Analysis of surface texture generated by a flexible magnetic abrasive brush

8 Pages·0.57 MB·English

by  Singh D.K. (et al.)

Wear259(2005)1254–1261
Analysis of surface texture generated by
a flexible magnetic abrasive brush
Dhirendra K. Singha,1, V.K. Jaina,∗, V. Raghurama, R. Komandurib,2
aMechanicalEngineeringDepartment,IndianInstituteofTechnology,Kanpur208016,India
bSchoolofMechanicalandAerospaceEngineering,OklahomaStateUniversity,Stillwater,OK,USA
Received28July2004;receivedinrevisedform21January2005;accepted2February2005
Abstract
Theapplicationofmagneticfieldinthecontrolofmanufacturingprocesseshasbecomeofinterestinrecentpast.Inmagneticabrasive
finishing(MAF)process,magneticforceplaysadominantroleintheformationofflexiblemagneticabrasivebrush(FMAB)anddeveloping
abrasionpressure.Theprocessisstillinitsinfancyinmanyrespects.Mostofthepreviousresearchhasexploredtheprocesscharacteristics
andmechanismfromamacroscopicpointofviewusingsurfaceroughnessprofiles.Thispaperexaminesthemicroscopicchangesinthe
surfacetextureresultingfromtheMAFprocesstocharacterisethebehaviorofabrasiveparticlesduringfinishing.Inadditiontothesurface
roughness measurement, atomic force and scanning electron microscopy have been carried out to gain insight of the wear pattern of the
finishedsurface.Theobservedsurfacetextureindicatesthattheprocesscreatesmicroscratcheshavingwidthlessthan0.5(cid:1)monthefinished
surface.Moreover,thesurfaceisfinishedbytheshearingofthepeaksresultingincircularlaysformedbytherotationoftheFMAB.
©2005PublishedbyElsevierB.V.
Keywords: Magneticabrasivefinishing;Surfaceroughness;AFM;SEM
1. Introduction metallicparts,aswellasotheradvancedengineeringmate-
rialparts.
Finishing operations in the metal working industries are Themagneticfieldassistedfinishingprocessesarebased
critical and an expensive phase of overall production pro- on the electro-magnetic behavior of the magnetic abrasive
cesses. The application of magnetic field in the control of particles in the magnetic field. In magnetic abrasive finish-
manufacturingprocessesingeneralandfinishinginparticu- ing(MAF)process,magneticforceplaysadominantrolefor
lar has become of interest. For example, magnetic abrasive the formation of flexible magnetic abrasive brush (FMAB)
flowmachining,magneticfloatpolishing,magnetorheologi- and developing abrasion pressure. The studies on magnetic
cal abrasive flow finishing, and magnetic abrasive finishing fieldassistedfinishingprocessesarebeingcarriedoutatin-
(MAF) are some of such processes developed in the recent dustriallevelinadditiontoresearchanddevelopmenthouses
past[1].Magneticfieldassistedmanufacturingprocessesare [2].Forthelight,brittleandhighlycorrosionresistantcom-
relatively new finishing processes and they are becoming ponentsbeingusedinhigh-techindustries,thisprocesscan
popular in finishing, cleaning, deburring and burnishing of beappliedtofinishthecomponentsuptonanolevelsurface
roughness[3,4].Thesalientfeatureofthisprocessistheuse
of controllable magnetic field to direct the chains of ferro-
∗ Correspondingauthor.Tel.:[phone]; magnetic particles having abrasive particles trapped within
fax:[phone]/0007. and between them, to adapt the contour of the workpiece
E-mailaddresses:[email protected](D.K.Singh),[email protected]
surfacetobefinished.Thenatureofthebrushisflexibleto
(V.K.Jain).
access the surface where the conventional tools are hardly
1 OndeputationfromM.M.M.EngineeringCollege,Gorakhpur,India.
2 Tel.:[phone];fax:[phone]. applicable,e.g.insidepipesandbenttubes[5].
0043-1648/$–seefrontmatter©2005PublishedbyElsevierB.V.
doi:10.1016/j.wear.2005.02.030
D.K.Singhetal./Wear259(2005)1254–1261 1255
InMAF,ahomogeneousmechanicalmixtureofSiCabra- workpiecesurfacetoremovematerial.Themagneticforceis
siveandferromagneticironparticlesisused.Ironparticlesare influencedbythemagneticfielddistributionwhichismainly
attractedtowardseachotheralongthemagneticlinesofforce affectedbythesize,shape,andmaterialoftheelectromagnet
duetodipoleinteractionsandformaflexiblemagneticabra- alongwiththecurrenttothecoilofthemagnet,workinggap,
sive brush. The FMAB has multiple, random cutting edges andmagneticpropertyoftheferromagneticparticlesmixed
anditbehaveslikeamultipointcuttingtool.Thedensityand withtheSiCparticles.
strengthofthebrushcanbevariedbychangingthemagnitude Magneticabrasivefinishingprocessisstillinitsinfancyin
ofthemagneticfieldintheworkingzone.Theabrasivepar- manyrespects.Mostofthepreviousresearchhasexploredthe
ticles trapped between the iron particles and the workpiece process characteristics and mechanism from a macroscopic
surfaceoriginatemicroindentationsintotheworkpiecesur- pointofviewusingsurfaceroughnessprofiles[6–8].Thein-
face. This results in the removal of the material during the process behavior of abrasive particles has been monitored
rotation of the brush, and smoothening micro-unevenness. by measuring the finishing torque during the process [9].
SiC abrasive particles do not have magnetic property and Few researchers investigated the material removal mecha-
arecompressedbytherotatingmagneticbrushwhichtrans- nismduringMAFprocess[10].Thispaperreportsthesurface
fersforcestotheabrasiveparticles,whichinteractwiththe texturesobtainedduringexperimentation[11]byexamining
Fig.1. (a)Schematicviewofplanemagneticabrasivefinishingprocesssetup,((cid:2))ironparticles,( )abrasiveparticles;(b)photographofFMAB;(c)workpiece
fixtureandworkpiece.Alldimensionsareinmm.
1256 D.K.Singhetal./Wear259(2005)1254–1261
Fig.2. Changeinfluxdensityalongradialdistancefromtheouterpole,
workinggap=1.50mm[11]. Fig.3. Variationofmagneticforcewithinputcurrentatdifferentworking
gaps.
Fig. 4. Surface roughness profiles: (a) before MAF; (b) after MAF at input current to the magnet=0.88A, working gap=1.50mm, abrasive grain mesh
no.=500,no.ofcycles=11;(c)beforeMAF;(d)afterMAFatinputcurrenttothemagnet=0.88A,workinggap=1.75mm,abrasivegrainmeshno.=600,no.
ofcycles=9;(e)afterMAFatinputcurrenttothemagnet=0.75A,workinggap=1.75mm,abrasivegrainmeshno.=800,andno.ofcycles=9.
D.K.Singhetal./Wear259(2005)1254–1261 1257
themicroscopicchangestocharacterizethebehaviorofabra- themachinetablemovesfromthestartingpointtoadistance
sive cutting edges while removing material. To understand of20.0mmforwardandthen20.0mmbackward.Themove-
thebasicbehavioroftheprocessatmicro/nanolevel,atomic ment of the table takes 5.0min to complete one cycle. The
force and scanning electron microscopy have been carried number of cycles has been counted by an electronic circuit
outtogaininsightofthewearpatternonthesurfaceofthe activatedbythetwolimitswitches.
workpiece. Both forces, i.e. normal (magnetic) and cutting forces,
actingduringtheMAFprocesshavebeenmeasuredusinga
ring-typedynamometer[11].Theforcesignalsfromthedy-
2. Experimentalsetupandprocedure namometerhavebeenacquiredusingsignalconditionerand
virtual instrument software (Labview). Cutting force is ba-
Theschematicdiagramofaplanemagneticabrasivefin- sicallyamechanicalforcecausedbytherotationofFMAB.
ishingapparatusisshowninFig.1a.Theenlargedviewofthe The friction between the magnetic particles and workpiece
FMABisshowninFig.1b.Thedimensionsoftheworkpiece willdefinitelybethereduringactualmachining,andthisfric-
fixture and workpiece are shown in Fig. 1c. The flat-faced tionforcehasnotbeenseparatedoutfromthecuttingforce.
electromagnet has been designed in such a way that its en- When the cutting force (Fc) is greater than the resistance
tirefacecomesincontactwiththeflatworkpiecesurface.The offered for deformation by the work material, the abrasive
centralpartofthemagnetactsasanorthpoleandouteroneas particle will remove material from the workpiece. If Fc is
southpole.WhenactivatedbyaDCpowersupply,magnetic smaller than the resistance offered for deformation by the
fieldinthecenterpoleradiallyreturnstotheoutershellwith workpiece (which depends on depth of indentation), then
minimumleakagefield.Theendresultisstrongconcentrated the abrasive particle will rotate without removing any ma-
magneticfieldstrengthonthecenterpoleandcomparatively terial leading to the reduced depth of indentation to the ex-
thinlydistributedmagneticlinesofforceontheoutershell. tentthatFcbecomeslargerthantheresistanceofferedbythe
Thevariationofmagneticfluxdensity,alongtheradialdis- workpiece.
tance(O,X,Y,ZinFig.1a)byvaryinginputcurrentisshown Experimentswereplannedusingthestatisticaldesignof
inFig.2.Themagneticflux(Φ)passesthroughtheferromag- experiments technique, namely central composite rotatable
neticparticlesandworkpiececompletingthemagneticcircuit design with half replicate, to get useful inferences by per-
(Fig.1a).Theworkpieceandworkpiecefixturearemadeof formingminimumnumberofexperiments.Parametricstudy
thesameferromagneticalloysteel.Theworkinggapisfilled oftheprocesswasperformed[11]usingthedevelopedempir-
with a homogeneous mechanical mixture of silicon carbide ical models. The scanning electron microscope and atomic
abrasiveparticlesandferromagneticironparticles(meshno. force microscope images of the workpieces were obtained
300)intheratioof1:3byweight,respectively.Afreshmix- before and after MAF. The samples were cleaned using an
tureisusedforeachexperiment.Onecompletecyclemeans ultrasoniccleanerfor10min.Thesurfaceroughnessvalues
Fig.5. SEMphotographsofsurfaceproducedby:(a)grinding;(b)MAFatcurrent=0.88A,workinggap=1.5mm,grainmeshno.=500,no.ofcycles=11;
(c)MAFatcurrent=0.75A,workinggap=1.75mm,grainmeshno.=600,no.ofcycles=9;(d)MAFatcurrent0.75A,workinggap=1.75mm,grainmesh
no.=800andno.ofcycles=9.
1258 D.K.Singhetal./Wear259(2005)1254–1261
aredeterminedbymeasuringRa(centerlineaveragevalue)
beforeandafterMAF,bySurfanalyzerSystem-5000(Mahr
Inc., USA) keeping the cutoff length equal to 0.8mm [12].
Measurementshavebeenmadeinthesameareaofthesurface
obtainedbygrindingandbymagneticabrasivefinishing.The
measurementsweremadeperpendiculartothelaysobtained
byboththeprocesses.
3. Resultsanddiscussion
Toremovematerialfromthepeaksoftheworkpiecesur-
face, the strength of the FMAB must be high enough to
overcome the resistance offered by the workpiece material
to deform. The magnetic force controlled by the input cur-
rent to the coil of the electromagnet, plays a dominant role
in strengthening the brush as well as in controlling micro
indentations by active abrasive particles trapped randomly
betweentheironparticlesandtheworkpiecesurface.Asthe
current/magneticfieldstrengthincreases,themagnetization
of iron particles increases hence they come closer to each
other.TheseparticlesarehavingtrappedSiCabrasiveparti-
cles between them. As a result, the density of the brush as
wellasmechanicalstrengthofthebrushgetincreased.Hence,
brushisstrengthenedbyincreasingthefieldstrengthinthe
workinggap.
Thenormalmagneticforcecalibrationcurve(Fig.3)indi-
catesthatthereisacloserelationshipbetweenthemagnetic
force/finishing pressure and the supplied current at differ-
ent working gaps. This relationship suggests that the depth
ofpenetrationbyabrasiveparticleintheworkpiece,canbe
controlledbyvaryingcurrenttotheelectromagnet.
The surface roughness profiles alone do not reflect the
behavior of abrasive cutting edges. Therefore, the scanning
electron microscope and atomic force microscope images
ofthemagneticabrasivefinishedworkpiecesweretakento
provide an in-depth comparison of the surfaces generated
by FMAB. All samples to be subjected to MAF were pre-
finishedbysurfacegrinding.Thesurfaceroughnessprofiles
oftheworkpiecesurfacesobtainedbeforeandafterfinishing
are shown in Fig. 4a–e. The corresponding SEM and AFM
micrographs of surface texture generated before and after
MAF are shown in Figs. 5 and 6, respectively. The images
ofthesurfacebeforeandafterMAFprocesswithhorizontal
cross sections at certain places are shown in Fig. 7. It has
beenfoundthatthesurfaceroughnessvaluedecreaseswith
increasing field strength, and the use of finer grain (higher
mesh number) has become effective in obtaining smoother
surfaces.
Fig. 5a–d show typical SEM micrographs of the as-
receivedgroundsurfaceandmagneticabrasivefinishedsur-
faces.Theobservationsrevealthatthefinishingofworkpiece
Fig.6. AFMimageofthesurfacetexturegeneratedby:(a)surfacegrind-
surface in this process is done by scratching/micro-cutting.
ing; (b) MAF process at input current to the magnet=0.88A, working
However, at certain locations some deep scratches/cuts are
gap=1.50mm,abrasivegrainmeshno.=500,andno.ofcycles=11;(c)
alsoobservedwhichmaybeduetothelocalizedlargerpres- MAFprocessatinputcurrenttothemagnet=0.75A,workinggap=1.75mm,
sureonthegrain. abrasivegrainmeshno.=800,andno.ofcycles=9.
D.K.Singhetal./Wear259(2005)1254–1261 1259
Fig.7. AFMimageofthecrosssection(a)beforeand(b–c)afterMAF.
Howevergrindingmarks,pitsanddigsshowninFig.5a (finer abrasive particles). Fig. 6a shows rough surface with
disappearafterMAFinFig.5b–d,butfinescratchingmarks many steep-sided grooves with width less than 10(cid:1)m. The
produced by the FMAB appear on the surface. These fine surface generated by surface grinding (Fig. 5a) consists of
scratches would disappear by using higher mesh number deepscratchesproducedbytheinteractionofabrasivecutting
1260 D.K.Singhetal./Wear259(2005)1254–1261
pointswiththeworkpiecesurface.Sidewaydisplacementin FMABathighermagneticfieldstrength.Fig.7bandcshow
someofthescratchescanalsobeseeninFigs.5aand7a.The thesurfacetexturegeneratedbytheflexiblemagneticabra-
groovesofwidthlessthan10(cid:1)mareseeninatomicforcemi- sivebrushconsistingofsomepits.Fig.7bandcclearlyshow
crograph (Fig. 6a) resulting in rough surface (Fig. 4a). The themagneticabrasivefinishedsurfaceconsistingofshallow
initialsurfaceroughnessprofilehasperiodicpeaksandval- lays.
leysgeneratedbysurfacegrindingasshowninFig.4a.Most
ofthepeakshavebeenshearedofftoamuchsmallerheight
bytherotationofflexiblemagneticabrasivebrush(Fig.4b,
4. Conclusions
dande)resultinginimprovedsurfacefinish.Itcanalsobe
seenintheprofilethatthewidthofthepeaksandvalleyshas
Following inferences have been derived on the basis of
alsobeenreduced.Thismeansthatsurfaceprofilesproduced
aboveresultsanddiscussion.
during grinding have been sheared off and the new surface
profiles(peaksandvalleys)havebeenproducedduringMAF • TheSEM/AFManalysisshowsthatthefinishedsurfacehas
process.Thewidthandheightoftheseprofilesarequitedif-
fine scratches/micro-cuts which are farther distant apart
ferentfromthoseobtainedbygrindingprocess.Thesurface
resultinginsmoothenedsurface.Butthesefinescratches
finish can be further improved by using higher grain mesh
would also disappear/become invisible by using higher
number(smallergrainsizein(cid:1)m)asshowninFig.4e.This
meshnumber(finerabrasiveparticles).
isdepictedintheSEMmicrographs(Figs.5dand6c). • The analysis of the surface finished by MAF process re-
Keepingthesamecompositionofferromagneticandabra-
vealsthatthemicro-cuttingandscratchingarethemecha-
siveparticles,smallerthegrainsize(highergrainmeshnum-
nismsresponsibleforfinishing.
ber) chosen, smaller will be the depth of penetration. As a • The magnetic abrasive brush, which is flexible, changes
result, final work surface profile will have smaller width of
its shape to adapt to the workpiece surface irregularities,
the peaks and valleys hence lower Ra value. Finally better
therebyremovingthematerialfromthepeaksofthework-
surfacefinish(Figs.4eand5d)isobtained.Thegritmotion
piecesurface.Further,duetonon-uniformstrengthofthe
relativetotheworkpieceisalsoeasilyidentifiedfromthedi-
FMAB, the finished surface is also non-uniform in na-
rectionalityofthescratchesformedbytherotationofFMAB.
ture as is evident from the micrographs. Hence, if jum-
ItcanbeseenfromtheSEMmicrographs(Fig.5b–d)that
bling/refreshing of the ferromagnetic and abrasive parti-
someareasofthesurfacearequitesmooth,butstillthereare
clescantakeplaceduringMAF,thenitwouldgivemore
some fine scratches which can be attributed to the abrasive
uniformsurfaceafterMAFinlessertime.
particlesactingassharpindentersandhavingmorelocalized
strengthofthebrushtoindentdeepercomparedtootherabra-
sives.Thescratchwidthseemstobelessthan0.5(cid:1)mandthe
Acknowledgements
lay marks can be seen farther apart resulting in reduced Ra
value(Fig.4dande).
The authors acknowledge the financial support of De-
The AFM image of the ground surface (Fig. 6a) shows
partment of Science and Technology, Government of In-
peaks as high as 500nm which have been sheared-off by
dia for the project no. SR/S3/RM/025/2003 on “Investiga-
theflexiblemagneticabrasivebrushresultinginheightsless
tionsintoMagneticAbrasiveFinishing(MAF)ofPlaneSur-
than200nm(Fig.6bandc).Theheightsofthepeaksarenon-
faces”. Authors also acknowledge with thanks the help of
uniformbecauseFMABstrengthaswellasabrasiveparticles’
Prof.M.Sachchidanand,ElectricalEngineeringDepartment,
protrusion heights are non-uniform. Smaller peaks indicate
I.I.T.Kanpur.Mr.DineshDeva,ChemicalEngineeringDe-
theareainwhichabrasiveparticleswereheldmorestrongly
partment, and Mr. Kisun K. Saren. Mechanical Engineer-
than other areas and hence could reduce the peak heights
ingDepartment,IndianInstituteofTechnologyKanpurhave
more compared to other areas. From this discussion, it can
helped in carrying out the experiments and analysis of the
beconcludedthattheFMABstrengthisnon-uniformandthe
work. The International Divisions of the National Science
distributionofactivecuttingedgesinteractingwiththework-
Foundation (Washington) and Department of Science and
piecesurfaceisnothomogenousinthebrush.Thetopography
Technology, New Delhi, is acknowledged with thanks for
oftheworkpiecesurfacesbeforeandaftertheMAFprocess
thesupporttothejointUS–Indiaproject.
has been obtained from AFM as shown in Fig. 7. Fig. 7a
showsdeepunidirectionalcuttingmarksanddeepgroovesof
differentwidthsduetohardandvaryingprotrudingheightof
grainsembeddedinthebondedgrindingwheel.Thenumber References
ofactiveabrasivegrainsinMAFisflexible,andgetsincreased
ordecreasedbecausetheyarebondedbythemagneticforce [1] V.K. Jain, Advanced Machining Processes, Allied Publishers, New
Delhi,2002.
whichchangesdependinguponthenumberofthesurround-
[2] T. Mori, K. Hirota, Y. Kawashima, Clarification of magnetic abra-
ing iron particles and the magnitude of the magnetic field.
sive finishing mechanism, J. Mater. Possess. Tech. 143–144 (2003)
Therefore,grindingmarkshavebeenquicklyreplacedbythe 682–686.
D.K.Singhetal./Wear259(2005)1254–1261 1261
[3] M.Fox,K.Agrawal,T.Shinmura,R.Komanduri,Magneticabrasive [8] D.K. Singh, V.K. Jain, V. Raghuram, Superfinishing of alloy steel
finishingofrollers,Ann.CIRP43(1)(1994)181–184. using magnetic abrasive finishing process, in: Proceedings of the
[4] T. Shinmura, K. Takajava, E. Hatano, Study on magnetic abrasive 18thAnnualASPEMeeting,2003.
process—application to plane finishing, Bull. Jpn. Soc. Prec. Eng. [9] H.Yamaguchi,T.Shinmura,Studyofaninternalmagneticabrasive
19(4)(1985)289–291. finishingusingpolerotationsystem,Prec.Eng.24(2000)237–244.
[5] H. Yamaguchi, T. Shinmura, Internal finishing process for alumina [10] H. Yamaguchi, T. Shinmura, Study of the surface modification re-
ceramic components by a magnetic field assisted finishing process, sulting from an internal magnetic abrasive finishing process, Wear
Prec.Eng.28(2004)135–142. 225–229(1999)246–255.
[6] K. Takajava, E. Hatano, Study on magnetic abrasive process, Bull. [11] D.K. Singh, V.K. Jain, V. Raghuram, Parametric study of magnetic
Jpn.Soc.Prec.Eng.21(2)(1987)139–141. abrasivefinishingprocess,J.Mater.Possess.Tech.149(2004)22–29.
[7] T. Shinmura, T. Aizawa, Study on magnetic abrasive finishing pro- [12] H.Degnall,ExploringSurfaceTexture,seconded.,RankTaylorHob-
cess,Bull.Jpn.Soc.Prec.Eng.23(3)(1989)236–239. sonLimited,Leicester,England,1986.