Powder Metallurgy

Powder Metallurgy

• Introduction• The Use Of metal powder in industrial application• P/M Manufacturing Techniques• Application general Case studies• Advantages • Disadvantages

Introduction…..

• Definition:

“ Powder metallurgy is an art and science of producing fine metal powder and then making objects from individual , mixed or alloyed metal powder with or without the inclusion of non metallic constituents”

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• For making a component by P/M (i) The metal in The Powder Form must be able to respond to solid

phase welding (ii) The metal powder must be capable of sufficiently close packing

under pressure to permit welding to take place and in case of alloying , be capable of being sufficiently intimately mixed

Powder metallurgy consist three main steps• A) Powder Production• B) Compacting • C) Sintering

(A)Powder Production

•Atomization

• Reduction• Electrolysis• Crushing• Etc…

(A) Powder production By Atomization• Gas Atomization ---Spherical powder Particals ---Good “flow ability”

• Water Atomization ---Irregular powder Particals ---Good Compatibility

(B) Compacting of Metal Powder

• Compaction is the step where the blended powders are pressed into various shapes in dies

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• Purposes of compaction are to obtain the required shape, density and particle-to-particle contact

• Pressed powder is known as green compact

• Density depends on the pressure applied

• Higher the density of the compacted part, the higher are its strength and elastic modulus

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• May be necessary to use multiple punches to ensure that the density is more uniform throughout the part

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• Compacting pressure required depends on the characteristics and shape of the particles, method of blending and lubricant

( c ) Sintering

Heat treatment to promote metallurgical integrity

•Metallurgical bonding•Densification (Shrinkage)•Pore Elimination

Sintering

• Sintering is the process whereby green compacts are heated in a furnace to below the melting point but high enough to allow bonding (fusion) of the individual particles

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• Strength of the bond between the particles depends on the complex mechanisms of diffusion of:

1. Plastic flow

2. Evaporation of volatile materials in the compact

3. Recrystallization

4. Grain growth

5. Pore shrinkage

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• Continuous-sintering furnaces have 3 chambers:

1. Burn-off chamber

2. High-temperature chamber

3. Cooling chamber

• The sintering mechanisms are diffusion, vapor-phase transport, and liquid-phase sintering

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Mechanical Properties

• Affecting mechanical properties are temperature, time, and processing history

• Porosity cannot be avoided completely due to voids remaining after compaction and gases evolve during sintering

Case Study 1Component: Auto Transmission sprockets

Parameter of auto transmission sprockets

• Size: OD drive:90-100mm OD driven:100-106mm• Weight: Drive:450-590 g Driven:505-570g• Alloy :steel• Tensile strength: 860MPa• Elongation:1.5%• Apparent Hardness: 60 HRC• Density:7.8 g/cm3,surface density 7.0g/cm3,core density• Heat Treatment: vacuum carburizing• Annual Production:20,00,000

Description:-

• Steel is mainly used in manufacturing process of auto transmission sprockets.

• Auto transmission sprockets are commonly manufacture by powder metallurgy process.

• High-performance PM steel automatic transmission sprockets-one drive and one driven-are compacted, sintered and selectively densified.

• The teeth are further densified by cold working process and then vacuum carburized, producing a precisely controlled case on critical journal and tooth flank surface.

• This provides high strength ,exceptional bearing and surface durability.

• The surface density of parts is 7.8g/cm3,and its gradually falling to lower level towards the core.

• The core regions are not highly stress and remain at a density of 7 g/cm3.

• There are two components in a set in each transmission that transmit power from the engine to the transmission via silent chain.

Case studies : 3 Main Bearing Cap for Automobile Engines

Details

• Weight : 0.755 kg• Alloy : proprietary steel• Tensile Strength : 450 MPa• Elongation : 3%• Apparent Hardness : 70 HRB• Density : 6.6 g/cm^3• Fatigue Endurance Limit : 160 Mpa• Secondary Operations : Machining• Alternative Process : Nodular iron casting

Description :

• This main bearing cap (mbc) is used in general motors engines. The engine contains three caps weighing about 2.2 kg.

• Main bearing caps guide and retain the engine crankshaft which must be held securely in place but turn freely.

• The MBC is attached to the engine block with bolts through long bolt holes which also locate the cap along the axis of the engine.

• The part is fit in the channel and it is fit in block fore stability.

• The joint faces must be flat to ensure solid contact with the block.• The surface directly under the bolt head must be flat and parallel to

ensure uniform pressure at the high clamp loads used.• There is a notch in the arch of the cap which locates the bearing

shells in place.

• MBCs made from gray cast iron, the competitive material, are cast in to a sand mold to produce a “loaf”, which required broaching, drilling, spot facing, and milling before the loaf is cut into individual MBC

• This process produces a 60% yield of main bearing caps from the cast iron loaf

• PM provided the necessary fatigue strength,quality,machinability and economy of near-net-shape-design.

Advantages Of Powder Metallurgy

• 1. Powder metallurgy produces near net shape components. The technique required few or no secondary operations.

• 2. Parts of powder metallurgy can be produce from high melting point refractory metals with less cost and difficulties.

• 3. The tolerance of components produced by this technique have quite high tolerance, therefore no further machining is not required.

• 4. This technique involves high Production Rate along with low Unit Cost.

• 5. It can produce complicated forms with a uniform microstructure.

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• 6. Powder metallurgy has full capacity for producing a variety of alloying systems and particulate composites.

• 7. This technique has flexibilities for producing PM parts with specific physical and mechanical properties like hardness, strength, density and porosity.

• 8. Powder metallurgy can be used to produce bi-metallic products, porous bearing and sintered carbide.

• 9. Powder metallurgy makes use of 100% raw material as no material is wasted as scrap during process

Disadvantages of powder metallurgy• 1. The production of powder for metallurgy is very high.• 2. The products of metallurgy can have limited shapes and features.• 3. This technique causes potential workforce health problems from

atmospheric contamination of the workplace.• 4. The tooling and equipments require for powder metallurgy are

very expensive, therefore becomes main issue with low production volume.

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• 5. It’s difficult to produce large and complex shaped parts with powder metallurgy.

• 6. The parts produce by powder metallurgy have low ductility and strength.

• 7. Finally divided powder like aluminum, magnesium, titanium and zirconium are fire hazard and explosive in nature.

• 8. This technique is not useful for low melting powder such as zinc, cadmium and tin as they show thermal difficulties during sintering operations.

References

www.google.comwww.wikipedia.orgwww.youtube.comMaterial Science and Physical metallurgy by O.P Khanna

Prepared by…..

130110120019 Bhavin Kevar130110120028 Tanuj Parikh130110120034 Harshil Patel1301101200 Roshan Patel1301101200 Shubham Shanghvi

Guided by,

Prof. Tejas D Patel Prof. Saurin M Sheth

Thank You