M. PRADEEPKUMAR et al.: EVOLUTIONARY OPTIMIZATION OF WIRE EDM PROCESS FOR THE SURFACE FINISH ... 663–669 EVOLUTIONARY OPTIMIZATION OF WIRE EDM PROCESS FOR THE SURFACE FINISH ON A MAGNESIUM AZ91D ALLOY USING AN ANN AND A GENETIC ALGORITHM RAZVOJ OPTIMIZACIJE PROCESA @I^NE EROZIJE ZA KON^NO POVR[INSKO OBDELAVO MAGNEZIJEVE ZLITINE AZ91D Z UPORABO UMETNE NEVRONSKE MRE@E IN GENETSKEGA ALGORITMA Madhesan Pradeepkumar 1* , Thangaraj Jesudas 2 , Chandrasekaran Sasikumar 3 , Mani Narasimharajan 4 1 Department of Mechanical Engineering, Sona College of Technology, Salem, Tamil Nadu, 636005, India 2 Department of Mechatronics, Mahendra Engineering College, Namakkal, India 3 Department of Mechanical Engineering, Bannari Amman Institute of Technology Sathyamangalam - 638 401, India 4 Department of Mechanical Engineering, Mahendra Institute of Technology, Namakkal, India Prejem rokopisa – received: 2024-02-12; sprejem za objavo – accepted for publication: 2024-09-05 doi:10.17222/mit.2024.1107 In this research the optimizations of the wire EDM process parameters to achieve a minimal surface roughness on a magnesium AZ91D alloy have been carried out. The experiments were conducted with three machining factors, i.e., the pulse-on time, the pulse-off time, and the wire feed, using a Box-Behnken design of experiment. The effects of the Artificial Neural Network (ANN) and the Response Surface Methodology (RSM) models were compared and studied, and it has been found that the ANN approach predicts the perfect output response. The genetic algorithm (GA) was then utilized to determine the best machining pa- rameters to provide a better surface finish using the projected ANN outcomes, which were then used to build a quadratic equa- tion. Furthermore, the optimum machining parameters were identified for a better surface finish through the integration of the ANN and GA approach. Based on the aforementioned findings, this study showed that the suggested methods are capable of predicting the optimum machining parameters, which would be beneficial in the low-cost manufacturing sector. Keywords: ANN, genetic algorithm, magnesium alloy, wire EDM, optimization V ~lanku avtorji opisujejo raziskavo optimizacije procesnih parametrov `i~ne erozije (EDM; angl.: Electrical Discharge Ma- chining), da bi dosegli najmanj{o mo`no hrapavost povr{ine na Mg zlitini tipa AZ91D. Avtorji so, na osnovi Box-Behnkenovega eksperimentalnega dizajna, izvajali preizkuse pri treh izbranih faktorjih mehanske obdelave in sicer: ~asu v`iga elektri~nega impulza, ~asu izklopa elektri~nega impulza in hitrosti dodajanja `ice. Med seboj so primerjali in {tudirali u~inke modelov umetne nevronske mre`e (ANN; angl.: Artificial Neural Network) in metodologije povr{inskega odgovora (RSM; angl.: Re- sponse Surface Methodology). Ugotovili so, da z ANN modeliranjem lahko napovejo mnogo bolj{e izhodne odgovore kot z RSM modelom. Genetski algoritm (GA) so uporabili za dolo~itev najbolj{ih procesnih parametrov erozije z uporabo dobljenih ANN podatkov, ki so jih nato uporabili za izdelavo kvadratne ene~be. Nadalje pa so avtorji ugotovili, da so optimalne procesne parametre mehanske obdelave z `i~no erozijo za najbolj{o kakovost povr{ine dobili z integracijo ANN in GA pristopa. Na osnovi v ~lanku navedenih ugotovitev so avtorji sposobni napovedati optimalne procesne parametre EDM, ki bi lahko bili cenovno zelo ugodni tudi za druge uporabnike mehanske obdelave materialov z postopkom `i~ne erozije. Klju~ne besede: umetne nevronske mre`e, genetski algoritm, zlitina na osnovi magnezija, `i~na erozija, optimizacija 1 INTRODUCTION Magnesium alloys have exceptional strength-to- weight ratios and are extensively utilized in industries; a number of aircraft and automobile industries are focus- ing on products made with magnesium alloys. 1 Wire EDM is an un-conventional thermo-electrical machining process where the work materials are machined by a con- tinuous discrete spark among the work and the tool elec- trode while they are immersed in a liquefied dielectric medium. The continuous discrete spark erodes the work piece in complex shapes in accordance with a computer- ized, numerically controlled program. 2 The evaluation of the quality of a component, the surface finish, is a neces- sary element for production industries. Surface rough- ness is an important performance characteristic for the EDM process, and it became a factor in the quality and economy characteristics. The operator’s expertise and the manufacturer’s guidelines play a big role in choosing the right machining parameters for the wire EDM. As a re- sult, for newer materials, the machining parameters in wire EDM must be optimized using experimental tech- niques. The main objective of the wire EDM manufac- turers and users is to succeed in establishing better sta- bility and higher productivity of the wire EDM process. 3 Dewangan et al. 4 studied the influence of pulse cur- rent, pulse-on time, tool work time, and tool lift time in relation to the surface integrity on the EDM of AISI P20 tool steel using the RSM and the TOPSIS methods. The study reports that the optimal solution was obtained Materiali in tehnologije / Materials and technology 58 (2024) 5, 663–669 663 UDK 546.46:621.9.048 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(5)663(2024) *Corresponding author's e-mail: pradeepkumar@sonatech.ac.in (Madhesan Pradeepkumar) based on five decision makers’ preferences for different process parameters. Vinoth and Pradeep 5 have studied the conventional EDM and the cryogenic EDM processes on the machining of an aluminum metal matrix compos- ite and they reported that the discharge current, pulse-on time, and gap voltage have a significant effect on the electrode wear and surface roughness. Kavimani et al. 6 have studied the impact of the machining parameters on wire electrical discharge machining performance in mag- nesium composites, finding that the MRR and surface roughness are factors to consider. Gangadharudu et al. 7 studied a multi-response optimization with the use of the principal component analysis based on the grey tech- nique to find the optimum process parameters for a metal-matrix composite on the EDM process; they dis- covered a setting of the process parameters through evo- lutionary optimization techniques. Murahari et al. 8 have evaluated the effects of the EDM process parameters in terms of the output response material removal rate, sur- face roughness, tool wear rate, and recast layer thickness on the machining of Ti-6Al-4V using an analysis of the variance and the F-test. Tripathy et al. 9 studied the ma- chining parameter optimization for multiple responses on the numeral process variables on the EDM of the H-11 die steel using the TOPSIS and the grey relational analy- sis and they investigated the effect of process variables like powder concentration, peak current, pulse-on time, duty cycle, and gap voltage based on the response of the material removal rate, tool wear rate, electrode wear ra- tio, and surface roughness. Rai et al. 10 investigated the cutting forces and the shear plane temperature in end milling with the use of an ANN. They used 15 neurons in the feedforward neural network with a backpropa- gation algorithm. In terms of the cutting tool, the geo- metrical parameters, the cutting parameters, and the work piece material properties, as well as the three com- ponents of the cutting forces and the shear plane temperature were used as the output layers. The study demonstrated that the ANN model shows a close agree- ment between the experimental and the numerical re- sults. Vishal et al. 11 studied the optimization of the pro- cess parameters in terms of kerf width in the EDM process on a stainless-steel 304L. They used the Taguchi L32 orthogonal design of experiment to conduct experi- ments and analysis of the variance, and the study discov- ered that the mathematical model hasa4%error in com- parison to the experimental results. Yýldýzel et al. 12 have investigated the modulus of rapture values for glass fiber reinforced in a concrete block with the use of an ANN integrated with an artificial bee colony and they con- cluded that the model provides most appropriate perfor- mance compared with multiple linear regression. The literature survey of this research has helped in furthering a number of researchers on the process param- eters optimization by the use of the RSM, and ANN tools for different materials; however the researches on the EDM process of advanced materials like magnesium AZ91D alloy were rarely conducted. In addition, the conventional optimization techniques were preferred in the research over the evolutionary techniques. In this re- search work we focus on a prediction of best machining parameters to attain minimal surface roughness on wire EDM of a Mg AZ91D alloy through the integration of two evolutionary optimization techniques of the RSM technique, the ANN methodology, and the GA methodol- ogy. 2 EXPERIMENTAL PART In this paper the study was conducted on a wire EDM on a modern material, i.e., a magnesium AZ91D alloy, and the effective RSM Box-Behnken experimental M. PRADEEPKUMAR et al.: EVOLUTIONARY OPTIMIZATION OF WIRE EDM PROCESS FOR THE SURFACE FINISH ... 664 Materiali in tehnologije / Materials and technology 58 (2024) 5, 663–669 Figure 1: Proposed investigational methodology design 13 was chosen to conduct the experiments. 14 Box-Behnken designs are a robust and efficient design for a quadratic model for optimization by avoiding un- necessary combinations of experiments like corner points and star points of the design. The purpose of the identical experiments in Box-Bhenken design is to iden- tify the proper experimentation and minimize bias from uncontrolled variables. The results were analyzed as well as compared with the ANN methodology, 15 and the ANN resulting model was employed to produce a quadratic equation, which was then used as the fitness function for a GA to forecast the optimum machining parameters for an excellent surface quality. The proposed investigational methodology is shown in Figure 1. 2.1 Experimental Process The wire cut EDM process was conducted on a mag- nesium alloy with use of a CNC Wire EDM machine ELECTRONICA-ELCOT EL-10 VGA. The machining parameters of pulse-on time (T on ), pulse-off time off (T off ), and wire feed (W f ) were set at the three levels as shown in Table 1. The cutting process was performed with the use of a copper wire of 0.25 mm diameter. A to- tal of 17 trials were conducted using the interaction of the three machining parameters at the lower, medium, and higher levels in accordance with the recommenda- tions of the Box-Behnken design of experiment. The re- sults of the output response surface-roughness measure- ment using the Mitutoyo Surftest 211 equipment are shown in Table 2. Table 1: Machining parameters and their levels Wire-EDM- Machining Parameters Unit Levels Lower (–1) Medium (0) Higher (1) T on μs 4 7 10 Toff μs 4 7 10 Wf mm/min 1 2 3 Table 2: Box-Behnken Design of Experiments Run T on (μs) T off (μs) W f (mm/min) Experiment R a (μm) 1 –1 –1 0 1.25 2 1 –1 0 1.04 3– 1101 . 4 4110 0.74 5 –1 0 –1 1.19 6 1 0 –1 0.81 7 –1 0 1 1.13 8101 0.71 9 0 –1 –1 0.89 10 0 1 –1 1.15 11 0 –1 1 1.12 12 0 1 1 0.69 13 0 0 0 0.84 14 0 0 0 0.89 15 0 0 0 0.91 16 0 0 0 0.87 17 0 0 0 0.90 2.2 Response surface methodology (RSM) An experimental modeling method known as the RSM is used to establish the relationship among the re- sponses and the control variables 16 . To determine the ef- fects of wire feed (W f ), pulse-on time (T on ), and pulse-off time (T off ) on the surface finish (R a ), the present research employs RSM. The response Y = N, f, ap Y = (T on , T off ,W f ) (1) R a = (T on , T off ,W f ) (2) The present study’s second-order RSM model is pro- vided by: YXX XX ii i k ij i j ij k ii i i k =+ + + === ∑∑∑ 0 1 2 1 (3) n are the interacting coefficient terms. 17 2.3 Artificial Neural Network (ANN) ANNs are based on biological nervous systems. They consist of an enormous number of interconnected factors called neurons. The interactions between the neurons and the process information are stored in the brain by regula- tion among the neurons; as a result, the neurons form a network which mimics a biological nervous machine. 18 The input layer, hidden layer, and output layer are the three levels that make up the ANN computational method. Each layer contains a distinct type of neuron, and all the layers are connected in succeeding layers. 19 In this wire EDM operation, the ANN tool was uti- lized to identify the optimum machining parameters for obtaining a minimal surface roughness. A 3-8-1 neural network structure was developed by using the three ma- chining parameters T on , T off , and W f as the input neurons (input layer) and one hidden layer of eight neurons to generate one output neuron as surface roughness (output layer). The experimental data was used as the training data for the ANN model. The experiment was conducted with the training and testing sample datasets of 15 each. A random training data set was utilized to train the neu- ral network, and a backpropagation technique was em- ployed to train the feedforward network. The backpropa- gation algorithm is based on the gradient-descent method, and it uses iterations of the weights to update the goal and training mean square error values. The hid- den-layer and output-layer activation functions were set to logsig and tansig, respectively to achievie the surface roughness output. 20 In MATLAB, learning functions were assigned to traingdx and learngd, respectively, for the ANN training function. 2.4 Genetic Algorithm (GA) The use of evolutionary biology principles is utilized to address problems using the evolutionary optimization technique known as Genetic Algorithm (GA), and it in- M. PRADEEPKUMAR et al.: EVOLUTIONARY OPTIMIZATION OF WIRE EDM PROCESS FOR THE SURFACE FINISH ... Materiali in tehnologije / Materials and technology 58 (2024) 5, 663–669 665 cludes genetic inheritance, natural selection, mutation, and crossover. 21 Starting from a set of chromosomes or capability solutions that are randomly selected from the character of bit strings, a GA optimal solution is gener- ated. As a result, a population is formed by a whole set of these chromosomes, and the chromosomes change across many iterations or generations; as a result, new generations are created using the crossover and mutation approach. The chromosomes are further evaluated using certain fitness condition standards and the most appropri- ate chromosomes are stored, while the others are dis- carded. This system repeats till one chromosome ascends to high-quality fitness, whereupon it is assumed to be the most appropriate solution to the problem. 22 The GA has been successfully used in an extensive variety of prob- lems due to its simplicity, ease of procedure, and global perception. The ANN resultant quadratic model Equa- tion (4) was utilized for the objective function, the popu- lation size was set at 200, and the crossover probability was at 0.8, the mutation rate was distributed uniformly at 0.1, the stall generation was set at 100, and the stopping criteria were best fit. The GA was conducted to mini- mize the objective function, and the ranges of the input parameters are as shown in Table 3. Table 3: Parameter range for GA optimization Parameter Range for GA optimization Ton 1μs T on 10 μs Toff 1μs T on 10 μs Wf 1 mm/min W f 5 mm/min Objective function as Minimize: R a (T on , T off , W f ) 3 RESULTS AND DISCUSSION 3.1 Parameter Effects on Surface Roughness The analysis of the values of the machining parame- ters in the wire EDM process, developed by the use of the RSM method, is presented in Figure 2. It demon- strates that as the value of T on increases the surface roughness decreases linearly, predicting that a small change in T on would severely affect the surface rough- ness. In terms of T off , a lower rate of T off produces a higher surface roughness; moreover, when the T off in- creases the roughness value decreases until the middle level. Thereafter, it slightly increases until the higher level. In terms of W f , the figure depicts that increasing W f provides a greater surface roughness till level 2 (2 mm/min); thereafter, the roughness value decreases until the higher level of W f . The analysis of the variance (ANOVA) was derived on the basis of the RSM Box-Behnken experimental de- sign and is presented in Table 4. The primary objective of the ANOVA is to pinpoint cutting parameters that in- fluence thc characteristics of quality. According to ANOVA Table 4, the model contributed 99.50 percent of the total variance, whereas the errors percentage contri- bution was only 0.65 percent. This indicated that the ex- periment was carried out with the proper machining pa- rameters. Therefore, it can be observed that in the first-order interactions T on has a larger percentage (52.05%) contribution to the surface roughness while the remaining parameters T off and W f have a significantly smaller contribution of 1.911% and 2.83%, respectively. Table 4: Analysis of variance Source DF SS MS F-Value Contribu- tion T on 1 0.348613 0.026042 41.86 52.05% T off 1 0.012800 0.000165 0.26 1.911% W f 1 0.019012 0.039296 63.16 2.83% Ton *Ton 1 0.056963 0.052346 84.14 8.50% Toff *Toff 1 0.053188 0.054720 87.95 7.94% W f *W f 1 0.053188 0.004725 7.60 0.70% T on *T off 1 0.050625 0.050625 81.37 7.55% Ton *Wf 1 0.000400 0.000400 0.64 0.05% Toff *Wf 1 0.119025 0.119025 191.31 17.77% Error 7 0.004355 0.000622 0.65% Total 16 0.669706 Furthermore, the analysis suggests that a small varia- tion in the T on factor would affect the surface-finish char- acteristics on the magnesium material. In view of the second order, T on has a higher influence of 8.50 % com- pared to the other factors; moreover, Table 4 presents that the T on and T off has an effect on the surface rough- ness. The regression value for this operation was 99.35 %, which says that the Box-Behnken design of the experiment was the best technique to design for evaluat- ing the parameters in this wire EDM process. The ANOVA suggests that T on has a larger contribution in the wire cut EDM operation in comparison to the other pa- rameters. For better visibility and understanding of the effects of machining parameters on the output response surface roughness, the 3D surface plots in Figure 3 were cre- ated. Figure 3a indicates that a lower rate of T on and a higher rate of T off produce a higher surface roughness of 1.3 μm on this wire EDM process; furthermore, higher M. PRADEEPKUMAR et al.: EVOLUTIONARY OPTIMIZATION OF WIRE EDM PROCESS FOR THE SURFACE FINISH ... 666 Materiali in tehnologije / Materials and technology 58 (2024) 5, 663–669 Figure 2: Main effect plots for surface roughness rates of both T on and T off would yield a better surface fin- ish. Figure 3b displays the contribution of T on and W f in the wire EDM process. It shows that both the factors at lower levels give a higher surface roughness; conse- quently, higher levels of both the parameters yield a better surface finish. In terms of the interaction of T off and W f , the 3D surface plot was drawn, see Figure 3c. The figure shows that when the EDM process is con- ducted with a lower level of T off in correspondence to a higher level of W f , a higher surface roughness on the ma- terial is produced. Similarly, a lower level of W f with a higher level of T off also produces a higher roughness on the surface of the magnesium alloy. However, higher lev- els of both the parameters gave a better surface finish of 0.69 μm in this EDM process on the magnesium alloy. The RSM evaluation reveals the relationship between input parameters and the output response in terms of a quadratic model and the 3D surface plots indicate that T on and W f have the most impact on the output response when considering the surface roughness. The RSM pre- dicted values are closer to the experimental values at a higher level of T on at 10 μs, a middle level of T off at 7 μs, and a higher level of W f at 3 mm/min provide a better surface finish of approximately 0.69 μm and displayed in Table 5. R a = 1.18947 – (0.1488*T on ) + (0.0118*T off )+ + (0.5110*W f ) + (0.0123*T on *T on )+ + (0.01267*T off *T off ) – (0.0335*W f *W f )– – (0.0125*T on *T off ) – (0.00333*T on *W f )– – (0.0575*T off *W f ) (4) 3.2 Optimization Once the proposed neural network model has under- gone 1000 training iterations, the predicted surface roughness results were generated. An analysis of the net- work reveals a 0.99 correlation coefficient, meaning that there is a strong relationship between the experimental and projected values for this ANN model. Figure 4 dis- plays the results of the ANN model’s evaluation of the network’s performance, which is based on the correlation coefficient between the output and target values for the test data. A well-trained network can accurately predict surface roughness values, as shown by the ANN model’s average relative error between the experimental and pre- dicted values of 1.31 percent. An error % line chart of the predicted surface rough- ness values using RSM and ANN approaches is shown in Figure 5. A comparison between the chart and actual values shows that the ANN model generates a smaller er- ror than the RSM model. The ANN model’s predicted values are closer to the experimental values; conse- quently, it provides a better surface finish value of 0.71 μm with the optimal combination of the machining parameters in the higher level of T on at 10 μs, the middle level of T off at 7 μs, and the higher level of W f at 3 mm/min. In this optimization study, the ANN model M. PRADEEPKUMAR et al.: EVOLUTIONARY OPTIMIZATION OF WIRE EDM PROCESS FOR THE SURFACE FINISH ... Materiali in tehnologije / Materials and technology 58 (2024) 5, 663–669 667 Figure 4: Artificial neural network - regression model Figure 3: 3D Surface plot for surface roughness provides accurate values of the output response in com- parison to the experimental values; thereby proving its ability to train the model more efficiently. The GA optimization was conducted based on the ge- netic parameters stated above with integration of results obtained from ANN; moreover, the best fit was attained for the given machining parameters ranges. Figure 6 de- picts that the better the surface roughness has achieved a value of 0.4820 μm with the optimized values of the cut- ting parameters are at the higher levels with T on at 10 μs, T off at 10 μs, and W f at 3 mm/min. The outcomes of the confirmation test, which was carried out in accordance with the suggestions of the ANN and GA procedures, are shown in Table 5. It is noted that both the ANN and GA model provide a lower error percentage; moreover, both approaches work better as optimization tools for machin- ing parameter optimization for modern materials. Table 5: Evaluation of predicted model Machining Parameters Surface Roughness R a (μm) Error % T on T off W f RSM Pre- dicted ANN Pre- dicted GA Pre- dicted Confir- mation Test 10 7 3 0.691 0.73 5.47 10 7 3 0.711 0.74 3.91 10 10 3 0.4820 0.50 3.60 4 CONCLUSIONS The application of evolutionary techniques to predict optimized cutting parameters in the wire EDM process on a modern material, i.e., the magnesium alloy AZ91D, is the focus of this research. Through the Box-Behnken experimental methodology, the RSM quadratic model has been developed to predict and examine analytical models for attaining better cutting parameters on achiev- ing a minimal surface roughness. Using the evolutionary method of the ANN and GA approaches, the following conclusions were drawn: • The RSM main effect plot suggests a minimum sur- face roughness of 0.69 μm with the desired parameter levels; also, the Box-Behnken experimental design yields a predicted regression (R 2 ) value of 96.36, in- dicating the Box-Behnken design to be the most effi- cient way of designing an experiment. The ANOVA shows that the T on has a bigger contribution of 52.32 percent in this experiment; additionally, it shows that even the smallest adjustment in this parameter affects the component’s surface finish. • When compared to t heexperimental values, the ANN model projected values are more accurate, resulting in a better surface finish value of 0.71 μm with the optimal combination of machining parameters of T on at 10 μs, T off at7μsandW f at 3 mm/min. The RSM and ANN methodologies had an average error of 1.38 % and 1.31 %, respectively, when compared to the experimental results. 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Appl, 26 (2021) 5, doi:10.3390/mca26010005 M. PRADEEPKUMAR et al.: EVOLUTIONARY OPTIMIZATION OF WIRE EDM PROCESS FOR THE SURFACE FINISH ... Materiali in tehnologije / Materials and technology 58 (2024) 5, 663–669 669