Composite Extrusion of Thin Aluminum Profiles with High Reinforcing Volume

Abstract

Extruded aluminium profiles with a variety of different cross-sections are mainly used in lightweight structures for transportation means. Examples are stringer profiles in the fuselage of airplanes or profiles in chassis of trains and cars. Nowadays, the mass reduction of a lightweight structure is an important issue to achieve lower fuel consumption and CO2 emissions. With an increased portion of aluminium profiles the mass of structures can be reduced considerably in contrast to the application of steel parts, due to the lower density of aluminium. However, this is coupled with disadvantages such as the lower specific stiffness and strength of the material. One possibility to improve the mechanical properties of aluminium profiles without a considerable increase of their weight is the embedding of reinforcing elements during the extrusion process. Special porthole extrusion dies are used to feed reinforcing elements in form of high strength steel wires separate from the aluminium material flow. In the welding chamber of the die both materials bond together to a composite profile. To achieve a high advantage of the technology for lightweight applications a high reinforcing volume of aluminium profiles is targeted. A comparatively high reinforcing volume can be reached either by a high number of reinforcing elements or through a reduction of the profile wall thickness. A high number of reinforcing elements leads to a small distance between the single elements in the profile cross-section. The paper will show the results of an experimental and numerical analysis which were carried out to determine the minimum distance between the reinforcing elements as well as the minimum profile thickness. In the trials different arrangements of the elements in the profile cross-section and profile thicknesses were considered. Main parameters which have an influence on the process stability were analyzed and a process window for the manufacture of thin profiles with high reinforcing volume was deduced.

Process Limits of Extrusion of Multimaterial Components

“…In Ref. [9], a minimal profile thickness of 0.45 mm was achieved. Besides the minimal profile thickness and the minimal space between elements, the feeding of the elements has to be considered.…”

“…A high number of reinforcing elements leads to a small distance between the single elements in the profile cross section as well as to an increasing of the extrusion force [9]. In previous studies, experimental and numerical analyses were carried out to determine the minimum distance between the reinforcing elements and the minimum allowable profile thickness [9].…”

“…A high number of reinforcing elements leads to a small distance between the single elements in the profile cross section as well as to an increasing of the extrusion force [9]. In previous studies, experimental and numerical analyses were carried out to determine the minimum distance between the reinforcing elements and the minimum allowable profile thickness [9]. Furthermore, in the studies made by Schikorra [7] and Schom€ acker [8], the reinforcement ratio, which is defined as the ratio between the cross section of the reinforcement elements and the cross section of the extruded profile, was 1.7% which is too low to detect an increase of the specific strength of the profile.…”

“…Figure 20 shows the experimentally obtained wall thickness measurements of the sleeve material wall thickness along the extruded profile. The error bars are illustrating the maximum and minimum values of the measured wall thicknesses over the cross section [9].…”

Simulation of Composite Hot Extrusion with High Reinforcing Volumes

“…Schikkora and Kleiner (2006) used a simple axisymmetric FEM model to investigate the influence of the die geometry on the material flow and the stresses in the RE during the extrusion of a round bar with a single RE in the center. Furthermore, Pietzka et al (2013) considered a simplified approach in order to determine the deflection of the RE in a rectangular, flat profile. A slender strip with two RE was modeled to mimic the material flow near the symmetry plane of the profile.…”