In this project we use numerical simulation as a tool to improve our understanding of the fundamentals of injection moulding. Some characteristics of the injection moulding process:
Local high cooling rates (~10.000 K/s) and large temperature gradients (~100 K/mm)
High shear rates (~ 10.000 s-1)
Non-Newtonian fluid mechanics
Commercial software for simulating the injection moulding process is useful for optimising part quality and reducing cycle time. However, these software packages can not deal with the features in the micrometer range on our components.
Macroscale and microscale simulations
A challenge compared to conventional simulations is the large differences in size scales. The thickness of the component can be 10 000 times larger than a typical dimension of the microfeatures. We solve this using a stepwise approach where we perform simulations on the macroscale and couple these with local simulations on the microscale. Below is an image from a microscale simulation, showing flow into microfeatures.
In addition, the characteristic physical phenomena on the microscale may differ from those on the macroscale. Effects such as surface tension and wall adhesion, which can be neglected on the macroscale, can be dominant effects for the filling of features on the sub-micrometer scale. We have included such effects in microscale simulations. The figure below shows the flow of a polycarbonate melt into a pillar. The only driving force is the wall adhesion.
