Post moulding thermal characterization of polymer components

Industries seek to anticipate product dimensional measurements to quickly control the process and ensure production conformity. The anticipation of the dimensional measurement is often prevented due to dimensional instabilities of the produced parts. In the case of injection moulded polymer components, one of the main instabilities is represented by expansion due to temperature changes. This work proposes a methodology consisting in the prediction of the dimensions at reference temperature conditions using information from measurements performed within few minutes from the moulding process. An industrial component consisting of a thin wall tubular part made of POM (polyoxymethylene) has been selected for the investigation. The measuring equipment included an inductive probe, two thermocouples for concurrent measurements of length and temperature. The dimension at reference temperature conditions is estimated using the information from the transitory cooling period subsequent to the moulding process and through the definition of an apparent coefficient of thermal expansion. Further development of themethodology must be introduced to tackle other dimensional instabilities, such as hygroscopic swelling, stress relaxation and recrystallization.