Quite often, the designer of a cold forging process has to bear in mind so many small details that some other really important ones, that could compromise the whole project, can be inadvertently overlooked. We have sometimes noticed this in complex extrusion dies where the designer has forgotten to include a back relief after the extrusion.
If reduction is performed without a reduction ring, then there will be too much friction surface between the material and the die. We must prevent this situation because, due to the pressures and frictions involved, the material will tend to grasp and glue to the internal surface of the extrusion die and this will consequently crack. If the reduction diameter is open few microns, the friction surface will be considerably reduced and the calibrating zone will have a much longer span life. About 2 mm length should be enough.
This we call the reduction ring of an extrusion die.