Powder Met. Complete Ranjeet

7/27/2019 Powder Met. Complete Ranjeet

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INTRODUCTIONPowder metallurgy is process in which the metal or alloy powder is

compacted into desired shape & heated below melting point to get the bending

between the particles.

Simple shape parts can be produced with high accuracy without wastage& the component is ready to use.

The parts made with powder metallurgy technique can be shaped to sizewith high precision.

Refractory materials can be produced by powder metallurgy process. The

production of components by powder metallurgy, metallurgy involves a series ofsteps .

1) Manufacture of powder

2) Blending

3) Compacting

4) Pre sintering & sintering

5) Secondary operation

a) Sizingb) Coining

c) Machining

d) Plating

e) Heat treatment


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MANUFACTURE OF METALLIC POWDERMost commonly copper base & iron base metals are used. Stainless steel,

Titanium, Nickel, & chromium metal powders are also used. The particle size

of powder is 0.1micron to several mm. The method used for metallic powder

production are mechanical method, solid state reduction, atomization,

electrolysis, shotting.

MECHANICAL METHOD:-

Meta re disintegrated through produce powder. By crushing, rolling &

milling. The crushed metals are ground by ball mill in which many steel balls

metallic powder to grind size.

CRUSHING:-

This method is used for the brittle materials. The crushing equipment

used for crushing brittle materials may be rapidly moving hammers. Jaw

crushers or gyratory crushes. The powders produced by this method are of

angular shape which is subsequently reduced to powder by milling to attain the

required fitness of the powder.

MILLING:-

This is the most important & widely used method of producing powders of

the required grad of fineness. Though the milling or grinding process is best

suited to brittle materials. Yet it can be used for malleable & ductile materials.

It involves the application of impact force on the material being powdered. The


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milling action is carried out by the use of ball mill, rod mill, impact mill, eddy

mill etc.

ATOMIZATION:-

In this process the liquid molten metal is forced through a nozzle into

stream water or air it breaks the molten metal into small droplets by rapidly

freezing the droplets before they come in contact with each other the metallic

powder is produced pressure is 2 to 30 N/m2 .

SOLID STATE REDUCTION:-

It is used for producing iron powder metal or alloy is crushed & mixed

with carbon it is passed through a continuous furnace. The reaction takes place

which produces a sponge metal is crushed & filter & the non metal is removed

from the metallic powder.ELECTROLYIS:-

The metal plates are placed in a tank of electrolyte (Acidic solution). The

plate connected to the positive terminal acts as anode & the other is connected


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to the negative terminal & it acts as cathode. When the high electric current is

passed through the anode & cathode. Then the powder will be deposited on the

cathode plate. The cathode plate is removed from the tank & metallic powder is

collected after drying.

SHOTTING:-

The molten metal is made to pass through a sieve & the particles aredropped in a liquid (water/ kerosene).

BLENDINGA no. of different powders with desired properties is mixed to achieve

necessary balance of the final properties of the product. Blending refers to themixing of same metal or alloy powder of different size distribution to reduce the

porosity level in the powder metallurgy product. The powders are mixed with

other additives to help with alloying process & lubrication. The main function

of lubrication is to reduce the friction between the powder particles & die walls

during the compaction & ejection process.


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COMPACTING Compacting is the process of converting the lose powder into compact

material of definite shape & size. This is called green compact.

The compacting is carried out of room temperature in a dia setup. The die consist of a cavity same as the desired component. The powder is poured into the cavity & level. The punches work from the top & bottom of the dia. The power is compress to 1/3 of its volume.

Core is used for making hollow cylindrical component.

The die is made of high grad steel. Carbide die is used for long production. The pressure used for compaction machined or hydraulic pressure,

Pr.100-1000MN/m2


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By using singular punch the compaction will not uniform. The powders near

to the punch gets compress more because the compacting force will not travel

all along the depth of the component.

For thin part single punch is needed. But thicker part two punch isnecessary.

For complicated shape component more than two punches isrequired.

PRE-SINTERING It is the process of heating the green compact to a temperature below the

sintering temperature.

It is done to remove the lubricants & binders add during the blendingprocess.

All metals do not require pre-sintering. Tungsten carbide required pre-sintering.


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SINTERING After compaction the finished work piece is heated in a furnace to a

temperature close to the melting point of base metal. It is called sintering

process. This is carried out in a control atmospheric furnace. It is also carried out under hydrogen or vacuum. Sintering process powder particles are binded together to achieve the

final strength & hardness needed in the finished product. Sintering depends on time, temperature & sintering atmosphere.

The work piece dimension changes during the sintering process. Bronze expand during sintering process. In powder metallurgy process sintering is done by mesh belt furnace. For ferrous component sintering temperature 11000 - 12000 c alloy & cu-

8000 -8500c.


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HIGH TEMPERATURE SINTERINGTo increase the mechanical properties of the powder metallurgy

component sintering is done at 1500c higher temperature it is called high

temperature sintering.

SINTER HARDENINGSinter hardening is done by control cooling rate.


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CHARACTERISTICKS OF METAL POWDER1. CHEMICAL COMPOSITION & PURITY:-

The chemical composition is an outstanding characteristic of the metal

powders. It usually reveals the type & percentage of impurities present in the

metal powders. The impurities greatly influence the physical & mechanical

properties of the powdered metals.

2.SIZE OF PARTICLE & ITS DISTRIBUTION:-The size of particles is an important characteristic of metal powders. It

has a great influence over density, porosity, compressibility, & shrinkage

during sintering. The size of the particle may be determined by many methods,but the simplest & the most popular method is a sieve method.

3.SHAPE OF PARTICLE:-The shape of particle may be flat, angular, ragged, and spherical or

dendrites. It has great influence over porosity, compactness & strength of the

part produced. It permits Automatic feeding of powder flow, the maintains of

pre determined tolerances and the control of deformation during sintering &

cooling.

4.COMPRESSIBILITY:-The compressibility of metal powders is defined as the ratio of initial

volume of the powder to the final volume after compression. It generally varies

from 2:1 to 3:1.

5.SINTERING ABILITY:-The sintering ability is that property of a metal powder due to which it

provides & promotes adhesion between all the particles. On sintering at

controlled temperature. The sintering ability of the metal powder should be

high in order to produce the parts successfully.


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ADVANTAGES There is no wastage of material.

The component is ready to use.

Close dimensional accuracy is maintained. Non-metallic components can be applied in any proportion. Density, porosity, & particle size can be controlled as required. Metal & ceramics can be mixed. Magnetic core having desired properties can be manufacture. Production rate is very high. High skill labour is not required. Wide variation in composition. Wide property variation. Scrap is eliminated or reduced.

DISADVANTAGE Production of metallic powder is expansive process & difficult process. Size of the component is limited. Strength is less. Impact strength is less. Elongation of component is poor. The die is required in powder metallurgy process is expansive. Complex shape component have low strength because of non-uniform

density.

Dimensional changes during sintering.

Density variation.


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Health and safety hazards.

Example:-

Gears, cams, pawl, liver Parts of automobiles, aircraft, gas, turbine, refrigerator &

vacuum cleaner.

Parts of gun, self lubricating bearing & filters.APPLICATION OF POWDER METRALLURGY:-

Cemented carbide cutting tools. Heavy duty brake pads. Magnetic cores for transformers. Antifriction bearing. Bulb filaments.

PRODUCTS OF POWDER METRALLURGY:-

Porous or permeable products such as bearing, filter, & pressure or flowregulators.

Products of complex shapes that would require considerable machiningwhen made by other processes.

Products made from materials that are difficult to machine or materialswith high melting points.

Products where the combined properties of two or more metals aredesired.

Products where the p/m process produces dearly superior properties. Products where the p/m process offers & economic advantage.


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BASIC RULES FOR THE DESIGN OF POWDER METRALLURGY:-

Parts can be designed to take advantage of the fact that certain forms &properties can be produced by p/m that are impossible, impractical, oruneconomical, by any other method.

The design should be consist with available equipment. Consideration should be made for product tolerance.

Design should consider and compensate for dimensional changes that willoccur after pressing.

DEFECTS IN P/M:-

Improper density (green compact) Improper bonding (after compacting & sintering presence of foreign

materials)

Inhomogeneous properties (improper lubrication)

ECONOMICS OF POWDER METRALLURGY Competitive with casting & forging. High initial cost.


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Economical for quantities over 10,000 pieces. Reduces or eliminates

scraps

Summary Powder metallurgy can produce products out of materials that are

otherwise very difficult to manufacture.

P/M products can be designed to provide the targeted properties.

Variations in product size, production rate, quantity, mechanicalproperties, & cost.


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SPECIAL CASTING:-

This operation is performed after the completion of powder metallurgy process.

INTRODUCTION:-

The liquid molten metal is poured into a casting cavity & allows it to solidify after

solidification the final component is taken out by breaking or opening the mould.

DIE CASTING:-

Die casting is the casting process where the molten metal is injected at high

pressure into a metallic die. Here liquid molten metal is forced in pressure. So it is called

pressure die casting.

It is used as permanent mould.

DESCRIPTION:-

In die casting the die consist of two parts one is stationary half & other is moving

half. The stationary half is fixed to the die casting machine & the moving half is taken out

for injection of the casting. When the two parts are separate lubricant is sprayed. On the

die cavity so that the casting will not stick to the die. Then the two dies are closed &

clamped. The required amount of molten metal is injected into the die. The air present in

the die cavity is removed through the air vents. The casting is solidified by passing cold

water in the water channels. Then the die is opened & casting is rejected. Ejectors are

provided in the moving half. It is of two types.

1) Hot chamber die casting

2) Cold chamber die casting


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COMPLETE PROCESS OF POWDER METALLURGY


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CONCLUSION P/M is a proven technology dating back centuries. By utilizing 97% original material, cost and energy are minimized Properties and dimensions are easily controlled. Wide variety of P/M application which are still increasing.


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REFERANCE Manufacturing engineering & technology, serope kalpakjian & Steven

R.schimid, 4th edition, Pearson education, Delhi.

Introduction to physical metallurgy, Sidney H.Avner, 2nd edition, McGrawHill, New York.

Material science & metallurgy V.D. kodgire, 5th edition, Everestpublishing house, Pune.

History of powder metallurgy, P.Ramakrishna, Indian journal history ofscience, 18 (1), 109-114, 1983.

Report on Aluminum powder metallurgy, B.Verlinden & L Froyen,Belgium.

Powder metallurgy parts manufacturing, 1997 economic census,manufacturing industry series.

Powder metallurgy, prof Onwubolu. ASM metals handbook 7.


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THE END


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Powder Met. Complete Ranjeet

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