The document discusses the process of extrusion. It begins with an introduction to extrusion, defining it as reducing the cross-section of metal by forcing it to flow through a die under high pressure. It then covers the basic extrusion process using diagrams. The document goes on to classify extrusion processes and describe various types like direct/indirect, hot/cold, lateral, and hydrostatic extrusion. It also covers die design, defects, variables that affect extrusion, and applications of extrusion.

1. Source: George E. Dieter
Presentation by HP

2. Objectives:
Introduction
Classification of extrusion processes
Extrusion equipment (Presses, dies and tools)
Hot extrusion
Deformation, lubrication, and defects in extrusion
Analysis of the extrusion process
Cold extrusion and cold-forming
Hydrostatic extrusion
Extrusion of tubing
Production of seamless pipe and tubing

3. What is extrusion?
• It is the process by which a block of metal is
reduced in cross-section by forcing it to flow
through a die orifice under high pressure
The products of extrusion are generally called "extrudates".
Extruded partBilletRam
Die
ContainerDummy plate
(extrusion pad)

4. Process
• A heated billet cut from continuous casting is located in a
heated container.
• By applying pressure by means of a ram to one end of the
billet the metal flows through the die, located at the other end
of the container to produce a section, the cross sectional
shape of which is defined by the shape of the die
Extruded partBilletRam
Die
ContainerDummy plate
(extrusion pad)

5. • In general, extrusion is used to produce cylindrical bars
or hollow tubes or for the starting stock for drawing rod,
cold extrusion or forged products.
• Most metals are hot extruded due to large amount of
forces required in extrusion.
• Complex shape can be extruded from the more readily
extrudable metals such as aluminium.
• If better properties are required then it may be heat
treated or cold worked
Extruded partBilletRam
Die

6. • The reaction of the extrusion billet with the container and die
results in high compressive stresses which are effective in
reducing cracking of materials during primary breakdown
from the ingot.
Extruded partBillet
Die
Pressure
Compressive stresses will help in increasing the utilisation of
extrusion in the working of metals that are difficult to form like
stainless steels, nickel-based alloys, and other high-temperature
materials.

7. Cold Extrusion
Cold extrusion is the process done at room temperature or
slightly elevated temperatures.
 This process can be used for most materials-subject to
designing robust enough tooling that can withstand the
stresses created by extrusion.
Examples of the metals that can be extruded are lead, tin,
aluminium alloys, copper, titanium, molybdenum, vanadium,
steel. Examples of parts that are cold extruded are collapsible
tubes, aluminium cans, cylinders, gear blanks.
Advantages:
 No oxidation takes place.
 Good mechanical properties due to severe cold working as long as
the temperatures created are below the recrystallization
temperature.
 Good surface finish with the use of proper lubricants.

9. Hot extrusion
Hot extrusion is done at fairly high temperatures
approximately 50 to 75 % of the melting point of the metal.
• The pressures can range from 35-700 MPa
• The most commonly used extrusion process is the hot direct
process.
• The cross-sectional shape of the extrusion is defined by the
shape of the die.
• Due to the high temperatures and pressures and its
detrimental effect on the die life as well as other
components, good lubrication is necessary.
• Oil and graphite work at lower temperatures, whereas at
higher temperatures glass powder is used.

10. Cold extrusion
• It is done at room temp or
near room temp
• The advantages of this
over hot extrusion are the
lack of oxidation, higher
strength due to cold
working, closer tolerances,
better surface finish, and
fast extrusion
Hot extrusion
• It is fairly done at high temp
(0.5-0.7 Tm) (above
recrystallization temp)
• Good lubrication is needed
since it works at elevated
temp (glass powders are
used)
• Due to the high temperatures
and pressures and its
detrimental effect on the die
life as well as other
components.
• So, good lubrication is
necessary.

12. Extrusion of lead sheath on electrical cable

13. • Typical parts produced by extrusion are trim parts used
in automotive and construction applications, window
frame members, railings, aircraft structural parts.
Example: Aluminium extrusions are used in commercial and
domestic buildings for window and door frame systems,
prefabricated houses/building structures, roofing and
exterior cladding, curtain walling, shop fronts, etc.
Furthermore, extrusions are also used in transport for
airframes, road and rail vehicles and in marine applications.

14. Classification of extrusion processes
There are several ways to classify metal extrusion processes
By Direction
• Direct / Indirect extrusion
• Forward / backward extrusion
By temperature Hot / cold extrusion
By equipment Horizontal and vertical extrusion

15. Methods of
extrusion
Direct/forward
Indirect/backward
Lateral
Extrusion forging
Impact Extrusion
Hooker extrusion
Hydrostatic extrusion

16. Direct/forward extrusion
The metal billet is placed in a container and driven through the die
by the ram.
The dummy block or pressure plate, is placed at the end of the ram
in contact with the billet.
Friction is at the die and container wall  requires higher pressure
than indirect extrusion.
Extruded partBilletRam
Die
ContainerDummy plate
(extrusion pad)

17. 1 Extrusion
2 Die backer
3 Die
4 Billet
5 Dummy block
6 Pressing ram
7 Container liner
8 Container body

18. Process:
Hot metal billet is placed in the container
Compressive forces are applied on the metal billet by ram
(hydraulically driven)
Compressive forces will make the metal advance in the
container, and then through the die opening
Hot metal is placed in
the container
Metal is pressed by Ram
Metal will advance in
container, and then
through die
Metal will flow through
the die opening
Extruded metal will
further be processed

19. Extruded partBillet
Die
ContainerClosure plate
Ram
Indirect extrusion
 The hollow ram containing the die is kept stationary and the container
with the billet is caused to move.
 Friction at the die only (no relative movement at the container wall)
requires roughly constant pressure.
 Hollow ram limits the applied load.

20. Typical curves of extrusion Vs. ram travel for direct and
indirect extrusion

21. Lateral extrusion
• Container is in vertical
position and the die is
located in the side
• The metal is kept in the
container such that the
vertical ram applies force on
the metal
• The extruded part comes
out from the bottom die
• This is suitable for very light
alloys that have low melting
points

22. Equal channel angular extrusion
• Equal channel angular extrusion (ECAE) is an extrusion process is
developed to refine the microstructure of metals and alloys,
thereby improving their strength according to the Hall-Petch
relationship.
• It is also known as “ECAP (Equal Channel Angular Pressing)”

23. • ECAE is unique because significant cold work can be
accomplished without reduction in the cross sectional area of the
deformed workpiece.
• In conventional deformation processes like rolling, forging,
extrusion, and drawing, strain is introduced by reduction in the
cross sectional area.
• ECAE produces significant deformation strain without reducing
the cross sectional area.
• This is accomplished by extruding the work piece around a
corner.
• For example, a square cross section bar of metal is forced through a
channel with a 90o angle.
• The cross section of the channel is equal on entry and exit.
• The complex deformation of the metal as it flows around the
corner produces very high strain.
• Because the cross section remains the same, a work piece can be
extruded multiple times with each pass introducing additional
strain.

24. Extrusion-forging
• It’s a combination of
extrusion and forging
• Metal is extruded
through die while
being forged
• Used for poppet valves
in IC engines
Punch
Hot metal
Die holder
Die holder

25. Punch
Completion of extrusion forging process

26. Impact Extrusion
• Impact extrusion is a cold manufacturing process similar
to extrusion and drawing by which products are made with a metal slug.
• The slug is pressed at a high velocity with extreme force into a die/mould by a
punch.
• Process is restricted to soft metals like lead, aluminum, and copper
 It uses heavy duty mechanical
presses
 Metal collapsible tubes,
disposable tubes, ointment
tubes, deodorant bottles are
produced by this process

28. Impact Extrusion
Advantages
• Simple and very
economical
• Suitable for collapsible
tubes
• Production cost very low
• Excellent surface finish
• Fast production rates
Limitations
• Limited to soft metals like
Pb, Al, and Cu
• More wear
• Feeding lubricant is bit
difficult since it splashes
out

29. Hooker Extrusion

30. Hydrostatic Extrusion
• In this process the billet is completely surrounded by a
pressurized liquid, except where the billet contacts the die.
• This process can be done hot, warm, or cold, however the
temperature is limited by the stability of the fluid used.
• The process must be carried out in a sealed cylinder to
contain the hydrostatic medium.
• The fluid can be pressurized in two ways:
• Constant-rate extrusion: A ram or plunger is used to pressurize the
fluid inside the container.
• Constant-pressure extrusion: A pump is used, possibly with a pressure
intensifier, to pressurize the fluid, which is then pumped to the
container.

31. Pressure is applied through a fluid surrounding the billet
Fluid pressure forces the billet into die
Die compresses the metal with very less friction

32. Hydrostatic Extrusion
Advantages
• No friction between the
container and the billet reduces
force requirements.
• This ultimately allows for faster
speeds, higher reduction ratios,
and lower billet temperatures.
• Usually the ductility of the
material increases when high
pressures are applied.
• An even flow of material.
• Large billets and large cross-
sections can be extruded.
• No billet residue is left on the
container walls.
Limitations
• The billets have to be
prepared by tapering one
end so that it matches the
die entry angle.
• Only cold extrusion is
possible
• It can be difficult to contain
the fluid, under the effects
of high pressures (up to 2
GPa).

33. Extrusion of seamless tubes
(With a fixed mandrel)
BilletRam
Die
ContainerDummy plate
(extrusion pad)
Mandrel

34. Extrusion of seamless tubes
(With a floating mandrel)
BilletRam
Die
ContainerDummy plate
(extrusion pad)
Mandrel

35. • Both the operations can be carried out with hallow
billet or solid one
• Solid billets are always preferable since creating a
hallow billet consumes time and wastes more
material
BilletRam
Die
ContainerDummy plate
(extrusion pad)
Mandrel

36. Imp extrusion variables
1) Yield strength of the material (temp increases
yield strength decreases thereby extrusion force
decreases )
2) The type of extrusion
3) Extrusion Ratio
4) The working temp
5) The speed of deformation
6) Frictional conditions

37. • Extrusion Ratio: it is the ratio
of the cross-sectional area of
the billet (Ao) to final cross-
sectional area after extrusion
(Af)
𝑅 =
𝐴 𝑜
𝐴 𝑓
• Extrusion ratios reach about
40:1 for hot extrusion of steel
and may be as high as 400:1 for
Al.
• Extrusion ratios will increase
with increase in temp

38. Extrusion Circumscribing circle
CCD = Circumscribing
Circle Diameter is the
diameter of the smallest circle
into which the extruded part can
fit
• CCD will increase when
components are big irregular
• CCD of the square or
rectangular section is just
connecting the diagonals

39. Ram Speed:
• Increasing ram speed produces an increase in the
extrusion pressure
• A tenfold increase in the speed results in about a 50%
increase in pressure
• Greater cooling of the billet occurs at low extrusion
speeds
• When the ram moves slowly, billet cools fast and the
pressure required for direct extrusion will increase

40. Extrusion pressure
is the extrusion
force divided by
the cross-sectional
area of the billet.
Rapid rise in ‘P’
during initial ram
travel is due to the
initial compression
of the billet to fill
the container
For direct
extrusion the metal
begins to flow
through the die at
the maximum
value of pressure
(breakthrough
pressure)

41. Effect of temp:
• Decreased flow stress or deformation resistance due to
increasing extrusion temperature.
• Use minimum temperature to provide metal with
suitable plasticity.
• The top working temperature should be safely below
the melting point or hot-shortness range.
• Oxidation of billet and extrusion tools.
• Softening of dies and tools.
• Difficult to provide adequate lubrication.

42. The temperature of the workpiece in
metal working depends on:
1. The initial temperature of the tools and the
materials
2. Heat generated due to plastic deformation
3. Heat generated by friction at the die/material
interface (highest)
4. Heat transfer between the deforming material
and the dies and surrounding environment

43. Relationships between extrusion ratio,
temperature and pressure
• For a given extrusion pressure, extrusion ratio R
increases with increasing Extrusion temperature.
• For a given extrusion temperature, a larger
extrusion ratio R can be obtained with a higher
extrusion pressure.
Extrusion temperature
Extrusion pressure
Extrusion Ratio (R)

44. Die design
• Die design is at the heart of efficient extrusion production.
• Dies must withstand considerable amount of stresses,
thermal shock, and oxidation.
Die Design considerations:
• Wall thickness: different wall thicknesses in one section
should be avoided.
• Simple shapes: the more simple shape the more cost
effective.
• Symmetrical: more accurate.
• Sharp or rounded corners: sharp corners should be avoided.
• Size to weight ratio
• Tolerances: tolerances are added to allow some distortions

45. Die materials
Dies are made from highly alloy tools steels or ceramics
(zirconia, Si3N4 ). (for cold extrusion offering longer tool life
and reduced lubricant used, good wear resistance).
Wall thickness as small as 0.5 mm (on flat dies) or 0.7 mm
(on hollow dies) can be made for aluminium extrusion.
Heat treatments such as nitriding are required (several
times) to increase hardness (1000-1100 Hv or 65-70 HRC).
This improves die life. Avoiding unscheduled press
shutdown.

46. • Metal entering the die will
form a dead zone and
shears internally to form its
own die angle.
• A parallel land on the exit
side of the die helps
strengthen the die and
allow for reworking of the
flat face on the entrance
side of the die without
increasing the exit diameter.
• Requires good lubricants.
• Decreasing die angle increasing
homogeneity, lower extrusion
pressure (but beyond a point the
friction in the die surfaces
becomes too great.
• For most operation, 45o < α < 60o
Flat-faced dies Dies with conical entrance angle

47. • The die stack consists of the die, which is supported by a die holder
and a bolster, all of which are held in a die head.
• The entire assembly is sealed against the container on a conical
seating surface by pressure applied by a wedge.
• A liner is shrunk in a more massive container to withstand high
pressures.
• The follower pad is placed between the hot billet and the ram for
protection purpose. Follower pads are therefore replaced
periodically since they are subject to many cycles of thermal shock.

48. (a) Low container friction and a well-lubricated billet – nearly homogeneous
deformation.
b) Increased container wall friction, producing a dead zone of stagnant metal at corners
which undergoes little deformation. Essentially pure elongation in the centre and
extensive shear along the sides of the billet.The latter leads to redundant work
c) For high friction at the container-billet interface, metal flow is concentrated toward the
centre and an internal shear plane develops – due to cold container. In the sticky friction,
the metal will separate internally along the shear zone. A thin skin will be left in a
container and a new metal surface is obtained.
d) Low container friction and a well lubricated billet in indirect extrusion.

50. Extrusion Defects
• Defects in extruded products occur predominantly
due to friction and non-homogeneous material
flow.
• Further, temperature variations across the billet
during hot extrusion can also lead to
inhomogeneous deformation.
• Three types of defects are prominent in extrusion.
• They are:
1. Inhomogeneous deformation
2. Surface cracks
3. Internal cracks

51. • Inhomogeneous deformation in direct extrusion
provide the dead zone along the outer surface of the billet
due to the movement of the metal in the centre being
higher than the periphery.
• After 2/3 of the billet is extruded, the outer surface of the
billet (normally with oxidised skin) moves toward the
centre and extrudes to the through the die, resulting in
internal oxide stringers transverse section can be seen as an
annular ring of oxide.
Container wall
friction
Container wall
temp
Extrusion Defects
Extrusion Defects

52. • Surface cracking, ranging from a badly roughened surface
to repetitive transverse cracking called fir-tree cracking, see
Fig.
• 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.
• The most common case is too high ram speed for the
extrusion temperature.
• At lower temperature, sticking in the die land and the
sudden building up of pressure and then breakaway will
cause transverse cracking.
Surface cracks from heavy die
friction in extrusion

53. Internal cracks or centre burst:
• It occurs because the stresses within the workpiece
break the material causing cracks to form along the
central axis of the extruded region
• High die angles will favour centre cracking
• Metal must be free from inclusions to avoid centre
burst
• High extrusion ratio also will favour centre burst

54. Analysis of extrusion process
• As we have seen the slab analysis for wire
drawing, the analysis of extrusion process is
much simpler
• Extrusion stress ( 𝜎 𝑥 ) or die pressure Pd is
calculated by
𝐏 𝐝 = 𝛔 𝐱 =
𝛔 𝐨 𝟏 + 𝐁
𝐁
𝟏 − 𝐑 𝐁
𝐵 = 𝜇 𝑐𝑜𝑡𝛼; 𝑤ℎ𝑒𝑟𝑒 𝜇 = 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛

55. Thank You
