4.1 production of metal powders - compaction - sintering and finishing.pdf

UNIT-IV Processing of Metal powders,

Ceramics and Glasses

Powder Metallurgy

• producing metal or alloy powders, and using them to make finished or semi-finished products.

• Particulate technology

P/M Processing Steps

Elemental or alloy

metal powders Additives (Graphite,

lubricants)

Blending

Compaction

Sintering

Optional Finishing operations

Finished product

Production of Metal Powders

ATOMIZATION

• Produces a liquid-metal stream by injecting molten metal through a small orifice

• The stream is broken up by jets of inert gas or air , Water

Atomization

Centrifugal Atomization

• The process in which the molten-metal drops onto a rapidly rotating disk or cup

• The centrifugal forces break up the molten-metal stream to generate particles

Centrifugal Atomization

Mechanical Alloying

• Also known as pulverization

• Involves roll crushing, milling in a ball mill, or grinding of brittle or less ductile metals into small particles

• Brittle materials have angular shapes

• Ductile metals are flaky and not particularly suitable for P/M

Compaction

• Methods of Compaction : Application of high pressure to the powders to form them

into the required shape – Green compact

•Mechanical Pressing

•Hot Isostatic pressing

•Cold Isostatic pressing

Compaction pressures : 100Mpa to 1000 Mpa

Isostatic pressing : 1500 -30,000 psi

Compaction : Die/Punch Tooling

Compaction cycle

Pressing in PM: (1) filling die cavity with powder by automatic feeder; (2) initial and (3) final positions of upper and lower punches during pressing, (4) part ejection.

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Cold Isostatic Pressing

Sintering • Compressed metal powder is heated in a controlled

atmosphere furnace.

• to a temperature below its melting point which allows the bonding of materials to impart strength and hardness

Stages of product in P/M

Applications of P/M

• Abrasives: metal polishing wheels, grinding media

• Agriculture: lawn & garden equipments.

• Aerospace: jet engines, heat shields, rocket nozzles

• Ceramics: high temperature components, thermal shields, fuel cells

• Electronic: capacitors, resistors, contacts

• Hardware: locks, wrenches, cutting tools

• Manufacturing: dies, tools, bearings