friction stir welding - wing skin

[DHambley]

Is FSW possible for the wing skin on large (like 747) aircraft. The stress on the lower skin during deflection testing must be concentrated on discontinuities such as rivet points. I would think the overall thickness of the skin could be reduced if these weak points weren't there, saving tons of weight. What is the typical thickness of the skin of the lower wings of these large aircraft. Is is usually 2024-T3?

 

[ESPcomposites]

How are the fatigue properties? The other thing is what about disassembly and repair? Is the process as reliable as a hole filling rivet, which is quite good in fact. I suppose I am just asking more questions, but I am pretty sure it has been evaluated. Hole filling rivets just have a lot of good history and any major process/material change is more challening and has more unknowns than usually anticipated.

Brian

http://www.espcomposites.com

 

[rb1957]

i would think there's more to gain on the upper surface. discrete elements on the lower surface make for good crack stoppers.

a concern with usig FSW on wings would be the very HCF environment and the very flexible structure ... a fuselage sees one big fatigue cycle per flight (with a whole bunch of small gust cycles superimposed) and very small deflections.

 

[Dan320]

Silly question perhaps, but what would the benefit be? The skins are typically not joined to one another but Hi-Lok´ed to the spar flanges individually.

 

[rb1957]

i thought he was talking about attaching the stringers to the skin, like in fuselage construction; and once you do it for stringers you could also do it for spars

 

[SWComposites]

A few comments:
- 747 wings are really, really large so process scale-up is not going to be trivial
- discrete (fastened) stiffeners and spar have significant benefits for damage tolerance with fatigue cracks
- due to damage tolerance considerations, the weight savings is not what you think if might be
- if the weight savings really was "tons of weight" the process would have already been used
- you have to design for repair, which means fasteners, so you have to design for fastener holes anyway

 

[Dan320]

I can't see how FSW can be used to attach 1/4" thick wing skins to a spar flange at least as thick in itself.
Maybe I'm thick too, but...

 

[MikeHalloran]

I think the OP's suggestion had to do with using FSW to make skins that are, say, 1/4" thick where they attach to spar flanges, and 1/8" or 1/16", or "thin", elsewhere.

I.e., an additive process instead of a subtractive process like milling.



Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

FSW is an alternative process to discrete fastening of stringers to skin panels. one advantage is you don't need as same pad-ups, and you're not building in a whole bunch of stress concentrations/crack starters, and maybe you're saving some manufacturing time/$s; probably you're just "robbing peter to pay paul", moving the money from one expense (labour) to another (new process).

however you need to be careful that you don't make the structure "unrepairable" ... (by not providing sufficient material to discretely attach repairs)

that said, it'll be interesting to see how Boeing repair the 787 (and Airbus the 350 ?) once in-service damage starts ... bonded repair dblrs ??

 

[MikeHalloran]

Damn, I missed a meeting. ....again.

I thought FSW was inherently a _butt_welding process which limits it to joining the edges of two sheets of possibly different thickness, or joining the edge of a sheet to the edge of a flange.

So I didn't see how you could use it to attach a sheet to the _face_ of a flange, i.e., making the joint repairable with rivets.

But Wikipedia says there is such a thing as a FS _spot_ weld: "Friction stir spot welding is successfully used for the bonnet and rear doors of the Mazda RX-8 and the boot lid of the Toyota Prius."

I found an AWS paper with photos of FS spot welds.

http://www.google.com/url?sa=t&source=web&cd=3&ved=0CCUQFjAC&url=http://

http://www.aws.org/wj/supplement/wj...q_zSdaYSg&sig2=ImxdnK9XCzgcunmkKS2qmw&cad=rja

The tool side of the spot weld has a large cavity, not unlike a Tog-L-Loc joint in appearance. Not the sort of thing you'd want to have on aircraft skins.
Still promising for terrestrial applications.



Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

i think airbus are using it on the 380 fuselage ...

 

[SWComposites]

"it'll be interesting to see how Boeing repair the 787 (and Airbus the 350 ?) once in-service damage starts ... bonded repair dblrs ?? "
- bonded scarf repairs
- some bonded doubler repairs
- some bolted repairs

 

[ESPcomposites]

"it'll be interesting to see how Boeing repair the 787 (and Airbus the 350 ?) once in-service damage starts ... bonded repair dblrs ?? "

My guess is that bolted repairs will be the common choice, at least initially. Bonded doubler repairs are good, but only address certain types of damage. Scarf repairs have proven to be difficult to do with a high enough level of confidence, even at production facilities. It is going to be even a greater challenge outside of that environment. I think the initial thought was scarf repairs might be a first choice, but that seems to have changed.

However, after there is more confidence and need for bonded repairs, I suspect the trend may change from bolted to bonded.

There are some other things as well and some details I have intentionally left though. Sorry to get off topic.


Brian

http://www.espcomposites.com

 

[KirbyWan]

MikeHalloran,

FSW can also be used to produce a linear suface weld between a sheet and underlying support. The rotary bit just needs to extend into the support piece and it will stir the two materials together in a super plastic phase. I think Eclipse Aviation was working on qualifying this process, though I must admit I only know what I've learned from technical literature. I did a report on it in college, which does not make me an expert.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[Dan320]

There could possibly be specific cases where FSW is advatageous compared to other joining methods. However, there must be significant gains to offset cost of engineering, testing and certification.

 

[palomc]

rb1957: Airbus uses laser beam welding for some of the stringers on the lower fuselage.

 

[thruthefence]

Didn't Martin (or somebody) make ICBM's with this process? Of course, there's no 'repair' problems to deal with on ICBM's.

 

[YoungTurk]

Kirby, how can one make a linear weld at a stacked joint without, at a minimum, "keyhole" type ends? The only think I can think of is at the partial assembly level if the weld mechanism can weld the entire length, entering and exiting on free edges. This would obviously limit the number of applications.

It seems the rocket industry has been making use of this method for awhile. Most recently the Orion team has been trumpeting FSW fabrication.

Orion weld operations take place on a Universal Weld System II (UWS II) that includes a 22-foot diameter turntable, a self-reacting friction stir weld head and a modular t-grid floor. The system affords virtually unlimited five-axis welding on fixture-mounted hardware. The UWS II is part of the National Center for Advanced Manufacturing, managed by the University of New Orleans Foundation in partnership with NASA and the State of Louisiana.

The friction stir welding process advances the state-of-the-art for circumferential welds, yielding higher strength and higher quality welds at a lower cost.

Same question for circumferential welds - how can they be continuous?

http://www.aviationnews.eu/2010/06/...final-friction-stir-weld-on-orion-spacecraft/

http://en.wikipedia.org/wiki/Friction_stir_welding#Applications

 

[KirbyWan]

YoungTurk,

I think they do start at a free edge. And as for circumfrential welds I saw a video of one where after the weld was started, they mig welded a runoff plate before it got all the way around. That was for a steel pipe and it looked like a university research lab.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[kellnerp]

The main fuel tank on the space shuttle is friction stir welded. That is a pretty large scale structure. And there are fatigue issues even though the tank is destroyed on each flight, but reliability is a much larger concern than with aircraft.

Axles for bulldozers are frequently friction welded and don't seem to have problems with fatigue. That is one of the benefits of this method.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."