Experimental and numerical investigations of cavity filling process in injection moulding for microcantilever structures

Microinjection moulding of high-aspect-ratio microstructures is important for the fabrication of various microsystem components. Successful microinjection moulding technologies may depend on accurate understanding of the cavity filling process of a polymer melt and a reasonable prediction of the filling degree in a microchannel. To date, there has been a lack of adequate investigations of the filling process in injection moulding for microcantilever structures. In this study, the microinjection moulding of microcantilevers was performed with dynamic mould temperature control and cavity pressure measurement. The influences of injection flow rate, peak cavity pressure, melt temperature, and mould temperature on the filling length were observed. A simple, one-dimensional analytical model was developed that describes the relationship of the four process parameters with the filling length. The measured cavity pressure profiles were applied to the numerical analyses. The model was validated by comparison with both experimental measurements and simulation results and showed acceptable agreement among the processing parameters. The development of the cavity pressure and the temperature transition of the melt in the microchannels had a critical influence on the filling process. The increase in the mould temperature over the glass transition temperature during a filling stage using the mould temperature control system was the most effective way to maximize the filling length. The combination of the theoretical model and cavity pressure measurements can be used to predict the filling length and design the injection mould for high-aspect-ratio microstructures.