Material Extrusion-based Additive Manufacturing Research Articles

The effect of interface enhancement on the mechanical properties of fibre-reinforced PA6 matrix composites in material extrusion-based additive manufacturing

The effect of interface enhancement on the mechanical properties of fibre-reinforced PA6 matrix composites in material extrusion-based additive manufacturing

Effect of oxide nanoparticles in aqueous alumina inks for material extrusion additive manufacturing

The effects of the addition of nanoparticles (NPs) of alumina (NA) and silica (NS) on the rheological properties of aqueous-based ceramic inks for material extrusion-based additive manufacturing (ME-AM) and sinterability of printed ceramic components were investigated. The inks were first designed using bimodal particle sizes of NPs with micro-alumina, and their solids fraction in printable inks was found to be dependent on the functionalization properties of NPs. NAs create a lubricating effect in the ink system and improve solids-loading in the ink. Meanwhile, NSs form silanol bonds in aqueous-based inks that increase viscosity and reduce solids-loading for a printable ME-AM ink. The inks containing NPs with higher solids-loading and optimized rheology were printed using ME-AM, and the printed components were sintered at 1400–1550 ºC. Adding NPs in the ink significantly improved the sinterability of printed shapes by enhancing sintering kinetics and filling-effects, with NS having a more significant effect than NA.

Optimizing metal part distortion in the material extrusion-thermal debinding-sintering process: An experimental and numerical study

The thermal debinding-sintering process plays an essential role in the context of material extrusion-based additive manufacturing (AM) for producing parts using metal injection molding (MIM). During thermal debinding, metal parts often experience material distortion and porosity, which negatively impacts their mechanical properties. Slowing down the debinding speed is a common approach to mitigate material distortion and porosity. However, this leads to a significant increase in the debinding time. In this study, we carried out debinding-sintering experiments to optimize the distortion and porosity in metal parts. These metal parts were manufactured utilizing bronze/polylactide (PLA) blend filaments and placed in crucibles of different sizes (small, medium, and large), with different heating rates and holding times. The results revealed that the small crucible yielded higher porosity levels in the metal parts, which could be reduced from 23% to 12% by extending both the heating and holding times. In contrast, the medium crucible managed to reduce porosity to approximately 15% without requiring an extension of the processing time. The large crucible, on the other hand, couldn't achieve further porosity reduction due to challenges in reaching the desired temperature. To gain a deeper insight into temperature distribution during the debinding process, we performed numerical simulations using the computational fluid dynamics (CFD) technique and obtained temperature profiles within the kiln using the three crucibles. Ultimately, we carried out standard mechanical tests on the resulting metal parts and evaluated the thermal debinding procedure under various conditions. The approach we employed, combining experiments and numerical simulations, demonstrated significant promise for enhancing the quality of metal parts in the thermal debinding-sintering process.

Additive Manufacturing of Fiber‐Reinforced Zirconia‐Toughened Alumina Ceramic Matrix Composites by Material Extrusion‐Based Technology

Material extrusion‐based additive manufacturing becomes interesting to fabricate oxide ceramic matrix composites. Herein, 0–30 vol% alumina fibers are added to zirconia‐toughened alumina powder mixture and extruded into filaments. Shrinkage and mechanical properties of filaments and 3D‐printed samples are investigated. Thermomechanical analysis is conducted on filaments with and without fiber content indicating lower shrinkage in the direction of fiber alignment during the sintering process. The flexural strength of the extruded filaments and printed bars is measured through a 4‐point bending test. Filaments containing 15 vol% fiber exhibit the highest flexural strength of 110 MPa, with additional fiber content leading to a reduction in flexural strength. Using Weibull calculation, it is observed that printed bars without fibers result in significantly lower bending strength in comparison to the filaments because of the presence of printing failures. Bars with 10 vol% fibers, printed with 0° infill orientation achieve the same mechanical properties as the filaments, even though in microcomputed tomography gaps between printed lines and voids between raster lines can be observed. These results demonstrate that fiber reinforcement of ceramics offers a great potential to avoid the reduction of mechanical properties by printing defects.

Flow mechanisms and their influence on the properties of EGaIn-graphene-poly(ethylene) oxide composites during material extrusion-based additive manufacturing

Polymer composites featuring room temperature liquid alloy particles complimenting other conductive fillers enable unique thermal and electrical properties. Direct-ink-writing approach is an intriguing processing path for these material systems, offering high resolution microstructural and property control. This paper investigates the composition-process-property relationships for material extrusion-based additive manufacturing of EGaIn-Graphene-Poly(ethylene) Oxide composites. Particularly, the influence of composite composition, printing nozzle size and flow rate on electrical conductivity is studied through a mechanistic approach. In that, capillary rheometry and flow modeling was performed to describe the contribution of shear flow and wall slip to the ink flow and how they drive the conductivity of printed structures for various composite ink compositions and process parameters. Influence of composition on material property and process driven conductivity were separately analyzed. Results indicate that EGaIn particles hinder material property-driven baseline average conductivity at high graphene loading. Shear flow and wall slip both increase conductivity. Graphene and total active material concentration increase wall slip and decrease shear flow, leading to a net negative effect of total active material concentration on conductivity. These findings will contribute to composite and process design towards additive manufacturing of composites with as-designed properties.

Design and fabrication of bioinspired pattern driven magnetic actuators

Additive manufacturing (AM) has drawn significant attention in the fabrication of soft actuators due to its unique capability of printing geometrically complex parts. This research presents the design and development of an AM process for bioinspired, deformable, and magnetic stimuli-responsive actuator arms. The actuator arms were fabricated via the material extrusion-based AM process with magnetic particle-polymer composite filaments. Inspired by the rhombus cellular structure found in nature, different design parameters, such as the line width of the interior rhombus sides, and 3D printing parameters were studied and optimized to fabricate actuator arms that exhibit enhanced flexibility while being magnetically actuated. The trigger distance and deformation experiments revealed that the width of the rhomboids’ sides played a critical role in magnetic and bending properties. It was found that the sample with a line width of 550 µm and printing layer thickness of 0.05 mm had the maximum deflection with a measured bending angle of 34 degrees. The magnetic property measurement exhibited that the sample with a line width of 550 µm showed the maximum magnetic flux density of 3.2 mT. The trigger distance results also supported this result. A maximum trigger distance of 8.25 mm was measured for the arm with a line width of 550 µm. Additionally, tensile tests showed that the sample exhibited a 17.7 MPa tensile strength, 1.8 GPa elastic modulus, and 1.3% elongation. Based on these results, we successfully fabricated a 3D printed magnetic gripper with two rhombus cellular structured arms which showed grasping and extensive load lifting capability (up to ∼140 times its weight).

Rapid manufacture of sodium polyaluminate electrolyte ceramics for solid state batteries via direct ink writing

Solid-state electrolyte structures using sodium polyaluminate ceramics, have been fabricated for the first time using direct ink writing; a material extrusion-based additive manufacturing process. A series of test samples were prepared using a high solids loading (80 wt%; 51.2 vol%) ceramic paste formulations with suitable rheological characteristics for 3D printing. Following optimum densification via conventional sintering at 1600 °C for 30 min, the additively manufactured electrolyte test samples exhibited an ionic conductivity of σ = 0.14 ± 0.019 S·cm−1 at 300 °C and density of ρ = 3.1 ± 0.02 g·cm−3 (relative density of 95%). These results suggest that direct ink writing of sodium polyaluminates is a promising approach for electrolyte manufacture. Additionally, this approach shows great potential for manufacturing complete solid-state battery structures, through multi-material direct ink writing.

Exploring a Novel Material and Approach in 3D-Printed Wrist-Hand Orthoses

This article proposes the integration of two novel aspects into the production of 3D-printed customized wrist-hand orthoses. One aspect involves the material, particularly Colorfabb varioShore thermoplastic polyurethane (TPU) filament with an active foaming agent, which allows adjusting the 3D-printed orthoses’ mechanical properties via process parameters such as printing temperature. Consequently, within the same printing process, by using a single extrusion nozzle, orthoses with varying stiffness levels can be produced, aiming at both immobilization rigidity and skin-comfortable softness. This capability is harnessed by 3D-printing the orthosis in a flat shape via material extrusion-based additive manufacturing, which represents the other novel aspect. Subsequently, the orthosis conforms to the user’s upper limb shape after secure attachment, or by thermoforming in the case of a bi-material solution. A dedicated design web app, which relies on key patient hand measurement input, is also proposed, differing from the 3D scanning and modeling approach that requires engineering expertise and 3D scan data processing. The evaluation of varioShore TPU orthoses with diverse designs was conducted considering printing time, cost, maximum flexion angle, comfort, and perceived wrist stability as criteria. As some of the produced TPU orthoses lacked the necessary stiffness around the wrist or did not properly fit the palm shape, bi-material orthoses including polylactic acid (PLA) inserts of varying sizes were 3D-printed and assessed, showing an improved stiffness around the wrist and a better hand shape conformity. The findings demonstrated the potential of this innovative approach in creating bi-material upper limb orthoses, capitalizing on various characteristics such as varioShore properties, PLA thermoforming capabilities, and the design flexibility provided by additive manufacturing technology.

Tailoring the crystalline structures and mechanical properties of polyamide 1012 specimens by material extrusion-based additive manufacturing

In this work, the evolution of the crystalline structures of MEAM-printed polyamide1012 (PA1012) parts with the nozzle temperatures (Tn) and thermal annealing temperatures (Ta) was investigated. It is found that Tn plays an important role in determining the crystalline structure of PA1012 parts. The freshly-printed PA1012 parts crystalize as γ crystals at Tn lower than 230 °C. With Tn increasing to above 230 °C, a small amount of α phase coexists with γ phase in the PA1012 parts. Also, the thermal annealing treatment can tailor the crystalline structure of the MEAM-printed PA1012 parts. Specifically, the crystalline structure exhibits a transformation from γ phase to α crystal, after annealing the PA1012 parts at a Ta higher than 90 °C for 10 min. Due to the presence of a high content of γ phase, the Brill transition occurs at a low temperature for the MEAM-printed PA1012 parts, implying a close relationship between the H-bond sheet structures and the formation of γ phase. Moreover, the crystalline structure exerts a significant influence on the mechanical properties of the PA1012 parts. The samples with only γ phase exhibit much higher tensile strength and Young's modulus, but much lower ductility, compared to those containing only α crystal. Hence, this work provides effective pathways for regulating crystalline structures as well as mechanical properties of MEAM-printed long-chain polyamide materials.

Effect of Process Parameters on the Hardness of 3D-printed Thermoplastic Polyurethane that Includes Foaming Agent

Recent progress in Material Extrusion-based Additive Manufacturing (MEX) has introduced active foaming agents in filaments composition, thus allowing for the tuning, by various process parameters, the hardness and the mechanical behavior of 3D-printed parts. In case of thermoplastic polyurethane (TPU) filaments, these advances significantly broaden the range of applications, particularly in the domains of comfort and orthotics (wrist-hand orthoses, insoles), offering the dual benefits of design flexibility inherent in MEX and the comfort of lightweight and customizable structures. However, the field is still in its early stages, with only a limited number of research efforts dedicated to characterizing these novel materials. In this context, this study is focused on determining the influence of printing temperature (190�C, 220�C, 240�C), infill density (25%, 35%, 45%) and infill pattern (honeycomb, gyroid) over the hardness of cylindrical specimens made of Colorfabb varioShore TPU. A comprehensive methodology of calibration is also presented as mandatory for obtaining good quality and accurate products by establishing correlations between flow rate and printing temperatures. The findings showed that the printing temperature is the most relevant factor impacting the hardness of varioShore TPU prints. At a printing temperature of 190�C, which corresponds to less foamed prints, the honeycomb infill yielded higher hardness compared to the gyroid infill, but the difference was not significant. Also, at 220�C and 240�C, the mean values of hardness remain relatively consistent, regardless of infill density and pattern.

Polycarbonate composites for material extrusion-based additive manufacturing of thermally conductive objects

Enhanced thermally conductive polymer composites can be used in many engineering applications where either the physicochemical properties of plastics or the processing properties of plastics are required. Rapid prototyping is currently being addressed for a number of applications that require good heat transfer properties. Such applications include various types of heat exchangers containing coolant/heating fluid as well as passive heat sinks for standard heat removal from various types of heat-generating products. The present work is focused on the research of thermally conductive composites for printing such structures using additive manufacturing (AM), namely material extrusion. In this study, a number of parameters of the composites were investigated that affect the final properties of the printed structures; these include the TC (Thermal Conductivity), mechanical properties, and printability of the composites, depending on the composition, but also the printing direction. The composites studied were made up of a matrix of PC (Polycarbonate) and a mixture of different thermally conductive fillers, specifically, h-BN (Hexagonal Boron Nitride), EG (Expanded Graphite), PCFs (Pitch-based Carbon Fibers) and Al (Aluminum Particles). Different types of thermally conductive composites were studied, from binary to ternary combinations of fillers. One of the best-performing composites was achieved for the combination of all four types of filler, where thermal conductivity along the printing direction was achieved for the PC matrix with 30 wt% of the mixture of all fillers. Up to 1.56 W m−1 K−1 was achieved, which is 5-fold higher than for neat PC. Although these composites have approximately half the tensile strength only, the hardness is similar to that of the neat PC. The behavior of fillers was observed by SEM analysis. Al, EG, and PCFs behave predictably. Unusual behavior was observed in the case of PC only with h-BN, where the filler migration from the matrix to the voids between the non-fused printing paths occurred, likely caused by a larger amount of dispersion component of the overall surface energy of h-BN. Such phenomena could be used in the optimized form in the future so that segregated thermally conductive structures could be created using material extrusion-based AM and allow even higher thermal conductivity of final structures.

Desiccant Dehumidification System Developed Using Additive Manufacturing and Biodegradable Materials

Traditional dehumidification equipment is based on vapour compression units. However, they depend mainly on electrical energy and use polluting gases. An alternative to this equipment is desiccant dehumidification systems, which is based on adsorbent materials. These desiccant systems are an efficient way of removing moisture from the air in buildings with high latent loads. This work presents a new way to manufacture fixed-bed desiccant elements that can remove moisture from an air flow. The desiccant element is obtained by material extrusion-based additive manufacturing (fused filament fabrication or FFF). This technology is cost-effective and provides a precision and finish suitable for the intended use. The filament used is Pine, consisting of an easy printable thermoplastic matrix (polylactic acid, PLA, 80 wt%) and a filler based on pine wood powder (20 wt%). This composite material reached a water absorption capacity of 11.5 %. The experimental results of the desiccant air unit demonstrated high dehumidification capacity, up to 39 mg/s, for a regeneration air temperature of 50 °C. The volumetric adsorption rate was also high, up to 30 g/s·m3, for low pressure drop values, below 522 Pa. The proposed method allows the customised, on-demand and just-in-time manufacturing of air dehumidification systems based on the use of biodegradable desiccant materials of organic origin. Such solutions contribute to the circular economy promoted by The United Nations in the Sustainable Development Goals.

A Coherent Assessment of the Compressive Strain Rate Response of PC, PETG, PMMA, and TPU Thermoplastics in MEX Additive Manufacturing.

In this study, we successfully address a significant research and engineering gap by quantitatively assessing the impact of varying compressive loading rates on the mechanical behavior of four popular thermoplastic polymers in material-extrusion-based (MEX) 3D printing. Raw powders of polycarbonate (PC), polyethylene terephthalate glycol (PETG), polymethyl methacrylate (PMMA), and thermoplastic polyurethane (TPU) were processed through melt extrusion, and the filaments were used to 3D-print the test samples. For completeness, thermogravimetric analysis and a compressive test following the ASTM-D695 standard were conducted. Ultimately, the compressive strength and yield stress, the compressive modulus of elasticity and toughness, and the maximum compressive sensitivity index were thoroughly documented. Specimens were tested in strain rates from 1.3 mm/min to 200 mm/min. The compressive strength (40% for the PMMA) and stiffness (29% for the TPU) increased with the increase in the strain rate in all polymers tested. PC had the highest strain rate sensitivity. Significant variations in deformation and fracture modes were observed and thoroughly documented throughout this study. Our findings can be useful in industrial engineering as valued design optimization input parameters in various applications involving the above-mentioned polymeric materials.

Topology optimization for material extrusion-based additive manufacturing processes with weak bead bonding

Topology optimization (TO) is a powerful design tool that has been used to design lightweight high-performing structures. Additive manufacturing (AM) is a favoured fabrication method for TO designs because of its high precision and flexibility to realize complex optimized structures. This paper describes a new TO approach that can account for fabrication characteristics and constraints of extrusion-based AM. The fabrication process is mimicked as the design is generated by enforcing a fixed radius feature size in design outputs, and introducing a secondary material between adjacent beads. Lowering the stiffness of this additional material allows for consideration of the weak bead bonds in extrusion-printed materials and promotes continuity of design features. The user can control the radius of the discrete feature size and the relative stiffness of the weak bond. The algorithm is demonstrated on benchmark TO problems in 2D. The design results contain both a description of the physical layout of the structure and a design variable distribution that can be used as a trace for the raster path. The design results are found to respond to user specifications on bead size and relative bond weakening. Continuity of the raster path increases as the stiffness of the bead bonding decreases.

Large-scale material extrusion-based additive manufacturing of short carbon fibre-reinforced silicon carbide ceramic matrix composite preforms

ABSTRACT Large-scale short carbon fibre-reinforced silicon carbide (Csf/SiC) ceramic matrix composites (CMCs) have important applications in the field of aerospace engineering. This study proposed the use of material extrusion based additive manufacturing to fabricate large-scale C sf/SiC CMC preforms. In this paper, we determined how the key material extrusion parameters, including solid loading, nozzle diameter and layer height impact the stability of the additively manufactured C sf/SiC CMCs. The solid loading significantly influenced the stability of the C sf/SiC CMCs, and the slurry with 50 vol.% solid loading was better for additive manufacturing. The layer height played a significant role in the void formation in CMCs. It was appropriate for structure retention to set the layer height as 60–75% of the nozzle diameter. The effect of angle from vertical on the stability of out-of-plane structure was also investigated. When the angle was over 40o, the out-of-plane structure additively manufactured without supports tended to collapse. Large-scale C sf/SiC CMC preforms with out-of-plane structures were finally successfully fabricated. This study is believed to provide some fundamental understanding for the fabrication of large-scale fibre-reinforced ceramic matrix composites.

Non-planar bioprinting with molding assistance for irregular wound shape

Most human organs and tissues have different shapes, which vary per individual. When printing biomedical scaffolds using material extrusion-based additive manufacturing bioprinters, sacrificial layers are generally used to support the suspended parts of the scaffold. However, the in-process generation of sacrificial layers is time-consuming and the scaffold can be damaged when removing the sacrificial layers. In this study, a novel non-planar grid slicing (NPGS) process was proposed for printing irregularly shaped tissues with low aspect ratios (for example, skin wounds), where the required 3D shape is formed following the deposition of non-planar paths, layer-by-layer. By stacking layers of bioink onto a non-planar support base, the NPGS process considerably reduced the total length of the deposition paths and number of fragmented paths. Therefore, it can reduce the use of costly bioink and improve the success rate of the scaffold printing. The proposed NPGS process and traditional planar slicing (TPS) process were used to fabricate scaffolds that conform to the shape and depth of two clinical wounds. Compared to TPS, NPGS reduced the total length of the deposition paths and number of fragmented paths (paths shorter than 5 mm) by 49.2% and 59.6%, respectively. In animal testing, a large irregular wound was created on the rat's dorsal skin and treated with tri-cell-laden hydrogel printed by the NPGS process, demonstrating full repair after 28 days. The NPGS process shows great potential for customized biofabrication in tissue engineering.

Selected design rules for material extrusion-based additive manufacturing of alumina based nozzles and heat exchangers considering limitations in printing, debinding, and sintering

Selected design rules for material extrusion-based additive manufacturing of alumina based nozzles and heat exchangers considering limitations in printing, debinding, and sintering

Effect of process parameters on performances measured in filament and pellets-based additively manufactured parts

Among all the additive manufacturing (AM) technologies, the material extrusion-based AM is the most popular, and widely used for prototyping, rapid tooling, and direct part production in the current scenario. In material extrusion AM (MEAM), a solid form of material is converted to a semi-molten form and extruded out of a nozzle to deposit in a layer-by-layer manner. Nowadays MEAM three-dimensional (3D) printers are very popular among different application sectors. This motivates us to develop various commercial as well as open-source entry-level 3D printers such as the development of filament extruder 3D printers, pellet extruder 3D printer, or a combination of both. However, to develop or operate these printers, preliminary knowledge of various extrusion parameters is required to obtain the desired quality in the fabricated parts. Therefore, an initial attempt has been made to provide information related to various extrusion parameters such as definition, working range, and the effect of these parameters on performance measured. The impact of process parameters on the performance of either filament extrusion AM or pellet/granules extrusion AM has only been investigated in the studies available in the literature. However, this study provides a comprehensive review of the effects of process parameters on performance measurements for both types of extrusion-based AM processes. In this research work, along with a detailed review of previous works, a study of various process parameters, modeling, and methodology has been provided. The statistical modeling approach, histogram normal plots have been provided along with mean, standard deviation, and percentage to decide the optimum process parameters based on data available in the existing literature.

Selection of infill parameters considering their effects on operational and mechanical performance for material extrusion of CFR-PEEK

PurposeAs newer high performance polymers in mechanical properties become available for material extrusion-based additive manufacturing, determining infill parameter settings becomes more important to achieve both operational and mechanical performance of printed outputs. For the material extrusion of carbon fiber reinforced poly-ether-ether-ketone (CFR-PEEK), this study aims not only to identify the effects of infill parameters on both operational and mechanical performance but also to derive appropriate infill settings through a multicriteria decision-making process considering the conflicting effects.Design/methodology/approachA full-factorial experimental design to investigate the effects of two major infill parameters (i.e. infill pattern and density) on each performance measure (i.e. printing time, sample mass, energy consumption and maximum tensile load) is separately performed to derive the best infill settings for each measure. Focusing on energy consumption for operational performance and maximum tensile load for mechanical performance, the technique for order preference by similarity to ideal solution is further used to identify the most appropriate infill settings given relative preferences on the conflicting performance measures.FindingsThe results show that the honeycomb pattern type with 25% density is consistently identified as the best for the operational performance measures, while the triangular pattern with 100% density is the best for the mechanical performance measure. Moreover, it is suggested that certain ranges of preference weights on operational and mechanical performance can guide the best parameter settings for the overall material extrusion performance of CFR-PEEK.Originality/valueThe findings from this study can help practitioners selectively decide on infill parameters by considering both operational and mechanical aspects and their possible trade-offs.

A review of void reduction strategies in material extrusion-based additive manufacturing

A review of void reduction strategies in material extrusion-based additive manufacturing