Bending

I need to make another bracket for my trailer. About 18" long, x2" wide, x 1/4" thick, with two 80 degree bends in it, and two 1/2" holes drilled, one
on each end. The bends will give it a final X shape.
I had one of these fail. They are the brackets that hold my drop down ramps on the back of my trailer.
Question: Do I bend them cold, or heat them and then bend them?
Explain your answer, please.
Steve
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Steve B wrote:

You bend them cold if you have the equipment to do so (big press brake or something) else you heat them and bend them by trial and error to get them right. Cold is stronger because you don't get grain growth from heating, but a trailer hitch should be overdesigned to the point where the slight difference between cold/hot is insignificant. If you had one fail, it likely wasn't designed heavily enough, it probably wasn't in the way you fabricated it.
That's all my opinion, guaranteed to be worth at least as much as what you paid for it. I dislike giving design opinions on something critical - please be aware that no matter what anyone on a newsgroup says, YOU are responsible for this design, and try to be at least a bit conservative.
Grant
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Sorry you missed it. They have no part of the hitch, but are only the brackets that hold the ramps upright during transit.
Steve
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Steve B wrote:

It depends on how sharp the bend is. If it sharp, you need to warm it up, because the grain is getting cornier the more you stress it. Exception is forging. Just bend some rod and look at the grain on the outside to see what hapens on a sharp bend.
Nick
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Nick sez:
"It depends on how sharp the bend is. If it sharp, you need to warm it up,

I suppose the German/English translation from "grain" is corn, huh ? Maybe you shoulda said "wheatier", or "oatsier", maybe "barleyier". Just kidding, Nick! At least you got in an intelligent comment before Iggy jumped in a took off with the thread.
Bob Swinney

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Robert Swinney wrote:

I think I didn't want to write it that way. New try: It gets grainy. On the surface you will see a grainy structure and that's where a lot of small cracks just have started.
Nick
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I'd heat and bend. Depending on loads, a cold bend might be perfectly appropriate, but you indicated that failure has already occured.
Bending cold will stretch the grain structure and set up stress that will add to the stresses that previously failed the part. Bending at red heat will minimise the stress and grain stretching.
Wes S
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I could do it either way. A couple of questions: -Did you make the failed part? If so, how did you do that one? -Was a sharp tool used in that bending process---- one that might have left a cold shut? Were the bends inspected and any cold shuts completely filed away? -What was the original material? Was it, for example, a material the could work harden with the pounding it would receive in its application? -If it was bent hot, was it allowed to slow cool, or was it quenched to hurry the cooling process?
I think that addressing the issues above is at least as important as whether you bend it hot or cold. Bending a real low carbon, simple steel won't do much to its structure, but you could anneal the bends if you wanted to make sure.
Pete Stanaitis --------------------------------
Steve B wrote:

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"Steve B" wrote: (clip) Question: Do I bend them cold, or heat them and then bend them? (clip) ^^^^^^^^^^^^^^^^^^^^^ That depends. What bending equipment do you have? What radius can you accept at the bends? Is your torch big enough to bring a piece like that to a nice cherry red?
Consider sawing part way through the metal, and bending it cold . Then fill in the vees that are formed, with welds.
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wrote:

A cogent response to "hot vs cold" would depend some on the material and its history. In practical terms, it also depends on what equipment you have available. I would bend it hot -- and then I would look at what failed and where, and reinforce the design accordingly so it wouldn't matter if the bend wasn't quite as strong as parent metal. Production designs are not always "best" but are usually lowest cost for acceptable function and reliabiity -- "acceptable" being defined as often by the beancounters as by the designers and fabricators. This is before the lawyers stick all the labels on that make any problem the fault of the user.
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Steve B wrote:

1/4" x 2" is easy work for a Hossfeld bender, You could even beef it up to 3/8 and still be able to pull it cold.
I'm a little confused how two 80 deg. bends get you an x shape? Did you miss the Z key?
Stuart
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I've been trying to figure that out as well. :)

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wrote:

picky, picky, picky.
Yeah, I guess I hit X instead of Z. Sorry.
Steve
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Only 1/4" - easy with my 20 ton press and handy bend.
I bent 1/4" x 10" without a thought.
Just a way from you. But mail isn't bad.
Martin Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
Steve B wrote:

-
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