A Combined Experimental and Modeling Study for Pellet-Fed Extrusion-Based Additive Manufacturing to Evaluate the Impact of the Melting Efficiency

Abstract

To improve the product quality of polymeric parts realized through extrusion-based additive manufacturing (EAM) utilizing pellets, a good control of the melting is required. In the present work, we demonstrate the strength of a previously developed melt removal using a drag framework to support such improvement. This model, downscaled from conventional extrusion, is successfully validated for pellet-based EAM—hence, micro-extrusion—employing three material types with different measured rheological behavior, i.e., acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA) and styrene-ethylene-butylene-styrene polymer (SEBS). The model’s validation is made possible by conducting for the first time dedicated EAM screw-freezing experiments combined with appropriate image/data analysis and inputting rheological data. It is showcased that the (overall) processing temperature is crucial to enable similar melting efficiencies. The melting mechanism can vary with the material type. For ABS, an initially large contribution of viscous heat dissipation is observed, while for PLA and SEBS thermal conduction is always more relevant. It is highlighted based on scanning electron microscopy (SEM) analysis that upon properly tuning the finalization of the melting point within the envisaged melting zone, better final material properties are achieved. The model can be further used to find an optimal balance between processing time (e.g., by variation of the screw frequency) and material product performance (e.g., strength of the printed polymeric part).

Comparing pellet‐ and filament‐based additive manufacturing with conventional processing for ABS and PLA parts

“…Fused filament fabrication (FFF) techniques for the layerby-layer production of final polymeric parts, fusing polymer filaments in the molten state, are rather established. [1][2][3][4][5][6][7][8][9][10][11][12] A competitive less mature additive manufacturing (AM) technique, as mainly developed in the last two decades, is (PBAM). In PBAM, polymers in the form of granules instead of filaments are fed in small single-screw extruders (SSEs) to allow for material deposition and solidification.…”

“…In PBAM, polymers in the form of granules instead of filaments are fed in small single-screw extruders (SSEs) to allow for material deposition and solidification. 1,2,[13][14][15][16][17][18][19][20][21] Such extrusion-based AM (EAM) overcomes limitations of filament-based AM, allowing applications for soft and brittle polymers that can be more challenging to 3D print. 22,23 The cost of the pellet feedstock material is also lower compared to the filament counterpart 23 and EAM allows to bypass the filament production extrusion process so that less degradation of the material is expected.…”

Setting the Optimal Laser Power for Sustainable Powder Bed Fusion Processing of Elastomeric Polyesters: A Combined Experimental and Theoretical Study

“…AM production methods offer remarkable advantages, such as considerably shorter times to develop prototypes, large freedom of geometrical design, and a fine resolution [ 6 , 7 , 8 , 9 ]. AM technologies encompass a broad range of possibilities, including fused deposition modeling (FDM) [ 10 ] or fused filament fabrication (FFF) [ 11 ], powder bed fusion (PBF) [ 12 ], pellet-extrusion-based AM [ 13 ], and stereolithography (SLA) [ 14 ]. Each of these technologies has specific advantages and has been developed for AM production of polymeric materials such as polylactic acid (PLA), acrylonitrile-butadiene-styrene (ABS), and polyamide 12 (PA12) [ 15 ].…”

A proposed mechanism for solid bed encapsulation: Based on comparing three dimensional andone‐dimensionalscrew melting models

“…[ 4,5 ] Several other proposed mechanisms have been investigated, including dispersed solids melting, [ 6 ] the application of grooved extruders, [ 7 ] a film thickness only function of the down channel coordinate, [ 8 ] the melt film as a function of both width and down channel coordinates, [ 9 ] a cylinder side only model, [ 10 ] a mathematical and experimental investigation, [ 11 ] modeling of polymer melting in a working channel, [ 12 ] and melting in 3D printing. [ 13,14 ]…”

“…[4,5] Several other proposed mechanisms have been investigated, including dispersed solids melting, [6] the application of grooved extruders, [7] a film thickness only function of the down channel coordinate, [8] the melt film as a function of both width and down channel coordinates, [9] a cylinder side only model, [10] a mathematical and experimental investigation, [11] modeling of polymer melting in a working channel, [12] and melting in 3D printing. [13,14] In this paper, three melting mechanism developments are presented for single screw extruders starting with the historic proposal of Tadmor. The introduction of model changes are detailed based on the evolution of the melting mechanisms using screw rotation theory.…”