Finite element modelling of cold extrusion with experimental verification

This thesis represents a contribution to the research of the extrusion process, specifically the forward cold extrusion of aluminium. The extrusion process was analysed using a combination of experimental research and statistical analysis of the results. The influence of the combined effects of three independent variables (die angle, die reduction ratio and die land) upon three process characteristics (maximum extrusion force, extruded component superficial roughness and hardness) was analysed. With the aim of increasing the application domain of the experimentally obtained results, a numerical model of the process was designed. The force data obtained from the finite element simulations was compared to the force data obtained experimentally. The thesis is structured in 6 chapters. Chapter 1 presents the background and the rationale of this research, outlining the novel aspects comprised in the thesis. Chapter 2 contains a review of the published papers with focus on the influence of the die geometry, lubrication · conditions on the extrusion force and extruded component characteristics. Chapter 3 presents the experimental programme namely the extrusion die specifically designed and built for the purpose of this research, the data acquisition system and the statistical fundamentals of the experimental design used. Chapter 4 consists of a presentation of the statistical method employed for the analysis of the experimental results, together with a display of the six mathematical models obtained (three models of the maximum extrusion force, component surface hardness and roughness for the experiments where Cu-Pb lubricant was used, and three more models of the same characteristic for the experiments where Zn stearate lubricant was used). Response surface graphs were presented and discussed, together with an enor prediction analysis for each model. Chapter 5 presents the finite element software employed for the numerical modelling of the extrusion process. Descriptions of the parametrical model of the extrusion process as well as the obtained results are presented. Comparison was made between the experimental results, the numerical simulation results and the available results obtained from the published papers. Chapter 6 outlines the conclusion of the research and recommendations for further development of the models obtained.