This topic is related to mechanical engineering extrusion of metals

1. EXTRUSION OF
METALS
CIVIL - FABRICATION PROCESS
As well
MECH - PRODUCTION TECHNOLOGY
Prepared
by Sk

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

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".

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. Extruded partBilletRam
• 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
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
steels, nickel-based alloys, and other high-temperaturestainless
materials.

7. Extrusion
ByDirection
By
Equipment
Indirect /
Backward
Direct /
Forward
ByOperating
Temperature
Hot Cold Horizontal Vertical
Classification of extrusion processes

8. 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 verticalextrusion

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

10. Cold Extrusion
Cold extrusion is the process done at room temperature or
slightly elevatedtemperatures.
 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.

11. COLD EXTRUSION
ADVANTAGES
• Improved Mechanical
properties.
• Good control of
dimensional tolerances.
• Improved surfacefinish.
• No need for heating
billet.
• No oxidation takesplace.
DISADVANTAGES
• Tooling cost is high, therefore
large production lot size is
required.
• Special coating is required to
reduce friction and to maintain
a lubricant film throughout.
• Limited deformation can be
obtained.

13. 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
detrimental effect on the die
and pressures and its
life as well as other
components, good lubrication isnecessary.
• Oil and graphite work at lower temperatures, whereas at
higher temperatures glass powder is used.

14. HOT EXTRUSION
ADVANTAGES
Complex solid or hollow
shapescanbeproduced.
Small quantitiescan be
economically produced.
Delivery timesare often far
shorter than alternative
processes.
DISADVANTAGES
High equipment set up and
maintenance cost.
Extrusion process for metals is at
very high temperatures.
Die is preheated to increase its
life, so there are chances of
oxidation of hot billet.
Process Wastage is higher as
compared to rolling
Non-homogeneous.

16. 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
• Good
since
temp
used)
(0.5-0.7 Tm) (above
recrystallization temp)
lubrication is needed
it works at elevated
(glass powders are
• 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.

17. 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 thebillet.
Friction is at the die and container wall  requires higher pressure
than indirect extrusion.
Extruded partBilletRam
Die
ContainerDummy plate
(extrusion pad)

18. 1 Extrusion
2 Die backer
3 Die
4 Billet
5 Dummy block
6 Pressing ram
7 Container liner
8 Container body

19.  To repeatedly transmit the force of the ram, at high
temperature, tothe alloy.
 To expand quickly under load and maintain a secure seal with the
container wall.
 Toseparate cleanly from the billet at the end of the stroke.
 To cause no gas entrapment that can result in blistering, or
damage the face of the container and/or dummy block.
 Tocompensate for minorpress misalignment.
 Tobe quickly and easily removedand replaced.
 Tofunction effectively until a production run is complete.
Function Of DummyBlock

20. 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 byRam
Metal will advance in
container, and then
through die
Metal will flow through
the die opening
Extruded metal will
further be processed

21. Extruded partBillet
Die
ContainerClosure plate
Ram
Indirect extrusion / Backward 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.

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

23. Lateral extrusion
• Container
position
is in vertical
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
outfrom the bottom die
• This is suitable for very light
alloys that have low melting
points

24. 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

26. Impact Extrusion
Advantages
• Simple and very
economical
• Suitable for collapsible
tubes
• Production cost very low
• Excellent surface finish
• Fast production rates
•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

27.  Although the process is generally performed cold, considerable heating
results from the high speed deformation.
 A short lengths of hollow shapes, such as collapsible toothpaste tubes or
spraycans.
 Requires soft materials such asAl, Pb, Cuor Sn.
Applications

28. 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.

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

30. Hydrostatic Extrusion
• No friction between the
container and the billet reduces
force requirements.
• This ultimately allows for faster
speeds, higher reduction ratios,
and lower billettemperatures.
• Usually the ductility of the
material increases when high
pressures are applied.
• An evenflow of material.
• Large billets and large cross-
sections can be extruded.
• No billet residue is left on the
container walls.
Advantages 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).

31.  The layout of operating machine is horizontal and
movement of billet aswell asof ram is horizontal in
direction.
 15-50MN capacity.
 It is mostly used for
Commercial extrusion of bars
and shapes.
Horizontal extrusionprocess

32. Vertical extrusionprocess
• The movement of billet and ram is vertical in orientation.
• 3-20MN capacity.
• Mainly used in the production of thin-wall tubing.

33. TUBE EXTRUSION & PIPE MAKING
•Tubes can be produced by extrusion by attaching a mandrel to the end of the
ram. The clearance between the mandrel and the die wall determines the wall
thickness of the tube.
•Tubes are produced either by starting with a hollow billet or by atwo- step
extrusion in which a solid billet is first pierced and then extruded.

34. Extrusion of tubing
•To produce tubing by extrusion from a
solid billet, the ram may also be fitted with
a piercing mandrel. As the ram moves
forward, the metal is forced over the
mandrel and through the hole in the die,
causing a long hollow tube. Just like
toothpaste, only hollow.
Extrusion of tubing from a solid billet
Extrusion of tubing from a hollow billet
•If the billets are hollow, a rod that matches
the diameter of the cast hole in the billet (but
slightly smaller than the hole in the die at the
opposite end of the chamber) are used.
•Note: the bore of the hole will become
oxidized resulting in a tube with an
oxidized inside surface.

35. EXTRUSION TUBING WITH A PORTHOLE
DIE •The metal is forced to flow into
separate streams and around the
central bridge, which supports a short
mandrel.
•The separate streams of metal
which flow through the ports are
brought together in a welding
chamber surrounding the mandrel,
and the metal exits from the die as a
tube.
•Since the separate metal streams
are jointed within the die, where there
is no atmosphere contamination, a
perfectly sound weld isobtained.
•Porthole extrusion is usedto
produce hollow unsymmetrical
shapes in aluminium alloys.
A sketch of a porthole extrusion die
Porthole extrusion
Example: pyramid porthole dies

36. Extrusion of seamless tubes
(With a fixedmandrel)
Ram
Die
ContainerDummy plate
(extrusion pad)
BilleMtandrel

37. Extrusion of seamless tubes
(With a floatingmandrel)
Ram
Die
ContainerDummy plate
(extrusion pad)
BilletMandrel

38. • 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
Ram
Die
ContainerDummy plate
(extrusion pad)
M a ndrelBillet

39. DIE MATERIALS
Commonlyused materials areTool Steelsand Carbides
Diamonddies are used for fine wire.
For improved wear resistance, steel dies may be chromium
plated, and carbide dies maybe coated with titanium nitride
For Hot drawing, cast-steel dies are used .
Dies are made from highly alloy tools steels or ceramics
(Si3N4).
Heat treatments such as nitriding are required (several times) to
increase hardness (1000-1100Hvor 65-70HRC). Thisimproves dielife.

40. LUBRICATION
NEED-
Proper lubrication is essential in extruding, in order to
improve die life, reduce drawing forces and
temperature, and improve surfacefinish.
Typesof Lubrication-
a) Wet : Dies and Rods are completely immersed in
lubricant.
b) Dry : Surface of the rod to be drawn is coated witha
lubricant.
c) Coating: Rod or Wire is coated with asoft metal that
acts asasolid lubricant.
d) Ultrasonic Vibration :of thedies and mandrels.

41. 1. Typeof extrusion
2. Extrusion ratio
3. Working temperature
4. Deformation
5. Frictional conditions at the die andthe containerwall
Factors affecting the extrusion force

42. MATHEMATICAL
RELATIONS
1.Extrusionratio, R-
It is defined as the ratio of the initial cross-sectional area ,
Ao, of the billet to the final cross-sectional area , Af, after
extrusion.
fA
R 
A0R~40:1for hot extrusion of steels.
R~400:1 for aluminum.
2.Fractional reduction in area, r -
A 0
r  1 
A f
1  r
R 
1

43. Contd..
3. Velocity -
Velocity of extruded product =(Ram velocity) x (R)
4. Extrusion force -
where k =extrusionconstant,
fA
A0
0P  kA ln

44. Forces in Extrusion
Process Variables in Direct Extrusion
Process variables in direct extrusion. The die angle, reduction in cross-
section, extrusion speed, billet temperature, and lubrication all affect the
extrusion pressure.

45. Extrusion Force
Extrusion constant k for various metals at different temperatures.
Source: After P. Loewenstein
Extrusion force, F  Aol ln
 Ao

Af 

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

47. • 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

48. • 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

49. 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

50. Thank You
