Numerical and experimental evaluation of an alternative mechanism for wall thickness variations of hollow profiles applying a porthole die

Abstract The cross sections of conventionally extruded profiles remain constant along the length of the extrudates due to application of static, rigid dies. The profile cross section is dimensioned according to the expected loads applied during technical application. Mostly, the loads are not distributed homogeneously upon the length of a product. Thus, locally over-dimensioned profile areas are the result. In order to optimize the profile design and therefore obtain lighter products, load adapted tailored profiles should be manufactured. In this paper a mechanism for wall thickness variations of lightweight hollow profiles was investigated by finite element analysis (FEA) and experimental extrusion trials. The principle for manufacturing wall thickness variations is based on application of bending elements which work as bearing channel at the porthole die. Their deflection in direction of the die bearing would lead to wall thickness reductions. An increase of the wall thicknesses should be achieved by a deflection of the bending elements back into direction of their initial position due to the normal pressure of the flowing aluminum billet material. FEA of the material flow during extrusion was conducted in order to investigate the principle feasibility of the mechanism. The force requirements for wall thickness variations were also gained from the numeric simulations on the one hand. The force necessary for the deflection of the bending elements was also determined in an experimental test setup. The extrusion tryouts applying the developed mechanism revealed that the force of the hydraulic drive was successfully transmitted onto the moveable segments inside of the porthole die. Although subsequent to the extrusion experiments variations of the hollow profile wall thicknesses were observed, it was found out that they were not induced by the developed mechanism as intended. Instead, aluminum billet material filled even smallest voids and gaps inside of the mechanism causing deflection and failure of different components that effected the development of the wall thickness.