Direct Extrusion process
Direct extrusion process is shown in fig. The raw material used is a billet. It consists of a press operated ram and a cylinder or container into which the heated billet is placed. A dummy block is used between the ram and the hot metal. With application of ram pressure, the metal first plastically fills the cylindrical shape. And it is then forced out through the die opening until a small amount remains in the container.
Advantages of Direct Extrusion:-
1) close tolerance can be achieved with production of long shells
2) Direct extrusion can be employed for extruding solid circular or non-circular sections, hollow sections such as tubes or cups
Disadvantages of Direct Extrusion:-
1) Friction between the container and billet is high
2) greater forces are required
3) the corresponding extrusion pressure is also higher because of friction between container and billet.
Advantages of Indirect Extrusion:-
1) there is less friction between the container and billet.
2) Less forces are required for indirect extrusion.
3) Indirect extrusion can produce hollow (tubular) cross sections,
Disadvantages of Indirect Extrusion:-
1) Indirect extrusion cannot be used for extruding long extrudes.
2) Support of the ram becomes a problem as work length increases.