How are bicycle rims made? / Curved extrusion

A component I wish to manufacture (A-level Product design student here) is basically a metal (aluminium or steel) keyboard rail+slider mechanism, but one whose profile is swept around a curve of radius roughly 1.5m.

The closest components I can find which are close to this are bicycle rims. But no matter how hard I try, I cannot imagine how an extruded profile can be curved. And bicycle manufacturer’s websites are reluctant to explain!

Please could anyone explain to me how an extruded profile (metal) can be swept around a curve? Or at least, direct me to a resource where I can find this out.

EDIT: The closest I can get is “3 bed rolling” (? ) from my design teacher but all i have is a name, and a vague image in my mind of the extruded profile being fed through three rollers.

I’d need to research it first, but of the top of my head could the rim be extruded, then ‘pressed’? (rather than rolled). My bike is ancient, but ti looks like there has been somekind of pressing (ie, the rolling on the edge of the lip). The combination of extrusion and pressing would give it its final cross section.

Could be wrong…

An alternative method:

I think they’re extruded then passed through offset rollers which would give the rim it’s round shape. The seam is welded, then machined.

I could be wrong.

Thank you all!

That link was handy, gives an idea of what I need to create. I’m going to upload a sketch of what I want to create, and what impression I have of how this can be done, hopefully someone can clarify the situation for me.

EDIT, from the link posted earlier:

As we said, all rims begin as long, essentially straight extrusions and then undergo a rolling process to make them into ‘hoops’. No matter what the joining process, in order to build wheels that are straight and true the rims must be both ‘round’ and ‘flat’. The process of rolling the alloy extrusion into a rim compresses the grain structure of the alloy on the inside face and also stretches the grain structure on the outside edge. When the ends are joined there is a residual stress in the structure much like a bicycle frame after welding. The patented True Track Technology process stress relieves, work hardens, and fully straightens the rim without ‘forcing’ the rim to be straight. Residual stresses are completely removed. When the process is complete it is checked for ‘perfect’ roundness and run out (flatness). If there is any variation the rim is cut and recycled, not re-worked until it is acceptable. For the wheel builder this ensures a flat, round rim from the start with no need to ‘correct’ the rim by spoke tension. For the user this means a rim that will be stable over time without need to ‘tweak’ spoke tension to keep the rim straight.

Thats pretty much what I need! I’m just having trouble visualising the process! Here it is as I imagine it:

(sorry about the media, I just grabbed the first thing to-hand!)

as I imagine it, I think that the two rollers in front of the extrusion die spin at different speeds, forcing the extruded shape to be bent. Further rollers would make sure the shape does not distort, and some sort of timed-saw would chop the shape at the correct length.

My design tutor says this process would favour thinner sectioned profiles (suits me fine).

Is there absolutely any more data on this process out there?

The process is called ROLL-FORMING
A better process (better but much more expensive) is the extension of it called, PROGRESSIVE ROLL-FORMING. it’s better because it rolls the extrusion in stages, minimizing the stress, but also more expensive to orger 10 rolls than just 3. But the video i saw for bike rim was a 3-rolls roller. (i’m guessing the progressive roller is more efficient with a continuous supply, making it hard to roll into circles without it rolling onto itself.)

Another important thing: The part should be cooled. It’ll then be COLD ROLLed (cold formed) therefore pressing particles closer together, in the same direction. resulting in much stronger parts. (kinda like forging)

:slight_smile: thank you for all of this! you’ve helped a great deal with my coursework!