Tube bending springback?

I'm trying to find information on springback when making large radius
bends in thinwall tubing. Everything I have been able to find relates
to the angular springback when bending around a relatively small fixed
radius form, where the actual radius isn't critical. However, what I
need to do is to bend the tube to a specified radius and angle (this
is for the propeller guard ring on a paramotor).
In my application, I need to bend 3/4" dia x .049 wall tubing into a
28" radius ring. Not knowing the springback, I made a test bends
around wooden forms, and found that the springback (angular or radius)
wasn't constant or proportional based on either the formed or final
radius. I can interpolate and try again (once I get some more
tubing), but there has to be a better way.
-Dana
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Reply to
Dana M. Hague
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Wait; it gets worse. The springback will be different for different mill lots of material, and for slight variations in wall thickness and diameter.
The good news: The radius is large enough that you don't have to bend it over a form; a three- roller bender should work. You just bend it to a large radius, and move one of the rollers to shrink the radius as you re-roll it, and keep measuring it against a template.
-Mike-
Reply to
Mike Halloran
hello Dana, there are many ways of bending tube. I think that a three rollers machine would suit you. The first time you do it, you will have to roll the tube three or four times tighter and tighter, and don't believe the final set up of the rollers can be good for direct to size bending: as you saw, springback is non linear. You will reach the proper set up by experience. Most probably, you could get the help of the machine builder, and that would be a great saving. You did not mention the alloy you use. Copper and Stainless steel are hardening, and determining a setup for a one pass bending will give a much better job. Your method might be quite good also, if you use a hard steel form. You could start with a too large one and machine it to the proper size, each time starting your test with a straight piece of tube. The help of a qualified pipe fitter who has the feeling for the job, would save many tests. That fellow could show you how to insert a piece of foil to increase the diameter of the block. Such a fellow could get the proper resulr in two steps, yours being an easy job. The tube must be in an annealed condition. It will come out slightly hardened, if you can do the job in one step. Don't forget the straight parts at the ends: you may have to chop them! yours robert hirschel "Dana M. Hague" a écrit dans le message de news: snipped-for-privacy@4ax.com...
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Reply to
Robert Hirschel

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