Advances in modeling transport phenomena in material-extrusion additivemanufacturing: Coupling momentum, heat, and mass transfer

Material-extrusion (MatEx) additive manufacturing involves layer-by-layer assembly ofextruded material onto a printer bed and has found applications in rapid prototyping.Both material and machining limitations lead to poor mechanical properties of printedparts. Such problems may be addressed via an improved understanding of thecomplex transport processes and multiphysics associated with the MatEx process.Thereby, this review paper describes the current (last 5 years) state of the art modelingapproaches based on momentum, heat and mass transfer that are employed in aneffort to achieve this understanding. We describe how specific details regardingpolymer chain orientation, viscoelastic behavior and crystallization are often neglectedand demonstrate that there is a key need to couple the transport phenomena. Such acombined modeling approach can expand MatEx applicability to broader applicationspace, thus we present prospective avenues to provide more comprehensive modelingand therefore new insights into enhancing MatEx performanc

Numerical Modeling of the Material Deposition and Contouring Precision in Fused Deposition Modeling

We present a numerical model of the material deposition in fused deposition modeling. The flow of the material extruded from the printing head nozzle is simulated within the computation fluid dynamics (CFD) paradigm. The molten thermoplastic is modeled as an incompressible Newtonian fluid with a free surface. The numerical model provides a prediction of the shape of the printed road. Four deposition strategies are investigated to print a road along a tool path with a 90° turn. The investigated scenarios include the ideal case of an extrusion rate synchronized with the printing speed, as well as the cases of a sharp tool path with a stop-at-turn trajectory, and a smoothed tool path with blended acceleration. The CFD simulation provides a way to optimize the tool path planning and the deposition strategy, in order to improve dimensional accuracy in extrusion-based additive manufacturing.Mechanical Engineerin

Combining Modeling and Measurements To Predict Crystal Morphology in Material Extrusion

Semicrystalline polymer melts are commonly used in material extrusion (MatEx) for 3D printing. Although flows have a profound effect on polymer crystallization, the relationship between typical MatEx deformation rates and printed-part crystal morphology is yet to be understood. Here, MatEx is used to print a wall of polylactic acid filaments. The linear rheology and quiescent crystallization kinetics are characterized, infrared imaging is used to measure temperature variations during the MatEx process, and optical microscopy is employed to determine the resulting crystal morphology before and after a postprinting thermal annealing process. Our flow-enhanced crystallization model demonstrates that MatEx-induced polymer stretch leads to a higher nucleation density and greater space filling in the weld regions between deposited filaments. Consequently, after annealing, the weld regions feature smaller spherulites than the filament center, as shown by optical microscopy. Finally, flow-induced crystallization is proposed as a method to improve weld toughness