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Nadhir Lebaal
Abstract
Die optimisation for extrusion of thermoplastic parts
Nadhir Lebaal - 15 June 2007
During this study, various aspects of process parameters optimization are considered. The objective of our research tasks is to homogenize the velocity distribution on the outlet side of the die, through the control and the optimization of the geometrical parameters and operating conditions, in order to obtain a "defects free workpiece". In this study optimization was carried out by using commercial software Rem3D®, based on the three-dimensional finite element method.
An optimization procedure, based on the response surface method, was proposed. This one enabled us to solve an implicit optimization problem whose evaluation of the objective and constraints functions requires several hours of CPU time. For that, all the functions are written in an explicit form by using either the diffuse approximation or the Kriging interpolation. Due to the presence of the nonlinear constraints, an iterative algorithm of type SQP, was used. To find the global optimum with precision and at lower cost, an auto-adaptive strategy of the research space is applied and several strategies making it possible to reactualize the approximations and the initial point were adopted.
In the first stage the objective was to identify the rheological behavior of a plastic using in situ experimental data. The comparison with measurements in capillary rheometry enabled us to check the rheological relevance of the parameters obtained by optimization.
The results of three other applications highlight the interest of the optimization of the geometrical and operational parameters of the extrusion process.
A die optimized numerically for multiple operating conditions and materials was produced. An experimental comparison allowed us to validate the whole procedures of simulation and optimization put in place. The experimental results and simulations show a good velocity distribution on the outlet side of the optimal die for a great range of flows and for various polymers.
Key-Words:
Optimization, Extrusion, Die, Rheology, Polymers, Numerical
simulation, SQP, Diffuse, Kriging, Design of experiment.
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