mech152-l22-1 (1.0) - 1 powder metallurgy. mech152-l22-1 (1.0) - 2 typical parts
TRANSCRIPT
MECH152-L22-1 (1.0) - 1
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