Witch method is better for the metal too keep itīs grain structure if you need to bend it

Cold or semi warm?Why?

 

We had a mandrel bender at our shop and whether it was stainless, brass or aluminum, they were always bent cold. I also worked with Curt LeDuc for a while and he had a non-mandrel type bender and he bent all his chrome moly cold also.

 

Ok

iīm thinking about stength because the grain structure/molecules/atoms in iron would shift and go out of balance when bent cold?

 

What are you bending? We bend stuff hot(if its thick) and cold if it can be done without heat, Structural or not. I build service rigs for a living and TONS of hot bends are done, on individual given parts. It depends on what you are trying to achieve, structurally. Sometimes its stronger to do a grooved 3 pass(or so) with a cap, but theres no need for that on a car...

It also depends on what your trying to have visually for a finished product.

-Matt

 

For thick items it is unavoidable to heat it up to bend it. For automotive, and even off-road racing, everything can be done cold. Heating up metal changes the structure of the molecules and if you don't get it back to room temperature in the proper manner, strength is compromised.

 

iīm going to build a roll cage for offroad 4x4 rock crawler and the cage needs to handle 7x its weight

Alot of the guys are using milde steel 4" and quite offen the cages get bent

I will use 4340 or 4310 cold rolled and need to bend it bur havent decided in with or thickness but iīm trying to know if itīs better to bend it cold,room temprature or a given heat vs material thickness ect..

It will see alot of rollovers

www.heimska.com/video/ttt.wmv

 

Unless your putting the metal in an extremley high stress enviornment, heating them wont really do much for compromising strength. Like cvman said, if its cooled at room temperature, it should be fine, but when you dunk it in water or cool it too fast, it will collide the molecules and throw them all to the outer part of the material, making the piece harder, but very brittle due to the lack of "inner" molecules

 

it would be cooled down "normaly" as in room temp

 

That was a cool video! I saw an Icelandic hillclimb video that almost no one made it to the top

 

I use 1 3/4" DOM tubing. ERW tubing is not as strong.

I bought a manual mandrel bend tool from www.tricktools.com

Very nice and easy to use

 

from my experiences and alot of my buddies who are big into the 4x4 world, Mild steel is fine for virtually all off road applications, as long as you design and brace your rig right you wont have any problems. The majority of failures occur from poor design or shotty workmanship. The majority of chassis never need to get bigger than 2in. Most everybody runs 1.75 mild steel, im not entirely sure about the wall but i think the most common is around 0.185 but dont quote me.

check out www.whiteknight.ca ive got a few friends overthere and some of those canadians build some sick rigs, plus theres alot of information.

www.pirate4x4.com is another great one lots of info.


Cold bending doesnt effect these type of materials enough to worry about in your application. -john

 

I would be more worried about the 'cage breaking next to the welds, especially if its chrome moly, 4340, 4310. When you bend it cold, it will elongate the grain of the material in the direction it was stretched. When you heat it back up and properly cool it, you're trying to normalize the grain structure. Well, when you weld near that bend, all bets are off, because you just re-heated the metal. If you're really serious and don't want it to break or bend: bend it, weld it and then take the cage/chassis in somewhere to have it properly heat treated by specialists.

 

Mild steel is fine, and cheap, but you pay the price in weight. 4130 is the same weight as mild steel tubing, but twice as strong, so you can reduce wall thickness to reduce weight. Curt Leduc builds all of his race chassis out of 4130. He races desert (class 8) and CORR, and his sons race, too. I have seen the condition of the trucks coming back after the races, and they hold together real nice. He does not normalize after welding, and has no problem with cracks near the weld, and he beats the hell out of his trucks. I think not normalizing 4130 is fine for the off road world, but for aircraft and other critical parts I would recommend it, to be safe.

 

when bends are performed "cold", this is actually considered "cold work" which is a form of strain hardening. The material will show an increase in both yield and tensile strength, or become both harder and stronger, but ductility will decrease, it will become more brittle, when bending hollow tubing, the cross sectional area is what determines the % cold work, and cross sectional area should not change all that much, so the % cold work should be pretty low which means the material will gain slight strength and hardness but not much as well as become slightly more brittle but not anything that should be worried about