Simulation of the filling process in micro channels for polymeric materials

There is some evidence indicating that polymeric flows in micro channels differ significantly from those in macro geometries. As micro molding is attracting more attention these days, efforts need to be made to identify the significant factors that influence microscale polymeric flow behaviors and to develop new simulation schemes for micro molding. In this study, we have investigated the consequences of microscale phenomena, particularly size-dependent viscosity, wall slip and surface tension, on the filling process of polymeric materials into micro channels. The standard scheme of two and half dimensions for injection molding simulation was modified to include these microscale effects. With data currently available for polystyrene, the simulation results indicate the importance of employing size-dependent viscosity and wall slip to predict micro filling behaviors. It appears that wall slip should always occur in channels downsized to several micrometers or less, because the wall stress would otherwise be enormous. The surface tension effects turn out to be less important and can be neglected in micro injection molding in which high injection pressure is employed.