Powder metallurgy for Sintered Products

Powder Metallurgy

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Introduction Powder Metallurgy or PM is a process of producing components or materials from powders made

of metal.

Different geometries can be obtained by this process. This may also include non metal powders.

PM or Powder Metallurgy reduces the metal removal process to obtain a desired structure, reduces yield loss while manufacturing and cut down cost.


Iron Metal Powder

Introduction Powders are generally compressed by applying heat to obtain a specific geometry followed by

sintering to achieve a solid part.

Many unique materials can be made which is impossible to mold or melt.

For example tungsten carbide used for cutting and is used to make other metals is made by powder metallurgy.

Some other products are:

• Automotive parts

• Sintered Filter (http://catalystrecoveryfilter.com/ , http://sparger.in/ , sintered disc for sensor protection etc)

• Porous oil impregnated bearing

• Diamond tool

• Electrical contact


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Steps for Powdered Metallurgy:1. Powder Manufacturing

• Metal used in manufacturing of powder are SS316L, Titanium, SS304, FeCrAl, 904L, Nickel and many more.

• The two most common processes used in manufacturing of PM are:

a) Sponge Iron Process

b) Atomization

Sponge Iron Process

A magnetite (Fe3O4) ore with lime and coke are placed in a silicon carbide retort. The retort is heated in a kiln thereafter where a slag and a sponge iron cake are formed due to reduction process.

The iron cake is then crushed and annealed after separating from the slag. The powder obtained is very irregular in shape containing internal pores

which looks like a sponge.


Steps for Powdered Metallurgy:

Sponge Iron Process Contd.


SPONGE IRON PARTICLE SHAPE


GAS ATOMIZATION

A hot liquid metal stream is passed from a orifice at high velocity to generate turbulence and just before the molten liquid stream exit the orifice a gas is injected which creates this turbulence (gas expands due to heating and creates turbulence).

The liquid stream is then collected in a collection volume filled with gas where further turbulence is created. With the help of a cyclonic separation, air and powder stream the PM particles are separated.

The particles obtained are non porous, smaller, have more breadth in size and are cleaner allowing better compaction. Particles have a pear or spherical structure with an oxide layer over them.



Water Atomization It is a technique in which atomized water at

high stream is introduced on a molten liquid metal stream which converts the liquid metal stream into drops and cools down the metal powder before it reaches the collection bottom.



PM metal particles characteristics: After manufacturing of metal powder

different sizes are obtained with the help of screens which is made up of wire mesh. The screens separate the metal powder depending upon the sizes.



Metal Powder Shape The flow characteristic and powder density depends

on the shape of the metal powder. Different techniques results in appearance of metal powder.

Water atomization produces irregular shapes with no internal porosity.

Gas atomization produces spherical shapes with no internal porosity.

Oxide reduction gives irregular shape with substantial amount of internal porosity.

Milling and other mechanical techniques gives variety of shapes.

Chemical techniques produce a range of shapes from spherical to angular.


“ATOMIZATION - THE PRODUCTION OF METAL POWDERS" A. LAWLEY, MPIF -THE IMAGES ARE OBTAINED FROM DIFFERENT PROCESSES SUCH AS FIG. 1-SPONGE IRON PROCESS, FIG.2-ELECTROLYTIC PROCESS FOR COPPER PARTICLES, FIG. 3-MECHANICAL PROCESS FOR ALUMINUM, FIG. 4-IRON WATER ATOMIZATION & FIG. 5-NICKEL GAS ATOMIZATION.


Metal Powder Compaction It is a process of compressing the metal powder in a vertically

oriented tool by applying pressure from top to bottom using a external force in this case a punch tool.

After getting the desired shape or structure the compacted shape is ejected from the die cavity.

This is the most cost effective manufacturing from rest of the process. Two most commonly used processes are:a) Die press Technologyb) Isostatic Pressing and Compaction



Die press Technology Die Press technology can be achieved by hydraulic presses,

mechanical and servo-electrical techniques, on a larger scale hydraulic presses are commonly used.

The steps involved in a production cycle are:

A known volume of feedstock is filled in a die cavity.

Pressure is applied from the top and bottom by using punches for compressing, this generally reduces the density gradient level within compact.

Compacted metal is ejected using the pressure applied by the lower punch.

The metal powder product is removed from the top using the fill shoe.



Major advantage of this technique is this, that it can make complex geometries. The dimensions which can be achieved are:

Area less than 0.65 square centimeter and larger than 160 square centimeter and from 2.54 centimeter to 20 centimeter in length are possible.



Isostatic Pressing and Compaction The metal powder is placed in a mold and then a external pressure is applied by

using a gas or fluid as a source. The compacted product is then sintered in a furnace which bonds or fuses the

metal particles and increases the strength of the material. i. Hot Isostatic Pressing Heat is applied to the metal powder from 480 degree Celsius to 1230 degree

Celsius by compressing and sintering the part simultaneously. An inert gas such as Argon is used to prevent any chemical reactions during operation.

ii. Cold isostatic pressing In this technique a fluid is used to pressurize the mold at room temperature. This

is followed by sintering the metal powder. A liquid is used as a medium to distribute the pressure uniformly.


Industries where the powdered metallurgy are used :

Automotive products

Fluid technology

Bearings

Mechatronics

Filter Applications (Refer www.catalystrecoveryfilter.com & www.sparger.in for more details)

Industrial porous metal content

Read the next step, sintering by clicking the link http://catalystrecoveryfilter.com/free-resources/api-research-papers/ scroll through the articles to view sintering process.


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Powder metallurgy for Sintered Products

Engineering

Transcript of Powder metallurgy for Sintered Products