POWDER METALLURGYPOWDER METALLURGY

PRODUCTION PRODUCTION TECHNOLOGYTECHNOLOGY

By, By,

Avinash Jayashankar.Avinash Jayashankar. Gaurav Dave.Gaurav Dave.

Mechanical Department 3 AMechanical Department 3 A R V College Of EngineeringR V College Of Engineering

Classification of Metal Fabrication Classification of Metal Fabrication ProcessesProcesses

IntroductionIntroduction

DEFINITION:DEFINITION:

Powder metallurgy (usually abbreviated as P/M) has been defined as the science of Powder metallurgy (usually abbreviated as P/M) has been defined as the science of producing metal powders and making semi finished and finished objects from producing metal powders and making semi finished and finished objects from individual, mixed or alloyed powders with or without the addition of non-metallic individual, mixed or alloyed powders with or without the addition of non-metallic constituents.constituents.

Powder metallurgy involves:Powder metallurgy involves:

1)Mixing of elemental or alloyed powders with additives and lubricants.1)Mixing of elemental or alloyed powders with additives and lubricants.2)Compacting the mixtures in a suitable die and heating the resulting green compacts 2)Compacting the mixtures in a suitable die and heating the resulting green compacts

in a controlled atmosphere furnace so as to bond the particles metallurgically.in a controlled atmosphere furnace so as to bond the particles metallurgically.3) The resulting parts are of sufficient strength and density for diverse applications.3) The resulting parts are of sufficient strength and density for diverse applications.

Manufacturing process involving Powder Metallurgy

Video Video manufacturing manufacturing processprocess

Why P/M?Why P/M?

Production of newer material combinations.Production of newer material combinations. Production of components from refractory metals.Production of components from refractory metals. Production of special alloys.Production of special alloys. Porous and Self Lubricating Bearings.Porous and Self Lubricating Bearings.

Production of Metal PowdersProduction of Metal Powders

The particle size of powders falls into a The particle size of powders falls into a range of range of 1-1001-100 micrometers with the micrometers with the range of range of 10-2010-20 micron being predominant micron being predominant. . There are various methods of There are various methods of manufacturing powders of this size, but manufacturing powders of this size, but those commonly used are:those commonly used are:

AtomisationAtomisation ReductionReduction ElectrolysisElectrolysis CrushingCrushing MillingMilling

Atomization:Atomization:

• The molten metal is directed to an orifice.The molten metal is directed to an orifice.• As it emerges, a high pressure stream of As it emerges, a high pressure stream of

gas or liquid impinges on it causing it to gas or liquid impinges on it causing it to atomize into fine particles.atomize into fine particles.

• An inert gas is employed in order to An inert gas is employed in order to improve the purity of the powder.improve the purity of the powder.

• It is used mostly for low melting point It is used mostly for low melting point metals because of the corrosive action of metals because of the corrosive action of the metal on the orifice at high the metal on the orifice at high temperatures.temperatures.

Video: atomization ---

Methods of metal-powder production by atomization:

(a)melt atomization (b) atomization with a rotating consumable electrode.

Reduction:Reduction:

• The compounds of metals usually oxides are The compounds of metals usually oxides are reduced with CO or Hreduced with CO or H22 at temperatures below the at temperatures below the melting point of the metal, in an atmosphere melting point of the metal, in an atmosphere controlled furnacecontrolled furnace

• The reduced product is then crushed and ground.The reduced product is then crushed and ground.• The advantages of this methods are-convenient, The advantages of this methods are-convenient,

economical and flexible.economical and flexible.• Powders of W, Mo, Ni and Co are manufactured Powders of W, Mo, Ni and Co are manufactured

by this method.by this method.

Reduction process

Electrolysis:Electrolysis:

• Production of extremely pure powders of copper and iron.Production of extremely pure powders of copper and iron.• It is similar to electroplating.It is similar to electroplating.

Crushing:Crushing:

• Equipment used are stamps, hammers, jaw crushers or Equipment used are stamps, hammers, jaw crushers or gyratory crushers.gyratory crushers.

• Used for ferrous and non ferrous alloys.Used for ferrous and non ferrous alloys.

Methods of mechanical comminution, to obtain fine particles: Methods of mechanical comminution, to obtain fine particles:

(a) roll crushing (b) ball mill and, (c) hammer milling(a) roll crushing (b) ball mill and, (c) hammer milling

Milling:Milling:

A large mass of the metal goes through heavy A large mass of the metal goes through heavy crushing machines and then through crushing crushing machines and then through crushing rolls and finally through a milling machine to rolls and finally through a milling machine to produce finer grades of powder.produce finer grades of powder.

Blending and Mixing of Blending and Mixing of PowdersPowders

Reasons for blending:Reasons for blending: To add lubricantsTo add lubricants (to powder) ,to reduce friction during pressing (to powder) ,to reduce friction during pressing

operations. Powder particles get coated with lubricants. This reduces die operations. Powder particles get coated with lubricants. This reduces die wear and lowers the pressure required for pressing.wear and lowers the pressure required for pressing.

To To mix the powders of different materialsmix the powders of different materials i.e. i.e. alloying actionsalloying actions in order to in order to obtain properties of heat resistance, friction, heavy weight and hardness.obtain properties of heat resistance, friction, heavy weight and hardness.

To obtain To obtain uniform distribution of particle sizesuniform distribution of particle sizes To add volatizing agents to give a desired amount of porosityTo add volatizing agents to give a desired amount of porosity

Different powders in correct proportions are thoroughly mixed either wet or Different powders in correct proportions are thoroughly mixed either wet or dry in a ball mill. In wet mixing, water or a solvent is used to obtain better dry in a ball mill. In wet mixing, water or a solvent is used to obtain better mixing. Moreover, wet mixing :mixing. Moreover, wet mixing :

Reduces dustReduces dust Lessens explosion hazardsLessens explosion hazards which are present with some finely divided which are present with some finely divided

powderspowders Prevents surface oxidationPrevents surface oxidation

Proper blending and mixing of powders are essential for the uniformity of Proper blending and mixing of powders are essential for the uniformity of finished products. However,finished products. However,overmixing overmixing should be avoided since it should be avoided since it may may decrease particle size and work harden the particles.decrease particle size and work harden the particles.

Blending Machines

CompactingCompacting

• After blending and mixing the next step is that of compacting or After blending and mixing the next step is that of compacting or pressing the powders into their semi finished form prior to pressing the powders into their semi finished form prior to sintering.sintering.

• The purpose of compacting is to The purpose of compacting is to consolidate the powder into the consolidate the powder into the desireddesired shape and as closely as possible to final dimensionsshape and as closely as possible to final dimensions taking taking into account any dimensional change that results from sintering.into account any dimensional change that results from sintering.

• Compacting also Compacting also strengthens the metal for handling.strengthens the metal for handling.• Powders are compacted using high pressures. The Powders are compacted using high pressures. The degree of degree of

pressure required depends upon the required density of the final pressure required depends upon the required density of the final productproduct and the ease with the powder particles will weld together. and the ease with the powder particles will weld together.

• Compacting pressures maybe applied in the following ways:Compacting pressures maybe applied in the following ways:-die pressing-die pressing-roll pressing-roll pressing-extrusion-extrusion

Die PressingDie Pressing

• This is done in special presses that This is done in special presses that include a feed hopper for the powder, include a feed hopper for the powder, the shaping die to form the product, an the shaping die to form the product, an upper punch and a lower punch to apply upper punch and a lower punch to apply proper pressures on to the powder being proper pressures on to the powder being compacted.compacted.

• Weighed quantity of the powder is Weighed quantity of the powder is placed in the die through the hopper placed in the die through the hopper and compressed under pressureand compressed under pressure

• 100-1000 MN/m2100-1000 MN/m2Video: Die PressingVideo: Die Pressing

Roll PressingRoll Pressing

• Its used for production of continuous Its used for production of continuous strip section.strip section.

• It consists of 2 rolls of appropriate It consists of 2 rolls of appropriate size into which a regulated stream of size into which a regulated stream of powder is guidedpowder is guided

• The rolls apply the necessary The rolls apply the necessary compacting pressure in a continuous compacting pressure in a continuous sequence, thus obtaining a compact sequence, thus obtaining a compact strip of compact metalstrip of compact metal

Extrusion Extrusion MethodMethod This method does not give efficient control as that given by This method does not give efficient control as that given by

the above two methods.the above two methods. It is difficult to obtain high densities and some porosity is It is difficult to obtain high densities and some porosity is

always leftalways left

Video: Extrusion methodVideo: Extrusion method

SinteringSintering

The compacted metal is now taken in a furnace The compacted metal is now taken in a furnace and heated to a temperature below the melting and heated to a temperature below the melting point in an inert or reducing atmosphere.point in an inert or reducing atmosphere.

The relationship between sintering time and The relationship between sintering time and temperature is given by the following formula:temperature is given by the following formula:

log(tlog(t11/t/t22)=(E)=(Eaa/R)*(1/T/R)*(1/T11-1/T-1/T22)) The volatile impurities are driven out .The volatile impurities are driven out . Sintering results in the increase in the strength of Sintering results in the increase in the strength of

the compacted powder due to metallurgical the compacted powder due to metallurgical bonding.bonding.

Secondary OperationsSecondary Operations In many cases, the metal parts maybe used in the In many cases, the metal parts maybe used in the as-as-

sinteredsintered form but in other cases secondary operations form but in other cases secondary operations maybe required to obtain certain desired properties, maybe required to obtain certain desired properties, these include:these include:

SizingSizing CoiningCoining MachiningMachining Heat treatmentHeat treatment JoiningJoining PlatingPlating InfiltrationInfiltration impregnationimpregnation

Advantages of Powder Advantages of Powder Metallurgy processMetallurgy process

• Good dimensional accuracy and surface finishGood dimensional accuracy and surface finish is is obtained hence eliminating the need for obtained hence eliminating the need for machiningmachining

• Cleaner and quieter operationCleaner and quieter operation and and longer lifelonger life of of componentscomponents

• High production ratesHigh production rates• Defect free components Defect free components • No material is wasted as scrapNo material is wasted as scrap• Highly skilled and qualified labour not requiredHighly skilled and qualified labour not required• Parts with Parts with wide variations in compositionswide variations in compositions and and

materials can be producedmaterials can be produced

Connecting RodsConnecting Rods

Forged on the leftForged on the leftP/M on the rightP/M on the right

-Warm compaction method with 1650-ton press-Warm compaction method with 1650-ton press-Teeth are molded net shape: -Teeth are molded net shape: -No machining-No machining -UTS = 155,000 psi -UTS = 155,000 psi -30% cost savings over the original forged part -30% cost savings over the original forged part

P/M Transmission Gear

Disadvantages of Powder Disadvantages of Powder Metallurgy ProcessMetallurgy Process

• Complicated shapesComplicated shapes which can be produced by casting cannot which can be produced by casting cannot be made by powder metallurgy, because metallic powders lack be made by powder metallurgy, because metallic powders lack the ability to flow to the extent of molten metals.the ability to flow to the extent of molten metals.

• Parts made in most cases do not have as good physical Parts made in most cases do not have as good physical properties as wrought or cast parts.properties as wrought or cast parts.

• Relatively costlyRelatively costly because :a) tool cost because :a) tool cost b) powdered metal costb) powdered metal cost• Extreme Extreme carecare is required in is required in handling pyrophoric powdershandling pyrophoric powders( e.g.- ( e.g.-

Mg, Th, Zr etc.,) to prevent fires or explosions and with Mg, Th, Zr etc.,) to prevent fires or explosions and with toxic toxic powderspowders( e.g.. U, Be, Th etc.,) to minimise health hazards.( e.g.. U, Be, Th etc.,) to minimise health hazards.

• Powder metallurgy is Powder metallurgy is not economical for small scale not economical for small scale productions.productions.

• Parts pressed from Parts pressed from top ends tend to be less ends at the top ends tend to be less ends at the bottom.bottom.

Applications of P/MApplications of P/M

• Only Practical method for mass Only Practical method for mass production of refractory metals( Mo, production of refractory metals( Mo, W, Tantalum)W, Tantalum)

• Porous BearingsPorous Bearings• Automotive Industry: Clutch Facings Automotive Industry: Clutch Facings

and Brake Linings.and Brake Linings.• Cutting Tools: Tungsten Carbide Cutting Tools: Tungsten Carbide

Tipped toolsTipped tools

Isostatic PressingIsostatic Pressing

• Modern developmentModern development• Product is more uniform than conventional pressing, as Product is more uniform than conventional pressing, as

pressure is applied in all directions.pressure is applied in all directions.• Classified as cold isostatic pressing and hot isostatic pressing.Classified as cold isostatic pressing and hot isostatic pressing.

Cold Isostatic Pressing

1)Done at room temperature2)Powder placed in an elastomeric material3)Fluid used is water or oil

Hot Isostatic Pressing

1)High temperature pressing2)Inert gas is used, which is reclaimed after every cycle