Indirect / Backward Extrusion

 Indirect Extrusion

In this type of extrusion both the billet and container remain fixed and a hollow ram (desired shape of the cavity) applies suitable pressure to the stationary billet.

Advantage:

1. Less friction as compare to direct extrusion
2. Force remains constant
3. High accuracy
4. Good grain structures
5. Enhance Mechanical properties
6. Because of low friction, less heat develop during indirect extrusion
7. Chamber has more life in indirect extrusion due to low friction and heat
8. Suitable for small cross-sections

Disadvantages:

1. Due to less (or no friction), the surface of the billet can affect the surface of  the extrusion
2. There limit on how much extrude you can do it depends on the length of the stem
3. The surface of the billet can be badly affected if there is  impurity in the billet

want to read: Normalizing Vs ANNEALING and their difference