OPTIMIZATION OF CNC TURNING PROCESS · PDF fileOPTIMIZATION OF CNC TURNING PROCESS PARAMETERS FOR PREDICTION OF ... and depth of cut using Analysis of Variance (ANOVA). ... characteristics

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Int. J. Mech. Eng. & Rob. Res. 2014 D Kanakaraja et al., 2014

OPTIMIZATION OF CNC TURNING PROCESSPARAMETERS FOR PREDICTION OF SURFACE

ROUGHNESS THROUGH TAGUCHI’S PARAMETRICDESIGN APPROACH

D Kanakaraja1*, D Anjan Kumar Reddy1, M Adinarayana1, and L Vamsi Krishna Reddy2

*Corresponding Author: D Kanakaraja,[email protected]

Metal cutting operations still represent the largest class of manufacturing operations whereturning is the most commonly employed material removal process and there are lots of studiesto investigate this complex process in both academic and industrial world. Predicting the bettercutting condition during turning is of great importance as it helps in getting the Surfaces qualitybefore machining starts. The major indication of surfaces quality on machined parts is surfaceroughness. Again, optimization of cutting parameters is one of the most important elements inany process planning of metal parts as economy of machining operation plays a key role ingaining competitive advantage. This paper presents an experimental study of main cuttingcondition in turning of SAE 8822 Alloy steel work and finding the influence of turning parametersduring turning. For experimentation over this proposed work, a CNC turning centre would beengaged for machining the SAE 8822 Alloy steel work piece material with carbide cutting toolinsert with a set of values for the given parameters. The experimentation is carried out consideringthree machining parameters: cutting speed, feed rate and depth of cut as independent variables.Design of Experiment (DOE) with Taguchi L9 Orthogonal Array (OA) is used for finding theoptimized solution. An attempt has been made to find the influence of turning parameters speed,feed, and depth of cut using Analysis of Variance (ANOVA). Finally, the ranges for best cuttingconditions are proposed for serial industrial production.

Keywords: Optimisation, CNC turning, Surface roughness, Taguchi orthogonal array, ANOVA

INTRODUCTIONThe selection of proper combination ofmachining parameters yields the desired

ISSN 2278 – 0149 www.ijmerr.comVol. 3, No. 4, October 2014

© 2014 IJMERR. All Rights Reserved

Int. J. Mech. Eng. & Rob. Res. 2014

1 Department of Mechanical Engg., Sir Vishveshwaraiah Institute of Science and Technology, Madanapalli, Andhra Pradesh, India.2 Department of Mechanical Engg., Sri Srinivasa Ramanujan Institute of Technology, Rotarypuram, Anantapuramu, Andhra Pradesh,

India.

surface finish, the proper combination ofmachining parameters is an important task asit determines the optimal values of surface

Research Paper

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roughness. The new methodologies andstandards are emerging day by day in reducingthe lead time in the fabrication of a new productwith good precision and high reliability.Advances in CNC/NC machining and highspeed machining technologies have boostedthe productivity of machining process.

The study of most important variableseffecting the quality characteristics and a planfor conducting such experiments is calledDesign of Experiments (DOE). In the presentwork a set of experiments are conducted onthe work piece SAE 8822 Alloy steel withcarbide cutting tool insert to evaluate the effectof machining parameters such as speed, feed,and depth of cut on surface roughness. Taguchiapproach is used to obtain the optimal settingsof these process parameters, and ANOVA isused to analyze the influence of the cuttingparameters during machining.

The general specification of coatedcemented carbide insert is CNMA 120408KBM10B. Cemented carbides are veryeffective in machining cast irons and certainabrasive non-ferrous alloys, but as such aregood for Cutting steels because wear cratersare developed on the face of the tool.

PLAN OF INVESTIGATIONThis investigation was planned to be carriedout in following steps

• Identifying the process parameters.

• Selection of the useful limits of the cuttingparameters, namely speed (v), feed (f), anddepth of cut (doc).

• Developing the design matrix.

• Conducting the experiment as per Taguchidesign matrix.

• Testing the significance of regression co-efficient and arriving at the final form of themathematical models.

• Presenting the main effects and thesignificant interactions between differentparameters in graphical forms.

• Analysis of results and conclusions.

METHODOLOGYIn this work, experimental results were usedfor Optimization of input machining parametersspeed, feed, and depth of cut using TaguchiTechnique for the response SurfaceRoughness. ANOVA is also used for Predictingthe influence of various parameters on Ra.

Taguchi MethodCompetitive crisis in manufacturing during the1970s and 1980s that gave rise to the modernquality movement, leading to the introductionof Taguchi methods to the US in the 1980s.Taguchi’s method is a system of designengineering to increase quality. TaguchiMethods refers to a collection of principleswhich make up the framework of a continuallyevolving approach to quality. Taguchi Methodsof Quality Engineering design is built aroundthree integral elements, the loss function,signal-to-noise ratio, and orthogonal arrays,which are each closely related to the definitionof quality. Taguchi method is a scientificallydisciplined mechanism for evaluating andimplementing improvements in products,processes, materials, equipment, andfacilities. These improvements are aimed atimproving the desired characteristics andsimultaneously reducing the number of defectsby studying the key variables controlling theprocess and optimizing the procedures or

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design to yield the best results. Taguchiproposed a standard procedure for applyinghis method for optimizing any process.

The objective of the robust design is to findthe controllable process parameter settings forwhich noise or variation has a minimal effecton the product’s or process’s functionalcharacteristics. It is to be noted that the aim isnot to find the parameter settings for theuncontrollable noise variables, but thecontrollable design variables. To attain thisobjective, the control parameters, also knownas inner array variables, are systematicallyvaried as stipulated by the inner orthogonalarray. For each experiment of the inner array,a series of new experiments are conductedby varying the level settings of theuncontrollable noise variables. The levelcombinations of noise variables are doneusing the outer orthogonal array.

The influence of noise on the performancecharacteristics can be found using the ratio.Where S is the standard deviation of theperformance parameters for each inner arrayexperiment and N is the total number ofexperiment in the outer orthogonal array. Thisratio indicates the functional variation due tonoise. Using this result, it is possible to predictwhich control parameter settings will make theprocess insensitive to noise. Taguchi methodfocuses on Robust Design through use of

• Signal-to-noise ratio

• Orthogonal arrays

Orthogonal ArraysAn orthogonal array is a type of experimentwhere the columns for the independentvariables are “orthogonal” to one another.Orthogonal arrays are employed to study the

effect of several control factors. Orthogonalarrays are used to investigate quality.Orthogonal arrays are not unique to Taguchi.They were discovered considerably earlier(Bendell, 1998). However Taguchi hassimplified their use by providing tabulated setsof standard orthogonal arrays andcorresponding linear graphs to fit specificprojects (Taguchi and Kenishi, 1987; and ASI,1989). A L9 Orthogonal array is shown in theTable 2

Table 2: Orthogonal Array (OA)

1. 1 1 1

2. 1 2 2

3. 1 3 3

4. 2 1 2

5. 2 2 3

6. 2 3 1

7. 3 1 3

8. 3 2 1

9. 3 3 2

S. No. Speed(rpm)

Feed(mm/rev)

Depth of Cut(mm)

Table 1: Process Parameters and TheirLevels

1 2557 0.06 0.6

2 2041 0.11 0.9

3 1693 1.27 1.2

Level Spindle Speed(s) (rpm)

Feed Rate (f)(mm/rev)

Depth of Cut(doc) (mm)

Selection of Orthogonal ArrayTo select an appropriate orthogonal array forthe experiments, the total degrees of freedomneed to be computed. The degrees of freedomare defined as the number of comparisonsbetween design parameters that need to bemade to determine which level is better and

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Table 3: Orthogonal Array with ProcessParameters

1. 2557 0.06 0.6

2. 2557 0.11 0.9

3. 2557 1.27 1.2

4. 2041 0.06 0.9

5. 2041 0.11 1.2

6. 2041 1.27 0.6

7. 1693 0.06 1.2

8. 1693 0.11 0.6

9. 1693 1.27 0.9

S. No. Speed s(rpm)

Feedf (mm/rev)

Depth of Cutdoc (mm)

specifically how much better it is. For example,a three-level design parameter counts for twodegrees of freedom. The degrees of freedomassociated with the interaction between twodesign parameters are given by the productof the degrees of freedom for the two designparameters.

Signal-to-Noise RatioThe signal-to-noise concept is closely relatedto the robustness of a product design. ARobust Design or product delivers strong„signal . It performs its expected function andcan cope with variations (“noise”), both internaland external. In signal-to-Noise Ratio, signalrepresents the desirable value and noiserepresents the undesirable value.

There are 3 Signal-to-Noise ratios ofcommon interest for optimization of StaticProblems.

1. Smaller-the-Better S/N = –10 log

r

i iyr 1

21

2. Larger-The-Better S/N = –10 log

r

iiyr 1 2

11

3. Nominal-The-Best S/N = –10 log

2

2

Analysis of Variance (ANOVA)The purpose of the analysis of variance(ANOVA) is to investigate which designparameters significantly affect the qualitycharacteristic. This is to accomplished byseparating the total variability of the S/N ratios,which is measured by the sum of the squareddeviations from the total mean S/N ratio, intocontributions by each of the design parametersand the error. Various terms in ANOVA are

• Sum of squares (SS)

• Mean Squares (MS)

• Percentage contribution

EXPERIMENTAL WORKThe work piece material selected forinvestigation is the SAE 8822. The chemicaland mechanical properties of the work pieceare shown in Tables 4 and 5 respectively.

The cutting experiments were carried outon Work piece by CNC Lathe under differentcutting conditions are shown in Table 3.Experimental data of SAE 8822 Steel whichwas used in experiments as shown in the Table

Figure 1: Experimental Set Up

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Element C Si Mn P S Cr Ni Mo

Content (%) 0.25 0.30 0.85 0.035 0.04 0.4 0.5 0.35

Table 4: Chemical Composition of SAE 8822 Alloy Steel

Metric 7.79 g/cm3 207 Gpa 0.30 245

Table 5: Mechanical Properties of SAE8822 Alloy Steel

Property Density ElasticModulus

PoissonsRatio

Hardness(BHN)

1. 2557 0.06 0.6 0.53

2. 2557 0.11 0.9 1.71

3. 2557 1.27 1.2 2.14

4. 2041 0.06 0.9 0.44

5. 2041 0.11 1.2 1.32

6. 2041 1.27 0.6 2.16

7. 1693 0.06 1.2 0.02

8. 1693 0.11 0.6 1.33

9. 1693 1.27 0.9 2.21

Table 6: Experimental Data for 3Parameters on Ra, for Carbide Tool

S. No. Speed S(rpm)

Feed, f(mm/rev)

Depthof Cut(mm)

SurfaceRoughness

Ra (m)

3. Tool material for this study was coatedcemented carbide insert. Taguchi parameteroptimization method was used to evaluate thebest possible combination for minimumsurface roughness during turning operation.

RESULTS AND DISCUSSIONIn the Taguchi method the results of theexperiments are analyzed to achieve one ormore of the following three objectives:

• To establish the best or the optimumcondition for a product or a process.

• To estimate the contribution of individualfactors.

• To estimate the response under theoptimum conditions.

Studying the main effects of each of thefactors identifies the optimum condition(Figures 2 and 3). The process involves minorarithmetic manipulation of the numerical resultand usually can be done with the help of asimple calculator. The main effects indicate thegeneral trend of the influence of the factors.Knowing the characteristic, i.e., whether ahigher or lower value produces the preferredresult, the levels of the factors, which areexpected to produce the best results, can bepredicted.

The knowledge of the contribution ofindividual factors is the key to deciding thenature of the control to be established on aproduction process. The analysis of variance(ANOVA) is the statistical treatment mostcommonly applied to the results of theexperiment to determine the percentcontribution of each factor. Study of theANOVA table for a given analysis helps to

Figure 2: Plots of Main Effects for Meansfor Surface Roughness (Ra)

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Figure 3: S/N Ratio for SurfaceRoughness (Ra)

Table 7: Response Table for Signalto Noise Ratios for Carbide Tool [Ra]

1 –1.553 5.533 –2.177

2 –1.87 –4.422 –3.433

3 –2.380 –6.588 –2.001

Delta (maxmin) 1.296 11.207 0.511

Rank 2 1 3

Level Speed(S) Feed (f) Depth of

Cut (d)

Table 8: Response Table for Meansfor Carbide Tool [Ra]

1 1.55232 0.6003 1.4015

2 1.4904 1.5051 1.9211

3 1.6499 2.3999 1.0241

Delta (maxmin) 0.2466 1.9021 0.0835

Rank 2 1 3

Level Speed(S) Feed (f) Depth of

Cut (d)

determine which of the factors need controland which do not. In this study, an L9Orthogonal array with was used. Responsetables for Noise ratios and means are shownin Tables 7 and 8.

CONCLUSIONThe results obtained in this study lead toconclusions for turning of EN 24 afterconducting the experiments and analyzing theresulting data.

• From the results obtained by experiment,the influence of surface roughness (Ra) isdepend on feed and next is followed byspeed and depth of cut.

• Taguchi method is applied for optimizationof cutting parameters.

FUTURE SCOPE OF THEWORK• The work can be extended for Multi objective

optimization like Material Removal Rate,Power Consumption, Tool life, Productioncost and Production time.

• The use of ANN, Genetic algorithms, whichhave the ability to adapt to the problembeing solved and are suggested by theevolutionary process of nature selection.

• The effect of tool Vibration, Work piecehardness, Cutting fluid, Nose radius, Toolmaterial and Acoustic emission can beconsidered as cutting parameters as theyhave great inf luence on Surfaceroughness.

REFERENCES1. Ajeet Kumar Rai, Richa Dubey, Shalini

Yadav and Vivek Sachan Turning (2013),“Parameters Optimization for SurfaceRoughness by Taguchi Method”,International Journal of MechanicalEngineering and Technology (IJMET),Vol. 4, No. 3, pp. 203-211.

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2. Ballal Yuvaraj P, Inamdar K H and PatilP V (2012), “Application of TaguchiMethod for Design of Experiments inTurning Gray Cast Iron”, IJERA, Vol. 2,No. 3, pp. 1391-1397.

3. Childs T, Maekawa K, Obikawa T andYamane Y (2000), “Metal Cutting Theoryand Application”, New York, USA.

4. Erasan Alsan, NecipCamscuBurakBingoren, “Design of Optimization ofCutting Parameters When TurningHardened AISI 4140 Steel (63 HRC) withAl2O3+TiCN Mixed Ceramic Tool Materialand Design”, Date Received 21.07.2005and Date Accepted 06.01.2006.

5. Javidi A, Riegger U and Eichlseder W(2008), “The Effect of Machining on theSurface Integrity and Fatigue Life”,International Journal of Fatigue, Vol. 30,pp. 2050-2055.

6. Mahendra Korat, Neeraj Agarwal,“Optimization of Different MachiningParameters of En 24 Alloy Steel in CNCTurning by Use of Taguchi Method”,International Journal of Engineering

Research and Application, Vol. 2, ISSN:2248-9622.

7. Montgomentry D C (1997), Design andAnalysis of Experiments, 4th Edition,Wiley, New York.

8. Raghunandan B V, Bhandarkar S L andPankaj Kr. Singh (2013), “AnExperimental Mathematical Modelling ofSurface Roughness in Turning Opertionof En19 with Carbide Tool”, InternationalJournal of Mechanical Engineering andResearch, Vol. 3, No. 5, pp. 495-502.

9. Shirpurkar P P, Kamble P D, Bobde S Rand Patil V V (2014), “Optimization ofCNC Turning Process Parameters forPrediction of Surface Roughness byTaguchi Orthogonal Array”, InternationalJournal of Engineering Research &Technology (IJERT), Vol. 3, No. 1.

10. Suleyman Neseli, Suleyman Yald Z andErol Turkes (2011), “Optimization of ToolGeometry Parameters for TurningOperations Based on the ResponseSurface Methodology”, Measurement,Vol. 44, pp. 580-587.

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OPTIMIZATION OF CNC TURNING PROCESS · PDF fileOPTIMIZATION OF CNC TURNING PROCESS PARAMETERS FOR PREDICTION OF ... and depth of cut using Analysis of Variance (ANOVA). ... characteristics