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3.2.1WorkpieceandCuttingInserts

Inthisstudy,hotrolledASTM4140steelwasselectedastheworkpiecematerial.Theworkpiecepropertiesarelistedasfollows:

Description:

Hotrolledalloysteelbars,SAE4140H（UNSH4140）

Dimensions:

15cmDiameterx62.25cmlength

HeatTreatment:

Vacuumdegassed/processed,Cal-Altreated,annealedandspecialstraightened,conformingtoASTMA322andA304

Chemicalcompositions:

ThecompositionoftheworkpiecematerialislistedinTable3.1accordingtotheASTMstandards.TheexperimentwascarriedoutinaccordancewiththeinternationalstandardorganizationISO3685-93[46],theexperimentwasstoppedandtheworkpiecewaschangedwhenthelength/diameterratioreached10tomeettherequirementsofISO3685[46].Thehardnessofeachbarwascheckedacrossthediameter,andtheaveragehardnessmeasurementwas29HRC.ThetypesoftestedcuttingtoolinsertsarelistedonTable3.1accordingtotheISOdesignation.ThreetypesofcuttinginsertswereusedintheexperimentasillustratedinTable3-2;

andthecoatingpropertiesarealsolistedinTable3-3.TheconfigurationoftheinvestigatedthreecuttinginsertswasthesameaslistedinTable3.4.ThegeneralcuttinginsertassembledgeometryisshowninFigure3-2.TheinsertsweremountedrigidlyonatoolholderaredepictedinFigure3-3withanISOdesignationofSVJBR2525M16.

Table3-1ChemicalcompositionofASTM4140steelusedinthetest

Cuttinginserts

ISODesignation

Substrate

Grade

Company

Uncoated

cemented

Carbide

VBMT160408

.........

KC313

Kennametal

TiAlN

KC313

KC5010

TiN-TiCN-TiN

KC732

Table3-2Typesofthetestedcuttinginserts

Carbon

Manganese

Phosphorus

Sulfur

Silicon

Nickel

Chromium

0.4

0.91

0.017

0.02

0.24

0.10

1.01

Tin

0.008

Aluminum

0.030

Vanadium

0.002

Calcium

0.0064

Molly

0.2

Copper

0.12

Table3-3Coatingsproperties

Coating

Thickness

Numberoflayers

TiALN

3.5µ

1

3µ

-3t-1t

3

（TiCNintermediate）

3.2.2CoolantProperties

Itisacommonbeliefthatcoolantemulsionhelpsinreducingwearrateandcuttingtemperature.Thecoolantusedinthetestwaswaterbasedemulsionhascommercialname`Novick'

.Itismixedwithwaterataconcentrationof10%.ThecoolantcompositionincludesthelistedchemicalsinTable3.5.Previousresearchersonthebettercoolantstreamdirectionsmadedifferentsuggestions.Taylor[17]indicatedthattoreducetoolwearthecuttingfluidistobedirectedatthebackofthechip（directionA）.PigottandColwell[47]foundthatbyusinghighstreamjetofcoolantaimedindirectionBitwasabletoreducetoolwear.SmartandTrent[48]investigatedthedirectionofcoolantinreducingthetoolwearandfoundthatthemosteffectivedirectionbetweenallothersuggestedoptionswasdirectionB.Therefore,coolantwasappliedindirectionBaslistedinFigure3.4fromanozzlewithdiameterof1.3cmandaflowrateof7.1liters/minute.However,thecurrentstudyshowedthatthisisnotnecessarilytrueinallcasesascoolantextendsthetoollife.Itwasfoundthatcoolantemulsionhelpedreducetoollifebyactivatingcertainwearmechanismathighspeedmachining（HSM）.DetailedexplanationsofthistypeofcoolanteffectwillbediscussedinChapter5.Furthermore,abriefsummaryandexplanationoftypesandusageofcoolantwillbecoveredinChapter5.

Table3-4Assembledcuttingtoolgeometry

Toolgeometry

Dimension

Noseradius

0.8（mm）

Bakerakeangle

0°

Endreliefangle

5'

Endcutting-edgeangle

52°

Sidecutting-edgeangle

30

Siderakeangle

0'

Sidereliefangle

Table3-5Coolantchemicalcompositions

Sulfate

20-30%

Aromaticalcohol

3-5%

Propyleneglycolether

Petroleumoil

30-35%

Nonionicsurfactant

Chlorinatedalkenepolymer

Angulartool

Designation

Backrake0°

Siderake0°

Endrelief5°

Siderelief5°

Endcuttingedge52°

Sidecuttingedge3°

Noseradius0.88mm

Noseradius

CuttingBackrakeangle

Figure3-2Assembledtoolgeometry

Figure3-3Photographofthecuttinginsertfixedonthetoolholder

AB

Figure3-4coolantstreamdirection.

3.3CuttingConditions

BasedonI803685[46]fivecuttingspeedswereusedthroughoutthetestingaslistedonTable3-6.Cuttingspeedscorrespondingto410m/minforthecoatedcarbidetoolsand180m/minfortheuncoatedcarbidetoolswereapproximatelytheupperlimitoftheapplicationrange.Sinceanyfurtherincrementresultedinveryshortcuttingtoollifeorprematuretooldamagesoonafterthetestwasstarted.

Theturningexperimentswerecarriedoutunderdryandwetcuttingconditionsatdifferentcuttingspeeds,whilefixingbothfeedrateat0.14mm/revanddepthofcutat（1mm）.Fivecuttingspeedswereselectedforthethreetypesofcuttinginserts,aslistedinTable3-6.

3.4ExperimentalProcedureofToolLifeTesting

AClausing1300lathewithmaximum7.5HPwasusedfalloysteelSAE4140Hworkpiece,andtheturningprocesswascarriedoutinthewayortheturningoftheHotrolledpreviouslydescribed.ATachometerwasusedtomeasuretherotationalspeedbeforeeachsinglecutoccurredontheworkpieceinordertoensurethatthecuttingwasperformedattheexactspeed.

Anopticalmicroscopewasusedtomeasuretheflankwearofthecuttinginserts.Theexperimentwasterminatedifeitherofthetwofollowingconditionsoccurred

1-Themaximumflankwear0.7mmand/or;

2-Theaverageflankwear0.6mm.

Preliminaryexperimentswerecarriedoutinordertodeterminethewearlimit.Itwasfoundthatthecuttinginsertswerewornoutregularlyontheflankside.Therfore,VB,nax=0.7mm,ischosentobethewearlimitforthetoollife.Theflankwearwasobservedandmeasuredatvariouscuttingintervalsthroughouttheexperiments.Figure（3-5）showsflankwearasafunctionofcuttingtimeforthecementedcarbide（KC313）underdryandwetconditions,andincludesonlythreecuttingspeedsforclarity.

Figure3-6presentstheflankwearasafunctionofcuttingtimeforsandwichcoatedinserts（KC732）underdryandwetconditions.Figure3-7showstheflankwearasafunctionofcuttingtimeforTiALNcoatedcuttinginserts（KC5010）.Previousfiguresincludedthreecuttingspeeds.Clarityofcuttingspeedcurvesarepresentedattheattachedappendixforbothconditionsofmachining.Theaforementionedfigures,presenttheeffectofcoolantemulsioninextendingthetoollifefortheKC313,andKC732cuttinginserts;

especiallyafter3minutesforKC313,andafter7minutesforKC732ofcutting.However,theusageofcoolantemulsiononKC5010showednegativeinfluence.

Figure3-5,andFigure3-6showthatatanysetofturningconditions,theflankwearincreasedatahigherratea