Upsetting of bi-metallic ring billets

This report examines the behaviour of bi-metallic components during the cold upsetting process. Each component consists of a solid inner cylinder around which is fitted a ring of a different material. In the first case experimental studies are conducted of a ring of mild steel C45E material surrounded by a softer C15E core. These tests are used to validate the finite-element models. The finite-element method is then used to extend the initial tests to a wider range of cylinder and ring geometries. It is also used to explore a second case where the materials are reversed to give a bi-metallic component with a stronger core. The principal objective is examine how contact between the inner cylinder and outer ring is maintained during the upsetting process. It is apparent that the geometries of the two component parts of the billet are the dominant factors affecting deformation, as the influence of changing the material has only a very small effect. With an initial height/outer diameter ratio of 1.5, contact at the cylinder/ring interface is maintained over the most of the initially contacting surfaces. A small cavity is formed when the inner/outer ring diameter reaches 0.6. Above this value the cavity will become larger, and at 0.8 the wall thickness is sufficiently thin to allow a double-barrel outer profile to develop with two cavities. With an initial height/outer diameter ratio of 1.0 or less, the formation of interfacial cavities is much less and demonstrates the viability of producing bi-metallic components in this way.