Bending 1/4" 6061

[hmc710]

Hi All,
Bent a piece of 6061 aluminum in the press brake and it fractured at the bend. Then heated a piece up with a propane torch and bent it, but definately could see stress cracks on the outside of the bend. 6061 is suppposed to be very workable. Is there a nominal temp that would allow us to bend 1/4" 6061 without getting any stress cracks? We are using a 1/4" radius top die and the bottom die has 2-1/2" spread and I am easing the brake down to perform the bend.
Thanks,
HMC710

500 degs didn't work, snapped it right in half.... 6061 is T651, will review my alcoa sheets...Boy, did I pick the wrong temper

[mc-motorsports]

If I remember right, heat it to 800* and let it air cool if you can't do it in a controlled enviroment. Otherwise, annealing should be done at 775 F for 2 to 3 hours followed by controlled cooling at 50 f per hour down to 500 F, then air cool.

Or use 3003 which is used for frames and such where the material goes though a bender.

6061 is cheaper, has better corrosion resistance, overall appearance and is more easily welded as I remember. But if you want to cold form 6061, you need to anneal it first. T4 or T6 will tend to crack.
The other thing is your probably getting cracks starting at the edge? Make sure the edges have smooth cuts, or polish them up a bit and put a slight radius on the corners where you'll be bending. Might help just that little bit that matters.

[mc-motorsports]

Originally Posted by hmc710 500 degs didn't work, snapped it right in half.... 6061 is T651, will review my alcoa sheets...Boy, did I pick the wrong temper

You didn't quench it, did you?

[mactec54]

Hi hmc710

It sounds like you have cast 6061 plate which won't bend very well without cracking no matter what you do to it

[Dorsal]

Bending 6061 at 1T radius? You won't get success unless that material has been annealed to dead-soft, and maybe not then. Think of it this way, the radius on the inside of the bend is 1/4", on the outside is 1/2", so around the inside of the circle there will be (2 X pi X r, or) 1.5708" of material while around the outside there needs to be 3.1416" of material. Presuming you are trying to make a 90° bend, the ID has 0.3927" and the OD has 0.7854" of material - You have exceeded the limits of Poisson's ratio, and the limits of plastic deformation of aluminum.
If your corner needs to be that tight, weld the 2 plates together at your angle.

[RMDMARINE]

HMC710

1) Are you using true flat bar or sheared material? If sheared you have to bend it across the grain, the grain runs the long lenght of the plate, for instance a 4x8 sheet the grain runs the 8ft direction. If true bar like 1/4x 3 you can only bend it across the 3in side.

2) The way you anneal the 6061-t6 is to use an oxy-acet torch with no oxy turned on, with the acet turned on an lit smoke the back of the bend area, then turn the oxy on to a long blue center flame and heat the bend area till the acet is burned off, do not go to a oxidizing flame (short blue cone). You now have the aluminum at its annealed state of 800degs, you can now bend it (while it is hot) but slowly. If it cracks you may have to increase the punch radius.
I bend 6061-t6 and 7075-t6 all day long with a 3/16 radius punch, I might loose 1 in 50 where I cheated and did not burn off all the acet in the bend area. One pointer, do not get the material to hot or it will crack just like it was cold.

RMD

[RogerRetro]

6061-0 is fully annealed, and if you want a quality product with engineered integrity, you will use 6061-0 and heat treat to the desired/required temper after bending.

Regards,
Roger

Originally Posted by hmc710 Hi All, Bent a piece of 6061 aluminum in the press brake and it fractured at the bend. Then heated a piece up with a propane torch and bent it, but definately could see stress cracks on the outside of the bend. 6061 is suppposed to be very workable. Is there a nominal temp that would allow us to bend 1/4" 6061 without getting any stress cracks? We are using a 1/4" radius top die and the bottom die has 2-1/2" spread and I am easing the brake down to perform the bend. Thanks, HMC710 500 degs didn't work, snapped it right in half.... 6061 is T651, will review my alcoa sheets...Boy, did I pick the wrong temper

[hmc710]

Thanks for all the info, great stuff. I did not know about the going with the grain on plate and tube. I ended up putting the plate in the oven and heating up to 880 with a soak and slow cool which should have been a full anneal. Bent the plate slowly with no problems. I didn't have enough spare material to try the torch method.