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Statements• Thesa7sfactoryperformanceofanaircra+requirescon7nuousmaintenance
• Repairsmustbestrongenoughtocarryalloftheloadswiththerequiredfactorofsafety! Repairmustnothavetoomuchstrength
• Extrastrengthcancausedamage
Statements• Theproblemofrepairingadamagedsec7onisusuallysolvedbyduplica7ngtheoriginalpartinstrength,kindofmaterial,anddimensions.! “Followthemanufacturer’srecommendedprocedures”
! Youdon’tknowwhattheengineeringwasthinking! AC43.13-1BistheFAA’sguidance
• AC43.13-1Btakeprecedenceovertextbook
• Ascratchorgougeinthesurfaceofahighlystressedpieceofmetalcausesastressconcentra7onatthepointofdamage(“stressriser”)andcouldleadtofailureofthepart.
Shear
The stress that resists the force tending to cause one layer of material to slide over an adjacent layer.
Think of shears cutting
Bearing
The surface pressure acting on a joint face directly as a result of the force applied by a fastener.
Tools• Alwayshaveatleastonemachinist’srulein1/32”(or1/64”)
• Pens! Nopencils! Sharpies
• Bluedoesn’tbleedthroughpaintasbad! Useinsteadofscribing
• Demo! Rivetspacer! Nibbler
Tools• Demo
! Deburringtools
• Drilling! Markwithacenterpunch! Metaltwistdrillbitshave118°head
• Stainlesssteeluse140°! Topreventsurfaceska7ngonaluminum,handtwistacoupleof7mebeforeapplyingpower
! CuZngoilhelpsremovechipsandisnotusedonsheetmetal
! Forlargeholes,startwithasmallbitandthenenlarge
Tools• Drilling
! Generalruleforspeed• Hardmetal–slowandmorepressure,so+metal–fastandlowpressure
! Useawoodbackerwhendrillingsheetmetal! Useadrillguide/holdersifpossible! Useadrillstopsin7ghtareas! Useadrillpressforcri7calrepairs! Forcomplicatedpa^erns:
• Drillsmallerholesfirst• Alignpa^ern• Enlargepa^ern
! Don’tbetooproudorlazytousesupporttools
Tools• Reamers
! Usedtoenlargeandsmoothahole! Usedtocreateapreciseholediameter! Verybri^le! Turnonlyoneway! Followthedirec7onsfordrillingtheini7alhole
Aluminum• Usedonaircra+becauseitislightandeasytowork
• Purealuminumisveryweak• Methodstoincreasestrengthandhardness
! Otherchemicalsareaddedtomakeanalloy• 2024isthemostcommonsheetmetalalloy• 2117isthemostcommonrivetalloy• Alloysusuallyreducecorrosionresistance
! Heattreatmentandtempering! Workorstrainhardening! Agehardening
• Aluminumalloysgetharderwithage
Aluminum• Wrought(worked/beaten)aluminumdesigna7on:! (4digitalloy)–(temper&hardness)
• e.g.2024-T3• Firstdigit(e.g.2XXX)indicatestheprimaryalloyingagent
• Alcad™orclad–very,verythinlayerofpurealuminumusetoprotectagainstcorrosion! Can’tbereheated! Can’tbewelded
• Thiswhyaircra+arerivetednotwelded! Easytoscratchornick
• Exposesbasemetaltocorrosion
SolidRivets• Solidshankrivetsarethemostcommontypeofrivetusedonaircra+! Mostusedofallfasters
• Rive7ngVideo• RivetHeadTypes:
! Universal• 470->AN470orMS20470
! CountersunkorFlush• 426->AN426orMS20426• 100°headangle
SolidRivets• A–1100–Purealuminum
! Tooso+forstructuraluse! Fordecora7vetrimonly
• AD–2117! Mostcommonrivettype! Heattreatedbythemanufactureranddoes’trequireheattreatmentbeforebeingdriven
• B–5056! Usedformagnesiumalloystructures
• M–Monel! Usedfornickel-steel
SolidRivets• D–2017&DD–2024
! “Icebox”rivets• Annealedandstoredinafreezertoretardhardening• Removedfromfreezerjustbeforeuse
! ModernmanufacturingnowuseEtyperivets! Mustbereheattreatedifle+outtoolong! Onceinstalled,cantakeupto4daystofullyageharden
• MildSteel! Usedforsteel
SolidRivets• Materialsubs7tu7on
! Followthemanufacturer’srecommendedprocedures
! D-2017–3/16”(#6)orless• ReplacewithAD–2117of1/32”diameterlarger
! Onesizebigger
! DD-2024–5/32(#5)orless• ReplacewithAD–2117of1/32”diameterlarger
! Onesizebigger
RivetSets
Theradiusofthecupinarivetsetisslightlygreaterthantheradiusoftherivethead.Thisallowstheblowsfromtherivetguntobeconcentratedontherivethead.
SolidRivetMaterial• A–1100–Purealuminum• B–5056–Usedonmagnesium• AD–2117–Mostcommontype;hasdimple• D–2017–“Icebox”• DD–2024–“Icebox”
RivetDimensioning• Diameterisin1/32’s
! #3–3/32,#4-4/32(1/8),#5-5/32
• Lengthisin1/16! AN470–sha+length! AN426–fullrivetlength
RivetDesigna7on• (HeadType)(Material)(Diameterin1/32s)–(Lengthin1/16’s)
• Universalhead,2117,3/32diameter,5/16length! AN470AD3-5orMS20470AD3-5
• Countersunkhead,1100,1/8(4/32)diameter,1/2(8/16)length! AN426A4-8orMS20426A4-8
RivetLayout• RivetStresses
! Shear• Forcerequiredtocutarivet• Arepairorpatchshouldbedesignedsoitisundershearstress
! Tension• Resistancetotensionisbearing• Tensionstresspullingapatchapart
Dimpling• Coindimpling
! Rivetisthemaledie
• RadiusDimpling! Handsqueezer! Sta7onarydimpler
• Hotdimpling! Usesheateddimplingdiestoensurethemetalflowsbe^erduringthedimplingprocess
• Dimpling,duetothenestlingeffect,givesastrongerjointthanthenon-flushtype.
Countersinking• Removemetaltoinstallrivet• Reducesstrengthofmetal• Edgedistanceisgreaterthanwhenuniversalheadfasteners! 2½D
• 100°countersink• Sheetmetalmustbethickerthanrivethead• Usemicrostopcountersink
BlindRivets• Canbeinstallfromoneside
! Installedwith“puller”tool
• PopRivet! Poprivetinstalla7on! Usedforno-structuralworkonly! Hollowa+erinstalla7on
BlindRivets• “CherryRivets”
! Notyourhardwarestorerivets! Widevariety–CherryLock,CherryMax,Huck-Clinch,HuckMax,Olympic-Loc
! CherryMaxAnima7on! CherryMaxcanreplaceasolidrivetofthesamesizediameter
• Somemechanicsareconcernedabouttherivetsvibra7ngloose
! InstallCherryMaxRivet! Hardtoremove
• Readprocessonpage4-49
Dzus™Fastener• Lengthspecifiedin1/100(0.01)inchincrements• Diameterspecifiedin1/16inchincrements• Headmarkingsarebodydiameter,typeofhead,andlengthofthefastener
• Reten7ongrommet/collarcommonlycomeloose
MetalBendingLayoutProcedure1. Obtainthedimensionsoftheshape2. Determinesizeofthestockor“wheretocut”3. Locatebrakereferencelinesor“whereto
bend”4. Cutstock5. Markcentersor“wheretodrill”6. Drillholes
! Ifjoiningmul7plepieces,drilla+erbending
7. Bendmetal
WhyBendAllowance?• Metalcannotbebentataperfect90°angle
! Itwillbreakorcrack
• Aroundbendisusedtopreventbreaking! Thebendisdefinedbyitsradius–bendradius! Thebendispor7onofacircle
• Apor7onofacircleisshorterthanaperfect90°
WhyShorter?• Theshortestdistancebetweentwopointsinaline
• Aperfect90°isthelongest• Acurvedbendisshorterthanaperfect90°
! Thebiggertheradius,theshorterdistance
• Theheartofabendradiuscalcula7onistodeterminethisshorterdistance
TheBendingTool• ThetooliscalledaBrake
! CorniceBrake! FingerBrake
• Clampingbarholdsthemetalanddeterminesradius! Clamp/Fingerscanbechangedtosetradius
• Wheretoplacethemetal?! Thefront/noseoftheclamp
• Thegoalofthecalcula7onsaretodeterminewherethenosegoes
Calcula7onGoals• Determinethematerialdimensions/measurements! Itiseasiertocutthematerialbeforebendingit
• Markwherebendsshouldbelocated! Onlyreferenceonthebrakeisthenoseoftheclamp–sightline
! Determine/markwherethenosewillgo! Noseloca7oniscalledthe“BrakeReferenceLine”
Terms/Vocabulary• MoldLinesDimension(MLD)–Themethodofdefiningapartonadrawing! Example–2”X4”X2”channel! Thelengthofasideiftherewasnobend! Drawnasifthebendisaperfect90°(0radiusbend)
• BendRadius(R)–Thesizeofthecurveusedtobendthemetal! Radiusofthebrakeclampnose! Insideradiusofbend
Terms/Vocabulary• DevelopedWidth(DW)–Materialneededtomakeapiece/item! YoubookcallsitTotalDevelopedWidth(TDW)! TotalofallBendTangentLineDimensions(BTLD)plusallBendAllowances(BA)
• Allthestraightpartsplusthebentareas
Calcula7onOrder1. MLD-DetermineMoldLineDimensionsfrom
problem2. R-Radius
! Getfromproblem! OrMinimumbendradius
• AC43.13-1BTable4-6• FAA-H-8083-31Vol.1Figure4-125
Calcula7onOrder3. BA–BendAllowance
! FAA-H-8083-31Vol.1Figure4-129! BA=(0.01743XR+0.0078XT)Xdegreeofbend
• Bookhastypos• R=Radius&Tisthicknessofmaterial
! SampleR=.25”&T=.040”and90°bend» BA=(0.01743X0.25)+(0.0078X0.04)X90=0.420255”» BA=0.421”fromFAA-H-8083-31
Calcula7onOrder4. SB–Setback
! For90°,SB=T+R• Tisthicknessofmaterial&R=Radius
! SB=K(T+R)• For90°,K=1• Kcharts
! AC43.13-1BTable4-7! FAA-H-8083-31Vol.1Figure4-123
Calcula7onOrder6. DW-DevelopedWidth
! TotalofalltheBendTangentLineDimensions+alltheBendAllowances
! DW=TotalofalltheBTLD(s)+allBA(s)
Calcula7onOrder7. BrakeReferenceLine(SightLine)
! BrakeReferenceLine=BendTangentLineDimension+Radius
! BrakeReferenceLine=BTLD+Radius
Example• Example:.032”2024-T3Dimension=2”forbothside,90°bend! MinimumRadius=R=0.128->roundto0.125”! BA=0.218”! SB=T+R
• SB=0.032”+0.125”=0.157”! BTLD=MLD–SB
• BTLD=2”–0.157”=1.843”! DW=BTLD+BA+BTLD
• DW=1.843”+0.218”+1.843”=3.904”
! BrakeReferenceLine=BTLD+R• BrakeReferenceLine=1.843”+0.125”=1.968”
Example• Example:.0807075-T6–5”X6”X5”channel
! MinimumRadius=R=0.44”or(7/16)=0.438”! BA=0.745”! SB=T+R
• SB=0.080”+0.438”=0.518”! BTLD=MLD–SB
• BTLD(side)=5”–0.518”=4.482”• BTLD(bo^om)=6”–2X0.518”=4.964”
! DW=BTLD+BA+BTLD+BA+BTLD• DW=4.482”+0.745”+4.964”+0.745”+4.482”=15.418”
! BrakeReferenceLine=4.482”+0.438”=4.92”(frombothsides)
Prac7ceProblems• .032”2024-T5,Side1=23/8”,Side2=5.4”,90°bend
• .040”6061-T5–2.5”X1”X2.75”channel,allbends90°
• .100”2024-T5,Side1=13/8”,Side2=29/16”,110°bend
MetalWorking• Followmanufacturer’srecommendedprocedures
• FollowAC43-13• Heattreatuntreatedmetals
! Treatedmetalsmustbeformedcold
• Topreventcorrosion,useaprotec7velayerbetweendissimilarmetals! Paintortape
• Whenusingaformblock,startattheedgesandworktothecenter
• Usereliefholesatbendintersec7ons
InspectforDamage• Lookfor:
! Corrosion• Treatorreplace
! Cracks! Elongatedholes! Dents,scratches,nicks,pits&cuts! Wrinklesorbents! Looserivets
• “Smoking”rivetsareindica7onofrubbingorfreZng• Tippedrivets
! Ifthereisone,thereisusuallyawholerowinthesamedirec7on
! Lookforforcetransmission
PatchingSheetMetalDamage• ConsultManufacturer’srepairmanualand/orAC43-13forbestrepairmethod! Thegoalistoreturnthestructuretoitsoriginalstrength
! Manufacturermaylimitwhatyoucanrepair
• Supportdamagedarea• Stopdrillcracksorcutoutdamage.
! Leavenostressrisers–nosharpcorners
• Calculatethenumberofrivets! Trytomakeyourrepairbasedontherivetshearstrength
PatchingSheetMetalDamage• Makeapaperdesignofapatch
! Markholestoinsurenointerference! Usetransparencyifpossible
• Createapatch! Samematerialandsamethicknessorgreater! Patchwillgounderskinifpossible
• Makefillerplugifneeded–flushpatch• Drillholes• Applycorrosioninhibitor/primer• Applysealantforpressurizedrepairs
NumberofRivets–AC43.13-1B• UseTables4-9,4-10or4-11forrivetsperinch.
! Page4-37,4-38or4-39! Checknotes
• #Rivets=LengthofcrackXRivetsperinch• #Rivetsisonlyforoneside.• Thetotalrivetsusedis2X#Rivets
RivetSpacing• Rivetpitch-thedistancebetweenthecentersofadjacentrivetsinthesamerow.! Minimum–3D;Maximum–10D! Typical6Dto8D
• Transversepitch-theperpendiculardistancebetweenrivetrows! 75%ofrivetpitch! Minimum–21/2D
• EdgeDistance–2Dto4D
YourGuides• Followmanufacturer’sinstruc7ons
! Maintenance/Repairmanual! Copyrivetholepa^ern! Usesamematerialandrivets
• UseAC43.13-1BPar4-58
SampleQues7ons• Shallowscratchesinsheetmetalmayberepairedby! burnishing
• Whenapieceofaluminumalloyistobebentusingaminimumradiusforthetypeandthicknessofmaterial! thelayoutshouldbemadesothatthebendwillbe90°tothegrainofthesheet.
! AC43-13-1B4-55Bsays“preferably”
SampleQues7ons• Ifitisnecessarytocomputeabendallowanceproblemandbendallowancetablesarenotavailable,theneutralaxisofthebendcanbe! foundbyaddingapproximatelyone-halfofthestockthicknesstothebendradius.
• Youcandis7nguishbetweenaluminumandaluminumalloyby! tes7ngwitha10percentsolu7onofcaus7csoda.