Mimimum bend radius for die formed steel

[switchguy]

I have a 3/8" by 1 1/4" 1018 steel bar that has holes punched, sheared to length and is then bent in a forming die. The inside radius is 1/2". A hydraulic press is used and the bending operation is much quicker than a typical press break. We are loosing a number of pieces from each stick as the bar ruptures in the bend. I am looking for recommendations on mimimum bend radius for this type of application. Would prefer not to go the "trial and error" route as the die set must be annealed, modified and then re-heat treated. Any suggestions would be greatly appreciated.

 

[lifttrucks]

What is the inside angle of the bend? 90 degrees?

 

[switchguy]

Inside angle is 90 degrees, my apologies

 

[racookpe1978]

How many are cracking (per 100 bent?)

What is the maximum bend you can use without re-designing the gadget? (I understand the cracks are on the outside of the bend. True? Are there any failures of compression/waviness on the inside curve?)

Does the "bend" carry stress or is this just a "locator" piece for the holes?

 

[switchguy]

Failure rate is 20 to 40 % depending on the raw material lot. Want to keep inside radius as tight as possible but could go to 2t or 2 1/2t if necessary. Parts arecompletely failing, i.e. broken in two. The holes fix one leg of the part. The other leg acts as a stop and does see some load (approx 150 lb on a 3" leg)

 

[mcgyvr]

If you can accept up to 2t or 2 1/2t I'd simply go with that first.. A larger bend radius will def. help. How about changing to a different alloy..

 

[lifttrucks]

As mchyvr said - a different raw material may be able to accept the 1/2" radius. For sharp bends, 1018 requires stress relieving.

 

[tr1ntx]

How long have these failures been occurring?

You say the failure rate varies by lot, do the different lots come from the same supplier?

I don't know that you necessarily need to switch to a different grade, the problem may be the "temper" of the material. (I think temper would still apply to 3/8" bar, though it's generally referenced with sheet.)

Number 2 temper (or "half hard") is supposed to be able to bend 90 degrees without cracking. No. 3 (or "quarter hard") should go flat on itself (180 deg).

Another possibility for the problem initial quality of the steel to begin with. We used to have this problem with steels from anywhere except Japan and Korea. Even the American stuff would crack sometimes, though not as bad as the cheapest imports. If I remember right, the American steel from Nucor had this problem more than others. (That is a big IF, I may have that completely backwards.)

I assume your purchaser is sourcing this from the cheapest possible, so I will opine that that is the root of the problem. You're probably getting Chinese or Romanian or Russian crap steel. Evaluate the retooling costs vs. the material savings.

If you can live with 2t, that should work. The 1.33t that you currently have might be a little aggressive for 3/8" mat'l, except that which is annealed or of sufficiently high quality to allow such bending. I forget the cutoff point of when 1 x thickness is too aggressive for general grade steel, I've seen a lot of stuff thicker than 1/4" be at 1.5t, then again I've seen 3/4" and 1" bent like you do in a die to less than 1 x thickness, but it wasn't "just call 'em up and get the cheapest we can get" steel either.

 

[tr1ntx]

Oops! left something out:

"Another possibility for the problem MAY BE THE initial quality of the steel to begin with."

 

[rb1957]

apologies in advance, i havn't read all the posts ...

what about adding the holes after you bend the bar ?

pervious post mentions mat'l strength ... do you need to form the bar in it's final HT ? maybe form a normalised bar and heat treat to required strength.

 

[ornerynorsk]

1018 has come to mean junk steel, in my opinion. It is not the material it used to be 30 years ago. Much of it is being sourced "offshore" and has questionable certs, at best, and is coming in half hard or worse. I've had the stuff rupture at nearly 4T radius, particulalrly once you're greater than 3/16 thickness.

As other posters have mentioned, a larger radius will be required. If you have some room to play with the mechanical props, M1020HR, A36 or Grade 50 HSLA will give much better forming results.

 

[TJOrlowski]

Are you forming this part hard-way or easy-way? If you're forming this easy-way (short-side of the bar in the plane of bending [the part stands 1-1/4" off the floor]), then anyone with a 1" die should be able to roll form your 1/2" radius.

As others have said, depending on the quality of your material, it may need to be annealed or hot-formed, then heat treated after forming.

-TJ Orlowski