mprocesses notes 15

8/11/2019 MProcesses Notes 15

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Powder MetalProcessing

ManufacturingProcesses


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Outline

IntroductionPowder ManufacturingPowder Metallurgy ProcessSinteringOther Powder Metal ProcessesPowder Metal ProductsPowder Metallurgy Design


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Powder Metallurgy


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Powder Metallurgy

Metal

Powder

Metal Product


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Examples of Powder

Metal ProductsGearsCamsCranksBearingsRoller bearing cagesHousingsLight bulb filamentsSprinkler mechanisms


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Powder Metal Materials

Elemental A pure metal, most commonlyiron, aluminum or copper

Prealloyed

An alloy of the requiredcomposition, most commonlycopper alloys, stainless steel or

high-speed steel


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Powder Manufacturing

Conversion of molten metal topowder

Atomization


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Powder Manufacturing

Other methods of producingpowder:

- Chemical reduction ofparticulate compounds

- Electrolytic deposition

- Pulverization or grinding ofbrittle materials

- Thermal decomposition

- Precipitation from solutions- Condensation of metal vapors


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Particle Shape


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Particle Size

The process of separating particlesby size is called classification


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Particle Size

Micrograph of screened powder particles, showingthat particles may be longer than the mesh is wide


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Particle Size

void

smaller, more numerous voids

voids filled by smaller particles,small voids remain

Mixing particles of different sizes allows decreasedporosity and a higher packing ratio


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Powder Metallurgy

Process


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Blending and Mixing

BlendingCombining powders of the same materialbut possibly different particle sizes

MixingCombining powders of different materials


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Compaction

High pressure is applied to squeezethe powder into the desired shape


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Example of a Powder

Press


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Sintering

Heats the powder below the meltingpoint to allow solid-state diffusion

and bond the particles together


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Sintering

Diagram of particles in sintering, showing thepossible movements of atoms


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Sintering


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Sintering


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Sintering Production

Lines


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Examples of Sintering

Production Lines


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Sintering

Strength of sintered structures as related to density,showing that the strength is higher when the density

is higher (less residual porosity)


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Other Powder Metal

ProcessesCold Isostatic PressingHot Isostatic PressingInjection MoldingPowder RollingPowder ExtrusionPlasma Spraying


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Isostatic Pressing

Uses pressurized fluid to compress thepowder equally in all directions

Cold Isostatic Pressing

Compaction performed at roomtemperature

Hot Isostatic PressingPerformed at high temperatures andpressures


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Example of an Isostatic

Press


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Injection Molding

The powder is mixed with a binderand molded, and the binder is

removed before sintering


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Powder Rolling

Powder is compressed in a rolling millto form a strip


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Powder Extrusion

The powder can be extruded within acontainer or after being formed into

billets


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Plasma Spraying

Uses a plasma arc to propel moltendroplets at a surface at a high

velocity, forming a high-densitystructure


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Plasma Spraying


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Powder Metal Products

1. Porous or permeableproducts

2. Products of complex shapes3. Products made of materials

that are difficult to machine orhave high melting points

4. Products which require thecombined properties ofmultiple materials

5. Products in which powdermetallurgy produces superiorproperties


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Powder Metallurgy

Design1. The shape must permit removal

from the die

2. The shape should not have thinwalls or sharp corners3. The shape should permit the

construction of strong tooling

4. The shape of the part should bewithin the thickness range forwhich the powder can be properlycompacted

5. The part should have as fewchanges in section thickness aspossible


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Powder Metallurgy

Design6. Parts can be designed to take

advantage of the capabilities of

the powder metallurgy process7. The design should be consistentwith available equipment

8. Consideration should be given for

product tolerances9. Design should consider the

dimensional changes that occurafter pressing, such as shrinkageduring sintering


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Powder Metallurgy

Design


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Powder Metallurgy

Design


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Powder Metallurgy

Advantages1. Elimination/reduction of

machining

2. High production rates3. Complex shapes can be

produced

4. Wide composition variationsare possible

5. Wide property variations are

possible6. Scrap is eliminated or

reduced


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Powder Metallurgy

Disadvantages1. Inferior strength properties2. Relatively high die cost3. High material cost


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Summary

Powder metallurgy can createparts that would otherwise be

difficult to form, including thosewith complex shapes orporosity

Sintering bonds particlestogether by allowing atoms tomove, forming necks and grainboundaries between theparticles


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mprocesses notes 15

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