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POWDER METALLURGY
POWDER METALLURGY
Manufacturing Process
Manufacturing Process
Lecture
Lecture
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POWDER METALLURGY
POWDER METALLURGY
Manufacturing Process
Manufacturing Process
Lecture
Lecture
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04/25/21
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Introduction
Introduction
Powder metallurgy, or P/M (pronounced
Powder metallurgy, or P/M (pronounced
PM), is a
PM), is a
for forming metal parts
by heating compacted metal
by heating compacted metal
to
just below their melting points.
just below their melting points.
Powder metallurgy is the study of the
Powder metallurgy is the study of the
processing of metal powders, including
processing of metal powders, including
the fabrication, characterisation, and
the fabrication, characterisation, and
conversion of metal powders into useful
conversion of metal powders into useful
engineering components.
engineering components.
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What do we learn?
What do we learn?
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Introduction to Powder
Introduction to Powder
Metallurgy
Metallurgy
Attraction of P/M : the
Attraction of P/M : the
ability
to
fabricate
ability
to
fabricate
high quality, complex
high quality, complex
parts
to
close
parts
to
close
tolerances
in
an
tolerances
in
an
economical manner.
economical manner.
Automated operation :
Automated operation :
low relative energy
low relative energy
consumption,
high
consumption,
high
material
utilisation,
material
utilisation,
and low capital costs.
and low capital costs.
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POWDER METALLURGY PROCESS
POWDER METALLURGY PROCESS
TOPICS
COVERED IN
THIS LECTURE
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Advantages of the P/M
Advantages of the P/M
Process
Process
Eliminates or minimises
Eliminates or minimises
machining.
machining.
Eliminates or minimises
Eliminates or minimises
scrap loses.
scrap loses.
Maintains
close
Maintains
close
dimensional tolerances.
dimensional tolerances.
Permits a wide variety of
Permits a wide variety of
alloy systems.
alloy systems.
Produces
good
surface
Produces
good
surface
finishes.
finishes.
Provides materials which
Provides materials which
may be heat-treated for
may be heat-treated for
increased
strength
or
increased
strength
or
increased wear resistance.
increased wear resistance.
Provides
controlled
Provides
controlled
porosity for self-lubrication
porosity for self-lubrication
or filtration.
or filtration.
Facilitates manufacture of
Facilitates manufacture of
complex or unique shapes
complex or unique shapes
which would be impractical
which would be impractical
or impossible with other
or impossible with other
metalworking processes.
metalworking processes.
Suited to moderate-to high
Suited to moderate-to high
volume
component
volume
component
production requirements.
production requirements.
Offers
long-term
Offers
long-term
performance reliability in
performance reliability in
critical applications.
critical applications.
Cost effective.
Cost effective.
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Applications for Metal
Applications for Metal
Powders
Powders
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POWDER CHARACTERISTICS
POWDER CHARACTERISTICS
P/M deals with particles
P/M deals with particles
that are larger than
that are larger than
smoke (0.01 to 1
smoke (0.01 to 1
m),
m),
but smaller than sand
but smaller than sand
(0.1 to 3 mm). Many
(0.1 to 3 mm). Many
metal
powders
are
metal
powders
are
similar in size to the
similar in size to the
diameter of a human
diameter of a human
hair (25-200
hair (25-200
m).
m).
What is a particle ?
What is a particle ?
Collecting
a
Collecting
a
representative sample of
representative sample of
powder for analysis can
powder for analysis can
be difficult. Sampling
be difficult. Sampling
errors can be avoided
errors can be avoided
using some simple rules.
using some simple rules.
Particle size and
Particle size and
distribution.
distribution.
Particle shape and its
Particle shape and its
variation with particle
variation with particle
size.
size.
Surface area
Surface area
Interparticle friction
Interparticle friction
Flow and packing
Flow and packing
The internal particle
The internal particle
structure
structure
Composition,
Composition,
homogeneity, and
homogeneity, and
contamination.
contamination.
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Particle Size
Particle Size
Particle size is a
Particle size is a
determination of the
determination of the
dimensions
of
a
dimensions
of
a
particle.
particle.
Most particle size
Most particle size
analysers use one
analysers use one
geometric
geometric
parameter and make
parameter and make
the assumption of a
the assumption of a
spherical
particle
spherical
particle
shape.
shape.
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Particle Size Distribution
Particle Size Distribution
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Particle Shape
Particle Shape
Particle shape influences
Particle shape influences
packing,
flow,
and
packing,
flow,
and
compressibility,
compressibility,
provides information on
provides information on
the powder fabrication
the powder fabrication
route, and helps explain
route, and helps explain
many
processing
many
processing
characteristics.
characteristics.
Particle shape varies with
Particle shape varies with
size and manufacturing
size and manufacturing
technique.*
technique.*
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Variations in Shape
Variations in Shape
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*Water Atomisation Process
*Water Atomisation Process
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Powder Structure
Powder Structure
A
magnified
cross
A
magnified
cross
section
through
a
section
through
a
powder
reveals
powder
reveals
artifacts that indicate
artifacts that indicate
Fabrication conditions
Fabrication conditions
Possible processing
Possible processing
problems
problems
Internal pores,
Internal pores,
segregation,
segregation,
inclusions, and oxides.
inclusions, and oxides.
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Powder Chemistries
Powder Chemistries
There are 3 groups of powder:
There are 3 groups of powder:
1.
1.
The elemental powders are
The elemental powders are
relatively high purity materials
relatively high purity materials
where chemical analysis focuses
where chemical analysis focuses
on the impurity concentration.
on the impurity concentration.
2.
2.
Premixed powders are
Premixed powders are
combinations of two or more
combinations of two or more
distinct powders that will
distinct powders that will
diffusionally alloy in sintering
diffusionally alloy in sintering
(concerns: impurity levels and
(concerns: impurity levels and
proper compounding of the
proper compounding of the
mixture).
mixture).
3.
3.
The prealloyed powders
The prealloyed powders
constitute micro-castings with
constitute micro-castings with
multiple elements in a
multiple elements in a
predetermined ratio (concerns:
predetermined ratio (concerns:
alloy composition and impurity
alloy composition and impurity
concentrations).
concentrations).
Surface Conditions:
Surface Conditions:
-
Oxides
Oxides
-
Adsorbed organic films
Adsorbed organic films
-
The presence of
The presence of
surface coatings like
surface coatings like
silica to determine
silica to determine
appropriate cleaning
appropriate cleaning
treatments
treatments
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Powder Adjustment to Improve Packing and
Powder Adjustment to Improve Packing and
Flow
Flow
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Packing Structures
Packing Structures
The packing density
The packing density
dictates the die fill,
dictates the die fill,
binder content, and
binder content, and
shrinkage in sintering.
shrinkage in sintering.
The greater the surface
The greater the surface
roughness or the more
roughness or the more
irregular the particle
irregular the particle
shape, the lower the
shape, the lower the
packing density.
packing density.
For common P/M
For common P/M
powders the packing
powders the packing
density ranges from
density ranges from
30-65% of theoretical.
30-65% of theoretical.
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Mixing and Blending
Mixing and Blending
Mixing and blending are
Mixing and blending are
necessary :
necessary :
to prepare unique
to prepare unique
particle size
particle size
distribution.
distribution.
Combine powders to
Combine powders to
generate new alloys
generate new alloys
during sintering.
during sintering.
Add lubricants for
Add lubricants for
compaction
compaction
To prepare a powder-
To prepare a powder-
binder mixture for
binder mixture for
shaping.
shaping.
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Shaping and Compaction
Shaping and Compaction
Injection Molding
Injection Molding
Slurry Techniques :
Slurry Techniques :
Slip casting and tape
Slip casting and tape
casting
casting
Freezing technique
Freezing technique
Extrusion
Extrusion
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Injection Molding
Slurry
Techniques
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COMPACTION
COMPACTION
To achieve greater
To achieve greater
densities requires
densities requires
an external
an external
pressure.
pressure.
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Stages of Compaction
Stages of Compaction
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Conventional Compaction
Conventional Compaction
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Density Lines after Compacted
Density Lines after Compacted
Powder
Powder
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SINTERING
SINTERING
Sintering is the
Sintering is the
bonding together of
bonding together of
particles at high
particles at high
temperatures.
temperatures.
T < Tm by solid-state
T < Tm by solid-state
atomic transport
atomic transport
(solid-state sintering)
(solid-state sintering)
Involves formation of
Involves formation of
a liquid phase (liquid-
a liquid phase (liquid-
state sintering)
state sintering)
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Sintering Theory
Sintering Theory
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Pore Structures in Sintering
Pore Structures in Sintering
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Liquid Phase Sintering
Liquid Phase Sintering
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Practical Sintering
Practical Sintering
Operations
Operations
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SECONDARY OPERATIONS
SECONDARY OPERATIONS