POWDER METALLURGY POWDER METALLURGY (UNIT-4) (UNIT-4)

Presented by:-Presented by:- SHIVAM (2SHIVAM (2NDND YEAR) YEAR) MECHANICAL ENGINEERINGMECHANICAL ENGINEERING

J.P. INSTITUTE OF ENGG. & TECHNOLOGY J.P. INSTITUTE OF ENGG. & TECHNOLOGY MEERUTMEERUT

APRIL 7APRIL 7THTH, 2014, 2014

Powder metallurgy Powder metallurgy process (PMP)process (PMP)

• It is manufacturing process in which It is manufacturing process in which metal powders are sometimes mixed metal powders are sometimes mixed with metals or non metal powders.with metals or non metal powders.

• When non alloyable metals are melted When non alloyable metals are melted together, these will not mix and will together, these will not mix and will separate like oil and water. Example- separate like oil and water. Example- nickel and silver are combined by PMP nickel and silver are combined by PMP to produce electrical circuit.to produce electrical circuit.

PMPPMP

• By PMP, metals and nonmetals can be By PMP, metals and nonmetals can be mixed together to obtain unique mixed together to obtain unique properties. For example, while properties. For example, while manufacturing brake band for manufacturing brake band for aeroplanes, the breaks must be able to aeroplanes, the breaks must be able to withstand high temp. and also should withstand high temp. and also should contain wear resistance and friction contain wear resistance and friction material. This can be achieved by material. This can be achieved by mixing copper and tin powder in lead, mixing copper and tin powder in lead, iron, silica and graphite.iron, silica and graphite.

PMP ProcessPMP Process

• Process for making powderProcess for making powder• Mixing of additives (lubricants and binders) so Mixing of additives (lubricants and binders) so

that they can be easily pressed in dies.that they can be easily pressed in dies.• Pressing of powders in dies under pressure of Pressing of powders in dies under pressure of

1400 MPa.1400 MPa.• Sintering :- heating in controlled atmosphere to Sintering :- heating in controlled atmosphere to

temp below melting point.temp below melting point.• Secondary manufacturing and finishing Secondary manufacturing and finishing

operations if required.operations if required.

POWDER METALLURGYPOWDER METALLURGY PROCESS PROCESS

• Powder metallurgy is a highly developed Powder metallurgy is a highly developed method of manufacturing reliable ferrous and method of manufacturing reliable ferrous and non ferrous parts. Powdered metals used are non ferrous parts. Powdered metals used are brass, bronze, stainless steel and ironbrass, bronze, stainless steel and iron

• The basics steps of P-M are :The basics steps of P-M are : Powder productionPowder production Blending and mixing elemental or alloy powdersBlending and mixing elemental or alloy powders Compaction in a dieCompaction in a die SinteringSintering Secondary or finishing operationsSecondary or finishing operations

PM PROCESS…..PM PROCESS…..

POWDER PREPARATIONPOWDER PREPARATION

High purity metal powders produced High purity metal powders produced by these processes….by these processes….AtomizationAtomizationMechanical ComminutionMechanical ComminutionChemical ReductionChemical ReductionElectrolytic TechniquesElectrolytic TechniquesAgglomerationAgglomeration

ATOMIZATIONATOMIZATION

Atomization is the process used to produce the largest Atomization is the process used to produce the largest

tonnage of metal powders. tonnage of metal powders. •In water and gas atomization the raw material is melted then In water and gas atomization the raw material is melted then the liquid metal is broken into individual particles.the liquid metal is broken into individual particles.• To accomplish this the melt stock is melted in the To accomplish this the melt stock is melted in the furnace.After the bath is homogenous, it is transferred to a furnace.After the bath is homogenous, it is transferred to a tundish which is a reservoir .tundish which is a reservoir .•As the metal stream exits the tundish it is struck by a high As the metal stream exits the tundish it is struck by a high velocity stream of the atomizing medium (WATER ,AIR OR velocity stream of the atomizing medium (WATER ,AIR OR INERT GASES).INERT GASES).•The molten metal stream is disintegrated into fine droplets The molten metal stream is disintegrated into fine droplets which solidify during their fall through the atomizing tank . which solidify during their fall through the atomizing tank . Particles are collected at the bottom of the tank.Particles are collected at the bottom of the tank.

ATOMIZATION…..ATOMIZATION…..

MECHANICAL COMMINUTION MECHANICAL COMMINUTION

• Mechanical comminution methods such as lathe turning Mechanical comminution methods such as lathe turning and chipping, comprise the second power manufacturing and chipping, comprise the second power manufacturing group.group.

• Such methods are used to produce hard and brittle Such methods are used to produce hard and brittle powders that would be used in alloying , blending, and powders that would be used in alloying , blending, and work hardening or as oxide powders.work hardening or as oxide powders.

• Milling is the primary method for reducing the size of Milling is the primary method for reducing the size of large particles and particle agglomerates. large particles and particle agglomerates.

• Ball hammer, vibratory, attrition,and tumbler mills are Ball hammer, vibratory, attrition,and tumbler mills are some of the commercially available comminuting some of the commercially available comminuting devices.devices.

Mechanical Comminution to Obtain Mechanical Comminution to Obtain Fine ParticlesFine Particles

Methods of mechanical comminution to obtain fine particles:

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

Chemical MethodsChemical Methods• Chemical methods included the production of metal powders Chemical methods included the production of metal powders

by the reduction of metallic oxides, precipitation from solution by the reduction of metallic oxides, precipitation from solution (hydrometallurgy) and thermal decomposition (carbonyl).(hydrometallurgy) and thermal decomposition (carbonyl).

• Materials used for subsequent oxide reduction are iron Materials used for subsequent oxide reduction are iron ore(magnetite),mill scale, and metallic materials oxidized for ore(magnetite),mill scale, and metallic materials oxidized for oxide reduction.oxide reduction.

• In the case of iron ore, a refractory tube is filled with iron ore In the case of iron ore, a refractory tube is filled with iron ore and a mixture consisting of coal,coke and limestone. Then and a mixture consisting of coal,coke and limestone. Then tube is passed through a kiln at~1200°C . The mixture tube is passed through a kiln at~1200°C . The mixture decomposes, poducing atmosphere inside the tube and the decomposes, poducing atmosphere inside the tube and the magnetite ore is converted to metallic Fe.magnetite ore is converted to metallic Fe.

• Mill scale and oxidized metallic products are annealed to Mill scale and oxidized metallic products are annealed to reduce both the oxygen and carbon contentsreduce both the oxygen and carbon contents

ELECTROLYTIC DEPOSITIONELECTROLYTIC DEPOSITION

Electrolytic deposition involves the Electrolytic deposition involves the precipitation of a metallic element at the precipitation of a metallic element at the cathode of a electrolytic cell.The most cathode of a electrolytic cell.The most common application is in the production of common application is in the production of copper powder .copper powder .

AGGLOMERATIONAGGLOMERATION• The most common method of agglomeration is where the The most common method of agglomeration is where the

constituents are physically mixes together with an constituents are physically mixes together with an organic binder. The solvent is driven off and the resultant organic binder. The solvent is driven off and the resultant material sized. This process is used in the manufacture of material sized. This process is used in the manufacture of NiAl ,AlSi-polyester powders.NiAl ,AlSi-polyester powders.

• The use of spray drying has become another method for The use of spray drying has become another method for the agglomeration of powders. In this a slurry is formed the agglomeration of powders. In this a slurry is formed with the constituents and this is then fed into a rotary with the constituents and this is then fed into a rotary spray head. The slurry forms an atomized cloud which is spray head. The slurry forms an atomized cloud which is solidified by an opposing warm air steam to produce a solidified by an opposing warm air steam to produce a powder.powder.

• There are also methods of mechanical a agglomeration There are also methods of mechanical a agglomeration where a hard constituent is mechanically driven into a where a hard constituent is mechanically driven into a softer matrix particle to from a composite powder.softer matrix particle to from a composite powder.

Blending or MixingBlending or Mixing

• The purpose of mixing is to provide a homogenous mixture and to incorporate the lubricant. The mixing is done in shaking ⁄ rotating containers called blenders.

• Powders of different metals and other materials may be mixed in order to impart special physical and mechanical properties through metallic alloying.

• Lubricants(stearic acid, stearin, metallic stearates) may be mixed to improve the powders’ flow characteristics.

• Binders such as wax or thermoplastic polymers are added to improve green strength.

• Over mixing can occur and should be avoided because it increases density and reduces green strength.

• The blending or mixing done by follwing blenders……

Bowl Geometries in Bowl Geometries in Blending Metal PowdersBlending Metal Powders

Some common bowl geometries for mixing or blending powders

. A mixer suitable for blending metal powders.

COMPACTION METHODSCOMPACTION METHODS

• Compaction can be performed by multiple sub processes Compaction can be performed by multiple sub processes in either hot compaction or cold compaction.in either hot compaction or cold compaction.

• In the hot compaction category are Isostatic, Extrusion, In the hot compaction category are Isostatic, Extrusion, Die compacting spraying and pressureless sintering.Die compacting spraying and pressureless sintering.

• In the cold compaction category are Die In the cold compaction category are Die compacting ,Isostatic , Rolling Slip casting and Injection compacting ,Isostatic , Rolling Slip casting and Injection moulding.moulding.

• In compaction method similar to forming process– the In compaction method similar to forming process– the die is a cavity in the shape of the lower half of the part, die is a cavity in the shape of the lower half of the part, and the powder is poured into the cavity. The upper and the powder is poured into the cavity. The upper portion of the shape is made by the punch, which is portion of the shape is made by the punch, which is pressed down on the powder to achieve the required pressed down on the powder to achieve the required compaction.compaction.

Compaction Methods……Compaction Methods……

SinteringSintering

• Sintering is the means by which powder particles are welded together and a strong metal part is produced.

• In this stage the part acquires the strength needed to fulfill the intended role as an engineering component.

• After compaction the components pass through a sintering furnace. This typically has two heating zones, the first removes the lubricant and the second higher temp zone allows diffusion and bonding between powder particles.

• The furnace used is usually a contonuos belt furnace or vacuum furnace

Sintering…..Sintering…..

• The operation is almost invariably carried out under a The operation is almost invariably carried out under a protective atmosphere, because of the large surface protective atmosphere, because of the large surface areas involved.areas involved.

• Control over heating rate, time, temperature and Control over heating rate, time, temperature and atmosphere is required for reproducible results.atmosphere is required for reproducible results.

• The sintering temperature are between 60 to 90% of the The sintering temperature are between 60 to 90% of the melting point of the particular metal or alloys. melting point of the particular metal or alloys.

• At these temp the atoms are free to diffuse. Also At these temp the atoms are free to diffuse. Also recrystallization occurs and the interparticle boundaries recrystallization occurs and the interparticle boundaries become grain boundaries.become grain boundaries.

• Neck like junction are formed between particles as Neck like junction are formed between particles as recrystallization takes place.recrystallization takes place.

Secondary ProcessSecondary Process

• Secondary operations are performed to increase density, Secondary operations are performed to increase density, improve surface finish and accuracy, or accomplish improve surface finish and accuracy, or accomplish additional shaping of the sintered part.additional shaping of the sintered part.

• Secondary operations include :Secondary operations include : Repressing: Pressing the sinters part in a closed die to Repressing: Pressing the sinters part in a closed die to

increase density and improve properties.increase density and improve properties. Coining: Pressworking operation on a sintered part to Coining: Pressworking operation on a sintered part to

press details into its surface.press details into its surface. Sizing: Pressing a sintered part to improve dimensional Sizing: Pressing a sintered part to improve dimensional

accuracy.accuracy. Machining: Creates geometric features that cannot be Machining: Creates geometric features that cannot be

achieved by pressing, such as threads, side holes and achieved by pressing, such as threads, side holes and other details.other details.

Secondary Process…Secondary Process…

Forging: Hot forming partial shapes .Forging: Hot forming partial shapes . Heat Treating: for additional hardening.Heat Treating: for additional hardening. Steam Treating: To obtain an oxide surface coating.Steam Treating: To obtain an oxide surface coating. Plating: to obtain specific surface finish and colour.Plating: to obtain specific surface finish and colour. Joining: To assemble related parts with typical joining Joining: To assemble related parts with typical joining

methods, welding, brazing etc.methods, welding, brazing etc. Infiltration: The pores can also be filled by a matal of Infiltration: The pores can also be filled by a matal of

lower melting point.lower melting point.

Advantages Advantages

• Little or no wastage of material.Little or no wastage of material.• Secondary manufacturing process can be Secondary manufacturing process can be

reduced or eliminated.reduced or eliminated.• Process can be used for the metals which can Process can be used for the metals which can

not be easily cast or machined like tungsten not be easily cast or machined like tungsten whose melting point is 3000whose melting point is 300000c.c.

• Maintains close dimensional toleranceMaintains close dimensional tolerance• Produces good surface finishProduces good surface finish• Allows combination of materials which cannot Allows combination of materials which cannot

be prodices in any other waybe prodices in any other way

DisadvantagesDisadvantages

• Metallic powder are expansive.Metallic powder are expansive.• High tooling and equipment cost.High tooling and equipment cost.• The size will always change on sintering.The size will always change on sintering.• Variation in density throughout part may be Variation in density throughout part may be

problem.problem.• Potential workforce health problems from Potential workforce health problems from

atmospherics contamination of the workplace.atmospherics contamination of the workplace.• In general PM parts have low resistance to In general PM parts have low resistance to

shock loading and lower physical propreties shock loading and lower physical propreties than wrought metals.than wrought metals.

Applications of PM…Applications of PM…• Automobile Industry: motors, gear assemblies, brake Automobile Industry: motors, gear assemblies, brake

pads.pads.• Abrasives: polishing and grinding wheels.Abrasives: polishing and grinding wheels.• Manufacturing: cutting and drilling tools.Manufacturing: cutting and drilling tools.• Electric and Magnetic devices: magnets, soft Electric and Magnetic devices: magnets, soft

magnetic cores, batteries.magnetic cores, batteries.• Medical and Dental: prostheses, amalgams.Medical and Dental: prostheses, amalgams.• Aerospace: motors, heat shieldsAerospace: motors, heat shields• Welding: solder, electrodesWelding: solder, electrodes• Energy: electrodes, fuel cellsEnergy: electrodes, fuel cells• Other: porous filters, bearings, sporting goodsOther: porous filters, bearings, sporting goods

Any QuestionsAny Questions

THANK YOU THANK YOU

MECHANICALMECHANICAL for your kind attentionfor your kind attention

BEST OF LUCK BEST OF LUCK

BE HAPPYBE HAPPY

DO YOUR BEST IN EXAMDO YOUR BEST IN EXAM