Powder Metallurgy: Overview

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Powder Metallurgy Overview
1. General and Unique Features
2. Fundamental Mechanics
3. Product Quality and Control
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1. General and Unique Features

• Small size lt 2-3 kg maximum up to 20 kg

• Net shape 0.005 in.

- Very little waste of material (no runner,
riser, etc)
- Production of porous metal parts filters,
oil-impregnated bearings and gears
- Applicability to any type of metals a unique
way for those metals (e.g., Tungsten) which can
hardly be handled by other methods
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1. General and Unique Features
Disadvantages

• High cost metallic powder, tooling equipment
  cost

• Difficulties in storing and handling powders

- Difficulties in part geometry, coz metallic
powders DO NOT flow laterally
- Variation in density throughout the part
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2. Fundamental Mechanics
2.1 The PM process can be divided into (a)
preparation of powder, (b) operation (e.g.,
compaction, sintering, etc.)
2.2 Characterization of Powders
- Size and distribution
- Shape and internal structure
- Surface area
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Size and distribution
Measurement of Size and distribution
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Particle shape and internal structure
Open pores and closed pores concept
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Inter-particle friction
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True density, bulk density, packing factor,
porosity
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2.3 Production of Powders
Atomization
Chemical approach
2.4 Pressing and Sintering
Mixing, Compaction, Sintering
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Compaction
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Compaction
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Compaction force
Projected area of the part
Compaction pressure required for the given powder
materials
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3. PM Product Quality and Control
3.1 Classification of PM products (four classes)
Simple THICK shapes Require press from both
directions
Simple Thin shapes Require press from 1 direction
2-level thickness Require press from both
directions
multi-level thickness Require press from both
directions
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3. PM Product Quality and Control
Design for Manufacturing NOT RECOMMENDED
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3. PM Product Quality and Control
Design for Manufacturing RECOMMENDED
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3. PM Product Quality and Control
Design for Manufacturing
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3. PM Product Quality and Control
Design for Manufacturing
Wall thickness should be a minimum of 0.060 in
between holes or a hole and the outside part wall.
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Examples
In a certain pressing operation, the metallic
powder fed into the open die has a packing factor
of 0.5. The pressing operation reduces the powder
to two-thirds of its starting volume. In the
subsequent sintering operation, shrinkage amounts
to 10 on a volume basis. Given that these are
the only factors that affect the structure of the
finished part, determine its final porosity
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There is a relationship between the porosity (PO)
and the packaging factor (PF), i.e., PO PF
1 PO (volume of pores / bulk volume) PF
(bulk density / true density) Because the
density is defined as the ratio of (mass /
volume), the PF is also defined as PF (true
volume / bulk volume) Now our question is to
find the PO at the final stage. We try to find
the PF at the final stage as by doing so we can
find the PO at the final state using POPF1
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PF final? PF (true volume / bulk volume)