180 bend in 1 1/4 square steel bar stock

edwin dirnbeck · Jul 10, 2021

I need to make a U SHAPED PR0DUCT . Material is common 1 1/4 square a36 hot rolled steel bar stock.I cant find a chart that tells min bend radius, Plenty of info on round tube bending but not much on solid square stock, I would like to do this COLD. Thanks in advance for any help.Edwin Dirnbeck

Gordon Heaton · Jul 10, 2021

Well, Edwin, since nobody's commented I'll offer my opinion. A36 bends pretty easily and my wild guess is that you could go as tight as 4-5" radius without cracking. You would get serious deformation of the cross-section in the bend. How tight do you want to bend, and can you live with 'squished' appearance?

Conrad Hoffman · Jul 10, 2021

Cold? FTLOG why? If there's some volume I wonder if an induction heater could quickly get the area up to temp?

Garwood · Jul 10, 2021

The bend radius is determined by your tool design and tonnage.

I bend 3" of 1/2" A36 cold with about a .1" radius. Takes a couple hundred tons to really get that last .050" or so squashed in at the end.

I would not expect any cracks to form in A36.

Depending on the kind of press you are using, like say, a press brake, you really need to consider the point load on the ram and either oversize the machine or use some POS that's already swaybacked and ready for the scrap pile.

dian · Jul 10, 2021

i would think 4-5" inside diameter. how are you going to do it? bender?

Garwood · Jul 10, 2021

dian said:
i would think 4-5" inside diameter. how are you going to do it? bender?

There's about 10,000 kinds of machines that would fall under "Bender".

I think the way the OP has meshed "tubing" into his question he is probably thinking some kind of rotary draw process.

If I wanted to make a U-shaped product from 1.25" hot rolled square bar I'd be looking at a wiper style tool running in a large OBI style press.

fciron · Jul 10, 2021

I usually expect to be able to bend hot-rolled steel over on itself 180° without cracking. (That's bending perpendicular to the direction of rolling, if you try to bend flat or sheet parallel to the "grain" it's a different story.)

I'm pretty sure I've seen that bend spec in a description of A-36 steel, but I don't remember where.

edwin dirnbeck · Jul 10, 2021

Gordon Heaton said:
Well, Edwin, since nobody's commented I'll offer my opinion. A36 bends pretty easily and my wild guess is that you could go as tight as 4-5" radius without cracking. You would get serious deformation of the cross-section in the bend. How tight do you want to bend, and can you live with 'squished' appearance?

Gordon,Thank you for your reply. Squashed would not matter.But no cracking is allowed. Edwin Dirnbeck

edwin dirnbeck · Jul 10, 2021

Thanks to all who replied. I am looking at a rotary rebar bender that is able to bend 1 1/4 ROUND GRADE 60 REBAR. I THINK that A36 has around 36,000 psi yield strength and grade 60 rebar has around 60,000 psi. I know that 1 1/4 round is a lot easier to bend than 1 1/4 square. I am hopeing to get a full 180 degree bend with a 2 1/2 inch inside radius. Edwin Dirnbeck

Nmbmxer · Jul 10, 2021

Are area moment of inertia for a 1.25” sq is .203in4, a 1.25” round is .120in4, a ratio of 1.69. The ratio of ys is about 1.67 so I’d think it would be about the same force to bend the material.

edwin dirnbeck · Jul 11, 2021

Nmbmxer said:
Are area moment of inertia for a 1.25” sq is .203in4, a 1.25” round is .120in4, a ratio of 1.69. The ratio of ys is about 1.67 so I’d think it would be about the same force to bend the material.

Dear Nmbmxer, Thanks for the reply,I think. Edwin Dirnbeck

BT Fabrication · Jul 12, 2021

about 4X bend radius would be good to bend cold, it all depends on the CLR you go with and tensile and elasticity it has.
FYI it will deform a bit no matter what, and get some big hydraulics to bend it.

and 2.5" inside radius? that's a mandrel bender only. anything else will kink and crush flat, that's about a 3" CLR which is super tight and will most likely crack the tube from the stretching.

Gordon Heaton · Jul 12, 2021

BT Fabrication said:
. . .that's about a 3" CLR which is super tight and will most likely crack the tube from the stretching.

Its solid, not tube.

Ries · Jul 12, 2021

I have bent a fair amount of 1" square cold on the hossfeld bender, both A36 and 304 stainless. Usually not less than a 2" radius.

But if I was doing it in any quantity, I would do it hot, using, as mentioned above, an induction heater.
"hot" doesnt have to mean yellow heat- I had a friend who made stick shift levers for aftermarket trannys as a subcontractor, and he did em black hot- they got chrome plated afterwards, so they had to stay smooth and clean.
Heating the 1 1/4" up to even 500 to 800 degrees will make it a LOT easier to bend.
Its how the pros do it.

edwin dirnbeck · Jul 13, 2021

BT Fabrication said:
about 4X bend radius would be good to bend cold, it all depends on the CLR you go with and tensile and elasticity it has.
FYI it will deform a bit no matter what, and get some big hydraulics to bend it.

and 2.5" inside radius? that's a mandrel bender only. anything else will kink and crush flat, that's about a 3" CLR which is super tight and will most likely crack the tube from the stretching.

Thank you,but i am bending 1 1/4 square BAR STOCK

edwin dirnbeck · Jul 13, 2021

Ries said:
I have bent a fair amount of 1" square cold on the hossfeld bender, both A36 and 304 stainless. Usually not less than a 2" radius.

But if I was doing it in any quantity, I would do it hot, using, as mentioned above, an induction heater.
"hot" doesnt have to mean yellow heat- I had a friend who made stick shift levers for aftermarket trannys as a subcontractor, and he did em black hot- they got chrome plated afterwards, so they had to stay smooth and clean.
Heating the 1 1/4" up to even 500 to 800 degrees will make it a LOT easier to bend.
Its how the pros do it.

REIS,THANK YOU THANK YOU. i HAVE BEEN SEACHING FOR INFO ON "WARM" BENDING. It is amazing how much experience people on this site have and are willing to share. Edwin Dirnbeck

Ries · Jul 13, 2021

edwin dirnbeck said:
REIS,THANK YOU THANK YOU. i HAVE BEEN SEACHING FOR INFO ON "WARM" BENDING. It is amazing how much experience people on this site have and are willing to share. Edwin Dirnbeck

even the cheap chinese induction heaters on ebay have the ability to regulate time and amperage, and you can easily roll your own custom copper tubing coils, so you should be able to experiment and come up with the perfect time and amps to have just the heat you want.
Unfortunately, the friend who was the expert passed away some years ago.

dian · Jul 14, 2021

fciron said:
I usually expect to be able to bend hot-rolled steel over on itself 180° without cracking. (That's bending perpendicular to the direction of rolling, if you try to bend flat or sheet parallel to the "grain" it's a different story.)

I'm pretty sure I've seen that bend spec in a description of A-36 steel, but I don't remember where.

you make a very good point. hes bending paraller to rolling direction (i just barely managed to avoid "grain direction" as that controversial) which doesnt allow as tight a radius as perpendicular bending.

i always thought of this as pretty weird: paraller has higher tensile plasticity/elongation and fracture toughness, but cant be bend as much? doent really make sence intuitively.

Phil in Montana · Jul 14, 2021

It will bend easy, but the bar will not be sqr in the cross section of the bend, will probably deform a 1/8 inch top to bottom with a 4 inch rad, like a trapezoid...Phil

edwin dirnbeck · Jul 16, 2021

Phil in Montana said:
It will bend easy, but the bar will not be sqr in the cross section of the bend, will probably deform a 1/8 inch top to bottom with a 4 inch rad, like a trapezoid...Phil

Thank you, the deformation wont be a problem. Edwin Dirnbeck

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