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PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY
Edited by: B.H.V. Topping, G. Montero and R. Montenegro
Design of Profile Extrusion Dies: An Automatic Approach
J.M. Nóbrega and O.S. Carneiro
Institute for Polymers and Composites, IPC, Department of Polymer Engineering, University of Minho, Guimarães, Portugal
J.M. Nóbrega, O.S. Carneiro, "Design of Profile Extrusion Dies: An Automatic Approach", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Fifth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 24, 2006. doi:10.4203/ccp.84.24
Keywords: extrusion die design, optimisation, finite volumes, flow balance.
As a result of the large number of phenomena and restrictions involved and the complexity of the polymer melt rheological behaviour, extrusion die design was, and still is, more an art than a science . In fact, traditionally the design of a new die was based on experimental trial-and-error procedures, which are very time, human, machine and raw materials consuming and do not guarantee the achievement of the optimal solution. Currently, and due to the availability of numerical modelling codes, this trial-and-error design approach is being progressively transformed from experimental into a numerical based operation, however, it is still dependent on the designer's experience . The advantages of this approach are an overall reduction in the cost of the project and a higher probability of finding the optimal solution. Recently, there is a trend towards the automatic die design concept [3,4,5] with the objective to turn its design as automatic as possible, ideally without any user intervention, and to guarantee the achievement of the optimal solution. In this case, the process is almost all carried out by the computer, with obvious savings in the time consumed and in the remaining resources.
The authors of the present work have successfully implemented and validated a numerical code able to automatically balance the flow in profile extrusion dies [3,6,7]. To accomplish this, several problems had to be solved, namely: geometry parameterisation, minimisation of the computation time, evaluation of the quality of each trial geometry and the optimisation technique. The parameterisation problem was solved by the division of the profile cross section into elemental sections and by the introduction of an additional region in the die flow channel, which allowed the definition of the die geometry through some parameters. The minimisation of the computation time was achieved by the employment of a numerical code based in the finite volume method coupled with a progressive mesh refinement technique. An objective function was proposed to evaluate the performance of each trial geometry. For optimisation purposes two algorithms were implemented, one based on the simplex method and other in the traditional trial-and-error approach usually employed in the design of these tools, and two alternative design strategies were developed.
A case study is used to compare the adequacy of several die design strategies implemented, not only in terms of the performance attained for the resulting dies when used in the conditions adopted in their optimisation, but also in terms of their robustness when those conditions are varied. The results obtained allowed the following conclusions:
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