the entrance for one-directional fluid flow during the process. Garnet abrasives achieved better polished roughness and a lower material removal rate than alumina abrasives. The taper angle of the target holes changed slightly from positive to negative after AWFP. The corner edge was slightly rounded on the fluid inlet side. Using a bidirectional fluid resulted in better dimensional uniformity and surface roughness at the entrance and exit. This study verified that AWFP can remove the recast layer and microcracks on the hole wall caused by EDD and reduce the surface roughness from an initial Ra of 5.7 μm to an Ra of 0.6 μm.

Multi-response optimization of the electrical discharge drilling operation: A trade-off relation between the quality and efficiency

In this work, the tool rotational speed (T), dielectric pressure (W), feed rate (F), and voltage (V) of the electrical discharge drilling (EDD) operation are optimized to decrease the extension of the drilled hole (EH) and improve the material removal rate (MRR). The Kriging models were utilized to present performance measures, while the Entropy approach and improved quantum-behaved particle swarm optimization algorithm (IQPSO) algorithm were employed to compute the weights and determine optimal factors. The findings presented that the optimal T, W, F, and V are 550 rpm, 36 kg/cm2, 30 mm/s, and 70 V, respectively. The EH is reduced by 33.0%, while the MRR is enhanced by 39.4%, as compared to the common values. The Kriging models provided acceptable accuracy for the prediction purpose. The V and F had significant impacts on the EH and MRR. The optimal data could be utilized to enhance the performance measures for the practical EDD process. The method comprising the Kriging, Entropy, and IQPSO was a prominent solution to deal with complicated optimization issues for the EDD operation.

Experimental investigation of hole geometry during electric discharge drilling of aerospace material sheet

In this research paper experimental investigation of hole geometry during electric discharge drilling (EDD) is reported on Arial material Inconel-718. Electric discharge drilling is extensively used for aerospace equipment and component manufacturing. Proper geometry and close dimensional tolerance play a very important role during operations and functioning of aerospace parts. One of the important application of electric discharge drilling is in creating cooling hole in gas channels of gas turbine engines and similar other high temperature applications. In order to understand the parametric effect on hole geometry during electrical discharge drilling on Inconel-718, experiments are conducted according to the Box-behnken design of experiments. Four main electric discharge drilling parameters considered: Flushing pressure, Discharge current, Pulse on time and Duty cycle factor. Parametric effects and their interactive influence on hole geometry are studied by plotting contour plots. Favourable range of process parameter: Flushing pressure (kPa): 26 – 30, Discharge current (amp): 2–2.5, Pulse on time (µs): 6 – 6.5, Duty cycle factor (%): 50 – 55. After validating the established favourable range, improved hole geometry in term of better circular hole is observed in range of 0.989 to 0.992. Reported results can be useful to aerospace equipment manufacturers for getting improved geometry of drilled hole and also main recommendation is useful developing efficient automation of EDD process for quality production.

Experimental investigations of electrical discharge micro-drilling for Mg-alloy and multi-response optimization using MOGA-ANN

Electric Discharge Drilling (EDD), a spark erosion drilling process, is designed to produce small to large size holes in high-strength and heat-resistant materials with the greatest precision. Magnesium (Mg) based alloy is potential material for biodegradable medical implants, and EDD can be employed to create perforated implants for tissue engineering. The present study was carried out to investigate the EDD process for Mg-alloy using a face-centered central composite design (FCCD) and the effect of input process variables such as discharge current (I p ), spark-on time (T on ), spark-off time (T off ) and work height (WH) have been evaluated on response characteristics; drilling rate (DR), tool wear ratio (TWR) and hole overcut (HO). Analysis of Variance (ANOVA) suggests that Ip, T on , T off and WH are the most significant factor affecting the response characteristics under 95% confidence level. Based on the response surface methodology (RSM), regression equations have been developed between the input process variables and response characteristics. Further, an artificial neural network (ANN) model is developed, and a multi-objective genetic algorithm (MOGA) was utilized to optimize the multi-response objectives. It has been found that the best combination of input parameters while using RSM is: Ip; 4 amp, T on ; 30 µs, T off ; 48 µs, WH: 10 mm, and the predicted values of DR, TWR and HO were Ip; 129.22 mm/min, TWR; 0.142 and HO; 87.26 µm respectively whereas in the Multi-objective Genetic algorithm artificial neural network (MOGA-ANN) hybrid technique, optimal balance results achieved are DR of 142.527 mm/min, with TWR and HO 0.168, 98.258 µm respectively at optimal input parameters. The optimal results obtained with MOGA-ANN are validated experimentally.

A Mathematical Model to Assess the Material Removal Rate during Gas-Assisted Electrical Discharge Drilling Process

This research work investigates the use of Gas-Assisted Electrical Discharge Drilling (GAEDD) of high carbon-chromium die steel. The poor material removal rate (MRR) is one of the profound drawbacks of the traditional Electrical Discharge Drilling (EDD) process. Hence, over the years researchers have been feeling the requisite to develop an advanced strategy that can enhance the MRR. This study has examined the utilization of compressed gas in conventional EDM under the constraint state to assess MRR. The impact of procedure parameters likedischarge current, pulse on time, duty cycle, electrode speed, and discharge gas pressure, on MRR, has been explored too. In addition, Variance Analysis (ANOVA) was performed to determine the significant parameters affecting the MRR. During the examination, a mathematical model was established MRR employing Buckingham π-theorem while the GAEDD was being applied. The experiment and anticipated values of the model show a noteworthy impact of the coefficient of thermal expansion in GAEDD of high carbon-chromium steel. In addition, the Response Surface Method (RSM) model has also been evolved. The comparative analysis of the models developed shows considerable agreement in anticipation. Moreover, the semi-empirical model appears to be even more adaptable especially in comparison to the RSM-based model. In fact, the conclusion of this work is that the dimensional analysis model is an effective and reliable strategy to precise EDD response prediction.

Investigation of the Machinability of the Inconel 718 Superalloy during the Electrical Discharge Drilling Process

The properties of the Inconel 718 superalloy are used in the manufacturing of aircraft components; its properties, including high hardness and toughness, cause machining difficulties when using the conventional method. To circumvent this, non-conventional techniques are used, among which electrical discharge machining (EDM) is a good alternative. However, the nature of removing material using the EDM process causes the thermophysical properties of Inconel 718 to hinder its machinability; thus, a more extensive analysis of the influence of these properties on the EDM process, and a machinability analysis of this material in a wider range, using more process parameters, are required. In this study, we investigated the drilling of micro-holes into the Inconel 718 superalloy using the EDM process. An experiment was conducted to evaluate the impact of five process parameters with a wide range of values (open voltage, time of the impulse, current amplitude, the inlet dielectric fluid pressure, and tube electrode rotation) on the process’s performance (drilling speed, linear tool wear, the side gap thickness, and the aspect ratio of holes). The analysis shows that the thermal conductivity of this superalloy significantly influences the effective drilling of holes. The combination of a higher current amplitude (I ≥ 3.99 A) with an extended pulse time (ton ≥ 550 µs) can provide a satisfactory hole accuracy (side gap thickness ≤ 100 µm), homogeneity of the hole entrance edge without re-solidified material, and a depth-to-diameter ratio of about 19. Obtaining a high dimensional shape accuracy of holes has an enormous effect on their usability in the structure of the components in the aviation industry.

Experimental study on fabricating micro-holes in DD5 single-crystal nickel-based superalloy using electrical discharge drilling

The single-crystal superalloy materials have been rapidly developed and widely used in advanced thermal structural components due to their excellent comprehensive physical and chemical properties under high-temperature service conditions. However, conventional micro-hole making results in defects such as edge breakage and burr. In this study, the electrical discharge drilling (EDD) combined with helical microelectrode is first adopted to fabricate DD5 single-crystal nickel-based superalloy. The effects of tool geometry and machining parameters on subsurface damage layer, micro-hole taper, surface morphology, surface roughness and machining time were investigated in detail. Experimental results indicated that helical microelectrode can obtained smoother surface without debris deposition and thinner subsurface damage layer depth lack of micro-cracks compared with cylindrical microelectrodes. Additionally, the computational fluid dynamics model was developed to analyze working fluid movement and reveal effective debris removal mechanism of helical microelectrode. The vortices will be generated in lateral gap fluid between micro-hole and helical microelectrode and have a certain delay time. The surface roughness and dimensional precision of micro-holes fabricated by helical micro-electrodes are greatly improved and machining efficiency is also improved by 30.94% compared to cylindrical microelectrodes. This work could provide theoretical and process guidance to assist in realizing high surface quality and low subsurface damage of micro-holes obtained with EDD process.

Multicharacteristics optimization of electrical discharge micro hole drilling in Mg alloy using hybrid approach of GRA–regression–PSO

PurposeMagnesium alloys are becoming prominent as an alternative to the permanent biomedical implants. In present work, electric discharge drilling (EDD) process has been investigated and optimized for ZM21 Mg alloy that can be used for producing perforated bone implants having geometrically precise micro holes.Design/methodology/approachPlanning of experiments has been carried out in accordance to the Taguchi mixed L18 orthogonal array (OA). The hole overcut (HO), circularity at entrance (Cent) and circularity at exit (Cext) of drilled micro holes were measured as response characteristics during experimentation corresponding to different settings of EDD input parameters. For optimizing multiresponse characteristics, the hybrid approach of grey relational analysis, regression analysis and particle swarm optimization has been implemented.FindingsIt is found from hybrid approach that brass electrode along with Ip; 3 Amp, Ton; 50 µs and Toff; 52 µs outperformed over all other parametric settings against the collective result of response characteristics. The experimental values of response characteristics at suggested optimized setting are HO: 93.48 µm; Cent: 0.988 and Cext: 0.992, respectively.Originality/valueThe optimization of EDD process for developing perforated Mg alloy bone implants, using hybrid approach is still missing.

Multi-Response Optimization of Electrical Discharge Drilling Process of SS304 for Energy Efficiency, Product Quality, and Productivity.

The electrical discharge drilling (EDD) process is an effective machining approach to produce various holes in difficult-to-cut materials. However, the energy efficiency of the EDD operation has not thoroughly been considered in published works. The aim of the current work is to optimize varied parameters for enhancing the material removal rate (MRR), saving drilled energy (ED), and decreasing the expansion of the hole (HE) for the EDD process. Three advanced factors, including the gap voltage adjustor (GAP), capacitance parallel connection (CAP), and servo sensitivity selection (SV), are considered. The predictive models of the performances were proposed with the support of the adaptive neuro-based fuzzy inference system (ANFIS). An integrative approach combining the analytic hierarchy process (AHP) and the neighborhood cultivation genetic algorithm (NCGA) was employed to select optimal factors. The findings revealed the optimal values of the CAP, GAP, and SV were 6, 5, and 4, respectively. Moreover, the ED and HE were decreased by 16.78% and 28.68%, while the MRR was enhanced by 89.72%, respectively, as compared to the common setting values. The explored outcome can be employed as a technical solution to enhance the energy efficiency, drilled quality, and productivity of the EDD operation.

Development and Experimental Study of Electrical Discharge Drilling (EDD) Process for Titanium Alloy

Advanced engineering materials viz. titanium alloy, nickel alloy, heat-treated steels, superalloy, high-strength temperature-resistant alloys (HSTR) and metal matrix composites (MMCs), etc. are extensively being used in defence, automobile, aerospace, missiles and nuclear applications. Drilling holes in such advanced engineering materials are challenging due to their superior mechanical, electrical and thermal properties. Electrical discharge drilling (EDD) process is a very efficient hybrid machining process (HMP) for making holes in advanced engineering materials irrespective of their hardness and toughness. In the present work, an experimental setup of EDD process has been developed, and the effect of input parameters on the process performance of EDD is studied in terms of output parameters namely material removal rate (MRR) and tool wear rate (TWR). It has been observed from experimental study that the copper tool of 2-mm diameter is suitable for machining of small hole on titanium alloy with minimum TWR. Further, when tool rotation is increased from 600 to 900 rpm, about 17% more MRR and 34% reduction in TWR is observed.

Multi-objective optimization of electrical discharge drilling (EDD) process using PCA based grey relational analysis

Low material removal rate (MRR) and formation of recast layer are major limitations of EDM which restrict large scale application of EDM in advanced manufacturing industries such as aerospace, defence, automobile, medical etc. Electrical Discharge Drilling (EDD) is a proficient machining process for machining of electrically conductive hard and tough materials. It is a combination of EDM and conventional drilling however in EDD process, tool and workpiece are not in mechanical contact as in case of conventional drilling process. The material is removed by melting and evaporation and at the same time tool rotation assists the process by improved flushing of debris particles from machining zone. In present work, holes of 2 mm diameter are machined in Ti-6Al-4V using EDD process. The experiments were performed on conventional EDM machine with a detachable in-house developed experimental setup for tool rotation. The experiments are designed using Taguchi’s L27 OA. Further, optimization of EDD process is performed using PCA based GRA method. The optimum values of process parameters for EDD of Ti-6Al-4V is obtained as IP = 21 Amp, TON = 90 µs, TOFF = 15 µs and tool rotation = 600 rpm. It is found that EDD at optimum parameters have resulted in about 30.64% increased MRR along with 16.57% greater TWR as compared to mean MRR and mean TWR at 21 Amp pulse current.

Experimental Analysis of Electrical Discharge Drilling (EDD) of Carbon-Carbon Composite

Abstract The research in the area of space exploration and aviation industries gave rise to the requirement of advanced engineering materials which can withstand very high temperature without significantly affecting their properties. Carbon-carbon (C/C) composite is relatively a new advanced engineering material with extraordinary mechanical and thermal properties.The processing of C/C composite is very challenging due to its brittle nature. In the present work, holes of 1mm diameter have been successfully machined on carbon-carbon composites with the help of Electrical Discharge Drilling (EDD) process. Pulse current, pulse-on-time (TON), pulse-off-time (TOFF) and tool rotation are selected as input process parameters whereas response parameters taken in present study are MRR and TWR. After experimentation, it has beenperceived that electrical discharge drilling can be used for making accurate holes in carbon-carbon composite. Further, scanning electron microscope (SEM) analysis is performed in order to examine the surface characteristics of hole machined with EDD process

Process optimization and comparative analysis of EDM and EDD process in machining Al6063/10% SiC metal matrix composites

In this work, a comparative investigation of electric discharge machining (EDM) and electric discharge drilling (EDD) hasbeen presented to evaluate the performance measures for machining blind holes in Al6063/10% SiC metal matrix composites(MMCs). The work has been conducted with an aim of optimizing the material removal rate (MRR), tool wear rate (TWR), andsurface roughness (SR). The input parameters chosen for machining are (i) discharged current, (ii) pulse-on time, and (iii) dutyfactor. The Taguchi’s L9 orthogonal array has been applied to design the experiments. The grey relational analysis has also beenused to determine the optimal level of input parameters to achieve better results. Analysis of variances (ANOVA) has beenapplied to perform the statistical analysis of the experimental data. The results have shown that discharge current is the mostinfluencing factor that affects the multiple performance characteristics in both EDM and EDD processes.

Electrical Discharge Drilling of micro-hole on Inconel 718 using Rotary Tubular Electrode

Abstract Micro drilling process plays a vital role in modern high end applications in the field of aerospace, nuclear and micro mould making industries. Conventional micro drilling poses challenges not only type of tools but also its precise rotation for an improved hole geometry. Micro EDM process is capable of meeting current industrial requirements. In this paper, an attempt is made to investigate the influence of the characteristics of Inconel 718 on electric discharge drilling process for 0.5 mm diameter micro hole with tubular brass electrode of same size. Experiments were conducted using demineralized water as dielectric medium by varying current, pulse-on time and pulse-off time in three levels while keeping electrode diameter, spindle speed, feed rate and material thickness constant. Taguchi analysis was performed on L9 orthogonal array experimental results show that the effects of input parameters are having varying contributions on output parameters material removal rate, hole taper and its change in hole size called diameter over cut during process

Multi-objective optimization of vibration assisted electrical discharge drilling process using PCA based GRA method

Nowadays, quality and cost of the biomedical products are the key issues for the medical industries to sustain in the global market. Such industries are highly concerned with the machining and high-quality finishing of products manufactured by biocompatible materials. The utility of medical products manufactured by biocompatible materials are increased day by day. In order to that, industries are looking for the advanced technologies for machining such materials and also focusing on optimizing the cost of product without compromising in quality. In view of the above-mentioned problem, Hybrid machining processes are becoming the best possible solution for improving the MRR and surface finish. In present research, a hybrid approach of Vibration Assisted Electrical Discharge Drilling (VA-EDD) is used for processing of Titanium alloy. This paper presents a multi-objective optimization of the VA-EDD process for Ti-6Al-4V to provide higher MRR with a good surface finish. The experiments were conducted using a face-centered central composite design (CCD) of response surface methodology (RSM). The machining characteristics, MRR and SR have been optimized simultaneously by using Principal Component Analysis (PCA) based Grey Relational Analysis (GRA). The VA-EDD process was optimized for getting the optimal levels of process parameter for higher MRR and lower Ra value. The results reveal that the PCA based GRA approach have acquired the setting of optimal process parameters for the VA-EDD process as pulse current (Ip) = 15A, pulse on time (Ton) = 120 µs, pulse off time (Toff) = 15 µs, tool rotation (rpm) = 1200 rpm, and vibration amplitude = 8 µm.

Fabrication of High Aspect Ratio WC-Co Micro Electrodes for µ-EDM Application

Abstract Electrode wear is a prominent issue in µ-EDM as it impairs the geometrical accuracy of the job. WC-Co composite possess high melting temperature, good thermal conductivity and high mechanical rigidity, which makes it a suitable material for micro electrodes for µ-EDM application. In present work, cylindrical micro electrodes of high aspect ratio have been fabricated rapidly from rectangular sheet of WC-6%Co. To fabricate, high aspect micro electrodes from rectangular sheet, a new methodology has been adopted that comprises of slicing of WC-Co rectangular sheet in required width using wire electrical discharge machining (WEDM), followed by electrical discharge drilling (EDD) using tubular electrodes at pre-decided location on sliced strip to obtain cylindrical electrodes. The different trials have been conducted on WC-6%Co to obtain the micro electrodes in the range of diameter 500µm to 150 µm. Discharge current in EDD process has significant influence on diameter and aspect ratio of fabricated micro electrodes. Micro electrode with highest aspect ratio of 45 has been obtained.

A modified electrode design for improving process performance of electric discharge drilling

The present experimental investigation aims at improvement of the response characteristics during electric discharge drilling process. It is a well-established fact that aspect ratio of a drilled hole in Electric Discharge Drilling (EDD) process is limited due to the occurrence of arcing and short circuiting, resulting from ineffectiveness of flushing at larger depth. The prevention of accumulation of debris during EDD is important in order to improve the material removal rate (MRR) and aspect ratio of the hole. This can be achieved by designing shaped tool electrodes which can easily evacuate the debris from the machining zone. In the present experimental investigation, a novel tool electrode has been fabricated by drilling an inclined through hole into the tool electrode (Patent pending). The proposed electrode was found effective in eliminating the accumulation of debris in the machining zone. Moreover, the need of flushing during the process has been totally eliminated making it a self-flushing electrode. The images captured using high speed camera supports the mechanism explained for the debris evacuation. The proposed electrode (diameter 0.8 mm) can drill a hole of depth greater than 9.8 mm in Ti6Al4V which is the highest depth ever reported in the literature for Ti6Al4V using electric discharge drilling. The effect on other response parameters such as machining time, hole taper and corner radius has also been investigated and compared with the holes drilled by solid cylindrical electrode. The fabrication time of the proposed electrode is lower than time reported in the literature. Therefore, the proposed electrode is capable of producing holes of high aspect ratio with minimum electrode fabrication time, thus, improving the overall productivity and reducing the cycle time.

Electric discharge drilling of micro holes in CFRP laminates

Carbon fiber reinforced plastics (CFRPs) are being used in various applications due to their light weight and good mechanical properties. However, conventional hole making in CFRPs results in defects like delamination and fiber pullout. Literature confirms the feasibility of producing defect-free holes using electric discharge drilling (EDD). The researchers have studied macro EDD in CFRPs but drilling of micro holes in CFRPs using electric discharge drilling has not completely investigated. The present research endeavor is an attempt to experimentally investigate the micro EDD process for CFRPs. A tungsten carbide electrode of diameter 120 μm was used as a tool electrode. Several experiments were conducted using different tool geometries (i.e. solid, single notch and double notch) at different values of voltage, capacitance and tool speed. Single notch electrode was found to be the best electrode in getting high material removal rate (MRR), moderate tool wear rate (TWR) and high aspect ratio (29.17). At lower values of discharge energy, a better surface quality was observed during morphological analysis. A comparison was performed between the aspect ratio achieved in the present study and that available in the literature, the tabulated results highlight the achievements of the present experimental endeavor.

Grey relational analysis-based genetic algorithm optimization of electrical discharge drilling of Nimonic-90 superalloy

Nickel-based superalloys are being increasingly used in aerospace, automotive industries due to their excellent thermo-mechanical properties. These applications require complex shapes and profiles which may not be obtained by conventional machining processes. These materials are also known as difficult-to-machine due to their excellent thermo-mechanical properties. The electrical discharge drilling proves its suitability in the precision drilling of superalloys. During, the electrical discharge drilling of these materials, hole taper, hole circularity and hole dilation are key attributes which influence the drilled hole quality. In this research paper, the experiments have been conducted by L27 orthogonal array and this experimental data have been utilized for developing the models of different geometrical quality characteristics such as hole circularity, hole taper and hole dilation. Further, a new hybrid approach grey relational analysis-based genetic algorithm has been proposed and implemented for the multi-objective optimization of different quality characteristics. The effects of different process parameters on various geometrical quality characteristics have also been discussed. Finally, the confirmation tests have been performed to validate the predicted results obtained by the proposed hybrid methodology to the experimental results. It has been observed by the comparison results that the machining performance in the electrical discharge drilling process has been remarkably improved through proposed approach.

Multiple Rock Breakdown in Electrodischarge Technology

The article covers the research of the electric strength and fracture of rocks that are undergone multiple breakdowns generated by electric discharge rock fracture and drilling technologies. The research outcomes allow proposing an experimental technology able to determine operating high voltage pulse values in the electric discharge drilling process where one should take into account such factors as the rock re-crushing and the drill bit shift cyclicity.