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Title Validation and optimization of FEM simulation of micro injection moulded parts
Author Molin, Mauro Dal
Tosello, Guido (Institut for Produktion og Ledelse, Danmarks Tekniske Universitet, DTU, DK-2800 Kgs. Lyngby, Denmark)
Supervisor Hansen, Hans Nørgaard (Institut for Produktion og Ledelse, Danmarks Tekniske Universitet, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2007
Abstract In manufacturing polymer micro products, numerical simulations are used with the same purposes as in conventional injection moulding, mainly the optimization of micro components design, the optimization of process parameters and the decrease of production costs. Dedicated simulation software fails to correctly describe the melt flow in microstructures, mostly because phenomena such as the tendency of polymers to slip in micro channels, micro scale surface effects and micro scale rheological behaviour are not considered. Therefore, accuracy of computer aided engineering simulations still needs to be improved. The main objective of this work is to evaluate whether the present numerical commercial codes are suitable to characterize melt flow patterns in a micro-cavity. The proposed approach consists of the determination of the flow pattern by using the weld lines as flow markers. This is an alternative technique to the “short shot” method (comparison between simulation and partial filling steps), which predicts the shape of the free surfaces with a large approximation due to stress relaxation and thermal contraction. Furthermore, short shots of micro injection moulded parts can be very difficult to obtain due to the micro volume involved, especially if compared with the tolerance on the shot volume control. In this project, simulations of the flow in a special micro cavity previously designed and manufactured by micro electro discharge machining (μEDM) were performed. Three dimensional filling simulations were performed using the software package Moldflow Plastics Insight MPI 4.1. Firstly, an extensive study of the simulation setup was carried out. In particular, the experimental ram speed profile was calculated and implemented in the simulation software. With the developed procedure, the simulated filling time resulted to be closer to the experimental one. As consequence, an improved accuracy of the simulation was obtained. Secondly, simulated weld lines were determined reconstructing their path by subsequent simulation steps collection and compared with the experimental ones. The influence on the simulation software of micro scale rheology, viscosity pressure dependence, thermal exchange coefficient and elongational viscosity model was investigated. Finally, quantitative discrepancies of the position and direction of the weld lines were found, confirming the limitation of the software when simulating the filling of micro injection moulded parts.
Pages 236
Fulltext
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Admin Creation date: 2008-02-08    Update date: 2008-02-08    Source: dtu    ID: 210413    Original MXD