EVOLUTION OF THE CHARGE WELDS: TOWARDS A NOVEL ANALYTICAL FORMULATION

Charge welds are, together with the seam welds, defects generated during the continuous extrusion of metallic materials. However, while the seam welds can exhibit the same resistance of the basic material if proper levels of pressure, contact time and temperature are applied, charge welds are always contained parts of the profile with lower mechanical properties. Indeed, at the end of each process stroke, the back end of the old billet material that completely fill the die starts to interact with the front side of the new billet loaded into the press that is usually contaminated by oxides, dust or lubricant thus producing a transition zone that extends to a variable length. It comes then clear that the length of the profile marked by the charge welds need to be scrapped and an accurate prediction and reduction of this portion become mandatory, not only for the final user of the profile, in order to avoid in-service product failures, but also for extruders and die makers to increase process efficiency. In this context, aim of the present work was to compare the experimental -numerical investigations performed by the authors in terms of charge welds extensions with the predictions of the analytical models nowadays reported in literature. The final global aim work was to assess the applicability of these models in the everyday industrial practice.