Additive Manufacturing Fabrication Research Articles

Physics-informed machine learning for defect identification in fused filament fabrication additive manufacturing

Physics-informed machine learning for defect identification in fused filament fabrication additive manufacturing

Refined W-3.5Nb alloy fabricated by electron beam melting via doped carbon

Electron beam melting (EBM) is a promising powder bed fusion additive manufacturing (AM) technology for the preparation of complex refractory components due to the significant advantages of vacuum environment and high level in energy utilization, scanning speed and temperature in the build chamber. However, the fabrication of crack-free and refined W-based alloy remains a challenge. This study aims to address this problem by introducing 0.7 wt% carbon in EBM W-3.5Nb alloy. Results revealed that the as built W-3.5Nb alloy had a typical columnar structure with obvious solidification cracks along the grain boundary. Doping 0.7 wt% carbon generated refined microstructure, which was composed of the initial dendrite of tungsten and the eutectic phase in the dendrites gap. Due to the low distribution coefficient of carbon, the nucleation at the bottom of the molten pool was caused by constitutional supercooling in the front of liquid solidification in a single molten pool, and velocity of the solidification front was reduced by carbon concentration leading increased thermal supercooling. Supercooling (thermal supercooling together with constitutional supercooling) refined the microstructure of W-3.5Nb alloy effectively. Meanwhile, due to the formation of eutectic phase with low melting point, the fluidity of liquid phase at the terminal solidification was improved and the solidification cracks along the grain boundary were reduced. The carbon addition also played a significant role in alloy strengthening. The microhardness of the alloy increased from 382 HV to 696 HV, and the compressive strength increased from 962.89 MPa to 1892.56 MPa. These findings offer a new perspective on the AM fabrication of high-quality W-based alloys.

Mechanical Performance, Structure and Fractography of ABS Manufactured by the Fused Filament Fabrication Additive Manufacturing

Fused filament fabrication (FFF) is the most widely used additive manufacturing (AM) technology for printing thermoplastic materials, among them the ABS. A significant problem of 3D-printed parts manufactured by AM-FFF is the anisotropy of their mechanical properties. Thus, it is of great importance to understand the impact of the build strategy of the mechanical properties and failure mechanisms of AM-FFF ABS components. This research aims, at least partly, to fill this gap by studying the structure and mechanical behavior by performing fracture surface analysis of AM-FFF ABS specimens under the three-point bend test. For this purpose, three build orientations (flat, on-edge and upright), each built at 0°/90° and -45°/+45° raster angles and oblique printed samples (0°, 15°, 30°, 45°, 60°, and 75°) built at -45°/+45° raster angles were prepared. The results revealed that the build direction with the lowest density, the flexural modulus of elasticity, flexural strength, and deflection was in the upright direction for both 0°/90° and -45°/+45° raster orientations. Overall, two main failure modes were observed for the tested specimens: (1) inter-layer/inter-raster bond failure, which is the main contributor to failure of all upright samples and (2) intra-layer/trans-raster failure, which is the main contributor to failure of flat and on-edge specimens printed at -45°/+45° raster orientation. The results of the oblique printed samples demonstrate that a single crack initiation can transform into a few inter-laminar and intra-laminar fracture surfaces due to competing stress fields and structural gradients

Durability of Vacuum Infusion Tooling Produced from Fused Granular Fabrication Additive Manufacturing.

Fused Granular Fabrication Additive Manufacturing (FGF AM) has the capability to create tooling that is lower cost than conventionally manufactured tooling and still has sufficient properties for many applications. A vacuum infusion (VI) mold was printed from fiberglass-acrylonitrile butadiene styrene (ABS) and evaluated for wear and suitability for small VI runs. The mold was designed to accentuate high wear as a "worst case" scenario. The mold was able to produce 10 parts successfully before any noticeable change occurred to the surface finish. By 14 parts, the surface finish had roughened sufficiently that demolding was difficult and resulted in damage to the part. Profilometry measurements showed a 7 × increase in roughness over the run. No significant tool wear or change in geometry was detected. Even longer life would be expected for typical tooling designs since the test mold was deliberately designed to accentuate wear and demolding issues. Based on these results, similar FGF molds are a feasible option for short run VI production for prototyping or low-volume composites manufacturing, possibly at lower cost and quicker turnaround time than machined aluminum molds.

Additive manufactured cardiovascular scaffold integrated with SU-8 based wireless pressure sensor

Herein, we proposed a SU-8 based wireless pressure sensor integrated with a polycaprolactone (PCL) based bioresorbable scaffold (BRS) for the detection of biological cues. The PCL-based BRS and pressure sensor are fabricated using a custom-designed additive manufacturing method and a modified photolithography technique. Firstly, we optimized the additive manufacturing fabrication parameters to realize the highly reliable scaffold with uniform strut width and thickness. Then, utilizing the optimized additive manufacturing conditions, we fabricated three distinct types of scaffolds, namely scaffold A, scaffold B, and scaffold C, each with a unique architecture. The preliminary characteristics of the fabricated scaffolds demonstrated that the scaffold A architecture exhibited superior properties, including 0.048 N mm−1 radial force, 1.64% foreshortening, and 14.1% recoil compared to the scaffolds B and C. The Inductor-Capacitor (LC)-pressure sensor is integrated into the PCL-based BRS using a water-soluble polyvinyl alcohol adhesive layer. The reliability of the fabricated LC-pressure sensor is confirmed by measuring its change capacitance and resonance frequency at different applied pressures. The proposed LC-pressure sensor integrated PCL-based BRS is evaluated in a pressure range of 0–280 mmHg. The resonant frequency of the fabricated smart scaffold changed linearly according to the pressure change indicating the high reliability of the proposed smart scaffold. We anticipate that the proposed pressure sensor integrated with the biodegradable PCL-based BRS would be used for biomedical applications owing to their facile fabrication process and excellent sensitivity.

Wire and arc additive manufacturing fabrication of ODS-RAFM steels and preliminary evaluation on microstructures and mechanical properties

Oxide-dispersion-strengthened reduced-activation ferritic/martensitic (ODS-RAFM) steels have promising applications in future fusion reactors, but the rapid and cost-efficient fabrication of ODS-RAFM steel components still remains a major challenge. In this study, wire and arc additive manufacturing (WAAM) techniques were developed to fabricate a thin-wall ODS-9Cr-RAFM steel part, using flux cored wires containing nano-Y2O3 as the [Y] and [O] sources and Ti as micro-alloying element. Their microstructures and mechanical properties before and after austenite-quenching were both investigated, and the results were compared with other 9Cr-RAFM counterparts without the addition of nano-Y2O3 and Ti. It was suggested that Y2O3 could decompose into [Y] and [O] during the rapid melting, and then precipitate along with Ti as Y2TiO5 mostly (and perhaps also TiO2) during the rapid solidification of WAAM. These oxides have fine nano-sizes with a high number density and can provide multi-fold benefits from refining the grain/sub-grain structures, promoting martensite transformation, to pinning dislocations. After the aus-quenching, a new, more stable nano-phase of Y2Ti2O7 was formed, with combined features of ultra-fine size, high number density, and high coherency. The as-quenched ODS-9Cr-RAFM specimens can achieve markedly high strengths with good plasticity, both at room temperature and elevated temperatures up to 650 °C, showing great promises of WAAM techniques for large-scale fabricating high-performance ODS-RAFM steel structural components.

Modeling SEBM process of tantalum lattices

PurposeSelective electron beam melting (SEBM) is one of the popular powder-bed additive manufacturing (AM) technologies. The purpose of this paper is to develop a simulation strategy for SEBM process to get data which are vital for realistic failure prediction and process parameters control for real complex components.Design/methodology/approachFocusing on the SEBM process of tantalum, this paper presents a three-dimensional thermo-mechanical modeling strategy based on ABAQUS and its subroutines. The simulation strategy used in this paper is developed for SEBM process of pure tantalum but could be extended to other AM fabrication technologies and other metals without difficulties.FindingsThe simulation of multi-track multi-layer SEBM process of tantalum was carried out to predict the temperature field, the molten pool evolution and the residual stress distribution. The key information such as inter-track molten pool overlapping ratio and inter-layer refusion state can be extracted from the obtained molten pool morphologies, which are vital for realistic failure prediction and process parameters control for real components. The authors finally demonstrate the capability of the strategy used by simulating a 2 mm × 2 mm × 10 mm lattice structure with total 200 layers.Originality/valueThe simulation of multi-track multi-layer SEBM process of tantalum was carried out. The key information such as inter-track molten pool overlapping ratio and inter-layer refusion state can be extracted. The authors finally demonstrate the capability of the strategy used by simulating a lattice structure. Not only temperature distribution but also stress evolution are captured. Our simulation strategy is developed for the SEBM process of pure tantalum, but it could be extended to other AM fabrication technologies and other metals without difficulties.

Linking Powder Properties, Printing Parameters, Post-Processing Methods, and Fatigue Properties in Additive Manufacturing of AlSi10Mg

Additive manufacturing (AM) of metals can be broadly accomplished via two defined technologies: powder bed fusion and directed energy deposition. During AM fabrication, the melted feedstock material experiences fast thermal cycling due to the layer-by-layer deposition process resulting in microstructures and properties that are drastically different from the traditionally manufactured parts. For AM to become a viable process for fabricating critical components made of high-performance structural alloys, such as AlSi10Mg, a comprehensive understanding is required toward developing the process-structure-property relationships prevalent in AM. AlSi10Mg, with its good castability, strength, hardness, and dynamic properties, is typically used to fabricate structural components that are required to withstand high loads. This alloy has been consolidated predominantly by the laser powder bed fusion (L-PBF) method and several critical mechanical properties, such as fatigue, have been reported to date. This article, first, summarizes the as-deposited and heat-treated microstructures of AlSi10Mg specimens fabricated by L-PBF. Then, the article discusses the linkages among the feedstock properties, printing parameters, specimen geometry, post-processing techniques, and fatigue properties. This discussion is followed by a section on the fatigue life prediction of AlSi10Mg specimens using computational modeling. Finally, the article identifies critical research gaps and pinpoints future research opportunities.

Multifunctionality of Nanoengineered Self‐Sensing Lattices Enabled by Additive Manufacturing

Enhanced mechanical performance across many parameters is achieved via nanoengineering of polymer lattices realized via fused filament fabrication additive manufacturing, as described in the article number 2200194 by Shanmugam Kumar and co-workers. The carbon nanotube comprised nanocomposite further provides multifunctionality via strain-and damage-sensing, to create a multifunctional high performance lattice for a variety of applications including patient-specific smart orthopedic braces.

Synthesis and dielectric characterisation of a low loss BaSrTiO3/ABS ceramic/polymer composite for fused filament fabrication additive manufacturing

Composite polymer/ceramic filaments for material extrusion-based fused filament fabrication additive manufacturing, using barium strontium titanium oxide (BST) ceramics and acrylonitrile butadiene styrene (ABS) thermoplastics were produced; their dielectric and physical properties have been characterised for the first time. The dielectric properties, relative permittivity (ε r ), quality factor ( Q×f ) and dielectric loss (tan δ ) were measured as a function of ceramic solid loading (%) at 5 GHz for 3D printed samples. A relative permittivity ε r = 6.05, Q×f = 10,433 GHz and dielectric loss tan δ = 0.007 were obtained for a BST/ABS ceramic polymer composite, with 50 wt% (15 vol%) solid loading. The composite materials exhibit reduced dielectric losses compared to standard laminates currently used in the radiofrequency (RF) and telecommunications industry. Based on polymer/ceramic composite filament, a prototype microstrip patch 5 G antenna and a hemispherical dielectric lens were designed and manufactured. Through testing, it shows good antenna performance with a centre frequency of f 0 = 3.78 GHz and a (−10 dB) bandwidth of 90.6 MHz. The dielectric lens increased the antenna gain by 3.86 dBi.

A new algorithm for optimal process parameters based on minimum building time in additive manufacturing

BackgroundAdditive manufacturing method is used for manufacturing of solid three-dimensional parts. It requires less human efforts and manufacturing time for parts is less. Different process parameters such as layer thickness, building orientation, infill type, and infill percentage affect the building time, model cost, mechanical properties, and surface roughness. The presented paper develops an algorithm for adapting layers and generating tool-paths. This algorithm can improve the fabrication efficiency and geometrical accuracy in the additive manufacturing (AM) of complex models. The proposed algorithm consists of three modules that identify the optimal process parameters, named as part building orientation, layer thickness, strategy type for internal filling, and slope of the tool-path.ResultsThe input is the PTS file that contains the points of the layers contour of the computer-aided design (CAD) model. All the modules for the proposed algorithm were implemented using the MATLAB R2019a programming language software. The main finding results showed that the fabrication with an adaptive layer thickness was more time-efficient. The build time was reduced up to 47.3%. The developed tool-path generation strategies (contour offset and zigzag line tool-path) can effectively balance the AM surface quality and fabrication efficiency requirements.ConclusionIn this research, the AM users can benefit by saving the cost and time. The parts were fabricated with a high degree of accuracy, and the surface finish was suitable for determining the optimal process parameter.

Design Aspects of Additive Manufacturing at Microscale: A Review.

Additive manufacturing (AM) technology has been researched and developed for almost three decades. Microscale AM is one of the fastest-growing fields of research within the AM area. Considerable progress has been made in the development and commercialization of new and innovative microscale AM processes, as well as several practical applications in a variety of fields. However, there are still significant challenges that exist in terms of design, available materials, processes, and the ability to fabricate true three-dimensional structures and systems at a microscale. For instance, microscale AM fabrication technologies are associated with certain limitations and constraints due to the scale aspect, which may require the establishment and use of specialized design methodologies in order to overcome them. The aim of this paper is to review the main processes, materials, and applications of the current microscale AM technology, to present future research needs for this technology, and to discuss the need for the introduction of a design methodology. Thus, one of the primary concerns of the current paper is to present the design aspects describing the comparative advantages and AM limitations at the microscale, as well as the selection of processes and materials.

Mechanical Properties of Recycled Polymer Materials in Additive Manufacturing

The publication focuses on the testing of the tensile strength of samples produced by Fused Filament Fabrication additive manufacturing technology. Three materials rPLA, rPETG and rPET were tested. These materials are recycled PLA (Polylactic Acid), PETG (Polyethylene Terephthalate Glucol) and PET (Polyethylene Terephthalate). These materials were used to create samples for tensile testing according to ASTM D638. In addition to testing the materials, the methodology was also tested using sets of specimens printed with no outer perimeters, one outer perimeter and two outer perimeters. Tensile diagrams were created from the measured data. Statistical processing and comparison of the measured data is performed in the publication. In the discussion, a comparison of the mechanical properties of recycled materials for 3D printing versus virgin materials for 3D printing by Fused Filament Fabrication technology is made.

Design and characterization of carbon fiber-reinforced PEEK/PEI blends for Fused Filament Fabrication additive manufacturing

We formulated high temperature-resistant thermoplastic composite materials featuring high thermal and mechanical properties for the Fused Filament Fabrication (FFF) additive manufacturing process. The composite materials were blends of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) with weight ratios of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 and 40/60 and all mixed using an extrusion process with 30 wt% chopped carbon fibers (CFs). Differential Scanning Calorimetry measurements on the blends showed a significant increase of the single glass transition temperature, Tg, (up to 37 °C for PEEK/PEI 40/60 formulation), when compared to the neat PEEK, indicating a good miscibility of PEEK and PEI. Microscopy observations using Scanning Electron Microscopy and X-ray microtomography revealed a good dispersion of CFs in the PEEK/PEI blend matrix and also the presence of some voids. Tensile mechanical testing results showed that the highest value of the Young’s Modulus (13 GPa), among all the formulations, is obtained for the composition of reinforced PEEK/PEI (80/20) which also exhibited the lowest degree of porosity (2.90%), and high printability in the FFF process (i.e., high visual quality of the printed parts with no major printing issues). The materials developed here will help move towards manufacturing of functional prototypes made of high-performance composites (e.g., high mechanical properties and high service temperature) using FFF additive manufacturing process for various aerospace applications.

Issues in Metal Matrix Composites Fabricated by Laser Powder Bed Fusion Technique: A Review

The success in metal matrix composites (MMCs) fabrication by laser powder bed fusion (L‐PBF) technique has opened doors to further advanced materials development. But the drive to produce fully dense MMCs from a combination of metal and ceramic materials still faces serious setbacks arising from the associated complex phenomena and defects formation. This article discusses some of the issues that encourage defects generation in particulate‐reinforced MMCs. It further presents an overview of the additive manufacturing (AM) defects influenced by reinforcement addition and mitigation strategies. The review seeks to broaden the scope of L‐PBF fabrication defects concerning MMCs, and give a perspective on tailor designing feedstock materials for AM fabrication of high‐quality MMCs. Powder particles segregation, inappropriate scanning strategy, and combine effect of influencing parameters (processing and material) and defects are issues not often accounted for that encourage processing defects in MMCs. A holistic approach that accounts for all the controllable and materials related parameters, irrespective of their negligible influences on the optimal processing window, is expected to enhance the quality of L‐PBF‐fabricated MMCs. Furthermore, tailor designing of the feedstock materials may offer enhanced reinforcement material dispersion within the matrix and help reduce attendant defects from uneven reinforcement particles dispersion.

3D topology optimization of sandwich structures with anisotropic shells

The development of a density-based 3D minimum compliance topology optimization approach for sandwich structures with anisotropic shells is presented. A constant thickness shell is enforced at the interface of a base structure through a two-step filtering approach. Homogenous effective properties of a cellular material are assigned to the base structure while the shell is treated as a constant stiffness laminate with anisotropic properties. Local shell normal vectors are obtained from the density gradient introduced in the second filtering step and local material orientations in the shell’s tangent plane are approximated based on the fabrication process of the structure. Simple approximating strategies using the Gauss map are presented for a fabric draping process and the fused filament fabrication additive manufacturing process. The effect of material anisotropy on the optimal topology is studied on the Messerschmitt Bölkow Blohm beam benchmark problem. An application to composite structures is then presented where a square, simply supported laminate is reinforced on one face by a topology optimized sandwich structure. Though manufacturability cannot be ensured in the current implementation, careful consideration of the optimization parameters allow to constrain the problem towards manufacturable solutions using additively manufactured cores.

Fused Filament Fabrication of Bioresorbable Stent on a Rotating Mandrel

Bioresorbable stents have the potential to restore patency to blood vessels while minimising the risk of long-term complications. Bioresorbable stents can dissolve after restoring flow to a blocked artery, leaving behind a blood vessel with restored vascular tone. This can provide increased lumen gain, long-term vascular rehabilitation, and long-term healing. Additive manufacturing (AM) could offer new design freedom and patient-specific solutions; however, AM fabrication of bioresorbable stents, especially for specific patients, is challenging. In recent times, AM-based Fused Filament Fabrication (FFF) has gained popularity for printing stents by employing a rotating mandrel as a printing bed. However, using standard slicing methodology is challenging when generating extrusion profiles with strut dimensions at this size scale. By eliminating the requirement for a CAD model and instead slicing based on direct extrusion path generation from parametric curves, a method has been proposed for the FFF printing of bioresorbable stents on rotating mandrels. A Grasshopper (plugin in Rhinoceros) -based visual programming method was adopted for the generation of the required shapes of curves for the stent. The extrusion profile (gCode) was generated by Grasshopper for 3D printing on an FFF multi-axis machine. Poly (l-lactic) acid (PLLA) polymer material was chosen along with a standard zigzag stent shape for testing the proposed methodology. The extrusion temperature, nozzle speed, and extrusion values were varied as per the design of the experiment (Taguchi L9) approach to study their effect on the stent strut width and flexural strength. The optimisation was carried out to obtain a feasible relationship between parameters to print minimum strut width and maximum flexural strength. The proposed methodology successfully demonstrates printing complex stent shapes without a CAD model and slicing.

Robust design of an asymmetrically absorbing Willis acoustic metasurface subject to manufacturing-induced dimensional variations.

Advancements in additive manufacturing (AM) technology are promising for the creation of acoustic materials. Acoustic metamaterials and metasurfaces are of particular interest for the application of AM technologies as theoretical predictions suggest the need for precise arrangements of dissimilar materials within specified regions of space to reflect, transmit, guide, or absorb acoustic waves in ways that exceed the capabilities of currently available acoustic materials. This work presents the design of an acoustic metasurface (AMS) with Willis constitutive behavior, which is created from an array of multi-material inclusions embedded in an elastomeric matrix, which displays the asymmetric acoustic absorption. The finite element models of the AMS show that the asymmetric absorption is dependent on asymmetry in the distribution of materials within the inclusion and highly sensitive to small changes in the inclusion geometry. It is shown that the performance variability can be used to place constraints on the manufacturing-induced variability to ensure that an as-built AMS will perform using the as-designed parameters. The evaluation of the AMS performance is computationally expensive, thus, the design is performed with a classifier-based metamodel to support more efficient Monte Carlo simulations and quantify the sensitivity of the candidate design performance to the manufacturing variability. This work explores combinations of material choices and dimensional accuracies to demonstrate how a robust design approach can be used to help select AM fabrication methods or guide process development toward an AM process that is capable of fabricating acoustic material structures.

Fused Filament Fabrication Additive Manufacturing: Mechanical Response of Polyethylene Terephthalate Glycol

The additive manufacturing (AM) fused filament fabrication (FFF) technology is widely used today with different kinds of thermoplastic materials, including polyethylene terephthalate glycol (PETG). One of the major problems of parts produced by AM-FFF technology is the anisotropy of their mechanical properties. Therefore, it is very important to understand the effect of build strategy and post-processing on the mechanical properties and failure behavior of the FFF-PETG components. This research aims to examine the influence of 3D-print orientations, post-processing heat treatments and reinforcement of the material with carbon fibers, on the mechanical properties of FFF-PETG specimens. For this purpose, three different standard building orientations, flat, one-edge and upright specimens were printed. Tensile testing was carried out to obtain the mechanical properties of the FFF-PETG specimens for the different 3D-print orientations and post-processing. The specimens were characterized by visual testing, stereo microscopy, and SEM microscopy to examine the fracture surface after tensile test. The upright-melted specimens reached the same tensile strength as the as-printed flat and on-edge orientations specimens. The fracture surface of all three orientations is brittle and it typically starts by a mirror pattern that evolves into cleavage plates.

Structure and Fracture Visualization of Tilted ABS Specimens Processed via Fused Filament Fabrication Additive Manufacturing

Fused filament fabrication (FFF) technique is one of the most frequently used additive manufacturing (AM) technologies for printing ABS and many other thermoplastic materials. The anisotropy of the mechanical properties of 3D-printed parts manufactured by FFF technology is still of major concern when using this technique. Thus, the component’s orientation, build strategy and printing parameters affect the mechanical properties, and failure mechanisms are of crucial importance. This research aims to partly fill this gap by studying the structure and mechanical behavior of FFF-ABS specimens, and by performing fracture surface analysis by the three-point bend flexural test. A series of tests were conducted to determine the flexural properties of tilted specimens at 0°, 15°, 30°, 45°, 60° and 75° inclination angles relative to the machine platform. The work describes manufacture method of the specimens, experimental procedures, and outcomes from the mechanical and structural characterizations of the FFF-ABS specimens. Overall, two main failure modes were observed for the tested specimens: (1) inter-layer/ inter-raster bond failure (typical for upright specimens) and (2) intra-layer/trans-raster failure (typical for on-edge specimens). A mixed inter-layer/ intra-layer mode was found for the specimens tilted in-between the 15o and 60o range.