Aerospace Material Specification Notes 1

[Papasaurus]

Hi All,

It sure has been awhile...

Okay, in the past, I've become blindly accustomed to stating material specifications in my material callouts on my drawings, ex. MATERIAL: AL ALY 6061-T651 PLATE IAW AMS-QQ-A-250/11. That was all in defense and aerospace, and as far as I can remember the requirement was a given. Now I'm in more of a consumer electronics sector of aerospace, and such detail seems to not be as required. So I'm stuck with: AL 6061-T6, .250 thk.

I'm perusing back thru MIL-HDBK-5 and the MMPDS for guidance on these inclusions, but I wanted to hit up the community for your advice as well. As far as I know, all material certs are provided according to the contracts with the shops, but it still makes me itch not having it on the drawings.

I'm also uncomfortable with our basic aluminum abbreviation AL, instead of AL ALY, but that just makes me feel pedantic.

Thanks!

Ed Lee
CAD Admin / Sr. Mechanical Designer

https://www.linkedin.com/in/edwinlleejr/

 

[WKTaylor]

Drawoh...

CAUTION. I know what an 'air-bend' is!!!!! REALLY BAD sheet-metal bend-forming practice due to lack of the appropriate bend radius edge for the brake inner radius fingers. I fell short trying to get simple words to describe the process, so gave up for expediency... without using bad-words. Perhaps someone out-there can provide illustrations of proper brake--bending over an appropriately radiused edge; and of the jury-rigged'' air-bend' practice over a 'sharp-brake/clamp-edge' that has been backed-away from the ... gaaaag ... forgot the term... getting old...

NOTE.
In general the radius set-back is the same for 'guided brake forming around a true radius edge' as for an ‘air-bend brake form with a sharp radius'.

An old-sheet-metal-bender’s trick to eliminate need for a series of machined/precision brake-form edge radii [replaceable clamp-fingers with precision edge radii, various sizes] is as follows. This eliminates the need to make/accept garbage-quality 'air bends' and is economical even for small/low budget shops. The work-piece quality rises dramatically a the minor cost of being careful with the special sheet-metal radius sleeves, made/used as follows.

EXAMPLE...

Existing sheet metal brake- has an edge with a R0.016 bend radius... or an equivalent that was squared-off/deburred.

To make a R0.024 bend-edge: take a wide sheet of 6061-T4 0.008 thick sheet and bend-form it to nest tightly around the 0.016 fixed-radius edge. Leave this radius cuff in-place and bend the production sheet metal part around it for a tight/straight 0.024 inner BR.

To make a R0.032 bend-edge: take a wide sheet of 6061-T4 0.016 thick sheet and bend-form it to nest tightly around the 0.016 fixed-radius edge. Leave this radius cuff in-place and bend the production sheet metal part around it for a tight/straight 0.032 inner BR.

To make a R0.064 bend-edge: take a wide sheet of 6061-T4 0.032 thick sheet and bend-form it to nest tightly around the 0.032 radius edge created in the previous step. Leave these [2] radius cuffs in-place and bend the production sheet metal part around it for a tight/straight 0.064 inner BR.

To make a R0.096 bend-edge: take a wide sheet of 6061-T4 0.032 thick sheet and bend-form it to nest tightly around the 0.064 radius edge created in the previous step. Leave these [3] radius cuffs in-place and bend the production sheet metal part around it for a tight/straight 0.064 inner BR.

Etc...
NOTE. There with have to be obvious be clamp-height and off-set requirements to this kluged system that will limit use to relatively small radii. Reason for starting with precision machined fingers from the start [a few hundred-dollars per piece X length].

NOTE.
This trick works well for aluminum bending on a temporary basis... or when a really –odd BR is required. For longer-term production bending, substitute 3xx-1/8H CRES sheet for the 6061-T4 sheet, thicknesses noted. These sheet-stacks can be left as single/interchangeable... a few drops of light-weight oil between the BR cuff sheets helps them separate for smaller BRs cuff-stacks... and nest tightly with greater thickness stacks of cuffs for bigger BRs. OR these nested sheet-stacks can be can be spot-welded or flush tack-riveted together to remain as permanent radius guide sets, specific Radii.

NOTE.
Precision radius bending of thin sheet metal is as much art as science. It was a required skill I had to learn to help my dad build simple sheet-metal parts for his Thorp T-18 in the 1960s.


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]

 

[drawoh]

Papasaurus,

All of my internal airborne boxes were 5052-H32. If you select difficult material, you will have safety hazards due to bad workmanship, and/or a very limited choice of vendors. The sheet metal guys like 5052-H32. They know how to bend it properly. Once your walls are thick enough they won't vibrate, they will be strong enough. In your place, I would be way more concerned about fasteners, including rivets.

Would I be correct in assuming that your managers do not want to see screws through the front panels?

--
JHG

 

[Papasaurus]

Oh, we have no fasteners showing from the front already. Typically, the enclosure is surrounded by cabinetry or another product, or both, so in this case we have fastening hardware (FHMS) on the sides and top. I came in too late to suggest a rear-panel locking solution (tab and tuck). We do, in fact, use 5052 extensively, and this shop is quite deft at it. But I find it disconcerting to get resistance to a fairly straightforward task, just because it deviates from their day-to-day.

And I'm already going around with manufacturing about establishing a torque spec. We don't currently specify torquing on anything less than #8 hardware, but I'd like to change that. Coming from a spacecraft structural background, I'm aware of the importance of bolted joint design, and I tend to be hesitant about using Loctite.

Ed Lee
CAD Admin / Sr. Mechanical Designer

https://www.linkedin.com/in/edwinlleejr/

 

[drawoh]

Papasaurus,

For critical airborne structure, I was told to not use anything smaller than #8. I understand not using threadlocker on spacecraft. The only issue around electronics cabinets is that most threadlockers dissolve electronics. If your structure is a non-electronic sub-assembly, this is not a problem.

I try very hard to not use flat head screws on sheet metal.

--
JHG

 

[Papasaurus]

I just don't like using them at all, unless they have a socket head, and even then only at #10 and up. But "That's the way we've always done it".

These are, in fact, electronic enclosures, non-structural, food and beverage appliances.

Ed Lee
CAD Admin / Sr. Mechanical Designer

https://www.linkedin.com/in/edwinlleejr/

 

[3DDave]

I once specified a portable tester front flat panel hog out with 7075 as it was possible someone might use it as a step stool. Got a call from the anodize house all confused. Turns out my shop just used 6061, like they -always- did.

 

[drawoh]

...

These are, in fact, electronic enclosures, non-structural, food and beverage appliances.

If they are attached to an aircraft that might crash, they are structural.

--
JHG

 

[Papasaurus]

Correct, not airframe structural, but secured to the structure. Therefore must prove under the same loads. Bowling-ball-in-the-back-seat like. Which, again, compels me to keep specs in the material callout for verification. If it's not required by standard, then usually it would be a contract requirement.


Ed Lee
CAD Admin / Sr. Mechanical Designer

https://www.linkedin.com/in/edwinlleejr/