Extrusion is a manufacturing process to create objects of a fixed cross-sectional profile.  A material is pushed through a die of the desired cross-section.  The process begins by heating the stock material (if hot extrusion) and then it is loaded into the container in the press.  A "dummy block" is placed behind it where the ram then presses on the material to push it out of the die.  Afterwards the extrusion is stretched in order to straighten it. 

Advantages of the Extrusion process: 

• Ability to create very complex cross-sections.
• Can use brittle materials because the material only encounters compressive and shear stresses.
• Excellent surface finishes
• May increase the strength of material in metals.

The process is usually done with either hot or cold material and these materials include: 

• Metals
• Polymers
• Ceramics
• Concrete
• Modeling Clay