Three-dimensional material flow analysis of asymmetric hollow extrusions

All tube manufacturing processes induce some degree of eccentricity, as a result of the particular extrusion technique, combined with imperfect control of the process parameters. An eccentric tube is identified when the difference between the maximum wall thickness minus the minimum thickness is greater than zero. This is a typical problem for higher melting point materials including Zr, Cu, Ti and Fe and their alloys, where porthole die arrangements cannot be used. The major causes of tube eccentricity in extrusion have been analyzed in the past, and conclusions based on the results for stainless steel tubing are available in the literature. An additional degree of complexity is introduced when the extrusion profile is hollow and asymmetric. To study the complex flow through these dies, the physical modeling technique has been implemented, with the objective to optimize homogeneous flow within the billet in front of the extrusion die, and to correct for extrudate curvature. This is accomplished by examining the impact of general parameters of direct extrusion through non-axisymmetric hollow dies.