Nooman Ben Khalifa

Modeling Approach for the Determination of Material Flow and Welding Conditions in Porthole Die Extrusion with Gas Pocket Formation

The material flow in porthole dies is of crucial importance with regard to the seam weld quality in aluminum extrusion. Thus, experimental as well as numerical investigations on the effect of die geometry on the material flow were conducted. The experimental tests were performed on a 10 MN laboratory extrusion press. During the experimental trials, the extrusion ratio was varied by means of exchangeable die plates. Since the modular die allows removal of the aluminum in the welding chamber as well as in the feeders after the process, the material flow could be inspected in detail. The experimental results were used to improve the accuracy of FEA simulations, which were also conducted by commercial software. An attempt was made to improve the result quality of Eulerian FEA model regarding the simulation of an extrusion process with a gas pocket in the welding chamber. The influence of the modeling approach on the predicted material flow and on the contact pressure was analyzed and finally linked to the seam weld quality.

Extrusion Benchmark 2009 Experimental Analysis of Deflection in Extrusion Dies

In this paper experimental investigations aimed at measuring the die deformations during aluminum extrusion process is presented and discussed. A two-holes die generating two U-shape profiles with different supporting legs was produced and tested under strictly monitored conditions. The influence of die deformation on the speed, temperature distribution and distortion of the two profiles is reported and analyzed. AA6082 alloy was used as deforming material while H-13 hot-work tool steel was selected as die material. The experiments were repeated at least three times in the same conditions in order to achieve a statistical distribution of the acquired data: such data are then used as a reference for the 2009 edition of the extrusion benchmark.

Experimental and Numerical Analysis of Material Flow in Porthole Die Extrusion

The design of porthole dies for aluminum extrusion processes is very complex. For the accurate design, fundamental knowledge about material flow is of major importance. To gain these information, numerical methods are increasingly utilized. The accuracy of the simulation results depends mainly on the precision of the used boundary conditions in the model. Therefore, visioplastic analyses of the material flow inside a porthole die are presented in this paper. A special modular tool concept was developed to prepare and visualize the material flow inside the process. The results of the experimental analysis were used for the verification of numerical results which were calculated with the commercial software codes Deform3D and HyperXtrude.

Novel Five-Axis Forming Press for the Incremental Sheet-Bulk Metal Forming

The incremental procedure of sheet-bulk metal forming was classified into two different forming sequences, the discrete and the continuous. Based on these two groups, a movement matrix was developed, which captures required kinematic motions to manufacture a variety of functional components. With the objective of producing near-net-shape workpiece geometries within the Collaborative Research Centre TR73 – sheet-bulk metal forming, the required positioning accuracies of conventional metal forming machines exceed the current state of the art. Therefore, a suitable machine concept was developed and realized. This new machine represents a unique prototype for a flexible application of bulk forming operations to 2 – 3 mm sheets with five motion axes. During continuous forming, such as rolling, and also during simultaneous operations, increased lateral forces prevail. The machine was provided with a high stiffness. That enables a positioning accuracy which, also under load and at rest, correlates the high demands of the sheet-bulk metal forming within a range of ±0.01 mm.

Composite Extrusion of Thin Aluminum Profiles with High Reinforcing Volume

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.

Bridge Design Influences on the Pressure Conditions in the Welding Chamber for Porthole Die Extrusion

Porthole die extrusion of lightweight alloys is used for the production of profiles, which may have complex cross section geometries. The mechanical properties of these profiles are deeply affected by the seam welds, which are generated in hollow profiles along the whole length. The seam welds result from the rejoining of the material streams in the welding chamber of the porthole die. The joining phase and hence the seam weld quality are strongly influenced by the temperature and the pressure conditions in the welding chamber. Those process conditions can be adjusted by a proper die design. In this work, the focus lies on the feeder section of the extrusion die, which consists of a set of bridges, whose shapes influence the material entry in the welding chamber. A numerical study was carried out to investigate different bridge shapes with regard to the pressure inside the welding chamber and the punch load. Subsequently, the volume of the bridge was fixed to isolate and better investigate the influence of the shape. It was observed that bridge designs leading to higher flow distortion cause higher pressure decrement along the welding plane and, consequently, degradation of the welding conditions.

New Concepts for Cooling of Extrusion Dies Manufactured by Rapid Tooling

To prevent local overheating of the workpiece material in hot aluminum extrusion the influence of die cooling was investigated. Numerical simulations of extrusion revealed an advantage of the die bearing cooling, which can be accomplished by locating the cooling channels close to the die/bearing surface. Since the fabrication of especially geometric complex cooling channels located near the die surface is not possible by conventional manufacturing technologies, the technology of rapid tooling was introduced into hot aluminum extrusion and experimentally tested. Cooling channels near to the bearings show promising results allowing extensions of extrusion limits, especially the extrusion speed and therefore productivity.

Accurate Welding Line Prediction in Extrusion Processes

In contrast to conventional extrusion processes, where a lot of research is done on in the welding quality, in composite extrusion, research is investigated into the welding line positioning. As a result of the process principle, the reinforcing elements are embedded into the longitudinal welding line. Hence, an undefined material flow inside the welding chamber induces reinforcement deflection, which can lead to reduced mechanical properties, as momentum of inertia. Therefore and to reduce costly experimental investigations, a new method of an automated numerical welding line prediction was developed. The results form HyperXtrude finite element calculations are used for special particle tracing simulations to predict the welding line in the profile cross section accurately. The procedures of segmentation and characteristic extraction are presented to approximate the welding line by cubic spline functions. The method was fully programmed in the Java program language, and works well for all HyperXtrude process models consisting of tetrahedral elements.

Process Limits of Extrusion of Multimaterial Components

Three innovative extrusion processes for manufacturing of multimaterial parts are discussed: co-extrusion of discontinuously steel reinforced aluminum profiles, composite extrusion of continuously steel wire reinforced profiles, and composite rod extrusion. In the first two processes, the embedded steel elements are not deformable; while in the case of composite rod extrusion, both materials are deformed. By means of experimental and numerical analyses, the process parameters that mainly influence the reinforcement ratio, the extrusion force as well as the material distribution are analyzed. On the basis of the above, the analytical approaches are deduced to describe the process limits for the proposed technologies. The paper closes with examples of applications regarding the lightweight requirements as well as functional integrations by forming multimaterials.

Effects of Weld Line in Deep Drawing of Tailor Welded Blanks of High Strength Steels

Due to the increase of lightweight design in car bodies, there is a raise in use of tailored welded blanks (TWB). With these blanks it is possible to strengthen the car body where it is necessary. This can lead to less weight. In the case of tailored welded blanks, there is a weld line, which influences the deep drawing behavior significantly during forming. In the presented results two different high strength steels (HCT980X and HCT600X) are welded together. One forming operation is performed, in which the weld line is positioned differently. The results show the influence of the weld line on the forming behavior which is realized by the comparison of deep drawn monolithic parts with the deep drawn tailored welded blanks. While the monolithic parts could be formed without failure, the forming of tailored welded blanks was accompanied by cracks in dependency to the weld line orientation and the applied load in this region. The results also show that the failure occurs in the base material and that the weld line is not damaged by the applied load. After the characterization of the base materials and the weld material, a numerical modelling of the whole TWB could be realized in this work. Two different ways of modelling techniques of the weld line are compared and the necessity of the consideration of the weld line properties is demonstrated. Furthermore, in consideration of the weld line properties in the FE-Model, it is possible to show that the weld line resists the forming operation without failure.