ENGR 241 – Introduction To Manufacturing

Chapter 17:

Powder Processing

Powder Metallurgy

• Consists in compacting metal powders

into an specific shape (dies), and

heating them (without melting) to impart

strength.

Powder Metallurgy

• Process Steps

• powder production

• blending

• compaction

• sintering

• finishing operations

Powder Production• Atomization

• liquid-metal broken up by jets of gas, air or water.

• Reduction• fine metallic oxides are turned into metallic

particles.

• Electrolytic Deposition• metal immersed in aqueous solutions or fused

salts.

Powder Production (Cont.)• Carbonyls

• reaction with carbon monoxide

• Comminution• mechanical pulverization

• Mechanical Alloying• impact alloying

Blending of Metal Powders

• Use to impart special physical and

mechanical properties/characteristics

• Uniformity

• Lubricants (improve flow)

• Pyrophorism (high surface-area to volume

ratio).

Compaction of Metal Powders

• Powders are pressed into shapes (dies)

using hydraulic or mechanical presses.

• Green compacts (pre-forms at room temp)

• 24% porosity (in theory)

• MIM

Sintering

• Compressed metal powders heated in a

controlled atmosphere.

• Bonding of particles.

• Temperature, time, and atmosphere.

• Usually carried at 70 to 90% of the melting

point of the metal or alloy.

Finishing Operations

• Impregnating (oil)

• Infiltration (porosity)

• Heat treatment

• Machining

• Grinding

• Plating

• Forging (Coining)