Material engineering-Material Extrusion.ppt

Extrusion slide

1. 18/1
Extrusion Process
Extrusionisaprocessthatforcesmetalorplastictoflowthroughashaped
openingdie.Thematerialisplasticallydeformedunderthecompressioninthedie
cavity.Theprocesscanbecarriedouthotorcolddependingontheductilityofthe
material.
Thetoolingcostandsetupisexpensivefortheextrusionprocess,buttheactual
manufacturedpartcostisinexpensivewhenproducedinsignificantquantities.
Materialsthatcanbeextrudesarealuminum,copper,steel,magnesium,and
plastics.Aluminum,copperandplasticsaremostsuitableforextrusion.

2. 18/2
Extrusions Products
Typicalproductsmadebyextrusionarerailingsforslidingdoors,tubinghaving
variouscrosssections,structuralandarchitecturalshapes,anddoorandwindow
frames.Extrudedproductscanbecutintodesiredlengths,whichthenbecome
discretepartssuchasbrackets,gearsandcoathangers.
Aluminium sunroof channel Extruded aluminium roof rails.Side intrusion beams

3. 18/3
Extrusion Processes
Dependingontheductilityofthematerialusedextrusionscanbecariesoutvarious
ways:
HotExtrusion:Extrusioncarriedoutatelevatedtemperatures
Forwardordirectextrusionand
Backwardorindirectextrusion
ColdExtrusion:Extrusioncarriedoutaambienttemperature.Oftencombinedwith
forgingoperations
HydrostaticExtrusion:Pressureisappliedbyapistonthroughincompressiblefluid
mediumsurroundingthebillet

4. 18/4
Hot Extrusion
Extrusioniscarriedoutatelevatedtemperatures-formetalsandalloysthatdonot
havesufficientductilityatroomtemperature,orinordertoreducetheforces
required.Inthisextrusion,diewearcanbeexcessiveandcoolingofthehotbilletin
thechambercanbeaproblem,whichresultsinhighlynon-uniformdeformation.To
reducecoolingofthebilletandtoprolongdielife,extrusiondiesmaybepreheated,
asisdoneinhotforgingoperations.Hotbilletcausesthefollowingproblems:
Becausethebilletishot,itdevelopsanoxidefilmunlessheatedinaninert-atmosphere
furnace.Thisfilmcanbeabrasiveanditcanaffecttheflowpatternofthematerial.
Italsoresultsinanextrudedproductthatmaybeunacceptableincasesinwhichgood
surfacefinishisimportant.
Inordertoavoidtheformationofoxidefilmsonthehotextrudedproduct,the
dummyblockplacedaheadoftheramismadealittlesmallerindiameterthanthe
container.Asaresult,athincylindricalshell(skull),consistingmainlyofthe
oxidizedlayer,isleftinthecontainer.Theextrudedproductisthusfreeofoxides;
theskullislaterremovedfromthechamber.Thefollowingfiguresillustratethehot
extrusionprocessforproducingsolidproductsby
Forwardordirectextrusionprocessand
Backwardorindirectextrusionprocess

5. 18/5
Direct Extrusion
DirectExtrusion:Inthisextrusionprocess,theheatedbilletisplacedinthe
container.Aramtowardsthediepushesit.Themetalissubjectedtoplastic
deformation,slidesalongthewallsofthecontainerandisforcedtoflowthroughthe
dieopening.Attheendoftheextrudingoperation,asmallpieceofmetal,called
butt-endscrap,remainsinthecontainerandcannotbeextruded.Directextrusion
processisshowninthefollowingFigure

6. 18/6
Indirect Extrusion
IndirectExtrusion:Fortheproductionofsolidpart,thedieismountedonthe
endofahollowramandentersthecontainerasshowninthefollowingFigure,the
outerendofcontainerbeingclosedbyaclosureplate.Astheramtravels,thedie
appliespressureonthebilletandthedeformedmetalflowsthroughthedieopening
inthedirectionoppositetotherammotionsandtheproductisextrudedthrough
thehollowram.Inindirectextrusion,thereispracticallynoslipofbilletwith
respecttothecontainerwalls.

7. 18/7
Cold Extrusion
Thisprocessissimilartohotextrusionexceptthatthemetalsworkedpossessthe
plasticitynecessaryforsuccessfulformingwithoutheatingthem.Usually,These
metalshaveahighdegreeofductility.Coldextrusionisalsodonetoimprovethe
physicalpropertiesofametalandtoproduceafinishedpart.Coldextrusionisdone
mostlyonverticalmechanicalpressesbecausetheyarefastandsimple.Themethod
isfast,wastesnoorlittlematerialsandgiveshigheraccuracyandtolerance.The
widelyemployedcoldextrusionmethodisImpactextrusionorextrusionup
method.

8. 18/8
Impact Extrusion
ImpactExtrusion:Impactextrusionisperformedathigherspeedsandshorter
strokesthanconventionalextrusion.Itisformakingdiscreteparts.Formakingthin
wall-thicknessitemsbypermittinglargedeformationathighspeed.

9. 18/9
Hydrostatic Extrusion
ABilletthatissmallerthatthechamberisused.
TheChamberisfilledwithafluid.Pressureisthenappliedtothepressingstem
Thereisnofrictiontoovercome

10. 18/10
Tube-Drawing
Tube-drawingoperations,withandwithoutaninternalmandrel.Notethatavariety
ofdiametersandwallthicknessescanbeproducedfromthesameinitialtubestock.
Examples of tube-drawing operations, with and without an internal mandrel. Note that
a variety of diameters and wall thicknesses can be produced from the same initial
tube stock (which has been made by other processes).

11. 18/11
General Design Recommendations
Limitirregularshapes,sharpcorners,
andverythinsections.
Avoidthinwallssections
Commonlyspecifiedminimumwall
thicknessesinclude:
Aluminum1mm
Carbonsteels3mm
StainlessSteel5mm
Poor and good examples of cross-sections to be extruded. Note
the importance of eliminating sharp corners and of keeping
section thicknesses uniform.

12. 18/12
Extrusion Defects
SurfaceCracking:Crackingonbilletmaterialsoccursduetotemperature,
friction,punchspeed.
HighTemperatures
Crackfromalongthegrainboundaries.Typicallyoccurinaluminum, magnesium,
zincalloys
ColdTemperatures
Causedbystickingofbilletmaterialatthedieland
Knownasthe“BambooDefect”becauseofitssimilarappearancetobamboo
Pipe:Themetal-flowpatterntendstodrawoxidesandimpuritiestowardthecenter
ofthebillet
InternalCracking:Centerofextrudedproductdevelopscracks.
Attributedtoastateofhydrostatictinselstress
Cracksincreasewithincreasingdieangle,impuritiesanddecreasingextrusionratioand
friction

13. 18/13
Advantages
Therangeofextrudeditemsisverywide.Cross-sectionalshapesnotpossibleby
rollingcanbeextruded,suchasthosewithre-entrantsections.
Notimeislostwhenchangingshapessincethediesmaybyreadilyremovedand
replaced.
Dimensionalaccuracyofextrudedpartsisgenerallysuperiortothatofrolledones.
Inextrusion,theductilityofthemetalsishigherasthemetalinthecontainerisin
compositecompression,thisadvantagebeingofparticularimportanceinworking
poorlyplasticmetalsandalloys.
Verylargereductionsarepossibleascomparedtorolling,forwhichthereduction
perpassisgenerally2.
Automationinextrusionissimplerasitemsareproducedinasinglepassing.
Smallpartsinlargequantitiescanbemade.Forexample,toproduceasimplepump
gear,alonggearisextrudedandthenslicedintoanumberofindividualgears.
Itdoesnotneeddraftorflashtotrimandneedlessmachiningasitismoreaccurate
thanforging.

14. 18/14
Disadvantages
Processwasteinextrusionishigherthaninrolling,whereitisonly1to3%
In-homogeneityinstructureandpropertiesofanextrudedproductisgreaterdueto
differentflowsoftheaxialandtheouterlayersofblanks.
Servicelifeofextrusiontoolingisshorterbecauseofhighcontactstressesandslip
rates.
Relativelyhightoolingcosts,beingmadefromcostlyalloysteel.
Inproductivity,extrusionismuchinferiortorolling,particularlytoitscontinuous
varieties.
Costofextrusionaregenerallygreaterascomparedtoothertechniques

15. 18/15
Applications
Extrusionismorewidelyusedinthemanufactureofsolidandhollowsectionsfrom
poorlyplasticnon-ferrousmetalsandtheiralloys(aluminum,copper,brassand
bronzeetc.)
Steelandotherferrousalloyscanalsobesuccessfullyprocessedwiththe
developmentofmolten-glasslubricants.
Manufactureofsectionsandpipesofcomplexconfiguration.
Mediumandsmallbatchproduction
Manufactureofpartsofhighdimensionalaccuracy
Therangeofextrudeditemsisverywide:rodsfrom3to250mmindiameter,pipes
of20to400mmindiameterandwallthicknessof1mmandaboveandmore
complicatedshapeswhichcannotbeobtainedbyothermechanicalmethods.