Deformation and metal flow when extruding hollow aluminium profiles

A two–dimensional experimental grid pattern technique for mapping of deformation has been applied in porthole die extrusion of an aluminium alloy. Traditional grid patterns would erase in heavily deformed regions, while the grid pattern used in this investigation would sustain the very large deformation taking place as for instance in the shear zone during extrusion. Deformed grid patterns have been obtained as they would be after extrusion. From deformed grid patterns the deformation distribution inside this profile has been described. By means of comparing the original grid pattern inserted into the billet with the deformed pattern obtained after extrusion, useful information has been gained regarding metal flow in the extrusion process. Ths information has been systemized in a diagram called the emptying diagram. This diagram shows from which part of the billet different parts of the extruded profile are formed.