Micro-Injection Moulding

Micro-injection moulding is a new process, and as such it has not been
thoroughly investigated until now. The peculiarities related to the three
dimensional aspect of the cavity and the very small length and time scales at
stake make it a very specific technology compared to conventional injection
moulding.

The aim of this thesis is to pave the way for micro-injection moulding
modelling with a special emphasis on micro-cavity filling.

Besides giving insight into the process, this work demonstrates the importance
of visco-elastic effects and investigates further related issues. The
different steps adopted in this work are the following ones: first an
extensive review of the process is proposed, followed by a reflection on
micro-cavity filling and polymer behaviour which ends up with the choice of
the Giesekus model as an appropriate viscoelastic model for some polymers used
in this process. A chapter dedicated to polymer characterization conducted on
PC Lexan HF11110R, a micro-injection suited amorphous material, shows that the
Newtonian viscosity is very low. In this case, the model admissibility from a
mathematical and thermodynamic point of view is not guaranteed. This
admissibility is the object of a chapter which provides an analysis for the
Giesekus model completed with the PC Lexan material parameters. A further
mathematical consequence of a vanishing Newtonian viscosity is that the number
of inlet boundary conditions to be prescribed for the extra-stress tensor is
reduced to 4 instead of 6 in case of a non-vanishing Newtonian viscosity. A
specific numerical scheme to tackle this problem is proposed along with a
theta-splitting based method which allows us to separate the viscous and
visco-elastic effects in the governing equations and to treat subsequently a
modified Stokes sub-problem and a transport sub-problem. Finally, a micromixer
design and prototyping is presented as an application of this promising
process.