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Powder Metallurgy

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Typical Parts

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Powder Metallurgy - Pros

• Net shape manufacturing

• Minimum wastage of material

• Production of porous parts, typically for self-lubricating applications

• Produce parts from material difficult to process

• Produce parts with special alloying content

• Good dimensional control

• Can be automated for economic production

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Powder Metallurgy - Cons

• High tooling and equipment cost.

• Expensive raw material.

• Difficulty with storing and handling of powder.

• Limiting in geometry as the powder does not flow readily in die.

• Inhomogeneity of produced part.

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Features of Engineering Powders

• Particle size and distribution

• Particle shape and internal structure

• Surface area - Area / volume ratio

• Interparticle friction and flow characteristics

• Packing, density and porosity

• Chemistry and surface films

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Features of Engineering Powders

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Production of PM Parts

• Blending and Mixing of powder

• Compaction

• Sintering

• Secondary operations– Densification and sizing– Impregnation and infiltration– Heat treatment and finishing

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Blending & Mixing of Powders

1. Blending 2. Compacting 3. Sintering

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Blending & Mixing of Powders

a) rotating drum

b) rotating double cone

c) screw mixer

d) blade mixer

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Compaction1. Feeding

2. Initial compaction

3. Final compaction

4. Ejection

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Compaction

1. Feeding

2. Initial compaction

3. Final compaction

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Sintering

1. Initiation of bonding

2. Building necks

3. Pores reducing in size

4. Grain boundaries develop between particles

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Sintering

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Sintering

Sintering temperature and duration for different PM

MECH152-L22-1 (1.0) - 15Secondary Operation - Densification and Sizing

To increase density, improve accuracy, additional shaping of sintered parts:– Repressing: squeezing the part in a closed die.– Sizing: Pressing to improve dimensional

accuracy.– Coining: Presswork to produce details on part

surface.

MECH152-L22-1 (1.0) - 16Secondary Operation - Impregnation and Infiltration

Impregnation: filling the part with oils and fluids from a hot bath. Or parts are filled with polymer resins to prevent seepage of fluid.

Infiltration: Parts are filled with a molten metal. Melting point of filler metal must be below that of the PM part, e.g. copper infiltration.

MECH152-L22-1 (1.0) - 17Secondary Operation -Heat Treatment and Finishing

Heat Treatment - Hardening and strengthening the part.

Finishing - Electroplating and painting.

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Alternative Techniques

Isostatic Pressing

1. Feeding powder in flexible mold

2. Application of hydrostatic pressure

3. Part removal

MECH152-L22-1 (1.0) - 19Powder Rolling, Extrusion, and Forging

Rolling - forming meal strip stock

Extrusion - forming billets of high densification

Forging - forming parts in dies.

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Design Considerations

• Large batch size to make it cost effective, typically over 10,000.

• Controlled porosity parts.

• Special alloying elements parts.

• Limited geometry to allow die opening.

• Built-in chamfers and radii.

• Minimum wall thickness of 1.5 mm and minimum hole diameter of 1.5 mm.

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Design Considerations

Features to be avoided for PM parts

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Design Considerations

Permissible features for PM parts

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Design Considerations

Chamfers and radii

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Design Considerations