Parameter optimization of the process of AA6xxx and AA7xxx series aluminium extrusion
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The mechanical properties and surface qualities of extruded aluminium products depend greatly on the micro-structural changes during the extrusion process. A clear understanding of the hermodynamics and tribology of the aluminium extrusion process with respect to the die design parameters and process parameters, namely temperature and extrusion speed are necessary to decide the optimum values of machine settings. This research discusses the essential understanding of the process of aluminium extrusion, including the effects of die geometry and process parameters on flow patterns. It presents the development of a technique to find an optimal set of process and design parameter values for an isothermal process to extrude a product for a given shape and material properties with minimal defects. The inputs to this model are: the product geometry and its material data such as flow curve and microstructure during dynamic recrystallization. This is an inverse problem and the model is formulated as a non-linear least-squares minimization problem coupled with a finite element model for the extrusion process. The minimization problem where the geometry of a profile is simple is done by constructing an iterative procedure using an optimization routine such as MATLAB's lsqnonlin and at each iteration, the extrusion flow is solved using the finite element programme ABAQUS. However, the die design parameters for a complex geometry problem are different from a simple geometry problem. Further ABAQUS is not very efficient to handle adaptive meshing for a complex thin profile. The specialist finite element program DEFORM 3D for metal forming applications, which efficiently uses adaptive meshing controls to accommodate high workpiece deformations, is used to overcome the problem. The optimal values of the die design and process parameters are estimated by improving the techniques available in the literature and compared with experimental results.