Abstract
Additive manufacturing by material extrusion such as the widespread fused filament fabrication is able to improve 3D printed part performance by using short fiber reinforced composite materials. Fiber alignment is critical for the exploitation of their reinforcing effect. This work investigates the influence extrusion parameters have on the fiber alignment by conducting set of experiments on the process parameters determining whether the flow under the nozzle is convergent or divergent. A strong impact of flow conditions during extrusion line shaping on the fiber alignment is observed and two extremes are tested which show a large difference in strength, stiffness and strain at break in tensile testing along the extrusion lines. From highest to lowest fiber alignment, strength is reduced by 41% and stiffness by 54%. Fiber misalignment also leads to inhomogeneous strain fields in the layers when tested perpendicular to the extrusion lines. It is demonstrated that material flow after the nozzle has a high impact on the material properties of short fiber reinforced 3D printed parts and needs to be considered in process design.
Highlights
Additive manufacturing (AM) by material extrusion, such as the widespread fused filament fabrication (FFF), produces parts directly from digital files by melting plastics in a hot nozzle and depositing it along a toolpath
The results show a large impact of extrusion parameters on the alignment of fibers during FFF
All samples had a higher fiber misalignment than the filament used for printing which had a standard deviation of 5.4◦, and higher than an extrusion into air that had a standard deviation of 7.4◦, which increase was probably due to die swell effects as described in [44]
Summary
Additive manufacturing (AM) by material extrusion, such as the widespread fused filament fabrication (FFF), produces parts directly from digital files by melting plastics in a hot nozzle and depositing it along a toolpath. To explain more in detail, we introduce a local coordinate system in the material, based on the toolpath, to describe the of 24 material properties in Figure 1 that will be used in this article
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