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Abstract
Integrative simulation techniques for predicting component properties, based on the conditions during processing, are becoming increasingly important. The calculation of orientations in injection molding, which, in addition to mechanical and optical properties, also affect the thermal shrinkage behavior, are modeled on the basis of measurements that cannot take into account the pressure driven flow processes, which cause the orientations during the holding pressure phase. Previous investigations with a high-pressure capillary rheometer (HPC) and closed counter pressure chamber (CPC) showed the significant effect of a dynamically applied pressure on the flow behavior, depending on the temperature and the underlying compression rate. At a constant compression rate, an effective pressure difference between the measuring chamber and the CPC was observed, which resulted in a stop of flow through the capillary referred to as dynamic compression induced solidification. In order to extend the material understanding to the moment after dynamic solidification, an equilibrium time, which is needed until the pressure signals equalize, was evaluated and investigated in terms of a pressure, temperature and a possible compression rate dependency in this study. The findings show an exponential increase of the determined equilibrium time as a function of the holding pressure level and a decrease of the equilibrium time with increasing temperature. In case of supercritical compression in the area of a dynamic solidification, a compression rate dependency of the determined equilibrium times is also found. The measurement results show a temperature-invariant behavior, which allows the derivation of a master curve, according to the superposition principle, to calculate the pressure equilibrium time as a function of the holding pressure and the temperature.
Highlights
Shortening product life cycles and constantly increasing demands on product quality inevitably led to the use of injection molding simulations in the conception phase of the product development of polymer components
The shifting of the curves according to the superposition principle over the compression rate with a temperature shift factor α allows the derivation of a temperature-invariant master curve of the behavior of dynamic solidification, Figure 4b,c
This study shows the attempt to simulate the flow behavior in the holding pressure phase of the injection molding process, under laboratory conditions with a high-pressure capillary rheometer and a closed counterpressure chamber
Summary
Shortening product life cycles and constantly increasing demands on product quality inevitably led to the use of injection molding simulations in the conception phase of the product development of polymer components. By calculating the filling processes of the complex geometries of an injection mold before the mold is manufactured, possible errors can be identified early on and time-consuming and cost-intensive iteration loops can be avoided [1]. The calculation processes are divided into a filling, holding pressure, and cooling phase. The filling process of a cavity can be resolved and predicted with sufficient accuracy using innovative mold designs [2,3,4] as well as increasingly detailed and modified material models [5,6]. Integrative simulation techniques will be used to locally determine the influence of the component geometry and the manufacturing process on the material properties [7]. The aim of integrative simulations for amorphous polymers is, among other things, to predict the resulting optical, mechanical, and thermal component behavior on the basis of molecular orientations introduced during production [9]
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