20th International Forgemasters Meeting - IFM 2017

Upsetting is a basic operation of greatest importance, which is commonly used in heavy forging process. Slowness in research on upsetting impeded the development of technologies for heavy forgings making. Upsetting deformation is determined by the billet’s internal velocity fields (or displacement fields), therefore, the key to the research on the upsetting deformation is to get its true velocity field (or displacement field). To that end, variational principles for plastic mechanics was employed to study upsetting. Based on the upsetting deformation’s fundamental rules that were achieved from experiments and shop-floor production, kinematically permissible velocity fields were assumed and hence, the strain rate fields were obtained. Finally, the first variational principle for rigid-plastic materials was used to acquire the mathematical expression of the true velocity field. To verify their correctness, investigations on upsetting cases with end face friction factors of 0, 0.25, 0.5 and 0.75 were carried out. The calculations show reasonable results. Further comparisons between the analytical results and numerically simulated results indicate they agree well with each other. The conclusion can be drawn that the mathematical expressions achieved for the true velocity fields of upsetting are correct. The true velocity filed for ingot upsetting was established to analyze the Dead Metal Zones (DMZ) during ingot upsetting, which provides reliable reference for heavy forging makings. Keywords: upsetting; rigid-plastic materials; theories of plasticity; variational principles