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Greg Parent
08-17-2010, 11:44 AM
Hello all,
Is there a trick to bending 0.0625" thick aluminum plate without it cracking? I have a piece that is 5.5" long and 3.75" wide. I need to bend a 0.75" wide by 5.5" long tab to 45 degrees on each side of the 3.75" dimension. The plate is cracking every time I do this. Alloy and temper of the material is unknown. Would heating it up reduce its tendancy to crack? I have avoided doing this test as one side of the plate is painted.
Thanks for any input you may have.
Greg

Blackadder
08-17-2010, 11:58 AM
anneal it its the only way


put some household soap on it and heat till the soap turns brown then let it cool


Stuart

Mike P
08-17-2010, 11:59 AM
There is a definate grain to sheet goods. Look closely at the surface, you'll see the grain.

The best way to bend is perpendicular to the grain, so the grain lines cross the bend. In your case, you'd want the grain to run the 3.75" direction, so you can bend the edges against the grain.


The other thing to look at is the radius of the bend. For most aluminum sheet, the inside radius of the bend should at least be equal to the sheet thickness. If the alloy is higher strength and/or heat treated, the radius goes up to double the thickness (or more). Bending along the grain makes these radii even more important. You may find that you have to go to a 1/4" radius to keep from cracking.

Are you bending the sheet with sharp cornered vise jaws? If so, swap in a piece of wood with a slight radius on the corner and see how that works.

MuellerNick
08-17-2010, 11:59 AM
It depends on the alloy! If it is painted (not by you) on one side and is not a factory made part, then chances are very high that it is easy to bend.
But! That depends on your bending radius and also it makes a difference wether you bend lengthwise to the rolling direction (cracks) or not.

I'm too lazy to convert those odd inches to reasonable millimeters.


Nick

PaulT
08-17-2010, 12:00 PM
Its probably 6061 or a similar alloy that has been heat treated. Heating it to anneal it will definitely make it bend more easily, but the problem is you have to get it pretty hot, 700 to 800 degrees F or so, if you do have a way to get it that hot the paint will have to come off first. The panel won't be as strong after this annealing.

Paul T.
www.power-t.com

gary350
08-17-2010, 12:17 PM
Aluminum melts at 659.6 degree F or 660 degrees. Do not heat it hotter than about 600 deg.

Boiling point is 2327 degrees F.

Pouring temperature in a foundry is about 1800 degrees F.

Aluminum will not vaporize but aluminum dust is easily ignited and will explode.

Aluminum reacts with HCl, H2SO4, KOH, NaOH.

Willy
08-17-2010, 12:27 PM
Aluminum melts at 659.6 degree F or 660 degrees. Do not heat it hotter than about 600 deg.

Boiling point is 2327 degrees F.

Pouring temperature in a foundry is about 1800 degrees F.

Aluminum will not vaporize but aluminum dust is easily ignited and will explode.

Aluminum reacts with HCl, H2SO4, KOH, NaOH.



That would be 660 Celsius, or about 1220 F.

leesr
08-17-2010, 12:38 PM
basicly what all has said dito

the min bend radii is approx. 1 to 1-1/2 x the thickness of the sheet.

direction of grain flow is important.
if it cracks increase the bend radii
if it still cracks purchase aluminum that is in the annealed condition.
then bend it.
then have it aged at a heat treat facility.(minimum charge)
clean it
then paint it.

leesr

Thruthefence
08-17-2010, 12:40 PM
If it's one of the stronger alloys, eg 2024, heating it up may cause a phenomena called 'inter granular corrosion'. The heat causes the alloyed metals to precipitate out within the structure, and it will eventually exfoliate, actually shed flakes of corroded aluminum. The bending radius is the trick.

here's a link to the sheetmetal section of an aircraft repair manual:

http://www.lotus-europa.com/manuals/misc/aircraft_manual/Chapter%2004.pdf

scroll down to pg 14-15 & look for 'table 4-6' . This stuff is, of course related to aircraft repair, but it's good information.

gary350
08-17-2010, 01:07 PM
That would be 660 Celsius, or about 1220 F.


I looked this up in the Merck Index it says, melting point 660 degree, boiling point 2327 degrees. Page 44 Ninth Edition.
I assumed it was F because it does not say F or C.

This link says, mp 660 deg C 1220 deg F.

http://en.wikipedia.org/wiki/Aluminium

Another link says 659.6 deg.

KINGWELD
08-17-2010, 02:14 PM
The OP might want to consider getting some aluminum of known alloy.
Some 5052 or 3003 will bend with little problems.
3003 is used in heating and A/C applications.
Something to think about. Good luck.:)

Rich Carlstedt
08-17-2010, 02:52 PM
Do the soap trick
or
Use a magic marker and lay down an inkline on the bend
or
Use a candle and smoke the bend area.

If you heat the bend area with a torch, the aluminum will not melt.
You heat until the smoked area or the markers ink starts to disappear.( This is the annealing temperature )
Let cool and then bend
It occurs around 500 degrees, and some paints can withstand such a temp !
you may also want to use an electric stove burner.

I would mark the bare side with a line of ink
Lay a steel plate on either side of the line about 1/4 to 3/8" apart and then
go down the 'slot" with a focused MAPP or acetylene torch flame.
This should happen fairly quickly with little effect on the rest of the piece

leesr
08-17-2010, 04:45 PM
The OP might want to consider getting some aluminum of known alloy.
Some 5052 or 3003 will bend with little problems.
3003 is used in heating and A/C applications.
Something to think about. Good luck.:)

This Kingweld has the right Idea.

PaulT
08-17-2010, 06:19 PM
I say Rich wins.

Your Old Dog
08-17-2010, 06:54 PM
You got one of these handy in your shop?

http://www.youtube.com/watch?v=ZhGHALB4_hQ

Greg Parent
08-23-2010, 09:05 AM
Success...I took the aluminum plate outside and heated it up with a propane torch. Took it back in after it had cooled and put it in the bending jig. It bent without cracking....Yay!
I sanded the charred paint off and shot it with a coat of zinc chromate primer and a finishing coat of gloss white. Looks great and the customer is happy.
Thanks for the tips.