A die is the tool shape that the aluminium is pushed through to create the profile. Dies are made of tool steel (normally sis 2242). The die aperature, which corresponds to the desired cross section of the profile, is produced by spark erosion.
There are two main classes of profile – solid and hollow:
Solid profiles are produced using a flat, disc-shaped die.
Hollow profiles are produced using a two-part die.
In hollow dies, the mandrel (the part that shapes the cavity in the profile), is supported on a bridge. During extrusion, the metal separates around the bridge. The other part of the die shapes the outer contour of the profile.
Large and medium-sized profiles are pressed through a die with only one aperture. Smaller profiles can be advantageously pressed through multi-apertured dies – there may be as many as 16 apertures.
Die lifetime depends on the shape and desired surface quality of the profile.
Please read more in the Extrusion Design Guide, this will provide you with useful advice when starting a new extrusion design project.