Shear deformation leads to stretching of the molecules and a higher nucleation rate and, subsequently, to smaller spherulitic structures. Besides the influence of mold temperature, it is also known that the application of shear on the melt during the injection molding process strongly affects the crystallization behavior (flow-induced crystallization) and, as a consequence, the morphology of semicrystalline polymers. This includes the geometry of the nozzle and that the effect of pressure on the viscosity of the material must not be neglected. Although a generally good accordance was stated, it was recommended to include some further aspects in the simulations for more precise results. The correlation between simulations and experiments was investigated in terms of flow behavior, pressure build up along the flow path, warpage, and residual stresses. Especially in complex geometries, the experimental determination of these stresses yields very high experimental effort (if possible at all). Furthermore, such simulations allow us to assess the internal stresses that build up during the manufacturing process. The role of injection molding simulation for filling studies and the prediction of basic processing parameters and for the evaluation of optimum processing parameters to, for example, ensure dimensional stability has become more and more pronounced over the past years. For POM in specific, also a few studies are available. For standard polymers such as polypropylene, the morphology and mechanical properties of injection molded parts and their correlation have been quite well examined in the past. These parameters and conditions lead to the morphology, residual stresses, and mechanical properties and therefore the performance of the final part.
There is a strong correlation between process parameters that are set on the machine (input), such as holding pressure, temperature of the heaters, coolant inlet temperature, and cooling time, and resulting processing parameters (output), for example, melt temperature, mold temperature, cooling conditions, and crystallization conditions. The processing parameters during injection molding play a crucial role in the determination of the performance of the future part. Parts from very small to very large size and mass can be produced. Additionally, a rather high geometrical freedom is given. Short cycle times, high repeatability, and the possibility to partly or even fully automatize the process make it an excellent choice for high volume production. The dominant processing method for POM and polymers in general is injection molding.
It shows excellent (fracture) mechanical and tribological properties along with very good wear resistance and dimensional stability. The thermoplastic polymer polyoxymethylene (POM) is used in a broad field of structural applications such as bearing rolls and gear wheels and in the automotive industry. Its applicability, however, is still limited to 2.5D models in Autodesk Moldflow, which, of course, is insufficient for complex, thick-walled 3-dimensional parts. The simulation is found to be a powerful tool for morphology prediction in polymeric parts. Also, the evolution of these parameters along the flow path is plausible. Predicted spherulite size and crystalline orientation factor reveal a good qualitative correlation with optical micrographs. The simulations are found to be good accordance with the experiments. The crystallization kinetics data were measured, and simulations in 3D and 2.5D with and without crystallization analysis were conducted in Autodesk Moldflow. In order to investigate the potential of injection molding simulation for the prediction of the morphology, POM homopolymer specimens were injection molded. However, especially for semicrystalline polymers, the tools available for predicting the final morphology of injection molding parts still have significant limitations. It is well known that the processing conditions in polymer processing have a high impact on the resulting material morphology and consequently the component’s mechanical behavior.