Hammerforming

[DanH]

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?

[xblueh2o]

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.

[wilddog]

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.

[rzbill]

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?

[David-aviator]

Dan are you using an English wheel?

[Weasel]

Dan likes precision....
Dan likes quality...


.....hey Dan, you over there building your own heat treating oven today?

[DanH]

Originally Posted by rzbill

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?

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.

Originally Posted by David-aviator

Dan are you using an English wheel?

Wheel work is entirely different, thinning the material so it domes up.

Originally Posted by Weasel

hey Dan, you over there building your own heat treating oven today?

No, but I am finishing up my nostoc burner. Think of it as a 2000F lawnmower

http://en.wikipedia.org/wiki/Nostoc_commune

[DanH]

Bingo....education and recreation:

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

[aeroaddict]

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

[penguin]

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