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