VDLKSWAGENGRDUP

Groupstandard

VW01131Issue2024-08

Class.No.:01712

Descriptors:coefficientoffriction,fieldtesting,testbolt,testnut,threadedconnection,tighteningtorque

DeterminationofCoefficientsofFriction

MechanicalFastenerswithaMetricISOThread

Preface

Boltsandnutsareusuallytightenedinseveralstageswithafastpre-tighteningstageinordertoshortenassemblytime.Thefinaltighteningoperationisusuallyperformedwithreducedrotationalspeedandincreasinglyfrequentlyalsowithtorque-to-yieldtighteningprocedures.Withlargeran-glesofrotation,additionalfactorsthathaveanimpactonfrictiontakeeffect.Externalstandardsandregulationsdonotsufficientlytakethisfactintoaccount.

Thefriction-influencingfrictionpartnersoftheboltsandnutscanhaveverydiversesurfacetex-

tures.Noteveryconceivablefrictionpairingcanbesimulatedinstandardizedtests.Verysmoothandcohesivesurfacesorsurfacesthatareveryroughduetotheprocessingandmaterialstructurepresentparticularchallenges.Moreover,surfacedamagecanoccuronfastenedpaintedparts

whichleadstoextremefrictionconditionsandoftenproducesundesiredeffects.Screwingboltsorscrewsintodeepthreadedholesmadeinsoftmaterialsplacesspecificdemandsonthecoatingsystems.

Forinstance,wheelboltsaretightenedinseveralstagesduringinstallation(tightening,loosening,andfinaltighteningstages).Repeatfasteningoperationsmustalsobetakenintoconsideration

whenitcomestorework.Contrarytostandardizedlaboratorytests,seriesproductionconditionsusuallygeneratehighercoefficientsoffrictionwithsometimessignificantlylargerdispersion.

Furthermore,fortheevaluationofcoatingsystems,itisnecessarytoexaminethelooseningbe-haviornotonlyatroomtemperaturebutalsoathighertemperatures.ParticularlyorganiccoatingsystemswithahighPFAScontentorcoatingswithastackedlayerstructuresometimesexhibitverylowcoefficientsoffrictionathightemperatures.

Inthisstandard,empiricalvaluesfromnumerouspriortestsareusedtocreatesimplifiedtestspe-cificationsthatcoverasmanyofthedescribedbasicconditionsaspossibleusingsimplified

means.Extremeseriesproductioninstallationconditions,suchasparticularlyhighscrew-in

speeds,longguides,insufficientlyfastenedorvibratingcomponents,cannotbesimulatedinstand-ardizedtests.

Ifthetestsasperthisstandardarepassedsuccessfully,theprinciplethatitishighlylikelythatoth-erfrictionpairingsalsodonotresultinimpermissiblevaluesapplies.Ifanindividualcasedeviatesfromthisprinciple,specialtestsmustbeconductedthatarebasedonthemethodsandproceduresofthisstandard.

Alwaysusethelatestversionofthisstandard.

Thiselectronicallygeneratedstandardisauthenticandvalidwithoutsignature.

Noteontheverbsofobligationwithintherequirementssentences:Both'shall'and'must'aredefinedasbinding.

Page1of39

Allrightsreserved.Nopartofthisdocumentmaybeprovidedtothirdpartiesorreproducedwithoutthepriorconsent

ofoneoftheVolkswagenGroup’sStandardsdepartments.|internal

?VolkswagenAG

VWNORM-2023-12

Page2

VW01131:2024-08

Previousissues

VW01131-1:2010-02

VW01131-2:2010-02,2012-02

VW01131:2018-03

Changes

Comparedwiththemostrecentissuesofthestandardsreferredtointhe"Previousissues"section,thefollowingchangeshavebeenmade.

a)Standardedited

b)

Section

5.1.2revisedc)

Section

5.2revisedd)

Section

addede)

Section

5.3revisedf)

Section

5.4revised

g)Appendicesrevised

h)Appendix?TheoreticalratioML/MA“deleted

Contents

Page

1

Scope

3

2

Abbreviations

3

3

Symbols

4

4

Designation

5

5

Testing

5

5.1

Testconditionsfordeterminingthecoefficientoffriction

5

5.2

Devicestestparts

underandreference

6

5.3

Procedure

10

5.4

Results

18

5.5

Evaluation

20

5.6

Testreport/presentation

21

6

Applicable

documents

22

7

Bibliography

24

AppendixA

Testsequencesparameters

and

25

A.1

Standardtestsequencetest

forcoefficientoffriction

25

A.2

Fasteningparameters

26

A.3

Verificationtestparameter

ofthesuitabilityofthebedanddocumentation

27

A.4

Testsequencenewsystems

forthereleaseofcoatingforfasteners

29

AppendixB

DUTsparts,counter

andreferenceheadsurfaces

30

B.1

Certifiedpartscounter

andheadsurfaces

30

B.2

Rework

specificationsformachinedaluminumholestrips

31

AppendixC

Examples

ofevaluation

32

C.1

Examplesray

forcoefficientoffrictiondiagrams

32

C.2

Examplesray

forcoefficientoffrictiondistributiondiagrams

34

C.3

Examples

forcoefficientoffrictionstatistics

35

C.4Examplefordeterminingthebaselinecoefficientoffriction

37

C.5

Examplewarmtest

forevaluatingtheloosening

37

Page3VW01131:2024-08

AppendixD

Additionalinformation

38

D.1

Examplestorque

ofpossibleprogressions

38

D.2

Noteson

testingaluminumbolts

38

D.3

Simplifiedmeasurement

coefficientoffriction

39

1Scope

Thisstandardspecifiesthetestsetupandtestprocedurestodeterminecoefficientsoffrictionin

mechanicalfastenerswithmetricISOthreadsfromM5toM16.Thetestsequencerepresentstheprinciplesofdeterminingthecoefficientsoffrictionoffastenersatroomtemperature,whosetoler-ancesaredeterminedinVolkswagenstandard

VW01129

.Theseprinciplesarethebasisforallfur-thertests.

Thespecialcaseofdeterminingthecoefficientoffrictionunderthermalinfluence(warmloosen-ing),whichisprimarilyusedtoreleasenewcoatingsystems(surfaceprotectiontypes),isalsoad-dressed.

Theexaminationsoffaultsinthefasteningprocessaresimulatedandevaluatedasclosetofieldconditionsaspossible.Releasetestsinconjunctionwithcomponentsampleinspectionsarebasedonthisprocedurebutcanbeperformedusingasimplifiedprocedureifthereissufficientexperi-

encewithregardtothecoefficientsoffrictionbehaviorofsimilarpartfamilies.

Fastenerswithspecialdesigns(

VW01129

,?Fastenerswithspecialdesigns“section)canalsobetestedasperthisstandard.Thetestcanbealternativelyperformedwithcomparablepartswithoutspecialdesignmanufacturedwiththesameprocessorusingsub-testsofthisstandard(see

section5.2.6

and

sectionD.2

)ifspecialagreementsweremadeaboutdeterminingthecoefficientsoffrictionandevaluatingthetest.

2Abbreviations

Thefollowingabbreviationsareusedinthisdocument:

ENT

Developmentpartnumber

Fk

Propertyclass

HyperKVS

VolkswagenGroupEngineeringDataManagementSystem

i.O.

Testpassed

KTL

Cathodicelectrocoating

n.i.O.

NotOK

PFAS

Per-andpolyfluoroalkylsubstances

Sv

LockingserrationtypeSvasperVW60424

[1]

(RIPPsystem)

TOC

Tighteningoperationcycle(threadedconnection)

TOC1

Firsttighteningoperationcycle

TOC2...5

Repeattighteningoperationcycle(1to4)

Page4

VW01131:2024-08

3Symbols

Thesymbolslistedin

table1

applywhenusingthisstandard.

Table1–SymbolscomparedtosymbolsasperDINENISO16047

[2]

SymbolDesignationDINENISO16047

dNominaldiameterofthethreadd

dh(,min)Measured:Innerbearingsurfaceofthebolt/nutdiTheoretical:diameterofthethroughholedh

DkmEffectivediameterforthefrictiontorqueintheboltheadornutbearingsur-Dbface(theoreticalormeasured)

dW,maxMeasured:Outerbearingsurfacediameterofthebolt/nutdw,min

D0Theoretical:MinimumbearingsurfacediameterasperproductstandardD0

d2Largestpitchdiameteroftheexternalthread(see

VW11611

)d2FPTestforce—FVPreloadforceF

MATighteningtorqueT

MA,istAchievedtighteningtorqueattheendoftheboltingprocess—

MGThreadtorqueintighteningdirectionTth

MKFrictiontorqueinthebearingsurfaceTb

MLLooseningtorque(threadtorqueinlooseningdirection)—

MLGLooseningtorqueatthetimeofslidingfriction—

MLHLooseningtorqueatthetimeofstaticfriction(breakawaypeak)—

MSTighteningtorque,thresholdvalueinthefinaltighteningstage—

MS1Tighteningtorque,thresholdvalueinthepre-tighteningstage—

MS1,istTighteningtorque,measuredthresholdvalue—

MS1,sollTighteningtorque,thresholdvalueasper

tableA.2

—

MVAPre-tighteningtorque—

MVLLooseningtorqueinthepre-tighteningstage—

M2Finaltighteningtorque(calculated)—NNumberofthedeviceundertest(DUT)—nScrew-inspeed—PThreadpitchPWLLooseningangleinthepre-tighteningstage—αThreadpitchangle—κSwitch-offaccuracyattheswitch-overpoint—μgCoefficientoffrictioninthethreadintighteningdirectionμthμg,L?senCoefficientoffrictioninthethreadinlooseningdirection—μgesTotalcoefficientoffrictionμtotμges,L?sen,150°CTotalcoefficientoffrictionforlooseningoperationsat150°C—μkCoefficientoffrictioninthenutorboltheadbearingsurfaceμb

Page5VW01131:2024-08

4

5

5.1

5.1.1

Designation

CoefficientoffrictiontestingasperVW01131

Testing

Testconditionsfordeterminingthecoefficientoffriction

Ensuringcomparability

Duetoverydifferentbasicconditionsandawiderangeofmeasuringequipmentandmethods,co-efficientoffrictiontestscanonlybecomparediftheyarespecifiedwithinnarrowlimits.Withre-

specttothreadedconnections,thismeansthatpotentialinfluencesmustbesimulatedasclosetofieldconditionsaspossible.Thisincludesthreadedparts,theheadbearingsurface,thejointhard-nessaswellasthegriprangeandlengthofengagement.

5.1.2Requirementsfortheboltingtestbed

Thetighteningofthethreadedconnectionmustbecarriedoutwithastate-of-the-artstationary,

motorizedtestbed,ashand-operatedtorquewrenchesarenotsuitableastighteningormeasuringtoolsduetotheirsystematicinfluences.Thestateoftheartmustbeverifiedinaroundrobintest.Thestiffnessofthetestbedcannotbeinfluencedandspecificationsdonotyetexist.Therefore,

thecoordinationoftheopenloopcontroller,drive,andmeasuringtechnologyofthetestbedwithregardtotheexpectedmeasuringrangeandaninertiaaslowaspossiblearedecisive.Inparticu-lar,measurementsinthelowermeasuringrangeofthetestbed(<10%ofthenominalvalues)

mustbeconsideredascriticalhere.

Thetestbedmustbecalibratedforthemeasuringrangeusedineachcaseandbecapableofim-plementinghighscrew-inspeeds(standarddesiredvaluen=200rpm)andanintermittent,multi-stagetighteningprocess(pre-tightening–stop–finaltightening).Thetestbetmustbeequippedwithmeasuringsensorsthatrecordthemeasurandstorque,prestressingforce,andadditionalan-gleofrotationwithanuncertaintyof1%ofthemeasurandor1°,respectively,unlessotherwise

agreedupon.Thedigitalizationratemustbeatleast1kHz(recommended10kHz).Furthermore,itmustbepossibletoperformandevaluateuptofourrepeattighteningoperationcycles.Itmustbepossibletoimplementthespecificationsfortheswitch-offandswitch-overpointsfortherotationalspeedandadditionallyeitherforthetorqueorfortheprestressingforce.Thedocumentationoftheinternalsensordataofsetandactualvaluesattheswitch-overpointensuresacontinuouscontrolineachtest.Theverificationofthetestbedcapabilitydeterminedredundantlyusingexternalsen-sorsmustbeperformedonceforthemeasurementrange(see

sectionA.3

).Theachievedclassifi-cationoftheswitch-offaccuracy(classandκ-value

sectionA.3

)mustbedocumented.

Page6

VW01131:2024-08

5.2

5.2.1

Devicesundertestandreferenceparts

Componentselection

Dependingontheobjectiveofthetest,thepertinentsamples,productionparts,orirregularparts

mustbeusedforthetests.Ifthesepartscannotbeusedforgeometricalorfunctionalreasons,al-ternativepartsmustbeusedthatsimulatetheoriginalthreadedconnectiontypeascloselyaspos-sible.Forsimulatingthreadedconnectiontypesusedinproductionorirregularthreadedconnectiontypes,thefollowingbasicrulesmustbeobservedwhenselectingcomponents:

–AlternativeDUTsmayonlybeusediftheirinfluenceisknownornegligible.

–Thecomponentstobereplacedmustbesimulatedascloselyaspossiblewithregardtotheirfriction-influencingfactors(surfacefinish,strength,geometry).

Ifnewcoatingsystemsaretobereleasedorifthespecifiedbasicrulescannotbeadheredto,DUTsand/orreferencepartsmustbeused.Incaseofadispute,onlythosemeasurementsmustbeacceptedthatwereobtainedusingcertifiedDUTsand/orreferenceparts(see

sectionB.1

).

5.2.2Referencenuts

Forthetestingofbolts,thefollowingtwonuttypesarepermissible:

1.Squareweldnutsasper

VW60449

and

2.Hexagonnutasper

DINENISO

4033or

DINENISO

8674Inaddition,thefollowingbasicpropertiesmustbethesame:

–High-qualitydesign(type2)andpropertyclass10or12asper

DINENISO

898-2

–Threadwithtoleranceclass6Gasper

VW11624

(inplaincondition)

–Electro-galvanizedandthin-layerpassivated(Ofl-c340asperTechnicalSupplySpecification

TL217

and

VW13750

;layerthickness:6μmto12μm/sameasforweldnuts)

Figure1–Bolttest(example)–boltheadisbeingdriven

5.2.3Referencebolts

Forthetestingofnuts,referenceboltsasper

DINENISO4017

,or

DINENISO

8676,orcompara-blenutswithpropertyclass10.9mustbeused.Thethread(inplaincondition)mustcomplywith

toleranceclass6fasper

VW11624

.Thesurfacemustbeelectro-galvanizedandthin-layer

Page7VW01131:2024-08

passivated(Ofl-c340asper

TL217

or

VW13750

;layerthickness:6μmto12μm/sameasforweldnuts).

Figure2–Nuttest(example)–nutisbeingdriven

5.2.4Testboltsandtestnuts

Inordertoensurethecomparabilityoftestresults,thefollowingcertifiedtestboltsmustbeused:

–HexalobularsocketboltwithwasherwiththedimensionsM6x55andpropertyclass8.8asper

VW60429

(ENT.349.839).

NOTE1:Thewasherisalreadyinstalledinthecorrectposition.Duetothewasher'sconcavede-sign,theheadbearingsurfacetogetherwiththewasherbehavesasaconcavebolt.

–HexagonflangeboltwiththedimensionsM10x60andpropertyclass10.9asper

VW60572

(ENT.349.840)

NOTE2:Theflangebearingsurfaceisdesignedtobeslightlyconvex,sothattheboltbehavesasaconvexbolt.

Inbothcases,thethreadmusthavebeenmadeintoleranceclass6e(bottomthird)asper

VW11627

inordertostillhaveenoughclearanceforbeingpairedwithinternalthreadsoftoleranceclass6H.

NOTE3:Impactmarkshaveanegativeinfluenceandmustbeavoided.

Thesurfacefinishmustbeplainwithoutanycoatingandslightlyoiled(Ofl-a101asper

VW13750

).Forreleasetests,thesecomponentscanhavethelayerstructuretobereleasedimplemented.Forclose-to-productiontests,theusedcoatingmustbeanalogoustothecoatingusedinproduction.Testnutsfornuttestscanbefreelyselected,however,asperthespecificationsforthetestbolts,thethreadmustcomplywithtoleranceclass6Gandthesurfacefinishmustbeplain(

VW11624

).NOTE4:Testboltsandtestnutsmadeofothermaterialsandpertinenttestsarenotdescribedinthisstandard.Notesontestingaluminumboltscanbefoundin

sectionD.2

.

Page8

VW01131:2024-08

5.2.5Headcountersurfaces

Types

Inordertoensurethecomparabilityoftestresults,certifiedheadcountersurfacesmustbeused.Holesheetsmadeofonlytwomaterialsmustbeused:

–Thin,paintedbodysheetsmadeofsteelor

–Thickersheetsmadeofaluminummaterial

NOTE5:Thesystematicapproachofcoveringasmanygeneralconditionsaspossibleasdescri-bedintheprefacemustbeimplementedwiththesecertifiedheadcountersurfaces.

Usingadjustedmountingadaptersinthetestbed(holediameterandstiffness)keepspotentialde-flectionaslowaspossible.Theloadontheheadbearingsurfacescausedbypre-tensionforceandabrasioncanleadtoembedmentinthesurface.Usingbothsidesofthepaintedbodysheetsisnotrecommendedandmayonlyoccurinexceptionalcases,whereitcanbeverifiedthatthereisno

deformationordamagetothesurface.

Paintedsheettestpanel

Anexampleofapaintedsheettestpanelisshownin

figure3

andmustfulfillthefollowingrequire-ments:

–Bodysheetmadeofsteel(asper

DINEN

10111–DD12,material1.0398,unalloyedhot-rol-ledstrip,maximumhardness130HV).Thesurfacetexturemustbefreeofoverlaps(includingoverlapswithnon-metallicinclusions),blisters,cracks,andscratchesthatcanimpairtheproc-esscapability.

–Sheetthickness:(2±0,2)mm

–Throughholesasper

DINEN

20273,mediumseries,freeofburrswithoutcountersink

–Paintspecification(2-componentthick-layerKTL)

–2-componentthick-layercathodicsingle-layerdippainting(QualitySpecification

QPF087

)

–Color:black

–Pre-treatment:zincphosphating

–Dryfilmthicknessofthepaintstructure:(22±5)μmKTL:AquaEC3000

1)

consistingoftwocomponents:

1.Binder(materialno.ALE017100)

2.Pigmentpaste(materialno.ALE017043)

Figure3–Paintedsheettestpanel(KTL,black)

1)AquaEC3000istheproductdesignationbymanufacturerAxaltCoatingSystemsAustriaGmbH.

Thisinformationisonlyintendedforinformationalpurposesfortheusersofthisin-housestandard.Thisdoesnotsignifyanen-

dorsementofthementionedproductbytheVolkswagenGroup.Equivalentproductsmaybeusedifitcanbeverifiedthattheyleadtothesameresults.

Page9VW01131:2024-08

Aluminumholestrip

Anexampleofanaluminumholestripisshownin

figure4

andmustfulfillthefollowingrequire-ments:

–AluminumalloyENAW-6082[AlSiMgMn,T651]asper

DIN573-3

,

DINEN

485-1,

DINEN

485-2,and

DINEN

485-3

–Sheetthickness≥5mm(newpart≥10mm)

–Throughholesasper

DINEN

20273,mediumseries,freeofburrswithmaximumcountersinkof0,3×45°(whencalculatingDb,anevaluationmustbeconducted)

–Surfacemilledandsubsequentfinishingprocess,Rz=(15±5)μm

NOTE6:Formoreinformationonmeasurabilityandrework,see

sectionB.2

.

Theholestripscanbeusedseveraltimesafterthesurfacehasbeenmilledagain.Duringthisprocess,thespecifiedsurfaceconditionmustbere-established.Theminimumpermissiblethick-nessofthereworkedholestripmustbespecifiedtoavoiddeflectionordeformation–dependingontheexpectedpreloadforceineachcase–andmustnotfallbelow5mm.

Figure4–Aluminumholestrip

5.2.6Specialcases

Combinedcomponents

Whentestingcombinedcomponents(boltwithwasher/nutwithwasher),nospecialheadcountersurfaceisrequired.However,itmustbeensuredthatthecorrespondingwasherisnotrotatingdur-ingfasteningandthatthewasherisnotbentordeformedduetothepropertiesofthebearingsur-face.

Duetotheineffectivemeasurementstrategy(seenotein

section.1

orsee

section5.5.1

),thatevaluatestheindividualunderheadcoefficientoffrictiononthealuminumstrip,torque-to-yieldtighteningisnotnecessary.

Page10

VW01131:2024-08

Boltsandnutswithlockingserration

Thedifferenceinstrengthbetweentheheadcountersurfaceandtheboltsornutswithlockingser-rationtypeSvasperVW60424

[1]

isdecisivefortheirfunction.Exceedingthebearingstressoftheheadcountersurfaceandtheembedmentoftheprofilearealreadyincludedinthecalculation.Thisresultsinveryhighunderheadcoefficientsoffrictionthatareintendedtomakeloosening

moredifficult.Thismustbetakenintoaccountwhenevaluatingthesafetysystem.Forexample,onlythethreadfrictionmustthenbeconsideredorthetotalfrictioninrelationtootherreferenceparts.

Specialpartswithspecialapplication

Forspecificspecialpartsthatarenotusedinstandardapplications,theuseofsteelholestripsorsteelwashersasheadcountersurfacescanbeusefulfortesting.Theuseofthesecountersurfa-cesmustbedocumented.Forexample,suitableheadcountersurfacescanbetakenfromthe

rangeofproducts(seefootnotein

sectionB.1

).

Boltsandnutswithsmallheadbearingsurface

Inthecaseofhexagonheadboltswithoutflangeandsmallpanheadshapes,thetestingonthealuminumholestripcanonlybemadeusingreferencepartswithlargerheadbearingsurfaces.

5.3Procedure

5.3.1Preparationofreferenceparts

Foreachtest,new,unusedparts(bolts,nuts)andheadcountersurfacesmustbeused.

Referenceparts(e.g.,greasedforlong-termstorage)mustbethoroughlycleanedbeforefastening.Anexampleofthecleaningprocess(threestageswithcleaner'snaphthainanultrasonicbath)isshownin

figure5

butdependingonthepre-treatmentandgreasingoftheparts,theactualcleaningprocesscandeviatefromthisexample.Ifrepeattighteningoperationcyclesarecarriedoutduringthetest,thedescribedcleaningprocessmustbeperformedonlyonceatthestartofthetests.

However