Optimization Of Process Parameters Of Manual Arc Welding .
American Journal of Mechanical Engineering, 2015, Vol. 3, No. 3, 93-97Available online at http://pubs.sciepub.com/ajme/3/3/4 Science and Education PublishingDOI:10.12691/ajme-3-3-4Optimization of Process Parameters of Manual ArcWelding of Mild Steel Using Taguchi MethodA.O. Osayi, E.A.P. Egbe, S.A. Lawal*Department of Mechanical Engineering, School of Engineering and Engineering Technology, Federal University of Technology, PMB65 Minna, Nigeria*Corresponding author: lawalbert2003@yahoo.comReceived May 08, 2015; Revised June 08, 2015; Accepted June 15, 2015Abstract This study was based on design of experiment (DOE) using Taguchi method with four weldingparameters namely; welding current, (ii) welding speed, (iii) root gap and (iv) electrode angle considered forexperimentation. An orthogonal array of L9 experimental design was adopted and ultimate tensile strength wasinvestigated for each experimental run. The tensile test was carried out on extracted welded and unwelded specimensusing universal testing machine (UTM). Microstructures of the welded specimens were carried out and analyzed.Statistical analysis (ANOVA) and signal to noise ratio were used to study the significant effect of input parameterson ultimate tensile strength and optimized conditions for the process performance respectively. The results showedthat experiment number 7 has the highest ultimate tensile strength (UTS) of 487MPa and S/N ratio of 53.74 dB. TheS/N ratio of higher value indicates better characteristic of optimum MMAW process performance. The study showsthat the optimum condition is A3B1C3D2 at welding current 100A, electrode angle of 700, root gap of 3.3 mm and awelding speed of 3.6 mm/s .Keywords: ANOVA, welding speed, current, electrodeCite This Article: A.O. Osayi, E.A.P. Egbe, and S.A. Lawal, “Optimization of Process Parameters of ManualArc Welding of Mild Steel Using Taguchi Method.” American Journal of Mechanical Engineering, vol. 3, no. 3(2015): 93-97. doi: 10.12691/ajme-3-3-4.1. IntroductionWelding process is very critical to the development of anation because it is the hub on which modern industriesrevolve. Messler [1] stated that no secondary process hasbeen and continues to be more important to the survival,comfort and advancement of mankind than welding.According to him, welding has made it possible to buildour world. It is in view of this that many researchers haveemployed various optimization techniques to improvedifferent welding process parameters on both semi and fullautomated welding processes. Although, the semi and fullautomatic welding processes are more productive,experience has shown that due to complexity andeconomic cost of the equipment and their operations, thechoice of manual metal arc welding (MMAW) process isvery popular in developing countries. This is so because ofits several advantages such as low cost and simpleoperation. The MMAW process is portable and it caneasily be used in places where other welding methods arenot possible.Manual metal arc welding is also known as shieldedmetal arc welding (SMAW), or stick welding process. It isone of the oldest and most widely used arc weldingprocesses. The process involves the use of arc current tostrike an arc between the base material and a consumableelectrode rod. The electrode rod is made of a metal that iscompatible with the base material being welded and it iscovered with a flux. The heat generated melts a portion ofthe tip of the electrode, its coating and the base metal justbelow the arc. As the coating on the electrode melts, theflux gives off vapours that serve as a shielding gas andprovide layer of slag, both of which protect the weld fromatmospheric contamination. The slag formed duringwelding is chipped off from the weld after cooling.MMAW process can operate with both direct current (DC)or alternating current (AC) power supply depending oncoating design. The process is portable, versatile,inexpensive equipment and requires little operator training.Also, the electrode produces and regulates its flux, it haslower sensitivity to wind and draft than gas shieldedwelding process and the process is applicable in allpositions. On the hand, the process is slow and timewasting due to frequent changing of electrode andchipping of slag. Also, it is characterized with excessivespatter, arc stability and rough surface of weld bead andprovides limitation deposition rates compared to other arcwelding processes.With the incorporation of automation into the arcwelding process, many production companies adoptedcomplete experimental designs and mathematical modelsto investigate the relevant process parameters to obtainquality weld [2]. Ajay et al., [3] stated that high qualitycan be achieved by optimizing various quality attributes orby selecting an optimal process environment that isefficient enough to fetch the desire requirements for
American Journal of Mechanical Engineeringquality. Taguchi method has been found to be a powerfultool to improve overall process quality by optimizing thewelding process parameters in a way that variation isreduced to the barest minimum. Design of experiment(DOE) techniques had been used to carry out suchoptimization in the last two decades with a view toimproving on the mechanical properties of weld materials.Yoon et al., [4] optimized the parameters of welding7075-T6 aluminum alloy using Taguchi method. Amongother investigators who have also worked on theoptimization of welding variables using Taguchi methodare Kim and Lee [5]. They used the method to suggestoptimal combinations for process factors of hybridwelding methods to optimize the welding parameters ofresistance spot welding process.In this study, the application of Taguchi L9 orthogonalarray for the selection of manual metal arc weldingprocess parameters of welded mild steel plates wasinvestigated. The ultimate tensile strength and themicrostructures analysis were carried out on each samplesand analyzed. Signal-to-noise (S/N) ratio to determine theoptimal parameters that affect the response and ANOVAanalysis to determine the significant effect of the inputvariables on the ultimate tensile strength were bothinvestigated.2. Materials and Methods2.1 MaterialsThe base material used for this study is mild steel (AISIC1020) of 100 x 75 x 5 mm plate. Its chemicalcomposition analyzed by the Defence IndustryCorporation of Nigeria, Kaduna is approximately 0.23% C,940.35% Mn, 0.28% Si, 0.02% S, 0.04% P and 99.08% Fe.Mild steel was considered for this study because of itsavailability in the market and low cost. Mild steelelectrodes of 350 mm long and 3.25 mm diameter (E6010and E6013 steel grade 2, Oelikon) were used for the rootrunning and weld deposits respectively.2.2. Methods2.2.1. Welding ProcessA mild steel plate was cut into 100 75 5 mm (lengthand breadth and thickness) using cut-off machine. Thiswas followed by edge preparation and a single groove buttjoint was selected for the joining process in flat position.The surfaces and the prepared edges of the samples werethoroughly cleaned with wire brush to remove any dirt orunwanted inclusion that could affect the weld. In thisstudy, the welding process was a bit different from thenormal convectional manual welding process as theelectrode (electric arc) was constrained in stationaryposition while the workpiece moved relative to it. Thishelp to maintain relative stable welding speed andimprove the quality of the weld. A 400A capacity manualmetal arc welding machine with direct current (DC)straight polarity was used for the welding operations. Thisis because with DC, it is easier to maintain short arc in thestarting stage of welding operation. The E6010 electrodeswere first applied for the root running. Thereafter, thegrooves were cleaned before the E6013 electrodes wereused for the weld deposits in 2 – pass. Fifty fourworkpieces were used for this experiment that was carriedout in the Department of Mechanical Engineeringworkshop, Federal University of Technology Minna,Nigeria.Figure 1. Welding Rig2.2.2. Welding RigThe welding rig consists of a speed reduction electricmotor (1hp), three different sizes of belts andcorresponding pulleys, a shaft, tray, string, six ballbearings and the stand. The main feature of the rig is thevariable speed of workpiece relative to a stationaryelectrode or electric arc. The rotation of the electric motorwas converted to linear motion through the belt drivesystem and guided string as shown in Figure 1.Input welding parameters selected from the structuralcodes of American Welding Society [6], and manuals ofmetal arc welding system for this study are: weldingcurrent, welding speed, root gap and electrode angle. Eventhough, arc length is one of the critical welding parameters,it cannot be used as welding parameter in manual metalarc welding process. An orthogonal array of L9 wasselected for experimentation as shown in Table 1. Basedon the Taguchi orthogonal array designed, nine (9)experimental runs were conducted and each weldingprocess was repeated three (3) times under the sameconditions. These welding input parameters and theirlevels are shown in Table 2.
95American Journal of Mechanical EngineeringTable 1. An orthogonal array of L9 (34) matrixExperimental trialUTS (σ ) Process 321393321Table 2. Process parameters and their levelsInput parameterWelding current (A)0SymbolLevel 1Level 2Level 3A8090100Electrode angle ((0 )B707580Root gap (mm)C3.03.23.3Welding speed (mm/s)D2.63.64.42.2.3. Determination of Ultimate Tensile StrengthThe ultimate tensile strength of welded samples wasdetermined using universal tensile machine (UTM) (model:TERCOCE MT 3037) in the Department of MechanicalEngineering laboratory, Federal University of Technology,Minna- Nigeria. The tensile test specimens were extractedfrom the welded base metal with hacksaw and prepared tostandard size according to American Welding Society [7]and universal tensile machine manual. The weldreinforcement and backing strip were removed, flushedwith the surface of the specimen by grinding and filingwith a smooth file. The stress- strain curve was used todetermine the force and the ultimate tensile strength (UTS)was evaluated using equations 1 and 2Experimental trialFS1where F is the maximum loaded force, S is the crosssectional area and for rectangular test specimen used inthis experiment2Cross sec tional area ( S ) wtwhere w is the width and t is the thickness2.2.4. Determination of Microstructure of WeldedJointThe micro-examination operation includes: grinding,polishing, etching and viewing. Hand hacksaw was usedto cut test specimens from the welded plates as required.Grinding of each specimen was carried out using handgrinding deck of abrasive papers of different grade.Universal rotary wheels polishing machine of emery sheettype was used to carry out the polishing of the surface ofeach specimen to mirror-like in nature. The polishedsurfaces were etched with a natal (2% HNO3 98%alcohol) regent and thereafter, the specimens were washedin running water and dried. An Optika (N- 400 POL)metallurgical microscope (bench type) was used toexamine the specimens under magnification of x 400. Thelimitation of Optika (N-400 POL) metallurgicalmicroscope is the none availability of micron marker toidentify details in the microstructures.3. Results and DiscussionThe results of ultimate tensile strength as obtainedusing equations 1 and 2 for the experimental runs areshow in Table 3. The values shown are the average ofthree reading recorded for each experimental trial. Thesignal- to- noise ratios for each ultimate tensile strengthare equally included.Table 3. Ultimate Tensile Strength (UTS) and S/N ratio valuesUTS (Mpa)L1L2L3Average value(Mpa)S/N ratio .0448.053.139435.0433.0449.0439.052.85Unwelded sample429.0411.0-420.0-3.1. Analysis of Variance (ANOVA)The effect of each input parameters on the ultimatetensile strength was evaluated using variance analysis(ANOVA). The level of contribution of each of the inputparameter to the strength of the welded point is shown inTable 4. In the analysis of variance in this study, poolingmethod was adopted; this is because pooling is a processof disregarding an individual’s parameter’s contributionand thereafter adjusting the contributions of other processparameters [8]. Pooling is employed when there isindeterminate situation and the effect of parameter in aprocess is insignificant. This is done to obtain new nonzero estimates of sum of square and DOF of variancerespectively. Pooling process increases the percentagecontribution error because the sum of square for theparameter being pooled is usually added to the sum ofsquare error. In this study, the pooling effect is onparameter B (electrode angle) being the least effect on thewelding process.
American Journal of Mechanical EngineeringProcess parameterWelding currentElectrode angleRoot gapWelding speedErrorTotalSymbolACDETable 4. Analysis of Variance (ANOVA) for Ultimate Tensile 00.100.1820.350.010.4381.133.2. Signal – to - noise (S/N) RatioThe choice of the S/N ratio to be used depends on theperformance quality characteristics required. In weldingprocess, the higher the strength of the weld, the better andhence, the signal –to –noise (S/N) ratio of higher the better(HB) was used in this study as expressed in equation 0pooledS1n 1) 10 log ( i 1Nnyi 23where y responses for the given factor level combination,n number of responses in the factor level combinationand yi is the experimental results.Table 5. Main effect of process parametersWelding current AElectrode angle B52.5853.0753.1952.9953.2452.950.660.1214Table 5 depicts the corresponding values of S/N ratiosobtained from the conversion of UTS results. It wasobserved that experiment number 7 has the highest S/Nratio of 53.71dB, which indicates the best performancecharacteristic among the 9 runs of experiments conducted.96Root gap C52.9252.8753.220.353Welding speed D52.8053.2252.990.422It was observed that the welding current has significanteffect on the welding process while the electrode anglehas the least effect. It also indicates that the combinationprocess parameters A3B1C3D2 have the highest ormaximum S/N ratios respectively and therefore signifiesthe optimum condition for the welding process.Figure 2. Microstructure of welded component3.3. Microstructure of Welded JointFigure 2 (a- i) shows the microstructure of the weldingjoint under different welding conditions. Figure 2a showsthe microstructure obtained under the condition ofwelding current (80 A), electrode angle (70o), root gap(3.0 mm) and welding speed (2.6 mm/s). The grains werelarge and showing spheroidal globular of the
97American Journal of Mechanical Engineeringphotomicrograph due to low temperature and short timefor nucleation. Figure 2b shows microstructure obtainedunder the welding condition of welding current (80 A),electrode angle (750), root gap (3.2 mm) and weldingspeed (3.6 mm/s). The micrograph shows deformation thatproduced elongated grains.While Figure 2c shows the microstructure obtainedunder welding condition of welding current (80 A),electrode angle (800), root gap (3.3 mm) and weldingspeed (4.4 mm/s). The micrograph shows a mixture ofpearlite (dark) and ferrite (light). The grains were widelyspaced.In the same vein, Figure 2d show the microstructure ofthe welding condition of welding current (90 A), electrodeangle (700), root gap (3.2 mm) and welding speed (4.4mm/s). The grains were cohesively arranged and fine. AndFigure 2e shows the microstructure for welding conditionof welding current (90 A), electrode angle (750), root gap(3.3 mm) and welding speed (2.6 mm/s). The micrographshows partially grain-refined. Figure 2f shows themicrostructure obtained under the welding condition ofwelding current (90 A), electrode angle (800), root gap(3.0 mm) and welding speed (3.6 mm/s). The grains wereadhesively arranged and fine.Similarly, Figure 2g shows the microstructure forwelding condition of welding current (100 A), electrodeangle (700), (3.3 mm) and welding speed (3.6 mm/s). Themicrograph shows grain- refined, appears tiny anduniform pattern due to fast cooling rate. Figure 2h depictsthe microstructure obtained under the welding conditionof welding current (100 A), electrode angle (750), root gap(3.0 mm) and welding (4.4 mm/s). The grains are finestructurally. And Figure 2i shows the microstructureobtained under welding condition of welding current (100A), electrode angle (800), root gap (3.2 mm) and weldingspeed (2.6 mm/s). The grains were coarse due tooverheating in the weldment.experiment number 7 has the highest ultimate tensilestrength (UTS) and S/N ratio of 487 MPa and 53.74 dBrespectively. The study indicates that the optimumcondition is A3B1C3D2 which coincide with experimentnumber 7 in the orthogonal array. It was also observedthat the failures of all the test specimens extracted fromthe welded samples did not occur at the weldment pointwhich signifies a quality and strong weld joint. Themicrostructures show the various effects of the weldingparameters on the weld joint.Moreover, it was noted from results of ANOVA that thewelding current, root gap and welding speed aresignificant parameters in the welding process while theelectrode angle has least significant. Computation of theprojected optimum performance of the study using S/Nratio (Yopt) is 53.74 dB which is the same value withexperiment number 7 and it serve as confirmation test. Aconfirmation test would have been conducted if theoptimum condition was not among the experimental runs.Results from this study, indicated that Taguchi methodcan actually be used to optimize or improve the quality ofMMAW process.4. Conclusions[6]This study employed Taguchi method to optimizeprocess parameters of manual metal arc welding (MMAW)process for mild steel products. From the tensile testcarried out on welded samples it was observed that[7]References[1][2][3][4][5][8]Messler, R.W., Principles of welding processes. Wiley – VCHVerlag GmbH and Co. KGaA, Weinheim. 2004.Ill-Soo, K., Joon-Sik, S., Sang-Heon, L., Prasad K.D.V., OptimalDesign of Neural Networks for Control in Robotic arc Welding.Robotic and Computer-Integrated Manufacturing, 20, 57-63, 2004.Ajay, Saurav, Swapan, Gautan, Application of Vikor BasedTaguchi Method for Multi-Response Optimization. A Case Studyin Submerged Arc Welding (SAW), Proceedings of InternationalConference on Mechanical Engineering (ICME), 2009.Yoon, H., Byeong Hyeon, M., Chil Soon, L., Hyoung, K.D.Kyoun, K.Y. and Jo, P.W., Strength Charateristics on ResistanceSpot Welding of Aluminium Alloy Sheets by Taguchi Method,International Journal of Modern Physics B, 4, 297-302, 2006.Kim, H.R., Lee, K.Y., Application of Taguchi Method toDetermine Hybrid Welding Condions of Aliminium Alloy. Journalof International Research, 68, 296-300, 2009.American Welding Society, 550 N.W. LeJeune Road, Miami,FL33126, 1997.American Welding Society, 550 N.W. LeJeune Road, Miami,FL331, 2007.Roy, R.K., A Primer on Taguchi Method. Reinhold InternationalCompany Ltd, 11 New Lane, London EC4P4EE, England. 1990.
Input welding parameters selected from the structural codes of American Welding Society [6], and manuals of metal arc welding system for this study are: welding current, welding speed, root gap and electrode angle. Even though, arc length is one of the critical welding parameters, it cannot be u
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