||Validation and optimization of FEM simulation of micro injection moulded parts
||Molin, Mauro Dal
Tosello, Guido (Institut for Produktion og Ledelse, Danmarks Tekniske Universitet, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Hansen, Hans Nørgaard (Institut for Produktion og Ledelse, Danmarks Tekniske Universitet, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||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.
Creation date: 2008-02-08
Update date: 2008-02-08