We've had some problems when bending a part with the grain. They tend to crack quite badly, and we know that when we bend 90 degrees to the grain it won't crack. The question is, "is 90 degrees to the grain the best, or is 45 best"
I'm with you now. Are you cold bending the steel? Also, your radius could be too small for the bend when bending parallel to the grain. I haven't heard of a "best" way. I guess it depends on the method used. Here's a site that may be helpful;
90 deg. is best. You must be bending it pretty sharply to crack it "against" the grain (rolling) direction. You also may have some pretty "dirty" steel, chock full of non-metallic inclusions.
You could ask your steel supplier to try and provide you with heats with smaller grain size, low S and C, and with the Mn close to the mid-point or higher if the spec.
The material thickness vs the bend radius (as previously mentioned) can be an issue.
Someone else asked about this previously in one of the forums, maybe this one. This is known as the materials' anistropic properties, or the directional attributes of the material.
Thanks all. Here's some more info. As a standard practice we match the tool to the steel. Unless specified by our engineers. IE, if we are bending 1/4", we use a punch with a 1/4" radius and a die with a 2" opening. We use A36 structural for about everything. The engineering dept is considering adding grain direction orientation to some drawings. Is there a standard out there that they can refer to ?
A hydraulic press that operates slowly may give better results that a mechanical press that hits the metal fast and hard. We would use 1 1/2T or 2T for the bend radius on that thickness. Bedning 90 degrees to the grain will give the best results. I am not aware of any standards or codes that mention this though.
T refers to the metal thickness. It is the punch that controls. So, we would use a punch whose radius is 1.5T to 2T of the metal thickness ( 3/8" to 1/2" ). One more question - are you using bottoming dies or air-bending?
We also use 1 x mt for the punch, and 8 x mt for the die for air bending. Long story short, sometimes we get cracking in our steel from our usual vendor so we have to get our steel from another vendor. I am not sure if it has to do with a bad batch of bumpers or what it is.
(I am assuming we are talking about cracks along the full length of the bend, rather than just the ends of the bend)
We don't bend much flatbar length ways, but I would assume I'll see the same cracking. I neglected to mention that it's a36 plate, not flat bar. We have down draft burn tables not water. The cracks are usually on the ends of the bend. Typically, 1" or 1-1/2" long. (visible). We have to assume that the crack is full length. I've seen parts dropped 2 or 3 feet to the floor and split right in two.
The steel we get is all Canadian if that helps anyone.
