Investigations Into Continuous Extrusion

Abstract

Continuous extrusion is an important recent development in the production of long lengths of rod and wire. In the process the normally round or rectangular feedstock is forced by friction towards the die by the feed channel, where three distinct regions, the primary, transitional and tertiary zones must develop before extrusion can commence.Stresses and strains in the deforming material along the feed channel, together with the characteristic dimensions of these regions must be known before continuous extrusion machines and tooling can be designed with confidence and product properties predicted.A finite element computer program with quadrilateral two dimensional elements was used to calculate the various parameters in this non-steady state problem, when the development and spread of the transitional region in the billet must be predicted. The program is based on the assumption of rigid-plastic material behaviour and penalty function flow formulation was chosen. This is presented in the thesis in detail, together with other possible formulations and the advantages of the selected method are outlined.For the experiments an existing rig was redesigned and rebuilt to suit the particular task. Two subsequent operations were carried out: first the billet was laterally compressed to provide an initial grip on the material when the primary zone developed, followed by axial compression leading to the development of the transitional and tertiary zones, which are of main interest in the present work. The various parameters were recorded by an IBM microcomputer and Labmaster analogue to digital convertor.Experimental results were compared with theoretical findings obtained under the same conditions as in the experiments and suitability of the developed computer code assessed. Further, various parameters influencing the continuous extrusion processes Context, Linex and Conform were numerically assessed and conclusions drawn. The thesis concludes with suggestions for extending the theoretical model to predict the temperature distribution developed during the deformation process, together with possible implementation of a three dimensional model of the processes under consideration. ACKNOWLEDGEMENTS