Metal Powder Processing Techniques

8/17/2019 Metal Powder Processing Techniques

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METAL POWDER

PROCESSINGTECHNIQUES

BY:

ENGR. SAJID HUSSAIN SIYAL


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WE WILL DISCUSS:

Compacting / Pressing Pressure Techniques

ISO-STATIC COMPACTION / PRESSING

DIE PRESSING / COMPACTION

HOT COMPACT ION/PRESSING

HIGH ENERGY RATE FORMING

CONTINUOUS COMPACTION

VIBRATORY COMPACTION

Pressureless TechniquesSLIP CASTING

GRAVITY COMPACTION

CONTINUOUS PRESSURELESS COMPACTION


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COMPACTING /

PRESSING


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The most important operation in powder metallurgy is compacting

or pressing

Most compacting is done cold, although there are some

applications for which compacts are hot pressed

The purpose of compacting is to consolidate the powders into a

desire shape and as closely as possible to final dimensions, to

achieve the required strength and structural properties. The powders are compacted high pressure. The degree of pressure

required depends upon:

1. The required density of the final products.

2. The ease with which the powder particles will joined

compact together.


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PRESSURE TECHNIQUES

ISO-STATIC

COMPACTION /

PRESSING


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!n this process the powder is loaded into a fle"ible

#usually rubber$ air tight container #called a bag$, thatis inside a chamber of hydraulic fluid to which pressure is applied. The force of the applied pressurecompact the powder uniformly in all directionswhiles the final product ta%ing the shape of fle"iblecontainer. &fter cold iso'static pressing, the partsmust be fired #sintered$ to achieve the required

properties ( microstructure.This method is used tomanufacture the li%e par% plug, carbide tools and

bearings. !t is possible to obtain a very uniform green density

and a high degree of uniformity in properties.


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DIE COMPACTION


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Die compaction:)*ie compaction is the most widely used method. The usual sequence of

operation in die pressing is consists of to fill the die cavity through the+ooper with a definite volume of powder.

)&pplications of the required pressure by movement of the upper and lower

punches toward each other and finally ejection of green compact by the

lower punch.

)ressure commonly employed range from 2- ' - tons sq in.

)ressure may be obtained by either mechanical or hydraulic presses.

)Mechanical presses are available with pressure ratings of 1- to 1/- tons and

speeds of to 1/- stro%esmin.)!mportant features of mechanical presses are high speed production rate,

fle"ibility in design, simplicity #in design ( operation$ and economy in

operation, also relatively low investment ( maintenance cost.

)+ydraulic presses have higher pressure ratings up to /--- tons but slower

stro%e speeds generally less than 2- min.


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HOT COMPACTION /

PRESSING


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This method consists in applying pressure and

temperature simultaneously. Molding and sinteringta%e place at the same time, which results in higherdensities and greater productions. The advantages ofhot pressing as compared with cold compacting and

sintering are a reduction in shrin%age effect, alongwith higher strength, hardness, elongation anddensity. +ot pressing is used only to a limited e"tent,

primarily for the production of very hard cemented'

carbide parts. The principal disadvantage of thismethod is the high cost of dies to stand up under

pressure at elevated temperatures.


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HIGH ENERGRATE !ORMING


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These may be mechanical, pneumatic or

e"plosive or spar% discharge methods appliedin a closed die. The advantage of these

methods is the short time and high pressures

that can be attained. !t is also possible to uselow grade and very cheap powders and some

parts due to increased strength of the green

compacts may be used without subsequent

sintering. *isadvantages include high punch

and die wear, limited tolerances and high cost.


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CONTINUOUSCOMPACTION


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!t is applied primarily for simple shapes suchas rod, sheet, tube and plate. Most of the

commercial techniques involve flowing

loose powder between a set of verticallyoriented rolls. The roll gap is adjusted to

give a compact of desired properties. !n

general, the speed of powder rolling is much

less than that of conventional rolling

operations.


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"I#RATORCOMPACTION


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In this method, pressure and i!ration are

app"ied simu"taneous"# to a mass o$

po%der in a ri&id die. 'ompared %ithordinar# die (ompa(tion, this method

a""o%s the use o$ mu(h "o%er pressures to

a(hiee a &ien "ee" o$ densi$i(ation.


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PRESSURE LESS TECHNIQUES

SLIP CASTING


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0lip casting is widely used for ceramics but only to a

limited e"tent for metals. The process consists of first

preparing a slip containing the powder suspended in aliquid vehicle and additives to prevent particle

settling. The slip is then placed in a mold made of a

fluid absorbing material #such as laster of aris$ to

form the slip casting. &fter removal from the mold,

the slip casting is dried and sintered. This technique is

attractive for materials that are relatively

incompressible by conventional die compaction, butthe process does not lend itself to high production

rates because of the long time required for the liquid

to be removed through the porosity of the mold


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GRA"ITCOMPACTION:


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In this method, the die is $i""ed %ith "oose

po%der %hi(h is then sintered in the die.

)he die is usua""# made o$ an inert

materia" su(h as &raphite. Sin(e pressureis not used, parts are &enera""# more

porous. 'ommer(ia""# this method is used

$or the produ(tion o$ *+ $i"ters.


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CONTINUOUS

PRESSURELESS

COMPACTION


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This method is used to produce porous sheetfor electrodes in nickel-cadmium

rechargeable batteries. The powder may beapplied in the form of a slurry (similar to theslip in slip casting) to be coated on a metalscreen or solid metal sheet to produce unusual

composites. The green compact density is amost useful property, since it is an indicationof the effectiveness of compaction and alsodetermines the behavior of the materialduring subsequent sintering. Green densityseems to increase with increasing compactionpressure, increasing particle sie or apparentdensity, decreasing hardness and strength ofparticles and decreasing compaction speed.


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-uestions


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THE

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Metal Powder Processing Techniques