Dual bending for 1/2" OD SS tube

[CanosSSCS]

Hello all,

I am trying to achieve the shape of the image below. I've been able to create a U bend but I am running into problems when trying to add the 150 deg bend, and maintaining the center of each tube end on the same plane. Any advice would be appreciate.

Best,

Canos

 

[rb1957]

what material ?

what tools available ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[SWComposites]

looks like aero bars for a triathlon bike

 

[CanosSSCS]

The material is 0.5" OD stainless steel, with 0.035" wall thickness.

 

[rb1957]

yeah, my fault ... lost track of the header (when reading the text).

What tools do you have ? what heat treat (of the steel) ?? (Normalised ? Annealed ? 1/4 hard ??)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[TugboatEng]

Is the material becoming too hard to form or is the geometry not compatible with your tooling.

300 series stainless steel are relatively simple to anneal, heat them red hot and quench.

 

[EdStainless]

Both bends are easy, but together is another issue.
Are you sure that the original 180 is flat (all in one plane)?
Is the 180 symmetrical? (if it is being bent on a mandrel then it won't be)
How much stock are you leaving in the ends? 4"?
It needs to be enough to clamp onto while you form the 150 bend.
Build a die and wiper out of plywood and form both sides at once.
Getting the spring back right will take a bunch of trial and error.

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P.E. Metallurgy, consulting work welcomed

 

[3DDave]

I would bend the 150s to begin with, keeping them in plane, then find the center to make the 180.

 

[EdStainless]

The only problem with Dave's approach is that the legs will likely end up with ends pointing inward.
Keeping this symmetrical will a real difficult problem.
What is the tolerance that you are aiming for?
And measured in which plane?
+/- 1/16" would be considered tight.

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P.E. Metallurgy, consulting work welcomed

 

[3DDave]

They shouldn't. The 180 bend is 90 degrees to the 150s.

 

[dvd]

Is this seamless tubing?

How about a picture of your tooling?

 

[dik]

Can you fill it with sand and seal it, do the 180deg bend, put it in a vice and do the 150deg bend?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[MintJulep]

I am running into problems when trying to add the 150 deg bend

It would be really helpful for you to explain what type of problem.

Photos of your tooling, or a video of you process, and photos of a "failed" attempt would also be useful.

 

[CanosSSCS]

The U bend is done on an automatic tube bender, Ercolina, which uses a center former. The part is seamless, annealed stainless, schedule 40.

 

[BrianPetersen]

So, what is the issue? You're starting with a fixed-length tube, and the remaining straight length at each end is unequal after bending? or the straight lengths at each end are not parallel after bending (and not parallel in which direction? Is the 180 bend no longer 180, or are the two 150s not 150, or is the bend plane of the 150s not perpendicular in 3d space to the plane of the 180)? or what is the problem?

Option 1 tweak your CNC program to reflect reality.

Option 2 do the 180 in the CNC and use a custom fixture in a press to do the other two legs simultaneously.

Option 3 bend it long and use a post-bend operation to cut both legs to length.

 

[3DDave]

All I see at Ercolina are semi-automatic, manually managed, tube benders. Operators control the positioning and the altered orientation between bends; maybe you have the 2 axis positioning table?

My company got a tube bender; complained of inconsistent results, and wanted all the drawings to be changed. While that analysis was in work, someone found that spring-back could be measured and accounted for in the bending software and suddenly all the tubes were within drawing requirements. A miracle.

The exact amount of spring-back changes with slight variations in wall thickness and tube yield strength, so it's helpful to get enough material from a single mill run.

The trick is to measure the LRA that you are getting and compare that to the LRA you used and make adjustments in the opposite directions. If the 150's aren't 150, but 148, then change the LRA to 152 for those bends; that sort of thing.

 

[EdStainless]

You will never get there with seamless.
As soon as you get things adjusted for one piece the next one will be 20% thicker and spring back differently.
And then you will find pieces where the hole is eccentric to the OD, one edge will measure min wall and the other max wall.
I still doubt that your 180's are actually symmetrical.
What do your metrology folks say?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed