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Benoit GOELDEL, Julien VOISIN, Didier DUMUR, Mohamed EL MANSORI, Marc FRABOLOT
-Flexible right sized honing technology for fast engine finishing - CIRP Annals - Manufacturing
Technology - Vol. 62, n°1, p.327-330 - 2013
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Flexible
right
sized
honing
technology
for
fast
engine
finishing
B.
Goeldel
a,c,*
,
J.
Voisin
a,
D.
Dumur
(1)
b,
M.
El
Mansori
a,
M.
Frabolot
(3)
c aArts&Me´tiersParisTech,LMPF,EA4106Chaˆlons-en-Champagne,FrancebSUPELECSystemsSciences(E3S)EA4454,ControlDepartment,Gif-sur-Yvette,France c
RenaultS.A.S.PowertrainDivision,RueilMalmaison,France
Theconventional honingprocesswhich produces atextured liner surface with a honing angle close to 458 pertains in automotiveindustryforover40years.Theevolvingofpollution standardsinthelasttenyearshaschangedtheprocesswiththe application of a plateau honing technology. This technology removestherunning-inof theengineafter assembly[1].Some manufacturersareengagedinhelicalslidehoning(HSH,witha honingangleof1358)toincreaseengineperformancesbyreducing friction [2]. However, this process requires over-sized honing machinesandalongcycletime.Thelatestenginedevelopments tendtowardcrankcasemadeentirelyofaluminumofwhichonly functional cylinder surfaces are coated with shirts deposit extremelyhard. Thisdeposit ensurestheretention ofoil byits porosity;thesurfacemust,however,behonedtobeassmoothas possiblebeforeanassemblywiththepistonandrings.
Toreducethemanufacturingcycleandgetaright-sizedhoning machine for development, a new prototype of vertical honing machinewasdesignedwithhighdynamicperformances.Adigital controller allows thesynchronized control of the rotation and stroke axis and allows interpolation of trajectories. The radial expansion can be hence controlled in positionor in force. We soughtnewpathswiththe aimtoincrease productivityof the processandtogeneratenewtextures.
Thispapercompares theperformanceoftheprototype with thoseofconventionalmachinesbeforepresentingsomeoriginal newmethods.
1. Thehoningmachine
The honing operation of cylinder block liners consists of removingmaterialbyabrasioninsidethecylindersboredtoobtain agoodqualityofthecylindricalsurface.Thisqualityisdefinedat
threelevels:atthemacroscopiclevelthecylindricalshapemust satisfythedimensionalcriteria,roughnessatthemicroscopiclevel isspecifiedbythedesignersoftheengine,atthemesoscopiclevel, the surface appearance of a texture must be defined in the specificationofthesurface.Toachievetheseobjectives,thehoning operationmustimplementabrasivestonesthataremountedonan expansionhoningtool.Thehoningtoolhasthefeaturetopushthe stones forcontacting withthe cylindricalsurface. The material removedbyabrasionrequirescuttingspeed[3].Thecuttingspeed definedbytherelativespeedbetweentheabrasivegrainsandthe machinedsurfaceisgivenbythecombinationofamovementof rotationandtranslationofthehoningtoolaboutitsaxis.Fig. 1 showsthekinematicsofahoningmachinewithonepin.TheZ-axis ofthepinistheaxisofthehoningtoolandofthecylinder.
InconventionalhoningstrokesalongtheZ-axisarelinearand therotationalspeedisconstant.Followingthetrajectoryofthese movementsformhelicescrossedattheangle
a
/2.Thepatternleft bytheabrasivetracesthereforehasstreaksthatcrosseachotherat theanglea
,theangle ofgrinding. Tosatisfy differentlevelsof qualityofhonedsurface,thehoningoperationisoftendividedinto severalstages.Ingeneralonefirststep,theroughing,isperformed with large grains to obtain effective material removal and correctingtheshape.ThenthefinishingstepscancombineseveralKeywords: Honing Machine Superabrasive
ABSTRACT
Thepaperdiscussesaflexiblehoningtechnologybydescribingthenewprototypemachinewithits specificity.Threeoriginalmethodsproducedbytheflexiblehoningprototypehavebeenstudied.Apath combinesthetwocontemporarymethodsofindustrialhoning:thehelicalslidehoningat1358atthe bottomofthecylinderandtheconventionalhoningat458ontheupperpart.Thismethodofhoningshows theeffectivenessofspecificmotiontrackingtoremovetracesofinversions.Circulartrajectorieswithlarge radiicanbetraveledquicklywithoutconsumingtoomuchenergy.Thehighcuttingspeedpromotesthe removalofmaterialthussavingtime.Finally,themulti-circlepathscangetoriginaltexturesthusproving thefeasibilityofallpatterns.
Fig.1.Honingmachinekinematic.
* Correspondingauthorat:Arts&Me´tiersParisTech,LMPF,EA4106 Chaˆlons-en-Champagne,France.Tel.:+33661531023.
abrasives toachieve low roughness. Theconfiguration ofthese conventionaloperationsisoptimizedempiricallytoachievehigh productionrates.Theoptimizationoftheparameterscanbedone withtheaidofasimulation[4].
1.1. Characteristicsofclassicalhoning
Honingprocess,likedrilling,requiresonlytwoaxestofulfillthe motionofthetool:rotationandaxialtranslation.Likeanymachine toolandaccordingtotheconvention[5],therotationaxisofthe toolisdesignatedastheZ-axis.Onmostmachines,theworkpiece isfixed andthetoolperforms themovement.Traditionally, the linearactuatorisahydrauliccylindercontrolledinposition.The stock removal is obtained by generating a contact pressure between the stonesand thecylindrical surface of thecylinder bore.There are two differentkind of actuator to perform this movement:hydraulicandelectromechanicalsystems,asshownin Fig. 2. For hydraulic system, the cuttingforce is given by the hydraulicpressuresupplyoftheactuator.
Electromechanicalsystemsarenaturallydriveninposition.The positionsetpointisoftenexpressedinmicronsandcorrespondsto adiameterthatisabsoluteorrelativetoadvanceabrasivestones. Some techniquesfor detectingthe radial positionof contacted stones have been patented [6]. The observed diameter of the advanceoftheexpansionisnotnecessarilyidenticaltothereal diameterofthecylinder,becausethewearoftheabrasiveisnot takenintoaccount.Ontheotherhand,in-processmeasurement givesa truemeasureofthediameter.Thecontrolcalculatesthe abrasivewearbycomparingtheevolutionoftheactualdiameter andtheradialfeedoftheabrasivestones.
Theprincipleofdoubleexpansionhoningtoolwaspatentedin 1986byindustrialcompanyNagel[7].Adoubleexpansionhoning tool has two sets of stones that are separately operable. The superpositionof two concentric cams, depicted in Fig. 2, can activatebothsetsofstonesindependently.Thisdoubleexpansion allowstwosuccessivestepswithoutchangingtoolsinordertosave cycletime.Onconventionalmachines,thespindlesarefrequently equippedwithoneelectromechanicalexpansionandone hydrau-licalexpansion.
1.2. Characteristicsandperformanceoftheprototype
The prototype machinethat wedesigned operatesthesame typeofhoningtoolasconventionalmachines.
Inordertomeettheneedstoexceedthedynamicperformance ofexistingmachines,wechoseaninvertedarchitectureillustrated inFig. 3.
Thelinerisclampedinaworkpieceholderandisdrivenina translation motion. While the rotating tool remains at a fixed height. This solution minimizes the moving masses, prevents vibrationsand thejolts in thetool, and canpass on processes requiringhighcuttingspeedandstrongmomentum.Themotion lawgoverningthebeatisverydynamic.Thereversalofthespeedat theendofthestrokeinvolveshighacceleration.Theintegrationof ahighperformancelinearmotorof7kWontheprototypeallows
achievinghightravel speeds(60m/min)withhighacceleration (50m/s2). With the integrated incremental rule in the electric
motor,theautopilotprovides positioningat5
m
mthat ismuch moreaccuratethanhydraulicsystems(1mm).Ingeneral,onconventionalmachines,therotationisprovided by asynchronous electric motors controlled in speed (50– 2500rpm).The prototypemachineis equippedwithan electric motorwithpermanentmagnetmounteddirectlyon thespindle axis.Thistechnologycontrolledinpositionorinspeedensuresa torquegreaterthan50Nmatastandstillandatverylowspeed,up to450rpm.
Table 1 shows the main characteristics of the prototype machinecomparedtocurrentmachines.
Couplingthelinearmotorforthestrokeandmotortorquefor rotationenablesasynchronizedpilotinginpositionofthetwoaxes totrackoptimaltrajectory.Asanumericallycontrolled machine tool, it is possible to interpolate the linear or circular paths describedinISOlanguageG-Code[8].
Theaxisexpansionrequiresaspecialperformancetomeetthe specifications of the prototype machine. It must perform both functions of the two current systems. The selected hardware solutionistocombineanelectromechanicalactuatorandaforce sensorat theend oftherod. Theforcecontrolis performed by controlling the command on the force sensor. The machine includesasystemforacquisitionofallthephysicaldataoftheaxes andthesensors.
2. Honingpathwithvariableangle
Inconventionalhoning,theconstantrotationspeedduringthe inversionoftranslationattheendsofstrokegeneratesaparabolic trajectoryofabrasivestonesinthecylinder.Paper[9]showsthat the acceleration of inversion plays a role in the amount of horizontal traces. The prototype machine is programmed to interpolaterotation–andstrokeaxesinordertorespectapath definedbytheuser.Throughthehighdynamicperformanceofthe actuators,thisoperatingmodeallowsforprecisemonitoringofthe triangularsetpointpathtoremoveinversionstraces.
2.1. Definitionofthehoningpath
The path shown below includes a grooves angle change betweentheupperpartofthecylindricalsurfaceandthebottom. This multi-honing angle provides so-called mixed liners which have a pattern typical of HSH at the bottom to facilitate the
Fig.2.Twotechnologiesforexpansionaxis.
Fig.3.Machinewithinvertedstructure/photography.
Table1
Comparisonbetweentheprototypeandconventionalmachines.
Nagel Gehring Prototype Maximalstrokespeed 30m/min 25m/min 60m/min Accelerationofstroke 30m/s2
30m/s2
50m/s2
Rotationspeedwith torque>50Nm
50–2500rpm 50–2500rpm 0–450rpm Rotationacceleration Constantspeed Constantspeed 350rad/s2
dynamicflowandapatterntypicalofconventionalhoningonthe upperparttolimittheback-flowofoil.Wewanttoshowherethe feasibilityof sucha process,thebestcombinationofthesetwo patternsoptimizingengineperformanceshasstilltobedesigned bymeansofworkintribology.
2.2. Performanceoftheprocess
Linear interpolations for linking two adjacent programmed pointsarecrossedfollowingarampratelawtoslowdowninthe vicinity of target points. At the cusp, the cutting speed momentarilycancels inducing a nullmaterial removal. On the prototypethephenomenonisnotreallymarkedbecausetheramps of acceleration and deceleration are set to exploit the high performanceofthemachine.Thecycletimebyhoningmultiple angles is identical to the conventional method for the same thickness of material to be removed under the same cutting conditions.Linearinterpolationdoesnotaffecttheperformanceof thehoningprocessbutcorrectsinnateimperfectionsof conven-tionalsystems.
2.3. Surfacequalityobtained
Aseriesofsixlinerswereroughhonedandfinishhonedwith thistechniquebasedonthepathdescribedinFig.4.Thisfinishwas produced withidentical stonesIAS65/100 as finishing abrasive used in Renault conventional three step honing. The path is traversed with a target speed corresponding to the optimum cuttingspeed oftheabrasive,45m/min.Liketheexperimentof article[9],thetexturequalitywasassessedatthetopandbottom ofthecylinder.Fromthetop,wecancomparethequalityobserved in the liner with the classic honing at 458 equivalent to a conventionalmachine.Despitetheproximityofthereversalpoint with the measurement zone, the honing method by tracking trajectoryleavesalmostnotraceofinversions.Atthebottomofthe liner,honingangleof1358 coupledwiththespeedof45m/min cuttingputsthelinearaxisinfulluse.
Table2summarizesthedatafromtheclassicalexperiment.The criterion ‘‘visible traces’’comes fromthe visualanalysis of the entire surface by a process expert. The expert subjectively determinesifhorizontaltracesappearonthesurface.Thecriterion M-turndevelopedfortheanalysisofsuchsurfaceswasusedto quantifytheproportionofgroovesthatdidnotconformcompared togroovesthatdidconform.
The study conducted in [9] showed the influence of the accelerationontherateofnon-conformgrooves.Thedevelopment oftheprototype machineprovides away toremedysuch non-compliance.Eveninthetoughestconditions,witha highstroke
axisspeed,therespectofthesetpointtrajectoryavoidsinversions trace.Thismodeofoperationoftheprototypemachineimproves thequalityoftexturesontheconventionalgroundsurfaces. 3. Sinusoidalhoning
Trackingapathwithpointcuspsrequiresslowdownsandstops, evenveryshort,nearthesepoints.Withouttakingintoaccountthe texturethatisusuallyreferred,thetrajectorycanbeoptimizedto travelfasterwithoutstops.Weproposeatrajectorycurvebasedon sinusoidalcontrollawsandfollowingcircles.
3.1. Definitionofthehoningpath
Thistrajectoryfollowsasinglecircleonthecylinderheightand three circles on the perimeter. The large interpolation radius allows ahightravelspeed. Thetrajectoryshownin Fig. 5was obtainedatthecuttingspeedof60m/minalmostconstant.
Thispathdoesnotinvolvelargeaccelerationorjerk,itreduces energy consumption and machine wear.It canfor example be deployedinroughingoperation,withveryhighcuttingspeedfor maximummaterialremoval.Itcanthereforesavecycletime. 3.2. Performanceofthemethod
The comparison between the classic roughing process and sinusoidalhoningwasestablishedconsideringfiveseriesoftests performed withthesametoolsand thesamediamondabrasive D126.Theexpansionforceisconstantforalltestsandsetto1200N onthetoolrop.Foreachseriestheremovalmaterialthicknessis measuredaftera60shoning.Theenergyrequiredforeachtypeof testiscalculatedbyaveragingtheinstantaneouspoweracquired bythePC.Table3presentstheoverallresults.
Wenotethatatequivalentcuttingspeed,conventionalhoning andsinusoidalhoningguaranteealmostthesamecycletime.The cuttingspeedof90m/minisachievableonthesinusoidaltrajectory andreducesthecycletimeforroughing.Forequivalentcycletime and equalcuttingspeeds,the electricalpowerconsumedbythe machine is greatly reduced by the sinusoidal trajectory. As a conclusion,sinusoidalhoningreducescycletimesandconsumes lessenergythanthetraditionaldiamondroughhoning.
4. Multi-circleshoning
‘‘Multi-circles honing’’ is a new honing method based on specific honing paths to obtain circular patterns visibly inter-spersedonthesurfacetexture.Thesepathshavebeendeveloped usingsimulation[4]beforebeingimplementedontheprototype machine.
Fig.4.Classicalhoningpathanddoubleangle.
Table2
Comparisonbetweentheconventionalandanglecontrolledhoning. Method Classicala=458 Controlled
a=458 a=1358 Strokeacceleration(m/s2) 5 10 15 Max50 Max50
Visiblegrooves Yes Yes Low No No M-turncriteria 2.1 1.2 0.88 0.30 0.95
Fig.5.Sinusoidalhoningpathwithspeedandacceleration.
Table3
Comparisonbetweenconventionalandsinusoidalhoning. Method Classical458 Sinusoid
Cuttingspeed(m/min) 50 70 50 70 90 Materialremovalrate(mm3
/s) 0.57 1.34 0.67 1.46 1.83 Averagepower(kW) 2.5 4 1.8 2.5 3.7
4.1. Definitionofthehoningpath
Multi-circleshoningpathsarecharacterizedbythenumberNz ofcirclesovertheheightofthecylinderand thenumberNpof circlesontheperimeterofthecylinder.Theradiusofthecircleis denotedbyxinmmandthespeedofthetrajectoryyinmm/min.A multi-circlespathisdenotedbythenotation:NzNpRxFy.xis calculated based on the diameter of the cylinder through the relationship:
x¼
p
D2Np (1)
There are combinations between Nz and Np which allow homogeneouscoverageofthesurfacewithaminimumnumberof strokesequaltoNp,forexample,37,511,713,815.Fig.6 showstheplotofthetrajectoryforapointofthehoningtoolin multi-circleshoning815R7.56F35000inthereferenceframe associated with the cylindrical surface with the height of the cylinderonthey-axisandthecurvilinearpositionontheperimeter onthex-axis.
Thesolid lineisrelatedtothefirstrevolution.Thefollowing tracesareshifted.After16revolutionsand15strokes,onepointof thehoningtool wentallaroundthepattern.Thesurfaceof the cylinder is honed evenly with multi-path circles if a good combination of NpNz is selected and the cycle time is long enoughtocoveratleastNpstrokes.
4.2. Performanceofthemethod
One characteristic of multi-circles honing paths is the permanently oscillating cutting speed direction. This property canbeexploitedinthesamewayasinpolishingtoobtainverylow roughness.Aseriesoftestswasconductedtocomparethetime required in order to reduce themaximum roughness in finish honingwiththeabrasiveIAS65/100andSC500.Atthefinishing step,theinitialroughnessRawascloseto8
m
m.Attheendofthefinishing,theroughnessmustbelessthan 4
m
m to be reduced to 2m
m during the final step of super finishing.Theevolutionofthesurfaceroughnessasafunctionof timefordifferenthoningmethodsisshowninFig. 7.Eachpoint representssixmeasuredliners.Thecuttingspeedandexpansion forceareidenticalforeachabrasive:finishIAS65/100Vc=45m/ min, Fexp=800N, super finishing SC500 Vc=40m/min, Fexp=600N. We note that the measurement uncertainties reducewithtimeastheroughnessconvergestoitsstablevalue. Infinishingthemulti-circlemethod512reducesroughness Ratolessthan2m
minabout30swhile45sarerequiredwiththe conventionalmethod.Withfineabrasive,duringsuperfinishing, theminimumroughnessisreachedwithin24swithmulti-circles method815,comparedtomorethan50swithclassicalhoning. We note that the multi-circles paths guarantee a much more effective reduction in roughness. Multi-circles path gives the polishedappearanceasexpected.4.3. Surfacequalityobtained
Multi-circleshoninggivesasurfaceentirelynew.Fig. 8shows thepatternobservedwithnakedeyeandapreviewofthe3Dmicro geometryobservedwithaninterferometer.
Dependingontheabrasiveused,thepatternoftheintermingled circlesmaybemoreorlesspronounced.Thescopeofsuchamicro geometric structure of grooves is still under investigation. The resultsshowthefeasibilityofatexturingprocessusingabrasionto producealmosteverytypeofpattern.
5. Conclusion
This paper proposed the design and implementation of a prototype of honingmachine withhighdynamicactuators and efficientnumericalcontrol.Thedefinitionofthetrajectoryofthe abrasiveenablestoachievenewhoningtechniqueswithabetter control of the resulting surface. The three original methods presentedhavespecialfeaturesallowingtheextensionoftherange ofapplicationsofabrasiveprocess.Futureworkwillfocusonthe bestchoiceofabrasivesfortexturing.
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Fig.6.Multi-circleshoningpath815R7.56F35000.
Fig.7.Roughnessevolutioninfunctionofhoningmethod.
