An approximate model to calculate foldover and strains during cold upsetting of cylinders part 1: Formulation and evaluation of the foldover model

In this paper, a new approximate model to calculate foldover of a cylinder undergoing nonuniform compression test (simple upsetting) is presented. The model is formulated using constant-volume equations and workpiece geometry. In addition to foldover, the model can be used to calculate equatorial-axial strains. This eliminates the need for inscribing grids (when determining forming-limit diagrams) on the cylinder’s free surface to find these strains. Combined with friction-calibration curves (prepared using finite-element analysis) that relate foldover to friction, the model enables one to estimate the friction coefficient. This eliminates the need for a separate test (e.g., the ring test) to determine friction or evaluate type of lubrication to be used. When compared to finite-element results and experiments, the new model showed excellent results in calculating foldover, strains, and friction coefficient.