Powder Metal Manufacturing

8/2/2019 Powder Metal Manufacturing

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Mohamed Gamil


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PMreferstoarangeofmanufacturingandmetal

formingpractices

that

are

used

to

produce

net

or

nearnetshapepartsfrommixturesofmetaland

alloypowders

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3000B.C.

Egyptians

made

tools

with

powder

metallurgy

1900stungstenfilamentforlightbulb

1930scarbidetoolmaterials

1960sautomobileparts

1980saircraft

engine

turbine

parts

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Abilityto

create

complex

shapes

Highstrengthproperties

Low

material

waste Goodmicrostructurecontrol

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TABLE 17.1

Application Metals Uses

Abrasives

Aerospace

Automotive

Electrical/electronic

Heat treating

JoiningLubrication

Magnetic

Manufacturing

Medical/dental

MetallurgicalNuclear

Office equipment

Fe, Sn, Zn

Al, Be, Nb

Cu, Fe, W

Ag, Au, Mo

Mo, Pt, W

Cu, Fe, SnCu, Fe, Zn

Co, Fe, Ni

Cu, Mn, W

Ag, Au, W

Al, Ce, SiBe, Ni, W

Al, Fe, Ti

Cleaning, abrasive wheels

Jet engines, heat shields

Valve inserts, bushings, gears

Contacts, diode heat sinks

Furnace elements, thermocouples

Solders, electrodesGreases, abradable seals

Relays, magnets

Dies, tools, bearings

Implants, amalgams

Metal recovery, alloyingShielding, filters, reflectors

Electrostatic copiers, cams

Source: R. M. German.

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Afabricationtechniqueinvolvesthecompactionofpowderedmetal,followedbyaheattreatmenttoproduceamoredensepiece.

Powdermetallurgyisespeciallysuitableformetals havinglowductilities havinghighmeltingtemperatures

Powder Metallurgy

pressure

heat

point contactat low T

densification by diffusion athigher T

areacontact

densify

Production of P/M Parts:

Preparation of Metal Powders

Compaction (pressing)

Sintering (densification) atelevated temp.

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Figure 17.1 (a) Examples of typical partsmade by powder-metallurgy processes. (b)Upper trip lever for a commercialirrigation sprinkler, made by P/M. This

part is made of unleaded brass alloy; itreplaces a die-cast part, with a 60%savings. (c) Main-bearing powder metalcaps for 3.8 and 3.1 liter General Motorsautomotive engines..

(a)

(b)

(c)

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Outline of processes and operations involved in making powder-metallurgy parts.

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Mohamed Gamil


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Figure 17.3 Particleshapes in metal

powders, and theprocesses by whichthey are produced.Iron powders areproduced by many ofthese processes.

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Scanning-electron-microscopy photograph of iron-powder particlesmade by atomization. (b) Nickel-based superalloy (Udimet 700)powder particles made by the rotating electrode process; see Fig.17.5b. Source: Courtesy of P. G. Nash, Illinois Institute ofTechnology, Chicago.

(a) (b)

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Methods of metal-powder production by

atomization; (a) meltatomization; (b)atomization with arotating consumable

electrode.

Methods of mechanicalcomminution, to obtainfine particles: (a) rollcrushing, (b) ball mill, and

(c) hammer milling. Mohamed Gamil


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Some common equipment

geometries for mixing orblending powders: (a)cylindrical, (b) rotatingcube, (c) double cone, and(d) twin shell. Source:Reprinted with permissionfrom R. M. German,Powder Metallurgy Science.Princeton, NJ; Metal

Powder IndustriesFederation, 1984.

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Mohamed Gamil


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(a) Compaction of metalpowder to form abushing. The pressedpowder part is calledgreen compact. (b)Typical tool and die setfor compacting a spur

gear. Source: MetalPowder IndustriesFederation.

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TABLE 17.2

Metal

Pressure

(MPa)Aluminum

Brass

Bronze

IronTantalum

Tungsten

70275

400700

200275

35080070140

70140

Other materials

Aluminum oxideCarbon

Cemented carbides

Ferrites

110140140165

140400

110165

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Pressing is done underhigh pressure

A 7.3 MN (825 ton)mechanical press forcompacting metal powder.

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Figure 17.12 Schematic diagram of cold isostatic pressing, as applied toforming a tube. The powder is enclosed in a flexible container around asolid core rod. Pressure is applied isostatically to the assembly inside ahigh-pressure chamber. Source: Reprinted with permission from R.M.German, Powder Metallurgy Science. Princeton, NJ; Metal Powder

Industries Federation, 1984.

Figure 17.14 Schematic illustration of

hot isostatic pressing. The pressure andtemperature variation vs. time are shownin the diagram. Source: Preprinted withpermission from R.M. German, Powder

Metallurgy Science. Princeton, NJ; MetalPowder Industries Federation, 1984.

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Figure 17.15 An example ofpowder rolling. Source:Metals

Handbook(9th ed.), Vol. 7.

American Society for Metals.

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Figure 17.9 (a) Density of copper- and iron-powder compacts as a function of compacting pressure. Density greatlyinfluences the mechanical and physical properties of P/M parts. Source: F. V. Lenel, Powder Metallurgy: Principles and

Applications. Princeton, NJ; Metal Powder Industries Federation, 1980. (b) Effects of density on tensile strength,elongation, and electrical conductivity of copper powder. IACS means International Annealed Copper Standard for

electrical conductivity.

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Figure 17.16 Schematic illustration of two mechanisms for sintering metal powders: (a) solid-state materialtransport; (b) liquid-phase material transport. R = particle radius, r= neck radius, and = neckprofile radius.

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Examples of P/M parts, showing Bestdesign Practice.Note that sharp radii and reentrycorners should be avoided.

Threads and transverse holes have tobe produced separately by additionalmachining operations.

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TABLE 17.5

Process(*)

Density

(%)

Yield

strength

(MPa)

Ultimate

strength

(MPa)

Elongation

(%)

Reduction

of area

(%)

Cast

Cast and forged

Blended elemental (P+S)

Blended elemental (HIP)

Prealloyed (HIP)

100

100

98

> 99

100

840

875

786

805

880

930

965

875

875

975

7

14 40

8

9

14

15

14

17

26

(*) P+S = pressed and sintered, HIP = hot isostatically pressed.

Source: R.M. German.

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Usesasintering

atmosphere

and

asintering

furnace

Theatmospheretransfersheattothecompacted

powder,adjustsimpuritylevelsandremove

lubricants.

Atmospherecanbepurehydrogen,nitrogenor

ammonia.

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TABLE 17.3

Material

Temperature

( C)

Time

(Min)Copper, brass, and bronze

Iron and iron-graphite

Nickel

Stainless steels

Alnico alloys

(for permanent magnets)Ferrites

Tungsten carbide

Molybdenum

Tungsten

Tantalum

760900

10001150

10001150

11001290

12001300

12001500

14301500

2050

2350

2400

1045

845

3045

3060

120150

10600

2030

120

480

480

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TAB LE 17.6

W eight (kg)

Potential

cost

Part

Forged

billet P/M

Final

part

saving

(% )

F-14 Fuselage brace

F-18 Engine mount supportF-18 Arrestor hook support fitting

F-14 Nacelle frame

2.8

7.779.4

143

1.1

2.525.0

82

0.8

0.512.9

24.2

50

2025

50

Mohamed Gamil


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Mohamed Gamil

Powder Metal Manufacturing

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