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Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites K. Raju ⇑, M. Balakrishnan M. Kumarasamy College of Engineering, Karur 639113, India
a r t i c l e
i n f o
Article history: Received 30 July 2019 Received in revised form 24 October 2019 Accepted 5 November 2019 Available online xxxx Keywords: Aluminium Boron carbide Wire electrical discharge machining Scanning Electron Microscope Surface roughness Material removal rate
a b s t r a c t The main objective of this study is to investigate the optimum parameters opted for better material removal rate with good surface finish. The material for this study was selected as aluminium metal matrix composite fabricated by stir casting method with Al 6061 90 percentage and Boron Carbide 10 percentage as reinforcement. The study was conducted on wire electrical discharge machining machine where the selected parameters are pulse on time, current and pulse off time. Surface roughness and material removal rate was taken as output responses for the study. The X-ray Diffraction test confirms the presence of boron carbide particulate in prepared aluminium composite. The microstructure taken reveals the uniform mixing of boron carbide particulate. The Scanning Electron Microscope analysis was also taken to confirm the uniform mixing of boron carbide particulate with aluminium. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Materials Engineering and Characterization 2019.
1. Introduction Wire electrical discharge machining [WEDM] is a nontraditional machining process used in automobire and airspace sectors because machining intricate shapes even in hard materials, not possible with conventional machine [1]. Identification of optimum operating parameters for obtaining higher accuracy in WEDM is a big problem even with the up-to-date CNC WEDM machine. Thus the relationship between the cutting parameters and its performance are hard to get good accuracy [2–4]. Optimizations of operating parameters are important for machines like WEDM. Therefore optimization is very much necessary for accurate machining of each and every materials. Thus better performance can be obtained considering the parameters such as wire tension, wire velocity pulse on and off time, electrolyte, feed rate and flushing pressure etc. [5,6]. Gopalakannan et al., analysed that surface roughness [Ra] and material removal rate [MRR] are the two parameters influencing machining [7]. Marigoudar, & Sadashivappa, concluded that the increase of current and pulse on time produce deeper discharge craters due to increased discharge energy [8]. Prohaszka et al., stated that increasing pulse on time and current, material removal rate [MRR] increases and increase in pulse off time decreases material removal rate [9]. ⇑ Corresponding author.
Shandilya, et al., studied the quality of material removal rate in SiCp/6061 aluminum metal matrix composite [MMC] by varying the wire feed rate, voltage, pulse on and off time. The report shows that when increasing pulse time, voltage, and wire feed rate, proportionately there is an increase in MRR and Ra [10,11]. Tosun, experimented 42CrMo4 machining with copper as tool electrode and results that keeping the current, pulse duration, pulse interval and voltage at 25 A, 200 ms and 100 ms and 80 V respectively shows good material removal rate with reduced tool wear [12]. Yan, et al., found that the MRR in electro-discharge drilling [EDD] process increases when compared with elctctrical discharge machining, but the EDD process has severe problem with tool wear and accuracy [13]. Response parameter such as material removal rate, tool wear and surface finish depends on process parameters such as spark gap, pulse, current and open voltage [14,15]. The work of Zhao, et al., deals with the effect of input parameter over response parameter in WEDM of die steel [16]. Kanlayasiri, and Boonmung, thoroughly studied the various factors affecting the quality of the material in WEDM machining [17]. Chaudhary et al., stated that the machining of WEDM process is simple as in conventional machines with an advantage of machining harder, strengthen materials with good accuracy and machining complex shapes [18,19]. Vinod Kumar et al. machined Nimonic 90 which is a super-alloy based on nickel, and found out that the machining with wire EDM gives good surface finish [20].
E-mail address: [email protected] (K. Raju). https://doi.org/10.1016/j.matpr.2019.11.036 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Materials Engineering and Characterization 2019.
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
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K. Raju, M. Balakrishnan / Materials Today: Proceedings xxx (xxxx) xxx
Electrical discharge machining removes material by discharging spark from a pulsating direct-current power supply between the work piece and tool and hence metal vaporizes a small area of the work piece surface which is cooled by the dielectric fluid and is flushed away by the dielectric flow [21]. In WEDM there is a heat affected zone on the surface being machined developing a residual tensile stress causing micro cracks. Thus the thermal complexity can also affect the surface integrity of the material. Hence the accuracy of WEDM process requires appropriate selection of materials and machining parameters [22]. Nilesh and Brahmakar studied the wire EDM machining of Al6061/Al2O3p composite by varying the volume fractions of Al2O3p between 10% and 22%. Taguchi’s method was used for conducting and analyzing the experiments [15]. Considering the challenges in machining of WEDM process, an attempt is made to find the better MRR and Ra for machining of aluminium composite with boron carbide as reinforcements. 2. Methods 2.1. Stir casting method of MMC fabrication Stir casting method was identified for preparing the composites. Based on the density of reinforcements the volume fractions was selected as matrix 90% and reinforcement 10%. Aluminum 6061 was preheated and melted in resistance furnance. The B4C particulate was preheated at 550 °C for one to two hours making their surfaces oxidized. The preheated reinforcement was slowely added to the melted aluminium matrix manually and maintaining the stirrer at a constant speed of 300 rpm continuously for 10–15 min. The melt was maintained at temperature 750 °C to get uniform mixing and later it was poured in steel moulds of 20 mm diameter and 30 cm in length which was allowed to cool and taken as cast rod. The prepared samples were subjected to machinability analysis using WEDM.
Fig. 1. Optical Microscopic image of Al and B4C Composite.
2.2. Design of experiments For experimentation the workpiece is machined with the dimension of 18 18 5 mm. The wire diameter for entire machining was made constant. Operating parameters with three levels was taken as per Box Behnken Design. Current, Pulse on and off time was taken as the major factors and random run was taken for the design. The MRR is calculated by considering the difference in material weights before machining and after machining with the machining time. Mitutoyo SJ-210 portable tester was used to evaluate the surface roughness of the composite. The roughness values after every experiment were taken at dissimilar locations and mean value was taken as final value. Fig. 2. Scanning Electron Microscopic image of Al and B4C Composite.
3. Result and discussion 3.1. Metallurgical properties 3.1.1. Microstructure of Al 6061 and 10% B4C The microstructure photograph from Fig. 1 shows the evidence for the presence of reinforcement particulate in the composite matrix. The microstructure clearly shows the particle matrix interface has good adhesion without any macro/micro level cracks. This supports for further testing of composites. 3.1.2. SEM image of Al 6061and 10% B4C The Scanning Electron Microscope image of Fig. 2 shows the structure of the uniform mixing of aluminium and boron carbide powder. The particles are found throughout the materials. Fig. 3 confirms the presence of boron carbide in the composite.
3.1.3. XRD analysis The X ray diffraction test conform the presence of aluminium and the reinforced particulate of boron carbide which is shown in Fig. 4.
3.2. Selection of operating parameters There are various process parameters which accounts in machining the composite using WEDM. Out of these parameters pulse on time (Ton), pulse off time (Toff) and current (Ip) were selected as these parameters predicts the surface finish and machining rate greatly and also to reduce the experiment size making the analysis easier. The three parameters along with their
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
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K. Raju, M. Balakrishnan / Materials Today: Proceedings xxx (xxxx) xxx
of current, pulse on and off time was found out to be statistically more significant. Further input current was found out to be statistically significant. The effect of pulse off time is also important in predicting the SR. The interactions between the parameters did not have much statistical significance on the model for SR. The Table 5 shows the value for R2 and R2 adjusted. The higher the value of R2 it is noted that insignificant parameters artificially influence the response values. To solve this issue adjusted R2 is introduced for the addition of predictors in the model. A smaller difference in R2 and adj R2 indicates significant parameters are considered which does not have much problem during machining the composite. The values for both the models of MRR and SR clearly indicate that the deviation of values between R2 and adj R2 are sufficiently smaller. This establishes that both the models of MRR and SR are adequate. To identify with the impact of each process parameters on the individual responses, the analysis of variance for the parameters for both the models have been performed and illustrated in Table 5. It also depicts the coefficients associated with each variable. Table 6 shows the optimum response values for the varying levels of machining parameters. Fig. 3. EDS Analysis of the prepared Composite.
MRR ¼ 0:029733 ð0:005029 220Þ þ ð0:000383 230Þ þ ð0:004646 240Þ ð0:005417 50Þ þ ð0:001033 75Þ þ ð0:004383 100Þ þ ð0:004462 30Þ þ ð0:000250 40Þ ð0:004712 50Þ
ð1Þ
SR ¼ 4:2733 þ ð0:607 220Þ ð0:131 230Þ ð0:476 240Þ þ ð0:620 50Þ ð0:240 75Þ ð0:380 100Þ ð0:560 30Þ ð0:065 40Þ þ ð0:625 50Þ Fig. 4. XRD Analysis of Al and B4C Composite.
respective levels are taken and assigned three levels as low, medium and high respectively as shown in Table 1. Table 2 illustrates Box Behnken Design [BBD] experiments performed under this investigation and their corresponding responses measured using Wire EDM process. From the results obtained it is found that for the minimum current of 220 A the MRR was noted to be 0.0325 g/min with a surface roughness of 3.634 mm. By increasing the current to 230 A, there is also increase in material removal rate by 13.5% of value 0.0376 g/ min. Similarly the surface roughness is decreased by 6% as 3.423. Further increase in values of current to 240 A there is 20% increase in MRR and 40% decrease in Ra when compared to input current of 230 A as shown in Table 6. Tables 3 and 4 shows the analysis of variance for the second order model obtained for MRR and SR. The p values associated with the models are well below 0.05 and thus the models are statistically significant. The variance analysis proves that the most significant parameter are pulse on time and current. Further, the quadratic effects were more significant than the linear effects. The quadratic effects
ð2Þ
The mathematical models associated with material removal and surface roughness, have been analysed by multiple regression method and are illustrated by Eqs. (1) and (2) respectively. All the regression data and graphically obtained data were performed using ‘MINITAB 16’ software. The residual plots for output parametric values are compared and found correct. From the results obtained, it is clear that the percentage of machining rate and surface finish lies close to the normal plot showing that the values are correct based on R2 and adjusted R2. 3.3. Crack and recast layer thickness WEDM process is the heating and vaporizing of material followed by cooling which makes the surface to get damage by the formation of cracks along with huge thermal stress developed due to plastic deformation of material while machining. When smaller values of pulse on time is set, mean gap gets narrow increasing the spark leading to increased machining rate. The gap may be unstable at places leading to the breakage of wire and affects the surface. The huge thermal stress developed on wire breakage may lead to the development of surface crack affecting the material properties. Simultaneously a layer of material is developed on the surface of work material due to melting and
Table 1 Process Parameters and levels considered for the experiments. Symbol
Machining parameter
Unit
Low (0)
Medium (1)
High (2)
A B C
CURRENT PULSE ON PULSE OFF
A ms ms
220 50 30
230 75 40
240 100 50
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
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Table 2 Experimental results for BBD with three parameters and three levels. S. No
Machining parameters
Response parameters
A: Current A
B: Pulse on time ms
C: Pulse off time ms
A: Current A
B: Pulse on time ms
C: Pulse off time ms
MRR g/min
SR mm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 1 1 0 2 0 2 1 0 2 1 2 1 1 0
1 2 0 0 1 1 1 2 1 2 1 0 0 1 2
1 2 2 1 0 2 2 0 0 1 1 1 0 1 1
230 230 230 220 240 220 240 230 220 240 230 240 230 230 220
75 100 50 50 75 75 75 100 75 100 75 50 50 75 100
40 50 50 40 30 50 50 30 30 40 40 40 30 40 40
0.0304 0.0299 0.0198 0.0180 0.0375 0.0207 0.0311 0.0376 0.0325 0.0407 0.0316 0.0295 0.0306 0.0322 0.0289
3.902 4.475 5.386 5.726 3.531 5.367 3.995 3.423 3.634 2.990 3.862 4.367 3.896 3.749 4.489
Table 3 Analysis of variance and process parameters for MRR. Source
DF
Seq SS
Contribution
Adj SS
Adj MS
F-Value
P-Value
A B C Error Lack-of-Fit Pure Error Total
2 2 2 8 6 2 14
0.000188 0.000201 0.000169 0.000022 0.000021 0.000002 0.00058
32.41% 34.61% 29.13% 3.85% 3.56% 0.29% 100.00%
0.000188 0.000201 0.000169 0.000022 0.000021 0.000002
0.000094 0.0001 0.000084 0.000003 0.000003 0.000001
39.75 35.99 24.25
0.002 0.004 0.068
4.1
0.209
Table 4 Analysis of variance and process parameters for MRR. Source
DF
Seq SS
Contribution
Adj SS
Adj MS
F-Value
P-Value
A B C Error Lack-of-Fit Pure Error Total
2 2 2 8 6 2 14
2.4465 2.4576 2.8428 0.9111 0.8985 0.0126 8.658
28.26% 28.39% 32.83% 10.52% 10.38% 0.15% 100.00%
2.48877 2.47464 2.84276 0.91112 0.89853 0.01259
1.24438 1.23732 1.42138 0.11389 1.14975 0.0063
10.93 10.86 12.48
0.005 0.005 0.003
23.78
0.041
Table 5 Analysis R2 and Adj R2 for MRR and SR.
4. Conclusion
Responses
R2
Adj R2
P-value
MRR SR
96.15% 89.48%
93.26% 81.58%
0.003 0.011
Based on this study in analyzing operating parameters in WEDM process of aluminium 6061 90%, and Boron Carbide 10% metal matrix composite the following conclusions were made. Three process parameters selected for machining was current, pulse on time and pulse off time. Box Benhken design was selected for the experiment. The variance analysis indicates that current and pulse on time were highly influencing parameter among other parameters in predicting the machining rate and SR. Mathematical models for both MRR and SR were developed and the models were found to be quite adequate. Among the above three parameters with respect to MRR and surface roughness, the optimum parameters are current 240 A, Pulse on time 100 ms, Pulse off time 40 ms,
vaporization called as recast layer. This layer may be single or multiple based on the materials thermal conductivity, chemical composition and the selected process parameters. The layer thickness development depends upon the current and pulse on time where the major role is taken by the pulse on time. These recast layer has fine grained structured and differs from the base material changing the properties of materials at the machined places.
Table 6 Optimum response values for the different levels of machining parameters. Machining parameters
Response parameters
A: Current A
B: Pulse on time ms
C: Pulse off time ms
MRR g/min
SR mm
220 230 240
75 100 100
30 30 40
0.0325 0.0376 0.0407
3.634 3.423 2.99
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
K. Raju, M. Balakrishnan / Materials Today: Proceedings xxx (xxxx) xxx
and material removal rate is 0.0407 g/min and the surface finish was found out to be 2.99 mm. It is concluded that when current, pulse on time and pulse off time increases the material removal time increases and decrease surface roughness value. Similarly the decrease in process parameters decreases the material removal rate, decreasing the surface accuracy of composite.
[8]
[9]
[10]
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors wish to record their sincere thanks to the management of M. Kumarasamy College of Engineering, for providing stir casting facility and metallographic facilities to carry out this research work. References [1] A. Gatto., L. Luliano, Cutting mechanism and surface features of WED machined metal matrix composites, J. Mater. Process. Technol. 65 (1997) 209–214. [2] N. Tosun, The effect of cutting parameters on workpiece surface roughness in wire EDM, Mach. Sci. Technol. 7 (2) (2003) 209–219. [3] Yang, Optimization of wire electrical discharge machining process parameters for cutting tungsten, Int. J. Adv. Manuf. Technol. 60 (1) (2012) 135–147. [4] T. Ali, Parametric study and optimization of wire electrical discharge machining of Al-Cu-TiC-Si P/M composite, Int. J. Mach. Mach. Mater. 1 (2006) 380–395. [5] S. Sarkar., S. Mitra., B. Bhattacharyya, Parametric optimisation of wire electrical discharge machining of c titanium aluminide alloy through an artificial neural network model, Int. J. Adv. Manuf. Technol. 2 (2006) 501–508. [6] P. Shandilya., P.K. Jain., N.K. Jain, Modeling and analysis of surface roughness in WEDC of SiCP/6061 Al MMC through response surface methodology, Int. J. Eng. Sci. Technol. 3 (2011) 531–535. [7] S. Gopalakannan., T. Senthilvelan., S. Ranganathan, Modeling and Optimization of EDM Process Parameters on Machining of Al 7075-B4C MMC Using RSM, in:
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International Conference on Modeling Optimization and Computing, vol. 38, 2012, pp. 685–690. R.N. Marigoudar., K. Sadashivappa, Effect of machining parameters on MRR and surface roughness in machining of ZA43/SiCp composite by WEDM, Int. J. Appl. Sci. Eng. 11 (2013) 317–330. J. Prohaszka., A.G. Mamails., N.M. Vaxevanidis, The effect of electrode material on machinability in wire electro-discharge machining, J. Mater. Process. Technol. 69 (1997) 233–237. Shandilya Pragya, P.K. Jain, Experimental investigation during WEDC of SiCP/ 6061Al MMC, in: Annals for DAAAM & proceedings of the 21st International DAAAM Symposium, vol. 21, 2010, 1091–1092. P. Shandilya, P.K. Jain., N.K. Jain, Wire Electric Discharge Machining Of Metal Matrix Composite Materials, DAAAM International, vol. 30, 2011, 383–400. N. Tosun, The effect of the cutting parameters on performance of WEDM, KSME Int. J. 17 (2003) 816–824. B.H. Yan., H.C. Tsai., F.Y. Huang., L.C. Lee, Examination of wire electrical discharge machining of Al2O3/6061Al composites, Int. J. Mach. Tools Manuf. 45 (2005) 251–259. B.H. Yan., C.C. Wang., W.D. Liu., F.Y. Huang, Machining characteristics of A12o3/6061 Al composite using rotary EDM with a dislike electrode, Int. J. Adv. Manuf. Technol. 16 (5) (2000) 322–333. Nilesh G. Patil, P.K. Brahmakar, Some studies into wire electro-discharge machining of alumina Particulate-reinforced aluminum matrix composites, Int. J. Adv. Manuf. 48 (5–8) (2010) 537–555. J. Zhao., M. Kunieda., G. Yang., X. Yuan, Micro-EDM for an aluminum matrix composite, Key Eng. Mater. 447 (448) (2010) 233–237. K. Kanlayasiri., S. Boonmung, An investigation on effects of wire-EDM machining parameters on Surface roughness of newly developed DC53 dies steel, J. Mater. Process. Technol. 187 (188) (2007) 26–29. Chaudhary, Optimization of Wire Electric discharge machining process of D-2 steel using response surface methodology, Int. J. Eng. Res. Appl. 3 (3) (2013) 206–216. A.B. Puri., B. Bhattacharyya, An analysis and optimisation of the eometrical inaccuracy due to wire lag phenomenon in WEDM, Int. J. Mach. Tools Manuf. 1 (2003) 151–159. Vinod Kumar, Effect Of Wedm Parameters On Machinability Of Nimonic-90, in: Proceedings of the National Conference on Trends and Advances in Mechanical Engineering, YMCA University of Science & Technology, Faridabad, Haryana, 2012, pp.19–20. Ibrahem Maher, Improve wire EDM performance at different machining parameters, in: 8th Vienna International Conference on Mathematical Modelling, 48(1), 2015, pp. 105–110. I. Ogata., Y. Mukoyama, Residual stress on surface machined by wire electric discharge, J. Jpn. Soc. Precis. Eng. 25 (1991) 273–278.
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites K. Raju ⇑, M. Balakrishnan M. Kumarasamy College of Engineering, Karur 639113, India
a r t i c l e
i n f o
Article history: Received 30 July 2019 Received in revised form 24 October 2019 Accepted 5 November 2019 Available online xxxx Keywords: Aluminium Boron carbide Wire electrical discharge machining Scanning Electron Microscope Surface roughness Material removal rate
a b s t r a c t The main objective of this study is to investigate the optimum parameters opted for better material removal rate with good surface finish. The material for this study was selected as aluminium metal matrix composite fabricated by stir casting method with Al 6061 90 percentage and Boron Carbide 10 percentage as reinforcement. The study was conducted on wire electrical discharge machining machine where the selected parameters are pulse on time, current and pulse off time. Surface roughness and material removal rate was taken as output responses for the study. The X-ray Diffraction test confirms the presence of boron carbide particulate in prepared aluminium composite. The microstructure taken reveals the uniform mixing of boron carbide particulate. The Scanning Electron Microscope analysis was also taken to confirm the uniform mixing of boron carbide particulate with aluminium. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Materials Engineering and Characterization 2019.
1. Introduction Wire electrical discharge machining [WEDM] is a nontraditional machining process used in automobire and airspace sectors because machining intricate shapes even in hard materials, not possible with conventional machine [1]. Identification of optimum operating parameters for obtaining higher accuracy in WEDM is a big problem even with the up-to-date CNC WEDM machine. Thus the relationship between the cutting parameters and its performance are hard to get good accuracy [2–4]. Optimizations of operating parameters are important for machines like WEDM. Therefore optimization is very much necessary for accurate machining of each and every materials. Thus better performance can be obtained considering the parameters such as wire tension, wire velocity pulse on and off time, electrolyte, feed rate and flushing pressure etc. [5,6]. Gopalakannan et al., analysed that surface roughness [Ra] and material removal rate [MRR] are the two parameters influencing machining [7]. Marigoudar, & Sadashivappa, concluded that the increase of current and pulse on time produce deeper discharge craters due to increased discharge energy [8]. Prohaszka et al., stated that increasing pulse on time and current, material removal rate [MRR] increases and increase in pulse off time decreases material removal rate [9]. ⇑ Corresponding author.
Shandilya, et al., studied the quality of material removal rate in SiCp/6061 aluminum metal matrix composite [MMC] by varying the wire feed rate, voltage, pulse on and off time. The report shows that when increasing pulse time, voltage, and wire feed rate, proportionately there is an increase in MRR and Ra [10,11]. Tosun, experimented 42CrMo4 machining with copper as tool electrode and results that keeping the current, pulse duration, pulse interval and voltage at 25 A, 200 ms and 100 ms and 80 V respectively shows good material removal rate with reduced tool wear [12]. Yan, et al., found that the MRR in electro-discharge drilling [EDD] process increases when compared with elctctrical discharge machining, but the EDD process has severe problem with tool wear and accuracy [13]. Response parameter such as material removal rate, tool wear and surface finish depends on process parameters such as spark gap, pulse, current and open voltage [14,15]. The work of Zhao, et al., deals with the effect of input parameter over response parameter in WEDM of die steel [16]. Kanlayasiri, and Boonmung, thoroughly studied the various factors affecting the quality of the material in WEDM machining [17]. Chaudhary et al., stated that the machining of WEDM process is simple as in conventional machines with an advantage of machining harder, strengthen materials with good accuracy and machining complex shapes [18,19]. Vinod Kumar et al. machined Nimonic 90 which is a super-alloy based on nickel, and found out that the machining with wire EDM gives good surface finish [20].
E-mail address: [email protected] (K. Raju). https://doi.org/10.1016/j.matpr.2019.11.036 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Materials Engineering and Characterization 2019.
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
2
K. Raju, M. Balakrishnan / Materials Today: Proceedings xxx (xxxx) xxx
Electrical discharge machining removes material by discharging spark from a pulsating direct-current power supply between the work piece and tool and hence metal vaporizes a small area of the work piece surface which is cooled by the dielectric fluid and is flushed away by the dielectric flow [21]. In WEDM there is a heat affected zone on the surface being machined developing a residual tensile stress causing micro cracks. Thus the thermal complexity can also affect the surface integrity of the material. Hence the accuracy of WEDM process requires appropriate selection of materials and machining parameters [22]. Nilesh and Brahmakar studied the wire EDM machining of Al6061/Al2O3p composite by varying the volume fractions of Al2O3p between 10% and 22%. Taguchi’s method was used for conducting and analyzing the experiments [15]. Considering the challenges in machining of WEDM process, an attempt is made to find the better MRR and Ra for machining of aluminium composite with boron carbide as reinforcements. 2. Methods 2.1. Stir casting method of MMC fabrication Stir casting method was identified for preparing the composites. Based on the density of reinforcements the volume fractions was selected as matrix 90% and reinforcement 10%. Aluminum 6061 was preheated and melted in resistance furnance. The B4C particulate was preheated at 550 °C for one to two hours making their surfaces oxidized. The preheated reinforcement was slowely added to the melted aluminium matrix manually and maintaining the stirrer at a constant speed of 300 rpm continuously for 10–15 min. The melt was maintained at temperature 750 °C to get uniform mixing and later it was poured in steel moulds of 20 mm diameter and 30 cm in length which was allowed to cool and taken as cast rod. The prepared samples were subjected to machinability analysis using WEDM.
Fig. 1. Optical Microscopic image of Al and B4C Composite.
2.2. Design of experiments For experimentation the workpiece is machined with the dimension of 18 18 5 mm. The wire diameter for entire machining was made constant. Operating parameters with three levels was taken as per Box Behnken Design. Current, Pulse on and off time was taken as the major factors and random run was taken for the design. The MRR is calculated by considering the difference in material weights before machining and after machining with the machining time. Mitutoyo SJ-210 portable tester was used to evaluate the surface roughness of the composite. The roughness values after every experiment were taken at dissimilar locations and mean value was taken as final value. Fig. 2. Scanning Electron Microscopic image of Al and B4C Composite.
3. Result and discussion 3.1. Metallurgical properties 3.1.1. Microstructure of Al 6061 and 10% B4C The microstructure photograph from Fig. 1 shows the evidence for the presence of reinforcement particulate in the composite matrix. The microstructure clearly shows the particle matrix interface has good adhesion without any macro/micro level cracks. This supports for further testing of composites. 3.1.2. SEM image of Al 6061and 10% B4C The Scanning Electron Microscope image of Fig. 2 shows the structure of the uniform mixing of aluminium and boron carbide powder. The particles are found throughout the materials. Fig. 3 confirms the presence of boron carbide in the composite.
3.1.3. XRD analysis The X ray diffraction test conform the presence of aluminium and the reinforced particulate of boron carbide which is shown in Fig. 4.
3.2. Selection of operating parameters There are various process parameters which accounts in machining the composite using WEDM. Out of these parameters pulse on time (Ton), pulse off time (Toff) and current (Ip) were selected as these parameters predicts the surface finish and machining rate greatly and also to reduce the experiment size making the analysis easier. The three parameters along with their
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
3
K. Raju, M. Balakrishnan / Materials Today: Proceedings xxx (xxxx) xxx
of current, pulse on and off time was found out to be statistically more significant. Further input current was found out to be statistically significant. The effect of pulse off time is also important in predicting the SR. The interactions between the parameters did not have much statistical significance on the model for SR. The Table 5 shows the value for R2 and R2 adjusted. The higher the value of R2 it is noted that insignificant parameters artificially influence the response values. To solve this issue adjusted R2 is introduced for the addition of predictors in the model. A smaller difference in R2 and adj R2 indicates significant parameters are considered which does not have much problem during machining the composite. The values for both the models of MRR and SR clearly indicate that the deviation of values between R2 and adj R2 are sufficiently smaller. This establishes that both the models of MRR and SR are adequate. To identify with the impact of each process parameters on the individual responses, the analysis of variance for the parameters for both the models have been performed and illustrated in Table 5. It also depicts the coefficients associated with each variable. Table 6 shows the optimum response values for the varying levels of machining parameters. Fig. 3. EDS Analysis of the prepared Composite.
MRR ¼ 0:029733 ð0:005029 220Þ þ ð0:000383 230Þ þ ð0:004646 240Þ ð0:005417 50Þ þ ð0:001033 75Þ þ ð0:004383 100Þ þ ð0:004462 30Þ þ ð0:000250 40Þ ð0:004712 50Þ
ð1Þ
SR ¼ 4:2733 þ ð0:607 220Þ ð0:131 230Þ ð0:476 240Þ þ ð0:620 50Þ ð0:240 75Þ ð0:380 100Þ ð0:560 30Þ ð0:065 40Þ þ ð0:625 50Þ Fig. 4. XRD Analysis of Al and B4C Composite.
respective levels are taken and assigned three levels as low, medium and high respectively as shown in Table 1. Table 2 illustrates Box Behnken Design [BBD] experiments performed under this investigation and their corresponding responses measured using Wire EDM process. From the results obtained it is found that for the minimum current of 220 A the MRR was noted to be 0.0325 g/min with a surface roughness of 3.634 mm. By increasing the current to 230 A, there is also increase in material removal rate by 13.5% of value 0.0376 g/ min. Similarly the surface roughness is decreased by 6% as 3.423. Further increase in values of current to 240 A there is 20% increase in MRR and 40% decrease in Ra when compared to input current of 230 A as shown in Table 6. Tables 3 and 4 shows the analysis of variance for the second order model obtained for MRR and SR. The p values associated with the models are well below 0.05 and thus the models are statistically significant. The variance analysis proves that the most significant parameter are pulse on time and current. Further, the quadratic effects were more significant than the linear effects. The quadratic effects
ð2Þ
The mathematical models associated with material removal and surface roughness, have been analysed by multiple regression method and are illustrated by Eqs. (1) and (2) respectively. All the regression data and graphically obtained data were performed using ‘MINITAB 16’ software. The residual plots for output parametric values are compared and found correct. From the results obtained, it is clear that the percentage of machining rate and surface finish lies close to the normal plot showing that the values are correct based on R2 and adjusted R2. 3.3. Crack and recast layer thickness WEDM process is the heating and vaporizing of material followed by cooling which makes the surface to get damage by the formation of cracks along with huge thermal stress developed due to plastic deformation of material while machining. When smaller values of pulse on time is set, mean gap gets narrow increasing the spark leading to increased machining rate. The gap may be unstable at places leading to the breakage of wire and affects the surface. The huge thermal stress developed on wire breakage may lead to the development of surface crack affecting the material properties. Simultaneously a layer of material is developed on the surface of work material due to melting and
Table 1 Process Parameters and levels considered for the experiments. Symbol
Machining parameter
Unit
Low (0)
Medium (1)
High (2)
A B C
CURRENT PULSE ON PULSE OFF
A ms ms
220 50 30
230 75 40
240 100 50
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
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Table 2 Experimental results for BBD with three parameters and three levels. S. No
Machining parameters
Response parameters
A: Current A
B: Pulse on time ms
C: Pulse off time ms
A: Current A
B: Pulse on time ms
C: Pulse off time ms
MRR g/min
SR mm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 1 1 0 2 0 2 1 0 2 1 2 1 1 0
1 2 0 0 1 1 1 2 1 2 1 0 0 1 2
1 2 2 1 0 2 2 0 0 1 1 1 0 1 1
230 230 230 220 240 220 240 230 220 240 230 240 230 230 220
75 100 50 50 75 75 75 100 75 100 75 50 50 75 100
40 50 50 40 30 50 50 30 30 40 40 40 30 40 40
0.0304 0.0299 0.0198 0.0180 0.0375 0.0207 0.0311 0.0376 0.0325 0.0407 0.0316 0.0295 0.0306 0.0322 0.0289
3.902 4.475 5.386 5.726 3.531 5.367 3.995 3.423 3.634 2.990 3.862 4.367 3.896 3.749 4.489
Table 3 Analysis of variance and process parameters for MRR. Source
DF
Seq SS
Contribution
Adj SS
Adj MS
F-Value
P-Value
A B C Error Lack-of-Fit Pure Error Total
2 2 2 8 6 2 14
0.000188 0.000201 0.000169 0.000022 0.000021 0.000002 0.00058
32.41% 34.61% 29.13% 3.85% 3.56% 0.29% 100.00%
0.000188 0.000201 0.000169 0.000022 0.000021 0.000002
0.000094 0.0001 0.000084 0.000003 0.000003 0.000001
39.75 35.99 24.25
0.002 0.004 0.068
4.1
0.209
Table 4 Analysis of variance and process parameters for MRR. Source
DF
Seq SS
Contribution
Adj SS
Adj MS
F-Value
P-Value
A B C Error Lack-of-Fit Pure Error Total
2 2 2 8 6 2 14
2.4465 2.4576 2.8428 0.9111 0.8985 0.0126 8.658
28.26% 28.39% 32.83% 10.52% 10.38% 0.15% 100.00%
2.48877 2.47464 2.84276 0.91112 0.89853 0.01259
1.24438 1.23732 1.42138 0.11389 1.14975 0.0063
10.93 10.86 12.48
0.005 0.005 0.003
23.78
0.041
Table 5 Analysis R2 and Adj R2 for MRR and SR.
4. Conclusion
Responses
R2
Adj R2
P-value
MRR SR
96.15% 89.48%
93.26% 81.58%
0.003 0.011
Based on this study in analyzing operating parameters in WEDM process of aluminium 6061 90%, and Boron Carbide 10% metal matrix composite the following conclusions were made. Three process parameters selected for machining was current, pulse on time and pulse off time. Box Benhken design was selected for the experiment. The variance analysis indicates that current and pulse on time were highly influencing parameter among other parameters in predicting the machining rate and SR. Mathematical models for both MRR and SR were developed and the models were found to be quite adequate. Among the above three parameters with respect to MRR and surface roughness, the optimum parameters are current 240 A, Pulse on time 100 ms, Pulse off time 40 ms,
vaporization called as recast layer. This layer may be single or multiple based on the materials thermal conductivity, chemical composition and the selected process parameters. The layer thickness development depends upon the current and pulse on time where the major role is taken by the pulse on time. These recast layer has fine grained structured and differs from the base material changing the properties of materials at the machined places.
Table 6 Optimum response values for the different levels of machining parameters. Machining parameters
Response parameters
A: Current A
B: Pulse on time ms
C: Pulse off time ms
MRR g/min
SR mm
220 230 240
75 100 100
30 30 40
0.0325 0.0376 0.0407
3.634 3.423 2.99
Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036
K. Raju, M. Balakrishnan / Materials Today: Proceedings xxx (xxxx) xxx
and material removal rate is 0.0407 g/min and the surface finish was found out to be 2.99 mm. It is concluded that when current, pulse on time and pulse off time increases the material removal time increases and decrease surface roughness value. Similarly the decrease in process parameters decreases the material removal rate, decreasing the surface accuracy of composite.
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Please cite this article as: K. Raju and M. Balakrishnan, Experimental study and analysis of operating parameters in wire EDM process of aluminium metal matrix composites, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.036