Direct extrusion
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Indirect extrusion
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Simple, but the material must slide along the chamber wall.
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In this case, material does not move but die moves.
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High friction forces must be overcome.
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Low friction forces are generated as the mass of material does not move.
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High extrusion forces required but mechanically simple and uncomplicated
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25–30% less extruding force required as compared to direct extrusion. But hollow ram required limited application.
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High scrap or material waste—18–20% on an average.
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Low scrap or material waste only 5– 6% of billet weight.
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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) Fewer 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.
Support of the ram becomes a problem as work length increases.