Material characterization of injection molded thermo plastic materials for finite element analysis - Practical challenges

The Molding process of injection-molded plastics induces certain characteristics in the material that are not accurately modeled in the conventional FEM methodologies for Mechanical stress analysis and Modal analysis. This paper brings out the challenges that are encountered in the current simulation methodologies and discusses few of the methods practiced in the industry to overcome these challenges. Most critical challenge encountered in the FEM process revolves around accurate definition of the material model - namely orthotropic and anisotropic behavior. Modeling of such a behavior is warranted due to the variations in the fibre orientation induced by the injection molding process. The other challenges encountered are choice of appropriate simulation tool or interface for modeling the material, cost and learning curve for such a tool. In the specific cases related to Automotive Industry mentioned in this paper, Autodesk Mold flow is used for Injection Process simulation, prediction of fibre orientation and evaluating the data for material model (Orthotropic / Anisotropic). The date obtained from Mold flow is imported in the ANSYS Structural analysis tool for further Mechanical stress analysis and Modal analysis. Methods for avoiding the huge FE model from Mold flow simulation for further ANSYS CAE are also explained. Comparision of results from FE Model generated from Moldflow simulation and from ANSYS CAE for the same material model generated from Moldflow are discussed in detail. Methods for mapping fibre orientation from Fine Moldflow mesh to coarser structral mesh are also discussed. The effect on the stiffness prediction of components based on traditional FEM based material models and Material models adjusted to Fibre orientation are discussed.