Prediction and analysis of breakthrough extruding force based on a modified FE-model in large-scale extrusion process

Abstract

P91 steel is considered an appropriate material for high-quality pipes used in nuclear plant. In the extrusion process on 680-million-newton-tonnage forging and extruding machine to manufacture long seamless P91 pipes with large diameter and wall-thickness, the extruding force peak during the process will exceed 500 million newtons. For security consideration, prediction of extruding force, especially breakthrough force, must be accurate to avoid accidents like jamming. A modified finite element model has been developed to predict the extruding force in large-scale glass lubricant hot extrusion of P91 pipes and declare the relationship between the friction ratio and container temperature. On the basis of the practical extrusion results obtained on 360-million-newton-tonnage extruding machine and characteristics of large-scale extrusion, the billet cooling period and new viscous friction model on billet–container interface are added or established as the modification on the most significant sensitive factors. Using the modified model, the average temperature error after cooling is 3.23 °C and the maximum decrease of simulation results of breakthrough extruding force on 360-MN machine is 17 MN. The predicted results correspond to the decreasing tendency of the measured ones. The deviation between the simulated breakthrough extruding force and measured one on 680-MN machine is only 0.3%, which validates the accuracy of force-predicting model. This study may offer the basis for precise prediction for complete large-scale extrusion process and provide guidance to reduce the breakthrough force in the extrusion process.