Mechanism and Suppression of Excessive Decrease in Outside Diameter and Bending Phenomenon in Cold-Reduction of Steel Tube Diameter

Abstract

A numerical investigation by axi-symmetric finite element analysis (FEA) and an experimental investigation were carried out on the excessive decrease in the outside diameter of a tube and a bar that are cold-extruded through a die. The mechanism through which the excessive decrease in the outside diameter appears was made clear by FEA, and the discrepancy between the die diameter and the outside diameter of the extruded tube is quantitatively discussed. Throughout the course of this investigation, a peculiar phenomenon of bending was observed in the extruded tubes, and further investigation was carried out on the dominating parameter of this phenomenon. Eccentricity, i.e., the non-uniformity of the wall thickness in the cross section of the tube or the failure in realizing concentricity between the circles defining the outside and inside surfaces of the parent tube, is the parameter which most influenced the occurrence of the bending phenomenon. A new die design was proposed for the suppression of the bending phenomenon that occurred in the cold extrusion of a tube through a die. A numerical investigation by FEA and an experiment were carried out to determine the optimum die geometry for the suppression of the bending phenomenon.