The bending radius is also termed as center-line radius or CLR. It is the radius of the middle point of a pipe. It can be described as the distance between the center of curvature to the central axis of the pipe. When referring to the radius of a die, we are referring to the center-line radius (CLR) results from bending.
The bending radius of a pipe depends upon the desired shape. Considering the bending radius of a pipe before the bending process has initiated can help you achieve precise and most accurate bending results.
If you need larger radius bends then you should consider push or roll bending. For roll bending, the minimum roll bending radius is 7D, the bending can also work with a radius within &D that are tighter of course. But it also depends upon the thickness of the pipe wall and its material properties, so for effective results, you should always stick to the described data.
In a minimum roll bending radius there is no maximum limit to the radius, but to leave the tube straight that is itself an infinite bending radius. You can also ask your tube supplier for the types of tooling they provide and if they have anything regarding the tube diameter you intend to work with for designing your components.
Multiple bending radius as the name suggests it allows you to create more than one end at the same time. Regular benders are termed as single stack, as they can only control a single set of tooling. Using such single-stack benders is quite practical. You can remove a tube, change the tooling for another radius, and then make a new bend.
But many applications require two completely different bending radii. In this case you must use bending machines compatible with producing multiple radii.
These bending machines can be two stacks, three-stack, or also multiple stacks containing many toolsets for carrying out several operations.