Monitoring and modelling the deformation of an aluminium prototype mould insert under different injection moulding and clamping conditions

Abstract

The conventional material of prototype injection moulds is aluminium. Well-established techniques are available on the applicability of such moulds, yet their operational state is not analysed comprehensively. State monitoring has huge benefits because the mould can be protected from excessive loads and deformations and product quality can be monitored in real time. In this paper, we measured the operational strains, cavity pressure and temperature distribution of prototype injection moulds with the traditional state monitoring method, and analysed the combined effect of holding pressure and clamping force on the operational deformations and cavity pressures. Increasing the clamping force and the holding pressure results in higher operational strains and cavity pressures. The precision of core shift analysis was tested if it can predict operational deformations of aluminium injection moulds. Core shift analysis could accurately predict the maximal deformation but it is inaccurate regarding the time when it occurs. A novel modelling method was also introduced where pressure and temperature results of the injection moulding simulation can be imported into finite element (FE) mechanical simulations. This way, mould deformations can be modelled in mechanical FE simulation environment. The measured operational deformations were compared both with core shift analysis results and with the coupled IM-FE simulation results. Core shift simulation can predict maximal deformations with adequate precision but it does not consider thermal expansion effects properly. In order to improve the accuracy of the simulations, a coupled IM-FE method is necessary, where excellent agreement can be found between the measurements and the calculations. The new, combined modelling technique can improve the accuracy of mould deformation modelling because additional mould material models become available in a professional finite element software. It can be especially useful in the modelling of polymeric mould inserts where stiffness is heavily temperature-dependent and the material creeps.