I thought this may help others who do sheet metal design but are not working directly with the people doing the bending.
This is very specific to your tools, but I have found some trends in our tooling that could help other out.
The bend radius of sheets tends to fall between 1.33 and 1.5 times the thickness.
1.33 x Thickness applies when the tools have excess power for the bend
1.5 x Thickness applies when the tools do not have excess power for the bend
I'm curius as to what others have found as practial numbers for manufacturing.
These values are a bit smallter than recomended by say the sheet metal articals in magazines like the fabricator. Very good articals on sheet metal there.
I have found that the actual achieved inside radius, if a punch radius was used that is less than the material thickness, then the actual achieved inside radius equals approximately 94% of the material thickness. So, for 1/4" thick material, if the punch radius used is R.031" or anything less than R1/4", the achieved radius is about .234375" or 15/64". That is just what we've found in house. This also requires using a k factor of .22.
Different tooling and application = totally different results. It's cool to see other situations.
we use a break machine for thickness 1/4" and thicker
and 10' folding machine for 10 gage and thinner
Our goal is to avoid cracking because we make seal welded tanks that go on trucks.
May I ask your aplication and tooling?
Mostly are involved with making baghouses, bin vents, clean air plenums, cyclones, tanks, hoppers, troughs for screw conveyors, structural steel, ladders, handrails, and anything that needs machining.
For tooling, we are currently using limited tooling. Only have one press brake and other than for really short bends we are basically limited to an R.031 punch. We are about to start looking at getting at least one new press brake, hopefully soon.
MITSUBISHI RX4020 Jet pierce, PHXS head, Diamond Path Technology, High Peak Piercing, cutting speeds of up to 1,970 ipm, cuts up to 1" material thicknesses.
DURMA BPF 2560 BRAKE: 80-ton, capable of bending up to 1" of material, lengths up to 8'
MCA/DAVI 2017 Four Roll: ability to roll plate up to 15mm thick. Minimum roll diameter: 8"
HURCO TMM 10 live tooling mill lathe
HURCO VMX50i CNC mill: coolant-through-spindle technology for preserved accuracy, conversational part probing allows hands-free part and inspection probing, and tool probing for more accurate measurements.
The bottom die in a Press Brake plays a bigger role in the outcome of your inside/outside radius.
I worked with a New Holland plant that used one radius, and just changed their bottom die to achieve their desired outside radius.
We typically model using an internal bend radius of 1T for all parts.
Parts are thickness of 2-10mm, using CR4 for plate 3mm and below and S275 for heavier plate.
Typically 8-10m parts will be short bends, but the 10mm will press out at more like 1.3-1.5 T non the less.
It is rare that the part is highly stressed, so as long as the overall finished dimentions hold tollerance (which they do) we do not have any real issues.
One of my previous employers did a lot of long pressed in line with the grain, in effect to form a box section of 8 or 10mm thickness. For that 20mm rad swan neck tooling was used along with high grade low-sulpher steel such as Domex 600.
Linked is an artical that includes a photo of our main folding machine.
For fun, I have always called sheet metal design "Origami engineering"