Abstract
To increase productivity and thus reduce the unit cost, often micro moulding tools incorporate multiple cavities and the selected runner design and applied pressure are very important for achieving satisfactory moulding results. The main function of the runner system is to facilitate the flow of molten material from the injection nozzle into the mould cavity. Therefore, the microinjection filling process depends on the optimum design of runner systems and this is an important prerequisite for the production of high quality parts. In this context, the paper reports on an experimental study that investigates the flow behaviour of the polymer melts in microcavities with a particular focus on the relationship between the filling of micro parts and the size of the runner system. In particular, the runner size effects on the microinjection moulding process were investigated by focusing the research on only the filling stage of the process. The filling performance of spiral-like micro cavities was studied as a function of runner size in combination with melt temperature, mould temperature, injection speed, and holding pressure time employing the design of the experiment approach. In addition, the results were analysed further with melt flow simulation to identify the effects of the runner size together with flow properties of the polymers, PP and ABS, on the behaviour of the microinjection moulding process.