Bending aluminium

[paul]

I need to bend some 2mm thick aluminium strips (40mm wide) through 90 degrees and as accurately as possible. I've never worked with this material before, does anyone have any tips for holding or heating or anything?

TIA

[dickdastardly40]

Make the total width the width of both the straight sections minus Q, where Q is 0.43 times the bend radius plus 1.482 times the thickness.

This takes into account the stretching of the material.

Failing that put the strip into the vice on the half way line and dress it over with a mallet, no heat required and dress up the edges to width.

Hope this helps

Al

[Smifffy]

...not really, but one thing to bear in mind is that Aluminium doesn't change colour and go orange/red until it's just about to melt. So do be careful if you heat it.

I had the pleasure of visting a Aluminium rolling plant in (I think!) Newport back in about 1982. We were warned never to touch the stuff for the reason above (it can be very very hot but not show it).

The place was very impressive, in came big aluminium Ingots (I think 8'x4'x2') and out went rolls of kitchen foil.

Now's here's an interesting question - Why is only one side of Aluminium (Kitchen) Foil shiny ?

I found out on this visit.....

[Smifffy]

.....errr, the "not really" relates to Paul's original question, not Al's response!

[havoc]

While that calculation can be used I would still leave some spare and file to size. From experience with a sheet metal workshop: if a bend needed to be somewhat correct, they started from such a formula and checked before running a series, changing lenghts if needed.

Just an educated guess: so they don't stick so hard together they tear before coming apart.

[mackintosh]

Aluminum comes in at least two grades as I remember one being half hard. This may need softening to prevent cracking. If you rub soap over the area to be softened at heat until the soap turns black then allow to cool this will give a malleable result. I once had to beat a dome in aluminum and used this method as the material work hardens.
Bob

[steam4ian]

G'day Paul

I use the soap marker described by Bob. Only difference is that I just put a streak of soap and bend while hot. If I have to heat again I put on another soap marker.

Regards
Ian

[SteveW]

Guys,

Another vote for the soap indicator.

The point I'd like to add was in response to bending it while hot. Yet again at school I was introduced to the terms hot and cold short. I later tested these to my cost on brass, turns out it's "hot short".

Huh?

Think of short crust pastry, it crumbles as distinct from the (as explained by my metalwork teacher) high tensile stuff they make Cornish pasties with (like they don't fall apart in your lunch box).

If you think about it if you heat steel to red heat you can deform it safely. However try to deform brass at red heat and it'll will break, you have to let it cool slowly to anneal correctly before to try to bend it.

I'm not sure where alloy is on this one but I bet the type of alloy will have a bearing on bending hot or cold.

[simonwass]

smifffy said:

Now's here's an interesting question - Why is only one side of Aluminium (Kitchen) Foil shiny ?
I found out on this visit.....

Is it because 2 polished rollers wouldnt grip the foil to pull it through? The dull roller is the driving one, polished one the pinch roller?

[dickdastardly40]

Guys,

I really think you are over egging this.

To make a simple 'L' shaped bracket in unknown ally, try a scrap first, bend it in a vice. If it bends easily (generally it will) don't worry about heat. I've made various bracketry, boxes, drip trays, boot lockers, rag bins, steps etc etc over the years and have never needed to heat it. I've even made a mock-up opium press. True I had a shear and brake to hand but it bent just as easily in the vice with a 3lb air cooled adjuster.

I don't wish to in any way denigrate the quality of any of the advice but I don't believe heat is warranted here. No disrespect is intended or implied.

Regards

Al

[chris vine]

Hi Al,

I think you are probably correct here. I have come across some alloys (and particularly some stainless steels) which will crack if you try to bend them hot. Whereas they will bend perfectly when cold.

Chris.

[circlip]

If it "rings" it's likely to crack, if it sounds dead it'll bend. Not all Brasses will succumb to annealing. Ian.

[stantheman]

I have just caught up with this thread, and was about to say (honestly) that while I spent nearly all my working life as a sheet metal worker the last piece of advice is spot on. If we ever picked up an odd piece of aluminium alloy sheet of an unknown grade I always, if was not too large, threw it on the floor. A bit drastic but if it made a loud ringning sound it was a good bet it was possible to crack it when bending. Normal everyday sheet should not require any heat at all to bend it. In fact heat was hardly ever used to normalise aluminium alloys if they were that hard.
Stantheman.