###### Abstract  
This contribution provides a detailed comparison of the impact of various rheological models on the filling phase of injection molding simulations in order to enhance the accuracy of flow predictions and improve material processing. The challenge of accurately modeling polymer melt flow behavior under different temperature and shear rate conditions is crucial for optimizing injection molding processes. Therefore, the study examines commonly used rheological models, including Power-Law, Second-Order, Herschel-Bulkley, Carreau and Cross models. Using experimental data for validation, the accuracy of each model in predicting the flow front and viscosity distribution for a quadratic molded part with a PA66 polymer is evaluated. The Carreau-WLF Winter model showed the highest accuracy, with the lowest RMSE values, closely followed by the Carreau model. The Second-Order model exhibited significant deviations in the edge region from experimental results, indicating its limitations. Results indicate that models incorporating both shear rate and temperature dependencies, such as Carreau-WLF Winter, provide superior predictions compared to those including only shear rate dependence. These findings suggest that selecting appropriate rheological models can significantly enhance the predictive capability of injection molding simulations, leading to better process optimization and higher quality in manufactured parts. The study emphasizes the significance of comprehensive rheological analysis and identifies potential avenues for future research and industrial applications in polymer processing. n pacs: 27 August 2024 16 September 2024 18 September 202  
be identified are the Power-Law, Second-Order, Herschel-Bulkley, Bird-Carreau, Carreau, and Cross models. Each of these rheological models has its own specific parameters and properties that influence the simulation results. These models differ in their sensitivity to factors such as shear rate and temperature, which can have a significant impact on the predicted flow front, viscosity distribution, and ultimately the quality of the molded part [7; 8]. The studies by [PERSON] et al. [9] and [PERSON] et al. [10] demonstrate the potential of numerical modeling of the filling phase in injection molding with a full volumetric approach in the Ansys CFX software. In contrast to the approach taken by [PERSON] et al. [9], who model the polymer as a Newtonian fluid, [PERSON] et al. [10] employ an approximation to implement their own rheological relationships as a non-Newtonian fluid in Ansys CFX. An earlier study by [PERSON] et al. [5] has already addressed selected rheological models that are not commonly used [6]. These inquiries demonstrated a substantial divergence between injection molding simulation results and experiments. Such discrepancies can be attributed to the inaccurate modeling of rheological parameters and the simplified Hele-Shaw formulation used in combination with the chosen geometry. However, the selection of these models can significantly influence the simulation results. This demonstrates the necessity for a comprehensive comparison of these models. This study aims to provide a comparative analysis of different rheological models during the filling phase of injection molding simulations. The main objective is to evaluate the accuracy of selected rheological models in predicting the flow front behavior, viscosity distribution and their agreement with experimental data. This comparison allows for the identification of the strengths and weaknesses of each rheological model, as well as the acquisition of valuable insights for the selection of the most appropriate rheological model for injection molding simulations. It is important to note that the results of this study can only be considered indicative of other thermoplastic polymers, as they relate specifically to the employed thermoplastic polymer PA66.