2. Extrusion
Extrusion is a compression forming process in which the work
metal is forced to flow through a die opening to produce a
desired cross-sectional shape.
Parts have constant cross-section
Typical Products of Extrusion are Sliding Doors, tubing
having various cross-sections, structural and architectural
shapes and door and window frames.
4. Materials
Metals that are commonly extruded include
Aluminium: it is the most commonly extruded material. used to make s
frames, rails, and heat sinks
Copper: It is used to make pipe, wire, rods, bars, tubes, and welding
electrodes.
Lead and Tin: It is used to make pipes, wire, tubes, and cable sheathing.
Molten lead may also be used in place of billets on vertical extrusion presses
Zinc: Used to make rods, bar, tubes, hardware components, fitting, and
handrails.
Steel (1825 to 2375 F (1000 to 1300 C)) rods and tracks. Usually plain
carbon steel is extruded, but alloy steel and stainless steel can also be
extruded.
Titanium (1100 to 1825 F (600 to 1000 C) aircraft components including
seat tracks, engine rings, and other structural parts.
5. Plastic
Plastics extrusion commonly uses plastic chips or
pellets, which are usually dried in a hopper before going to
the feed screw.
A multitude of polymers are used in the production of plastic
tubing, pipes, rods, rails, seals, and sheets or films
Extrusion has application in food processing. Products such
as certain pastas many breakfast cereals premade
cookie,, jalebi some french fries certain baby foods dry pet
food.
6. Billet
Billet is the starting stock for the extrusion operation.
Extrusion billet may be a solid or hollow
form, commonly cylindrical, and is the length charged
into the extrusion press container.
Extrusion rates vary, depending on the alloy used and
the shape of the die. A hard alloy, given a complex
shape, may emerge from the press as slowly as one or
two feet per minute; a soft alloy taking on a simple
shape may be extruded at a rate of 180 feet per
minute, or even faster.
7. Extrusion Process
Extrusion process begins with billet, the aluminum material from
which profiles are extruded. The billet must be softened by heat
prior to extrusion. The heated billet is placed into the extrusion
press, a powerful hydraulic device wherein a ram pushes a dummy
block that forces the softened metal through a precision
opening, known as a die, to produce the desired shape.
10. The extrusion process has been likened to squeezing
toothpaste out of a tube. When pressure is applied at the
closed end, the paste is forced to flow through the open
end, accepting the round shape of the opening as it
emerges. If the opening is flattened, the paste will
emerge as a flat ribbon. Complex shapes can be
produced by complex openings.
Bakers, for example, use a collection of shaped nozzles
to decorate cakes with fancy bands of icing. They are
producing extruded shapes.
As suggested by these toothpaste
tubes, the shape of the extrusion
(profile) is determined by the
shape of the opening (die).
11. But we can’t make very many useful products out of toothpaste
or icing and we can’t squeeze aluminum out of a tube with your
fingers.
we can squeeze aluminum through a shaped opening, however,
with the aid of a powerful hydraulic press, producing an
incredible variety of useful products with almost any shape
imaginable.
These photos show a new length of
extrudate, just emerging from the press
(left) and the production of a profile in
progress (right).
12. Types OF Extrusion
Direct Extrusion
Indirect Extrusion
Hydraulic Extrusion
13. Direct Extrusion
Direct Extrusion (or) Forward Extrusion – In this type of
extrusion Billet is placed in a chamber and forced through a
die opening by a hydraulically-driven ram or pressing stem.
Figure 15.1 Schematic illustration of the direct extrusion process.
14. Direct Extrusion
Friction increases
the extrusion
force.
Hollow section is
formed using a
mandrel.
15. Indirect Extrusion
In the indirect process, the die is contained within the hollow
ram, which moves into the stationary billet from one end, forcing
the metal to flow into the ram, acquiring the shape of the die as it
does so.
Figure 15.3 Types of extrusion: (a) indirect; (b) hydrostatic; (c) lateral.
16. Indirect Extrusion
Metal is forced to flow
through the die in an
opposite direction to
the ram’s motion.
17. Difference
In the direct extrusion process, the die is
stationary and the ram forces the alloy through the
opening in the die While In the indirect
process, the die is contained within the hollow
ram, which moves into the stationary billet from
one end, forcing the metal to flow into the
ram, acquiring the shape of the die as it does so.
22. Extrusion Temperature Ranges for
Various Metals
C
Lead 200–250
Aluminum and its alloys 375–475
Copper and its alloys 650–975
Steels 875–1300
Refractory alloys 975–2200
23. Extrusion Defects
a) Centre-burst: internal crack due to excessive tensile stress at the
centre possibly because of high die angle, low extrusion ratio.
b) Piping: sink hole at the end of billet under direct extrusion.
c) Surface cracking: High part temperature due to low extrusion
speed and high strain rates.
24. Process Variables in Direct Extrusion
Figure 15.4 Process variables in direct extrusion. The die angle, reduction
in cross-section, extrusion speed, billet temperature, and lubrication all
affect the extrusion pressure.
Extrusion Ratio = Ao/Af
Ao – cross-sectional area of the billet
Af - cross-sectional area of extruded
product
25. Factors Influencing the Forces
Friction
Material Properties
Reduction In Area
Speed
Temperature
Geometry Of The Die
26. Advantages of Extrusion process
It has ability to create very complex cross-sections and
work materials that are brittle.
Material only encounters compressive and shear stresses.
Form finished parts with an excellent surface finish.
Minimize the cost of production.
Wide variety of cross-sections can be made.
