The mandrel is the tool positioned inside the tube and is firmly anchored to the back of the machine with a stretch resistant rod during bending. The shank or body of the mandrel is the portion over which the tube is drawn and initially determines the quality and shape of the outside of the bend. On bends in tube likely to collapse (due to a high relationship between the O/D and wall thickness), it will be necessary to extend the support beyond the tangent point by use of ball segments mounted to the shank. The number of balls required is relative to the bend radius, the O/D to wall thickness ratio and the bend angle. The function of the balls is to internally support the shape of the tube and prevent flattening occurring after leaving the tangent point. If flattening is permitted to occur or if the support is inadequate, it is likely wrinkles will form on the inside of the bend.
There should be a mandrel retraction unit fitted to your machine. This will retract the mandrel balls from inside the tube at, or just before, the end of the bending cycle; usually 2-5 degrees depending on the type of mandrel in use and lubricant. This is sometimes referred to as anticipated mandrel retraction. Knowing this we have manufactured a lubricant that has been proven to reduce friction and lengthen tool life. To find out more about this lubricant for your application contact us.
Mandrels to suit many shapes and planes