DanH

DanH

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Once upon a time, an RV was built from raw sheet by forming over hammerforms. Obviously we don't do much of that anymore, although there are some remaining plans-builders who do.

Anyway, this is a rescue project, a fuselage former for a Yak 50, the station being about a foot aft of the firewall. The airplane did a bit of belly crawling following a gear problem, happily on smooth grass, and the original former wasn't salvagable. Apparently the parts are no longer available from the Mother Country, so the repair required the fabrication of a new former.

I was able to pull measurements from another 50, and combined with the remains of the broken former, I got the shape nailed down in AutoCad. Took the .dwg file to a waterjet shop and had them cut the basic hammerform profile from a chunk of 3/4" 6061T6 plate pulled from my scrap bin. The rest is hand work, notably edge radius, lightening hole locations, and a die to press the lightening hole flanges.

First I tried a practice part in 2024-T3, just to see if I could avoid a trip to the heat treat shop. As expected, it wasn't possible to shrink T3 enough at the wide outer flange. Probably could have done it with flutes, but the original Russian part had none, and the goal was a exact copy. So, out came the 2024-0 soft stuff. One quick practice part to tune the tools, then this part. I'll probably send it to the rib shop that builds your RV ribs for Vans, and ask them to tuck it in with a batch for heat treating to the T3 level.

Hammerform on top, new Russian-American fuselage former on bottom. And yes, if your local Yak flyer happens to develop a bad belly rib, tell him you know where to get a duplicate ;)

 
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Hammer form

Looks good Dan, pretty satisfying making something from nothing .Lucky for most Vans came along otherwise there would be about 487 Thorpes finshed by now .
 
It looks as if there's no allowance for spring-back after forming. I've never worked with 2024-T0 before. Will it need any?

Dave
 
Try this

At my day job we heat treat every day, often some very interesting parts. If you were in Greensboro NC, Id have it done for you tomorrow. 2024-0, treated to 2024-T4 or T42 (T3 is only achieved by the mfg. of the alloy)is a simple process, and some warping will likely occur. Often, the part can be wired with safety wire to a rigid steel item which will prevent most of the warping. We use baskets made from perforated steel mesh, but have also used angle iron ect. If the quench process is done quickly and correctly, its is minimal. Most RV ribs require fluting to remove such twist/bowing, as we all know. Any straightening will be easiest just after the quench and prior to the age hardening, but I wouldn't worry too much about that. I make many parts for vintage birds at my home shop, and its always very rewarding..keep up the good work!
 
David Paule said:
It looks as if there's no allowance for spring-back after forming. I've never worked with 2024-T0 before. Will it need any?
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Not much. Actually, I did sand a springback allowance for the outside flange, as it is the widest, faces the skin, and the one requiring shrinking. None on the inside, as the flange is only 3/8" wide, and doesn't need to be perfectly 90 degrees to the web.

 
g zero said:
How could this problem be solved before heat treating ?
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I don't know if it can. It is long and skinny so I would expect it to curl up somewhat - just because of its basic shape - nothing to o do with how it was formed. The maddening thing is that right out of heat treat it will still be soft enough to correct for some period of time. But if your heat treater is on the other side of the country it's difficult.
 
This is all very interesting. I know little about the actual heat treat process. Is it possible to construct a jig or fixture to maintain shape?
 
I talked to my buddy who has a restoration shop and does a ton of scratch building. Along with a ton of other cool tools he has his own oven and does his own heat treat. This is what he has to say, and mind you I am paraphrasing and simplifying:
I showed him the picture of your part and he said oh yea, it will come out of the quench tank like a pretzel.
If I understand the process correctly...after the heat treat and quench the material will be around 75% of the way to T-3. Over the next couple hours it increases to around 90%. After around 96 hours it has reached full spec. The shape needs to be fixed as soon as possible after coming out of the quench tank. Within those couple hours while you can still move the material easily. It sounds like you will not be able to be there when it is treated so he gave a couple of suggestions. If you think the shop has people who care enough you can send the form block along with the part. When the part comes out of the quench they can hand form it as close to correct shape as possible and then put it back on the form block. Just pulling it out of quench and sticking it on the form block is not enough. There will need to be some hand work involved. Another route if you don't think the shop is willing to take that kind of time is to have them pull the part from the quench tank and immediately put the part on dry ice and over night it to you. The dry ice takes the two hour window and extends it. He said any shop who knows what they are doing will understand what you are asking for and have the ability to do that. If you can find a local shop to treat it he suggests match drilling the part to the fuselage while it is still O. Heat treat it, quench it, hand work it and get it cleco'd back in the fuselage within those couple hours and then leave it alone for several days. He asked if the material you made the part from was alclad or not. Apparently it makes a huge difference in how you heat treat. Be sure and inform the shop exactly what the material is so they can then use the correct "recipe" for treating it. He suggested getting a certificate so you know exactly how it was treated and then you can determine if they did the right thing. If it is wrong you may as well hang it on the wall as art because it isn't airworthy.

That was more than I wanted to know about heat treat but it was an interesting conversation. Learned a bunch.
 
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Wondering if you could attach the part to the form before treating and put the whole thing in the oven and then leave it attached for a few days until completed? I've never done any heat treating and don't know.
 
Waterjet or CNC plasma cut a steel form for the hardening process perhaps? Maybe offset it a bit smaller to negate the need to file a bunch of radii?
 
Dan likes precision....
Dan likes quality...


.....hey Dan, you over there building your own heat treating oven today?
 
rzbill said:
Waterjet or CNC plasma cut a steel form for the hardening process perhaps? Maybe offset it a bit smaller to negate the need to file a bunch of radii?
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Actually, I do have a 1/4" thick steel clamp plate. The profile is cut 1/4" undersize. Wouldn't be difficult to turn it into a heat treat fixture, if such a thing can be used in the process. I don't really need it for any future parts, as a plywood clamp plate works just as well.

David-aviator said:
Dan are you using an English wheel?
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Wheel work is entirely different, thinning the material so it domes up.

Weasel said:
hey Dan, you over there building your own heat treating oven today?
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No, but I am finishing up my nostoc burner. Think of it as a 2000F lawnmower ;)

http://en.wikipedia.org/wiki/Nostoc_commune
 
Bill E. is correct

In regards to heat treatment and distortion Bill E. is correct.

To reduce distortion during solution heat treating (condition/temper 0), the quench bath can be glycol instead of water. This will reduce the quench rate and distortion, will not completely eliminate it, but will reduce it. With proper racking (wire trying the parts) prior to heat treat and glycol quench, distortion can be minimized. Heat treat fixtures can be used, but then you get into all types of other issues; thermal expansion rates, distortion, ...

After heat treat and quench, the parts will naturally age/harden up to the T-4 temper. This process can take only hours depending on the gauge of the material, but for full temper to T-4, 96 hours is the industry standard.

As correctly mentioned by Sam, parts after heat treatment can be maintained soft by freezing the part. But as soon as the part is removed, the hardening process will start.

If one wants to reform the parts after heat treat, then it needs to be done ASAP, immediately after heat treatment or taken out of the freezer.

Dan
 
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Dan, really good lokking part! I started out in the aircraft business at Hawker Siddeley plant that made Harriers. We heat treated before bending and then age hardened. These are (around) 4% copper alloys, with the copper grains sitting on the aluminium grain boundaries and giving the increased mechanical properties. Heating and quenching dissolves the copper back into a solid solution, and makes the alloy much more ductile - but only for a couple of hours at room temp. Then the copper starts to precipitate out again. The heat treatment temperature is critical (510 C from memory), as is rapid quenching. Although an oven or salt bath (large vat of molten salt) are normally used, backstreet methods using a torch and carbolic soap (as a temperature indicator) are possible for thin sheet, with care. The metal can be held in the softened state in a freezer for a few days. Age hardening takes around a week to achieve original properties - which is fine for production work but can be a problem for a repair. Accelerated hardening is possible in an oven, but at a much lower temp than the softening, I believe it is sometimes not reversible. We used to bend the metal using wooden form tools made from sometimes called Jabroc in a rubber press - a large sheet of rubber (I this around 1' thick) was forced into the form tool using a hydraulic ram and forced the metal to bend to shape - everything came out straight, no flutes required! A facinating process to watch, but only really suitable for a production operation. Sadly the factory shut 20 years ago...
Pete
 
I think Univair still might do that hydroforming (big press using rubber for hydrostatic pressure) process. I know they used to.

Dave
 
wilddog said:
Wondering if you could attach the part to the form before treating and put the whole thing in the oven and then leave it attached for a few days until completed? I've never done any heat treating and don't know.
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I asked that question and the answer was essentially no. He said it introduces too many other variables.
 
wilddog said:
Wondering if you could attach the part to the form before treating and put the whole thing in the oven and then leave it attached for a few days until completed? I've never done any heat treating and don't know.
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Remember that the part has to be quenched rapidly. Adding additional thermal mass would impact the quench rate. I think insufficient quench rate is one cause of intergranular corrosion (as well as messing up the temper)
 
cool stuff

Nice parts and tools.
Usher precision ,as we all know makes the parts for Vans and they also do parts for individuals ---like me (check out my H1 inspired project).
The parts do warp quite a bit but you can easily adjust them with either a shrinker or flutes.
It also helped putting a few tabs on the blanks when it comes to curves etc.

cheers and carry on
 
rivetdriver said:
Usher precision ,as we all know makes the parts for Vans and they also do parts for individuals ---like me (check out my H1 inspired project).
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Oooo....You and Mark are on my list for a visit someday. That's a lot of talent in one place!

Gang, theses articles are really worth the reading time, if like me, heat treating aluminum is a new subject:

http://www.croucher.us/early-articles

I'm sending the part off to a qualified shop today. If it comes back pretzeled, so be it. With hard tooling in hand, I can make another easy enough. I'm really fascinated with the idea of doing most of the forming in the short "soft material" time window immediately after quench, so maybe that will be an alternative.

The other alternative is to back up, and just form in 2024-T3. Everything about this part will easily form in the harder material, except this outer flange, at the radius near the ends. You can see the gathers where I've shrunk the soft material. With T3 I suspect I would have to break that section into tabs rather than keeping it solid like the original Russian part.

 
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Maybe worth a try

If the heat treater is close by, why not try to coordinate with the vendor to be there post quench and have an ice box full of dry ice ready?

It's not like the part will immediately harden after quench and I'm sure if kept cold, it should be fine to reform.

Just FYI; I have age hardened parts in the kitchen oven before. Depending on the alloy, most alloys will age harden (T-4 to T-6) at around 250F.
 
Dan - check with your heat treating company. Many have freezers on site and will store your part. I can not remember how long it delays the aging but several days as I recall.

I have met with Usher and seen their operation and how they do Van's parts. Van's parts are simple and of relatively low precision. The same process would not work well for you. Your part is significantly more challenging.

Usher doesn't use steel forms unless there will be a large quantity. MDF is their preferred material for short runs. They use a very large press with the "rubber" mat approach. So, for those that don't have a nice chunk of steel or aluminum hanging around, you can make nice forms out of MDF that would be suitable to make quite a few parts before the form failed.

The Aluminum Association, the industry trade group for Aluminum manufacturers, publishes some excellent resources. I have a standards manual from 1984. Although dated, the standards have changed little and the composition of the alloys we use have not changed so it is still a good resource. It walks through heat treatment at length. Or, you can shell out $500 and get a new one!

The resources you exposed in this thread are appreciated. I have a lot of ribs to fabricate with my G.46 projects. It will be a fun challenge and I am encouraged by your work.
 
At my day job we make parts like Dans every day, but for Boeing and Airbus. Imagine a Vans like fuselage frame for a 737..we make them. The part Dan has formed would doubtfully be possible from 2024-T3, and if you were lucky enough to form it in the T3 condition, it would likely crack in service. I have a pretty good idea Dans part will be just fine after its cooked. We use phenolic or poured resin "tools" as we refer to the dies, and wood as well...Dan's machined aluminum tool is one that would last centuries!
 
OK gang, the frame is back from heat treat, and Bill was right, zero distortion...zip, nada, none.



Slipped right over the billet aluminum hammerform without force:



Still lays flat on the bench too.

 
Very cool!

I have enjoyed following this thread. Thanks to all those who've contributed. For me, the fact that this kind of stuff can be done by "regular guys" is very encouraging. Now, if we just lived in a country that believed it was important to maintain the capability to build new foundries and train people to run them, so we didn't have to depend on foreign materials... :(
 
4 easy steps

The process for 2024-0 taken to 2024-T42 (same as T3) is very simple. The part is "wired" into a basket which helps stabilize it for the quench. The part is then put into a controlled oven at 920 degrees F for a specified time based on thickness.. 43 minutes for this particular piece. It is then quenched in the glycol/water tank and then wash rinsed. An initial conductivity test (target of 28 or higher) is performed to see if initial heat treat has begun. For this alloy, complete treatment occurs at room temperature within 96 hrs. If the minimum passes at quench, it will go full hard. I watched this part climb 5 points in about 3 minutes. This was a complimentary "job" to help Dan, and show others the process...easy as 1-2-3-4 .
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