What's the best way to bend aluminum

The piece is only about 50cm wide and 40cm high and 4mm thick. It is a bracket . It needs to be bent in a straight line, only about 4mm high. What
techniques would you recommed with tools in a typical garage?
Thanks Stewart
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What
All aluminum is not created equally. Some alloys will bend readily, others will bend, but only across the grain. A good example is 6061-T6, which will likely break instead of bend. Can you provide more information on yours?
It can prove challenging to make such a short legged bend in something that rigid. I'm not convinced you'll be successful.
Harold
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Yeah, well either 6063 or 6061, but will probably use 4mm 6063. I guess an alternative would be to use 6061 2-2.5mm. The bracket needs to be reasonably strong. The height doesn't have to be 40cm and can be higher to accomodate an easier bend. Hope that helps.
Stewart

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    Hmm ... I *think* that we've got a problem of mixed units. We are accustomed to working in inches and thousandths thereof in Imperial units, or in mm *only*. Cm are not often used in a machine shop. And you are specifying mixed mm and cm.
    So -- your workpiece (translated) should be

    Now -- that "4mm high" at the end -- is that truly correct? and do you mean by it that the inside corner must have a right angle, instead of a radius, since the thickness is also 4mm? This is an unusually sharp bend, if that is truly what you are requesting, and increases the chances of the aluminum splitting.
    Or is it really 40mm, or even 400mm, as suggested in this fragment of your latest reply:

    Please re-post the request entirely in mm, and double check the dimensions -- including how sharp the bend needs to be. With an allowed radius, the aluminum is much more likely to survive the bend, and will be *much* stronger than a sharp bend would produce.
    And if you do mean that one leg after the bend should be only 4mm beyond the bend (sort of like this): || ==========================================================+
you might be better off doing this with a longer workpiece, and then cutting off the excess length of one leg.
    As for your final line of the original request:

Whose garage is typical? In *mine* there is a DiAcro 24" finger brake, which could (possibly) do the bend, though 4mm aluminum might be a bit much.
    A hydraulic brake, which presses a 'V' punch into a 'V' die to bend the work between them would be better for the task, I think. Some people in this newsgroup have hydaulic presses in their garage. But with 6061 or 6063 (T6 temper), this is again too sharp a bend.
    A really large and heavy duty vise might allow you to clamp the aluminum between the jaws, and use a length of 2x4 to transfer hammer blows to the part extending. above the jaws, but it can result in an ugly bend. And with 6061 (or probably 6063) in normal temper, you will be very likely to crack or brake the workpiece, no matter which means you use to attempt that sharp a bend. You want a very soft aluminum to manage that -- perhaps even pure aluminum.
    Converting your dimensions to inches (so I have a better feel of them) suggests that you don't have that big and heavy a vise in your garage. :-) (500mm by 400mm is 19.685", and 400mm is 15.748"
    The bends across the grain survive better than those along the grain (it likes to split along the grain), but you appear to be really asking for something too sharp. Given your dimensions, what *I* would be likely to do is to get some aluminum plate 8mm thick and of sufficient size to make the whole of your workpiece, and using a milling machine or a shaper, thin all but the sort leg of the "bend" to 4mm. I would do this especially if it needed to be a hard aluminum alloy, which does not bend well. And I have both milling machine and shaper in *my* garage -- but your workpiece is too large for *my* shaper.)
    Do you want to list what tools *you* have in *your* garage? Then perhaps we can focus our answers a bit more.
    It may be that the best way for *you* to do it is with a tool which is only in the garage when *you* are there -- your wallet. Find someone in town who does sheet metal work, and pay them to do it.
    Good Luck,         DoN.
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DoN-- or anyone--
how do you find which way the grain runs in aluminum? Without bending it, that is. Is there a way to tell visually?
I suspect it's only in extruded or rolled aluminum, not cast. Just curious.
Ken
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Well, 99% of the time there's a brushed finish which obviously will show up. Sure it can be applied crosswise, but what are the chances of that? Probably more likely you'll break the tap in it on the last operation or something... ;)

Ya. Castings have crystals which point radially in from the sides, up to the very center which tends to be more uniform. Certainly, a cast plate will be better than a rolled plate if you're working it in both directions. (Hmm.... wonder if hammered plate can be had anywhere...)
Continuous cast is a different animal...
Tim
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It's not always obvious, especially if the piece is small enough to not have any printing on it. My experience dictates that information on aluminum sheets is always printed parallel to the grain, or along the long distance. In other words, on a 4' x 8' sheet of aluminum, the grain would run parallel to the 8' side.
If you can see signs of rolling, that's a dead giveaway, too However, I've seen more than my share of aluminum that shows no sign of direction. In a T6, or other hardened condition, it might be prudent to make a tight bend on a small sample. If it's bent with the grain, it usually breaks. Against the grain (crosswise to the grain) it will tolerate a much tighter bend without breaking.
Hope this helps. Beyond what I've stated, I guess you could also acid etch, which would likely show grain quite well.
Harold
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The original size was 90mm wide and about 50mm high and 4mm thick. Things seem too complicated though so have made other plans to prevent having to bend it. Thanks though.
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    Hmm ... now that we are sure that it is that small, and the overall dimensions suggest that the length to be bent up was 40mm, not the 4mm stated (you must have meant "4cm" there), that sounds a lot closer to something which you could do, I think that my DiAcro brake could handle a piece of 4mm thick metal that small -- though I would have my doubts about something closer to its full 24" (609mm) capacity, where the design specs are for 16 Gauge steel (about 1.59mm).
    And with a large bench vise (with a depth of jaw from top of jaw to the part which projects into the base of the vise of at least 40mm, and preferably 50mm), a good heavy hammer, some angle iron, and a piece of 2x4 to spread the hammer's force, it should be possible to do it. I would advise rounding the edge of the angle iron with a file or a grinder to increase the bend radius of the aluminum, and ideally using heat to anneal it to reduce the chances of it cracking.
    As suggested by others, take small samples of the material and try bending them in both directions, to see which way the grain works. Probably pieces perhaps 6mm or so wide by about 25mm or so long would suffice for the test -- and a vise without the angle iron plates would do the job. Mark the pieces with different colors of magic marker on all sides so you will be able to identify which orientation each had. After bending, it will become apparent which way the grain runs by how the cracks form.
    Good Luck,         DoN.
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Stewart wrote:

If it's a sharp bend of more than 45 degrees, you'll have to anneal it otherwise it may crack. I forgot what the proper annealing temp is but think it's about 800 degrees F. Heat gently and evenly with a propane torch or gas range burner, then quench in water. Then it will be almost as soft as copper. It's quite easy to get the aluminum too hot, close to melting temp. I'll defer to those more knowledgeable to give the correct annealing temperature and how to judge it--something about a pine stick touched to the aluminum, leaving a char mark...
Does your garage have a vise? The jaws probably aren't suitable for precision bending, so you'll need a couple jaw protectors. Couple pieces of angle iron bedframe, or new 1" x 1/8 angle iron from the hardware store, cut to the width of the vise. You might want to round the corner of one piece of angle where the inside corner of the bend will be, with a file (every garage has a file, right?)
It will be difficult to bend 4 mm of 4 mm thick aluminum, or any metal, evenly. You could clamp that 4 mm section in the vise and bend down the larger section. But your average garage-type vise will likely not hold it evenly across the width and it may slip out of alignment. So you're probably better off to hold it by the larger section, and tap the 4 mm lip down evenly across with a garage-type hammer until you reach the desired angle. It would be easier if you could make your piece oversize, then cut it off to 4 mm afterward.
An alternative method is to lay the piece with the bend line over a V-groove cut to the desired angle in maple or other hard wood (or steel), and use maybe a mason's wide chisel to whack it good and hard with a big hammer. Either way, you should try to get the bend done with as few hammer hits as possible since each hit will retemper the aluminum and work-harden it to the point of being brittle and easy to crack.
Ken Grunke
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Thanks, helps alot. Guess will rty to use the torch method.

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I agree with everyone else, that putting a 4mm leg on 4 mm thick material will be extremely difficult. It will be hard to hold, but also, try to visualize where the material is coming from to fill in the arc of the bend. It has to come from the material on both sides, and the bend part will use up a good portion of the 4mm side.
Consider slotting the plate most of the way through, then making the bend and welding back to stiffen it in the bent position. Or, just place a 4mm square bar in position and weld it.
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Because of the short 4 mm leg, I would take a bigger piece, bend a reasonable size leg, say 10 mm, then cut it down to the 4 mm needed. In a "typical garage" I would use a vise and a hammer. Bob
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Stewart wrote:

OOps, the last two words are the big ones! You have a problem! I suppose you could put it in a big vise and wail away at it with a hammer. A bending brake of some sort is the desired tool, and it would have to be a big one to handle 4 mm material.
You are most likely going to have to heat it and quench in water to anneal the heat treat, or bending will be impossible without fracture. Even with annealing, it is going to be very difficult to bend this without tearing at the outer edge.
Really, if it needs strength and a flange equal to the thickness, I'd be thinking more of machining the whole part out of wrought aluminum stock, and forget bending something of this thickness.
Jon
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