how do they get holes in extruded profiles?

Kinda stupid question, unrelated to reprap, but i can't find the answer to such an esoteric question easily. I don't understand how they can make the interior voids in extruded aluminum t slot. the die defines the perimeter, so the interior should be solid, but it always has at least one channel running down the center, and on larger profiles, multiple channels.

Is it like fiber optics, where the holes are drilled in to the raw billet and as it's pulled the holes shrink proportionally? it doesn't seem like that same idea would work when squeezing metal through a die.

The die has internal blocks, attached further "upstream". The aluminum flows around it, meets on the other side, and flows back together. You don't see the seam on the final product because it passed through a die (forming it together) and/or because it was still somewhat molten, or at least above the welding temperature.

The same trick is also used when extruding metal/plastic pipe, all sorts of plastic profiles, macaroni, and other cereals (by which I mean breakfast cereals, other noddles, probably other things I'm forgetting.)

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I'm building it with Baling Wire

Ah very clever. see, i knew this was the place to ask. Thanks!

I know this post is old but, It think its funny that I asked myself the same question and first link I end up with on Google is here.

Another funny fact is that I am a PRISM user! Small world!

Good idea posting your question here Buback

Edited 1 time(s). Last edit at 03/13/2013 11:17PM by thecrazy.

Bump.
I came here too.
For the same reason.