Bending Aluminum

I want to bend a 3' long, 1/4" thick x 2" wide flat stock aluminum bar to roughly a 7" radius "U" shape which will give me a 14" (ID) gap
between ends. I'm reading methods of bending aluminum and some say heat while others say bend cold. Since it's not a tight bend, I would think cold bending would be fine, but obviously uncertain. I'm also uncertain if it's best to use 6061 aluminum or, as I read, a softer 5052 which is easier to bend. The overall use will not reach the rated tensile and yield strengths of either grade, therefore, the only issue is price.....5052 is more expensive.
Anyone offer suggestion with this type of work?
Thanks
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On 6/22/2014 6:18 AM, Meanie wrote:

Hi - this is almost a dead group - rec.crafts.metalworking is active.
What I would do is to get a short stick of each. And try cold. If you get what you want - you know. If not - buy another pair and try hot.
1/4" thick is tricky on short bends but just where are the cut off points 1/8 or 1/16 ?
Age might be another issue. Was it sheared or plasma or water cut might change the internal structure or not.
Expect to hear from others. I'm not a bending expert.
Martin
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    Agreed. Though you do have to either ignore the political discussions, or set up a good killfile. :-) Whatever you do, don't *reply* to those discussions. Those trolls don't need encouragement.

    Well ... what kind of heat source do you have? It is possible to temporarily anneal 6061-T6. If you have an acetylene torch, set it for a very smoky flame and cover the region to be bent with soot. Then go to a neutral flame, and keep playing the moving torch around the area to be bent until the soot vanishes. (This is hot enough to anneal it, but not hot enough to make it hot short -- where it crumbles at any attempt to move it.)
    Then, within a few hours, do your bend and then let it sit -- depending on how hard you really need it to be. It will *slowly* regain most of its hardness -- perhaps to a T4 or T5 level, but this can take weeks.
    I *hope* that you are bending it the "easy" way, not the "hard" way. (That is the inside and outside of the bend are the wide dimensions, and the edges are the narrow one.
    Note that 6061-T6 without annealing does not like bending in certain directions. It has "grain" (sort of like wood) as a result of the rolling process. The grain normally runs parallel to the long edge on 4x8' sheets, and I would think so on the bar stock as well. As long as you bend it at right angles to the grain, you are pretty good, as long as the bend is not too sharp. If you bend it so the bent edge is parallel to the grain, the grain tends to open up at the most highly stressed part on the outside of the bend.
    As for *how* to do the bend -- without special tools you will want to make a cylinder around which to bend it -- and it needs to be somewhat smaller than the desired finish internal radius. It will spring back somewhat. So you also need to bend to a point where the ends are past parallel by some amount.
    There are machines for the purpose too. But good ones are not cheap. One way to do it is with a slip roller -- but most of them are not strong enough for 1/4" thick stock. They are made for perhaps a maximum of 16 Gauge mild steel (a bit thicker aluminium, but not 1/4" thick. :-)
    How smooth do you want the bend to be? You might get a bender for a single use from something like Harbor Feight. It is a hydraulic tool.
    This one:
<http://www.harborfreight.com/http-www-harborfreight-com-12-ton-hydraulic-pipe-bender-32888-html.html>
(item#32888) is made for pipe, and you would have to modify it somewhat for aluminum. In particular, the bending die you use would have to have the curved area filled in for flat stock instead of round pipe -- and the rollers at the upper corners would have to be similarly modified. (If you have a lathe, you could turn new rollers for th epurpose. (Download the manual in pdf form an read about it before deciding to go this way. Look for the "User Manual" choice in the bar just below the "100% Satisfaction Guarantee" flag.) Anyway -- it will do 90 degrees at a time, so you would need two passes.
    Or -- this one:
<http://www.harborfreight.com/bench-top-bar-and-rod-bender-38471.html>
(item#38471) which does have cylindrical rollers, and is supposed to be satisfactory for 2" by 1/4" mild steel, so it should be able to do the aluminum without problems. It needs to be bolted to a bench top (as likely does the other one above). I'm not sure how large a radius it can produce, but I suspect that you will have to do the bend in a lot of short sections. Looking though the downloaded manual, I think that this will be the case.
    Good Luck,         DoN.
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The minimum bend radius for 5052 is roughly the material thickness, while for 6061 it is 2-3x the thickness. Since your thickness is 1/4" and your radius is 7" you are way above the minimum so 6061 cold will do just fine. If you don't need a perfectly smooth bend you can use a finger or press brake and make a series of small bends to get your overall shape, or if you need it smooth try to find a 14" diameter tube or pipe to use as a mandrel and bend it around that. You will get some springback so you really need a mandrel a little undersized, and you will bend it around more than 180 degrees, to get your desired shape, but you will have to experiment to determine how far. Actually, rolling it would be best. Unfortunately those little ring rollers like HarborFreight sells only handle up to 1" wide, not 2". Maybe find a local sheet metal shop and see if they will roll it for you. As a one-off for a hobbyist they may not charge anything, or no more than say 1/2 hour of shop time.
----- Regards, Carl Ijames "Martin Eastburn" wrote in message
On 6/22/2014 6:18 AM, Meanie wrote:

Hi - this is almost a dead group - rec.crafts.metalworking is active.
What I would do is to get a short stick of each. And try cold. If you get what you want - you know. If not - buy another pair and try hot.
1/4" thick is tricky on short bends but just where are the cut off points 1/8 or 1/16 ?
Age might be another issue. Was it sheared or plasma or water cut might change the internal structure or not.
Expect to hear from others. I'm not a bending expert.
Martin
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This is what I use to bend flat stock: (Amazon.com product link shortened)
You can use the scale on the top to creep up to the angle you want, or make many small equal bends to form an arc. It's easier to bend a heavy piece squarely if you have a helper or jig up support under it. I use the tailgate and bed of my truck for the large immoveable workbench it needs, with the bender clamped to a beam tied to the bumper. -jsw
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7" radius in 6061 would be fine to bend cold. No need to anneal or any special treatment.
--
Steve W.

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