A numerical sensitivity study to determine the main influence parameters on the back-end defect

Productivity of unlubricated direct extrusion of aluminium alloys depends significantly on the so-called “back-end” defect which always occurs in the center of an extruded section on the end of one extrusion cycle. In structural sections this defect leads to an unacceptable decrease in product quality and so the length of the extruded section which contains this defect must be scrapped. The length of the scrap due to the back-end defect depends on different process parameters like friction, initial temperature of the billet or tool geometry. The objective of this work is to determine the most important parameters influencing the length of the back-end defect in an extruded profile by a numerical sensitivity study with finite elements.