Sheet Metal Forming for Aircraft skins

[rivetdriver]

welcome to the forum.
What exactly are you trying to make?
happy holidays

[longyard]

Tim,
A/C skins are usually make from 2024 aluminum which often requires heat treating after compound forming. Most of the aluminum work you'll see on this site is done with 3003 or 1100 aluminum. The latter two are very weldable. 2024 is not.

You'll learn a lot here as we have some great a/c workers here. However, don't mix up the alloys.

[AllyBill]

Originally Posted by longyard

Most of the aluminum work you'll see on this site is done with 3003 or 1100 aluminum. The latter two are very weldable. 2024 is not.

No one told me that until quite recently and by that time I'd been welding 2024 with great success for many years. It welds like any other grade in my experience.

Will

[longyard]

Originally Posted by AllyBill

No one told me that until quite recently and by that time I'd been welding 2024 with great success for many years. It welds like any other grade in my experience.

Will

FAA Advisory Circular 43.13-1B, Ch 4, Para 4-89, d, "AIRCRAFT PARTS NOT TO BE WELDED".

d. Nos. 2024 and 7075 Aluminum. Do not
weld these two aluminum alloys (that are often
used in aircraft construction) because the heat
from the welding process will cause severe
cracking.

[AllyBill]

Not welded 7075 so can't comment there.
2024 can crack if you weld it in one of its higher tempers depending on what you are trying to do, don't for instance try to insert a circular patch, but when properly annealed it welds like any other grade and doesn't crack at all. When I say properly annealed I mean you take it to the heat treatment plant and have them do a full anneal and furnace cool, make your weld with strips of native material then have the heat treatment plant put the desired temper back. Never had a problem with it.

As a slight aside, the skins of the Handley-Page Victor wing were extensively spot-welded with no issues and they were 2024.

Will

[sblack]

Try to find copies of two videos by John Glover. Aluminm Shapes and Aircraft Shapes. They are old and were only put out on VHS but found mine on ebay. Also Kent White's videos called Shrinking Magic and Shaping Aluminm Wheel Pants and his Aluminm Welding videos (TMTechnologies.com) taught me a lot as well.

Much of the compound curved parts on light aircraft are fairings and not load bearing, so they are commonly made from 3003 which is easy to weld (If I can do it, you can) with a torch. There are some good threads here and on that metal shaping site on aircraft work. Good luck.

[KAD]

A very good read on what can/should be done with the different grades of aluminum. Also included is a complete description of the numbering systems and what alloys are used and why.

http://www.aircraftspruce.com/catalo...s/aluminfo.php


*Note: Spot welding is OK vs. arc/torch welding with some alloys....like 2024
It doesn't say that it can't be welded it says that it shouldn't be as it leaves the metal in a state prone to failure.
The word "Failure" when used in conjunction with "Aircraft" should be avoided as the phrase "search for the Black box" usually follows.
Likely a "proper application" question as opposed to a "can it be done" question......

[crystallographic]

Originally Posted by AllyBill

Not welded 7075 so can't comment there.
2024 can crack if you weld it in one of its higher tempers depending on what you are trying to do, don't for instance try to insert a circular patch, but when properly annealed it welds like any other grade and doesn't crack at all. When I say properly annealed I mean you take it to the heat treatment plant and have them do a full anneal and furnace cool, make your weld with strips of native material then have the heat treatment plant put the desired temper back. Never had a problem with it.

As a slight aside, the skins of the Handley-Page Victor wing were extensively spot-welded with no issues and they were 2024.

Will

Spot welding of 2024 T3 is very common on US airplanes. Going back to pre-WW2, many cowlings and "semi-structural" elements have been made using spot welding. One of the largest spot-welded airplane structural assemblies I have seen is the rear half fuselage of the Convair B36 "Peacemaker" - the behemoth that replaced the excellent Northrop YB49.
https://en.wikipedia.org/wiki/Convair_B-36_Peacemaker

I have seen a ski-plane ski marked "24S" (pre-1953 designation for 2024 T3) and it was gas welded. I have not seen other examples of tig or gas welding of 2024 alloy in aircraft production. I do know that the Aluminum Association rates 2024 weldability as a "D" - compared to alloy 2219, a ballistic material used in the early A10 Warthogs as a welded tub to protect the pilot - later replaced by welded titanium.

This article I grabbed on a quick search describes fairly recent aluminum welding recommendations:
https://books.google.com/books?id=DZ...uminum&f=false
It does not mention 2024 as being weldable.

Rockmount Research, on the other hand, sells a filler metal designed for 2024 and has for many years. It's specific applications in aerospace are above my pay-grade. I believe the filler is designated as "Neptune TIG."

I heard some years back that Trek Bicycles (and maybe Cannondale?) had their weld engineers work out welding of 2024 for their bike frames. So far, I have not spoken to anyone there about that.

I guess the bottom line is that some can weld it, but at the levels of the Aluminum Association and their tech reps, welding 2024 is rated as a "D" - or as Paul Dickerson told me once, "Screw it!" ... or rivet or bolt or bond it.

[BTromblay]

Hi Tim,
I work on airplanes as well, welcome to the forum.

Bill

[tfindlow]

Wow - lot's of feedback for a simple introduction...

As to what I'm up to - I'm working on a aluminum semi-monocoque tailcone that bolts to a chromoly-steel tube framework for the forward fuselage. Similar to the way that the Mooney M20 or North American T-6 are built. The tailcone is 2024-T3 alclad sheet, over aluminum frames, riveted together. The steel tube is gas welded 4130.

Like most tailcone designs - it's almost all flat-wrap; meaning no compound curves are necessary. However at the front of the cone, the straight line of the tailcone bottom needs to curve up to meet the straight line of the fuselage floor aft of the wing. And at the same time the lower corner radius on the tailcone needs to come to a "close to square" corner where the frame attaches to the lower longerons. This means there's one part of the tailcone which isn't a developable surface.

BellyPanel1.jpg

I'm currently trying to figure out how to go about constructing this - considering that my metal shaping skills are rudimentary at best.

I'm designing in Rhino-4; and have used the advanced flattening tool to "Squish" the proposed surface down onto into 2-D. The tool indicates that most of the work is in stretching and some small areas requiring shrinking; about 3% elongation each way. You can adjust the analysis to have all stretch and no shrink - but the amount of elongation goes up. I don't know whether this is within the range of forming for 2024-T3 for .032 or .040 sheet thickness, or whether it will have to be 2024-O and heat treated afterward.

BellyPanelFlat.jpg

In any case I'm trying to figure out an appropriate technique to apply to the problem. A lower skill threshold would be preferable for a novice like me - a 7 year apprenticeship is probably not on the cards at this time of my life. So I'd love any pointers as to where best to to aim my research...