Theoretical Evaluation of the Melting Efficiency for the Single-Screw Micro-Extrusion Process: The Case of 3D Printing of ABS

Abstract

One of the challenges for single-screw micro-extrusion or additive manufacturing (AM), thus 3D printing, of polymers is controlling the melting efficiency so that energy and equipment costs can be minimized. Here, a numerical model is presented for AM process design, selecting acrylonitrile–butadiene–styrene (ABS) as viscoelastic reference polymer. It is demonstrated that AM melting is different compared to conventional melting due to variation in extrusion dimensions, leading to a different balance in heating by conduction and viscous heat dissipation as caused by the shearing between the melt layers in the associated film layer near the barrel. The thickness of this melt film layer is variable along the screw length, and it is shown that simplified models assuming an overall average value are too approximate. It is highlighted that the screw frequency, pitch angle and compression ratio are important process parameters to control the point of melt finalization. In addition, the power-law index reflecting the shear thinning nature of the polymer melt is showcased as a key parameter. Moreover, AM process results assuming constant and temperature dependent specific heat capacities and thermal conductivities are compared. The current work opens the door for on-line AM process control, addressing all relevant operating and material parameters.

Effect of characteristic scale on the extrudate swelling behavior of polypropylene melt in a micro‐extrusion process

“…It should note that there were noticeable differences between the micro extruder and standard extruder in the extrusion process. Andrea La Gala et al [ 7 ] have demonstrated that the micro‐extrusion process can be described by a lower Brinkman number and a slower melting, in comparison with a conventional extrusion process at the same barrel temperature and screw speed. Their finding provided important referential merit for the process control in the micro‐extrusion experiment.…”

“…[ 5 ] Owing to the distinguishing feature of the flow channel with the characteristic scale at the micron level, the effect of extrudate swell behavior on the accuracy and precision of microproducts becomes much more significant than that in the conventional extrusion process. [ 6,7 ] Here, the term “characteristic scale” is adopted to represent the channel size in different types of the micro‐extrusion die due to the flexibility and extensibility of the meanings, such as the diameter D in the capillary die, [ 8 ] the height H in the slit die, [ 9 ] the gap H in the annular die, [ 10 ] and the average gap thickness D C in the micro profile die. [ 11 ] Therefore, it is crucial to investigate the extrudate swell behavior given the micro‐extrusion die design and process control.…”

Optimization and Scale-Up for Polymer Extrusion

“…Moreover, the following five main directions of development of the extrusion optimization and scaling-up can be distinguished: improvement of the models of extrusion processes which are the basis for optimization/scale-up procedures, and which could be based on the very promising concept of the coupled (DEM/CFD) modeling using the Discrete Element Method (DEM) for modeling of solid conveying and Computational Fluid Dynamics (CFD) for modeling of melting/melt flow [ 5 ]; coupling the models of starve fed extrusion and flood fed extrusion which would allow a smooth transition between them; extending the use of optimization/scale-up procedures to more demanding extrusion processes, e.g., extrusion of polymer blends, composites, filled polymers, reactive extrusions, and others; improvement of optimization procedures which was recently discussed in the literature [ 154 ]; extending the use of optimization/scale-up procedures to food processing [ 155 ], as well as to pharmaceutical industry [ 156 , 157 ], and 3D printing [ 158 ]. …”

“…extending the use of optimization/scale-up procedures to food processing [ 155 ], as well as to pharmaceutical industry [ 156 , 157 ], and 3D printing [ 158 ].…”

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

“…However, it must be recognized that a well-known manufacturing process, namely injection molding (IM), shares several aspects with PAM. It is worth noting, however, that some of the main assumptions applied in modeling the IM process cannot be used in the transition to a mathematical theory for MiE, mainly because of the smaller size of the extrusion system used (i.e., the 28 mm initial screw diameter in [ 7 ], in contrast with the 63.5 mm of IM machine studied in [ 8 , 9 , 10 ]).…”