Abstract
One of the major drawbacks of the thermoplastic Fused Filament Fabrication process (FFF) is the poor mechanical properties of the parts produced. This is mostly related to the macroporosities resulting from a limited coalescence between filaments. Coalescence is ruled by the viscosity and surface tension of a polymer. Thus, an accurate characterization of these two properties is required to model and optimize coalescence during filament deposition and cooling. In this work, a surface tension characterization procedure over a large temperature range (25–380 °C) is presented and applied to PolyEtherKetoneKetone (PEKK) material. Additionally, the Newtonian viscosity is characterized with rheometry. The coalescence is then simulated by coupling an existing semi-analytical model with a previously presented 2D heat transfer finite element simulation model. The results show the importance of the temperature dependent implementation of surface tension. Additionally, a parametric study provides an industrial understanding of the FFF process.
Highlights
Fused Filament Fabrication (FFF) is an additive manufacturing process
The first section of this paper describes the characterization of surface tension and viscosity of an aeronautical grade PEKK polymer up to its processing temperature
Adhesion begins with intimate contact, followed by coalescence of the extruded filaments, and interface healing
Summary
Fused Filament Fabrication (FFF) is an additive manufacturing process. Including other processes, such as stereolithography and selective laser melting, all additive manufacturing products and services will reach $15.8 billion USD in revenue in 2020 and $35.6 billion USD in 2024 [1]. The filament solidifies as it cools down with its environment and additional layers can be subsequently deposited This process offers the advantage of producing parts with complex geometry, with a wide choice of materials, and without requiring the use of a molding cavity. It is of primary importance to accurately characterize these two material properties up to processing temperatures Aeronautical grade thermoplastics, such as the PolyArylEtherKetone (PAEK) family, are commonly used to manufacture structural or semi-structural parts. They have a 59% variation for the temperature range of 345–367 °C; this could be due to different polymer molecular masses, which were not mentioned by the authors.
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