制造工程与技术热加工1112docx.docx
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制造工程与技术热加工1112docx.docx
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制造工程与技术热加工1112docx
MetalCastingProcesses
CHAPTER11
PARTII
MetalCastinaProcess
•InvestmentCasting
•VacuumCasting
•Permanent-MoldCasting
•SlushCasting
•PressureCasting
•DieCasting
•CentrifugalCasting
InvestmentCasting
•Alsocalledlost-waxprocess
•Firstused4000一3000BC
•Thepatternismadeofwaxorofaplasticbymoldingorrapidprototypingtechniques
•Terminvestmentderivesfromthefactthatthepatternisinvestedwiththerefractorymaterial
•Needcarefulhandlingbecausetheyarenotstrongenoughtowithstandtheforcesinvolvedinmoldmaking
•Waxcanberecoveredandreused
InvestmentCastingProcess
b
Initialpattern,traditionallywax,isproducedslightlylargerthanfinalmetalpart・
Waxassemblyisthen
successivelydippedin
ceramicslurryandstuccoed
withsandtoproduceshell.
Metaldeliverysystemisthen
assembledonthepattern.
Thegatingsystemisusually
madefromstandardwax
shapes.
Waxassemblyisthensuccessiuelvdippedinceramicslurryandstuccoedwithsandtoproduceshell.
Metaldeliverysystemisthenassembledonthepattern.Thegatingsystemisusuallymadefromstandardwaxshapes.
InvestmentCasting
•One-piecemold
一Driedintheair
一Heatedto90-175C
一Heldinvertedfor12hrstomeltoutwax
一Themoldisthenheatedto650-1150Cforabout4hrsdependingonthemetaltobecasttodriveoffthewaterofcrystallization
一Afterthemetalhasbeenpouredthemoldisbrokenupandthecastisremoved
一Anumberofpatternscanbejoinedtomakeonemoldcalledatreewhichincreasesproductionrate
One-piecemold-con't
一Smallparts
•Thetreecanbeinsertedontoaflaskandfilledwithslurryinvestment
•Theinvestmentisthenplacedintoachamberandevacuatedtoremoveairbubbles
•Nextitisplacedinavacuumdrawingmachinetoproducefinedetail一Notacheapprocess
一Producesfinedetails
一Goodsurfacefinish
一Fewornofinishingoperations
一Canproduceintricatepartsfrompartsweighing1g一35Kg
•Ex:
Investmentdiecastingexamples
3.SHELLBUILDING:
Theshellisbuiltbyimmersingtheassemblyinaliquidceramicslurryandthenintoabedofextremelyfinesand.Uptoeight
Schematicillustrationofinvestmentcasting
1.WAXINJECTION:
Waxreplicasofthedesiredcastingsareproducedbyinjectionmolding.Thesereplicasarecalledpatterns.
2.ASSEMBLY:
Thepatternsareattachedtoacentralwaxstick,calledasprue,toformacastingclusterorassembly.
layersmaybeappliedinthismanner.
4.DEWAX:
Oncetheceramicisdry,thewaxismeltedout,creatinganegativeimpressionoftheassemblywithintheshell・
7.CUTOFF
Thepartsarecutawayfromthecentralsprueusingahighspeedfrictionsaw・
•6.KNOCKOUT
Whenthemetalhascooledandsolidified,theceramicshellisbrokenoffbyvibrationorwaterblasting.
•5.CONVENTIONALCASTING
Intheconventionalprocess,theshellisfilledwithmoltenmetalbygravitypouring.Asthemetalcools,thepartsandgates,sprueandpouringcupbecomeonesolidcasting.
•8.FINISHEDCASTINGS
Afterminorfinishingoperations,themetalcastings-identicaltotheoriginalwaxpatterns-arereadyforshipmenttothecustomer.
CeramioShellCasting
一Variationoftheinvestment-castingprocess
一Usessametypeofwaxorplasticpatternasinvestmentcasting
一Pattenisthendippedintofluidizedbedof
•Fine・grainedfusedsilica
•Zirconflour
一Patternisthendippedintocoarsergrainedsilicatobuildupadditionalcoatingsandproperthicknesstowithstandthethermalshockofpouring
一Therestoftheprocedurefollowstheinvestmentcastingprocess
Fig:
Investmentcastingofanintegrallycastrotorforagasturbine.(a)Waxpatternassembly,(b)Ceramicshellaroundwaxpattern.(c)Waxmeltedoutandthemoldisfilledunderavacuum,withmoltensuperalloy.
(d)Thecastrotorproducedtonetornear-netshape.
1.
2.
3.
4.
Mixtureoffinesandandurethaneismoldedovermetaldiesacuredwithaminevapor
Themoldispartiallyimmersedintomoltenmetalheldinaninductionfurnace
Themetalismeltedinairorinavacuum
(b)
huhictionfuniace
Casting
Vacuum/
j
J
/Mold
/Mold
Moltenmetal
5.Altemativetoinvestment,shell-mold,andgreervsandcasting
6.Relativelylowcost
Themoltenmetalisusually55Cabovetheliquidustemperature一beginstosolidifywithinafractionofasecond
Permanent-MolclCasting
•Calledhard-moldcasting
•Twohalvesofamoldaremadefrommaterialssuchasiron,steel,bronze,orotheralloys
•Themoldcavityandgatingsystemaremachinedintothemold
•Sandaggregateareplacedintothemoldpriortocastingforproducingcavities
•Typicalcorematerialsare
一Oil-bondedorresin-bonedsand
一Plaster
一Graphite
一Grayiron
一Low-carbonsteel
一Hot-workeddiesteel
•Moldcavitysurfacesarecoatedwithrefractoryslurrytoincreasethelifeofthemoldeveryfewcastings
•Mechanicalejectorsareusedtoremovecomplexparts
•Canproducehighproductionrates
•Goodsurfacefinish
ShushCasting
•Moltenmetalispouredintothemetalmold
•Adesiredthicknessofthesolidifiedskinisobtained
•Theremainingmetalispouredout
•Themoldhalvesarethenopenedandthecastingisremoved
PressureCastirg
•Usedagraphiteormetalmold
•Moltenmetalisforcedintothemoldbygaspressure
•Thepressureismaintaineduntilthemetalsolidifiesinthemold
•Usedforhigh-qualitycastings
PressureCastoia
(b)
Air|irc?
SAiirs
RNrwdorymbc
AHflK
卫lumlmi
盹dhoid讪卿IGrapliilvmvN
pol,r,r,«baslnG他Chill
11
WhedHubPlolc
(a)Thebottom-pressurecastingprocessutilizesgraphitemoldsfortheproductinofsteelrailroadwheels・(b)Gravitypouringmethodofcastingarailroadwheel.Notethatthepouringbasinalsoservesasariser.
DieCasting
•Furtherexampleofpermanent-moldcasting
•Moltenmetalisforcedintothediecavityatpressuresrangingfrom.7MPa一700MPa
•Partsmadefromhererangefrom:
一Handtools
一Toys
一Applianeecomponents
•Therearetwobasictypesofdiecastingmachines
一Hot-chamber・involvestheuseofapistontopushmoltenmetalintothediecavity
一Cold-chamber一moltenmetalispouredintotheinjectionchamber&theshotchamberisnotheated
HotchamberDiecastingDrocess
MoltenMeta)
•1・Thedieisclosedandthepistonrises,openingtheportandallowingmoltenmetaltofillthecylinder.
•2.Theplungermovesdownandsealstheportpushingthemoltenmetalthroughthegooseneckandnozzleintothediecavity,whereitisheldunderpressureuntilitsolidifies・
▲
•3・Thedieopensandthecores,ifany,retract.Thecastingremainsinonlyonedie,theejectorside.Theplungerreturns,allowingresidualmoltenmetaltoflowbackthroughthenozzleandgooseneck.
•4.Ejectorpinspushthecastingoutoftheejectordie.Astheplungeruncoversthefillinghole,moltenmetalflowsthroughtheinlettorefillthegooseneck,asinstep
(1).
•2.Theplungerpushesthemoltenmetalintothediecavitywhereitisheldunderpressureuntilsolidification.
1.Thedieisclosedandthemoltenmetalisladledintothecold-chambershotsleeve・
•4・Ejectorpinspushthecastingoutoftheejectordieandtheplungerreturnstoitsoriginalposition.
•3・Thedieopensandtheplungeradvances,toensurethatthecastingremainsintheejectordie.Cores,ifany,retract.
ProcessCapabilitiesandMachineSelection
一Diesareratedaccordingtotheirclampingforcethatisneeded
一Factorsinvolvedinselectionofdiecastmachinesare
•Diesize
•Pistonstroke
•Shotpressure
•Cost
一Die-castingdies
•Singlecavity
•Multiple-cavity
•Combination-cavity
•Unitdies
一RatioofDieweighttopartweightis1000to1
一Surfacecrackingisaproblemwithdiesduetothehotmetalthatispouredintothem
一Hasabilitytoproducestronghigh-qualitypartswithcomplexshapes
一Gooddimensionalaccuracyandsurfacedetails
Varioustypesofcavitiesinadiecastingdie.
a)
b)
d)Unitdie
•800tonhotchamberdiecastingmachine,DAM8005.Thisisthelargest
hotchambermachineintheworldandcostsabout$1.25million.
CentrifuqalCasting
•Utilizestheinertialforcescausedbyrotationtodistributethemoltenmetalintothemoldcavities
•Firstusedinthe1800';s
•Threetypesofcentrifugalcasting
一Truecentrifugalcasting
一Semicentrifugalcasting
一Centrifuging
Mokl
Drivesliah
■RqIHts-~1
Schematicillustrationofthecentrifugalcastingprocess.Pipes,cylinderliners,andsimilarlyshapedpartscanbecastwiththisprocess.
SemicentrifuqalCastingProcess
(a)Schematicillustrationofthesemicentrifugalcastingprocess.Wheelswithspokescanbecastbythisprocess・(b)Schematicillustrationoicastingbycentrifuging.Themoldsareplacedattheperipheryofthemachine,andthemoltenmetalisforcedintothemoldsbycentrifugalforce・
(a)MeltMetal
SqueezeCastinq
「
(c)Closedieandapplypressure
(d)Ejectsqueezecastingandchargemeltstockandrepeatcycle
(b)Pourmoltenmetalintodie
Sequenceofoperationsinthesqueeze-castingprocess・Thisprocesscombinestheadvantagesofcastingandforging.
SinqleCrystalCastinqofTurbinesblades
Haiit-
hwffleg
heal
Radiant
Columnar
«
io
Fig:
Methodsofcastingturbineblades.(a)directionalsolidification;(b)methodtoproduceasinglecrystalblade;and(c)asingle-crystalbladewithconstructionportionstillattached.
SingleCrystaLCasting
■iu
会一3纟*.q£
k.•IB;I
■“il
Fig:
Twomethodsofcrystalgrowing:
(a)crystalpullingand(b)thefloatingzonemethod・Crystalgrowingisespecially
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