Forming of 6061-T6511 extrusion 3

[stressguyMike]

Good morning,

I am working on a 6 ft. long extrusion m/f 6061-T6511. The part is thick, 0.125 in.

The part must be bent to a large radius. The max offset from horizontal is nearly 8 in.

Currently, the drawing has the part formed in the -T6511 condition. The drawing also has a note that says the formed part must be inspected for cracking and local buckling.

If I analyze the part as a 72 in. simply supported beam with max mid-span deflection equal to 8 in. I get a bending stress essentially equal to Ftu.

Therefore, I proposed to the designers the following options:
1. Procure in -T4511 condition, form, then heat treat to -T6511
2. Form in the W condition, age to -T42, then heat treat to -T62
3. Anneal the material, form in annealed condition, heat treat & age to -T62

So a number of questions:

1. Is this a legit issue?
2. If this is legit, what about all the formed parts out there, hat sections, channels, etc. that are formed. As long as min bend radii is met, no need to stress relieve.

Looking forward to some enlightenment!
Thank you,
Mike

 

[rb1957]

1. absolutely. your analysis (comparing a forming operation to a SS static beam) is not really appropriate, as the forming operation intends to exceed Fty.

2. min bend rad should start with 3t and be developed by testing (trial and error). Your proposals seem reasonable, forming in T6 can be tried (if the guys in the shop think it may work) but will probably fail. post-forming HT to T6xx is best, forming in O or W condition is best.

another day in paradise, or is paradise one day closer ?

 

[stressguyMike]

rb1957,

Thanks for the quick response.

So would it be proper to say forming stresses are > than Fty but should be less than Ftu?

Also, all the formed parts in aircraft, including frames, stringers, etc, are they stress relieved after forming? If not are the residual stresses due to forming considered with operational stresses? For both ultimate & fatigue loading I've never seen forming stress superimposed also. What justifies this?

I've seen parts that need to be formed to a radius less than min bend radii. Thus they are formed in the O condition and then heat treated to T62 for instance.

Mike

 

[rb1957]

"So would it be proper to say forming stresses are > than Fty but should be less than Ftu?" ... yes !

"... are they stress relieved after forming?" no, but if they are important to carrying primary loads then either ...
a) stress relieve, or
b) superimpose these plastic stresses (and you'll have little left over to carry airplane loads).
If you have serious primary loads to carry, stress relieve.

Yes, forming in O condition permits smaller bend radii.

If you're forming in O condition and HT post-forming, consider using a "proper" Al (7075 or 2024).


another day in paradise, or is paradise one day closer ?

 

[berkshire]

If the part is bent with an 8" rise over 72 " you are most likely bending to a radius of 80" plus or minus. You should be able to roll that in a 3 roll angle roller without heat treat. You will have 6 to 8 degrees of springback so you will have to over roll a little to get your desired shape. You could also stretch form the part That should form net, however if you over stretch it at T6 you will snap it. If you have any joggles or other sharp bends then all bets are off.
B.E.

You are judged not by what you know, but by what you can do.

 

[berkshire]

Mike,
You have cross posted this in Metals and metallurgy engineering .
Make a reference to this post in the other forum, so that you do not dilute your answers.

Or better yet delete the other post.
B.E.

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

A quick inspection of MMPDS-12 reveals...

6061-T6xxx has relatively modest 10% strain to failure... but 'more telling', there is only ~3-KSI separating Ftu and Fty. Anything MORE THAN very mild/smooth cold roll forming... is likely to come close to fracturing the material.

6061-T4xxx has relatively robust 16% strain to failure... but 'more telling', -T4xxx has mechanical properties topping out ~10-KSI lower than for -T6xxx temper materials... AND there is actually ~10-KSI separating [-T4] Ftu and [-T4] Fty. Even aggressive roll forming will be relatively 'easy' to accomplish with no potential for damage. IN this case, a simple Age-HT from -T4 to -T6 after forming will do two valuable services for You: (a) avoid solution HT/Quench processing with potential for distortion; and will (b) actually stress relieve the formed material. CAUTION: I suggest You ensure that part is Age-HT to -T6xxx in an oven with minimal potential for distortion... IF possible use Age-HT holding fixtures to ensure 'droop' or 'un-springing/straining' doesn't occur.



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[berkshire]

WKTaylor,
Using T4 material and age hardening to T6 would solve a lot of Stress guy Mikes handling problems, in fact that is something he proposed himself.

I know that when I worked for GD Convair we had a fuselage ring doubler Made from 6061T6511, not too different from the one he is describing, that we just rolled to shape in an angle roller, specifically to avoid the time and trouble of heat treat.
B.E.

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

Berkshire...

Yep... my answer was a reaffirmation to SGM's already thought-out processes... from an M&P perspective.

NOTE. One time I had a bunch of 6061-T4 sheet metal electrical panels miss-manufactured: a bent flange was miss-located. Instead of re-making them at great expense, an old liaison guy [with lots of practical A&P&I experience] recommended that we have the miss-located-flange 'gently pounded-flat'... then re-bend the flange in the proper location. Penetrant NDI showed 'no defects' and they turned-out OK!! Same problem/solution with some minor engine sheet-metal baffle parts... 'they would be heat-soaked soon-enough'!

My 'PERSONAL GD' 'fun-NOTEs'.
For a few years I was a USAF Depot structures engineer [Jr-assistant] on the F-106A/B. Loved that jet. I found an old 1F-106-3 SRM I had as a personal copy, stored in an old shipping-box for over 20-years. Gave it to the F-106 association which [surprisingly enough] didn't have a copy

https://www.f-106deltadart.com/.

They found it useful almost immediately for disassembly/transportation/storage and repairs.

I think I also have an old GD stress analysis manual and process sheets for the rivet-bonding methods they used for integral tanks.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

For 'extrusion geeks' only...

MIL-HDBK-301 [CX] MILITARY HANDBOOK OF AIRCRAFT EXTRUDED SHAPES AND DIES [1959]
MIL-HDBK-301-ADD1 [CX] MILITARY HANDBOOK OF AIRCRAFT EXTRUDED SHAPES AND DIES [1965]

AFML-TR-73-211 DESIGN GUIDE FOR USE OF STRUCTURAL SHAPES IN AIRCRAFT APPLICATIONS

From the Aluminum Association...
ALUMINUM EXTRUSION MANUAL
VISUAL QUALITY CHARACTERISTICS OF ALUMINUM EXTRUSIONS
ALUMINUM IMPACTS DESIGN MANUAL AND APPLICATIONS GUIDE
DRAFTING STANDARDS FOR ALUMINUM EXTRUDED PRODUCTS
and 'just because they might be useful'...
FORMING AND MACHINING ALUMINUM
WELDING ALUMINUM: THEORY AND PRACTICE
ALUMINUM BRAZING HANDBOOK
ALUMINUM DESIGN MANUAL
ALUMINUM STANDARDS AND DATA
ALUMINUM FORGING DESIGN MANUAL
TEMPERS FOR ALUMINUM AND ALUMINUM ALLOY PRODUCTS



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Sparweb]

And never go without access to a Tiernay/Transtar/"whatever they are now" catalog.

A much-improved, searchable website still works (for now):

https://aircraftextrusion.com/about/tiernay-metals/

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[WKTaylor]

SparWeb...

A much-improved, searchable website still works (for now):

https://aircraftextrusion.com/about/tiernay-metals...

Good find!

I still have the last Tiernay paper catalog on my bookshelf and occasionally go hunting for extrusions 'like a kid thru a Sears Christmas catalog'.

Last I heard Castle Metals was the local mid-west distributor of Tiernay extruded and roll-formed shapes.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]