Numerical and experimental analysis of bead cross-sectional geometry in fused filament fabrication

Fused filament fabrication (FFF) stands as a prominent thermoplastic additive manufacturing technique that has a wide range of potential applications. However, the conventional FFF process encounters limitations in unconventional environments, particularly in environments devoid of gravity, such as in extraterrestrial environments or in limited manufacturing conditions where maintaining consistent nozzle standoff distance becomes a challenging task. Fluctuations in nozzle standoff distance lead to inadequate material adhesion and dimensional errors, which results in a high failure rate and prolonged completion time. Thus, the conventional FFF process requires continuous monitoring or human intervention to ensure successful operation. To overcome the shortcomings of the traditional FFF process, an electric field-assisted FFF (E-FFF) process can be utilized to reduce the need for constant supervision and enable reliable production of parts. The E-FFF process integrates a high-voltage power supply unit with a standard FFF printer, generating an electrostatic force between the nozzle and the build plate. The generated electrostatic force can effectively attract the extruded molten polymer toward the build plate, even at a larger z-height of up to 1200 μm in unconventional build platform orientations such as vertical or reverse printing orientation. In this paper, finite element analysis is used to simulate the FFF and E-FFF process. The simulation focuses on the adhesion between extruded material and build plate with extended nozzle standoff distances and predicts the minimum voltage required to achieve a good material adhesion in unconventional orientations for the E-FFF process. The simulation model demonstrated its efficacy by estimating the minimum required voltage levels necessary for successful printing within the E-FFF process across a range of nozzle standoff distances in unconventional orientations.

The mechanical properties of components manufactured ("printed") by the Fused Filament Fabrication (FFF) process are usually limited by the cohesion achieved between melt-processed thermoplastic filament strands perpendicular to the filament deposition direction. This significantly limits the usefulness of the FFF process and commercial FFF printers for the production of a wide range of functional components and consumer goods, so that the FFF process is currently used for the production of prototypes for visualization purposes only. In order to open up potential markets for structural components in the future, the realization of an optimized bonding layer quality via a significantly improved cohesion between the filament strands is essential. Since the mechanical properties of polymeric materials generally depend on the density of molecular entanglements and tie molecules in the material structure, it is of the utmost importance to realize the highest possible density of such entanglements and tie molecules between the individual filament layers also in FFF components. The present work deals with different methods of heat input to improve the entanglement and tie molecule density in the bonding layer of FFF components through enhanced polymer diffusion at temperatures far above the glass transition temperature for amorphous plastics or the melting temperature for semi-crystalline plastics, respectively. Heat can be either globally or locally introduced by conduction, convection, and radiation, the latter being the most effective for the FFF process when applied locally via properly controlled laser radiation. Ideally, a compact, cost effective and easy to use radiation source is used for this purpose. Hence, a setup based on a diode laser is presented in this work. Furthermore, an idealized calculation of the amount of heat required to promote the formation of interfilament bonds and thus to achieve an increased mechanical property profile was carried out. Two types of materials commonly used for the FFF process, polylactic acid (PLA) and acrylic-butadiene-styrene copolymer (ABS), were used for the experimental procedure. After producing a special monofilament with improved laser absorption characteristics, test specimens were produced. As a reference, test specimens made of the same materials were printed with the conventional FFF process. The differently manufactured test specimens were characterized optically and visually, using a stereomicroscope, and mechanically, using tensile tests. In addition, specimens were produced with a specially designed device for local heat input onto the substrate layer region just ahead of the new filament deposition. The effectiveness of this laser-assisted method could be proven in tests by adjusting the process parameters of the FFF process. After finding the optimum printing speed (equivalent to the laser power applied) for the materials PLA and ABS, an optical examination of the fracture surfaces of test specimens with filaments laid down perpendicular to an applied tensile load showed a significant increase in plastic deformation capacity, indicative of an improved interfilament bonding. This was confirmed by the mechanical property values determined in tensile tests. Thus, for optimized printing speeds, an increase in tensile strength values of ~20% for PLA and ~7% for ABS was achieved. For elongation at break, the improvements were ~21% for PLA and ~34% for ABS, respectively. The methodology of laser-assisted FFF printing thus offers great potential for mechanically and structurally optimized functional components with specifically introduced anisotropy. • Interfilament entanglements control strength of printed polymer parts. • Novel diode laser-assisted fused filament fabrication process (FFF) is presented. • Enhanced local laser absorption and heat introduction via specific additives. • improved bonding layer strength of FFF components was achieved.

There is in-depth understanding of the effects and interactions of various process parameters on the mechanical properties and dimensional accuracy of parts produced through fused filament fabrication (FFF). Surprisingly, local cooling in FFF has been largely overlooked and is only rudimentarily implemented. It is, however, a decisive element of the thermal conditions governing the FFF process and of particular importance when processing high-temperature polymers such as polyether ether ketone (PEEK). This study, therefore, proposes an innovative local cooling strategy, which allows for feature-specific local cooling (FLoC). This is enabled by a newly developed hardware in combination with a G-code postprocessing script. The system was implemented on a commercially available FFF printer and its potential was demonstrated by addressing typical drawbacks of the FFF process. Specifically, with FLoC, the conflicting requirements for optimal tensile strength versus optimal dimensional accuracy could be balanced. Indeed, feature-specific (i.e., perimeter vs. infill) control of thermal conditions resulted in a significant increase in ultimate tensile strength and in strain at failure in upright printed PEEK tensile bars compared with those manufactured with constant local cooling-without sacrificing the dimensional accuracy. Furthermore, to improve the surface quality of downward-facing structures the controlled introduction of predetermined breaking points at feature-specific part/support interfaces was demonstrated. The findings of this study prove the importance and capabilities of the new advanced local cooling system in high-temperature FFF and provide further directions on the process development of FFF in general.

Fused filament fabrication (FFF) is an additive manufacturing process, which constructs physical items by fused melt material, selectively deposited layer-by-layer through a heated extrusion mechanism. Parameters’ selection and control in FFF are of utmost importance since they significantly affect the surface quality (SQ) and dimensional accuracy (DA) of the FFF printed parts. In the present paper, initially, the FFF process is briefly presented. Next, a cause-and-effect diagram exhibits the process parameters’ categorization with the SQ and DA of the manufactured parts. Then, according to the robust design theory, the process parameters are divided into three classes, i.e., the signal, the control, and the noise. This classification supports the selection of appropriate FFF printers, according to the control parameters, whereas it facilitates the optimization of the SQ and DA of printed parts, concerning the signal parameters. Finally, the impact of each parameter on SQ and DA is presented, supported by an extensive literature review. Overall, the process parameters’ optimization is critical for the SQ and DA. Therefore, they should be adjusted to achieve higher quality and less post-processing work.

The Additive Manufacturing (AM) process of Fused Filament Fabrication (FFF) deals with the manufacturing of parts by adding multiple layers of fused material. The FFF process is often used for rapid prototyping or the fabrication of small batches of highly specific parts. However, FFF’s reliability is comparatively lower than other manufacturing processes. The accuracy of a product’s geometry in the FFF process is significantly influenced by process errors such as nozzle clogging, improper build platform temperature settings, and incorrect leveling calibration, leading to defects like geometric deviation or deformation. In this study, an investigation is performed on the geometric deformations in monolayer parts produced through the FFF process, focusing on the effects of simulated extruder clogs and under-extrusion region-specific induced defects. A dataset composed of images obtained from monolayer parts was produced, and the analysis employed MATLAB’s Image Processing Toolbox to perform histogram-based statistics, area measurements, and pixel-to-millimeter conversion, enabling the assessment of angle divergence and deformation extent across three printing conditions: regular printing, under-extrusion (D1), and retraction (D2). Results from the D1 condition indicate moderate geometric deformation, with 36% of the parts showing angle deviations between 0.6 and 0.8 degrees. Deformations ranged up to 1.8 degrees, and affected areas varied from 10 to over 50 mm², with most concentrated between 30 and 35 mm². These results reveal consistent yet variable impacts of under-extrusion. In contrast, D2 parts exhibited smaller, more centralized defects, with affected areas mostly between 10 and 18 mm², peaking around 14 mm². Despite their smaller size, the central region of the defects poses greater risks to structural integrity. The findings emphasize the criticality of early detection and stringent quality control in the FFF process, revealing that even minor and region-specific initial layer defects can significantly compromise the quality of finished products.

Purpose This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle geometry. This paper also focuses on the manufacturing feasibility of the nozzles and 3D printing of the molten beads using the developed nozzles. Design/methodology/approach The flow of a highly viscous polymer from a nozzle, the melt expansion in free space and the deposition of the melt on a moving platform are captured using the FLUENT volume of fluid (VOF) method based computational fluid dynamics code. The free surface motion of the material is captured in VOF, which is governed by the hydrodynamics of the two-phase flow. The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian and non-isothermal flow is assumed. Under such assumptions, the spreading characteristic of the polymer is simulated with different nozzle-exit geometries. The governing equations are solved on a regular stationary grid following a transient algorithm, where the boundary between the polymer and the air is tracked by piecewise linear interface construction (PLIC) to reconstruct the free surface. The prototype nozzles were also manufactured, and the deposition of the molten beads on a flatbed was performed using a commercial 3D printer. The deposited bead cross-sections were examined through optical microscopic examination, and the cross-sectional profiles were compared with those obtained in the numerical simulations. Findings The numerical model successfully predicted the spreading characteristics and the cross-sectional shape of the extruded bead. The cross-sectional shape of the bead varied from elliptical (with circular nozzle) to trapezoidal (with square and star nozzles) where the top and bottom surfaces are significantly flattened (which is desirable to reduce the void spaces in the cross-section). The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment. The quantitative comparison of the cross-sectional profiles against experimental observation also indicated a favorable agreement. The significant improvement observed in the bead cross-section with the square and star nozzles is the flattening of the surfaces. Originality/value The developed numerical algorithm attempts to address the fundamental challenge of voids and bonding in the FFF process. It presents a new approach to increase the inter-bead bonding and reduce the inter-bead voids in 3D printing of polymers by modifying the bead cross-sectional shape through the modification of nozzle exit-geometry. The change in bead cross-sectional shape from elliptical (circular) to trapezoidal (square and star) cross-section is supposed to increase the contact surface area and inter-bead bonding while in contact with adjacent beads.

The purpose of this research was to investigate the suitability of the Fused Filament Fabrication (FFF) process for low pressure/vacuum environment. This included investigating the ability of an FFF printer to function in a vacuum and evaluation of the dimensional accuracy and mechanical properties of the manufactured components. For this purpose, a commercially available FFF printer using polycarbonate as raw material was placed in a vacuum environment of 10 mbar. Test components were then fabricated in vacuum with a control group fabricated in a normal atmosphere (1 bar). Test components were evaluated for dimensional and mass accuracy, quality and presence of defects. Flexural, tensile and compressive testing was carried out according to ASTM D790, D638 and D695 respectively. Dimensional analysis of components showed equivalent small deviation for both environments. Components fabricated in the vacuum environment had 5.4% higher tensile yield strength and 59% higher extension at break compared to components printed in a normal atmosphere indicating an increased strength and ductility. Components tested in compression had approximately 11.2% higher compressive strength when printed in a vacuum environment. No differences were observed during the flexural test. In space, due to the vacuum environment, polymers and organic material are susceptible to release molecules via an outgassing process. Assessment of the molecular organic contamination generate during the printing process in vacuum is low and seems to mostly originated from the components of the printer. The results provided demonstrated the possibility to use the FFF process in a vacuum environment to fabricate dimensionally accurate, high-quality polycarbonate components with a variety of geometries without loss of mechanical performance. This work provides a proof of concept that FFF can be used to develop out-of-earth manufacturing technologies (in orbit/in space/on planet) allowing part production for new maintenance and repair strategy or to potentially manufacture entire structure more efficiently overpassing launch constrain by using only raw material brought from earth.

Fused filament fabrication (FFF) is one of the most popular additive manufacturing (AM) processes due to its simplicity and low initial and maintenance costs. However, good printing results such as high dimensionality, avoidance of cooling cracks, and warping are directly related to heat control in the process and require precise settings of printing parameters. Therefore, accurate prediction and understanding of temperature peaks and cooling behavior in a local area and in a larger part are important in FFF, as in other AM processes. To analyze the temperature peaks and cooling behavior, we simulated the heat distribution, including convective heat transfer, in a cuboid sample. The model uses the finite difference method (FDM), which is advantageous for parallel computing on graphics processing units and makes temperature simulations also of larger parts feasible. After the verification process, we validate the simulation with an in situ measurement during FFF printing. We conclude the process simulation with a parameter study in which we vary the function of the heat transfer coefficient and part size. For smaller parts, we found that the print bed temperature is crucial for the temperature gradient. The approximations of the heat transfer process play only a secondary role. For larger components, the opposite effect can be observed. The description of heat transfer plays a decisive role for the heat distribution in the component, whereas the bed temperature determines the temperature distribution only in the immediate vicinity of the bed. The developed FFF process model thus provides a good basis for further investigations and can be easily extended by additional effects or transferred to other AM processes.

Electric field-assisted fused filament fabrication process for robust additive manufacturing in unconventional orientations

Additive manufacturing (AM) is not necessarily a new process but an advanced method for manufacturing complex three-dimensional (3D) parts. Among the several advantages of AM are the affordable cost, capability of building objects with complex structures for small-batch production, and raw material versatility. There are several sub-categories of AM, among which is fused filament fabrication (FFF), also commonly known as fused deposition modeling (FDM). FFF has been one of the most widely used additive manufacturing techniques due to its cost-efficiency, simplicity, and widespread availability. The FFF process is mainly used to create 3D parts made of thermoplastic polymers, and complex physical phenomena such as melt flow, heat transfer, solidification, crystallization, etc. are involved in the FFF process. Different techniques have been developed and employed to analyze these phenomena, including experimental, analytical, numerical, and finite element analysis (FEA). This study specifically aims to provide a comprehensive review of the developed numerical models and simulation tools used to analyze melt flow behavior, heat transfer, crystallization and solidification kinetics, structural analysis, and the material characterization of polymeric components in the FFF process. The strengths and weaknesses of these numerical models are discussed, simplifications and assumptions are highlighted, and an outlook on future work in the numerical modeling and FE simulation of FFF is provided.

Thermal characterization of short carbon fiber reinforced high temperature polymer material produced using the fused filament fabrication process

The advancement of Additive Manufacturing (AM) technologies, particularly Fused Filament Fabrication (FFF), has significantly broadened the possibilities for precision manufacturing. However, FFF remains susceptible to geometric distortions that can compromise part quality. This study investigates fundamental layer features in monolayer FFF parts produced under three printing conditions: a standard scenario (H) and two defect induced cases (D1 and D2) introduced via G-code modifications. Using optical microscopy and geometric analysis, we measured region specific features, including contour and raster widths, gap distances, and their variability. Under condition H, contour widths in the right region showed high precision, with mean values of 0.6343 mm (CW1), 0.5886 mm (CW2), and 0.6043 mm (CW3), and standard deviations below 0.07 mm. In contrast, defect condition D1 exhibited reduced uniformity, with CW1 and CW2 decreasing to 0.4647 mm and 0.4402 mm, respectively. In the upper region, D1 led to a pronounced degradation: CW1b decreased to 0.3795 mm and gap dimensions became more variable (e.g., G1b = 0.1884 mm, standard deviation = 0.0346 mm). Under condition D2, the central region exhibited the most severe distortion, with the “d” feature mean reaching 20.17 mm and a standard deviation of 2.41 mm. In addition, monolayer features such as RWA and RWP increased markedly under D2 compared to H, reaching 0.6587 mm and 0.5680 mm, respectively. These findings show that extrusion irregularities can critically affect geometric fidelity. Our results quantitatively link process anomalies to feature deviations in FFF printing, reinforcing the need for improved monitoring and correction mechanisms. Beyond quantifying feature changes under induced defects, this study aims to provide actionable first layer acceptance windows to support in situ monitoring. In practice, the signatures reported here (e.g., raster after width ≥ 0.60 mm and inter raster gap ≈ 0.35 mm under D2; contour widths ≤ 0.50 mm under D1) enable simple camera based screening or ML labeling to (i) flag the defect class in real time and (ii) trigger corrective actions, such as pausing the build or adjusting flow and retraction settings. Future work will explore real time defect detection and adaptive G-code compensation to improve dimensional accuracy and repeatability.

Synergistic effect of plasticizer and nucleating agent on crystallization behavior of polylactide during fused filament fabrication

Fused Filament Fabrication (FFF), a process parameters-dependent manufacturing method, currently dominates the additive manufacturing (AM) sector because of its prominent ability to produce parts with intricate profiles, customise products, and minimise waste. Though the effects of FFF process parameters were investigated experimentally, recent research highlighted the importance of developing numerical modelling and computational methods on optimising the FFF printing process and FFF-printed materials. This study aims to investigate the tensile strength (TS) of FFF-printed high-impact polystyrene (HIPS) via devising a systematic testing and analysis framework, which combines experimental testing, representative volume element (RVE)-finite element method (FEM), rule of mixture (ROM), and artificial neural networks (ANN). HIPS samples are fabricated using FFF considering the variations of infill density, layer thickness, nozzle temperature, raster angle, and build orientation, and tested with standard tensile testing. The rule of mixtures (ROM) and its modified version (MROM) are employed to calculate the TS of longitudinally and transversely built samples at various infill densities, respectively, while an ANN model is constructed to investigate the effect of material anisotropy precisely. The optimal ANN architecture is built with five hidden layers with the number of neurons in each layer as 44, 82, 169, 362, and 50. Although both MROM and ANN perform well on the validation set, ANN exhibits superior accuracy with only a maximum error of 0.13% for training set and 11% for validation set. The combination of the RVE-FEM, MROM, and ANN approaches can significantly improve the FFF printing process of polymers for optimisation.

On the elastic stress singularities and mode I notch stress intensity factor for 3D printed polymers