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64 Extrusions
Compression forming process in which the work
metal is forced to flow through a die opening to
produce a desired cross-sectional shape
In general extrusion is used to produce long parts of
uniform cross-sections
Can be hot or cold
Hot ndash steels
Cold ndashsoft metals
Aluminium extrusions are used in
commercial and domestic buildings for
window and door frame systems
Aluminium for windows and doors
633 How would you go about making a stepped extrusion that has increasingly
larger crosssections along its length Is it possible Would your process be
economical and suitable for high production runs Explain
the smaller diameter is extruded first in the smallest opening
The next step will be extruding the part using a die with a larger opening the next step
will be extruding the part using a die with a larger opening than the first and second
die and the so on the part different cross sections will can be extruded by changing
the die to a larger opening
Extrusion Process Direct(forward extrusion)
Indirect (backward extrusion)
Hydrostatic ndash billet is smaller in diameter than
chamber and fluid pressure forces billet by a ram
Impact extrusion ndash suitable for hollow shapes
Classification of extrusion processes
Solid parts
Direct extrusion
A ram force the metal flow through one or
more die openings in a die
Significant friction
Remove oxide layer by a dummy block
Best applied to parts
having an outer diameter
of 254 mm (1 in) or more
Hollow Section
8
Hollow Section
The starting billet with a hole parallel to its axis
A mandrel attached to the dummy block
Shape factor ratio of the perimeter to its
cross-sectional area the larger the ratio the
more difficult the process
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Aluminium extrusions are used in
commercial and domestic buildings for
window and door frame systems
Aluminium for windows and doors
633 How would you go about making a stepped extrusion that has increasingly
larger crosssections along its length Is it possible Would your process be
economical and suitable for high production runs Explain
the smaller diameter is extruded first in the smallest opening
The next step will be extruding the part using a die with a larger opening the next step
will be extruding the part using a die with a larger opening than the first and second
die and the so on the part different cross sections will can be extruded by changing
the die to a larger opening
Extrusion Process Direct(forward extrusion)
Indirect (backward extrusion)
Hydrostatic ndash billet is smaller in diameter than
chamber and fluid pressure forces billet by a ram
Impact extrusion ndash suitable for hollow shapes
Classification of extrusion processes
Solid parts
Direct extrusion
A ram force the metal flow through one or
more die openings in a die
Significant friction
Remove oxide layer by a dummy block
Best applied to parts
having an outer diameter
of 254 mm (1 in) or more
Hollow Section
8
Hollow Section
The starting billet with a hole parallel to its axis
A mandrel attached to the dummy block
Shape factor ratio of the perimeter to its
cross-sectional area the larger the ratio the
more difficult the process
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
633 How would you go about making a stepped extrusion that has increasingly
larger crosssections along its length Is it possible Would your process be
economical and suitable for high production runs Explain
the smaller diameter is extruded first in the smallest opening
The next step will be extruding the part using a die with a larger opening the next step
will be extruding the part using a die with a larger opening than the first and second
die and the so on the part different cross sections will can be extruded by changing
the die to a larger opening
Extrusion Process Direct(forward extrusion)
Indirect (backward extrusion)
Hydrostatic ndash billet is smaller in diameter than
chamber and fluid pressure forces billet by a ram
Impact extrusion ndash suitable for hollow shapes
Classification of extrusion processes
Solid parts
Direct extrusion
A ram force the metal flow through one or
more die openings in a die
Significant friction
Remove oxide layer by a dummy block
Best applied to parts
having an outer diameter
of 254 mm (1 in) or more
Hollow Section
8
Hollow Section
The starting billet with a hole parallel to its axis
A mandrel attached to the dummy block
Shape factor ratio of the perimeter to its
cross-sectional area the larger the ratio the
more difficult the process
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Extrusion Process Direct(forward extrusion)
Indirect (backward extrusion)
Hydrostatic ndash billet is smaller in diameter than
chamber and fluid pressure forces billet by a ram
Impact extrusion ndash suitable for hollow shapes
Classification of extrusion processes
Solid parts
Direct extrusion
A ram force the metal flow through one or
more die openings in a die
Significant friction
Remove oxide layer by a dummy block
Best applied to parts
having an outer diameter
of 254 mm (1 in) or more
Hollow Section
8
Hollow Section
The starting billet with a hole parallel to its axis
A mandrel attached to the dummy block
Shape factor ratio of the perimeter to its
cross-sectional area the larger the ratio the
more difficult the process
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Solid parts
Direct extrusion
A ram force the metal flow through one or
more die openings in a die
Significant friction
Remove oxide layer by a dummy block
Best applied to parts
having an outer diameter
of 254 mm (1 in) or more
Hollow Section
8
Hollow Section
The starting billet with a hole parallel to its axis
A mandrel attached to the dummy block
Shape factor ratio of the perimeter to its
cross-sectional area the larger the ratio the
more difficult the process
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Hollow Section
8
Hollow Section
The starting billet with a hole parallel to its axis
A mandrel attached to the dummy block
Shape factor ratio of the perimeter to its
cross-sectional area the larger the ratio the
more difficult the process
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
8
Hollow Section
The starting billet with a hole parallel to its axis
A mandrel attached to the dummy block
Shape factor ratio of the perimeter to its
cross-sectional area the larger the ratio the
more difficult the process
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
The metal billet is placed in a container and driven through the die by the ram
bull The dummy block or pressure plate is placed at the end of the ram in contact
with the billet
bull Friction is at the die and container wall requires higher pressure than indirect
extrusion
Indirect extrusion
This is generally used for extruding symmetrically shaped parts
having a closed end
1048707 Extrusion pressure 30 lower than direct
method
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
bull The hollow ram containing the die is kept stationary and the container with the
billet is caused to move
bull Friction at the die only (no relative movement at the container wall) requires
roughly constant pressure
bull Hollow ram limits the applied load
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Hydrostatic Extrusion
No friction
Increased ductility
Preparation of the tapered work billet
The rate with which
the billet moves when
pressing in the
direction of the die is
thus not equal to the
ram speed but is
proportional to the
displaced
hydrostatics medium
volume
The billet in the container is surrounded with fluid
media-The billet is forced through the die by a high
hydrostatic fluid pressure
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
bull The billet may have large length to diameter ratio and may have an
irregular cross section
Products
ndash helical gears
ndash copper wire
bull Materials
ndash brittle materials
ndash cast iron
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Advantages and disadvantages in hydrostatic extrusion
Advantages
bull Eliminating the large friction force between the billet and the container
wall
bull Possible to use dies with a very low semicone angle (α ~ 20o)
bull Achieving of hydrodynamic lubrication in the die
Limitations
bull Not suitable for hot-working due to pressurised liquid
bull A practical limit on fluid pressure of around 17 GPa
currently exists because of the strength of the container
bull The liquid should not solidify at high pressure this limits
the obtainable extrusion ratios Mild steel R should be less
than 201 Aluminium R can achieve up to 2001
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Impact Extrusion
Impact loading
Usually cold extrusion
Restricted to softer
metals lead tin Al amp Cu
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Similar to indirect extrusion
Punch descends rapidly on the blank which is extruded backward
The extruded parts are stripped by the use of a stripper plate because they tend to stick to the punch
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
638 Under what circumstances is backwards extrusion preferable to direct
extrusion When is hydrostatic extrusion preferable to direct extrusion
backwards extrusion is preferable if there is significant friction between the
workpiece and the chamber because there is no movement between the bodies
involve
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Cold Extrusion
Combination of operations such as direct and indirect extrusion and forging
-small machine parts such as spark plug bodies shafts pins and
hollow cylinders or cans
Precision cold-forming can result in high production of parts with
good dimensional control and good surface finish
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Production steps for a cold extruded spark plug
A cross-section of the metal part aboveshowing the grain flow pattern
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Hot Extrusion
Extrusion is carried out at elevated temperatures ndash for metals
and alloys that do not have sufficient ductility at room
temperature or in order to reduce the forces required
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Fig Types of metal flow in extruding with square dies (a) Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions of the billet in the chamber This type of pattern observed in metals whose strength increases rapidly with decreasing temperature leads to defect known as pipe or extrusion defect
three different metal flow patterns have been observed during the process of
extrusion depending upon the prevailing conditions
641 Metal Flow in Extrusion
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
(a)Flow pattern obtained at low friction or in indirect extrusion (b) Pattern obtained with high friction at the billet-chamber interfaces (c) Pattern obtained at high friction or with cooling of the outer regions
of the billet in the chamber
Types of metal flow in extruding with square dies
This type is observed in Metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe or extrusion defect
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
23
Metal Flow
Elongated grain structure (preferred
orientation)
Dead-metal zone metal trapped by the die
angle
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Surface cracking due to high temp and friction
Sticking along die land
Piping associated with direct extrusion
Centerburst due to tensile stresses
centerburst piping surface cracking
644 Defects in Extrusion1 Surface cracking
2 Pipe tailpipe fishtailing
3 Internal Cracking
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
2) Surface cracking ranging from a badly roughened surface to repetitive
transverse cracking called fir-tree cracking
This is due to longitudinal tensile stresses generated as the extrusion passes
through the die
In hot extrusion this form of cracking usually is intergranular and is associated with
hot shortness
bull The most common case is too high ram speed for the extrusion temperature
bull At lower temperature sticking in the die land and the sudden building up of pressure
and then breakaway will cause transverse cracking
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Piping (tail-piping fish-pipe)
ndash Drawing surface oxides and impurities toward the center of the
billets
ndash Results in significant length lost
ndash Minimized by machining the billets first to make flow more
uniform
Metal flow pattern draws surface
oxides and impurities toward the
center of the billet like a funnel
To prevent modify flow pattern to be more
uniform control friction and minimize
temperature gradients remove scale and
impurities by machining or chemical
etching prior to extrusion
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
The tendency toward chevron cracking increases if the two plastic zones do
not meet
the plastic zone can be made larger either by decreasing the die angel or by
increasing the reduction in cross-section (or both)
can occur at low extrusion ratio due to low frictional conditions on the zone of
deformation at the extrusion die
bullIncreases with increased die angle impurities
bullDecreases with increased extrusion ratio and friction
Chevron cracking (central burst) in extruded round steel bars
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
Design Guidelines
Symmetry of cross-section
Avoidance of sharp corners
Avoidance of extreme changes of the cross-section
645 Extrusion practices
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
bull Extrusion-Die Configurations
(a)
(b)
(c)
Typical extrusion-die configurations (a) die for nonferrous metals (b) die for ferrous metals
die for T-shaped extrusion made of
hot-work die steel and used with
molten glass as a lubricant
die for T-shaped extrusion
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes
(a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders This part is 8 mm (516 in) thick and is sawed from the extrusion (b)-(d) Components of various dies for extruding intricate hollow shapes