UNSAFE wrote:Cast is easy to figure out, pour liquid metal in a mold and let it harden. A billet is a solid chunk that is machined to shape and an extrusion is forced thru a die like a pasta maker.
Correct. More or less.
is the billet made by extrusion?
Billet is just a colloquial term for bar stock. To make things confusing, a large diameter piece of bar stock (billet) which is extruded to a smaller size is an extrusion. But if it forms a new section of bar stock, there's nothing stopping you from calling it billet even though the process which created it was extrusion. You can't tell the difference looking at it on the shelf in any machine shop, it all looks the same.
And in the case of the cylinders how much or what difference would it make?
The difference is most likely in the cost of production. I suspect it's cheaper to buy an extrusion with a hole already in the center of it, vice drilling and machining a piece of round stock. Think they're expensive now? Add machine costs to that...
Either way, they are no different from each other metallurgically. Now if they began with a billet of forged aluminum they would have a stronger product still, but again cost was probably the determining factor. Let's remember what they are making here- one off cylinders for very expensive racing engines. They wanted to be able to reach those racing teams, but not be so expensive that a regular guy couldn't buy them either.
Here's the best way to understand it:
These cylinders started life as billet aluminum. They were then extruded to their rough shape: a round piece with a hole in it, and could be called extrusions or billet (since hollow billet also exists) at that point. Then the were cut to length, and their name changed again to a 'blank'. Then they were machined to their final shape, fins and all.
Tomato, tomAto. I choose to call them billet cylinders, that's what the company calls them. Want to call they something else? Fine, but they started life as a billet. Seems fair, no?