MAURBHANJ SCHOOL OF ENGINEERING

BARIPADA : 757107 , ODISHA

CHAPTER – 04

TOPIC- POWDER METALLURGY

BRANCH- MECH.

SEMISTER- 3^rd

SUBJECT- PRODUCTION TECHNOLOGY

FACULTY- ER KHAGESWAR PATRA

Estd:.1994

Powder Metallurgy

• Essentially, Powder Metallurgy (PM) is an art & science of producing metal or metallic powders, and using them to make finished or semi-finished products.
• Particulate technology is probably the oldest forming technique known to man.
• There are archeological evidences to prove that the ancient man knew something about it.

Powder Metallurgy

• An important point that comes out :
• The entire material need not be melted to fuse it.
• The working temperature is well below the melting point of the major constituent, making it a very suitable method to work with refractory materials, such as: W, Mo, Ta, Nb, oxides, carbides, etc.
• It began with Platinum technology about 4 centuries ago... in those days, Platinum, [MP = 1774°C], was "refractory", and could not be melted.

Powder Metallurgy Process

• Powder production
• Blending or mixing
• Powder compaction
• Sintering
• Finishing Operations

Powder Metallurgy Process

Powder Metallurgy Processing

Usual PM production sequence

Blending and mixing (Rotating drums, blade and screw mixers)

• Pressing - powders are compressed into desired shape to produce green compact

Accomplished in press using punch-and-die tooling designed for the part

• Sintering – green compacts are heated to bond the particles into a hard, rigid mass.

Performed at temperatures below the melting point of the metal

Production of Metallic Powders

• In general, producers of metallic powders are not the same companies as those that make PM parts

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• Any metal can be made into powder form
• Three principal methods by which metallic powders are commercially produced
• Atomization (by gas, water, also centrifugal one)
• Chemical
• Electrolytic
• In addition, mechanical methods are occasionally used to reduce powder sizes

Particle Shapes in Metal Powders

Blending and Mixing of Powders

• For successful results in compaction and sintering, the starting powders must be homogenized (powders should be blended and mixed).
• Blending - powders of same chemistry but possibly different particle sizes are intermingled.
• Different particle sizes are often blended to reduce porosity
• Mixing – powders of different chemistries are combined.
• PM technology allows mixing various metals into alloys that would be difficult or impossible to produce by other means.

Blending or Mixing

• Blending a coarser fraction with a finer fraction ensures that the interstices between large particles will be filled out.
• Powders of different metals and other materials may be mixed in order to impart special physical and mechanical properties through metallic alloying.
• Lubricants may be mixed to improve the powder's flow characteristics.
• Binders such as wax or thermoplastic polymers are added to improve green strength.

Blending

To make a homogeneous mass with uniform distribution of particle size and composition.

• Powders made by different processes have different sizes and shapes
• Mixing powders of different metals/materials

Combining is generally carried out in

• Air or inert gases to avoid oxidation
• Liquids for better mixing, elimination of dusts and reducedexplosion hazards

Compaction

Application of high pressure to the powders to form them into the required shape.

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Conventional compaction method is pressing, in which opposing punches squeeze the powders contained in a die.

• The work part after pressing is called a green compact, the word green meaning not yet fully processed.

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• The green strength of the part when pressed is adequatefor handling but far less than after sintering.

Compacting

• Press powder into the desired shape and size in dies using a hydraulic or mechanical press
• Pressed powder is known as “green compact”
• Stages of metal powder compaction:

Compacting

Powders do not flow like liquid, they simply compress until an equal and opposing force is created.

- This opposing force is created from a combination of

1. Resistance by the bottom punch and
2. friction between the particles and die surface

Compacting consolidates and dandifies the component fortransportation to the sintering furnace.

Compacting consists of automatically feeding a controlled amount of mixed powder into a precision die, after which it is compacted.

Compacting

Compacting is usually performed at room temperature. Pressures range from 10 tons per square inch (tons/in²) (138 MPa) to 60 tons/in² (827 MPa), or more.

Thank you

CREATED BY: ER KHAGESWAR PATRA