Thermomechanical model for predicting forces in injection molding

Injection molding remains the dominant manufacturing process for high-volume production of complex thermoplastic parts. A comprehensive understanding of the loads acting on the mold and the injected part during both injection and ejection phases is crucial. Current design guidelines for ejection systems largely rely on empirical knowledge, often leading to over-design and reduced usable mold area that could otherwise be dedicated to more efficient cooling or more compact ejection systems. This work addresses these limitations by developing a numerical–computational model to estimate ejection forces in injection molding processes. The proposed approach integrates rheological and thermomechanical simulations, covering the process from filling to ejection. The model performance is assessed through comparison with experimental data obtained from instrumented molds. Two case studies are presented to evaluate its behavior under different conditions. The first case study considers a simple tubular geometry and shows good agreement with experimental data, with a maximum deviation of 20% for the analyzed conditions. The second case study involves a more complex geometry from the electronics industry. In this case, the results indicate a deviation of approximately 3% relative to the average measured ejection force for the most reliable dataset, although the experimental validation is limited in scope. These results suggest that the proposed approach is capable of capturing the main trends of ejection forces, while highlighting the need for further experimental validation, particularly for complex geometries.