Investigation of enhancing EDM machining performance of INCONEL alloy using composite electrodes

In this research, an attempt was made to reinforce aluminium with graphite particles and use it as a tool material with the objective of combining the properties of aluminium and graphite. The micrograph confirms that the graphite particles were uniformly distributed over the aluminium matrix, density reduces and thermal conductivity increases with the addition of graphite particles. Material Removal Rate (MRR) peaks at 12 A current before declining due to plasma channel expansion, an optimal Ton of 8 μs ws observed, with 4 μs Toff yielding higher MRR. Copper electrodes excel due to thermal conductivity, while 5% graphite in aluminum boosts MRR to 31.89 mm3 min−1, additional graphite decreases MRR. TWR rises with shorter Toff until 6 μs, then decreases. Gap control impacts TWR, with lower spark gaps causing higher TWR due to intense material removal, and higher gaps leading to increased TWR due to incomplete flushing. Copper electrodes have the lowest TWR due to their high melting temperature. The addition of graphite in aluminum reduces TWR at low currents but is less effective at higher currents. Surface roughness (Ra) decreases with higher current, reaching a minimum of 7.02 μm at 12 A. Optimal Ton is 8 μs (7.56 μm), while shorter Toff at 4 μs and a 3 mm gap yield the best Ra of 7.36 μm with A4 composite tool. Copper electrodes result in higher Ra at higher currents, while graphite in aluminum improves surface quality, especially at 5% content. Arcing, an undesirable electrical discharge phenomenon in EDM, adversely affects machining. Experiments revealed a strong correlation between high duty cycles, duty ratios, and arcing propensity, with composite tools being more susceptible due to their variable conductivity. In contrast, non-composite tools, exemplified by copper, withstand higher duty ratios without arcing.


Introduction
Electric Discharge Machining (EDM) is a non-traditional machining process that employs electrical discharges to remove material from a workpiece [1].EDM has evolved into a precise and versatile method for machining conductive materials, offering advantages such as minimal tool wear and the ability to machine intricate shapes and hardened materials [2].With applications in aerospace, medical, and precision engineering industries, EDM plays a pivotal role in modern manufacturing [3].In EDM, process parameters namely current, voltage, pulse on-time, pulse off-time, and gap distance are key factors that directly influence Material Removal Rate (MRR), Tool Wear Rate (TWR), Surface Finish (Ra) and accuracy [4][5][6].The discharge current influences the spark intensity and the amount of material removed during each discharge.Higher current values result in increased material removal rates, but they can also lead to excessive tool wear and rougher surface finishes [7,8].The voltage generates higher spark energy; however, excessive voltage levels can cause instability in the spark gap [9].Longer pulse on-times generate more heat and Pulse off-time is crucial to prevent overheating and maintain process stability [10].Gap distance, determines the energy concentration in the spark gap, smaller gap distances are generally associated with higher accuracy but lead to slower MRR [11].
The choice of tool material significantly influences the efficiency and precision of material removal and extensive research conducted on various EDM tool materials, including copper, graphite, copper tungsten, brass, and aluminium [12][13][14].Copper electrodes renowned for its excellent electrical conductivity and thermal stability are particularly effective for roughing operations due to their high removal rate capabilities and high precision [13].Graphite with high melting point, electrical conductivity and excellent wear resistance are capable of achieving fine Ra making them indispensable in the production of molds and dies [14].Copper tungsten with the exceptional hardness and wear resistance are well-suited for applications requiring high MRR and prolonged electrode life.Aluminium proffered fast MRR and are often used when heat dissipation is a critical concern [15].Brass exhibits low thermal conductivity, which restricts heat dissipation, while its low melting point contributes to rapid melting of the electrode material [16].Somu et al machined Inconel 718 utilizing Copper-Graphite (CG) composite tool reinforced with 5, 10, 15% graphite.CG-5% exhibited the best MRR and lowest TWR due to the bridging effect, high thermal conductivity, and lower density of the tool material [17].Tsai et al conducted EDM of medium carbon steel utilizing Cr/Cu-based composite electrodes.The result revealed that improvement in machining performance, reduced recast layer thickness, and enhanced corrosion resistance [18].Senthilkumar et al developed copper-based metal matrix composite tool for EDM od die steel.The results revealed that Cu-B 4 C composite with 40% boron carbide reinforcement exhibited enhanced MRR and TWR in comparison to traditional copper electrodes [19].Prosun Mandal et al developed Copper-Single Wall Carbon Nanotube (Cu-SWCNT) nanocomposite coated 6061 aluminum electrode as an EDM tool, The coated electrode attained 14.52% improvement in MRR and 29.6% reduction in TWR in comparison with uncoated electrodes [20].Li et al investigated the machining of Ti-6Al-4V alloy using a Cu-SiC composite electrode.Machined surfaces exhibited irregular compound structures, debris droplets, shallow craters, and micro-pores.The use of the Cu-SiC electrode resulted in fewer microcracks compared to the Cu electrode [21].Similarly ZrB2-40 wt% Cu composite exhibited high MRR and lower TWR [22].
The field of optimization techniques has seen remarkable advancements in recent years, Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), and Grey Relational Analysis (GRA) are the most commonly used optimization technique [7,11,23].TOPSIS, originally developed by Hwang and Yoon in 1981, is a multi-criteria decision-making method that assists in ranking alternatives based on their proximity to an ideal solution while simultaneously considering their proximity to a worst-case scenario [12].VIKOR, introduced by Opricovic in 1998, offers a compromise solution for multiple criteria decision-making problems by minimizing the maximum individual regret [24].Grey Relational Analysis (GRA), on the other hand, stems from grey system theory and focuses on solving complex decision-making problems in uncertain and imprecise environments [25].From the literature survey, it was evident that tonnes of works were performed on the EDM by varying its process parameters and tool materials.But works related to utilizing aluminium composites as the tool materials were scarcely available.Hence in this work, an attempt was made to machine Inconel 718 alloy utilizing Aluminium composites reinforced with different weight proportion of graphite particles as a tool material.The surface topography was analysed using the Scanning Electron Microscope (SEM) and optimized using VIKOR optimization technique.The main objective of the study is to bridge the gap evident in the scarcity of research concerning the utilization of aluminium composites as EDM tool materials.Machining Inconel 718 alloy utilizing aluminium composites reinforced with varying proportions of graphite particles, this research seeks to integrate the unique properties of aluminum and graphite to enhance machining performance and productivity.This novelty addresses the lack of research in this particular area, propelling the EDM sector towards improved efficiency and advancement.

Tool and workpiece
The aluminium alloy, with a composition in table 1, heated to a temperature of 850 °C within a graphite crucible via an induction furnace.Simultaneously, graphite particles, sized at 0.5 μm, were preheated to 250 °C and introduced to the molten alloy.Preheated particles reduces moisture content, improving matrix and reinforcement wettability and smaller size particles uniformly dispersed in the aluminum matrix.This blend

Experimental procedure
The design of experimental runs was structured utilizing a Taguchi L25 orthogonal array.The selection of input parameters was based on preliminary experiments using aluminium and copper electrodes, with the assumption that all trials would yield a stable discharge.Machining experiments were conducted utilizing the Elektra M2A die sinker EDM machine.The parameters A, Ton, Toff, and GC were varied, as outlined in table 3 and the dielectric fluid employed was conventional EDM oil.Electrodes used encompassed AG5, AG10, AG15, Copper (C), and Aluminum (A).Trial runs were used to determine the parameters, and the array was chosen based on a literature review.Responses in the form of Material Removal Rate (MRR), Tool Wear Rate (TWR), and Surface Finish (Ra) were meticulously recorded.Each specimen underwent 10 min of machining, with a consistently maintained positive polarity throughout the experiments.The surface topography of the machined samples was inspected using the SEM (JEOL JSM-6480LV).

Calculation of MRR, TWR and Ra
MRR and TWR were computed based on the weight differences before and after machining, normalized by the product of material density and machining duration, as expressed in equations (1) and (2), respectively.Weight measurements were executed using a precision wensar weigh balancing machine.Meanwhile, the Ra value was assessed using the SJ210 Mitutoyo surface roughness tester, with the mean value derived from measurements at 10 distinct locations.

Whereas
Aa and Ab represent the initial and final mass of the workpiece (measured in grams).
Ba and Bb signify the initial and final mass of the tool (measured in grams).s denotes the machining duration (minutes).
The density of the tool is represented by ρ (in g/cc).Volumetric MRR & TWR in mm 3 /min

Microstructure of composites
The micrograph of composites as shown in figure 1 reveals that the graphite particles are uniformly over the aluminium matrix.This uniformity ensures consistent electrical conductivity and thermal properties throughout the composite tool.In EDM, the distribution of electrical discharges across the tool's surface greatly influences material removal and the generation of heat.With uniform distribution, the composite tool can efficiently conduct and disperse electrical discharges, resulting in stable machining conditions.The results demonstrated a consistent reduction in density with the incorporation of graphite particles into the aluminum matrix as shown in table 4. Specifically, aluminum exhibited a density of 2.61 g cm −3 , which decreased as the graphite content increased.Notably, aluminum with a 15% graphite content reached a density of 2.52 g cm −3 .This reduction in density suggests that the AG composites offer advantages in terms of improved MRR, as lower density materials are generally more susceptible to EDM material removal.Copper, with a high thermal conductivity of 403 W mK −1 , outperformed aluminum, which had a thermal conductivity of 237 W mK −1 .However, it is intriguing to note that the AG composites exhibited an increase in thermal conductivity with rising graphite content.For instance, aluminum with 15% graphite achieved a notably higher thermal conductivity of 259 W mK −1 .This phenomenon suggests that AG composites possess the potential to enhance the EDM process by facilitating improved heat dissipation.

Influence of various process parameters on the MRR of inconel alloy
The interaction impact of the various process parameters on the MRR of Inconel alloy was shown in the figure 2.
The current, a most influential process parameter of the EDM as reported by the various researchers, MRR upsurges with increase in current until the saddle point of 12 A, thereafter it reduces.The increase in MRR was ascribed to the fact that the higher current produces the heat of high intensity which removes more volume of materials from the surface [26].When the current was tuned beyond 12 A, expansion of plasma channel occurred, hence MRR reduces.The generated heat was hang inside the spark gap for stipulated period of time and it was referred to as the Ton and the MRR upsurges with raise in Ton until the 8 μs, thenceforth reduces.At the Ton of 10 μs, heat held inside the spark gap for extended period of time which removes high volume of materials results in the densification of machined debris.Owing to which machined particles were not completely flushed away results in the reduction of MRR [27].
A maximum MRR of 30.06 mm 3 min −1 was attained when the Toff was tuned at 4 μs and it drastically reduces to 14.786 mm 3 min −1 when there is shift in Toff to 10 μs.At higher Toff, no heat was generated for the longer period of time hence the, hence lower volume of materials was removed from the surface resulting in lower MRR.The Toff should be ideal, as this time was used to flush the machined debris.With regards to the gap control, maximum MRR of 28.86 mm 3 min −1 was attained for the parametric value of 5 mm.At lower spark gap owing to the high heat intensity, as the high volume of material were removed, because of inadequate flushing MRR reduces.At higher spark gap the voltage was not sufficient to break down the dielectric fluid which results in the reduction of MRR [28].The five electrodes were utilised for the investigation, of which copper electrode possess the MRR of 30.53 mm 3 min −1 whereas aluminium records 14.83 mm 3 min −1 which was alluded to the fact thermal conductivity of the electrode.Because of this enhanced property it generates lot of heat during machining process which erodes material at higher rate [29].Remarkably, when five percent of graphite particles were added to the aluminium, specimens obtained the maximum MRR of 31.89mm 3 min −1 .By using composite material as the tool during machining the reinforced particles detached from the tool surface and enters the spark gap.These particles moves in a zigzag fashion and causes the bridging effect which increases the heat intensity, hence MRR increases.With further increase in the weight percentage of graphite particles, MRR reduces drastically and reaches a minimum of 7.54 mm 3 min −1 [30].
When the copper was used as the electrode, MRR increases until the gap distance of 6 mm and in case of A1 tool it improves till 10 mm.When A, A2, A3 were used as the electrode, MRR reduces with increase in the gap distance.As discussed earlier, 4 μs was the optimal Toff, as all the electrode used for the investigation proffers maximum MRR.In case of Ton, MRR increases linearly when Cu was used as the electrode, it declines after 8 μs in case of A1 composite tool [31].The optimal current for copper tool was 9 A and in case of composite tool it increased to 12 A, as the MRR of 49.97 mm 3 min −1 and 46.37 mm 3 min −1 was recorded for the above mentioned parametric setting respectively [32].

Influence of various process parameters on the TWR of inconel alloy
The influence of various process parameter on the TWR was depicted in the figure 3. The TWR increases with raise in current, generated spark removes material from the work piece as well as tool material [33].At higher current owing to the high intensity, it erodes high quantity of materials from the electrodes, results in increase in TWR.In case of Ton, a maximum of 1.79 mm 3 min −1 was recorded for 6 μs and it reduces to 1.12 mm 3 min −1 when the Ton was increased to 10 μs [34].The results revealed that the most of the generated heat was transferred to the work piece.The TWR increases with raise in Toff until the saddle point of 6 μs, thereafter it reduces.The TWR ranges between 0.7 mm 3 min −1 to 0.8 mm 3 min −1 when the parametric was tuned either at higher or lower parametric level.The TWR reduces with increase in spark gap until the saddle point of 5 mm, thereafter it increases.As discussed earlier, at lower spark gap because of high intensity more materials were  removed from the material and at high gap distance, owing to the complete flushing higher volume of materials were removed from the surface [35].
As expected, Cu possess the least TWR followed by the A1 composite tool.The least TWR was elucidated to the fact that Cu posses high melting temperature of 1100 °C in comparison with the aluminium 720 °C.When A1 was used as the electrode, as discussed earlier graphite particles from the composite surface gets detached and enter inside the spark gap [36].The space between the electrode gets increased to maintain the gap distance which reduces the TWR.When the Gr weight percentage exceeds beyond 5%, TWR increases rapidly to 2.43 mm 3 min −1 owing to the uncontrolled sparking [37].The interaction impact of distinct process parameters was depicted in the figure 4. The interaction between the choice of electrode material and the current employed significantly influenced the tool wear rate (TWR) in the EDM process.The observed trends can be attributed to several factors, including the conductivity and thermal properties of the electrode materials, the wear characteristics of graphite, and the impact of the EDM process parameters [38].Copper's excellent electrical and thermal conductivity makes it a suitable electrode material, resulting in lower wear at low current (3 A).However, as the current increased, the enhanced spark intensity led to more wear on the copper electrode.Conversely, aluminum electrodes demonstrated varying TWR behaviors.The introduction of graphite in small proportions (A1) notably reduced wear at low current.This reduction could be attributed to the lubricating and protective properties of graphite.At higher currents, however, the impact of graphite became less pronounced, possibly due to its reduced influence in the face of more intense electrical discharges [39].
Copper electrodes (C) maintained a significantly higher TWR of 2.06 mm 3 min −1 .In contrast, aluminum electrodes (A) demonstrated a notably reduced TWR of 0.80 mm 3 min −1 .The introduction of graphite in varying proportions (A1, A2, A3) led to fluctuating TWR values, with A3 displaying the highest TWR of 4.16 mm 3 min −1 .These results can be attributed to the complex interplay of factors, including the electrode material's thermal conductivity [40], the protective properties of graphite, and the impact of varying pulse ontimes.Copper electrodes (C), due to their excellent thermal conductivity, exhibited relatively low TWR values at shorter pulse on-times (2 μs, 4 μs).Aluminum electrodes (A) showed significantly higher TWR values at shorter pulse on-times, indicating increased wear.The introduction of graphite into the aluminum electrode materials led to varying wear outcomes, with 5% graphite (A1) exhibiting favorable wear-reducing effects.The interaction of gap control and electrode has relatively little influence since the TWR ranges from 0.011 mm 3 min −1 to 0.05 mm 3 min −1 when copper is utilised as the electrode.When A1 was used as the electrode TWR increases with raise in Toff and in case of C, no major fluctuation was observed and it reduces when A3 was used as the electrode.When the current is increased from 12 A to 15 A, the TWR for the C tool changes -from medium to severe.When using composite as the tool material, the shift range was 9 A.

Influence of various process parameters on the Ra of inconel alloy
The influence of distinct process parameters on the Ra of Inconel alloy was depicted in the figure 4. The surface roughness of the composites reduces with increase in the parametric value of current and a minimum average Ra value of 7.02 μm was attained for 12 A current.At higher current in the presence of graphite particles owing to the bridging effect, increment of spark gap occurred which facilitate the complete removal of machined debris from the gap hence surface quality enhances [41].With raise in Ton Ra slightly reduces and reaches a minimum of 7.56 μm for 8 μs and with further raise in Ton to 10 μs Ra drastically increases to 9.68 μm.The optimal Toff and gap control for obtaining better surface quality was 4 μs and 3 mm respectively.Best surface quality of 7.36 μm was attained when A4 composite were used as the tool material, because of the bridging effect, spark gap increased and complete flushing of machined debris occurred which eliminates the formation of remelted layers on the surface which results in the enhancement of surface quality [42].
The interaction impact of distinct process parameters were depicted in the figure 6.When C was used as the electrode Ra worsens with increase in the gap distance and for 10 mm, Ra value of 10.58 μm was recorded.For the same parametric setting Ra value of 10.12, 4.27, 6.34 and 11.31 m was attained for the tools of A, A1, A2 and A3 respectively [43].When the Toff was tuned at 4 μs and A1 was used as the tool, a minimum Ra value of 4.26 μm was attained and it was increased to 5.48 μm when aluminium was used as the electrode.With regards to the Ton, a minimum Ra of 6.67 μm was attained for copper tool and it was reduced to 4.2 when A1 tool was utilized at 8 μs Ton.The observed results can be attributed to the intricate interplay of pulse-on time and electrode material properties [44].At shorter pulse-on times (2 μs), copper electrodes produced a smoother surface, whereas aluminum electrodes showed a rougher finish.As the pulse-on time increased, copper electrodes produced rougher surfaces, while aluminum electrodes exhibited smoother finishes.The addition of graphite particles influenced the surface finish, with 5% graphite content (A1) generally leading to improved surface quality [45].Conversely, higher graphite content (A3, A2) resulted in rougher surface finishes.With respect to the current, graphite content and electrode material copper electrodes (C) produced rougher surfaces at higher currents (12 A, 15 A), suggesting that higher current intensities can lead to increased material removal and a coarser finish.Conversely, aluminum electrodes (A) showed smoother surfaces at these current settings.The introduction of graphite, especially at 5% (A1), contributed to improved surface finishes, as reflected by the lower Ra values.

Arcing
Arcing, a critical phenomenon often encountered in machining operations which involves the formation of an unwanted electrical discharge path, leading to localized melting and material erosion.Arcing affects machining accuracy, surface integrity, and tool wear.The experiments in which arcing is observed, specifically experiments 6, 11, 12, 13, 14, and 21, exhibit a distinctive pattern.These experiments display higher duty cycles and duty ratios compared to those where arcing does not occur.The results indicated that a substantial correlation between duty cycle, duty ratio, and the propensity for arcing during EDM.Elevated values of duty cycle and duty ratio correspond to prolonged active discharge periods [46].A higher duty cycle means that the electrical discharge remains active for a more extended period during the machining process.In Experiment 2, the duty cycle is 50%, indicating that the electrical discharge is active half of the time.An extended active discharge period can lead to localized temperature increases within the composite electrode.This could contribute to arcing, especially if the material's thermal properties are not conducive to efficient heat dissipation.For the experiments utilizing composite materials, the influence of these parameters becomes more pronounced.The mechanism at play is the generation of heightened thermal energy during prolonged discharges, affecting the tool's integrity [47].Composite tools, especially those with conductive components like graphite, might be particularly vulnerable to the increased thermal energy, leading to localized material degradation and the onset of arcing.
Lemma 1: For composite tools in electrical discharge machining (EDM), as the duty cycle increases, the likelihood of arcing also increases, due to the varying electrical conductivity of composite materials.
In Experiment 6, a composite tool (A2 -Aluminium-10% Graphite) exhibited arcing.This experiment had a duty cycle of 4 μs 'on' and 6 μs 'off.'In Experiments 11, 12, 13, and 14, which also used composite tools, arcing occurred.These experiments had varying duty cycles, ranging from 2 μs 'on' and 6 μs 'off' to 6 μs 'on' and 10 μs 'off.' Lemma 2: Non-composite tools in EDM can withstand higher duty ratios, where the 'on' time is a larger proportion of the total pulse cycle, as they maintain stable and predictable electrical conductivity.
Experiments 1 and 16 utilize non-composite tools made of copper, with a 50% duty cycle and a duty ratio of 0.5.In both cases, no arcing observed [48].This demonstrates that non-composite tools can handle a higher duty ratio without experiencing arcing.Their consistent and high electrical conductivity, as seen with copper, contributes to stable EDM performance under varying duty ratios.

Machined surface morphology
The machined surface morphology of Inconel alloy processed with Aluminium tool was depicted in the figure.At lower magnification of 100X, the surface revealed the globules and uneven machined surface as depicted in figure 5(a).EDM, machining takes places by means of melting and vaporization, When the voltage was applied the material from the surface of the Inconel gets melted, owing to the incomplete flushing some of the melted materials redeposited over the machined surface which reduce the surface quality [49].The uneven machined surface was formed because of uneven heat distribution, which occurs because of uneven tool wear.At higher magnification, larger globules of diameter more than 10 μm was observed as shown in figure 5(b).Because of the extreme heat some of the areas were completely burnt away.
When machined with A3 composite tool, globules of diameters greater than 100 μm was observed as depicted in the figure 6(a) the result portrayed that when composite tool of higher weight percentage was used poor quality surface was attained.The coating of globules was observed which elucidate that the flushing was very worse, and this feature confirmed that almost all of the machined materials were redeposited over the surface [50].At higher magnification, globules and uneven machined surface were clearly visible and a new creature called pock marks were observed as shown in figure 6(b).While machining, some of the vapours were entrapped inside the melting zone and when releasing it release a unique feature referred as the pock marks.Inconel machined using the A1 composite tool showed very tiny globules as shown in figure 7(a) and it was present entirely over the surface which confirmed that the generated heat was uniformly distributed.The micro pits along with remelted layer were clearly visible on the surface.At higher magnification picture displayed remelted layer of size less than 10 μm as shown in figure 7(b) which confirmed that the addition of graphite facilitate the flushing.

VIKOR
VIKOR optimization method was implemented to discern the optimal parametric combination.The initial phase involves the formation of the choice matrix denoted as Bij, where 'i' represents the number of responses was applied to standardize the decision matrix [52].
The subsequent stage involves a comparative analysis of the best and worst values for each criterion derived from the normalized matrix, in accordance with equations (4) and (5) [53].Specifically, Si-max denotes the maximum value of Si, while Si-min signifies the minimum value of Si, both in the presence of R (i-max), which represents the maximum value of Ri, and R (i-min), signifying the minimum value of Ri.The variable 'k,' falling within the range of 0 to 1, serves as the weight assigned to the 'majority of criteria' approach, commonly designated as 0.5.To establish the ranking lists as presented in table 6, the values of Ri, Si, and Ti are individually ordered for alternatives, subsequently scaled within the range of 0 to 1 [54].

Conclusion
The Inconel alloy was EDM using the aluminium composite electrodes and its performance was compared with the conventional electrode and following results were obtained (1) Highest MRR was recorded when A1 composite was used as the electrode alluded to the thermal conductivity of materials and bridging effect.when the weight percentage of graphite content exceeds 5% results in uncontrolled spark generation which leads to the reduction of MRR.
(2) The A1 composite tool has the least TWR, followed by Cu.The fact that copper has a higher melting temperature than aluminum-1100 °C as contrasted to 720 °C.When A1 was utilised as the electrode, graphite particles from the composite surface became dislodged and entered the spark gap.To keep the gap distance constant, the spacing between the electrodes raised and lower the TWR.
(3) Ra of the samples reduces, when machined using composite electrodes owing to the facts complete flushing of machined debris and expansion of spark gap.The pits, craters, globues and uneven machined surface are some of the features observed on the machined surface topography.
(4) The parameters were tuned using the VIKOR approach, and it was found that the best productivity was achieved with the parametric combination of 12 A current, 8 μs Ton, 4 μs Toff, and 7 mm gap distance machined with C1 composite tool.

Limitation and scope for future work
Due to processing limitations, the stir processing method utilised in this work limited the composite production to a maximum of 20 weight percent graphite in aluminium.Subsequent research endeavours ought to take into account alternative methods of fabrication, such as powder metallurgy, which provide greater versatility in integrating elevated levels of graphite in aluminium composites without any restrictions.This will facilitate the examination of an expanded array of composite compositions and their impact on the efficiency of machining.Furthermore, investigating different material combinations like copper-graphite and tungsten-graphite provide information on new composite formulations with a range of qualities that are advantageous for machining applications.

Figure 1 .
Figure 1.Micrograph showing uniform distribution of graphite particles over the aluminium matrix.

Figure 2 .
Figure 2. Impact of various process parameter on MRR of Inconel 718 alloy.

Figure 3 .
Figure 3. Impact of various process parameter on TWR of Inconel 718 alloy.

Figure 4 .
Figure 4. Impact of various process parameter on Ra of Inconel 718 alloy.

Figure 5 .
Figure 5. Surface morphology of Inconel 718 alloy machined with Aluminium tool (a) At lower Magnification (b) At higher Magnification.

Figure 6 .
Figure 6.Surface morphology of Inconel 718 alloy machined with A3 tool (a) At lower Magnification (b) At higher Magnification.

Figure 7 .
Figure 7. Surface morphology of Inconel 718 alloy machined with A1 tool (a) At lower Magnification (b) At higher Magnification.

Table 1 .
Chemical composition of AA6061 aluminium alloy.The uniform distribution of graphite particles within the aluminum matrix was verified through EDS mapping.The liquid immersion and hot plate system method was used to determine the composite density and thermal conductivity.The workpiece for experimentation was Inconel 718 alloy, found its application in aerospace and automotive sectors owing to its high strength, corrosion resistance and suitable for high temperature application, measuring 12 mm in diameter and 20 mm in length, sourced from Kanungo Ferromet Private Limited, Mumbai.The chemical composition of this alloy is delineated in table 2.

Table 3 .
Process parameters and its variables.

Table 4 .
Density and thermal conductivity of electrode materials.

Table 5 .
Experimental results and formation of decision matrix.

Table 6 .
[51]mization of process parameters through VIKOR optimization Technique.signifiesthequantity of experimental runs[51].In the context of the current study, a 19 × 4 decision matrix was established, as outlined in table5.Any instances of open circuits and arcing during the experiments were promptly addressed.Subsequently, equation