Dimensions of the deposited strand in the material extrusion process: Experimental and numerical investigations
Résumé
The material extrusion process is investigated by focusing on the geometry of a single strand extruded through a printing nozzle and deposited on a substrate of a 3D printer. An experimental protocol is set to determine the width W , and the height H, of a strand. The geometry depends mainly on the nozzle diameter D, the gap between the substrate and the tip of the nozzle g, the extrusion velocity U and the printing velocity V. The relevant parameter to determine W/D and H/g is reduced to one dimensionless parameter equal to (D/g)(U/V). A computational multiphase flow is described using a level set approach and a finite element method. The heat transfer is also taken into account in the set of governing equations. The polymer is considered as a generalised Newtonian fluid. An accurate description of the interface between the polymer and the surrounding air is developed based on an anisotropic remeshing procedure. Two different situations are numerically solved for which: (i) a first case with a g/D ratio less than one and (ii) a second case with a g/D ratio larger than one. In the first situation, the spreading below the nozzle is more or less radial around the vertical axis of the extruder which is not the case in the second situation. The numerical shape geometry is in good agreement with experimental observations. The thermal cooling underlines that the relevant parameters are the perimeter and the area of the strand cross-section and the Péclet number based on the printing velocity. The numerical predictions of W/D and H/g agree with experimental results.
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