Definition of extrusion
Extrusion may be defined as the manufacturing process in which a block of metal enclosed in a container and is forced to flow through an small opening of a specific shape and size called a die .
Extrusion related terms you must know
Extrusion dies are circular steel plates or disks with considerable thickness and having one or more openings to create the desired profile. They are made from H-13 die steel and heat-treated as they have to withstand high pressure and temperature caused by forcing the hot billet through the die.
The extrusion process starts with the heating of the billet. The billet are usually heated upto a temperature such that the material becomes easily malleable and ductile.
Extrusion is more widely used in manufacturing of solid and hollow sections from non-ferrous metals and their alloys ( aluminium alloys, copper, brass and bronze etc.), but steel and other ferrous alloys can also be successfully processed with the development of molten-glass lubricants.
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Types of extrusion:
Hot extrusion :
Hot extrusion is a process in which the billet is heated before extrusion. Hot extrusion is done above the material’s recrystallization temperature this not only helps the material from work hardening but also it becomes easier to push the material through the die.
Materials that are commonly cold extruded include:
- niobium, and steel.
Examples of products produced by this process are: collapsible tubes, fire extinguisher cases, shock absorber cylinders and gear blanks.
Advantages of extrusion:
- The range of extruded items is very wide. Cross- sectional shapes not possible by rolling can be extruded, such as those with re-entrant sections.
- No time is lost when changing shapes since the dies may be readily removed and replaced.
- Dimensional accuracy of extruded parts is generally superior to that of rolled ones.
- Automation in extrusion is simpler as items are produced in single passing.
- Extrusions are lighter, more sound and stronger than castings.
- Extrusion are more accurate than castings and require less post-extrusion finishing processes.
Limitations of extrusion process:
- Process waste in extrusion is higher than rolling, where it is only 1 to 3%.
- Relatively high tooling cost, being made from costly alloys steel.
- In productivity, extrusion is much inferior to rolling, particularly to its continuous varieties.
- Cost of extrusion are generally greater as compared to other techniques.
- Service life of extrusion tooling is shorter because of high contact stresses and slip rates.
- Only shapes with constant cross-section can be produced.
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