Comparison between computed and measured fibre orientation in injection moulded parts

Short fibre reinforced thermoplastic materials play an important role in automotive industries due to their excellent processing behaviour, reasonable good mechanical performance, high design freedom and cheap prices. Although the thermo-mechanical requirements for the materials used increase the development cycles decrease. Numerical simulation, FEA, analysis can be a strong assistant when judging designs and reducing cost and time consuming experimental tests. The mechanical properties for short fibre reinforced thermoplastics are mainly dominated by fibre orientation which results from injection moulding process. Several commercial tools offering 3D flow simulation are on the market, each of them with strengths and weaknesses and a lot of opportunities for future application in part design. In cooperation with Ecole Nationale Superieure des Mines de Paris a study was carried out in order to compare two different injection moulding simulation tools (MOLDFLOW MPI® and REM-3D®) with experimental data concerning fibre orientation prediction. The study contains investigations on the accuracy and sources of measurement errors on the well-established surface ellipse method on polished surfaces and gives an overview on the state-of-the art in this field. On the other hand simulation results compared with measurements on a sample geometry taken at different locations indicate that the accuracy of the simulation needs some improvement, too. Areas of fairly good agreement and those of significant differences are discussed. The importance of accurate fibre orientation on subsequent thermo-mechanical analysis is stressed out by comparing experimental data with simulated deformation behaviour. As a conclusion, alternatives both for experimental setup and algorithms used for the numerical prediction of fibre orientation so far based on the well-known Folgar-Tucker model are proposed. The limitations of this model for real parts will be discussed for this purpose.