Extrusion-based Manufacturing Process Research Articles

Numerical simulation of the extrusion process of viscoplastic materials using a radial point interpolation method

PurposeFused Filament Fabrication (FFF) is an extrusion-based manufacturing process using fused thermoplastics. Despite its low cost, the FFF is not extensively used in high-value industrial sectors mainly due to parts' anisotropy (related to the deposition strategy) and residual stresses (caused by successive heating cycles). Thus, this study aims to investigate the process improvement and the optimization of the printed parts.Design/methodology/approachIn this work, a meshless technique – the Radial Point Interpolation Method (RPIM) – is used to numerically simulate the viscoplastic extrusion process – the initial phase of the FFF. Unlike the FEM, in meshless methods, there is no pre-established relationship between the nodes so the nodal mesh will not face mesh distortions and the discretization can easily be modified by adding or removing nodes from the initial nodal mesh. The accuracy of the obtained results highlights the importance of using meshless techniques in this field.FindingsMeshless methods show particular relevance in this topic since the nodes can be distributed to match the layer-by-layer growing condition of the printing process.Originality/valueUsing the flow formulation combined with the heat transfer formulation presented here for the first time within an in-house RPIM code, an algorithm is proposed, implemented and validated for benchmark examples.

Influence of fiber alignment on pseudoductility and microcracking in a cementitious carbon fiber composite material

This research examines the effect of fiber alignment on the performance of an exceptionally tough 3D-printable short carbon fiber reinforced cementitious composite material, the flexural strength of which can exceed 100 N/mm2. The material shows pseudoductility caused by strain-hardening and microcracking. An extrusion-based manufacturing process allows accurate control over the spatial alignment of the fibers’ orientation, since extrusion through a tight nozzle leads to nearly unidirectional alignment of the fibers with respect to the directional movement of the nozzle. Specimens were investigated using mechanical tests (flexural and tensile load), augmented by non-destructive methods such as X-ray 3D computed tomography and acoustic emission analysis to gain insight into the microstructure. Additionally, digital image correlation is used to visualize the microcracking process. X-ray CT confirms that about 70% of fibers show less than 10° deviation from the extrusion direction. Systematic variations of the fiber alignment with respect to the direction of tensile load show that carbon fibers enhance the flexural strength of the test specimens as long as their alignment angle does not deviate by more than 20° from the direction of the acting tensile stress. Acoustic emission analysis is capable of evaluating the spatiotemporal degradation behavior during loading and shows consistent results with the microstructural damage observed in CT scans. The strong connection of fiber alignment and flexural strength ties into a change from ductile to brittle failure caused by degradation on a microstructural level, as seen by complementary results acquired from the aforementioned methods of investigation.

Processability of SS316L powder - binder mixtures for vertical extrusion and deposition on table tests

ABSTRACT Metal injection molding (MIM) feedstocks are mixtures made of a solid metal powder and a viscous polymeric binder. Vertical extrusion of MIM feedstock has seldom been investigated in the scientific literature, but it is the enabling technology for extrusion-based additive manufacturing processes (EAM). The EAM process adopts the movement of an extruder, relative to a build table, to deposit thin strands (roads) of the mixture and grow a 3D object, layer by layer. EAM may find applications for the consumer as well as industrial products. This paper addresses some of the challenges involved in achieving a consistent flow of molten feedstock mixture and discusses the consequences of the main process parameters on the extrusion-based manufacturing process. This work also relates the rheological behaviour of feedstock to the extrusion process, aiming at the dimensional stability of parts. An experimental study was performed on SS316L feedstock with a water-soluble binder system, by varying the percentage powder content of the mixtures, the extrusion temperature, the extrusion rate, the deposition table speed and the nozzle shape. The study evidences and explains why higher powder loading values and lower extrusion temperatures are the most useful conditions in order to obtain a stable flow with reduced swelling/shrinking phenomena.