metal powder processing techniques
TRANSCRIPT
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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
END