Novel Simulation Methodology for the Estimation of the Flow Mark Risk Associated with the Injection of Mass Colored Plastic Materials

Abstract

Due to their desired metallic effect, the so called “special effect” plastic materials are increasingly used in the automotive industry. Aluminum flakes fillers are commonly used in the automotive industry, especially for mid and large exterior trim plastic parts. However, an important drawback of these materials is the high risk of generating undesirable flow marks on the visible side of the part. In this context, this study focuses on developing a novel simulation methodology in order to predict the flow marks produced by the differential orientation of the Al flakes. In a first step, a physical reasoning that explains the link between the presence of technical features on the part skin (e.g. clips, ribs) and the flow perturbations at the source of Al flake orientations is proposed. This reveals the importance of the 3D fountain flow at the flow front for the transport of oriented particles at the part surface. In a second step, a new simulation methodology was developed and implemented in Moldflow injection molding software. The novelty of the simulation method consists in adapting the fiber orientation model to a simple midplane mesh approach, with the aim of predicting the flow mark zones. Even if the 3D fountain flow is not modeled for a midplane approach, one can still predict the flow mark generation zones by analyzing the flow perturbation generated at the core zone. This is one important feature of the present simulation methodology and is based on the physical reasoning proposed in the first step. Finally this new simulation methodology was applied to the injection of an exterior trim part developed by Renault and a correlation between the simulation results and the injection trails was undertaken. The risk zones revealed in the simulations correlates well with the flow mark zones obtained on physical parts, validating thus the present approach.