Influence of work hardening ratio of parent tube on undershooting phenomenon in cold tube extrusion

The influence of carbon steel work hardening ratio on the intensity of undershooting of outside diameter was investigated in the cold extrusion of carbon steel tube. Steel tubes with carbon contents ranging from ∼0 to 1·0 wt-% were subjected to cold extrusion through a die and the intensity of undershooting of attaining the outside diameter was measured to evaluate the influence of the work hardening ratio. As an index of work hardening ratio, the so called n value was determined for each parent material using a stress–strain curve drawn by carrying out a tensile test. The n value decreases with increasing carbon content and the higher the n value, the higher is the intensity of undershooting. Elastic–plastic finite element analysis was carried out to simulate the experimental data and also, to design an appropriate die geometry for suppressing the undershooting phenomenon. The solution was the adoption of a double taper die for the suppression of the undershooting phenomenon due to the work hardening ratio.