Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  

Go Back   > >

Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

Thread Tools Search this Thread
Old 01-30-08, 02:23 PM   #1
King of the molehills
Thread Starter
bcoppola's Avatar
Join Date: May 2006
Location: Detroit 'burbs, east side.
Bikes: '04 Giant OCR2, '87 Schwinn World Sport F/G conversion, '85 Schwinn Super Le Tour, '92 Trek 820
Posts: 1,195
Bending aluminum

First of all, let me state that I know the answer, as far as repairing a bike goes, is NO! The question is purely out of curiosity and I thought this the best place to ask (I wandered in from 50+) since I don't hang out on metallurgy forums.

And I am not now and never will be a frame builder. I will never try this at home. Promise.

So: If one desires to bend or otherwise re-form an item made of aluminum alloy while retaining its strength, how is it done? I assume there are highly skilled and possibly industrial processes used. Is there anything besides basically melting it and then casting/forging/machining anew?

I know hydroforming is one high tech fabrication method. Industrial for sure.

Like I said, just wondering. Hey, I think of crap like this cooped up inside.

Last edited by bcoppola; 01-30-08 at 02:32 PM.
bcoppola is offline   Reply With Quote
Old 01-30-08, 04:29 PM   #2
Senior Member
jerrymcdougal's Avatar
Join Date: Oct 2006
Bikes: 86' Davidson Impulse, 83' Windsor Professional
Posts: 439
Im just guessing, but maybe post-bending heat treating? I'm sure someone knows.
jerrymcdougal is offline   Reply With Quote
Old 01-30-08, 06:10 PM   #3
Senior Member
iqaro's Avatar
Join Date: Sep 2007
Location: Yopal (Colombia)
Bikes: Commuter: Stolen Red Kinesis frame - 26*1.9" Slicks "La Zorra" Touring: Steel frame Shimano600 gruppo 700*38 slicks
Posts: 63
Aluminium and steel have very different cold hardening properties, so you can rebend a steel pipe and actually increase its strenght altought reducing its ductility: structural steel have roughly a ~300000psi ultimate strength, if you start with a ~100000psi steel, you can cold form it a couple times before it reach its ultimate stress. So, I won´t rebend a bike frame made of Reynolds high tensile steel tubing, because is near that limit.

Aluminum has 1/3 of steel Young's Modulus -70GPa (10million psi) vs 200GPa (29million psi), and also a lower ultimate strengh (aerospace aluminium alloys have an ultimate strength of ~75000 psi, so when you rebend an aluminium tube probably it is near that limit, and will break easily.
iqaro is offline   Reply With Quote
Old 02-01-08, 05:41 PM   #4
I give up!
cujet's Avatar
Join Date: Jan 2007
Location: Jupiter, FL
Bikes: Homemade Ti, Hab frame
Posts: 87
From an aircraft mechanics point of view, high strength aluminum is not easily bent without cracking. Depending on the alloy involved and the heat treatment.

6061-T6, a common sheetmetal alloy in aircraft use will not make a sharp 90 degree bend without cracking. If I use a gentle radius, I can bend it through 90 degrees. However, 6061-T0 will bend to nearly any shape required without much risk of cracking. It can then be brought to a harder condition after machining.
cujet is offline   Reply With Quote
Old 02-01-08, 11:36 PM   #5
Uber Goober
StephenH's Avatar
Join Date: Sep 2007
Location: Dallas area, Texas
Posts: 11,209
So: If one desires to bend or otherwise re-form an item made of aluminum alloy while retaining its strength, how is it done?

It would depend on what they actually use. If some of the strength comes from cold working, there's really not much you can do to reform while retaining strength. You could anneal and then form it, but strength would be gone. If it's a heat-treatable alloy, you could anneal it, form it, then re-heat treat it. For practical repairs, just re-form it and if it breaks, it breaks.
"be careful this rando stuff is addictive and dan's the 'pusher'."
StephenH is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

All times are GMT -6. The time now is 10:17 AM.