Geometry factor and redundancy effects in extrusion of rod

The problem of relating effects of redundancy, or unnecessary macroshearing, to the geometry of the forming pass has been investigated for a number of metal-forming operations. Relatively simple expressions linking redundancy to geometry, via the relevant geometry factors, have been established for the drawing of rod and wire, among other processes. Because of the basic geometrical similarity with the extrusion of rod, these functional relationships are often used directly in this operation to predict the response of the material to changing pass design. The validity of this approach has become questionable in view of experimental and theoretical work undertaken recently. The present paper indicates that redundant shearing strains depend on the homogeneous strain rate and in consequence of that, a unique equation relating redundancy to geometry factors, otherwise applicable to drawing, may not be sufficient in the case of extrusion. To obtain a valid assessment of the level and pattern of redundant shears, it becomes necessary to consider the strain rate distribution in the processed material.