Today we will learn about extrusion process working, types,
application, advantages and disadvantages. Extrusion is a metal forming process
in which metal or work piece is forced to flow through a die to reduce its
cross section or convert it into desire shape. This process is extensively used
in pipes and steel rods manufacturing. The force used to extrude the work piece
is compressive in nature. This process is similar to drawing process except
drawing process uses tensile stress to extend the metal work piece. The
compressive force allows large deformation compare to drawing in single pass.
The most common material extruded are plastic and aluminum.
Extrusion Process:
Working Principle:
- First billet or ingot (metal work piece of standard size) is produced.
- This billet is heated in hot extrusion or remains at room temperature and placed into a extrusion press (Extrusion press is like a piston cylinder device in which metal is placed in cylinder and pushed by a piston. The upper portion of cylinder is fitted with die).
- Now a compressive force is applied to this part by a plunger fitted into the press which pushes the billet towards die.
- The die is small opening of required cross section. This high compressive force allow the work metal to flow through die and convert into desire shape.
- Now the extruded part remove from press and is heat treated for better mechanical properties.
This is basic working of extrusion process.
Types of Extrusion:
Extrusion process can be classified into following types.
According to the direction of flow of metal
Direct Extrusion:
In this type of extrusion process, metal is forced to flow
in the direction of feed of punch. The punch moves toward die during extrusion.
This process required higher force due to higher friction between billet and
container.
Indirect Extrusion:
In this process, metal is flow toward opposite direction of
plunger movement. The die is fitted at opposite side of punch movement. In this
process, the metal is allowed to flow through annular space between punch and
container.
Hydrostatic Extrusion:
This process uses fluid to apply pressure on billet. In this
process, the friction is eliminated because the billet is neither contact with
cylinder wall or plunger. There is a fluid between the billet and plunger. The
plunger applies force on fluid which further applied on billet. Normally
vegetable oils are used as fluid.This process accomplished by leakage problem and
uncontrolled speed of extrusion.
According to the working temperature
Hot Extrusion:
If the extrusion process takes place above recrystallization
temperature which is about 50-60% of its melting temperature, the process is
known as hot extrusion.
Advantages:
- Low force required compare to cold working.
- Easy to work in hot form.
- The product is free from stain hardening.
Disadvantages:
- Low surface finish due to scale formation on extruded part.
- Increase die wear.
- High maintenance required.
Cold Extrusion:
If the extrusion process takes place below crystallization
temperature or room temperature, the process is known as cold extrusion. Aluminum
cans, cylinder, collapsible tubes etc. are example of this process.
Advantages:
- High mechanical properties.
- High surface finish
- No oxidation at metal surface.
Disadvantages:
- High force required.
- Product is accomplished with strain hardening.
Application:
- Extrusion is widely used in production of tubes and hollow pipes.
- Aluminum extrusion is used in structure work in many industries.
- This process is used to produce frames, doors, window etc. in automotive industries.
- Extrusion is widely used to produce plastic objects.
Advantages and Disadvantages:
Advantages:
- High extrusion ratio (It is the ratio of billet cross section area to extruded part cross section area).
- It can easily create complex cross section.
- This working can be done with both brittle and ductile materials.
- High mechanical properties can achieved by cold extrusion.
Disadvantages:
- High initial or setup cost.
- High compressive force required.
Today we have learnt about extrusion process working, types,
application, advantages and disadvantages. If you have any query regarding this
article, ask by commenting. If you like this article, don’t forget to share it
on social networks. Subscribe our website for more interesting articles.