Models and experimental results in plastic deformation processes: the reverse extrusion

Abstract In plastic deformation study, it is fundamental to discover the parameters influencing the process; in fact, only after the identification of these parameters, is it possible to design a better die so decreasing the intermediate steps and the number of scraps due to insufficient die filling. Many authors have dealt with this problem and their studies have clearly shown how, besides the geometric parameters of the die and the initial billet shapes, the material resistance features (work hardening) and the lubrication conditions (low friction, high friction, adherence) are of great relevance. The present work shows the results obtained from studying the reverse extrusion operations: these operations can be compared with the rising phase in forming between closed dies. In particular attention was focused on both the friction influence and punch geometry. The principal results concern deformations and compression forces obtained in the experimental section while extruding aluminum test pieces either with lubricants or without at room temperature. Because the final aim is to forecast the material behaviour in more complex operations by computer simulation, the experimental results have been compared with the analytical ones obtained through an F.E.M. program realized by the authors.