Nozzle clogging during direct ink writing of polymer matrix composites – A numerical simulation insight into the process

Enhancing properties of composite materials through aligned reinforcements in Direct Ink Writing (DIW), an extrusion-based additive manufacturing (AM) process, is a critical objective in engineering applications. The DIW process involves study of complex multiphase flow to determine the directionality of the reinforcement. Advanced numerical techniques are to be delployed to study the interplay of various forces and process parameters in the process. In this study, we use coupled Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) numerical techniques to investigate the flow of a graphite-reinforced PVA polymer matrix through a nozzle, a process not easily achievable through experimental means. The drag force, pressure gradient force, and virtual mass force are found significant based on a comprehensive analysis of simulation and experimental data. Non-linear regression analysis is performed to quantify the impact of these forces on reinforcement alignment. The orientation angle of reinforcements is chosen as the output parameter, with input parameters comprising nozzle outlet diameter, reinforcement aspect ratio, volume flow rate, polymer viscosity, and reinforcement concentration. Additionally, the nozzle clogging during printing is studied using the developed model. Nozzle rotation is proposed as an effective method to mitigate clogging, further enhancing the efficiency of the reinforcement alignment process. This research advances our understanding of composite material printing and offers practical solution for optimizing the alignment of reinforcements in polymer matrices, paving the way for developing high-performance composite materials with tailored properties using extrusion based AM processes.