Effects of Entry Porthole Shape on Extrusion Pressure and Dimensional Accuracy of Extruded Pipes at Hollow Die Extrusion

摘要

The effects of paper porthole on the extrusion pressure of rectangular extruded pipes are investigated using the extrusion test. The extrusion pressure of a circular taper porthole is lower than that of a straight porthole, while the extrusion pressure of the radial tape porthole is much lower. Because the areas of plastic deformation zone in the taper porthole and the welding chamber are increasing, the degree of circularity of the taper porthole worsens. However it is useful for the improvement of the circularity of the radial taper porthole with setting a longer mandrel, because the extrusion pressure is low in all porthole shapes tested and longer mandrels enable more accurate sizing of the inside diameter of a hollow.