Prediction of central bursting defects in rod extrusion process with upper bound analysis method

The prediction of central bursting defects in the rod extrusion process through conical dies using the upper bound analysis is investigated. A kinematically admissible velocity field, including the radial and angular velocity components, is proposed. A new criterion is presented to predict the occurrence of the central bursting defects. Parameter bobt, which represents the risk probability of cracking, is proposed. It is calculated using the shape of the boundary at the entrance by minimizing the total power dissipation during the extrusion process. When bobt is equal to or greater than bcr, central bursting occurs. Furthermore, the quantitative relationships between central bursting defects and process parameters (semi die angle, reduction in area and frictional factor) are studied. The results show that the central bursting defects are affected primarily by the reduction in area and the friction factor. The presented criterion is verified by comparing with the FEM simulation data and the results of the published paper.