Gas Assisted Injection Moulding: Principles for the Robust Layout of Process and Molding
Hans-Peter Heim
KTP - Institut für Kunststofftechnik - University Paderborn
Germany

Keywords: gas, injection-moulding, multi-component

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Gas assisted injection moulding as well as other multi component injection moulding processes shows complex process behaviour – especially when the layout of the part is concerned. In addition to that process parameters like the pre filling level and gas pressure have to be set up very carefully to ensure a robust process by means of process capability and accuracy.
This article deals with a systematic procedure to evaluate a robust process design for both the geometry of the moulded part and process parameters to fit customer´s and manufacturer´s requirements.
Starting with a well designed moulding it is possible – by application of a volume balance for relevant areas of the part – to create a graphic representation of the deternimation of the filling level for molded parts with bi- or multi-directional gas-conducting geometries for an optimum and a sub-optimum layout of the partial filling. This tool enables the manufacturer to evaluate the correct filling level and to avoid a break-through of the gas.
In addition to that a serial production has to take care of process fluctuations. To take this into account the next step for a robust process design is the setup of a correct filling level according to process instabilities such as deviations of filling, material properties or feeding an melting behaviour. With the aid of some basic experimental investigations and the application of multivariate statistics the correct filling level can be achieved. The article shows how to work with this tool to achieve a robust design.
At the end the article shows how this procedure can be integrated in the state of the art of design guidelines for gas assisted injection moulding