Cutting Tool Wear

Cutting Tool Wear

1. Dr.JayantaKr.Mahato
Assoc.Professor
MechanicalEngineeringDept.
ShobhitDeemedto-beUniversity
Contact:[email protected]

2. Introduction:ToolWear
Wearislossofmaterialonanasperityormicro-
contact,orsmallerscale,downtomolecularor
atomicremovalmechanisms.Itusuallyprogresses
continuously.
Toolweardescribesthegradualfailureofcutting
toolsduetoregularoperation.
Itisatermoftenassociatedwithtippedtools,tool
bits,ordrillbitthatareusedwithmachinetools.
Gradualfailureofcuttingtoolsduetoregular
operationsisalsoknownastoolwear.
Toolfailureimpliesthatthetoolhasreacheda
pointbeyondwhichitwillnotfunctionsatisfactorily
untilitisre-sharpened.
Dr.JayantaKr.Mahato,Asst.Prof.,MechanicalEngineering
2

3. Modesof cuttingtool failure
FRACTURE FAILURE:
□Thismodeoffailureoccursduetomechanical breakage dueto
excessiveforcesandshocksatthetoolpointcausingittofailsuddenlyby
brittlefracture.
Alsoknownasmechanicalchipping.
□Suchkindoftoolfailureisrandomandcatastrophicinnature,resultsin
prematurelossoftoolandhenceisextremelydetrimental.
TEMPERATURE FAILURE:
□Thisfailureoccurswhenthecuttingtemperatureistoohighforthetool
material,causingthematerialatthetoolpointtosoften,whichleadsto
plasticdeformationandlossofthesharpedge.
□Thistypeoffailurealsooccursrapidly,resultsinprematurelossoftool
andisquitedetrimentalandunwanted.Note:Bothoftheabovekindsof
toolfailureneedtobepreventedbyusingsuitabletoolmaterialsand
geometrydependingupontheworkmaterialandcuttingcondition.
GRADUAL WEAR:
Gradualwearingofthecuttingedgecauseslossoftoolshape,reduction
incuttingefficiency,anaccelerationofwearingasthetoolbecomes
heavilyworn,andfinallytoolfailureinamannersimilartoatemperature
failure.
Gradualwearispreferredbecauseitleadstothelongestpossibleuseof
thetool,optionofchangingthetoolbeforethefinalcatastrophiclossof
thecuttingedgeoccurs,withtheassociatedeconomicadvantageofthat
longeruse.

4. Waysofmeasuringtoollife
Numberofpiecesofworkmachined.
Totalvolumeofmaterial removed.
Totallength ofcut.
Limitingvalueofsurface finish.
Increaseincuttingforces.
Dimensionalaccuracy.
Overheatingandfuming.
Presenceofchatter.
Dr.JayantaKr.Mahato,Asst.Prof.,MechanicalEngineering

5. Toolweardependingfactors
1.Typeoftoolmaterialanditshardness
2.Typeandconditionofworkpiecematerial
3.Dimensionsofcut(Feedanddepth ofcut)
4.Cuttingspeed
5.Toolgeometry
6.Tooltemperature(functionofcuttingspeed,
feedanddepthofcut)
7.Typeofcuttingfluid
Dr.JayantaKr.Mahato,Asst.Prof.,MechanicalEngineering
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6. Classificationoftoolwear
Thetoolwaresareclassifiedintothefollowingtypes:
1.Craterwearontoolface
2.Flankwear
3.LocalizedwearsuchastheroundingofCuttingedge
(Nosewear/Cornerwear)
4.Chippingofthecuttingedge

7. CraterWear
Itconsistsofacavityorconcavesection
onthetoolface/rakefaceformedand
growsfromtheactionofthechipsliding
againstthesurface.
High stresses and temperatures
characterize thetool–chip contact
wearinginterface,contributingtothe
action.
Thecratercanbemeasuredeitherbyits
depthoritsarea.
Craterwearaffectsthemechanicsofthe
processincreasingtheactualrakeangle
ofthecuttingtoolandconsequently,
makingcuttingeasier.
Atthesametime,thecraterwear
weakensthetoolwedgeandincreases
thepossibilityfortoolbreakage.
Thiswearpredominatesathighspeed.In
general,craterwearisofarelatively
smallconcern.

8. CausesofCraterWear
Thecraterwearismainly
causeddueto:
□The presence of friction
betweenthechip-toolinterface,
□The abrasion action of
microchipspresentatthechip-
toolinterface.
□The abrasive action of
fragmentsofBuiltupEdge(BUE)
atthechip-toolinterfaceand
diffusionwear.
□Thediffusionwears,duetothe
atomicattractionbetween the
toolandworktheatomsofthe
toolmaterialwillgetdiffusedand
depositedovertheworkpiece
calleddiffusionwear.

9. FlankWear
Itoccursonthetoolflankasaresultoffrictionbetween
themachinedsurfaceoftheworkpieceandthetoolflank.
Flankwearappearsintheformofso-calledwearlandand
ismeasuredbythewidthofthiswearland,VB.
Flankwearaffectstothegreatextendthemechanicsof
cutting.
Anextremeconditionofflankwearoftenappearsonthe
cuttingedgeatthelocationcorrespondingtotheoriginal
surfaceoftheworkpart.Thisiscallednotchwear.It
occursbecausetheoriginalworksurfaceisharderand/or
moreabrasivethantheinternalmaterial,whichcouldbe
causedbyworkhardeningfromcolddrawingorprevious
machining,sandparticlesinthesurfacefromcasting,or
otherreasons.Asaconsequence ofthehardersurface,
wearisacceleratedatthislocation.
Cuttingforcesincreasesignificantlywithflankwear.Ifthe
amountofflankwearexceedssomecriticalvalue(VB>
0.5~0.6mm)thentheexcessivecuttingforcemaycause
toolfailure.
Thiswearpredominatesatlowspeed.

10. CausesofFlankWear
work
Theflankwearismainlycauseddueto:
□Thepresenceoffrictionatthetool
interface.
□Theabrasiveactionofmicrochipsorpowdered
particlespresentatthetoolworkinterfaceand
diffusionwear.
□Thediffusionwears,duetotheatomic
attractionbetweenthetoolandworktheatoms
ofthetoolmaterialwillgetdiffusedand
depositedovertheworkpiececalledasdiffusion
wear.
Dr.JayantaKr.Mahato,Asst.Prof.,MechanicalEngineering
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11. CornerwearornoseWear
Itoccursonthetoolcorner.
□Itcanbeconsideredasapartofthewearlandand
respectivelyflankwearsincethereisnodistinguished
boundarybetweenthecornerwearandflankwearland.
□Weconsidercornerwearasaseparateweartype
becauseofitsimportancefortheprecisionofmachining.
□Cornerwearactuallyshortensthecuttingtoolthus
increasinggraduallythedimensionofmachined surface
andintroducing asignificantdimensional errorin
machining,whichcanreachvaluesofabout0.03~0.05mm.

13. Dr.JayantaKr.Mahato,Asst.Prof.,MechanicalEngineering

14. ControlofTool Wear
Therateoftoolwearstrongly
depends on the cutting
temperature;therefore any
measures which couldbe
appliedtoreducethecutting
temperaturewouldreducethe
toolwearaswell.
Use of cutting fluids,
lubricantsisanothermethod.
Additionalmeasurestoreduce
thetoolwearincludethe
application of advanced
cuttingtoolmaterials,suchas
coated carbides, ceramics,
etc.
Thefigureshowstheprocess
parametersthatinfluencethe
rateoftoolwear:
Dr.JayantaKr.Mahato,Asst.Prof.,MechanicalEngineering