Originally Posted by
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.
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.
An open mind is a virtue...so long as all the common sense has not leaked out.