A Monitoring Method for Viscosity and Print Quality in Screw-based Material Extrusion Additive Manufacturing

Screw-based material extrusion, an additive manufacturing (AM) technique utilizing thermoplastic pellets, provides notable advantages in material variety and industrial scalability compared to conventional filament-based AM. The viscosity of the molten polymer can significantly affect flow behavior, bead formation, and interlayer adhesion, thereby influencing the final part quality. Despite the importance of viscosity monitoring, real-time sensing technologies have rarely been applied to screw-based AM due to the complexity of the extrusion mechanism. In this study, a non-invasive, cost-effective method was proposed to estimate the viscosity of molten polymers and evaluate printing quality during extrusion. A Hall-effect current sensor was attached to the screw motor to measure real-time motor current, which was then correlated with screw torque and used to infer the polymer’s rheological properties. Experiments were conducted with two polymer types (amorphous and semi-crystalline) to validate the correlation between motor current and polymer viscosity as well as printed part quality. The proposed method demonstrated the feasibility of using motor current as a proxy for real-time viscosity monitoring in screw-based material extrusion. This approach contributes to the development of a reliable process monitoring framework for improving process stability and ensuring consistent part quality in industrial AM applications.