# Wedm Process Optimization for Machining Characteristcis of AISI 52100 Grade Alloy Steel

Authors: Debabrata Rath; Pratap Chandra Padhi; Sudhir Kumar; Inderjeet Singh; N. Nagaprasad; Ramaswamy Krishnaraj
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

The present study deals with one of such investigations, which focuses on optimization of the different machining parameters of WEDM for AISI 52100 grade steel. For this work, a standard design of experimentation (DOE) based on Taguchi L27 orthogonal array (OA) has been used by selecting 6 different input parameters of the WEDM for optimization of two output characteristics (surface roughness (Ra) and dimensional deviation (DD). The results suggest that Pulse on Time (Ton): 1µs, Pulse off time: 18µs; Wire Feed (WF): 12mm/min, Spark Gap Set Voltage (SV): 20V, Wire Tension (WT): 1650, and Servo Feed (SF): 8units) are the best condition for the machining AISI 52100 grade steel as the roughness value (Roughness value: 1.02Ra) and dimensional deviation (Dimensional deviation: 0.02) obtained for these settings came to be least. From the result analysis of the current study, the pulse on time (Ton) was ranked at 1st, spark gap voltage came to be as 2nd rank parameter and pulse off (Toff) time was ranked 3rd, and wire tension was ranked at 4th position which significantly contributed towards the wire-EDM machining of AISI 52100 grade steel. Morphological analysis such as semi electron microscopic (SEM) analysis and 3D surface rendering also supported the observed surface and dimensional behaviour.


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## Body

## 1. Introduction

Wire electric discharge machining (WEDM) is an electrothermal machining process in which material removal takes place by the erosion of metal particles removed from the workpiece by high-intensity electric sparks carried out on the metallic wire [1, 2]. In EDM, both the workpiece and the cutting tool (wire electrode) are submerged in the di-electric fluid [3]. The di-electric fluid is constantly removed and filtered to erode the particles, and a thin electrode wire is fed into the workpiece. The toolpath motion of the Wire EDM is similar to a CNC machine operated through a computer program for the pre-defined three-dimensional shape [4]. The wire-cut EDM is popularly used in the fabrication of aerospace, automobile, and tooling components in precision. The EDM is capable of efficiently making complex geometrical parts, hard to machine materials which are quite difficult in the conventional machining processes [5]. Henceforth, this technology is a very promising area of research in the past few decades and has been explored by numerous authors for parameter optimization.Wire EDM has been successfully employed on different materials, viz. metals, ceramics, and composites in the past [6, 7]. Different materials for the electrodes/wire, viz. brass, copper, and composite wires [8–10], have also been surveyed by different researchers in the past for achieving better cutting rates and surface quality in wire EDM. Similarly, works are presented on the optimization of process parameters to obtain minimum tool wear and better surface quality. However, the performance of the wire EDM process still needs advancement due to sluggish material cutting rate, the inefficiency of producing sharp corners, high cost, and lack of large-scale production capacity associated with the wire-EDM process [11].Ming et al. [12] presented an assessment of the research trends in EDM techniques by considering process parameters, energy distribution, and discharge energy along with the mechanical indicators like metal removal, tool wear ratio, surface topography, etc., and contrasted EDM with conventional machining processes. The environmental and economic impacts were also deliberated by the author, along with the applications. Kumar et al. [13] also reviewed the utilization of the EDM technique for surface modifications and its phenomenon of surface composition after the EDM operation to explore its properties. Hou et al. [14] performed wire EDM on Nickel-titanium shape memory alloy to explore the surface characteristics, including surface damage, shape recovering capability, and hardness characteristics. The authors reported a decrease in roughness from 2.79 µm to 0.12 µm.Paulson et al. [15] investigated titanium super-alloy by expending the Taguchi method for attaining the highest material removal along with minimum surface roughness. The peak current increase directly influences the above two output parameters, and the same trend has been observed for pulse-off time. The optimum peak current of 3A was reported from the grey relational analysis, and the pulse-on and pulse-off time were achieved to be 30 µs and 9µs, respectively. Tombul et al. [16] presented a comparative analysis of wire-EDM of steel at different heights by using brass wire and coated electrodes of three distinct diameters for comparison. 12 specimens were fabricated and tested for surface roughness of the specimen. It was concluded that the cutting rate is considerably increased using 0.4mm wire at the cost of increased surface roughness. Kadam et al. [17] studied the roundness error in wire EDM for three metals, viz. H13, EN24, and SS316 by varying cutting speeds from 4.80-7.87mm/s with other parameters staying fixed. It was concluded that the roundness error is more evident at lower cutting speed and vice-versa. In another study, Liao et al. [18] tried to attain good surface roughness in wire-EDM by controlling the parameters at the final stage of machining. A good surface roughness of 0.22 µm is achieved after optimizing the control parameters of the machine. A study by Shabgard et al. [19] has revealed the parametric effect of input variables on WEDM cut surface recast layer thickness and heated zone of Inconel 617 materials. From the study, it is outlined that the pulse current and duration happen to be the key aspects of the development of RTL and HAZ. Similarly, Kumar et al. [20] analyzed the surface topography of Inconel 825 material in the WEDM workpiece and witnessed a reducing trend of the surface finish with an increase in the duration of the pulse. The study also ensured that the formation of surface crack, recast layer, and HAZ has relation to pulse duration and peaks current. The study was extended by Anish Kumar et al. [21], who scrutinized the influence of controlling parameters on MRR and surface roughness during wire EDM of CP-Ti G2 biocompatible material using a desirability' function hybrid with a machine learning algorithm. On the same grounds, the wire EDM was successfully employed and tested for optimal machining of Carbon fiber reinforced plastic [22], The employment of the wire-EDM process has been lucratively done on different types of ceramics also by researchers in the past. Grigoriev [23] presented a detailed review on the EDM of different ceramics, viz. ZrO2, Al2O3, SiAlON, Si3N4, AlN, etc., via comparison. The authors established different surface quality and other mechanical and electrical aspects of the machined ceramics of different conductivity. For different electrodes and di-electric mediums, maximum depth and operation time was summarized for all diverse range of ceramics. In another study by Lok and Lee [7], advanced ceramics viz. Sialon and Al2O3-TiC were tested lucratively utilizing EDM. The different machining conditions were scrutinized for comparison of the material removal rate and surface integrity. Banu et al. [24] reported an EDM for non-conductive ceramic viz. Zirconium Oxide (ZrO2) has tungsten as an electrode and discussed the hardness and machining properties under different input conditions. Similarly, many other studies have been reported in the literature for different conductive and non-conductive ceramics with EDM [25–28].Besides the experimental studies, multi-objective parametric optimizations have been carried out for the wire-EDM process by the authors using the Taguchi approach, desirability, grey relational analysis, etc. Kumar and Nishasoms [29] studied the operating parameters in wire EDM of Al (6082) and tungsten carbide composite employing multi-objective optimization using desirability function analysis. Likewise, Singh and Singh [30] utilized the Taguchi approach to achieve maximum cutting rate using cryogenic-treated D-3 steel and reported 50% less tool wear for cryogenically treated copper wire as compared to conventional wire at 4A and 8A current. A similar trend has been achieved for the brass electrode. Few more studies are available in the literature stating the optimal process parameters for wire EDM process obtained using Taguchi, desirability and grey relational analysis, etc. [31–37]. Bayraktar and Kara [38, 39] studied the cryogenic treatment condition for cutting tool material and milling operation for the optimization of surface roughness parameters.From the literature review it may be observed that several parameters of the wire-edm process affects the machining of object. Some of them are as mentioned below in Table1 with reference details.Table 1
Machining parameters of wire-EDM affecting the output responses.
S.No.Machining Parameter affecting the outputReference1Pulse currentPaulson et al. [15]; Singh and Singh [30], Grigoriev [23], Özbek et al. [40]2Cutting wire Dia and materialSingh and Singh [30], Grigoriev [23],3cutting speedsKadam et al. [17]4Pulse-off timeShabgard et al. [19], Kumar et al. [20]; Özbek et al. [40]5Pulse-On timeShabgard et al. [19], Kumar et al. [20]; Özbek et al. [40]6Electrode and mediumSingh and Singh [30]7Cutting materialHou et al. [14]; Anish Kumar et al. [21], Banu et al. [24]8Cutting depthÖzbek et al. [40]


### 1.1. Scope/Novelty for the present study

From the literature review, it has been observed that different researchers have worked on the wire-EDM processing of different grades of steel and other materials. The literature study reveals that the input processing parameters of wire-EDM exhibited a large effect on output responses of the process. But hitherto, little has been explored for the wire-EDM machining of AISI 52100 grade of bearing steel by varying 6 different processing parameters of wire-EDM at a time. Therefore, the present study investigates the effect of machining parameters of wire-EDM setup for AISI 52100 grade of steel [41]. The present study takes six factors of Wire-EDM process at a time in consideration. The six different parameters of the machining are used viz: Pulse on Time (Ton), Wire Feed (WF), Spark Gap Set Voltage (SV), Wire Tension (WT), Pulse-off-Time (Toff), and Servo Feed (SF) of three different level for optimization of the processing conditions for improving the machining desirability. The level of parameters and number of factors makes the study better with improved design of experiment for optimization.


## 1.1. Scope/Novelty for the present study

From the literature review, it has been observed that different researchers have worked on the wire-EDM processing of different grades of steel and other materials. The literature study reveals that the input processing parameters of wire-EDM exhibited a large effect on output responses of the process. But hitherto, little has been explored for the wire-EDM machining of AISI 52100 grade of bearing steel by varying 6 different processing parameters of wire-EDM at a time. Therefore, the present study investigates the effect of machining parameters of wire-EDM setup for AISI 52100 grade of steel [41]. The present study takes six factors of Wire-EDM process at a time in consideration. The six different parameters of the machining are used viz: Pulse on Time (Ton), Wire Feed (WF), Spark Gap Set Voltage (SV), Wire Tension (WT), Pulse-off-Time (Toff), and Servo Feed (SF) of three different level for optimization of the processing conditions for improving the machining desirability. The level of parameters and number of factors makes the study better with improved design of experiment for optimization.


## 2. Materials and Methods

### 2.1. Selection of workpiece material and method of machining

The study deals with machining of AISI 52100 grade of steel on the high precision machine of Ultracut-S2 5 axis computer numerically controlled (CNC) wire-EDM setup. There are several industrial usages of AISI 52100 grade steel viz. anti-friction bearings, punches taps, dies etc [42]. Six different parameters of the machining were used viz: Pulse on Time (Ton), Wire Feed (WF), Spark Gap Set Voltage (SV), Wire Tension (WT), Pulse-off-Time (Toff), and Servo Feed (SF) for optimization of the processing conditions for improving the machining desirability. For optimization, experimentation, and DOE selection, Taguchi l27 OA was used as a standard operating condition. Table 2 shows the Taguchi l27 OA for different input parameters of the machining. Some other machining parameters were also used but as fixed conditions (as given in Table 3) in the study because of two reasons (a) previous literature shows that their effect is nominal of performance and (b) to have standard DOE only 6 parameters with three levels can be used in Taguchi l27 DOE. Figure 1 shows the methodology used for the optimization of the processing condition of wire-EDM. Figure 2 shows the machining setup available in the Lab with real-time conditions of machining.Table 2
Taguchi l27 OA for the optimization of wire-EDM machining process for AISI52100 grade steel.
Pulse on Time (µ sec)Pulse OFF time (µ sec)Wire Feed (m/min)Wire tensionSpark Gap Voltage (V)Servo Feed (mm/min)111.581250204111.581250256111.5812503081141014502041141014502561141014503081181216502041181216502561181216503081.111.51016502061.111.51016502581.111.51016503041.1141212502061.1141212502581.1141212503041.118814502061.118814502581.118814503041.211.51214502081.211.51214502541.211.51214503061.214816502081.214816502541.214816503061.2181012502081.2181012502541.218101250306Table 3
Fixed conditions of Wire-EDM machining of AISI52100 grade steel.
Control FactorsSymbolsPC12 unitsDFP10 kg/cm2WT20 mmWD0.25mmWTZinc-coated copper wireShapeSquareAoCVerticalPC: Peak Current; WD: Wire Diameter; DFP: Di-electric fluid Pressure; WT: Wire type; WT: Workpiece thickness; AoC: Angle of cutFigure 1
Methodology for the optimization of wire-EDM machining process for AISI 52100.Figure 2
Real-time machining wire-EDM setup.


### 2.2. Selection of Output responses to be measured with workpiece dimensional details

Copper wire with a zinc coating (CuZn37) has been used for wire cutting/machining of the AISI 52100 metal. The selection of the wire for cutting and machining has been done based on its properties, such as resistance to short circuits (due to zinc coating on copper surface) and high precision cutting without any breakage of the wire (due to desirable tensile strength of the wire 900-920 N/mm2). The cubical object of AISI 52100 steel has been chosen for the size of 20∗20∗20 mm (weight 62.4g). For machining the initial setting of 0.035 mm of wire, an offset gap was maintained. The surface roughness value as an output characteristic has been measured as an average value from the mean surface roughness using the Surfcom 130 A instrument. The average surface roughness value (Ra) has been observed by using cut off length of 0.8mm after each experiment. Based on ISO:4287 standard, measurement of surface roughness was carried out at room temperature. Similarly, the second output dimensional deviation was observed by using a digital dimensional measuring instrument (Height master; Make-Mitutoyo) with an accuracy level of 0.0001 mm, and equation number 1 was employed for calculating the dimensional deviation [43–45].


### 2.3. Processing conditions and output Analysis technique

For machining of the AISI 52100, a metal water pressure of 10 Kg/cm2 was used with other input conditions. Whereas deionized water with a conductivity value of 12 units has been employed for the wire-EDM process. For reliability study of the DOE and experiments, randomly 6 experiments (experiment number 1, 5, 10, 15, 20, 25) were selected from the DOE and performed again with similar processing conditions. Two output parameters, surface roughness (Ra) and dimensional deviation (DD), which are important for the machined surfaces, have been selected as the output response for the present study. For analysis, part of the outputs obtained from the study MiniTab software 19.1 package tool has been used. Further, the best and the worst samples as per DOE have been selected for morphological analysis using SEM characterization. The SEM photomicrographic image was used for 3D surface rendering to characterize the rendered image analysis of the samples.(1)DimensionalDeviation%ge=Dimensionsofworkpeicebeforemachiningmm−DimensionsofworkpeiceaftermachiningDesiredDimension∗100.


## 2.1. Selection of workpiece material and method of machining

The study deals with machining of AISI 52100 grade of steel on the high precision machine of Ultracut-S2 5 axis computer numerically controlled (CNC) wire-EDM setup. There are several industrial usages of AISI 52100 grade steel viz. anti-friction bearings, punches taps, dies etc [42]. Six different parameters of the machining were used viz: Pulse on Time (Ton), Wire Feed (WF), Spark Gap Set Voltage (SV), Wire Tension (WT), Pulse-off-Time (Toff), and Servo Feed (SF) for optimization of the processing conditions for improving the machining desirability. For optimization, experimentation, and DOE selection, Taguchi l27 OA was used as a standard operating condition. Table 2 shows the Taguchi l27 OA for different input parameters of the machining. Some other machining parameters were also used but as fixed conditions (as given in Table 3) in the study because of two reasons (a) previous literature shows that their effect is nominal of performance and (b) to have standard DOE only 6 parameters with three levels can be used in Taguchi l27 DOE. Figure 1 shows the methodology used for the optimization of the processing condition of wire-EDM. Figure 2 shows the machining setup available in the Lab with real-time conditions of machining.Table 2
Taguchi l27 OA for the optimization of wire-EDM machining process for AISI52100 grade steel.
Pulse on Time (µ sec)Pulse OFF time (µ sec)Wire Feed (m/min)Wire tensionSpark Gap Voltage (V)Servo Feed (mm/min)111.581250204111.581250256111.5812503081141014502041141014502561141014503081181216502041181216502561181216503081.111.51016502061.111.51016502581.111.51016503041.1141212502061.1141212502581.1141212503041.118814502061.118814502581.118814503041.211.51214502081.211.51214502541.211.51214503061.214816502081.214816502541.214816503061.2181012502081.2181012502541.218101250306Table 3
Fixed conditions of Wire-EDM machining of AISI52100 grade steel.
Control FactorsSymbolsPC12 unitsDFP10 kg/cm2WT20 mmWD0.25mmWTZinc-coated copper wireShapeSquareAoCVerticalPC: Peak Current; WD: Wire Diameter; DFP: Di-electric fluid Pressure; WT: Wire type; WT: Workpiece thickness; AoC: Angle of cutFigure 1
Methodology for the optimization of wire-EDM machining process for AISI 52100.Figure 2
Real-time machining wire-EDM setup.


## 2.2. Selection of Output responses to be measured with workpiece dimensional details

Copper wire with a zinc coating (CuZn37) has been used for wire cutting/machining of the AISI 52100 metal. The selection of the wire for cutting and machining has been done based on its properties, such as resistance to short circuits (due to zinc coating on copper surface) and high precision cutting without any breakage of the wire (due to desirable tensile strength of the wire 900-920 N/mm2). The cubical object of AISI 52100 steel has been chosen for the size of 20∗20∗20 mm (weight 62.4g). For machining the initial setting of 0.035 mm of wire, an offset gap was maintained. The surface roughness value as an output characteristic has been measured as an average value from the mean surface roughness using the Surfcom 130 A instrument. The average surface roughness value (Ra) has been observed by using cut off length of 0.8mm after each experiment. Based on ISO:4287 standard, measurement of surface roughness was carried out at room temperature. Similarly, the second output dimensional deviation was observed by using a digital dimensional measuring instrument (Height master; Make-Mitutoyo) with an accuracy level of 0.0001 mm, and equation number 1 was employed for calculating the dimensional deviation [43–45].


## 2.3. Processing conditions and output Analysis technique

For machining of the AISI 52100, a metal water pressure of 10 Kg/cm2 was used with other input conditions. Whereas deionized water with a conductivity value of 12 units has been employed for the wire-EDM process. For reliability study of the DOE and experiments, randomly 6 experiments (experiment number 1, 5, 10, 15, 20, 25) were selected from the DOE and performed again with similar processing conditions. Two output parameters, surface roughness (Ra) and dimensional deviation (DD), which are important for the machined surfaces, have been selected as the output response for the present study. For analysis, part of the outputs obtained from the study MiniTab software 19.1 package tool has been used. Further, the best and the worst samples as per DOE have been selected for morphological analysis using SEM characterization. The SEM photomicrographic image was used for 3D surface rendering to characterize the rendered image analysis of the samples.(1)DimensionalDeviation%ge=Dimensionsofworkpeicebeforemachiningmm−DimensionsofworkpeiceaftermachiningDesiredDimension∗100.


## 3. Result and Discussion

### 3.1. Discussion for surface roughness and dimensional deviation

The machined workpieces according to the standard methodology using Taguchi L27 OA have been successfully prepared and tested for different output characteristics. The data set given in Table4 shows the values for the surface roughness and dimensional deviations for the corresponding processing parameters. From Table 4, it has been observed that experimental condition 9 (Pulse on Time (Ton): 1 µs, Pulse off time: 18 µs; Wire Feed (WF): 12 mm/min, Spark Gap Set Voltage (SV): 20 V, Wire Tension (WT): 1650, and Servo Feed (SF): 8units) has been obtained as the best condition for the machining with the wire-EDM process for AISI 52100 grade steel as the roughness value obtained for the sample was lowest among all (Roughness value: 1.02 Ra, dimensional deviation: 0.02). Similarly, from the Table 4, it has been ascertained that experimental condition 19 (Pulse on Time (Ton): 1.2 µs, Pulse off time: 11.5 µs; Wire Feed (WF): 12 mm/min, Spark Gap Set Voltage (SV): 20 V, Wire Tension (WT): 1450, and Servo Feed (SF): 8 units) as per DOE was the worst condition for the surface roughness (Roughness value: 2.98 Ra) and dimensional deviation (0.12) characteristics.Table 4
Surface roughness and dimensional deviation values for the selected machining DOE as per Taguchi l27 OA.
Process parametersProcess ResponsesTrial NoTonToffWFWTSVSFRa (µm)DD (%)1111.5812502041.540.0752111.5812502561.280.0613111.5812503081.130.04241141014502041.490.04551141014502561.220.04161141014503081.130.0371181216503041.310.04281181216502561.160.0391181216502081.020.02101.111.51016502062.210.075111.111.51016502582.190.071121.111.51016503041.820.055131.1141212502062.140.085141.1141212502581.720.065151.1141212503041.480.053161.118814502062.030.075171.118814502581.80.064181.118814503041.380.043191.211.51214502082.980.12201.211.51214502542.560.098211.211.51214503062.390.085221.214816502082.640.11231.214816502542.450.095241.214816503062.050.065251.2181012502082.540.105261.2181012502542.170.085271.2181012503061.630.08It may be observed that from the analysis of the processing condition for the best and the worst samples obtained by surface roughness testing. Figure3a shows the trend obtained for the surface roughness analysis, which depicts the best nature for sample no 19 and the worst results for sample no 9. This may be because surface roughness value largely depends upon the spark time (pulse on time Ton)), spark off time (Toff), and wire tension, as the other parameters was similar for both of the wire-EDM processing condition for sample 9 and 19 (see Table 4). As it may be observed that in processing condition 9 the spark off (Toff) time was 18µs which resulted in a lowering of temperature due to no current and ionization for a large time interval on the surface of the metal. The pulse on time (Ton) interval was 1 µs which again reduced the surface temperature of the metal, and the high wire tension of the zinc-coated copper wire together resulted in better machining characteristics.Figure 3
Web charts for the (a) surface roughness analysis and (b) dimensional deviation (% age) for AISI 52100 grade steel.
(a)(b)Similar results were obtained for the dimensional deviation characteristics as the lowest dimensional deviation of 0.02 was observed for sample 9, and the maximum dimensional deviation of 0.12 was observed for sample 19. High surface temperature and ionization of medium along with low wire tension resulted in poor surface characteristics of the wire-EDM machined AISI 52100 grade steel.The results obtained for the machined surface of AISI 52100 grade steel shows that processing condition 9 generates moderate surface temperature condition (due to low pulse on time (Ton): 1µs, and large pulse off time (Toff): 18 µs), and high wire tension of 1650 grams together contributed towards the best machining conditions for the wire-EDM process. Figure 3b shows the trends obtained for dimensional deviation of the wire-EDM processed AISI 52100 grade steel. The web chart depicts that sample 9 held a low value for dimensional deviation as the wire tension was highest at 1650, and surface temperature conditions were moderate due to low pulse on and high pulse off timings.


### 3.2. Optimization for the surface roughness and dimensional deviation values for the AISI 52100 grade steel machined with wire-EDM process

The data obtained in Table4 was further processed with Taguchi l27 OA using MiniTab 19.1 statistical tool for optimization of the processing parameters. Table 5 shows the analysis of variance (ANOVA) for the signal-to-noise (SN) ratios obtained by Taguchi analysis using surface roughness value data from Table 4. From Table 5, it has been ascertained that the factors pulse on time (Ton), pulse off time (Toff), and spark gap voltage (V) are the significant parameters as their p-value is less than 0.05. Whereas wire tension was also found to be a significant contributor in deciding the surface characteristics of the machined workpiece of AISI 52100 grade steel. Table 5 shows the rank Table for the SN ratio of the surface roughness values, and it may be ascertained that pulse on time (Ton) was ranked at 1st, spark gap voltage came to be as 2nd rank parameter, and pulse off (Toff) time was ranked 3rd, and wire tension was ranked at 4th position which significantly contributed towards the wire-EDM machining of AISI 52100 grade steel. Figure 4 shows the main effect plot for the SN ratios from which it can be observed that for the surface roughness low pulse on the value of 1 µs, high pulse off vale of 18 µs, wire feed of 8 mm/min, wire tension of 1250 grams, spark gap voltage of 30 V and servo feed of 6mm/min was the optimized condition for the surface roughness of machined workpiece. Figure 5 shows the four in one plot for SN ratios of surface roughness values, and it has been observed that the data obtained for the surface roughness value was normal as all the data lies near to the normal trend line as shown by the normal probability trend of Figure 5. The Anova analysis of the selected Taguchi L25 OA has been performed as per the standard technique as performed by previous researchers [45, 46].Table 5
SN ratio values for ANOVA of surface roughness values.
SourceDFSeq SSAdj SSAdj MSFPpercentage contributionPulse on Time (micro sec)2139.839139.83969.9196309.620.000174.91Pulse OFF time (micro sec)211.13611.1365.567824.660.00010.48Wire Feed (m/min)20.0330.0330.01640.070.9300.02Wire tension21.5671.5670.78373.470.0600.84Spark Gap Voltage (V)230.68030.68015.340067.930.000116.43Servo Feed (mm/min)20.2450.2450.12250.540.5930.13Residual Error143.1613.1610.2258Total26186.662Figure 4
Main effect plot for SN ratio of surface roughness values.Figure 5
Four in one plot for SN ratios of surface roughness values.


### 3.3. The calculation for the optimized/suggested set of processing parameters

Further, for the calculation of the optimized value for the suggested setting by Taguchi l27 OA, the signal-to-noise ratios obtained by the analysis were used. Table7 shows the SNRA values for the surface roughness and dimensional deviation as output response from Taguchi l27 OA analysis using MiniTab 19.1 statistical software package tool. Further, for the calculation of optimized values, (2) has been used. The calculation for the surface roughness value has been shown below. From the calculation, it has been observed that the value for the optimized setting was obtained to be 1.080 Ra which was very near to the value obtained for sample number 9 (surface roughness value as per experiment: 1.02Ra (see Table 4). Thus, the optimized setting as suggested by Taguchi l27 OA, which was outside the selected DOE, can be taken as experimental condition 9 in Table 4. A similar calculation can be made for the optimized value of dimensional deviation output characteristics.Table 6
Rank table for SN ratios of surface roughness values.
LevelPulse on TimePulse OFFWire FeedWireSpark GapServo Feedtime(m/min)tensionVoltage (V)(mm/min)1-1.891-5.675-4.829-4.528-6.135-4.8492-5.297-4.825-4.913-5.058-4.940-4.7613-7.415-4.103-4.861-5.017-3.527-4.993Delta5.5251.5710.0850.5302.6080.231Rank136425Table 7
SNRA values for the surface roughness and dimensional deviation values.
S.No.SNRA values for surface roughnessSNRA values for dimensional deviation1-3.75022.4992-2.14424.2933-1.06227.5354-3.46426.9365-1.72727.7446-1.06230.4587-2.34527.5358-1.28930.4589-0.17233.97910-6.88822.49911-6.80922.97512-5.20125.19313-6.60821.41214-4.71123.74215-3.40525.51416-6.15022.49917-5.10523.87618-2.79827.33119-9.48418.41620-8.16520.17521-7.56821.41222-8.43219.17223-7.78320.44624-6.23523.74225-8.09719.57626-6.72921.41227-4.24421.938∗Terms related to the calculation∗K= mean of the SNRA values (see Table 7 for example: mean of SNRA value for surface roughness parameter is 4.868∗The negative sign has been ignored, and the lower values ignoring negative values from rank Table 6 have been taken for further ηopt calculation.(2)ηopt=k+kA3–Z+kB1–Z+kC2–Z+kD2−Z+kE1−Z+kF3−Z.Yopt is the optimized value of peak elongationk=4.868 (See Table 7)kA1=1.891 (See Table 6)kB3=4.103 (See Table 6)kc3=4.861 (See Table 6)kD1=4.528 (See Table 6)kE3=3.527 (See Table 6)kF2=4.761 (See Table 6)For smaller is the better case(3)ηopt=4.868+1.891−4.868+4.103−4.868+4.861−4.868+4.528−4.868+3.527−4.868+4.761−4.868,ηopt=−0.669Zopt2=1/10^ηopt/10, ηopt=−0.669dB, yopt^2=1/10^−0.669/10, yopt^2=1.1665, yopt=1.080RaSo, the optimum roughness value = 1.080 Ra


### 3.4. SEM characterization for the wire-EDM machined AISI 52100 grade steel

The best (sample 9) and the poorest (sample 19) samples of the wire-EDM machined surfaces of AISI 52100 were further investigated under the SEM machine, which depicted that the sample 9 conditions of processing through wire-EDM supported the best morphological characteristics. The moderate temperature conditions (Pulse on (Ton): 1 µs, Pulse off time: 18 µs, and wire tension of 1650 grams) and larger value of wire tension resulted in low fluctuations in straightness on the machined surface for sample 9. Whereas, the high pulse on time: 1.2 µs, low pulse off time of 11.5 µs, and low wire tension of 1450 grams corresponding to high-temperature conditions of machining resulted in poor surface characteristics due to large fluctuation in machined surface straightness. Figure 6a shows the SEM image for sample 9, and 6b shows the SEM image for sample 19 [46]. Further, the SEM photomicrographic images were processed using the open source software package tool Gwyddion 2.59 for surface roughness profile creation using 3D rendering of the SEM image of the samples. Figure 7a shows the surface roughness and 3D rendered image for sample 9 which validated the observed output responses for the selected processing conditions. Surface roughness and 3D rendered image for sample 19 was illustrated in figure 7b. The surface roughness profile for sample 9 has shown a low surface roughness value of 29.85 nm. Similarly, sample 19 has shown a high surface roughness of 77.25 nm.Figure 6
SEM photomicrographic images for (a) sample 9 and (b) sample 19.
(a)(b)Figure 7
Surface roughness and 3D rendered image for (a) sample 9 and (b) sample 19.
(a)(b)


## 3.1. Discussion for surface roughness and dimensional deviation

The machined workpieces according to the standard methodology using Taguchi L27 OA have been successfully prepared and tested for different output characteristics. The data set given in Table4 shows the values for the surface roughness and dimensional deviations for the corresponding processing parameters. From Table 4, it has been observed that experimental condition 9 (Pulse on Time (Ton): 1 µs, Pulse off time: 18 µs; Wire Feed (WF): 12 mm/min, Spark Gap Set Voltage (SV): 20 V, Wire Tension (WT): 1650, and Servo Feed (SF): 8units) has been obtained as the best condition for the machining with the wire-EDM process for AISI 52100 grade steel as the roughness value obtained for the sample was lowest among all (Roughness value: 1.02 Ra, dimensional deviation: 0.02). Similarly, from the Table 4, it has been ascertained that experimental condition 19 (Pulse on Time (Ton): 1.2 µs, Pulse off time: 11.5 µs; Wire Feed (WF): 12 mm/min, Spark Gap Set Voltage (SV): 20 V, Wire Tension (WT): 1450, and Servo Feed (SF): 8 units) as per DOE was the worst condition for the surface roughness (Roughness value: 2.98 Ra) and dimensional deviation (0.12) characteristics.Table 4
Surface roughness and dimensional deviation values for the selected machining DOE as per Taguchi l27 OA.
Process parametersProcess ResponsesTrial NoTonToffWFWTSVSFRa (µm)DD (%)1111.5812502041.540.0752111.5812502561.280.0613111.5812503081.130.04241141014502041.490.04551141014502561.220.04161141014503081.130.0371181216503041.310.04281181216502561.160.0391181216502081.020.02101.111.51016502062.210.075111.111.51016502582.190.071121.111.51016503041.820.055131.1141212502062.140.085141.1141212502581.720.065151.1141212503041.480.053161.118814502062.030.075171.118814502581.80.064181.118814503041.380.043191.211.51214502082.980.12201.211.51214502542.560.098211.211.51214503062.390.085221.214816502082.640.11231.214816502542.450.095241.214816503062.050.065251.2181012502082.540.105261.2181012502542.170.085271.2181012503061.630.08It may be observed that from the analysis of the processing condition for the best and the worst samples obtained by surface roughness testing. Figure3a shows the trend obtained for the surface roughness analysis, which depicts the best nature for sample no 19 and the worst results for sample no 9. This may be because surface roughness value largely depends upon the spark time (pulse on time Ton)), spark off time (Toff), and wire tension, as the other parameters was similar for both of the wire-EDM processing condition for sample 9 and 19 (see Table 4). As it may be observed that in processing condition 9 the spark off (Toff) time was 18µs which resulted in a lowering of temperature due to no current and ionization for a large time interval on the surface of the metal. The pulse on time (Ton) interval was 1 µs which again reduced the surface temperature of the metal, and the high wire tension of the zinc-coated copper wire together resulted in better machining characteristics.Figure 3
Web charts for the (a) surface roughness analysis and (b) dimensional deviation (% age) for AISI 52100 grade steel.
(a)(b)Similar results were obtained for the dimensional deviation characteristics as the lowest dimensional deviation of 0.02 was observed for sample 9, and the maximum dimensional deviation of 0.12 was observed for sample 19. High surface temperature and ionization of medium along with low wire tension resulted in poor surface characteristics of the wire-EDM machined AISI 52100 grade steel.The results obtained for the machined surface of AISI 52100 grade steel shows that processing condition 9 generates moderate surface temperature condition (due to low pulse on time (Ton): 1µs, and large pulse off time (Toff): 18 µs), and high wire tension of 1650 grams together contributed towards the best machining conditions for the wire-EDM process. Figure 3b shows the trends obtained for dimensional deviation of the wire-EDM processed AISI 52100 grade steel. The web chart depicts that sample 9 held a low value for dimensional deviation as the wire tension was highest at 1650, and surface temperature conditions were moderate due to low pulse on and high pulse off timings.


## 3.2. Optimization for the surface roughness and dimensional deviation values for the AISI 52100 grade steel machined with wire-EDM process

The data obtained in Table4 was further processed with Taguchi l27 OA using MiniTab 19.1 statistical tool for optimization of the processing parameters. Table 5 shows the analysis of variance (ANOVA) for the signal-to-noise (SN) ratios obtained by Taguchi analysis using surface roughness value data from Table 4. From Table 5, it has been ascertained that the factors pulse on time (Ton), pulse off time (Toff), and spark gap voltage (V) are the significant parameters as their p-value is less than 0.05. Whereas wire tension was also found to be a significant contributor in deciding the surface characteristics of the machined workpiece of AISI 52100 grade steel. Table 5 shows the rank Table for the SN ratio of the surface roughness values, and it may be ascertained that pulse on time (Ton) was ranked at 1st, spark gap voltage came to be as 2nd rank parameter, and pulse off (Toff) time was ranked 3rd, and wire tension was ranked at 4th position which significantly contributed towards the wire-EDM machining of AISI 52100 grade steel. Figure 4 shows the main effect plot for the SN ratios from which it can be observed that for the surface roughness low pulse on the value of 1 µs, high pulse off vale of 18 µs, wire feed of 8 mm/min, wire tension of 1250 grams, spark gap voltage of 30 V and servo feed of 6mm/min was the optimized condition for the surface roughness of machined workpiece. Figure 5 shows the four in one plot for SN ratios of surface roughness values, and it has been observed that the data obtained for the surface roughness value was normal as all the data lies near to the normal trend line as shown by the normal probability trend of Figure 5. The Anova analysis of the selected Taguchi L25 OA has been performed as per the standard technique as performed by previous researchers [45, 46].Table 5
SN ratio values for ANOVA of surface roughness values.
SourceDFSeq SSAdj SSAdj MSFPpercentage contributionPulse on Time (micro sec)2139.839139.83969.9196309.620.000174.91Pulse OFF time (micro sec)211.13611.1365.567824.660.00010.48Wire Feed (m/min)20.0330.0330.01640.070.9300.02Wire tension21.5671.5670.78373.470.0600.84Spark Gap Voltage (V)230.68030.68015.340067.930.000116.43Servo Feed (mm/min)20.2450.2450.12250.540.5930.13Residual Error143.1613.1610.2258Total26186.662Figure 4
Main effect plot for SN ratio of surface roughness values.Figure 5
Four in one plot for SN ratios of surface roughness values.


## 3.3. The calculation for the optimized/suggested set of processing parameters

Further, for the calculation of the optimized value for the suggested setting by Taguchi l27 OA, the signal-to-noise ratios obtained by the analysis were used. Table7 shows the SNRA values for the surface roughness and dimensional deviation as output response from Taguchi l27 OA analysis using MiniTab 19.1 statistical software package tool. Further, for the calculation of optimized values, (2) has been used. The calculation for the surface roughness value has been shown below. From the calculation, it has been observed that the value for the optimized setting was obtained to be 1.080 Ra which was very near to the value obtained for sample number 9 (surface roughness value as per experiment: 1.02Ra (see Table 4). Thus, the optimized setting as suggested by Taguchi l27 OA, which was outside the selected DOE, can be taken as experimental condition 9 in Table 4. A similar calculation can be made for the optimized value of dimensional deviation output characteristics.Table 6
Rank table for SN ratios of surface roughness values.
LevelPulse on TimePulse OFFWire FeedWireSpark GapServo Feedtime(m/min)tensionVoltage (V)(mm/min)1-1.891-5.675-4.829-4.528-6.135-4.8492-5.297-4.825-4.913-5.058-4.940-4.7613-7.415-4.103-4.861-5.017-3.527-4.993Delta5.5251.5710.0850.5302.6080.231Rank136425Table 7
SNRA values for the surface roughness and dimensional deviation values.
S.No.SNRA values for surface roughnessSNRA values for dimensional deviation1-3.75022.4992-2.14424.2933-1.06227.5354-3.46426.9365-1.72727.7446-1.06230.4587-2.34527.5358-1.28930.4589-0.17233.97910-6.88822.49911-6.80922.97512-5.20125.19313-6.60821.41214-4.71123.74215-3.40525.51416-6.15022.49917-5.10523.87618-2.79827.33119-9.48418.41620-8.16520.17521-7.56821.41222-8.43219.17223-7.78320.44624-6.23523.74225-8.09719.57626-6.72921.41227-4.24421.938∗Terms related to the calculation∗K= mean of the SNRA values (see Table 7 for example: mean of SNRA value for surface roughness parameter is 4.868∗The negative sign has been ignored, and the lower values ignoring negative values from rank Table 6 have been taken for further ηopt calculation.(2)ηopt=k+kA3–Z+kB1–Z+kC2–Z+kD2−Z+kE1−Z+kF3−Z.Yopt is the optimized value of peak elongationk=4.868 (See Table 7)kA1=1.891 (See Table 6)kB3=4.103 (See Table 6)kc3=4.861 (See Table 6)kD1=4.528 (See Table 6)kE3=3.527 (See Table 6)kF2=4.761 (See Table 6)For smaller is the better case(3)ηopt=4.868+1.891−4.868+4.103−4.868+4.861−4.868+4.528−4.868+3.527−4.868+4.761−4.868,ηopt=−0.669Zopt2=1/10^ηopt/10, ηopt=−0.669dB, yopt^2=1/10^−0.669/10, yopt^2=1.1665, yopt=1.080RaSo, the optimum roughness value = 1.080 Ra


## 3.4. SEM characterization for the wire-EDM machined AISI 52100 grade steel

The best (sample 9) and the poorest (sample 19) samples of the wire-EDM machined surfaces of AISI 52100 were further investigated under the SEM machine, which depicted that the sample 9 conditions of processing through wire-EDM supported the best morphological characteristics. The moderate temperature conditions (Pulse on (Ton): 1 µs, Pulse off time: 18 µs, and wire tension of 1650 grams) and larger value of wire tension resulted in low fluctuations in straightness on the machined surface for sample 9. Whereas, the high pulse on time: 1.2 µs, low pulse off time of 11.5 µs, and low wire tension of 1450 grams corresponding to high-temperature conditions of machining resulted in poor surface characteristics due to large fluctuation in machined surface straightness. Figure 6a shows the SEM image for sample 9, and 6b shows the SEM image for sample 19 [46]. Further, the SEM photomicrographic images were processed using the open source software package tool Gwyddion 2.59 for surface roughness profile creation using 3D rendering of the SEM image of the samples. Figure 7a shows the surface roughness and 3D rendered image for sample 9 which validated the observed output responses for the selected processing conditions. Surface roughness and 3D rendered image for sample 19 was illustrated in figure 7b. The surface roughness profile for sample 9 has shown a low surface roughness value of 29.85 nm. Similarly, sample 19 has shown a high surface roughness of 77.25 nm.Figure 6
SEM photomicrographic images for (a) sample 9 and (b) sample 19.
(a)(b)Figure 7
Surface roughness and 3D rendered image for (a) sample 9 and (b) sample 19.
(a)(b)


## 4. Conclusions

The current work dealt with the machining of AISI 52100 grade steel on wire-EDM setup and investigated the effect of different input processing conditions of machining for geometrical and morphological characteristics. The study involved 6 input processing parameters of wire-EDM viz: Pulse on Time (Ton), Wire Feed (WF), Spark Gap Set Voltage (SV), Wire Tension (WT), Pulse-off-Time (Toff), and Servo Feed (SF). The study focused on the effect of these processing parameters on geometrical output (dimensional deviation) and morphological output (surface roughness). A standard set of DOE based on Taguchi l27 OA has been used for the optimization of the different input processing parameters, and the following are the conclusions [47] of the study.1.
The experimental condition 9 (Pulse on Time (Ton): 1µs, Pulse off time: 18µs; Wire Feed (WF): 12mm/min, Spark Gap Set Voltage (SV): 20V, Wire Tension (WT): 1650, and Servo Feed (SF): 8units) may be concluded as the best condition for the machining with the wire-EDM process for AISI 52100 grade steel.2.
The Pulse on Time (Ton): 1.2 µs, Pulse off time: 11.5 µs; Wire Feed (WF): 12mm/min, Spark Gap Set Voltage (SV): 20V, Wire Tension (WT): 1450, and Servo Feed (SF): 8units) as per DOE can be concluded as the worst condition for the processing of AISI 52100 grade steel.3.
Roughness value 1.02Ra and dimensional deviation: 0.02 can be concluded as the best values for the selected Taguchi L25 DOE model. Similarly, the surface roughness 2.98Ra and dimensional deviation of 0.12 can be concluded as worst values for output characteristics.4.
According to Taguchi l27 OA analysis, the pulse on time (Ton) was ranked at 1st, spark gap voltage came to be as 2nd rank parameter and pulse off (Toff) time was ranked 3rd, and wire tension was ranked at 4th position which significantly contributed towards the wire-EDM machining of AISI 52100 grade steel. Whereas the other input parameters contributed least towards the output responses.5.
The SEM and 3D rendered surface roughness analysis supported the observed trend and validated the reasons given for the observed behavior of surface roughness and dimensional deviation. The surface roughness profile for sample 9 has shown a low surface roughness value of 29.85 nm. Similarly, sample 19 has shown a high surface roughness of 77.25 nm.



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*Source: 6316799-2022-12-13.xml*