Extrusion is a metal forming process involving shaping a metal billet (hot or cold) by forcing it through a die with an opening.
The two possible schemes of extrusion are presented in the picture:
The metal billet is placed to the container of the extrusion press. The die with an opening is mounted at the end of the container.
When the hydraulically driven ram presses the billet, the metal starts to flow through the opening forming the extruded product of the required cross section.
In the direct extrusion the extruded metal flows in the direction of the ram motion.
In the indirect extrusion the metal flows in the direction opposite to the ram motion.
Indirect extrusion requires a lower force than direct process as there is no friction between the billet and inside walls of the container.
In the hot extrusion process the metal billet is preheated to the required temperature: 840°F - 930°F (450°C - 500°C) for extrusion aluminum alloys and 1300°F - 1470°F (700°C - 800°C) for Copper alloys.
The dies are manufactured from hard alloyed steels.
Extrusion is used for manufacturing round and hexagonal rods, tubes, various profiles (mainly aluminum) and other shapes.
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§ Rolling
§ Forging
§ Drawing
§ Imperfections of crystal structure
https://www.tntech.edu/me/courses/Zhang/ME30103110/Chap11pt5.ppt
http://courses.washington.edu/courseli/me355/Lectures/Sp2006/lecture10-11-Bulk%20Deformation%20Processes.ppt
http://iesu5.ust.hk/dfaculty/ajay/courses/ieem215/lecs/3_forming.pdf
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