From what I understand, aluminum rims are extruded through a die. Do they come out flat and then rolled into a hoop and welded? Do they come out of the die darn near round and then welded? More specifically, I was doing some post-ride maintenance on my bike and just got to wondering. My rims are Mavic CXP23’s which have a semi0"aero" profile (about 20mm or so). I guess my question is: with a medium or high profile aluminum rim, such as the Rolfs, Velocities, etc. the inside diameter is smaller than the outside diameter. If the extrusion comes out as flat stock that is then bent or rolled into a hoop, is there some material compression going on? If so, how are rinkles/valleys avioded? I’ve only had one cup of coffee, am I making any sence?
Thanks,
Brett
The rollforming process occurs over many sets of tools (dies). The number of dies and tool profile determine the rate at which the bend is induced .
A properly designed set of tools will roll perfect shapes without the valleys you are referring to. Worn tools will begin to introduce problems. The engineers who design and cut such tools will look for variences beyond the specification range as the rim builder designed. The rim builder will sign off on the tolerance of the tools used to create the rim.
Compression and stretching does occur when rollforming. It is not necessarily a bad thing.
I don’t know if all rims are extruded (heated billet forced through a die) or if some are rollformed (flat stock which has the profile induced by the tools. I imagine there are rims built both ways.