With mystery meta. "Youse pays yers nickle youse takes yer chances!"
Probably going to need a pretty healthy radius of bend for 3/16 anyway.
I have heated 5052 and let it sag to a from, but its really touchy. To much
heat and you get a puddle quick. 5052 is a bad example though because it
forms really well with bending equipment.
Some types of sheet really only like to bend in one direction. They break
if you bend them the other way.
If you have need for aluminum that can be heated to sag into a form,
look into the "superplastic" special aluminum alloys. That's what
they're made for. Typically they use some vacuum or some positive air
pressure, but it doesn't take much when you get them heated into the
They may be hard to get in small quantities, but a good supplier may
be able to get it.
Anneal by putting acetylene soot (rich flame) on the line to be
bent, and then heating with a neutral flame until it burns off the soot.
And bend (shortly afterwards) at right angles to the grain from
rolling. It will crack a *lot* easier if your bend is parallel to the
grain. (The grain often looks like single directional sanding.)
If it is a hardened alloy (e.g. 6061-T6) it will regain some of
the hardness over a period of time following the annealing, but it is
not likely to fully recover the T6 hardness.
If you are not sure about which direction the grain runs, before
the bending for real, cut off a bit of scrap stock (maybe 1" wide by
8-10" long) from two edges at right angles to each other, and try
bending each along the long way. See which cracks. Once you find the
right direction, cut off some more and experiment with radius, but you
probably want the centerline radius to at least be twice the thickness
of the aluminum.
My limited experience bending aluminum has had the results of cracking when
bending cold, success when heated with a propane torch. The aluminum I bent
was 3/8" thick X 3/4 width and a 3/4 radius bend.
Bend across the grain if it's mystery alloy. Bending parallel with the
grain will often result in cracking. If you have options, select the
largest possible radius for the bend. Study the surface to determine which
direction the grain runs, or, if it's marked by any means, you can safely
assume the marking to be parallel with the grain.
If you have any questions, and can tolerate the material being annealed,
blacken the surface with an acetylene torch, then preheat until the carbon
burns off. Quench in water, then make your bend. Be careful, as you'll be
working near the melting point.
The annealing process may or may no be necessary. Not all aluminum grades
are amenable to age hardening, so there may be no benefit in the heating
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