Finite-Elemente Modellierung des hydrostatischen Strangpressens von Magnesiumlegierungen

Barton, Gabriel; Kopp, Reiner (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2009)
Dissertation / PhD Thesis

Abstract

Magnesium and its alloys are characterised by a low density. The use of magnesium alloys as a lightweight construction material is growing rapidly. The processing is mostly done by high pressure die casting, since the processing by bulk and sheet forming processes is hindered by the specific physical properties of magnesium alloys, which prevent a effective forming process at room temperature. Only at elevated temperatures do these alloys have a sufficient formability to be processed by means of metal forming. The hydrostatic extrusion process is a process variant of the manufacturing processes extrusion. The particular characteristic of this extrusion process is the application of an active fluid medium, which surrounds the billet that is to be deformed. The pressure within the fluid applies the forming force onto the billet, forcing it through the die which forms the shape of the extruded product. This metal forming process is characterised by high compressive stresses in the deformation zone and very low friction at the contact area of the workpiece and the forming die. The combination of both properties allows for a successfull extrusion of materials that are usnually difficult to extrude. Additionally, high degrees of deformation can be reached in only one forming step. This specific combination of these process properties makes hydrostatic extrusion a predestinated manufacturing process for the production of profiles made from magnesium alloys. However, due to the complex handling of the pressure medium and the high pressures needed, hydrostatic extrusion is a very exotic process and not widely applied. The hydrostatic extrusion process takes place in a closed container and can therefore not be directly observed. A numerical simulation model of the hydrostatic extrusion process using the finite element method could be a useful tool to gain deeper process understanding. Furthermore it could be used for the design and optimisation of this extrusion process in order to enable the manufacturing of new profile geometries and the processing of new alloys. The finite-element method is a commonly used method for the numerical modelling of a large variety of bulk and sheet metal forming processes. The application of this modelling tool helps to gain a deeper understanding of the hydrostatic extrusion process. Today, the modelling of extrusion processes is still in its fledgling stages, due to the extremely large strains and high gradients involved. The work presented here, describes the development of a finite-element simulation model of the hydrostatic extrusion process of magnesium alloys and its validation.

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