Powder metallurgy

basics of powder metallurgy.....

1. 12/1/2014
Presented by:
Shailendra Pratap Singh (13MEBLA022)
Venkatesh (13MEBLA025)
Sahil Khambhati (13MEBLA008)
Yogita Pawar (13MEBLA013)
Shreya Badave (13MEBLA005)
Submittedto:
Mr. Bhaskar Goel
POWDER
METALLURGY

2. Powder Metallurgy
Essentially,PowderMetallurgy(PM)isanart&scienceof
producingmetalormetallicpowders,andusingthemtomake
finishedorsemi-finishedproducts.
Particulatetechnologyisprobablytheoldestformingtechnique
knowntoman.
Therearearcheologicalevidencestoprovethattheancientman
knewsomethingaboutit.
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3. Powder Metallurgy
Animportantpointthatcomesout:
The entire material need not be melted to fuse it.
Theworkingtemperatureiswellbelowthemeltingpointofthe
majorconstituent,makingitaverysuitablemethodtowork
withrefractorymaterials,suchas:W,Mo,Ta,Nb,oxides,
carbides,etc.
ItbeganwithPlatinumtechnologyabout4centuriesago…in
thosedays,Platinum,[MP=1774°C],was"refractory",and
couldnotbemelted.
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4. Powder Metallurgy Process
Powder production
Blending or mixing
Powder compaction
Sintering
Finishing Operations
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5. Powder Metallurgy Process
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6. Powder MetallurgyProcessing
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POWDER
PROCESSING
PROPERTIES
Powder fabrication
Size and shape characterization
Microstructure (e.g.. dendrite size)
Chemical homogeneity, and ppt. size
Compaction
Sintering
Forging/Hot pressing
Density, Porosity
Ductility, Strength
Conductivity
Other functional properties

7. Usual PM production sequence
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Blendingandmixing(Rotatingdrums,bladeand
screwmixers)
Pressing-powdersarecompressedintodesired
shapetoproducegreencompact
Accomplishedinpressusingpunch-and-die
toolingdesignedforthepart
Sintering–greencompactsareheatedtobondthe
particlesintoahard,rigidmass.
Performedattemperaturesbelowthemeltingpoint
ofthemetal

8. Production of Metallic Powders
Ingeneral,producersofmetallicpowdersarenotthesame
companiesasthosethatmakePMparts
Anymetalcanbemadeintopowderform
Threeprincipalmethodsbywhichmetallicpowdersare
commerciallyproduced
Atomization(bygas,water,alsocentrifugalone)
Chemical
Electrolytic
Inaddition,mechanicalmethodsareoccasionallyusedtoreduce
powdersizes
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9. Particle Shapes in Metal Powders
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10. Conventional powder
metallurgy production
sequence:
blending
compacting
Sintering
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11. Blending and Mixing of Powders
Blending-powdersofsamechemistrybutpossiblydifferent
particlesizesareintermingled
Differentparticlesizesareoftenblendedtoreduceporosity
Mixing-powdersofdifferentchemistriesarecombined.
PMtechnologyallowsmixingvariousmetalsintoalloysthatwould
bedifficultorimpossibletoproducebyothermeans.
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Forsuccessfulresultsincompactionandsintering,
thestartingpowdersmustbehomogenized
(powdersshouldbeblendedandmixed).

12. Blending or Mixing
Blendingacoarserfractionwithafinerfractionensuresthatthe
intersticesbetweenlargeparticleswillbefilledout.
Powdersofdifferentmetalsandothermaterialsmaybemixedin
ordertoimpartspecialphysicalandmechanicalproperties
throughmetallicalloying.
Lubricantsmaybemixedtoimprovethepowder’sflow
characteristics.
Binderssuchaswaxorthermoplasticpolymersareaddedto
improvegreenstrength.
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13. Blending
Tomakeahomogeneousmasswithuniformdistributionof
particlesizeandcomposition.
Powdersmadebydifferentprocesseshavedifferentsizesand
shapes
Mixingpowdersofdifferentmetals/materials
Combiningisgenerallycarriedoutin
Airorinertgasestoavoidoxidation
Liquidsforbettermixing,eliminationofdustsandreduced
explosionhazards
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14. Bowl Geometries for Blending
Powders
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A mixer suitable for blending metal
powders.
Some common equipment geometries used for
blending powders
(a) Cylindrical, (b) rotating cube, (c) double
cone, (d) twin shell

15. Compaction
Applicationofhighpressuretothepowderstoform
themintotherequiredshape.
Conventionalcompactionmethodispressing,inwhich
opposingpunchessqueezethepowderscontainedinadie.
Theworkpartafterpressingiscalledagreencompact,
thewordgreenmeaningnotyetfullyprocessed.
Thegreenstrengthofthepartwhenpressedisadequate
forhandlingbutfarlessthanaftersintering.
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16. Presspowderintothedesiredshapeandsizeindiesusinga
hydraulicormechanicalpress
Pressedpowderisknownas“greencompact”
Stagesofmetalpowdercompaction:
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Compacting

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Powdersdonotflowlikeliquid,theysimplycompressuntilan
equalandopposingforceiscreated.
–This opposing force is created from a combination of
(1)resistance by the bottom punch and
(2)friction between the particles and die surface
Compactingconsolidatesanddandifiesthecomponentfor
transportationtothesinteringfurnace.
Compactingconsistsofautomaticallyfeedingacontrolledamount
ofmixedpowderintoaprecisiondie,afterwhichitiscompacted.
Compacting

18. Compacting
Compactingisusuallyperformedatroomtemperature.Pressures
rangefrom10tonspersquareinch(tons/in
2
)(138MPa)to60
tons/in
2
(827MPa),ormore.
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Figure: (Left) Typical press for the compacting of metal powders. A removable die
set (right) allows the machine to be producing parts with one die set while another is
being fitted to produce a second product.

20. Compaction Sequence
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Figure: Typical compaction sequence for a single-level part, showing the
functions of the feed shoe, die core rod, and upper and lower punches. Loose
powder is shaded; compacted powder is solid black.

21. Friction problem in cold
compaction
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22. Sintering
Heattreatmenttobondthemetallicparticles,therebyincreasing
strengthandhardness.
Usuallycarriedoutatbetween70%and90%ofthemetal'smelting
point(absolutescale)
–Generallyagreedamongresearchersthattheprimarydriving
forceforsinteringisreductionofsurfaceenergy
–Partshrinkageoccursduringsinteringduetoporesize
reduction
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23. Partsareheatedto~80%ofmeltingtemperature.
Transformscompactedmechanicalbondstomuchstrongermetal
bonds.
Manypartsaredoneatthisstage.Somewillrequireadditional
processing.
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Sintering

24. Figure: Sintering on a microscopic scale: (1) particle bonding is
initiated at contact points; (2) contact points grow into "necks"; (3) the
pores between particles are reduced in size; and (4) grain boundaries
develop between particles in place of the necked regions.
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Sintering Sequence
Partsareheatedto0.7~0.9T
m.
Transformscompactedmechanicalbondstomuchstronger
metallicbonds.

25. Thirdstage:
Sinteredproductiscooledinacontrolledatmosphere.
–Preventsoxidationandthermalshock
Gasescommonlyusedforsintering:
H
2, N
2, inert gases or vacuum
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Sintering

26. Sintering Cycle and Furnace
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27. Powder Rolling
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28. Powder Metallurgy Merits
NearNettShapeispossible,therebyreducingthepost-production
costs,therefore:
Precisionpartscanbeproduced
Theproductioncanbefullyautomated,therefore,
Massproductionispossible
Productionrateishigh
Over-headcostsarelow
Breakevenpointisnottoolarge
Materiallossissmall
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29. Advantages of P/M
Virtuallyunlimitedchoiceofalloys,composites,and
associatedproperties
Refractorymaterialsarepopularbythisprocess
Canbeveryeconomicalatlargerunsizes(100,000
parts)
Longtermreliabilitythroughclosecontrolof
dimensionsandphysicalproperties
Widelatitudeofshapeanddesign
Verygoodmaterialutilization
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30. Limitations and Disadvantages
Hightoolingandequipmentcosts.
Metallicpowdersareexpensive.
Problemsinstoringandhandlingmetalpowders.
Degradationovertime,firehazardswithcertainmetals
Limitationsonpartgeometrybecausemetalpowdersdonot
readilyflowlaterallyinthedieduringpressing.
Variationsindensitythroughoutpartmaybeaproblem,
especiallyforcomplexgeometries.
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31. Powder Metallurgy Disadvantages
Porous !! Not always desired.
Large components cannot be produced on a large scale.
Some shapes are difficult to be produced by the conventional
p/m route.
Whatever, the merits are so many that P/M, as a forming
technique, is gaining popularity
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32. PM Parts
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33. Connecting Rods:
Forged on left; P/M on
right
Powdered Metal Transmission Gear
Warm compaction method with 1650-ton
press
Teeth are molded net shape: No machining
UTS = 155,000 psi
30% cost savings over the original forged part
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