Extrusion-based Additive Manufacturing Process Research Articles

Challenges to Improve Extrusion-Based Additive Manufacturing Process of Thermoplastics toward Sustainable Development.

This review aims to present the different approaches to lessen the environmental impact of the extrusion-based additive manufacturing (MEX) process of thermoplastic-based resins and protect the ecosystem. The benefits and drawbacks of each alternative, including the use of biomaterials or recycled materials as feedstock, energy efficiency, and polluting emissions reduction, have been examined. First, the technological option of using a pellet-fed printer wascompared to a filament-fed printer. Then, common biopolymers utilized in MEX applications are discussed, along with methods for improving the mechanical properties of associated printed products. The introduction of natural fillers in thermoplastic resins and the use of biocomposite filaments have been proposed to improve the specific performance of printed items, highlighting the numerous challenges related to their extrusion. Various polymers and fillers derived from recycling are presented as feeding raw materials for printers to reduce waste accumulation, showing the inferior qualities of the resulting goods when compared to printed products made from virgin materials. Finally, the energy consumption and emissions released into the atmosphere during the printing process are discussed, with the potential for both aspects to be controlled through material selection and operating conditions.

Ultraviolet and thermal dual-curing assisted extrusion-based additive manufacturing of lunar regolith simulant for in-site construction on the Moon

The establishment of a lunar base is crucial for lunar studies, resource extraction, and advancement in deep space exploration. Considering the limitations of rocket capacity and Earth-Moon transportation costs, lunar regolith is regarded as the most practical material for lunar base construction. Consequently, the in-situ additive manufacturing technology for simulated lunar regolith has been widely studied in recent years. This paper proposes a novel additive manufacturing approach for lunar regolith simulants. The simulants and several resins were mixed into a paste with high simulant content of 86 wt%, which was suitable for extrusion-based additive manufacturing process. To fully leverage the lunar environment, the feasibility of the ultraviolet (UV) and thermal curing of the resins was first verified, which was followed by the validation of the lunar regolith paste with the solid content of 86 wt%. After the characterization of the ultraviolet and heat curing properties, the paste was further 3D printed via the extrusion-based device. The extruded paste underwent preliminary curing in a UV environment and was then heated to approximate the daytime lunar conditions, achieving complete curing of the printed component. The cured parts exhibited a compressive strength of 9.83 ± 1.07 MPa, meeting the requirements for infrastructure construction in the low-gravity lunar environment. This work offers significant implications for future in-situ construction on the Moon using extrusion-based additive manufacturing of lunar regolith.

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.

Polyether Ketone Ketone (PEKK) matrix composites for material extrusion additive manufacturing

Despite the widespread use of fused filament fabrication (FFF) (an extrusion-based additive manufacturing process) to manufacture end-use parts for the aerospace industry, limited materials are available within this process that can be used for structural applications in the harsh space environment. Currently available high-performance polymers need to be improved by incorporating additives within the polymer matrix to achieve multi-functional properties. Additives such as graphene, graphene oxide, carbon nanotubes and boron carbide are known to improve mechanical and thermal properties and radiation shielding. This study aims to understand if these additives can be successfully incorporated into PEKK matrix to manufacture printable filaments for FFF. Graphene, graphene oxide (GO) and boron carbide (B4C) were compatibilised with PEKK matrix, and their mechanical, thermal and rheological properties were analysed and compared with commercially available carbon fibre and carbon nanotube-reinforced PEKK where appropriate. As rheological properties of the formulations confirmed that they were printable, filaments for FFF were then manufactured. Graphene–PEKK was the most printable filament followed by GO–PEKK while B4C–PEKK was not printable. TEM images of filament cross-section showed good dispersion of graphene and graphene oxide, while boron carbide formed large agglomerates; B4C also presented feeding issues due to its hardness which affected its printability. Dispersion of the additives was also confirmed by studying their X-ray diffraction (XRD) patterns, and chemical structures were assessed using FT-IR spectroscopy. Finally, parts were printed using selected composite filaments, and their porosity and surface roughness were compared with neat PEKK and commercial CNT-reinforced PEKK to develop an understanding of metrology and bulk material properties of the composites.

Implementation and evaluation of curved layer fused deposition modeling

Fused Deposition Modeling (FDM) is an extrusion-based additive manufacturing (AM) process in which a thermoplastic material is extruded through a nozzle. Although it was initially developed for rapid prototyping, advances in the FDM technology have rapidly increased its range of applications. However, the FDM process has inherent disadvantages, such as poor surface finish, severe anisotropic mechanical properties, and increased build time for high-resolution parts. This is the result of the layer-by-layer manufacturing process. To remedy these issues, Curved Layer Fused Deposition Modeling (CLFDM) offers a new building paradigm for FDM in which the material is deposited in curved nonplanar layers. The purpose of this study is to implement a curved-layer toolpath generation algorithm and quantify the benefits of the curved layered methodology over traditional planar layers in printing thin-contoured parts.

The influence of rheology in the fabrication of ceramic-based scaffold for bone tissue engineering

Abstract Bone tissue is the second most affected organ in the human body after blood. Tissue engineering is the area whereby a scaffold is used to regenerate the lost bone. However, the scaffold’s effectiveness is primarily based on the material and the fabrication process. The patient-specific structures are affected because of the fabrication process used to fabricate the scaffold as per requirement. In this regard, rheology plays an important role in the fabrication of the patient-specific scaffold, and it is a study of the flow of ink. This primarily affects both the conventional as well as the non-conventional fabrication processes. In this paper, the scaffold and bone tissue engineering, the different fabrication processes, and the importance of the rheological characterization are presented. In addition to this, the rheological properties of the developed HA/β-TCP composite slurry are evaluated for the extrusion-based additive manufacturing process. The developed ink’s rheological properties show that the flow behavior index of about 0.0497 ± 0.009, minimum flow stress required to make the ink flow of about 51.076 Pa at a strain rate of 0.111 %, and shape retention upto 75 % after 175 s are obtained. Also, different orientations are 3D printed using the developed slurry.

Correlation between filament deposition path, microstructural and mechanical properties of dense alumina parts printed by robocasting

Robocasting is an extrusion-based additive manufacturing (AM) process widely used to produce porous structures. It enables to build three-dimensional (3D) ceramic parts, thanks to computer numerical control of the filament deposition path onto a fabrication substrate. Despite its high potential, robocasting is much less explored than other AM techniques for producing dense parts. This work focused on the robocasting of dense alumina parts by varying the filament deposition path of an environmentally friendly paste. Taguchi method was used to establish a correlation between the printing parameters and the microstructural and mechanical properties of the sintered parts. Closed pores located between adjacent filaments were found to dictate crack propagation mechanisms, depending on the infill pattern. The optimal printing strategy led to 93% dense alumina samples having a flexural strength of 140 MPa, a Young’s modulus of 355 GPa and a Poisson’s ratio of 0.23.

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.

An evaluation of the shape-memory behavior and mechanical properties of polylactic acid/Ni80Cr20 continuous wire composite produced by extrusion-based additive manufacturing and in-melt simultaneous impregnation method

This study evaluates the mechanical and shape-memory properties of PLA/Ni80Cr20 continuous wire composite materials. The samples were produced using an extrusion-based additive manufacturing (AM) process with in-melt simultaneous impregnation of metal wire, followed by 3D printing. The reinforced samples were fabricated using metal wires of 0.1 and 0.15 mm in diameter and 5 and 10% volume percentages. The maximum mechanical (tensile and flexural) properties were obtained in the reinforced samples with a 10% volume percentage of metal wire of 0.1 mm in diameter. The samples exhibited a maximum ultimate tensile strength of 116 MPa, a maximum tensile modulus of 11.7 GPa, a maximum flexural strength of 221 MPa, and a maximum flexural modulus of 17.8 GPa. This research used a novel method to investigate the shape-memory properties of PLA. By applying a potential difference to the samples, the heat generated by the metal wire was absorbed by the matrix polymer, which increased the temperature of the material. This increase in temperature resulted in a change in the samples' shape. The effect of voltage on the wire was investigated, and a voltage of 40 V was applied to the U-shaped samples with special fixtures to measure the shape recovery and shape stabilization percentage. Based on the final results, it can be deduced that 3D-printed composite materials, along with appropriate wire type, wire diameter, voltage, and uniform temperature distribution, can be used as shape-memory materials for a wide range of applications with desired temperature conditions, especially in cases where direct heat cannot be applied to the sample.

Experimental and numerical investigation of rotating bending fatigue of polylactic acid 3D printed parts by an extrusion-based additive manufacturing method

This study investigates the impact of four parameters, namely layer height, nozzle temperature, infill percentage, and bed temperature, on the fatigue life of polylactic acid (PLA) printed parts using the extrusion-based additive manufacturing (AM) process. The experiments were designed using the Taguchi method, considering three levels for each parameter. The extent of the impact and the optimal values of the process variables were determined by using analysis of variance (ANOVA) and signal-to-noise ratio. To predict the fatigue behavior, an empirical model was presented, which was fitted to the fatigue results of the samples made with the optimal process variable values using the least squares method. Additionally, finite element simulations were conducted, and the results were compared with the experimental study findings. The results indicated that the optimal process variable values for maximum fatigue strength are a layer height of 0.3 mm, a nozzle temperature of 220 ℃, a 100 % infill and a bed temperature of 60 ℃. The ANOVA results revealed that the infill percentage, nozzle temperature, and layer height have the greatest influence on fatigue life, with respective contributions of 60.5 %, 28.1 %, and 7.7 %. The experimental modeling and finite element simulation results indicate that the proposed models predict fatigue behavior with regression coefficients of 96.3 % and 98.7 %, respectively.

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.

Experimental and numerical investigation of extrudate swell of polylactic acid via extrusion-based additive manufacturing process

Extrudate swell is a rheological phenomenon of polymers that occurs after the extrusion die exit due to relaxation of the residual molecular stress. This phenomenon is essential to ensure the accuracy and stability of components manufactured by Extrusion-based additive manufacturing (EAM) process. Extrudate swell can be affected by multiple factors including material properties and processing parameters that can be coupled and it is difficult to fully understand their effects, especially in absence of accurate online measurement devices. In this study, the extrudate swell was investigated experimentally as a function of the extrusion rate, melt temperature and nozzle diameter for polylactic acid (PLA) material. The Computational fluid dynamics (CFD) and level set method (LS) in COMSOL Multiphysics were used to simulate the polymer flow out of the extrusion nozzle. The simulation results matched well with experimental results and showed that the swell rate decreases with increasing temperature and nozzle diameter and decreasing extrusion rate. These results can be used to optimize the parameters of EAM processes.

Improving the manufacturability of highly materially restricted topology-optimized designs with Mixed Integer Linear Programming

This paper presents a new free-form topology optimization framework for highly materially restricted design situations. Highly materially restricted design situations are herein defined as being limited significantly by the combined demands on material use and manufacturability. The new framework uses the ground structure approach with frame elements and casts the design problem as a Mixed Integer Linear Program (MILP), ensuring a solution with a manufacturable discrete material distribution. This paper also presents an extension to hybrid mesh ground structures containing both frame and thin solid elements. In both cases, the user can easily tailor the resultant design to discrete fabrication requirements as e.g. relevant when using an extrusion-based Additive Manufacturing (AM) process that requires the design features to adhere to a discrete number of bead depositions. The new framework is numerically demonstrated on topology optimization benchmark examples. In addition, numerical and experimental comparisons are made to the conventional density-based topology optimization approach (with continuous density variables). When the design is highly restricted, the new MILP framework is in most tested cases found to generate solutions with improved numerical predictions on the compliance. For the experimentally validated case study, the numerical prediction is seen to significantly underestimate the experimentally observed performance gain. The experimental investigation additionally cements the high performance of density-based topology optimization in design situations with low levels of design restrictions. In these cases (6 out of 7 tested herein), the solutions generated with density-based topology optimization have comparable or preferable performance.

Biomass waste materials through extrusion-based additive manufacturing: A systematic literature review

Circular economy and bioeconomy models have increasingly spread the principles of sustainable development through different strategies such as reuse and recycling. Biomass waste and by-products are often considered valuable resources. Digital technologies, i.e., extrusion-based additive manufacturing, may potentially foster their exploitation as new materials, although the current framework has not been clearly defined yet. This work wants to systematically review the publications focused on new materials from biomass waste or by-products for extrusion-based additive manufacturing processes. The current situation was analyzed on 69 selected works from 2016 searched on Scopus and WoS, focusing on the different raw materials, new 3D printable materials, 3D printing processes, and potential applications. Afterward, the emerging trends were highlighted through selected best practices from the design practice and industrial sectors. Despite the significant development of thermoplastic reinforced materials, i.e., PLA-filled composites, a wide range of biomass waste and by-products have been studied, especially for small format low-cost Fused Filament Fabrication. Although the academic field may be less focused on exploiting these new circular materials, the interest in new applications is increasing within the design practice and industrial sectors, fostering new synergies within bioeconomy and circular economy contexts.

Additive manufacturing of cemented carbide using analogous powder injection molding feedstock

In this study, WC-8%Co cemented carbide was fabricated by extrusion-based additive manufacturing process using analogous powder injection molding feedstock. Feedstocks with powder loading content of 51 vol% (PW51) and 57 vol% (PW57) were prepared based on thermoplastic binder system composed of paraffin wax, high density polyethylene and ethylene-vinyl acetate. The results show that the extrusion of feedstock is steady and easily controlled. The binder is efficiently removed by solvent leaching and thermal decomposition. After sintering at 1400 °C, densified samples with a relative density beyond 99% are obtained. Sintered PW57 presents less and more isotropic shrinkage below 17.0%, showing a great significance in print accuracy and deformation control. Sintered PW57 has larger transverse rupture strength and fracture toughness of 1695 MPa and 7.27 Pa·m0.5, respectively. Vickers hardness of sintered PW51 is slightly larger because of finer WC grain size. Mechanical properties, microstructure and surface roughness of sintered samples are all acceptable in actual application. Three-dimensional printing using an extrusion-based additive manufacturing with analogous powder injection molding feedstock is an extremely practicable method to fabricate cemented carbide parts with complicated shape.

Three-Dimensional Printing of Highly Conducting PEDOT: PSS-Based Polymers

Abstract Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most successful conducting polymers for electronic applications. Most commonly, the spin coating process is used to fabricate PEDOT:PSS thin films from an aqueous solution, yet it is unsuitable for fabricating complicated two-dimensional (2D) structures. Extrusion-based additive manufacturing (AM) processes have been investigated for 3D printing PEDOT:PSS-based polymers with free-form architecture. However, such methods imply strict requirements on the rheological properties of materials and, as a result, have limited choices of appropriate materials. In the past, additives have been added to improve the 3D printing processability of PEDOT:PSS materials, which, however, usually deteriorate the electrical conductivity. This article reports a new type of PEDOT:PSS material capable of addressing the previously listed challenges and characterized by high processability and electrical conductivity (72 S/cm). In addition, a novel extrusion-based AM technology, electrostatically-assisted direct ink writing (eDIW), is investigated for printing materials containing PEDOT:PSS. The eDIW method prints lines at micro-scale resolution at an ultra-high speed (1.72 m/s). This combination is often deemed impossible in the framework of classical extrusion-based AM techniques. This work lays the foundation for future explorations of applications of PEDOT:PSS-based conducting polymers in fields that require superb properties and custom geometry, which were conventionally impossible.

Peridynamics topology optimization of three-dimensional structures with surface cracks for additive manufacturing

Additive manufacturing (AM) is an effective approach to fabricating intricate shapes obtained from topology optimization (TO). However, it may cause undesired manufacturing-induced defects/cracks due to high thermal residual stresses. This study proposes a PeriDynamics-enabled three-dimensional Topology Optimization method (PD-TO) for designing structures by considering surface cracks for the AM processes. The PD-TO approach employs a bi-directional evolutionary structural optimization method and uses particle discretization of geometry for mechanical analysis. Crack surfaces are generated by breaking three-dimensional nonlocal interactions of the particles, and thus, during the optimization process, complex multiple structural discontinuities can be diligently modeled. First, the proposed approach is validated by solving benchmark problems without cracks. For each benchmark geometry, the PD-TO analysis is then performed by considering different positions and numbers (single/multiple) of cracks. These analyses extensively investigate and demonstrate the effects of a priori knowledge of residual stress-induced damages/cracks on the optimum topology for additive manufacturing. Besides, the smoothing operation is applied to the optimum designs to transform voxel shapes into AM-friendly smooth surfaces. These geometries are manufactured by an extrusion-based AM process to demonstrate the practical engineering application of the proposed method. Finally, the comparison of numerical results is also supported by the experimental tests conducted on the optimized topologies. Overall, it is confirmed that the PD-TO approach is a viable and accurate optimization tool for additive manufacturing considering possible process-induced damages.

Impact of biomass ash content on biocomposite properties

Owing to its low cost and sustainable nature, lignocellulosic biomass has been utilized for reinforcing polymers, but it is crucial to understand the impact of high-ash concentrations in biomass on composite strength and processing. Biomass is not only desirable for biofuel production but could also have a strong market, if high-ash biomass is acceptable, for biocomposites. In this work, natural fibers (switchgrass and corn stover) were used to reinforce polylactic acid (PLA) to produce biocomposites. Natural fibers were pretreated to obtain fibers that contain different percentages of ash. The mechanical properties (such as Young's modulus, tensile strength, failure strain, storage modulus) of corn stover/PLA composites remained largely unaffected by the ash concentration of the biomass fibers, despite the large range of ash contents (2.2–11.9 wt%). However, the tensile strengths of switchgrass/PLA composites were slightly negatively affected by the ash concentration of the switchgrass fibers (0.7–2.1 wt%). Both the switchgrass/PLA and the corn stover/PLA composites exhibited a high-enough tensile strength (49–57 MPa) and suitable complex viscosity (2.0−7.0 kPa·s at the frequency of 3.2 rad/s). They are expected to be 3D-printable through an extrusion-based additive manufacturing process.

Understanding and investigating rheological properties of HA/β-TCP bio-ceramic composite ink for extrusion-based additive manufacturing process to fabricate bone scaffold

Fabricating the tailored bio-ceramic scaffold using conventional method is still a challenging task and it can be overcome by using the extrusion-based additive manufacturing(EAM) Process. However, fabricability of the scaffold with developed ink with suitable formulations is challenging. In EAM, ceramic Inks are prepared and extruded in such a way that it will fabricate the provided design in .STL file format. In this context, the flow behaviors of the ceramic inks are important to study and, in understanding the rheological properties of the prepared ink. As the rheology of the ink directly influences the accuracy of the printing. For this, In this paper a concepts related to understanding rheological properties for extrusion based additive Manufacturing is presented. Bioceramic composites of HA and β-TCP are selected to prepare composite ink. Further, Flow sweep behavior of the inks are studied ate 5˚C to 20˚C in the interval of 5˚C. The flow behavior index of the Ink at different temperature is presented and found that it gives shear thinning behavior with range of 0.01238±0.01596 and flow consistency parameter between 206.56 and 283.49 Pa.S. The Ink is giving optimal performance at 10˚C and using the same ink some single layer structures are being printed using the developed bioceramic Ink at 10˚C.