Hydroforming... at least that's what I think I need. 5

[RoarkS]

So thought of the day.

This is a follow on to my other heat treat thread. If I'm forming parts out of .025 and .032 2024... it was brought up that If I heat treat and quench I'll get a W condition that would be the ideal time to do forming. As suggested I've got 10 minutes to do it... got me thinking.

The wing ribs I'm planning on making were intended to be hand hammered to shape. The trick with these is that profile flange of the rib cannot be interrupted like a sheetmetal skinned rib can with where you can use fluting pliers or have relief cuts. This is a fabric covered wing, to my understanding it has to be smooth. I've tried flow forming, and hammering aluminum over a block and have had little success.

So here's the question:

Poor mans hydroforming press for 48" x 6" wing rib.

I've seen plenty of EAA harbor freight presses with rubber blocks and such. Just not big enough.

What I'm thinking...
Pour a concrete block with a 12" x 60" x 2" depression in the middle.

waterjet a top plate that has welded in anchors that go into the concrete block with a cut out for the depression.

The top plate has hinges and bolt downs for the "top box" I'm making this up as I type. Top box is a plate with reinforcements welded to the top, and a frame that holds a rubber sheet. I'm actually seeing the rubber sheet more less flush with the plate. not really a box. but there's a fluid port int the top plate and the rubber is what expands to do the forming.

So I take my nice CNC forms put them in the bottom. Pull the blank out of the oven, quench it, put it on the form. Cover it with a sacrificial sheet of rubber. hinge down the top box, secure it. then pressurize it. Part is formed, open it up pull good part out/repeat.

The question is how much pressure? I don't have specialized forming software. I tried running a Solidworks non-linear FEA to try out various pressures on thin sheet and I didn't get a nicely formed rib.
Obviously how much pressure would also dictate the size of the top box reinforcements.... the concrete I'll double check but I'm guessing it will be over built to begin with. As for a hydraulic source I saw a certain youtube fella do some neat things with a pressure washer.

Thoughts?

/I already had a real aerospace shop quote the job. Not gonna happen. I can buy 2 complete flying planes with for what they wanted. Besides don't tell me this doesn't sound like fun.

 

[verymadmac]

Concrete and pressure vessels sound like a giant claymore. The issue with pressure washers is to make sure they are really well bleed, otherwise they will store a lot of energy.

Metals handbook V14b lists forming as 1 to 7 ksi for typical forming pressures. For those thicknesses and that state I would expect the bottom end of that range. There are methods to improve conformity to the form block, should you not have sufficient pressure. I have pondered this problem before, possible concepts I have come up with are (not necessary practical)

100 tonne bottle jacks are readily available, 2 of them should just about do it.

Build a giant nut cracker type press with a couple of full lengths of RHS, add a couple of blocks and automotive winch.

A screw press, multi screws around the perimeter, keeping it even would be a pain.

Trapped rubber press, just like a standard rubber press but with a drop hammer. Possibly hard not to overload the forming box unless really over built.

The boring answer is to ask if you have considered to switch to stretch forming bulbed tee section then riveting to the web, given the much lower forming stresses involed.

 

[MikeHalloran]

The multiple screw press seems attractive, but the synchronization and timing constraints make it more interesting.

I'm thinking a couple of ~2" thick steel flat bars just a little bigger than the rib, with the actual tooling comprising laser-cut steel sheet bolted on.

And maybe six to twelve perimeter bolts into tapped holes with Never-Seez, wrenched by a small group of people working one or two flats at a time to a work song.

Driving the screws with a roller chain could work better for a single operator with more tooling money or fewer friends.



Mike Halloran
Corinth, NY, USA

 

[berkshire]

RoarkS ,
Is this for a production aircraft or a one off unit?
It sounds as though you may be better off, since you have a heat treat capability to buy T0 temper, do your forming, then heat treat and hand straighten.
The rubber box press may be your answer if you can get enough pressure on it. Here is a link to a maker of these things

https://beckwoodpress.com/applications/rubber-pad-forming/

> As you can see they are pretty big. The other alternative may be to ship the parts and your forming die to a Hydroformer and let them form the parts for you. You can then heat treat and straighten using the forming die when you get them back. You also may need to use a shrinker on some of your flanges to get your ribs straight, because you will have excess metal in those flanges.
B.E.


You are judged not by what you know, but by what you can do.

 

[verymadmac]

Given its a pretty long and narrow rib, one could possible make a bladder pressure from a 8" schedule 160 pipe wp 3.7 ksi (no a simple exercise but doable).

 

[berkshire]

very mad mac,
Ketema aerospace el Cajon California had a tube type hydro press of the type you describe, (it was about 2'-0" in diameter), that they made themselves , they were running 4000 to 6000psi on it. The big dis-advantage that it had, was that it took so long to get it bolted together that you would lose your W temper time if you were trying to form 2024, 7075 gave you enough time.
B.E.


You are judged not by what you know, but by what you can do.

 

[verymadmac]

Ketema aerospace el Cajon California had a tube type hydro press of the type you describe, (it was about 2'-0" in diameter), that they made themselves, they were running 4000 to 6000psi on it.

thats quite a piece of kit, bet it had a lot of Bolts in it at that size / pressure. Really needs a breech block type end on it for commercial use.

 

[rb1957]

am I right in thinking you're trying to form a flange around a corner ? you say the rib cannot be interrupted by relief cuts.

man, this sounds really tough, to maintain any sort of control over the thickness in this area.

the rib extends spar to spar, yes? you should be able to joggle the rib flange under the spar flange.

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

RS...

Rubber-pad forming.. Guerrin rubber-pad process. A very fat pad of compressible rubber is mechanically crushed-over a die to form a piece of aluminum sheet metal to typical rib or frame contour. As the rubber crushes it 'flows over the aluminum on the die' creating the part. This process is typically limited to small parts, due to huge press forces required.*

Hydroforming uses a 'similar set-up' but a thin/tough rubber diaphragm is used in-lieu-of the rubber-pad... crushing force is generated by hydraulically pressurizing the backside of the pad to several thousand PSI... which stretches/flows the rubber-diaphragm to crush-form the part shape.*

* In both cases '360-boundary containment' is usually required to direct the crushing forces and prevent pad or diaphragm 'squeeze/blow-out'. Also rubber-compatible lubricant is required over the die surface over the aluminum and on the rubber pad/diaphragm surfaces to allow smooth slippage and avoid tearing.

Aluminum Association AA FMA-17Forming and Machining Aluminum is a useful references for 'starters'... great discussions on 'forming' and 'machining' aluminum. I have my current copy thru corporate IHS subscription... but printed or on-line versions should be available.

Years ago I got a copy of an ancient text on the subject... that gave me the wisdom of the industry... Principles and Methods of Sheet-Metal Fabricating, George Sachs [my copy is 1951]... usefully oriented details for making classic aviation parts in manufacturing scale with 'industrial' and 'hand' tooling.

Handbook of Fabrication Processes [ASM] has a lot of great info also.

On the other-hand…

It might be in Your best interest to use classic hand-forming techniques... which are more of a craftsman's approach to making onsey-twosey parts. These techniques have been used for decades for making shallow ribs and frames by progressively/gently 'forming' sheet metal over a die using a soft rubber-mallet [more to the story than this simplified explanation]. There are also simple hand tools for making compound contoured sheet metal parts [English wheel, stretch/shrink forming, etc]. In these cases the parts have to remain in the '-O' condition for forming... then solution heat-treated and lightly straightened ['W' condition] then aged.

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]

 

[rb1957]

yes, but can you form a three sided corner ? I don't think I've ever seen that !?

another day in paradise, or is paradise one day closer ?

 

[RoarkS]

WKTaylor Thanks for the reading recommendations! That's half the fun of it. I bought a '51 and a later second edition of your "Principles and Methods of Sheet-Metal Fabricating, George Sachs"

I looked for AA FMA-17 looks like the $25 copy is a pretty bad B&W scan. Is it worth the $25?

Here's a render of the "standard rib" looks to be about 40 of them for the whole plane. Nose it cut out a good bit. There are 2 spar pass thrus.
(NACA M12 Profile 48" Chord)

Tube type hydropress huh... now that has my attention. What did they do for the "bed" that everything sat in.

Multi screw press isn't a horrible plan I don't suppose. Get my impact on a regulator and adjust it down I bet I could get that bolted down pretty quick.

If I plan for 3Ksi that opens up quite a few options.

 

[Sparweb]

A picture is worth 1000 words.

This could be made in a rubber press but not all at once. Better to put in the lightening holes and spar cut-outs after the flanges are formed. But there are warnings of many problems yet to come...

Since 80% of the rib material has been removed by lightening holes, it must be safe to assume that the rib doesn't really have much function in the aircraft, right? ...facetious comments aside, sorry... I believe this part will have significant warping problems no matter how it's manufactured. The lightening holes are so large they compromise the part. All forming processes leave internal stress in the material, and when multiple deformations interact they ALWAYS cause warping. Forming in O condition won't solve this. The rib will need to have these issues addressed.

The spar cut-outs have tiny relief corners but they're inside the bend radius. Cracking is almost guaranteed. Ribs are normally split into separate parts for this reason. (Heck, whether you cut them at manufacturing, or let them crack in flight, either way it makes itself into separate pieces!)

<rant>
CAD programs let you draw things that cannot be made. You fall int the trap of assuming full structural strength in application, and buttery plasticity in manufacturing. This model is evidence of that.
</rant>

http://www.sparweb.ca

 

[RoarkS]

I have to say it's pretty representative of what's on the print. First draft was 4/18/1929 They didn't know about cracking back then lol. There is an STC that replaces a good number of these with plywood because of cracking. especially over the fuel tank.

Its 2 wooden spars, these are wood screwed (AN 545-5-4) to the spars with a wood drag strut out at the interplane struts. These "ribs" are more less formers for the fabric. I wish I was comfortable enough to try something different. I hate the design. I really do. But I've flown on them and they work. It was the longest running aircraft without a structural AD until they started trying to build them again about 10 years ago. I would LOVE to have composite wings for this but that's something I know less about than hitting metal into shape.

 

[rb1957]

that may be the shape they ended up with … but do you Know it was made in one step, or possibly multiple steps like SW is suggesting ? Possibly they did it in one step and accepted a high scrap rate as the cost of doing business (not knowing any better) ?

what's happening at the acute angle at the T/E ? two separate flanges, or one (wrapping around the corner ??

forming the skin flange, then stamping the lightening holes then the spar penetrations sounds like a reasonable plan to me. If you cut the lightening holes first I can see that they may deform as you form the flange.



another day in paradise, or is paradise one day closer ?

 

[berkshire]

RoarkS (Mechanical),
The Ketema Hydroform tube used solid slabs of dense urethane to form the bed and they used very thick tooling that did not distort.
One thing I need to remind you about is that you will need tooling pins, these vary a little bit by Manufacture, but they are essentially a 1/4" diameter pin about 1/2" to 3/4" long with a 1/2" or 5/8" button on the top, these are usually lathe turned, some of them are knurled, others are not. They hold the part in place while the part is formed. If you are going to do the forming in two operations you could put them in the center of the lightening holes. You could also form the flanges for the lightening holes and cut the holes later one thing you will get is a narrowing of the formed flange top and bottom so you will have to allow metal and trim the flange to size on a router later. An overhead router with a star cutter works very well for this., you would be better off fly cutting the holes to avoid the micro cracking you get from a punched hole. Because of the way hydroforming works. you are going to have to do the spar cutout flanges in a separate operation possibly with a box folder or a press brake. This job would be a snap on a Verson Wheelon press if you can find anybody who has one near you.
B.E.


You are judged not by what you know, but by what you can do.

 

[RoarkS]

They certainly intend on it being done in a few steps.
The instruction pack for the prints say to use tooling pins where the lightning holes get knocked out. I've got a short list of CNC routers I hope to pull the trigger on before too much longer. Planning to use it to cut blanks... probably would make short work of cutting out the lightning holes and the spar flanges after the -W wears off. I have a few lightning hole punches that punch and flange in one hit that also happily form -T3.

By the way Berksire I just got "Forming Alcoa Aluminum" in. Good info tables are nice too. I love how they knew how to explain stuff back then.

I just called up my tooling rep to see if he knows anyone friendly in town with a Verson Wheelon press. That looks like exactly what I want... and a big version of what I envisioned with the "tube hyrdroform" I bet I could make a little one throw a PLC on it LOL!

Aside from my renewed interest in this old biplane I do seem to be getting more calls for forming complex replacement parts. I'm super intrigued with the forming in W... and want to try it.

 

[berkshire]

Roarks
The Verson Wheelon press is fast enough to form 2024 in the W temper, keep the parts in a container with dry ice until you are ready to throw them in the press. If you have more than one forming die like a left and right hand that bed is big enough to do several at once.
If you cut the blanks on a CNC router allow at least an extra 3/16" on the flange to allow for "drag in" when the when the raised flanges form on the lightening holes. You can also do your flange trimming with the CNC router if you clamp the parts down well to the table. Use a star cutter, or take several goes with a single flute up cut router bit, a wooden sacrificial backer behind the flange helps to keep the vibration down. When you cut the lightening holes leave tooling tabs on some of your holes, so your part does not skitter over the table on the last couple of holes. Good luck with this. By the way, are you prepared to share the aircraft make and model?
B.E.

You are judged not by what you know, but by what you can do.

 

[Compositepro]

I just happen to be watching "How its Made" and the segment showed the fabrication of a very similar rib.

https://www.youtube.com/watch?v=gbJxHaTrZww&pbjreload=101

The rib is at 1:49.

 

[RoarkS]

Nice! I've not seen that one. Megafactories when they are at the learjet facility has a great process clip also.

 

[WKTaylor]

BTW...

RS... Good FIND!! A long ago I had access to a copy of 'Forming ALCOA Aluminum'... but the company library lost track of their copy... I think I'll take Your cue and get a personal copy! BTW I think there were a few books published by ALCOA like this... including 'Welding ALCOA Aluminum' and 'Machining ALCOA Aluminum'. Anyone else aware of others like these published by ALCOA? I think there MAY be ones for extrusion, forging and casting... but not so obvious titles. Or NOT. 'Brain' is unsure. I know the Aluminum Association has basic publications on these topics, also.

Edit Note... just discovered... apparently ALCOA had a series of at least [6] books: Forming, Machining, Welding, Soldering, Brazing and Adhesive Bonding... ALCOA Aluminum.

NOTE. RE Lightening holes...
As a kid, helping dad build his Thorp T-18, I got to 'tag-along' [So Cal, 1960s] and meet the designer, John Thorp, on numerous occasions... when he spoke EVERYONE listened.

On the subject of 'lightening-holes' in ribs, frames, intercostals, webs, etc... Thorp was extremely cautious. He called them 'weakening-holes'. By removing the hole material, yes the part got lighter, but also weaker and usually required special effort/tooling/cost to flange the holes [round/odd shaped], etc...

It was the designer's 'balancing act' job to remove enough material to make the effort worthwhile weight-wise... while not costing too much in $$s/work/tooling-effort... and still be 'just strong/stiff/tough-enough' to be structurally sound. He admitted he learned this lesson early in his design career... and had seen this mistake repeated many times... poor judgment used in the effort to save a little weight.

"Simplicate and Add Lightness.” Ed Heinemann, Lead Design Engineer Douglas Military aircraft and Lockheed FW

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]