Die design for reducing tube outside diameter by cold pressing and mechanism of thinning and bending phenomenon

Numerical investigation by axisymmetric finite element analysis ( FEA) and experimental investigation were carried out on the excessive decrease in outside diameter occurring on a tube and a bar cold worked through a die by press. The mechanism through which excessive decrease in outside diameter appears was determined by FEA, and the cause of discrepancy between the die diameter and the outside diameter of cold worked tube was discussed. Throughout the course of this investigation, a peculiar phenomenon of bending was observed on the cold worked tubes, and further investigation was carried out on the dominating parameter of this bending phenomenon. Eccentricity, i.e. non-uniformity of wall thickness in the cross-section of tube or failure in concentricity between the circles defining outside and inside surfaces of parent tube, is the parameter that most influences the occurrence of bending phenomenon. Discussion and estimation were given on the mechanism through which this peculiar bending occurred.