Novel Billet Design for Co-extrusion of Bi-metallic Shapes and Tubes

Novel billet design was introduced in an effort to better control material flow during the co-extrusion of bi-metallic shapes and tubes. In order to minimize the amount of material that is extruded “out of geometrical tolerance” (measured by the interface location) as a result of non-concurrent material flow, the core length in the initial billet is shortened. Extrusion was simulated using DEFORM 2D™ finite element modeling (FEM) software and confirmed by actual extrusion experiments on an industrial press. Results for a specific billet geometry extruded using a selected extrusion ratio for plain carbon/stainless steel tubes are presented. It has been shown that by reducing the core length in the initial billet by approximately 10% - 20%, concurrent material flow is promoted and the amount of out of tolerance material is minimized. The presented innovation was first developed for solid bi-metallic profiles made from different aluminum alloys and then applied to bi-metallic ferrous tubes showing general application of the proposed invention.