Bending aluminium.

[Ribenapigeon]

I'm making a bracket and will need to make some ninety degree bends in some 4mm thick aluminium flat bar. I understand aluminium can fracture if the angle is too tight. So what's the best way to bend aluminium?

Cheers

[Islander]

In a vice with cardboard or something similar to protect the work and a round bar between the aluminium and the vice jaw you're bending towards so that you bend it around the radius of the bar.

[Suntan Sid]

You need to anneal the aluminium before bending!
Basically rub some soap onto the surfaces, heat gently, then bend.

Google "annealing aluminium" something will pop up on youtoob with a demo.
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[Ribenapigeon]

Thanks folks. Presumably a few seconds with a blow-torch will do?

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[Copycat73]

have you tried bendin a small off cut of said 4mm flat bar without heat or soap .. I think you`ll find it bends without any fractures...
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[bladerunner]

Depends on what grade of Ali your talking about and if it's been heat treated. Something like 7075 that's in T6 (heat treated) will snap before bending far. If you anneal it to T0 (softest state) then it's pretty plastic and will over time revert to a T4 condition (normalization over time)

If it's something like 6082 then it's pretty flexable and in T0 condition can even be shaped in press tools without fracturing
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[Pete.]

Aluminium is more likely to crack if bent very hot than cold as it passes through a brittle stage just before it gets to melting temp. Anneal it, let it cool, bend it.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Pete.]

Also the direction you bend rolled plate/sheet in makes a huge difference. It's much more ductile in the direction it's been rolled so if you can see the grain always bend it in that direction or it'll surface-tear on the outside of the bend.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[ZRX61]

Pointless taking notice of any answers until you post what grade of Al you have.
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[Ribenapigeon]

[c_dug]

What's the bracket going to hold?

I'd probably just have folded it by now and not worried too much about the stressing, I needed knock up some quick brackets at work for a broken exhibit about 2 years ago now, they were on my "to do properly" list for ages, but they've held fine despite the stress/tearing on the outer edge of the bend.
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[Ribenapigeon]

[........................]

Can't you just buy a ready made steel bracket?

[Ribenapigeon]

[........................]

[kramdra]

Aluminuim alloys seem more complex than this. The annealed area will have a random distribution of the alloy elements, after annealing they will move in solid solution and bunch together, creating hard, brittle areas. To do it properly requires heat treatment, holding it at temperature for some time.

Interesting subject I will be reading more about - relevant for welding ali. You will probably get away with it for most things but I would be very sceptical about using as a top box/pannier mount. 4mm aluminium wont be man enough for the sort of abuse mine gets.

[Ribenapigeon]

[stinkwheel]

You will geat away with one bend in 4mm bar. Bend it directly to the correct position first time.

Giving it a few heating/cooling cycles AFTER bending it will massively releive the internal stresses. For most aluminium, giving it an hour in your kitchen oven set to its maximum temperature then allowing ti to cool 'till it can be safely handled will work wonders.
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