The document discusses advances in abrasive flow machining (AFM) and orbital abrasive flow machining technologies. AFM uses a semisolid abrasive media to deburr, polish, or radius surfaces by flowing it over target areas. Orbital abrasive flow machining combines AFM with an orbital grinding motion to uniformly remove material from complex shapes. Both techniques can process a variety of materials and have applications in aerospace, automotive, and other industries.

1. - ~-
Z
Society of
Manufacturing
Engineers
2001
MROI -217
Advances in Abrasive
Flow Machining
author(s)
J. RANDALL GILMORE
OrbiTEX Division Manager
Extrude Hone Corporation
Irwin, Pennsylvania
abstract
Abrasive flow machining (AFM) is used to deburr, polish or radius surfaces
and edges by flowing a semisolid abrasive media over these areas. The
process embraces a wide range of feasible applications: from critical
aerospace and medical components to high production volumes of parts.
Orbital abrasive flow machining (orbital polishing) is a hybrid technology that
combines abrasive flow machining and orbital grinding, providing a
technology that can uniformly remove material from virtually any complex-
shaped component to achieve burr removal, radiusing or surface finish
improvement. The orbital polishing process is highly effective in finishing a
variety of materials including aluminum, tool steel, stainless steel, tungsten
carbide and ceramics.
conference
INTERNATIONAL HONING
April 4-5, 2001
Brookfield (Milwaukee), Wisconsin
terms
Abrasive Flow Radius
Deburring Honing
Polishing Orbital
Society of Manufacturing Engineers
One SME Drive l P.O. Box 930 l Dearborn, MI 48121
Phone (313) 271-l 500
www.sme.org
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

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Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

3. Advances In Abrasive Flow Machining Technology
Randy Gilmore
Extrude Hone Corporation
INTRODUCTION
Abrasive flow machining (AFM) is usedto deburr,polish or radiussurfacesand edgesby flowing a
semisolid abrasivemediaover theseareas.Theprocessembracesa wide rangeof feasibleapplications: from
critical aerospaceandmedical componentsto high productionvolumesof parts.AFM canreacheventhe most
inaccessibleareas,processingmultiple holes,slotsor edgesin oneoperation.The AFM processcanbe usedin a
wide rangeof finishing operations:it canprocessmanyareason a single workpiece or multiple parts
simultaneously; inaccessibleareasand complexinternal passagescanbefinished economically and productively;
automatic systemscanhandlethousandsof partsperday,greatlyreducing labor costsby eliminating tedious hand
work.
Orbital abrasiveflow machining (orbital polishing) is an emerginghybrid technology that combines
abrasiveflow machining andorbital grinding. This combinationprovidesatechnology that can uniformly remove
material from virtually any complex-shapedcomponentto achieveburr removal, radiusing or surfacefinish
improvement. Orbital polishing utilizes aviscoelasticpolymerladenwith abrasivesasthe polishing “tool.” Sincethe
polymer actsasapolishing tool only when underpressureor when it meetsarestriction, a mechanical action is
utilized to createthe restriction. The orbital polishing processhasbeendemonstratedto be highly effective in
finishing a variety of materialsincluding aluminum,tool steel,stainlesssteel,tungstencarbide and ceramics.
THE BASICS
The typical AFM systemusestwo vertically opposedcylinders which extrude an abrasivemedia backand
forth through passagesformedby the workpieceandtooling (Figure 1).Abrasive action occurswherever the media
entersand passesthrough the mostrestrictive passages.Theextrusion pressureis presetfrom 100to 3,000 psi, as
well asthe displacementper strokeand the numberof reciprocatingcycles.The processis abrasiveonly wherethe
flow is restricted:the extrusion area.The machiningactioncomparesto agrinding or lapping operation asthe
abrasivemediagently anduniformly honesthesurfaceor edges.Materials from soft aluminum to tough nickel
alloys, ceramicsandcarbidescanbe successfullymicro-machinedwith this process.
Figure I -Abrasive Flow Machining Process Schematic
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

4. 2
Tooling
Thetooling holdsthe workpiece in position anddirects the abrasivemediato the appropriateareas.Many
AFM applicationsrequireonly simple fixturin,.a- diestypically needno specialtooling; the die passageitself
providestherestriction for the flow path.For external edgesor surfaces,tooling is usedto restrict the flow between
the outsideof thepart andthe inside of the fixture (Figure 2). The tooling may also serveto restrict flow at areas
whereabrasionis desiredor to block the flow through areasto remain unaffected.
Figure 2 - For processing external edges, the part is contained within afixture toform aflow restriction between
the outside of the part and the inside of thefixture.
High productionfixtures aredesignedto facilitate part loadin,,0 unloading andcleaning. Often mountedto
indexing tables,thesefixtures may hold multiple partsfor processing in oneoperation.
Media
Themediais composedof apliable semisolid carrier and aconcentration of abrasivegrains(Figure 3). The
viscosity of thecarrierandthe abrasivegrain size,type and concentration canbe varied to achievespecific finishing
results.Higher viscosity, nearly solid mediais usedfor uniformly abradingthe walls of largepassages.Lower
viscosity mediais generallyappropriatefor radiusing edgesand for processingsmall passages.Whenforced into a
restrictivepassage,the viscosity of the mediatemporarily rises, holding the abrasivegrainsrigidly in place.The
mediaabradesthepassagesthrough which it flows only when in this viscous state.The viscosity returnsto normal
whenthethickenedportion of mediaexits the restrictive passage,producing little or no abrasion.
Mediaviscosity, extrusion pressureandpassagedimensions determinethe mediaflow rate(thespeedof the
abrasiveslugpassingthrough the restrictive passage)which affects the amount of abrasion,the uniformity of stock
removalandtheedgeradius size.The flow ratesarecalculated by dividing the flow volume by the processingtime.
Slowslugflow ratesarebestfor uniformly removing material; high slug flow ratesproducelargeredgeradii.
Theabrasivegrainsaremostcommonly madeof silicon carbide, although boron carbide,aluminum oxide
anddiamondmayalsobeused.Particlesizesrangefrom 0.0002 to 0.060 inch. The betterthe startingfinish, the
smallerthegrit sizeusedfor processin,.0 The larger abrasivescut at afasterrate,while the smallersizesprovide
finer finishesandaccessibilityto small holes.The depthof cut madeby the abrasivegrains atthe surfacedependson
theextrusionpressureapplied andon the stiffnessof the media aswell ason the sizeof the abrasivegrains.Air or
vacuummaybeusedto removethe mediafrom accessedareas.Final tracescanbe extractedin asolventwash.
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

5. Figure 3 - A central element of the AFMprocess is the media,
a polymer carrier mixed with abrasives.
In the AFM process,the abrasivecutting particlesbreakandbecomedull, and the abradedmaterial
becomespart of the abrasivemedia.The effectivelife of themediadependson anumber of factors including the
initial batch quantity, the abrasivesize andtype,the flow speedandthepart configuration. Typically a machine load
of media canbeusedfor weeks,processingthousandsof parts,beforereplacement.
Applications
AFM offersprecision,consistencyandflexibility to a wide rangeof applications in aerospace,automotive,
production anddie finishing. Other applicationshavebeendevelopedin areasasdiverseassurgical implants and
centrifugal pumps.The processwas initially developedto performcritical debut-ringof aircraft valve bodiesand
spools,providing burr freeinternal edges,routinely passing20X microscopicinspection while producing precisely
controlled edgeradii (Figure 4).
Figure I - Intersecting holes on an air
shown before a!nd
--
*craft turbine fuel control valve body
after processing
The AFM processcanbeapplied to awide rangeof part andpassagesizes-from gearsassmall as0.060
inch in diameterandorifices assmall as0.008inch to splineddie passages2 inchesacrossor turbine disks nearly 4
feet in diameter.Largeworkpiecescanbefixtured ontracksystemsfor transferringto andfrom the processing
station.
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

6. Oneof theprimary advantagesof the extrusion honing processlies in the uniformity of the polished
surface,especiallywhencomparedto tedious, manualfinishing methods.This advantageleadsto otherbenefits
directly associatedwith lower labor costswith improved part performance,longer life, lessscrapandrework and
reducedinspectiontimes.Precise,polished edgeradii areproduced on the edgesof fir treeslotsof turbine disks by a
numberof aircraft enginemanufacturersusing the abrasiveflow process.Uniform radii on both sidesof eachfir tree
aregeneratedin asingle controlled operation providing fatigue strength improvement (Figure 5).
Figure 3 - Extrude honed surfaces provide improved airflow,
increasing engine efficiency andperformance.
Aircraft turbine enginecomponentscanalsobereworked with AFM to remove cokeandcarbondeposits,
improve surfaceintegrity, or enhanceeddy current readings.In a seriesof testsperformed in cooperationwith
United Technologies,Pratt& Whitney, the ability of Extrude Hone’s abrasiveflow machining processto generate
residualcompressivestresseswasestablished.First effort testson titanium and nickel sampleshaveinducedresidual
compressivestressesup to 130ksi atthe surfacewith atotal depth of up to 0.002 inch. This offersconsiderable
potential for generatingcompressivestresses-particularly in areaswhich cannot be conveniently shotpeenedlike
impellers,IBR’s andblades-while simultaneously improving surfaceroughness.
One-Way Flow
Recentlydeveloped“one-way” AFM systemsflow the abrasivemediathrough the workpiecein only oneRecentlydeveloped“one-way” AFM systemsflow the abrasivemediathrough the workpiecein only one
direction for thoseapplicationswhich require little or no work to be doneon the exiting side.This patentedtechniquedirection for thoseapplicationswhich require little or no work to be doneon the exiting side.This patentedtechnique
allows themediato exit freely from the part for fastprocessinallows themediato exit freely from the part for fastprocessing,g, easycleaning and simple, quick-changetooling.easycleaning and simple, quick-changetooling.
WorkpiWorkpi
Figure 6 - One- WayAFM SchematicFigure 6 - One- WayAFM Schematic
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

7. 5
Flow resistanceof air cooling passageson blades,vanesandother componentscanbeprecisely “tuned”
with the one-wayflow process.Absolute removal of thermal machining recastafter EDM or lasermachining can
significantly improvethe fatigue strengthand life of highly stressedcomponents.The internalsof castturbine blades
arepolishedto increaseairflow (Figure 7). Media entersthrough the root sectionandexits through the trailing edge.
AFM canalsobeusedto radiusthe edgesof the turbulators or trip strips and/or sizethe cooling holes.
Figure 7 - Thefinalfinish on these cast blades is less than 20% of the original.
ExtrudeHone’sprocessis alsousedto improve the airflow of vane segmentswhich werepreviously
scrappedbecauseof insufficient airflow. By polishing the internal airflow passagesfor apredeterminedlength of
time, over95%of thepreviously discardedvanesegmentsare reworked to specification andplacedinto service.
The sprayholesof adieselinjector nozzle areAFM processedto provide increasedfuel flow (increased
hereby 20%).Notetheexit sideof the hole remainssharpwhile the processproducesauniform radius on the inside
diameter.The entry radius,finish improvementandtaper reduction all contribute to enhancingthe flow capacity and
durability of the orifice. Flow ratesof orifices canbe ‘tuned’ to within 2 1%of total flow.
Figure 8 - The spray holes of a diesel injector nozzle shown before and after processing
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

8. 6
Diesel injector bodiesand valves arealsoprocessedon one-way systemsto producegenerousradii on th
intersectionsof the high pressureholes to improve high cycle fatigue strength.Strict dimensionaltolerancesare
maintained (Figure 9).
Figure 9 - Intersecting holes on diesel injector bodies are processed
on one-way AFMsystems.
In an internal combustion engine, the major componentsthat comprisethe air/fuel induction system-
cylinder headsand intake manifold-are usually manufacturedby metalcasting.This processformsthe complical
passagewaysrequired to channelthe air/fuel mixture into the combustion chamberfor ignition. Thesepassageway
aretoo complex to be economically machined by conventional machining or grinding. The castpassagesvary in
shapeandposition and haverough, irregular surfaceswhich generate“boundary layer turbulence” which retards
airflow. This turbulence hassignificant impact on the performance,fuel efficiency andemissionsof automotive
e
ted
‘S
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

9. 7
engines.TheAFM processis not simply enlarging the airflow passages;testshave shownthat componentpassages
of like size,oneAFM’d andonenot, differ greatly in engine performance,even if massairflows aresimilar. The
AFM processis improving the surfacefinish on the passagewalls to allow for better airflow characteristicsthat will
resultin significant performanceimprovementsin an internal combustion engine 0.
Figure I o- Automotive engine intake manifolds are abrasive flowed to improve airflow, increase hot
andfuel economy.
esepowler torque
ORBITAL ABRASIVE FLOW MACHINING (ORBITAL POLISHING)
Orbital polishing utilizes much of the samemethodology asabrasiveflow machining, but addsa
mechanicalmotionto provide the ability to polish three-dimensional forms not possibleto bepolished by
conventionalabrasiveflow machining. This mechanicalmotion is typically ahorizontal planetaryoscillation that
createsrelativedisplacementbetweentooling andthe workpiece. The oscillation canbeoriented in planesother than
horizontal whenrequiredto addressgeometricfeaturesthat a horizontal oscillation alonecannotaccommodate.
Theseoscillationscanbein the vertical plane or acombination of horizontal andvertical planes,yielding an
elliptical or gyratory polishing action (Figure 11).
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

10. 8
Orbital Vibration
Viscoelastic
Figure I I - Orbital Polishing Schematic
Process Parameters
In addition to thoseparametersthat affectthe abrasiveflow process,orbital polishing is impactedby
parametersassociatedwith the mechanical motion, aswell. Orbital amplitudedeterminesthe materialremoval rate,
with higher amplitudes yielding higher materialremoval rates.However, orbital amplitudecannotbelargerthan the
minimum internal feature of the workpiece to bepolished. Whenpolishing smallinternal features,acorrespondingly
small orbital amplitude mustbeutilized to effectively polish all areas.
The speedof the oscillation, in combination with the orbital amplitude,alsodeterminesthematerial
removal rate.Unlike orbital amplitude, speedof oscillation is not impactedby thegeometryof theworkpiece.
Typically the oscillation speedis between400and 1200RPM.
Tooling
Unlike abrasiveflow machining, wherethe passagethrough the workpieceis therestriction, tooling for
orbital polishing must be constructedto createarestriction in three-dimensionalparts.Workpiecesthat areflat, near
flat, spherical,or gently slopedtypically do not require restrictive tooling. Forthoseinstanceswh,enrestrictive
tooling is required, a mandrel is constructedto the mirror imageof the workpiece.This mirror-imagedmandrelmust
be undersizedwith respectto the cavity to bepolishedto accommodatetheorbital amplitude.
The restrictive tooling for orbital polishing is commonly constructedby eitherconventionalmachining or
by casting.The material of preferencefor therestrictive tooling is pressuremoldednylon or polyurethane.Steelor
aluminum tooling is normally not desirabledueto cost,weight, difficulty of machining,andperformancein the
polishing process.Nylon andpolyurethane both exhibit goodwear characteristics,but moreimportantly these
material tend to compressunder media pressure,allowing the abrasivenatureof the mediato adhereto the
restrictive tooling, rather than the workpiece.
Media
The media employed for orbital polishing is similar to that usedin abrasiveflow machining in that it is a
viscoelastic abrasivepolymer. The polymer is ahighly viscous liquid at normalpressure,but whensubjectedto
elevatedpressuresor flow path restrictions transformsinstantaneouslyto asemi-solid.This semi-solidmediacanbe
likened to athree-dimensional grinding stonethat works uniformly on all surfaces.Orbital polishing mediais
typically of ahigher viscosity than abrasiveflow mediaandwill commonly havehigher concentrationsof abrasives.
For polishing of moststeels,aluminum andothermild materials,silicon carbideis the predominant
abrasivetype. When polishing harder materialsandor extremely hard surfacelayers,suchasthoseassociatedwith
someEDM finishes, boron carbide may beused.In someinstances,diamondmaybeemployedasthe abrasive.
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

11. 9
Typically, diamond is usedfor polishing tungstencarbideor other superhardmaterialsandis alsousedto achieve
extremely fine surfaceroughnessvalues (under2 pinch R,) or hig,hsurfaceluster.An orbital polishing systemis
shown in Figure 12.
Figure 12 - Orbital Polishing System
Applications
The orbital polishing processhasbeendemonstratedto be highly effectivein finishing avariety of
materialsincluding aluminum, tool steel,stainlesssteel,tungstencarbideandceramics.The processhasprovento
becapableof surfaceroughnessimprovementsof 20 to 1in most situations,but asgreatas50to 1attimes.As an
example,diesusedto produceproof coins for the United StatesMint werereceivedwith a20 pinch R,surface
roughnessand subsequentlyprocessedby orbital polishing to a surfaceroughnessof 0.4 lunch R, in acycle time of
seven(7) minutes (Figure 13).In this case,therequirementwas for very low surfaceroughnessandhigh surface
luster. Sincethe contour of the dieswasonly slightly convex, restrictive tooling wasnot required.Dueto the
requirementfor fine finish andhigh luster acombination of micron sizeddiamondabrasiveswereemployedin the
media.
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

12. to e:itren
injiec:tion
astLmgsf
hi]Psand
1Iuinch:
Figure I3 - Photos of coining diefor the United States Mint shown
before and after polishing
Orbital polishing appliesto awide variety of workpiecegeometries,from flat to slightly co
nely complex three-dimensionalgeometry.Otherapplication areascurrently being addressel
molds,blow molds andpunchesassociatedwith compactingdies,aswell asproduction COI
:encarbidecutting tool inserts,aluminumalloy automotive wheelsandprosthetic devices su
heartvalves. The surfaceof the milled workpieceshown in Figure 14wasimproved from a
finish.
nvex or cN
d inelude
nP(Itrents
,chaskne
20 pinch
one
su
,es,
to
:ave
ch
a
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

13. 11
Figure 14 - This mold cavity was polished in a 15 minute cycle
On the other end of thespectrum,theprocessis capableof massmaterial removal to enhancethe fatigue
strengthfor aerospacecomponents.Theprocesshasbeendemonstratedto beeffective in imparting compressive
residual stressto workpiecesthat,prior to orbital polishin,,0 displayedhigh valuesof residual tensional stress.
Figure I5 - Orthopedic components shown before and after polishing
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.

14. 12
Workpiecematerial,while having an impact on cycle time, is not alimiting factor in the processof orbital
polishing. Hardermaterials,suchastungsten carbide andcertain ceramicmaterials,mustbepolished with harder
abrasivegrainsandmayrealize longer polishing cycle times, but the processtypically is still considerablyfaster
thanthe manualpolishing processescommonly employed.
SUMMARY
Abrasive flow machining finishes surfacesandedgesby forcing aflowable abrasivemediathrough or
acrosstheworkpiece.Abrasion occursonly where the mediaflow is restricted;other areasremain unaffected.It can
processmanyselectedpassageson aworkpiece simultaneously, reaching eventypically inaccessibleareas.Several
or dozensof partscanbeprocessedin onefixture, yielding production ratesof up to hundredsof partsperhour. A
variety of finishing resultscanbeachievedby altering theprocessparameters.Tooling canbe designedto be
changedin minutesevenin production applications. The AFM processboastsreliability andaccuracy,typically
yielding a90% improvementin surfacefinishes with stockremoval controllable to within 10%of the stock
removed.
Orbital polishing is proving to beapromising technology for automaticpolishing, radiusing andburr
removalon awide variety of componentgeometriesandmaterials.Blind cavities, external geometries,punchfaces,
prostheticdevicesandamyriad of other componentscanbenefit from the advantagesof fasterpolishing time,
superiorsurfaceroughnessresults,uniformity, repeatability and cleanlinessoffered by orbital polishing. As arule,
orbital polishing canbeexpectedto improve surfaceroughnessby a factor of 5 or 10to 1routinely, with many
applicationsrealizing a20 to 1improvement,and in someextremecircumstancesasmuchasa 50 to improvement.
This emergingtechnology, while alreadyvery promisin,,0 is expectedto evolve in the coming monthsto becomea
widely-utilized finishing technology.
Copyright (c) 2001 Society of Manufacturing Engineers. All rights reserved.