Surface texture

Surface texture

1. Measurement of Surface Finish
•Basicunderstandingofsurfaceroughness.
•Indicationoffinishondrawing.
•ParametersofSurfaceroughness.
•Measurementmethods:contactandnoncontacttype.

2. INTRODUCTION
•Engineeringcomponentsaremanufacturedbycasting,forging,weldingetc…
•Thesecomponentsarethensubjectedtovariousmachiningoperationsforgettingrequired
geometricalsurfaces.
•Itisnotpracticallypossibletoproduceacomponenthavingageometricallyidealsurface.
•Thesurfacefinishaftermachiningdependsuponthematerial,vibration,deflection,speed,feed
andotherworkingconditions.
•Thesurfacefinishrequirementsdependuponthefunctionalrequirementsofthecomponentsto
beassembled.

3. Why Surface finish?
•Surfacefinish,alsoknownassurfacetextureorsurfacetopography,isthenatureofthesurface
asdefinedbycharacteristicssuchaslay,surfaceroughnessandwaviness.
•Surfacetextureisoneoftheimportantfactorsthatcontrolfrictionduringsliding.
•Toimprovelookandfeeloftheproduct.
•Fitbetweenparts.
•Tocontroltheprocessthatresultsinthesurfaceneeded.

4. Importance of surface finish
•Surfaceroughness,isimportantfromthepointofviewoffundamentproblemssuchasfriction
andwear,surfacecontact,lubrication,andtightnessofjoints.
•Itaffectsconductionofheat,cleanlinessandreflectivityofthesurface.
•Italsoaffectsthepositionalaccuracyofmatingparts,resistancetocorrosion.

5. Factors influencing surface finish
•Themachiningvariablesthatincludes:
a)Cuttingspeed
b)Depthofcut
c)Feed
•Geometryoftool.
•Workpieceandtoolmaterials,andtheirmechanicalproperties.
•Qualityandtypeofmachinetoolused.
•Lubricationused.
•Vibrationsbetweenworkpiece,cuttingtoolsandmachinetools.

6. Classification of Geometrical Irregularities
Thegeometricalirregularitiescanbeclassifiedas
•Firstorder
•Secondorder
•Thirdorder
•Fourthorder
1.FIRSTORDER:
Theseirregularitiesareformedinthemachine,duetoinaccuracies,thisirregularityalsocontainslackofstraightness
ofguideways,thisiscausedduetometalweightandcuttingforce.
2.SECONDORDER:
Irregularitiessuchaschattermarks,etc.areformedduetovibrations.Thistypeofirregularitiesiscalledsecond-
orderirregularities.
3.THIRDORDER:
Thisisformedduetothemachiningprocess,evenifthemachineisperfectandvibrationfreearecalledthirdorder
irregularities.
4.FOURTHORDER:
Thisisformedduetotheseparationofthechip,thisiscausedduetoruptureofmaterialarefourthorderirregularities.

7. Types of Surface Finish
Surfaceofabodyisitsboundarywhichseparatesitfromanotherbody.Generallytherearetwo
typesofsurfacesnamely:
NominalSurface:Atheoreticallygeometricallyperfectsurfaceiscalledasanominalsurface.
RoughSurface:Amagnifiedviewofanactualsurfaceisshown.Thissurfacehasnumeroussmall
peaksandvalleysthatdeviatefromthenominalsurface.Itisseenthatthesurfacehasacertain
degreeofroughnessandhenceitiscalledaroughsurface.
WavySurface:Asurfacehavingwavinessasshowninthefigureiscalledwavysurface.Waviness
iscausedby:
1.Deflectionsoftoolsandworkpiece.
2.Unevenlubrication.
3.Vibrations

8. Nomenclature of Surface texture
1.SurfaceRoughness:Itisthemicro-irregularitiesinasurfaceresultingfromtheactionof
productionprocess.
2.Profile:Itistheshapeofanysectionthroughasurface.
3.Flaw:Itisanirregularitythatoccursinasurfaceduetocracks,blowholes,scratches,etc.,
Unlessotherwisespecified,theeffectofflawsshouldnotbeaccountedinthemeasurementof
roughness.
4.SampleorCut-offlength:Theparticularlengththatistakenforsamplemeasurementonthe
surfaceiscalledascutoflength.Itisalsoknownasroughnesswidthcutoff.
5.Lay:Itisthedirectionofthepredominanttopsurfacegroovesthatareproducedbymachining.

9. 6.Waviness:Surfaceirregularitiesthatareofgreaterspacingthanroughness.

10. Analysis of surface finish
The assessment of average roughness is carried out by
a) Centre line average (CLA) value (Ra).
b) Root mean square (RMS) value (Rs).
c) Ten point method. (Rz)

11. Analysis of surface finish
a)Centre line average (CLA) value (Ra):
Raistheaverageheightfromameanlineofallordinatesofthesurface,regardlessofsign.Lety1,
y2,….,ynbetheheightoftheequallyspacedordinatesatpositions1,2,…n.
In Centre Line Average (C.L.A.) method;
Centre Line Average= ( y1+y2+y3+…….+yn)/ n

12. Another way of calculating Ra is shown in the figure.
As per BIS, the surface roughness is assessed in terms of C.L.A. value and is denoted
by Ra

13. b) Root mean square (R.M.S) value (Rs):
R.M.SRsisthesquarerootofthemeanofthesquaresofthesurfacemeasuredfromthemeanline.
Asy1,y2,……ynaretheheightsoftheequallyspacedordinatesatpositions1,2,3,…n,
In Root Mean Square(R.M.S.) method;
RootMean Square=
c)Tenpointheightmethod:Theaveragedifferencebetweenfivehighestpeaksandfivelowest
valleysofsurfaceistakenandirregularitiesarecalculatedby

14. Direction of lay
Thedirectionoflayisthedirectionofthepredominantsurfacepatternordinarilydeterminedbytheproduction
methodandisshownintable.

16. Roughness grade and symbols
Theprincipalcriterionofsurfaceroughness,Ramaybeindicatedbythecorresponding
roughnessgradenumber,asshowninTable

17. Roughness grade for various machining processes

18. Representation of surface roughness
Thevalueorvaluesdefiningtheprincipalcriterionofroughnessareaddedtothesymbolas
showninfigure
a=Roughnessvalue,Rainmicrometres
b=Productionmethod/treatmentofcoating
c=Samplinglength
d=Directionoflay
e=Machiningallowanceand
f=Otherroughnessvalues

19. Methods of measurement of Surface roughness
Therearebasicallytwomethodsformeasuringsurfacefinish,namely
1.ComparativeorQualitativeMethods
2.DirectMeasurementorQuantitativeMethods
ComparativeorQualitativeMethods
Inthesemethods,thesurfacetextureisassessedbyobservationofthesurface.Thesurfacetobe
testediscomparedwithknownvalueofroughnessspecimenandfinishedbysimilarmachining
process.Thevariousmethodswhichareusedforcomparisonare
1.TouchInspection.
2.VisualInspection.
3.MicroscopicInspection.
4.ScratchInspection.
5.MicroInterferometer.
6.Surfacephotographs.

20. Touch Inspection
•Themainlimitationofthismethodisthatthedegreeofsurfaceroughnesscan’tbeassessed.
•Alsotheminuteflawscan’tbedetected.
•Thismethodcansimplytellwhichsurfaceismorerough.Inthismethod,thefinger-tipis
movedalongthesurfaceataspeedofabout25mmpersecondandtheirregularitiesassmallas
0.01mmcanbeeasilydetected.
Visual Inspection
Inthismethod,thesurfaceisinspectedbynakedeyeandthismeasurementislimitedtorough
surfaces.
Microscopic Inspection
•Thisisprobablythebestmethodforexaminingthesurfacefinishbutsuffersduetolimitationthat
onlyasmallportionofthesurfacecanbeinspectedatatime.
•Thusseveralreadingsarerequiredtogetanaveragevalue.
•Inthismethod,amasterfinishedsurfaceisplacedunderthemicroscopicandcomparedwiththe
surfaceunderinspection.
•Inanothermethodastraightedgeisplacedonthesurfacetobeinspectedandabeamoflight
projectedatabout60°tothework.
•Thustheshadowscastintothesurfacescratchesaremagnifiedandthesurfaceirregularitiescanbe
studied.

21. Scratch Inspection
•Inthismethod,asoftermateriallikeleadbabbitorplasticisrubbedoverthesurfacetobe
inspected.
•Bydoingsoitcarriestheimpressionofthescratchesonthesurfaceswhichcanbeeasily
visualised.
Surface Photographs
•Inthismethodmagnifiedphotographsofthesurfacearetakenwithdifferenttypesofillumination.
•Incaseweuseverticalillumination,thendefectslikeirregularitiesandscratchesappearasdark
spotsandflatportionofthesurfaceappearsasbrightarea.
•Incaseofobliqueillumination,reverseisthecase.
•Photographswithdifferentilluminationarecomparedandtheresultsassessed.
Micro-Interferometer
•Inthismethod,anopticalflatisplacedonthesurfacetobeinspectedandilluminatedbya
monochromaticsourceoflight.
•Interferencebandsarestudiedthroughamicroscope.
•Defects,i.e.scratchesinthesurfaceappearasinterferencelinesextendingfromthedarkbandsinto
thebrightbands.

22. Direct Methods of Surface roughness
measurement
Instructor
Mr. GauravBharadwaj
AssistantProf.
DepartmentofME
GLAUniversity

23. Direct Measurement or Quantitative Methods
Someofthedirectmeasuringinstrumentsare
1.Stylusprobeinstruments
2.Tomlinsonsurfacemeter
Stylus probe instrument
Principle
Whenthestylusismovedoverthesurfacetobemeasured,theirregularitiesinthesurfacetexture
aremeasuredanditisusedtoassessthesurfacefinishoftheworkpiece.
Working
•Thestylustypeinstrumentsconsistofskid,stylus,amplifyingdeviceandrecordingdevice.
•Theskidisslowlymovedoverthesurfacebyhandorbymotordrive.
•Theskidfollowstheirregularitiesofsurfaceandstylusmovesalong
withskid.
•Whenthestylusmovesverticallyupanddown,thestylus
movementsaremagnified,amplifiedandrecordedtogetatrace.
•Thenthetraceisanalyzedbyanautomaticdevice.

24. Advantage:
1.Any desired roughness parameter can be recorded.
Disadvantages:
1. Fragile material cannot be measured.
2. High Initial cost.
3. Skilled operators are needed to operate.

25. Tomlinson Surface meter
Principle:Thisinstrumentusesmechanical-cum-opticalmeansformagnification.
Construction:
•Inthis,thediamondstylusonthesurfacefinishrecorderisheldbyspringpressureagainstthe
surfaceofalappedcylinder.
•Thelappedcylinderissupportedonesidebyprobeandothersidebyrollers.
•Thestylusisalsoattachedtothebodyoftheinstrument
byaleafspringanditsheightisadjustabletoenablethe
diamondtobepositionedandthelightspringsteelarmis
attachedtotheLappedcylinder.
•Thespringarmhasadiamondscriberattheendand
smokedglassisrestonthearm.

26. Working
•Whenmeasuringsurfacefinish,thebodyoftheinstrument
movesacrossthesurfacebyascrewrotation.
•Theverticalmovementoftheprobecausedbythesurface
irregularitiesmakesthehorizontallappedcylindertoroll.
•Thisrollingoflappedcylindercausesthemovementofthe
arm,So,thismovementinducesthediamondscriberon
smokedglass.
•Finally,themovementofscribertogetherwithhorizontal
movementproducesatraceonthesmokedglassplateand
thistraceismagnifiedbyanopticalprojector.

27. Thank you