Castings 2

[etch]

This is not a question but more a topic for debate.


With the Boeing COO Harry C. Stonecipher stating it time to "think out the box"
in 1989 Boeing and commercial Aircraft Group (BCAG) reportedly earned less than $0.01 on every dollar from airline sales.

In September 1998, Stonecipher belived he knew part of the solution. He participated in a videotaped interview, which was made availabel to his engineers, encouraging them to use more cast components, instead of forgings, assemblies or fabricated part, in the desing of the comapnies airplanes.

The impetus is that castings quality levels have improved dramatically sine the '60 and '70s, and that on average, Beoing could achieve at least a 20-35% cost reduction on tooling alone, by converting to an assembly of cast components alone

Now this has started to trickle through to us casting manufacturers, and at the moment we are casting a part (the leading edge) that i believe used to be 8 components joined, as one soild piece.

Now the question to all Aerospace people out there is " DO you see castings ever making large imparts into the traditional forging and joined markets? if not why?

 

[TVP]

There have been quite a few articles recently on the increased use of castings in the aerospace industry. The spring 2002 issue of Engineered Casting Solutions magazine covered this topic with several articles. There is even a web-only article by Steven Kennerknecht, who has been quite active in this area. The website is

http://www.castsolutions.com/

 

[butelja]

In the fighter plane part of Boeing, they have bragged a lot on the savings due to high speed machining. I saw an example for the F/A-18 where a floor pan that used to have >100 pieces (including rivets) was created from billet aluminum using high speed machining to make a thin wall ribbed one piece part.

 

[WKTaylor]

Folks...

Castings need to be integrated into the preliminary design stages of new (or new-generation models): redesign at product mid-life of a production-run at could produce only "iffy" savings and backwards compatibility for spare-parts.

Castings are limited to a few medium-strength/toughness alloys. Highly stressed components made from high strength and high-toughness alloys... hogged-out from billet, bar, plate, die foring, (etc), by high-speed machining... may STILL be the best solution for many straight-forward parts.

Undoubtedly, structural castings in aerospace could be of great economic and service value... especially where production runs warrent set-up and the potential for weight or assembly costs can be minimized.

I am a believer in castings!. The F-16 is a structural casting success story... the V-Stab sub-structural box, canopy frame and weapons pylons... to name a few... are classic examples of "trouble-free" structural castings. CAUTION: castings were designed-in from the beginning for cost/weight/assy-time savings so success was easy to obtain.

Note: the "Mindset" and inexperience of many Aerospace designers and structural analysts steers them away from materials or processes they are unfamiliar with; either due to: "benign ignorance" or out-right prejudice [we don't do it that way; casting quality is impossible obtain; "not enough numerical test data"; "not what the customer wanted"; etc].

This is a classic Example of the severe "mindset and experience problems" I indicated:

Several years ago I was in a meeting where F-15E weapons pylons were being discussed. The existing "multi-piece-part" pylons were seeing premature cracking failures from the hundreds of fastener holes. I casually suggested to the St Loiuus folks that they redesign the pylons using large/integral sand castings [following the F-16 lead]. You would have though that I was a hell's-angle wanting to date their teen-age daughters... the lead engineer looked at me, shook his head, said nothing else and walked-off with the other in-tow [mid-90s]. I THINK that I heard recently [2001?] that the F-15 folks were NOW recommending the USAF allow then to use structural castings and exotic hole cold-working processes to "dramatically improve durability". OH WELL...
Regards, Wil Taylor

 

[TVP]

Wow, I'm kinda stunned that someone in a "lead engineer" position would be so completely against castings. Obviously there are issues to understand like mechanical property variation, potential for casting defects, etc., but to act like castings cannot be adequately designed for aerospace/aircraft applications is absurd.

Wil, when you are referring to only "a few medium-strength/toughness alloys", are you considering only aluminum alloys? The titanium alloy Ti-6Al-4V is being used extensively (~ 54 investment castings) on the new F-22 airframe, but I guess one could make the argument that compared to Ti-10V-2Fe-3Al this is only a medium-strength alloy. Just curious what your thinking is on this one... FYI, the May 2002 issue of Advanced Materials & Processes magazine has a short review by Boeing & Lockheed Martin on the titanium alloys used on the F-22, and the use of castings is one of the topics discussed.

 

[WKTaylor]

TVP...

I, too, was a "bit" amazed at the close-minded nature of the lead-engineer I tried to talk with. However the F-15 was famous for heavy use of die-forgings and machings... with hardly ANY castings. It also employed [single-mindedly] some of the MOST expensive manufacturing techniques in existance... but that's another story...
NOTE: I also believe I tripped the "not-invented-here-switch".

Yes, I was primarily thinking Aluminum casting alloys... however, mechanical values for castings in most alloys are invariably, lower than for equivalent wrought product .. or they are "S" values with lots of "caveats" and application notices.

For instance... MIL-HDBK-5H Rates has bare-MINIMUM mechanical data on AMS4962 castings: which rates it's FTu about 95% of equivalent wrought forms.

Statistical confidence in mechanical properties, and the testing required to gain this confidence, make any new material in aerospace a "bear" to qualify. I suspect that structural casting design data (developed by rigorous testing and trials at great expen$e) will remain proprietary to each manufacturer... until they are "encouraged" by the government or DOD to submit the data for inclusion in MIL-HDBK-5 (or the CINDAS Aerospace Metals Handbooks). Regards, Wil Taylor

 

[applicae]

The latest generation of military aircraft used castings for hinge fittings - problem was the casting were not designed by senior level design personel initially and the assembly process was compromised for the first ships. Understanding casting design is part of the problem - understanding how to best design around the casting is another.
Obviously the vendors love to change the tooling to recover the cost they lost when underbidding the job to get it in the first place!

 

[etch]

i would also like to add that there seems to be a general lack of understanding of defects in castings, particulary concerning radiography.

We produce castings for aerospace, and at the moment the defect level is Level 1 shrinkage max. Now having conducted trials and examined what level one shrinkage looks like, this is a minute defect. If you show a potential customer a chart of varying degrees of defects, he is always going to want the highest possible level of defect free casting. I feel there has still to be a lot of education in the industry about castings. I would be intrested to get my hands on a piece of wrought product to examine for defect levels.

An example of this is...

We produced a speciality casting, very high complexity, the customer asked for no discernable defects. We had a small patch of level on shrinkage in an isolated area, and asked for a concession. It took 8 stress engineers to decided that it was okay, then they took the casting and drilled a 1cm draininge hole in the casting.

 

[knobhead]

From my point of view, as a production eng producing gas turbine parts, setting up a job with a precision casting takes a lot longer than setting up a job machining from solid, as your datums are already fixed.
That said, once you're up and running, a casting is far faster to produce a finish part from, although it's less 'forgiving' than bar, because any machining mistakes will scrap the part, whereas from solid you can 'move the final shape' within the bar if things go wrong.

I've never had any problems or worries about integrity. Excessive accuaracy is a sign of poor breeding. -Socrates.