Which one of the following statements is not correct for forward or direct extrusion process ?

Explanation:

Extrusion:

• Extrusion is the process in which the work-piece material is forced to flow through a die opening by applying a compressive force to produce a desired cross‑sectional shape.
• The metal is subjected to plastic deformation and it undergoes reduction and elongation during extrusion.
• The extrusion process is like squeezing toothpaste out of a tube.

Types of extrusion:

Forward or Direct Extrusion:

• The raw material used is billet.
• The billet is heated to its forging temperature and fed into the machine chamber.
• In this forward extrusion, the piston and outgoing material move in the same direction.
• The pressure is applied to the billet, forcing, and the material through the die.
• In forwarding direction since the billet moves inside the drum so pressure requires overcoming the friction will be more.
• The material sticks to the wall of die and scrap produced due to it is high.

Backward Extrusion or indirect Extrusion:

• In backward extrusion die is placed in the piston, so outgoing material will come out in the opposite direction that of the piston.
• In this process, the billet doesn’t move inside the chamber.
• So there is no friction between billet and drum.
• So less force is required in this method in comparison to the direct extrusion.
• A more complicated type of equipment is required because the plunger becomes weak due to the reduction in its effective area of cross-section.
• Scrap is comparatively low.