Influence of feed rate on damage development in hot ring rolling

As an incremental forming process of bulk metal, ring rolling provides a cost effective process route to manufacture seamless rings. Applications of ring rolling cover a wide range of products in aerospace, automotive and civil engineering industries. Under some process conditions, defects such as porosity can sometimes be found in hot rolled rings, which are manufactured from high alloyed steel ingots having macro segregations. For the reduction of the waste of material and improvement of product quality, a better understanding of the relations between segregation levels in the ingot, process parameters in the hot ring rolling and the occurrence of porosity is needed. In this research, a coupled thermo-mechanical multi-stage finite element model is used to simulate the hot ring rolling process including preform forging. The deformations, stresses and strains from the preforming steps are included as initial conditions for the rolling stage. Subroutines are implemented to represent the control algorithm for the motion of the rolls. A damage indicator is implemented in the material model. Simulations with different feed rate curves are carried out in order to see the influence on the occurrence of porosity. Hot ring rolling experiments in an industrial rolling mill are conducted to validate the numerical study. The results of simulation and experiment show good agreement.