When you start to bend thin wall, high strength tube in small radi the whole machine gets a lot more complex. Generally you will have some sort of mandrel that is inserted into the tube to prevent the collapse of the tube wall. Sometimes it is just one piece that is cut off an an angle and then generously radiused and polished, this is positioned so that it is just in line with the begining of the bend radius of the bend die and it wipes the inside of the tube to keep the outside wall from collapsing in. If the bend radius is real small say 2 x the tube diameter you may use a "ball mandrel" which looks like a number of polished balls that are connected together and feed into the tube, they are located such that as the tube is bent the balls go partially around the bend die so they wipe both the inside and outside wall to keep the wrinkles out. And if you are going to go with really thin wall, .020 say, and high strength material, 625 inconel say, you are then going to have a pusher which grips the tube behind the bend clamp and pushes the tube into the bend as the wiper shoe bends the tube around the die. This actually move metal into the outside of the bent tube and prevents it from tearing. Of course all of this causes big friction so it takes big power to make it happen. All of the good machines are hydraulic powered.
Tube bending is as much art as science. What save us is that we are bending heavy wall tubing that does not have an extremely hight yeild strength and we bend at pretty large radii so we don't see any of these problems but when you get into the stuff that Bak189 is working on it gets a little more interesting.
Rex