The paper shows the capability of state-of-the-art models and software to predict the fiber orientation distribution (FOD) on injection molded parts with a complex and thick-walled geometry. Predictions by the standard Folgar-Tucker model and the Reduced Strain Closure model were compared to measurements of the fiber orientation distribution obtained by X-ray Computed Tomography. Measurements and simulations were performed under different processing conditions to investigate the influence of injection velocity and packing pressure on the FOD. It was found that the predicted fiber orientation is in good qualitative agreement with the measurements. The measured orientation shows a distinct shell-core structure with high alignment of the fibers in flow direction in the shell layer and a orientation perpendicular to the flow direction in the core layer. While the orientation in the shell layer is predicted fairly well, a significant deviation is found in the prediction of the orientation in the core layer.

No abstract

The aim of this paper is to determine the reason for the large warpage of an injection molded chunky part made of glass fiber reinforced polyamide 6. State of the art commercial 3D injection molding simulation software was used to predict the warpage of the part. While the simulation predicted a product virtually free of warpage the molded parts showed a large deformation. Several molding experiments and X-ray computed tomography (μCT) scans of the moldings have been performed to figure out the reason for this. The μCT scans revealed voids in the thick walls of the part. It was found that these defects were the main cause of the unreliable simulation results. Therefore it is concluded that voids can have a major influence on the reliability of numerical warpage predictions. This paper shows a simplified method to determine the zones were voids will appear and shows the comparison with μCT-data.

No abstract

Prediction of shrinkage and warpage of injection molded plastic parts is a key issue of injection molding simulation. In the present work a U-shaped part is investigated experimentally and by means of state of the art injection molding simulation software. The part has thick walls in the corner where inner defects such as voids and porous zones may appear. Experiments and simulations were performed with POM and glass fiber reinforced polyamide. Measurements of pressure in the cavities and temperature profiles around the cavities were used to validate the numerical model. In case of POM it was found that warpage predictions are way off when the void volume is high and in good agreement when the void volume is minimized. No such correlation was observed in case of fiber reinforced materials. Here, shrinkage and warpage are dominated by the fiber orientation state with minor influence of the processing conditions. Predicted warpage was found to be extremely dependent on the used closure approximation.