Forming 1/4 CRS

[Chris@PREBOLA]

Hey guys new to the fourm aND SORTA NEW TO TOOL MAKING AS WELL WITH ONLY ABOUT 4 YEARS ON THE JOB I'm also the 2nd shift forman at the small company I work for

I'm Having some truble forming a 16 in long peice of 1/4 x4" CRS. We usuly don't form stuff this big and I'm not used to it I'm Having a lot of truble Getting the metal to form How I want and stay there not spring opean as it is.

well Heres what going on the peices of crs need to be formed 180 degrees into a U shape with a 2.250 Radius on the inside +.020 -.00000

We do almost evrthing in a hury and all I could scab togheter quick was a big Block of 4142 which I bored to 5.010 with the center line of the bore 3/4 of an inch into the block so that theres flats to form the part strait the upstaris of the die is nuthing more the Bar stock turned to 4.500 with the sides relived to keep the part from getting stuck .

I'm running it in a very old Fly wheel type Wisconisin Press Brake 80 tons when I hit ti it comes down and forms Great everything in spec But when I bring the ram up it springs out at least 4 inches at the top I've never had theses kind of issiues with the sheetmetal parts I normaly work with. Right now weve been hitting them this way then flatting them in a second OP but I wanna do it in One hit

Sory for such a long Question On my first post

Thanks for any help Chris

[Dukerc51]

http://www.polyprod.com/diethane.html

Check this out. They work very well.

[JKN]

Trying to bend 1/4" crs myself at 90 degrees but the radius moves away from the punch and will not hold the intended radius and then cracks unless I take a torch to the material and heat it to cherry red.
Not an ideal solution, I emailed that polyprod.com site but no response as to the correct die to purchase from them.
I guess they do not want my money.

[Dukerc51]

Trying to bend 1/4" crs myself at 90 degrees but the radius moves away from the punch and will not hold the intended radius and then cracks unless I take a torch to the material and heat it to cherry red.
Not an ideal solution, I emailed that polyprod.com site but no response as to the correct die to purchase from them.
I guess they do not want my money.

what die size are you using??

[JKN]

4" die, the cracking begins at around 45 degrees if i do not heat the steel.

[Geof]

Trying to bend 1/4" crs myself at 90 degrees but the radius moves away from the punch and will not hold the intended radius and then cracks unless I take a torch to the material and heat it to cherry red.
Not an ideal solution, I emailed that polyprod.com site but no response as to the correct die to purchase from them.
I guess they do not want my money.

The grain structure in cold rolled steel is elongated along the length of the bar, in other words the direction of the rolling and the material is work hardened to a small extent and has a lot of internal stresses.

When you bend across the bar the bend line is 90 degrees to the elongated crystals and you can get a very tight radius without cracking, but you will I think always get considerable springback so you have to overbend.

If you try a similar radius bend along the bar so the bend line is parallel to the elongated crystals you will nearly always get cracking.

One solution is to normalize the cold rolled or use hot rolled material but if you need the nice finish and dimensional precision of cold rolled always make sure the bend is across the the bar and design the die to overbend; which is why the urethane bottom dies are so useful.