Mike Kornely | Searcharxiv

arXiv2025

X-ray particle tracking velocimetry for steady-state rheological characterization: Case study of a complex polymer melt flow in material extrusion additive manufacturing

We introduce X-ray Particle Tracking Velocimetry (XPTV) as a promising method to quantitatively resolve the velocity field and associated rheological information of polymer melt flow within the nozzle of a fused filament fabrication (FFF) printer. Employing tungsten powder as tracer particles embedded within a polymer filament, we investigate melt flow dynamics through an aluminum nozzle in a custom setup comparable to commercial printers. The velocity profiles obtained via XPTV reveal significant deviations from classical Newtonian flow, highlighting complex heterogeneous and non-isothermal behavior within the melt. From these measurements, we determine the local infinitesimal strain rate tensor and correlate flow-induced non-Newtonian effects to spatially varying temperature distributions, reflecting incomplete thermal homogenization within the nozzle. We complement the experiments with computational fluid dynamics simulations of the flow inside the printing nozzle, incorporating filament melting through an enthalpy-porosity formulation and treating the air-polymer melt interface using a two-phase approach. The simulated velocity profiles agree closely with the XPTV measurements across the investigated operating conditions, supporting the experimental interpretation. Our findings demonstrate the capability of XPTV to quantify both velocity fields and rheological properties, underscoring its potential as a tool for investigating opaque polymer melt flows in additive manufacturing, industrial processing, and rheology. To our knowledge, this is the first application of XPTV to polymer melt rheology. It enables measurements that are inaccessible to conventional optical methods.

cond-mat.soft↗

arXiv2023

Analysis of melting and flow in the hot-end of a material extrusion 3D printer using X-ray computed tomography

This paper presents in-situ X-ray computed tomography (CT) experiments used to study the flow behavior within a conventional hot-end of a fused filament fabrication printer. Three types of experiments were performed to better understand the melt and flow behavior. In one experiment, 360{\deg} CT scans were conducted, focusing on the air gap between the filament and the nozzle wall. In a second experiment, the flow profile inside the nozzle was studied using radiography. To provide a good contrast to the surrounding nozzle material, filament was prepared containing small amounts of tungsten powder as a contrast agent. During a third test, the extruder forces were measured and compared with the X-ray results and the predictions of a numerical simulation. The CT scans showed that at higher filament speeds, less area of the nozzle wall is in contact with the melt. This means that a larger part of the barrel section is occupied by an air gap between the solid filament and the nozzle wall. In contrast to the filament speed, the influence of the heater temperature shows no discernible effect on the part of the nozzle filled with melt. Radiographic evaluation of the velocity profile revealed a parabolic distribution under the studied conditions, closely matching numerical simulations modeling the flow as isothermal and non-Newtonian. The study's findings offer potential for improving nozzle design. Furthermore, the presented experimental method can serve as a valuable tool for future validation of more complex numerical simulations.

physics.flu-dyn↗