Aluminum Rib - Work Hardening?

[Notatestpilot]

I’m using .025 thk 2024T4 and am hammering away in making the wing ribs over wood form blocks for my plans built project…
How do I know or determine if I’ve hit the aluminum material too much that it’s ‘work hardened’?

 

[tsts4]

Chances are you haven’t work hardened the aluminum. Not an expert but I think it’s work hardened when the force required for further deformation increase significantly. If you’re hammering trying to get the curved portion of the rib’s flanges to lay down against the forming block or remove some puckering—stop. You can’t. To get the flanges to their ideal 90* position in relation to the web you have to remove the rib from the form and use your mallet to tap them those final few degrees followed by fluting to straighten the rib out. EAA has a whole video series on this. Here’s one installment https://www.eaa.org/videos/hints-for-homebuilders/sheet-metal/1801255269

 

[Bell206]

How do I know or determine if I’ve hit the aluminum material too much that it’s ‘work hardened’?

What exactly are your concerns? In general, if you cold work a heat-treated aluminum alloy too much it will either resist your hammer blows and not form or crack. In my experience, I doubt you will ever get to that point fabricating your ribs in that manner nor is it something I usually worry about even when I flow-form parts with a rivet gun.

 

[Capt. Geoffrey Thorpe]

To get the flanges to their ideal 90* position in relation to the web

you build your form blocks with a relief angle cut into them.
(At least, based on my experience banging out ribs for a T-18 and the ends of my fuel tanks (those were fairly straight bends))

 

[tsts4]

you build your form blocks with a relief angle cut into them.
(At least, based on my experience banging out ribs for a T-18 and the ends of my fuel tanks (those were fairly straight bends))

That’s one method, but not the only one used. Sonex, for example, uses a continuous flange as if it were hydro formed. This creates a stronger rib but requires more finishing.

 

[Capt. Geoffrey Thorpe]

Sonex, for example, uses a continuous flange as if it were hydro formed.

T-18 as well.

 

[Dan Thomas]

If the form blocks have a relief angle to allow for springback, that helps. But if the block has rounded notches for fluting while the flange is being formed, that's better. Start the flute formation soon after starting the flange bend. Use a round bar against the aluminum, and tap it to form that flute.

 

[Notatestpilot]

No one answered my question of how do I know if the material has ‘work hardened’…

 

[Bell206]

No one answered my question of how do I know if the material has ‘work hardened’…

Yes they did, twice. Unless you have a different definition of work hardened?

Not an expert but I think it’s work hardened when the force required for further deformation increase significantly.

if you cold work a heat-treated aluminum alloy too much it will either resist your hammer blows and not form or crack.

 

[Notatestpilot]

If there is someone else on this forum that has an engineering background in metallurgy, please chime in...
(Respectfully, Bell206 please stand down.)

 

[Non Compos Mentis]

You are only bending it once.
In several small steps, but only one bend.

Work hardening happens when bent back and forth several times.
If you formed it, then pounded it back flat again, and formed it again several times, you may cause a problem.

Ya got no reason to worry

 

[Mtns2Skies]

If there is someone else on this forum that has an engineering background in metallurgy, please chime in...
(Respectfully, Bell206 please stand down.)

PE Mechanical engineer in Machine design here, with a materials emphasis. While this topic isn't quite as simple as putting a PT6 on a Piper Arrow it's also not rocket surgery.

This is correct:

You are only bending it once.
In several small steps, but only one bend.

Work hardening happens when bent back and forth several times.
If you formed it, then pounded it back flat again, and formed it again several times, you may cause a problem.

Ya got no reason to worry

Work hardening isn't a on/off switch - it isn't binary. It will gradually get harder as you work the material repeatedly, and eventually will be come brittle enough to fracture rather than deform. Aluminum can be annealed to undo work hardening.

 

[Bell206]

Work hardening happens when bent back and forth several times.

And just to add, it can happen when bending in only one direction. For example, if forming a compound curve with a tight radius you'll probably have to anneal the piece half a dozen times to complete the bend and forming especially when using 1100 or 3003 aluminum.

 

[Dan Thomas]

You are only bending it once.
In several small steps, but only one bend.

Work hardening happens when bent back and forth several times.

Pounding on it for a long time work-hardens it. An aluminum rivet will work-harden if too many blows are required to set it. It needs to be formed with as few blows as practicable. That aluminum rib also needs to be formed with minimal working.

 

[kmacht]

Here’s the answer to your question. You can’t. The only way to know would be to cut the bend and analyze the microstructure under a microscope.

The practical answers above are correct in that it would be very very hard to work harden a 2024 t4 rib having its flange hammered over a wooden form.

 

[Dan Thomas]

Here’s the answer to your question. You can’t. The only way to know would be to cut the bend and analyze the microstructure under a microscope.

You can see, with the naked eye, microcracking along the outside of the bend. The surface becomes dull.

 

[Mtns2Skies]

Here’s the answer to your question. You can’t. The only way to know would be to cut the bend and analyze the microstructure under a microscope.

Neither of those statements are true, and also the grain structure won't necessarily indicate the work hardening. You can test hardness with Brinell or Mohs Hardness tester which comparing to an annealed sample will tell you how work hardened it's become.

 

[Notatestpilot]

Thanks to everyone who responded. I’ll resume hammering and making my ribs!

 

[kmacht]

Neither of those statements are true, and also the grain structure won't necessarily indicate the work hardening. You can test hardness with Brinell or Mohs Hardness tester which comparing to an annealed sample will tell you how work hardened it's become.

You can measure hardness with a number of different (mostly destructive) methods but the only way to actually see if you are starting to work harden a part is by looking at the grain boundaries. All the other methods will only tell you after it has already become hardened a significant amount.

 

[pfarber]

. Aluminum can be annealed to undo work hardening.

And you will also destroy the original temper... because, you know, annealing will do that

 

[Timbeck2]

Hey Bell206 - you can comment in my threads any day my brother

 

[kontiki]

I believe I've seen procedures for using Eddy Current testers used to check hardness. I've never been involved first hand. If you aren't sure your ribs are good and you aren't comfortable using a good light and a magnifying glass, you could always get a dye penetrant kit and check for cracks that way.

 

[40YearDream]

The exact grade of the aluminum, along with prior heat treat or annealing, will make a large difference in how much work-hardening happens, all other factors being equal.