Experimental and Multi-Optimization Investigation of Machining (X210) Alloy Steel Using Angled EDM Electrodes

research dealing with this alloy. ARL spectrometer method was used to determine the percentage chemical composition. In the current experimental work, the Effect of different parameters such as electrode angle (EA), peak current (Ip), pulse on time (Pon), and pulse off time (Poff) have been investigated using response surface methodology (RSM). Microhardness reaches the maximum value with an electrode angle of 67.5º with increasing current and pulse. Responses (SR and MH) were modeled using RSM. It is found that the lowest SR is achieved when conducted with an electrode tilt of 45º. A high peak current (Ip) has also been discovered to raise SR further while decreasing pulse-off time. The primary effects of input parameters, specifically E.A, Ip, Pon, and Poff, were determined to impact the Ra and MH considerably. Peak current greatly affects 45º angled electrodes while keeping other parameters constant.


H I G H L I G H T S A B S T R A C T
• A new electrode design with horizontal flushing hole • The novel design improves Hardness and reduce surface roughness of Alloy Steel (X210).• A 3D contour diagrams are achieved to determine the importance of each parameter.• A good agreement between standard deviation and coefficient of variation for predicted and actuals values.• A 45º angled electrode has the lowest value of surface roughness.
Electrical Discharging Machining (EDM) offers broad capabilities that allow it to be used in the manufacturing, automotive, and aviation industries, as well as practically all disciplines of conductive material machining.This experimental and numerical work aims to use EDM to evaluate the surface of Alloy Steel (X210).
The experiments used the EDM copper electrode with a novel horizontal flushing hole.The findings of the investigations have been analyzed so that the best settings for the input process factors can be determined.Alloy tool steel (X210) is cut in dimensions by the Wire EDM (dk7740) (15 × 15 × 10 mm) with very little research dealing with this alloy.ARL spectrometer method was used to determine the percentage chemical composition.In the current experimental work, the Effect of different parameters such as electrode angle (EA), peak current (Ip), pulse on time (Pon), and pulse off time (Poff) have been investigated using response surface methodology (RSM).Microhardness reaches the maximum value with an electrode angle of 67.5º with increasing current and pulse.Responses (SR and MH) were modeled using RSM.It is found that the lowest SR is achieved when conducted with an electrode tilt of 45º.A high peak current (Ip) has also been discovered to raise SR further while decreasing pulse-off time.The primary effects of input parameters, specifically E.A, Ip, Pon, and Poff, were determined to impact the Ra and MH considerably.Peak current greatly affects 45º angled electrodes while keeping other parameters constant.

Introduction
Electrical Discharge Machining (EDM) is a commonly employed technique for machining difficult-to-machine metals.This process involves the removal of material from the workpiece by subjecting it to a series of electric sparks, which result in localized melting.The work material has been subjected to removal by the spark, resulting in the erosion of a small portion of the electrode tool substance.Machining complicated and hard materials with conventional methods could be inconvenient and time-wasting.Furthermore, the surface quality of the finished parts with traditional methods is low [1,2].Electrical Discharge Machining EDM acts on the rule of metal erosion by energy as a thermoelectric between the workpiece and the electrode tool.Due to the complex shape of the tool used to cut, it is possible to replace it with a conductive electrode and regulate the electrode's movements along related axes.EDM avoids the challenges encountered in conventional machining [3,4].The manufacturing industry faces a challenge whenever it must create slots or holes in hard substances while maintaining a high degree of geometrical accuracy.The existence of undercuts in EDM is one of the most important issues [5], which eventually affects the geometrical precision.It has been stated that the undercut, particularly in the case of die production by EDM [6,7], is extremely difficult to predict due to a complicated and non-linear relationship between tool wear, tool diameter, and process parameters.This can be particularly relevant when the undercut arises from tool wear [8,9].
Ahsan Khan et al. [10] investigated the effect of electrode shape on some of the variables for carbon steel with electrode copper material.The electrode geometries were square, diamond, triangle, and round.The round electrode was the best in MRR, followed by other shapes.Diamond electrode approved better MRR and EWR.Jitendra et al. [11] investigated a new tool design to enhance the performance of EDM.Zircaloy_2 is used along the Cu electrode with varying angles of rake by (0°, 45°, and 60°), different values in flat land (2 mm), and different relief angles.By increasing the rake angle, MRR is increased.
Nadeem et al. [12] reported using a conventional tool with relief angles added to the tool electrodes.WC and copper were the workpiece and electrode.Using relief-angled electrodes has resulted in a 49% reduction in the machining time.N. Pellicer et al. [13] Different electrode geometry is investigated in this paper.Rectangle and square geometry show high accuracy in groove processing due to the high EWR and machining stability.The triangular electrode is inefficient because the edges of the triangular shape wear speedy.
Rahul Davis et al. [14] Hollow and solid copper electrodes have been fabricated in this study for holes drilling in composites of quenched tool copper with high hardness.MRR is raised with increasing duty factor and current for two types of electrodes.Conical electrodes had a lesser roughness comprised of hollow electrodes.Hollow electrodes show an increase in tool wear compared to solid.Smrutirekha and Masanta [15] studied an experiment on hexagonal electrodes.Al alloy (A6063) plate was a workpiece.The increasing high current and spark power induced greater crater and improved MRR.Mahesh and Tajane [16] concluded that the best machining achievement is gained when the workpiece is the anode and the electrode is the cathode.The geometry of the electrode with a circular shape gives a high MRR and less tool wear percentage.Round shapes produce surfaces that are smoother and then square.
Junjie Li et al. [17] performed an electrode tool path simulated method to test all faces of molds to study all the uncut zones precisely that cannot be checked and performed by the other cutters.The efficiency of this EDM tool could be enhanced by 70%.Kamlesh et al. [18] presented a study on the effect of electrode geometry on surface quality and MRR.The electrode shape is the most impact factor that influences the functional measures.The Contribution rate of electrode shape is approximately (10-20)% for ANOVA and S/N ratio, and the quality of surface and MRR is enhanced at these values.Bhola Jha and Mohan Rao [19] reported on an EDM review of the papers on electrode tool design and manufacturing to optimize and minimize production time.Electrode Design and manufacturing had an essential role in EDM evolution in the future.There have been no reports of angled electrode work utilizing EDM Alloy steel (X210) as the working material.A limited amount of work is available on the multi-response optimization of the electrical discharge machining (EDM) process when using an angled electrode with a transverse hole electrode.

Novelty of The Study
There are numerous contribution to this work, as follow: New angled electrode (22.5° and 67.5°).Vertical flushing hole has been replaced with one having a side flushing hole.The workpiece is Alloy steel (X210).

Materials and Methods
Alloy tool steel (X210) is cut in dimensions by the Wire EDM (dk7740) (15 × 15 × 10 mm).The ARL spectrometer method was used to determine the percentage chemical composition (wt.%), given in Table 1.
According to the literature survey, no more studies selected those parameters besides the different angles of electrodes.Table 2 lists the values for the various process factors and variables.This study aimed to modify the standard cylindrical design by including several design types, notably by introducing electrodes angled on the sides of the tool.Figure 1 shows the geometry of electrodes with their angles.The tool was made of Cu and achieved in a 10 mm diameter rod of sparking area with 400 mm length and a transverse hole for flushing [20].A die sink EDM machine (CM 323-50N (CHAMBER) was used to generate a 10 mm hole on the surface of specimens.Based on initial experiments, a Schematic sketch of the progressive electrode design and machined surface is shown in Figure 2.
In hypothesis tests, the effective use of the P-value is evaluated to determine whether or not to reject a null hypothesis.The null hypothesis is assumed to be correct.In statistics, the p-value indicates significance, which is the probability of receiving a result at least as extreme as the one obtained.In many contexts, a p-value of 0.05 is considered significant [21].
The analysis of variance (ANOVA) method is utilized to illustrate the different sources of variation, the degree of freedom (DF), adjusted mean square error (Adj MS), adjusted sum square error (Adj SS), sequential sum square error (Seq SS), Fisher's statistical test (F-test), and the corresponding probability values (p-values) in the columns [22].
Experiments are designed to measure the influence of electrode angle geometry on response measures.All other parameters, such as Voltage value, Polarity, and dielectric type, were considered constant, as shown in Table 3. Actual images of the Cu tool are shown in Figure 3, and detailed descriptions of the tools are given in Table 4. Response parameters (SR and MH) are analyzed after EDM machining.The surface roughness was measured with a portable stylus-type Profile-meter, designed explicitly to measure surface roughness (SR), as shown in Figure 4. Hardness Tester THL306 roll special-purpose hardness tester is a professional measuring roll hardness tester.The Hardness Tester is located at Northern Technical University Labs.
Different electrode angles have been machined by a wire electric discharging machine (DK7740).This machine is widely used in mold, bulk production, electronic equipment, precision machinery, medical equipment, auto parts, aerospace and military industries, etc. Figure 5 shows an image of 30 specimens for DOE analysis in alloy steel.Different electrode angles have been machined by a wire electric discharging machine (DK7740).This machine is widely used in mold, bulk production, electronic equipment, precision machinery, medical equipment, auto parts, aerospace and military industries, etc. Figure 5 shows an image of 30 specimens for DOE analysis in alloy steel.

Surface Roughness Analysis
This experimental study focuses on the level of accuracy employed in achieving optimal surface quality throughout the surface alteration process of Alloy tool steel X210 through Electrical Discharge Machining (EDM).The trails are precisely planned and executed via response surface methodology.Design Expert 12 (DX 12) is utilized as the statistical program to generate the surface roughness (SR) regression model.The sum of squares, the lack of fit test, and mathematical model brief statistics were used to assess the constructed model's level of accuracy.An analysis of variance, often known as an ANOVA, is fulfilled to determine the importance of each parameter to keep SR at a minimum.To examine the effect that process variables have on SR, 3D contour diagrams are drawn.The results of the experiments on the surface roughness values are presented in Table 5.
The finding of the analysis of variance (ANOVA) for the constructed SR mathematical model is presented in Table 6.The F-value calculated for the expected SR model is 58.21, which implies that the model is statistically significant.The possibility of a higher F-value due to noise is only possible with a probability of 0.01%.In this case, (E-Angle) B(Current) C(Pulse-on) D(Pulse-off), BC, A², B², C 2 , and Dare discovered significant phrases (P-value less than 0.05).With an F-value of 1.36, "lack of fit" is statistically really significant compared to pure error.
The 0.9044 R 2 predicted and the 0.9560 R 2 adjusted agree with one another within a relatively small range (smaller than 0.2).The signal-to-noise term is calculated by using Adeq Precision.It's favored to achieve a ratio larger than 4. In this scenario, the signal intensity at 28.6435 is sufficient.A regression model for surface roughness (SR) is created using regression analysis.A statistically significant impact (P-value larger than 0.05) is not considered throughout the regression analysis.Equation 1shows the SR regression mathematical model.Figure 6 and Figure 7 illustrate the graphical representation of the relationship between normal probability, externally studentized residuals, and the actual versus predicted SR individually.The plot results suggest a linear relationship between the actual SR and expected SR data, indicating a strong concordance between the predicted and actual values of SR.Therefore, the proposed SR model is very important.These findings were generally consistent with the earlier research [23].The results indicate a rise in current with moderate pulse off.There is a prolonged rise in SR.This increase in surface roughness is due to the accumulation of sparks at the ends of electrodes.In this situation, the more durable heat energy in the machining area degrades the surface's features.Furthermore, the effect of the electrode angle fixed at 22.5º, along with the pulse of time (Poff) and peak current (Ip), on the minimum (SR), is illustrated in Figure 8d as a three-dimensional Contour diagram.This analysis keeps a constant pulse at a level of 150 μm.These results coincide with some research [12,15] The relationship between surface roughness (SR) and pulse-off time and peak current has been investigated, leading to the idea that as the pulse-off time increases and the current decreases, there is a gradual decrease in surface roughness, eventually achieving a minimum value.The reduction in surface roughness observed at an angle of 22.5º can be explained by the reduced availability of heat over a shorter duration.Therefore, a minimum in SR was noticed during the machining process.The effect of electrode angle at 45º with pulse off (μs) and pulse on (μs) on max SR at maintaining the level of peak current constant is illustrated in Figure 9a.The variance of max has been determined, and it is found that there is a continual acceleration in surface roughness for raising the pulse to maximum value with a high value of current at 45º electrode angle.

Regression
A high peak current (Ip) has also been discovered to raise SR further while simultaneously decreasing pulse-off time.Similarly, the influence of electrode angle at 22.5º with pulse off (Poff) and pulse on time (Pon) on min SR, while maintaining the level of Ip = 25 amperes maintain constant is illustrated in Figure 9b as a three-dimensional Contour diagram.It has been determined that for an increase in pulse off, there is a continual drop in SR based on the observed variations of pulse on at minimum value with electrode angle 22.5º.Additionally, a further reduction in stress response (SR) might be noticed along with a rise in pulse on time.(Pon) while keeping current at minimum value.The results presented were compatible with earlier research [2].

Miro-Hardness (MH) Analysis
This experimental study aims to achieve optimal work surface microhardness by modifying the surface of Alloy tool steel (X210) employing electrical discharge machining (EDM).Experiments have been adequately designed and executed, applying response surface methodology.Three microhardness readings were obtained from distinct sites, and the average was selected as the ultimate microhardness value.
Hardness Tester The THL306 roll special-purpose hardness tester, as shown in Figure 10, is a professional measuring roll hardness tester as Table 7 described.The experimental procedure involved modifying many factors.The final result is the average of three microhardness measurements used for further investigation.The microhardness (MH) regression model is created with the statistical program Design Expert 12 (DX 12).The sum of squares, lack of fit test, and model data summary are used to assess the adequacy of the constructed model.ANOVA has also been used to determine the influence of each parameter on maximizing MH.Three-dimensional Contour diagrams are created to investigate the effect of factors on microhardness (MH).Table 7 shows the mean values of the results of the microhardness measurements.
The utilization of analysis of variance assesses the adequacy of the developed model.The finding of the analysis of variance (ANOVA) for the created (MH) design is presented in Table 8.The F-value calculated for the expected MH model is 14.79, suggesting that the mathematical model is statistically significant.A greater F-value due to noise is only possible in 0.01% of cases.In this particular case, the parameters A (E-Angle), B (Current), C (Pulse-on), D (Pulse-off), BC, and A2 have been  identified as significant statistically (with a p-value smaller than 0.05).The F-value for the "lack of fit" is 1.15, suggesting that the lack of fit is statistically important compared to the pure error.The Predicted R² of 0.5244 is in reasoned acceptance with the Adjusted R² of 0.7404; i.e., the difference is less than 0.2.Adeq Precision measures the S/N ratio.A ratio larger than 4 is useful.In this case, 13.3878 indicates an adequate signal.Regression analysis is employed to construct a Microhardness (MH) regression model.In regression analysis, variables with non-significant P-values (higher than 0.05) are typically excluded from consideration.The mathematical regression model of MH is shown in Equation 2. Residual analysis has been used to assess the adequacy of the constructed regression model of (MH).Figures 11 and 12 illustrate the graphical representation of the relationship between externally studentized residuals and normal probability and the actual vs. predicted values of MH, respectively.The plot results suggest a linear relationship between the actual MH values and predicted MH values, indicating a strong agreement between the two sets of data.Therefore, the proposed MH approach has considerable significance.Response surface methodology creates three-dimensional (3D) Contour diagrams for the MH model in Design Expert 12 (DX 12).The correlation of the input variables and the micro-hardness can be better understood with 3D response Contour diagrams.Figure 13a shows a three-dimensional (3D) Contour diagram of an RSM model showing the impacts of electrode angle with Pulse-on and peak current on micro-hardness while keeping a constant amount of Poff = 110µs.It has been determined that there is a continuous increase in maximum MH with an electrode angle of 67.5o.There has been a rise in the magnitude of the highest current.It was noticed according to the variance of max MH, with peak current and pulse on.This increase in maximum MH at the highest current and pulse results from better-expelling power in the parking area, making melting and vaporizing the work material easier.

Regression
A significant quantity of thermal energy resulting from a max current can cause the breakdown of both the tool and the work material, ultimately leading to the melting of the work surface.The impact of the electrode angle fixed at (0º), along with the pulse on time (Pon) and peak current, on the minimal MH is illustrated in Figure 13b using a three-dimensional Contour diagram.The level of Poff remains at a constant value of 80 μs.The phenomenon of minimum (MH) shows variability in both the pulse on time and peak current, which variations in the electrical and physical characteristics of the copper electrode can explain.
Additionally, while maintaining the amount of Pon =300µs constant, Figure 13c illustrates the impact of electrode angle with pulse off (µs) and peak current on maximum MH.The correlation between the maximum microhardness (MH) at an angle of 67.5º and the current has been examined, leading to the inference that a rise in peak current at the maximum value with the pulse off results in an essential rise in microhardness.The enhancement in mental health is observed with the increase in pulse amplitude and current, which can be attributed to the prolonged pulse period.Consequently, the long-term presence of heat energy within the machining area leads to an enhancement in microhardness.
Figure 13d illustrates that the minimum MH decreases continuously when the peak current decreases to its minimum value with minimum pulse-off.Due to the low heating temperature for the shorter duration, MH decreases as pulse off time and peak current decrease.Hence, lower levels of Ip and Pon with a 22.5º electrode angle should be avoided to reduce hardness.
Figure 14a displays the maximum MH's response to varying the electrode angle from 67.5 degrees with Poff and Pon, yet keeping a constant current of 30 Amp, after observing the relationship between MH and pulse at maximum value with a relatively large current, it is determined that MH constantly increased at maximum value.Even while the peak current was rising, MH performance was getting better.
A significant quantity of thermal energy supplied for a prolonged time in the machining region is responsible for the increased MH that occurs with an increase in the pulse-off.
Similarly, the effects of electrode angle 22.5º with pulse off (μs) and pulse on time (μs) on Micro hardness, maintaining the level of Ip = 20 Ampere constant, is shown in Figure 14b.The microhardness varies with pulse on and pulse off at minimum value at lower pulse on and pulse off with minimum current (20 A).

Conclusions and Recommendations
In the present experimental work, the productivity accuracy of Alloy tool steel X210 components using copper electrodes in the form of different electrode angles with transverse holes has been investigated for the EDM process.The effect of different parameters such as electrode angle (EA), peak current (Ip), pulse on time (Pon), and pulse off time (Poff) have been investigated using response surface methodology (RSM).Experimental (DOE) techniques were designed for 30 runs for four parameters for five levels to investigate the effects on output results (SR and MH).
A Central Composite Design (CCD) statistics technique has been used.A complete analysis of variance (ANOVA) was done to determine the most influential parameters.Responses (SR and MH) were modeled using RSM.The experiment obtained the lowest SR reading of 3.44133 μm when conducted with an electrode tilt of 45º, a peak current of 15 A, a pulse on-time of 225 μs, and a pulse of time of 80º μs.
Experiments were conducted using a reduced peak current value as the primary contributing factor in achieving a desirable surface finish.At an electrode inclination of 67.5º, with a maximum current of 30 amperes, a pulse on duration of 300 µs, and a pulse off time of 110 µs, the highest value of MH recorded is 720 VH.High microhardness at an electrode inclination of 67.5º is achieved by increasing the peak current and pulse duration.Dies and pressing tool durability can be significantly increased by using this approach to increase microhardness, increasing resistance to wear and abrasion.It's clear from the coefficient of variation that (C.V) values with the range that gives the model precisions with the responses.A good agreement exists between predicted and actual values for both responses, surface roughness, and hardness.

Figure 2 :Figure 3 :
Figure 2: The geometry of the angled electrode and workpiece

Figure 8 :Figure 9 :
Figure 8: (a) Max SR vs. Pon and Current, (b) Min SR vs. Pon and current, (c) Max SR vs. Poff and current, (d) Min SR vs. Poff and Current

Table 2 :
Interesting factors and their levels Figure 1: Electrode types with different angles

Table 4 :
Experiment design

Table 5 :
SR values and experiment matrix

Table 6 :
ANOVA for SR

Table 7 :
MH value and experimental matrix