Mechanics of milling 48-2-2 gamma titanium aluminide

Mechanics

of

milling

48-2-2

gamma

titanium

aluminide

Abbas

Hussain

a

,

S.

Ehsan

Layegh

c

,

Ismail

Lazoglu

a,

*

,

Pedro-J.

Arrazola

b

,

Xabier

Lazcano

b

,

Patxi-X.

Aristimuño

b

,

Omer

Subasi

a

,

I.

Enes

Yigit

a

,

Çaglar

Öztürk

a

,

Çaglar

Yava

ş

d

a_{KocUniversity,ManufacturingandAutomationResearchCenter,Istanbul34450,Turkey} b_{MondragonUniversity,FacultyofEngineering,Mondragon20500,Spain}

c

MEFUniversity,Istanbul34396,Turkey

d

KarcanCuttingTools,Eskisehir26110,Turkey

ARTICLE INFO

Articlehistory:

Availableonline23June2020

Keywords: Milling

Gammatitaniumaluminide Coating

ABSTRACT

Accurateandfastpredictionofcuttingforcesisimportantinhigh-performancecuttingintheaerospace industry.Gammatitaniumaluminide(g-TiAl)isamaterialofchoiceforaerospaceandautomotive applicationsduetoitssuperiorthermo-mechanicalproperties.Nevertheless,itisadifficulttomachine material.ThisarticlepresentsthepredictionofcuttingforcesforTi-48Al-2Cr-2Nb(48-2-2)g-TiAlin millingprocessusingorthogonaltoobliquetransformationtechnique.Thenoveltyofthispaperliesin reportingtheorthogonaldatabaseof48-2-2g-TiAl.Fundamentalcuttingparameterssuchasshearstress, frictionangleandshearanglearecalculatedbasedonexperimentalmeasurements.Frictioncoefficients areidentifiedfortwodifferentcoatingconditionswhichareAlTiN,andAlCrNoncarbidetools.Predicted resultsarevalidatedwiththeexperimentalcuttingforcesduringend millingandball-endmilling operationsfordifferentcuttingconditions.Thesimulatedresultsshowedgoodagreementwiththe experimentalresults,whichconfirmsthevalidityoftheforcemodel.

©2020CIRP.

Introduction

Theuseofadvancedlightweightstructuralmaterialsisakey

pointforaerospaceandautomotiveapplicationstoimproveengine

performancesandefficiency,aswellastosatisfytheincreasingly

restrictiveenvironmentalregulations,aimedatreachingadecisive

lesseningofCO2emissions[1].Inthiscontext,intermetallic

aero-engine materials, such as

g

-TiAl, have been identified as

strategically critical materials to be used in both non-rotating

androtatingcomponents,e.g.blademanufacturing.Theyprovidea

remarkable strength-to-weight ratio, approximately half the

density of nickel-based superalloys, high stiffness, high elastic

modulus,strengthretentionatelevatedtemperatures,oxidation

resistance,andgoodcreepproperties[2,3].

However, the attractive mechanical and thermal properties,

becomea drawbackwhendealing withmachining,as itoccurs

with many other materials. As it has been shown in several

conventional machiningpublications, machinabilityof

g

-TiAl is

poorbecauseofitslowductilitycombinedwithhighhardnessand

brittleness at room temperature, low thermal expansion, low

fracture toughness and chemical reactivity with many tool

materials[4,5].Inconsequence,themachiningcostishigh,which

canrestrictthewidespreaduseofthesematerialsintheindustry.

Severalresearchstudieshavebeencarriedoutinthelastyears

dealingwiththemachinabilitypropertiesof

g

-TiAl.Mantleetal.

[6]investigatedthesurfaceintegrityof

g

-TiAl,Ti

–45Al–2Nb–2Mn-0.8vol.% TiB2XD by performing high-speed milling operations.

Experimentswerecarriedoutusingcoatedtungstencarbide

ball-endmillinupmillinganddownmillingdirections.Priaroneetal.

[7] studied the effect of cutting tool angles and cutting-edge

preparation in machinability of Ti-48Al-2Cr-2Nb EBM sintered

g

-TiAl.Allthemillingoperationswereperformedindownmilling

modewithcoatedanduncoatedcarbideendmills.Beranoagirre

etal.[8]providedthespecificcuttingforcecoefficientsobtained

fromthemechanisticcalibrationmethodforthreedifferenttypes

of

g

-TiAlalloys:theMoCuSitypeiningotandextrudedform,and

theTNBtypeiningotform.Theyperformedmillingexperiments

and studied thetool wear for differentcutting conditions and

foundthatthecuttingvelocityisthedeterminingfactorintoollife.

Settinerietal.[9]performedturningandmillingexperimentson

three different

g

-TiAl alloys:Ti–48Al–2Cr–2Nb, Ti–43.5Al–4Nb–

1Mo–0.1B,andTi–45Al–2Nb–2Mn-0.8vol.%TiB2XD,focusingon

machinability and material characterization. The experimental

results wereextremely dissimilar due to the differentalloying

elements which affected the mechanical and thermal material

properties.Hoodetal.[10]investigatedthesurfaceintegrityby

* Correspondingauthor.

E-mailaddress:ilazoglu@ku.edu.tr(I.Lazoglu).

https://doi.org/10.1016/j.cirpj.2020.05.001

1755-5817/©2020CIRP.

ContentslistsavailableatScienceDirect

CIRP

Journal

of

Manufacturing

Science

and

Technology

performingslotmillingonTi–45Al–2Nb–2Mn-0.8vol.%,TiB2using

AlTiNcoatedWCballnoseendmills.

Although machining of

g

-TiAl alloys has been previously

researchedintheliterature,nostudieshavebeencarriedoutto

develop an orthogonal cutting database for the prediction of

cuttingforcesfor

g

-TiAlinobliqueand3Dprocessessuchasflat

andball-endmilling.Thecreationofsuchadatabaseiscrucialfor

accurateandfastpredictionsofcuttingforcesemployedin

high-performancemachiningofaeronauticcomponentssuchasblades.

Thisimpliesthatindustrialparameterssuchassurfaceroughness,

the possibility of chatter or dimensional tolerances can be

accuratelypredicted.

Afundamentalcuttingparameter databaseindependentofcutter

geometryisrequiredtocalculatethecuttingforcesinamachining

operation.Thisdatabaseisthenusedtocalculatethespecificcutting

coefficients by applying an analytical orthogonal to oblique

transformation model [11]. In addition, this model allows the

predictionofcuttingforcesofcomplexoperationssuchasball-end

milling[12].Thisapproachcanalsobeimplementedtoinvestigate

theeffectsofcuttingparametersonmachiningperformance[13].

High-performancecoatingshavebecomeasuccessfulstandard

forincreasingtheefficiencyofmachiningtoolsintheindustryover

thelastdecade[14,15].Thecurrentstudyfocusesonestablishing

anorthogonalcuttingdatabasefor48-2-2

g

-TiAlfordifferenttool

coatings;AlTiNandAlCrNcoatings.Forcuttingforcepredictions,

an analytical force model and the orthogonal to oblique

transformationmethodisemployed.Themodelisthenvalidated

forendmillingandball-endmillingoperationsfordifferentcutting

conditions,demonstratinggoodagreementbetweenexperimental

andmodeledresults.

Mechanicsofmillingoperation

Millingoperationisoneofthemostfundamentalmetalcutting

operations that is extensively used in the manufacturing of

complex components in high-tech fields such as aerospace,

automotiveand biomedical industries. Unlike turning,which is

acontinuouscuttingoperation,millingisaninterrupted

machin-ing operation. During milling operation, the cutting edges

repeatedly enter and exit the engagement domain. Therefore,

the cutting forces are harmonic and the simulation of cutting

forcesismorecomplicated.Thegeometryofthemillingtooland

themechanicsoftheprocessareillustratedinFig.1(a).

Elemental cutting forces in end milling operation can be

analyticallymodeledusingEq.(1).InthissetofequationsdFt,dFr

anddFaarethedifferentialcuttingforcesintangential,radialand

axialdirections, respectively.Moreover,hð

f

Þand dz denotethe

uncutchipthicknessandelementallengthofthecuttingedgein

the axial direction. Ktc;Krc;Kac;Kte;Kre and Kae are the specific

cuttingandedgecoefficientsthatareassociatedwiththecutting

andploughingphenomenainthemetalcuttingprocess:

dFt¼½Ktchð

f

ÞþKtedz; dFr¼½Krchð

f

ÞþKtedz; dFa¼½Kachð

f

ÞþKaedz; 9 = ; ð1Þ

Theaccuracyoftheanalyticalmodelishighlydependentupon

theaccuratepredictionofthecuttingforcecoefficientsandedge

coefficients. Different approaches have been suggested in the

literaturetopredictthecuttingcoefficients[16–20].Theadvantage

ofusingorthogonaltoobliquetransformationtechniqueoverother

methodsisthatthecuttingcoefficientscanbepredictedbeforethe

manufacturingofthetool.Thismethodisindependentofcutter

geometryandcanbeusedtosimulatethecuttingforcesforany

metalcuttingprocessalike.Orthogonaltoobliquetransformation

techniqueisbasedonthemeasurementofchipthicknessesandthe

cuttingforcesinthetangentialandfeeddirectionsinanorthogonal

turning test. The measurements are used to calculate the

fundamental cutting parameters, including shear stress, shear

angleandfrictionangle.Transformationoftheseparametersare

then utilized to model oblique cutting processes such as the

milling operation. In this paper, using the orthogonal cutting

forces,thecuttingforcecoefficientsandedgecoefficientsinEq.(1)

are estimated [21]. The geometry of the orthogonal cutting is

illustratedinFig.1(b).Thefundamentalparametersfororthogonal

toobliquetransformationcanbepredictedfromEqs.(2)_–(6):

b

a¼

a

rþtan1 Ffc Ftc ð2Þ

m

¼tanð

b

aÞ ð3Þ

f

c¼

p

4¼ ð

b

a

a

rÞ 2 ð4Þ

t

s¼ Fcosð

f

cþ

b

a

a

rÞsin

f

c bh ð5Þ rc¼ tan_ð

f

cÞ

cosð

a

rÞðtanð

a

rÞtanð

f

cÞþ1Þ ð6Þ

where

b

_a;

a

r;Ffc;Ftc;

m

;

f

c;

t

s;F;b;handrcarefrictionangle,rake

angle,averagefeedcuttingforce,averagetangentialcuttingforce,

the coefficient of friction, shear angle, shear stress, average

resultantforce, thewidthofcut,uncutchipthickness,and chip

thicknessratioinorthogonalturning,respectively.Duetothelow

machinabilityof

g

-TiAl,theproducedchipsduringthemachining

processareexpectedtobediscontinuous,makingthedeformed

chip thickness measurement and empirical calculation of chip

ratio challenging. Totackle this problem, the minimum energy

principle is employed to estimate the shear angle as given in

Eq.(4).Thismodelassumesthattheshearstressontheshearplane

isequivalenttotheyieldshearstressofthematerialandthatthe

shearplaneisthin[22].

Cutter-workpieceengagementmodelforball-endmilling

Theball-endmillingprocessiswidelyusedinthemachiningof

freeformsurfacesespeciallyintheautomobile,aerospace,anddie

andmoldindustries.Owingtothegeometryoftheball-endmilling

tool, the engagement area does not remain constant and the

completecutting-edgelengthisnotincontactwiththeworkpiece

duringthefreeformsurfacemachining.Inthisstudy,thecutting

forcesforfreeformball-endmillingarepredictedbyemployinga

solid modeler-based engagement model to predict the contact

region between the tool and the workpiece. First, the contact

surfacebetweenthetoolandtheworkpieceiscalculatedateach

cutter location, then the swept volume of the cutting tool is

calculatedfromthecutterlocation(CL)file.Theentranceandexit

anglesofeachdiscretecuttingdiskarecalculatedaftersubtracting

thesweptvolumefromablankworkpiece.Theseanglesareusedas

an input for the force model. A detailed explanation of the

employedengagementmodelisprovidedin[23].Asamplecontact

regionforagivencutterlocationonafreeformmillingsurfaceis

showninFig.2.

Experimentalsetup

The experimental stage of this work consisted of both

orthogonal turning and milling of 48-2-2

g

-TiAl, a difficult to

cutmaterial.Theobtainedas-castworkpiecespecimenisreported

Fig.2.(a)CADmodelofthefreeformsurface;(b)CAMsimulationandtool-workpiececontactregion.

Fig.3.(a)Orthogonalturningsetupand(b)millingtestsetupandfor48-2-2g-TiAl machining(DAQ:dataacquisition).

tohave242HRCwith326MPayieldstrength,422MPaultimate

tensilestrengthand%1.7elasticstrainat23,and384MPayield

strength,474MPaultimatetensilestrengthand5.1%elasticstrain

at 650 [26,27]. Orthogonal turning tests were performed to

establishtheorthogonaldatabase,whereasthemillingtestswere

conductedtovalidatethepredictedcuttingforcesobtainedfrom

thedevelopeddatabase.

Orthogonalturningsetup

Orthogonal cuttingtests wereperformed ona MazakQuick

TurnNexus150turningcenterasshowninFig.3(a).Agrooved

48-2-2

g

-TiAlworkpiecewith55mmdiameterand2mmwidthofcut

wasusedduringtests.Theinclinationanglewassettozerodegrees

tohavean orthogonalcuttingcondition.Allexperimental tests

wereperformedfor40m/mincuttingvelocityand0.06,0.08and

0.100mm/revfeedrates.Cuttingoperationswereconductedwitha

4 rake angle and tungsten carbide inserts with two different

coatings: AlCrN and AlTiN coatings. With scanning electron

microscopemeasurements,theedgeradiioftheturninginserts

wereidentifiedas15

m

mfortheAlCrNcoatedtooland16

m

mfor

theAlTiNcoatedtool.Nocoolantwasusedduringthemachining

andcuttingforcesweremeasuredusingKistler9257Btabletype

dynamometer.

Millingsetup

A set of experimental tests consisting of flat and ball-end

milling wereperformed ona 5-axis MoriSeikiNMV5000DCG

machining center as shown in Fig. 3(b). Once again, all the

milling tests were conducted at dry conditions and a Kistler

9257B table type dynamometer was utilized for cutting force

datacollection.

Flatendmillingtestswereconductedwitha36.5_helixangle,

8 rakeangle,12mmdiameter,fourflutedtungstencarbideend

mills having two differentcoating conditions:AlCrNand AlTiN

coating.Thethicknessesofthecoatingsweremeasuredusinga

scanningelectronmicroscope(SEM)showninFig.4.Cuttingforce

datawasacquiredduringdownmillingoperationforthetoolpath

showninFig.5.ThecuttingconditionsaretabulatedinTable1.

Theestimatedcuttingforcesforball-endmillingwerevalidated

by performing down end milling and freeform surface milling

usingAlCrNcoated,fourfluted,tungstencarbideball-endmillwith

30 nominalhelix angle, 8mm nominal diameter, and 5 rake

angle.ThecuttingconditionsaretabulatedinTables2and3.The

cuttingtoolsusedinthestudyareshowninFig.6

Fig.5. Toolpathforflatendmilling.

Table1

Flatendmillingcuttingconditionsfor48-2-2g-TiAl. Cuttingvelocity [m/min] Depthofcut [mm] Widthofcut [mm] Feedrate [mm/tooth] 15 2 0.5 0.04,0.05,0.07,0.08 Table2

Ball-endmillingcuttingconditionsfor48-2-2g-TiAlindownendmilling. Cuttingvelocity [m/min] Depthofcut [mm] Widthofcut [mm] Feedrate [mm/tooth] 48 3 0.5 0.04,0.06,0.08 Table3

Ball-endmillingcuttingconditionsfor48-2-2g-TiAlinfreeformmilling. Cuttingvelocity [m/min] Stepover [mm] Feedrate [mm/tooth] 40 1 0.06

Resultsanddiscussion

Orthogonalcuttingof48-2-2

g

-TiAl

The measured tangential and feed forces from orthogonal

turningfordifferentfeedratesareshowninFig.7.Thesecutting

forceswereusedtocalculatethefundamentalcuttingparameters

suchasshearstress,shearangle,frictionangleandchipratio.The

calculatedorthogonalcuttingparametersfordifferentcoatingsare

tabulatedinTable4forthe4rakeangleinsert.Resultsshowed

thattheAlCrNcoatinghasasmallershearangleascomparedtothe

AlTiNcoating. In the cuttingprocess, thechip thickness,shear

angleand shear planeareinterrelatedtoeach other.A smaller

shearangleisassociatedwithalongershearplaneandarelatively

large chip thickness. On the other hand, a large shear angle

indicates a small shear plane and during the cutting process,

producedchipsarerelativelythinner[24].Theseresultinlessforce

needed to shear off the chips, implying that a lower friction

coefficientdictatestheprocess.

Thefrictioncoefficientplaysanimportantroleinthetoollife

and workpieceintegrity [25]. The friction coefficient identified

fromtheorthogonalturningshowedthattheAlCrNcoatinghad

thehighestfrictioncoefficientascomparedtotheAlTiNcoating.

Nosignificantchangeinshearstressisobservedbychangingthe

coatings.

Flatendmillingof48-2-2

g

-TiAl

Thecuttingcoefficientsformillingoperationweredetermined

fromorthogonaltoobliquetransformationtechnique,and

employ-ingtheanalyticalmodelshowninEq.(1)thecuttingforceswere

simulated.Thecalculatededgecuttingcoefficientsfrom

orthogo-nalforcedataareshowninTable4.Theestimatedandmeasured

cuttingforcescomponentforflatendmillingfordifferentcoatings

andfeedratesarecomparedinFigs.8and9.Itcanbeinferredfrom

Fig.8thatthesuggestedforcemodelisabletopredictthecutting

forceswithina20%errorbandforAlTiNcoatedtools.However,

while therecorded tangentialforces werefoundtobein close

agreementwiththeforceestimationmodelfortheAlCrNcoated

tool,thereisamismatchfortheradialforcecomparison.This

sub-Fig.7.Cuttingforcesmeasuredduringorthogonalturningof48-2-2g-TiAlfor4

rakeangleanddifferentcoatings.

Fig.8.MeasuredandestimatedcuttingforcesfortheAlTiNcoatedtoolforflatenddown-milling:Cuttingforcesin(a)tangentialand(b)radialdirectionswithafeedrateof 64mm/min;cuttingforcesin(c)tangentialand(d)radialdirectionswithafeedrateof88mm/min.

Table4

Orthogonaltoobliquedatabasefor48-2-2g-TiAl.

Parameters AlTiN AlCrN

Chipratio(rc) 0.540.01 0.460.01

Frictionangle(βa) 35.60.9 42.60.8

Frictioncoefficient(m) 0.720.02 0.920.02 Shearangle(fc) 29.20.3 25.70.2

Shearstress(ts) 289.114.2MPa 311.56.7MPa

Kte 78 71

optimalmatchcanbeattributedtothepotentialerrorsduringthe

machiningoperation thatcaused theradialcuttingforces tobe

lowerthanexpected.Regardless,ourestimationwassuccessfulin

predictingthe resultant forces (tangential and radial combine)

withminimalerrors.

Ball-endmillingof48-2-2

g

-TiAl

Down-end milling operations were performed using two

differentengagementconditionsasshowninFig.10.Acomparison

between the simulation and the experimental data for these

Fig.9.MeasuredandestimatedcuttingforcesfortheAlCrNcoatedtoolforflatenddown-milling:Cuttingforcesin(a)tangentialand(b)radialdirectionswithafeedrateof 64mm/min;cuttingforcesin(c)tangentialand(d)radialdirectionswithafeedrateof88mm/min.

Fig.10.Ball-endmillingengagementarea:(a)4thpass,and(b)6thpassdownmilling.

Fig.11.Comparisonbetweenthemeasuredandestimatedcuttingforcesfor4thpassdown-millingwiththefeedrateof480[mm/min]:Cuttingforcesin(a)theXdirection, and(b)theYdirection.

engagementconditionsareshowninFigs.11and12;validation

tests showed that the simulated and measured cutting forces

matchwellwithina15%errorband.

NACA 2429 airfoil pro_file was machined to validate the

accuracyoforthogonalparametersfor48-2-2

g

-TiAlonfreeform

surfacesasshowninFig.13.Themachiningwasperformedin4

layerswith6pathsineachlayer.Estimatedandmeasuredcutting

forcesintheXandYdirectionsforthethirdpathinthefourth

layerareshowninFig.14.Itcanbeinferredthatthetrendandthe

magnitudeofthesimulatedandexperimentalcuttingforcesare

in good agreement. The deviation in thecutting forcescan be

attributed to the instabilities that occur during machining

operations.

Chipmorphologyof48-2-2

g

-TiAl.

The chip morphology observation during the turning and

milling operation confirmed a serrated, discontinuous and

segmented chip geometry for all the cutting conditions. This

phenomenonisduetothebrittlenessandlowfracturetoughness

Fig.12.Comparisonbetweenthemeasuredandestimatedcuttingforcesfor6thpassdown-millingwiththefeedrateof480[mm/min]:Cuttingforcesin(a)theXdirection, and(b)theYdirection.

Fig.13. (a)Cuttingtoolpathforanairfoilgeometry;(b)machinedpart.

Fig.14.Comparisonbetweenthemeasuredandestimatedcuttingforcesofthe4thlayer,3rdtoolpasswith576[mm/min]feedrate;close-upviewforcuttingforcesin(a)the Xdirectionand(b)theYdirection.

of

g

-TiAl.Fig.15illustratesthechipmorphologyintheorthogonal

turningandmillingprocesses.

Conclusion

Thearticlepresentstheformationofanorthogonaldatabaseto

predictthefundamentalcuttingparametersof48-2-2

g

-TiAlforthe

firsttimeinliterature.Theeffectofcoatingonfrictioncoefficient,

shearstress,shearangleandcuttingforcesarealsoinvestigated.The

shearangleforAlCrNcoatedtoolwasfoundtobelessthantheAlTiN

coatedtool,andthefrictioncoefficientfortheAlCrNcoatedtoolwas

observedtobegreaterthantheAlTiNcoatedtool.Thedeveloped

databaseisemployedtopredictthecuttingforcesof48-2-2

g

-TiAl

formillingoperation.Ananalyticalforcemodelwasusedtosimulate

thecuttingforcesforendmillingandball-endmillingfordifferent

coatingsandcuttingconditions.Estimatedcuttingforces,validated

viaendmillingexperiments,werefoundwithin13%and20%error

bandforAlCrNandAlTiNcoatings,whereascuttingforcesvalidated

viaball-end millingexperimentsmatchedwell within15% error

bandforAlCrNcoating.Thisstudyaimstobeanimportantguidefor

machiningof48-2-2

g

-TiAlalloysandfacilitatingthetransitionfrom

processing traditional materials to advanced materials for

manufacturingindustries.

DeclarationofCompetingInterest

The authors declare that they have no known competing

financial interests or personal relationships that could have

appearedtoin_fluencetheworkreportedinthispaper.

Acknowledgments

TheauthorswouldliketothanktheScientificResearchCouncil

of Turkey (TUBITAK ProjectNo: 9140039), BasqueGovernment

(AeroTiAl,Projectnumber:ZL-2017/000245)andH2020(MMTech,

projectnumber:GA633776)fortheirfinancialsupportprovidedto

thecollaborativeresearchproject.

References

[1]Klocke,F.,Lung,D.,Arft,M.,Priarone,P.C.,Settineri,L.,2013,Onhigh-speed turningofathird-generationgammatitaniumaluminide.IntJAdvManuf Technol,65:155–163.http://dx.doi.org/10.1007/s00170-012-4157-5.

[2]Kothari, K.,Radhakrishnan, R.,Wereley, N.M.,2012,Advances ingamma titaniumaluminidesandtheirmanufacturingtechniques.ProgAerospSci, 55:1–16.http://dx.doi.org/10.1016/j.paerosci.2012.04.001.

[3]Mantle,A.L.,Aspinwall,D.K.,1997,Surfaceintegrityandfatiguelifeofturned gammatitaniumaluminide.JMaterProcessTechnol,72:413–420.http://dx. doi.org/10.1016/S0924-0136(97)00204-5.

[4]Aspinwall, D.K.,Dewes,R.C., Mantle,A.L.,2005,Themachiningofg-TiAI intermetallicalloys.CIRPAnn,54:99–104. http://dx.doi.org/10.1016/S0007-8506(07)60059-6.

[5]Hood,R.,Cooper,P., Aspinwall,D.K.,Soo,S.L.,Lee,D.S.,2015,Creep feed grindingofg-TiAlusingsinglelayerelectroplateddiamondsuperabrasive wheels. CIRP J Manuf Sci Technol, 11:36–44. http://dx.doi.org/10.1016/j. cirpj.2015.07.001.

[6]Mantle,A.L.,Aspinwall,D.K.,2001,Surfaceintegrityofahighspeedmilled gammatitaniumaluminide.JMaterProcessTechnol,118:143–150.http://dx. doi.org/10.1016/S0924-0136(01)00914-1.

[7]Priarone,P.C.,Rizzuti,S.,Settineri,L.,Vergnano,G.,2012,Effectsofcutting angle,edgepreparation,andnano-structuredcoatingonmillingperformance ofagammatitaniumaluminide.JMaterProcessTechnol,212:2619–2628. http://dx.doi.org/10.1016/j.jmatprotec.2012.07.021.

[8]Beranoagirre,A.,Olvera,D.,LópezDeLacalle,L.N.,2012,Millingofgamma titanium-aluminumalloys.IntJAdvManufTechnol,62:83–88.http://dx.doi. org/10.1007/s00170-011-3812-6.

[9]Settineri,L.,Priarone,P.C.,Arft,M.,Lung,D.,Stoyanov,T.,2014,Anevaluative approachtocorrelatemachinability,microstructures,andmaterialproperties ofgammatitaniumaluminides.CIRPAnnManufTechnol,63:57–60.http://dx. doi.org/10.1016/j.cirp.2014.03.068.

[10]Hood,R.,Aspinwall,D.K.,Soo,S.L.,Mantle,A.L.,Novovic,D.,2014,Workpiece surfaceintegritywhenslotmillingg-TiAlintermetallicalloy.CIRPAnnManuf Technol,63:53–56.http://dx.doi.org/10.1016/j.cirp.2014.03.071.

[11]Budak,E., Altintaş, Y., Armarego,E.J.A.,1996,Prediction ofmilling force coefficientsfromorthogonalcuttingdata.JManufSciEng,118:216–224.

[12]Lazoglu,I.,Boz,Y.,Erdim,H.,2011,Five-axismillingmechanicsforcomplexfree formsurfaces.CIRPAnnManufTechnol,60:117–120.http://dx.doi.org/10.1016/ j.cirp.2011.03.090.

[13]Layegh,S.E.,Lazoglu,K.I.,2017,3Dsurfacetopographyanalysisin5-axis ball-endmilling.CIRPAnnManufTechnol,66:133–136.http://dx.doi.org/10.1016/j. cirp.2017.04.021.

[14]Bobzin,K.,2017,High-performancecoatingsforcuttingtools.CIRPJManufSci Technol,18:1–9.http://dx.doi.org/10.1016/j.cirpj.2016.11.004.

[15]Swain,N.,Venkatesh,V.,Kumar,P.,Srinivas,G.,Ravishankar,S.,Barshilia,H.C., 2017, An experimental investigation onthe machining characteristics of Nimonic75usinguncoatedandTiAlNcoatedtungstencarbidemicro-end mills. CIRP J Manuf Sci Technol, 16:34–42. http://dx.doi.org/10.1016/j. cirpj.2016.07.005.

[16]Chiang,S.-T.,Tsai,C.-M.,Lee,A.-C.,1995,Analysisofcuttingforcesinball-end milling.JMaterProcessTechnol,47:231–249. http://dx.doi.org/10.1016/0924-0136(95)85001-5.

[17]Gradišek,J.,Kalveram,M.,Weinert,K.,2004,Mechanisticidentificationof specificforcecoefficientsforageneralendmill.IntJMachToolsManuf, 44:401–414.http://dx.doi.org/10.1016/j.ijmachtools.2003.10.001.

[18]Layegh,S.E.,Lazoglu,K.I.,2014,Anewidentificationmethodofspecificcutting coefficients forball endmilling. ProcCIRP,14:182–187.http://dx.doi.org/ 10.1016/j.procir.2014.03.059.

Fig.15.Chipmorphologyof48-2-2g-TiAl;inorthogonalturningat(a)0.08mmfeedrate,(b)0.100mmfeedrate,andinball-endmillingat(c)336mm/minfeedrate,(d) 480mm/minfeedrate.

[19]Yao,Z.Q.,Liang,X.G.,Luo,L.,Hu,J.,2013,Achatterfreecalibrationmethodfor determiningcutterrunoutandcuttingforcecoefficientsinball-endmilling.J MaterProcessTechnol,213:1575–1587. http://dx.doi.org/10.1016/j.jmatpro-tec.2013.03.023.

[20]Zhang,X., Zhang,J.,Zheng,X., Pang,B.,Zhao,W.,2017, Toolorientation optimizationof5-axisball-endmillingbasedonanaccuratecutter/workpiece engagementmodel.CIRPJManufSciTechnol,19:106–116.http://dx.doi.org/ 10.1016/j.cirpj.2017.06.003.

[21]AltintasYY.,(Ed.)(2012),Manufacturingautomation,in:manufacturing auto-mation:metalcuttingmechanics,machinetoolvibrations,andCNCdesign. 2nded.CambridgeUniversityPress,Cambridge,pp.pp.xiii–xiv.http://dx.doi. org/10.1017/CBO9780511843723.002.

[22]Merchant,M.E.,1945,Mechanicsofthemetalcuttingprocess.II.Plasticity conditionsinorthogonalcutting.JApplPhys,16:318–324.http://dx.doi.org/ 10.1063/1.1707596.

[23]Yigit,I.E.,SEL,K.,Lazoglu,I.,2015,Asolidmodelerbasedengagementmodel for5-axisballendmilling.ProcCIRP,31:179–184.http://dx.doi.org/10.1016/j. procir.2015.03.051.

[24]Stanford,M.,Lister,P.M.,Morgan,C.,Kibble,K.A.,2009,Investigationintothe useofgaseousandliquidnitrogenasacuttingfluidwhenturningBS 970-80A15(En32b)plaincarbon steelusingWC-Councoatedtooling.JMater Process Technol, 209:961–972. http://dx.doi.org/10.1016/j.jmatpro-tec.2008.03.003.

[25]Akmal,M., Layegh, K.S.E.,Lazoglu, I.,Akgün, A., Yavaş, Ç.,2017, Friction coefficientsonsurfacefinishofAlTiNcoatedtoolsinthemillingofTi6Al4V. ProcCIRP,58:596–600.http://dx.doi.org/10.1016/j.procir.2017.03.231. [26]Seifi,M.,Ghamarian,I.,Samimi,P.,Ackelid,U.,Collins,P.,Lewandowski,J.,2016,

MicrostructureandmechanicalpropertiesofTi-48Al-2Cr-2Nbmanufactured viaelectronbeammelting.Proc13thworldconftitan,1317–1322.http://dx. doi.org/10.1002/9781119296126.ch223.

[27] Draper,S.L.,Lerch,B.A.,2008,DurabilityassessmentofTiAlalloys..Retrieved fromhttps://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080047349.pdf.