Extrusion is a metalworking process that produces continuous lengths of material with a uniform cross-sectional shape. It works by forcing billet material through a restricted opening called a die. There are three main components in an extrusion press: the container, die, and ram. Extrusion can be used to manufacture rods, tubes, and a variety of shapes like circular, square, rectangular, and hexagonal. There are different methods of extrusion including direct, indirect, impact, and hydrostatic extrusion which uses pressurized fluid instead of friction to shape the material. Extrusion can be classified as hot or cold based on the temperature of the material during the process.

1. EXTRUSION

2. DEFINITION AND CONCEPT
Extrusion is a metal working process
that produces continuous lengths of
uniform , non-uniform cross-section-
al area from a metal billet , solid or
hollow , by causing the billet to flow
under high pressure through a restr-
icted opening called die which is so
shaped as to impart the required
form to the product .

3. Extrusion is mainly a hot working
process , starting generally with cast
billet and producing wrought sections
and tubes in one stage .
An extrusion press has three major
components :
1. The container
2. Die
3.Ram

4. In extrusion the metal takes in cross-
section the shape of the die .
For example :
When pressed from the back , the
tooth paste comes out of the front
small portion of the tooth paste tube
; this is an extrusion process .

5. EXTRUSION APPLICATIONS
Extrusion process is used to manufact-
ure :
1- Rods 2- tubes
3- A variety of circular , square ,
rectangular , hexagonal and
other shapes both in the solid
or hollow form .
4- Channel I , Z , T and others
.

6. EXAMPLES

9. EXTRUSION METHODS
1- Direct extrusion
2- Indirect extrusion
3- Impact extrusion
4- Hydrostatics extrusion

10. Direct (forward) extrusion
This is similar to forcing the
paste through the opening
of a toothpaste tube. The
billet slides relative to
the container wall ; the
wall friction increases the
ram force considerably. A
dummy block or pressure
plate is placed at the end
of the ram in contact with
the billet.

11. Indirect (reverse, inverted or
backward) extrusion:
Here, the die moves toward the billet; thus,
except at the die, there is no relative
motion at the billet-container interface. As
a consequence, the frictional forces are
lower and the power required for extrusion
is less than for direct extrusion.In practice
a hollow ram carries a die, while the other
end of the container is closed with a plate.
Frequently, for indirect extrusion, the ram
containing the die is kept stationary, and
the container with the billet is made to
move .

13. Impact extrusion
It is a form of indirect extrusion and is particularly
suitable for hollow shapes. It is usually performed
on a high-speed mechanical press. The punch
descends at a high speed and strikes the blank,
extruding it upwards. The thickness of the
extruded tubular section is a function of the
clearance between the punch and the die cavity.
Although the process is performed cold,
considerable heating results from the high-speed
deformation. Impact extrusion is restricted to
softer metals such as lead, tin aluminum and
copper.

14. Forward impact extrusion
Backward impact extrusion

15. Hydrostatic extrusion
In this process, the chamber is filled with a fluid that transmits the pressure to the billet,
which is then extruded through the die. There is no friction along the walls of the
container. Because the billet is subjected to uniform hydrostatic pressure, it does not
upset to fill the bore of the container as it would in conventional extrusion. This
means that the billet may have a large length to diameter ratio (even coils of wires
can be extruded) or it may have an irregular cross section. Because of the
pressurized fluid, lubrication is very effective, and the extruded product has good
surface finish and dimensional accuracy. Since friction is nearly absent, it is possible
to use dies with very low semi-cone angle which greatly minimizes the redundant
deformation. The only limitation with this process is the practical limit of fluid
pressure that may be used because of the constraint involving the strength of the
container and the requirement that the fluid not solidify at high pressure.

16. Extrusion Classifications

Classification based on temperature:

Usually, because of the large forces
required in extrusion, most metals are
extruded hot under the conditions where
the deformation resistance of the metal is
low. Cold extrusion is also possible for
many metals. On this basis we can classify
extrusion as:
1- Hot extrusion
2- Cold extrusion