What is extrusion?
Extrusion is a type of forming process (which is a type of manufacturing process) in which a metal is confined in a closed cavity and then allowed to flow through only one opening so that the metal takes the shape of opening.
This process is exactly same as squeezing toothpaste out of the tube. In this process we can see that the toothpaste becomes cylindrical (since the opening of tube is circular) when it comes out of tube.
Types of extrusion processes
Cold extrusion: Material which is to be extruded is below recrystallisation temperature
Hot extrusion: Material which is to be extruded is above recrystallisation temperature
With the help of above hierarchy diagram, we can easily understand types of various extrusion processes.
In forward or direct extrusion the direction of movement of ram and the extruded metal is same.
In backward or indirect extrusion the direction of movement of ram and the extruded metal is opposite.
Advantages of extrusion
- Low cost per part
- Flexibility of operation
- In hot extrusion, post execution alterations are easy because product is still in heated condition
- Continuous operation
- High production volumes
- Many types of raw materials can be used
- Good mixing (Compounding)
- Surface finish obtained is good
- Good mechanical properties obtained in cold extrusion
Disadvantages of extrusion
- Variations in size of product
- Product limitations because of only one type of cross section can be obtained at a time
- High initial cost setup
Applications of extrusion process
- Electrical wires, bars and tubes are some of the items produced by hot extrusion
- Collapsible tubes, gear blanks, aluminum cans, cylinders are some of the items produced by cold extrusion