State-monitoring and product quality measurement of additively manufactured injection mould inserts

Abstract

Additive technologies represent a state-of-the-art and innovative way in today’s mould making. They allow production of both metallic and polymeric moulds with relative simplicity and flexibility compared to conventional machining. Despite its possible benefits, this area is scarcely researched. In our work, we analysed in-mould applicability of epoxy-acrylate inserts manufactured by PolyJet technology. We created a comprehensive state monitoring method to quantify important process parameters like cavity pressure, strain and temperature of the inserts. We analysed the effect of holding pressure on the resulting cavity pressure and strain of the insert. We showed that strain of the insert gradually increased after the cycles and we identified characteristic segments of the injection moulding cycle on the strain-time curves. We also applied surface temperature measurements using a thermal imaging camera. The purpose of this measurement was to determine necessary delay time between cycles allowing inserts to cool below heat deflection temperature, so early failure could be prevented. By using thermal imaging camera, we measured cavity surface temperature distribution and demonstrated the effect of low thermal conductivity of the insert material. We also measured thickness and weight variation of injection moulded products to show the effect of holding pressure and mould deformation on final product quality. As we applied higher holding pressures, product mass and average product thickness grew.