MODULE II.pdfdfddstfyzddzdzezs$€_$€¥$_¥€

VhG$*6**66_*

1. Casting operation

2. CASTING
➢Castingisamanufacturingprocessbywhichtherequiredshapeandsizeoffinalproductis
obtainedbypouringamoltenliquidmaterialintoamold,whichcontainsahollowcavity
ofthedesiredshape,andthenallowedtosolidify.
➢Thesolidifiedpartisalsoknownasacasting,whichisejectedorbrokenoutofthemoldto
completetheprocess.
➢Castingmaterialsareusuallymetals.
➢Almostallmetalscanbecast.
➢Castingismostoftenusedformakingcomplexshapesthatwouldbeotherwisedifficultto
makebyothermethods.

3. Centrifugal casting
Themoldissetupandrotatedalonga
vertical(rpmisreasonable),or
horizontalaxis.
2.Themoldiscoatedwitharefractory
coating.
3.Whilerotatingmoltenmetalis
pouredin.
4.Themetalthatispouredinwillthen
distributeitselfovertherotatingwall.
5.Duringcoolinglowerdensity
impuritieswilltendtorisetowardsthe
centerofrotation.
6.Aftertheparthassolidified,itis
removedandfinished.

4. ➢CentrifugalCastingproduces:
➢Goodquality.
➢Accuratecasting.
➢Savesmaterial.
➢Denseproduct&havefinegrainedstructurewithuniform&high
physicalproperties.
➢Lesssubjectedtodirectionalvariationthanstaticcasting.

5. Permanent mouldcasting (gravity die casting)
•Acastingproducedbypouringmolten
metalinametallicmouldisknownas
permanentmouldcasting
•Thesemouldsaregenerallymadein
twohalves
•Thesprue,riser,runner,gatesand
ventsaremachinedintotheparting
surfaceofmouldhalves
•Theprocessisgenerallyusedfornon
ferrousmetalsandtheiralloys
•Hydraullicbrakecylinders,oilpump
bodies,carburetorbodiesetcare
madebythisprocess

7. SPECIAL CASTING PROCESS
➢Themovablediehalfistheejectordieandis
mountedtoamovableplaten,whichslidesalong
tiebars
➢Themetaliscontainedinanopenholdingpot,
whichisplacedinthefurnaceandmeltedtothe
neededtemperature.
➢Whentheplungerisinthe“up”position,the
moltenmetalflowsintotheshotchamber.
➢Astheplungermovesdown,itforcesthemolten
metalthroughagooseneckandintothedieat
injectionpressuresrangingfrom1,000–5,000psi.
➢Themachinepushesthemovingplatentowardsthe
coverdieandholdsitclosedwithgreatpressure
untilthemoltenmetalisinjected.
➢Theplungerremainsinthe“down”positiontohold
thepressurewhilethecasting“coolsoff.”After
solidification,theplungerisretractedandthecast
partiseitherejected,manuallyremovedfromthe
machineorpushedoffthecoverdie.
➢Thisejectionsystem,whichincludesanejectordie
andejectorpins,allowsthecastingtobepushed
outwhilereleasingthediehalves
Hot chamber die casting process
➢Hotchamberdiecastingisatypeofdiecastingthatuses
alloyswithlowmeltingtemperatures(i.e.Zinc,some
Magnesiumalloys.
➢Inahotchamberdiecastingmachine,thefixeddiehalf
iscalledacoverdie,whichismountedtoastationary
plateandalignswiththenozzleofthegooseneck.

8. HOT CHAMBER DIE CASTING

9. Cold chamber die casting
•Coldchamberdiecastingisatypeof
diecastingthatisusedforalloyswith
highmeltingtemperatures
•Asacontrastfromhotchamberdie
castingheremeltingunitisseparate.
•Moltenmetalisladledfromthe
furnaceintotheshotchamber
throughapouringhole
•Theplungerforcesmetalthroughthe
shotchamberintothedieatpressures
rangingfrom2,000and20,000psi.
•Theplungerholdsthepressureand
retractsaftersolidification.
Disadvantagesofdiecasting
1.Diecostingunitsarecostly
2.Noteconomicalforsmallruns
3.Allmetalsandalloyscannotbediecast
Advantagesofdiecasting
1.Productionrateishigh
2.Bettersurfacefinishanddetails
3.Closedimensionaltolerancecanbeobtained
4.Thinsectioncanbecasteasily
5.Labourcostpercastingislow

10. Cold Chamber Die Casting

12. INVESTMENT CASTING
➢Investmentcastingisamanufacturingprocessinwhichaliquidmaterial
ispouredintoaceramicmold,whichcontainsahollowcavityofthe
desiredshape,andthenallowedtosolidify.
➢Thesolidifiedpartisthecasting,whichisbrokenawayfromtheceramic
moldtocompletetheprocess.
➢Thestepswithintheinvestmentcastingprocessareasfollows:

13. Investment casting
•Createwaxpattern:Apatternthatreplicatesthefinished
partgeometryismadeusingawaxinjectiondie
•WaxAssembly:Next,thewaxpatternsareassembledonto
runnersandintoafinishedtreewhichisreadytobedipped.
•SlurryCoating:Theassemblyisthendippedintoahigh-grade
ceramicslurrytobuildaceramicshellaroundthewaxtree.
•Stuccoing:Aftertheslurrycoatingisdone,particlesofsand
aredroppedontothesurfaceofthewettreeassembly.This
helpstothickenandstrengthenthelayerofcoatingonthe
waxassemblysurface..
•Dewaxing:Thewaxinsidethenewlybuiltshellisnow
removed.Dewaxingisdoneusingasteam-dewaxing
autoclaveorflashfirefurnace.
•Casting:Nowthedesiredmoltenmetalispouredintothe
pre-heatedmoldcavity.
•Cooling:Themoldthensitstoallowthemoltenmetaltocool
andsolidifywhichthenbecomesthefinalcasting.
•ShellRemoval:Theshellmaterialisthenremovedthrough
processeshammerknockout,vibration,andsteelgrit
blasting.
•CutOff:Thefinishedpartsarethencutfreefromthegating
andrunnersystem.
•Finishing:Variousfinishingtechniquesarethenemployed
includinggrinding,sandblastingandcoatingtoachievethe
finalsurfaceneeded.

14. Investment casting

15. SlushCasting:
➢SlushCastingisaspecialtypeofpermanentmoldcastingtocreatea
hollowcastingwithoutusingcores.Intheprocessthematerialispoured
intothemoldandallowedtocooluntiladesiredwallthicknessisobtained,
thenotyetsolidifiedmoltenmetalispouredout.Itisarelatively
inexpensiveprocess.
➢Thisisusefulformakinghollowornamentalobjectssuchascandlesticks,
lamp'sholder,statuesetc.
➢Thethicknessoftheshelliscontrolledbytheamountoftimeallowed
beforethemoldisdrainedasshowninFig.(3)above.
➢Low-melting-pointmetalssuchaslead,zinc,andtinareused.
➢Theexteriorappearanceisimportant,butthestrengthandinterior
geometryofthecastingareminorconsiderations.

17. Casting Defects
1.ShiftorMismatch
Thedefectcausedduetomisalignmentofupperandlowerpart
ofthecastingandmisplacementofthecoreatpartingline.
2.Swell
Itistheenlargementofthemoldcavitybecauseofthemolten
metalpressure,whichresultsinlocalisedoroverall
enlargementofthecasting
3.Blowholes:
Whengasesentrappedonthesurfaceofthecastingdueto
solidifyingmetal,aroundedorovalcavityisformedcalledas
blowholes.Thesedefectsarealwayspresentinthecopepartof
themold.
4.Drop
Dropdefectoccurswhenthereiscrackingontheupper
surfaceofthesandandsandpiecesfallintothemolten
metal.
5.MetalPenetration
Thesecastingdefectsappearasanunevenandrough
surfaceofthecasting.Whenthesizeofsandgrainsislarges,
themoltenfusesintothesandandsolidifiesgivingusmetal
penetrationdefect.

18. 6. Shrinkage Cavity
•Theformationofcavityinthecastingdueto
volumetriccontractioniscalledasshrinkage
cavity.
8. Misrun
Whenthemoltenmetalsolidifiesbefore
completelyfillingthemoldcavityandleavesa
spaceinthemoldcalledasmisrun.
7. Cold Shut
Whenthemoltenmetalentersintothemoldfromtwogatesand
whenthesetwostreamsofmoltenmetalmeetatajunctionwith
lowtemperaturesthantheydonotfusewitheachotherand
solidifiescreatingacoldshut(appearaslineonthecasting).It
lookslikeacrackwithroundedge
9. Slag Inclusion
Thisdefectiscausedwhenthemoltenmetal
containingslagparticlesispouredinthemoldcavity
anditgetssolidifies.

20. ➢Mechanicalworkingofametalmeanstheplasticdeformationofametal
undertheactionofexternallyappliedforces.
➢Mechanicalworking(plasticdeformation)ofmetalsabovethe
recrystallisationtemperature(lowercriticaltemperature)butbelowthe
burningpointistermedashotworkingandtheworkingbelow
recrystallisationtemperatureistermedascoldworking.
➢Duringtheplasticdeformationofametaltheexistinggrainsorcrystals
aredistortedorbrokenout.Therefiningofmetalisdonebyheatingthe
metal,leadingtotheformationofnewgrainswithundistortedspace
lattice(crystal).Thisiscalled"recrystallisation".Thetemperatureat
whichrecrystallisationtakesplace,i.e.newgrainsareformedinthemetal
iscalledrecrystallisationtemperature.

21. COLDWORKINGOFMETALS
➢Themechanicalworkingofmetalsbelowrecrystallisationtemperature
iscalledcoldworking.Thecoldworkingisnormallydoneatroom
temperature.
Advantages
➢Accuratedimensionalcontrolcanbeobtainedbycoldworkingprocess.
➢Nosurfaceoxidationresultsintheprocess.
➢Bettersurfacefinishisobtained.
➢Strengthandhardnessofthemetalisincreased.
➢Thisisapossiblemethodtoincreasethehardnessofthosemetalswhich
donotrespondtoheattreatment.

22. Disadvantages
➢Higherpresureandheavierequipmentareneeded.
➢Onlysmallsizedcomponentscanbeeasilycoldworked.
➢Onlyductilemetalscanbeshapedthroughcoldworking
➢Grainstructureisnotrefined;residualstresseshaveharmful
effectsoncertainpropertiesofmetal

23. COLD WORKING OPERATIONS
The various widely used cold working operations are
➢Drawing
➢Squeezing
➢Bending
➢Extrusion
➢Shearing

24. 1.DRAWING
Itistheprocessofproducingvarious
cross-sectionsbyforcingofmetalthroughadiebymeansofa
tensileforce.Barsandsheetsofanycross-sectionorcomposition
maybecolddrawn.Someofthedrawingoperationsusedare
➢Wiredrawing
➢Deepdrawing
➢Stretchforming
➢Tubedrawing
➢Metalspinning

25. 2.Wiredrawing:
Allthemetalwiresare
producedbycolddrawing,throughthe
die.Thisprocessconsistsofforcingalarge
diameterrodthroughadie,thereby
reducingitscrosssectionalareaofthe
rod.Rawmaterialforwiredrawingishot
rolledbars.Thebarsarefirstcleanedto
removescaleandrust,andthencoated
withsomelubricantstoavoidcorrosion
andoxidation.Thewireisdrawnby
pullingtherod,throughseveraldiesof
decreasingdiameterstoobtainthewireof
thedesireddiameter.

28. Metalspinning(Coldspinning):
Metalspinningisan
operationofshapingsheetmetalbypressing
againstaformwhileitisrotating.Fig.2.9
showsacoldspinningoperation.The
operationisperformedonaspeedlathe.A
circularblankiscutandpositionedagainst
themetallicorwoodenformbyanadopter.
Aspinningtoolwithbluntedgeisusedand
whilethelatherotates,theblankisforcedto
theshapeoftheform.Aluminumandother
softmetalsaresuitedforcoldspinning.
Kettles,cookingutensils&lightreflectors
canbeproducedbythismethod.

30. BENDING
Thisprocessisalsoknownas
forming.Thebars,rods,structuralshapesand
sheetmetalsmaybebenttomanyshapesin
coldconditionsMechanicalworkingofmetals
Ram2.25throughdies.Thebendingcanbe
doneonaramtypemachineorrotarytypeof
machine.Inramtypemachine(Fig2.11)two
pressurediesaremountedinfixedpositionon
theframeofthemachineandarefreeto
rotateabouttheirmountingpins.Theformis
mounteddirectlytothepistonrodofthe
hydrauliccylinder

31. ➢Arotarytype,rollbendingmachineis
showninfig.2.12.
➢Itisemployedforbendingmetalplates
andstripsintocylindricalshapes.
➢Thismachineismadewiththreerollersof
similardiameter,twoofthemarefixedand
oneisadjustable.Asthemetalentersand
passesthroughtherolls,itsfinalcurvature
isdeterminedbythepositionthe
adjustableroll.
➢Anothertypeofrollformingisshownin
fig.2.13.Whiledesigningdiesandpunches
springbackofmetalsinbendingshouldbe
considered.

32. SQUEEZING
Itisaquickandwidelyusedwayofformingductile
metals.Insqueezing,themetalismadetoflowwithinthecavityofdieand
punch,toattainthedesiredshape.Thisprocessrequiresagreatamountof
pressureandisusuallyperformedinhydraulicpresses.Someofthe
importantsqueezingoperationsare
(1)coldrolling
(2)Upsetting
(3)coining,
(4)coldheading.
(5)Hobbing
(6)shotpeening.etc.

36. Cold heading (Cold forging)
Itisaformofswagingoperation
extensivelyusedformakingbolts,
rivets,andothersimilarheadedparts.
Aductilemetalrodhavingstandard
lengthisfedontothemachine,where
itisheldinapairofjawsand
subjectedtotwoorthreeblowsto
formtheheadroughly.Itisthen
repositionedinanotherdieforfinal
shapingandsizing.

38. SHEARING
Thisisaprocessofcuttingthe
metalusingthepunchanddie.Themetaltobe
cutisplacedbetweenthepunchanddieas
showninfig.Thepunchdescendsuponthe
metalpiececausingtheshearingaction.Some
oftheshearingoperationsare
(a)trimming
(b)punchingand
(c)blanking.etc.

41. COLDEXTRUSION
➢Theprocessofextrusioninvolvestheflowofmetalinitsplasticstate
throughashapeddieunderpressure.Themostcommoncoldextrusion
processisimpactextrusion.
➢Impactextrusion:-Inthisprocessofextrusiontheworkingmaterialis
placedintoablindholeofthedieandapunchwithclearanceisforcedin
tothediewhichcausesthemetaltoflowplasticallyaroundthepunch.
Whenthepunchmovesup,compressedairorstripperisusedtoseparate
thecomponentfromthepunch.Theapplicationoftheprocessarelimited
tosoftandductilematerialssuchaslead,tin,aluminum,zincandsomeof
theiralloys.Themainadvantagesofthisprocessisitsspeed,product
uniformityandlowscrapyield.Thisprocessisusedforthemanufacture
ofcollapsibletubes,(forshavingcream,toothpaste,medicines.etc)
condensercansandothersimilarthinwalledproducts.

43. HOTWORKINGOFMETALS
➢Mechanicalworkingofmetalsaboverecrystallisation
temperatureistermedas'hotworking'.Hotworkingcombines
thedeformationandrecrystallisation.Inadditiontomerechange
ofshape,hotworkingeffectsthemetalcharacteristicsand
properties.Thechangesinstructurefromhotworkingimprove
mechanicalpropertiessuchasductility,toughness,elongation
percentage,reductionofareapercentage,andresistancetoshock
andvibration.

44. Advantages
➢Porosityofthemetalismostlyeliminated
➢Sincethemetalisworkedaboverecrystallisationtemperaturerefinement
ofgrains(crystals)occurs.
➢Impuritiesintheformofinclusionsarebrokenupanddistributed
throughthemetal.
➢Physicalpropertiesaregenerallyimprovedduetorefinementofgrains.
➢Energyrequiredtochangetheshapeislesscomparedtocoldworking.
➢Itisarapidandeconomicalprocess.

45. Disadvantages
➢Closetolerancescannotbemaintained.
➢Toolingandhandlingcostishigh.
➢Rapidoxidationorscaleformationtakesplaceonthemetalsurface,
leadingtopoorsurfacefinish.
➢Toollifeisreducedasthetoolshavetoworkathightemperatures

46. HOTWORKINGPROCESSES
Thefollowingaresomeoftheimportanthot
workingprocesses.
(a)Hotrolling
(b)Hotpiercing
(c)Hotdrawing
(d)Hotextrusion
(e)Hotspinning

56. ProcessingStagesofPowderMetallurgy
➢Firsttheprimarymaterialispowderedanddividedintomanysmall
individualparticles.
➢Twoormoremetalandornonmetalsaremixedorblendedtogetherto
formahomogeneousmixture.
➢Theblendedmixisintroducedintoamoldcavityoradieandpressedto
produceaweakcohesivemasscalledasgreencompact.
➢Thegreencompactisthensubjectedtoveryhightemperatureand
pressureforaknowntimetogetahardenedmass.

57. StepsinvolvedinPMtechnique
1.Preparationofpowders:veryfinepowdersareobtainedusingvarious
techniques.
2.Blendingofpowders:Thefinepowdersaremixedalongwithalubricant.
Thelubricanthelpsinimpartinggoodfluiditytothepowders.
3.Compacting:Theblendedpowderiscompactedinamoldordie.
4.Sintering:Thecompactedmassissinteredatahightemperatureina
furnaceinacontrolledatmosphere.

58. 5.Sizing:Thesinteredcomponentispassedinamoldordiestotrim
thecomponentandachievehighdimensionalaccuracy.
6.Machining:Ifrequiredfinalmachiningisdoneonsomespecific
locationsincludingdrillingverysmallholes.
7.Treatment:Partsaresubjectedtodeburringandtumblingtoremove
anysmallprojectionsandothertreatmentslikeoilimpregnationtec.,
aregiven.
8.Inspection:Finallypartsareinspectedtocheckthequality.

62. SomeapplicationsPMareasfollows
➢Usedtoproduceporouspartse.gfilters.
➢Somecomponentsoftungstenemployedinjetenginesaremadebypowder
metallurgy.
➢Automobilecomponentssuchasclutchplates,connectingrods,camshafts
andpistonringsetc.
➢Manytypesofhardandsoftmagneticcomponents.
➢Grindingwheelsaremanufacturedbyusingsteelanddiamondpowder.
➢Nozzleforrocketsandmissilesaremadeusingsilverinfiltratedtungsten.
➢Itisusedtoproducecomplexshapedpartswhichrequiremachiningwhen
producedbyothermethodse.g.gears.
➢Electricalbushesformotorsaremadebycombiningmetallicandnon
metallicmaterial.
➢Somepartsusedinclocks,typewriters,calculators,permanentmagnetetc.
aremadebypowdermetallurgy

63. THANK YOU