Common Additive Manufacturing Research Articles

Acoustic emission monitoring of a laser powder bed fusion process

Additive manufacturing (AM) metal parts offers opportunities for various industrial applications. From individual production of spare parts for unique mechanical components to prototyping of complex structures, the possibilities of production using the additive manufacturing process are manifold. One common AM technique is the Laser Powder Bed Fusion (PBF-LB/M) process, where a laser is used to selectively melt metal powder and create the parts layer wise as designed in a model. During manufacturing certain defects like pores, cracks and lack of fusion may be created in the built parts. As AM parts often have complex geometries, a postprocess non-destructive testing is difficult or even not possible. Thus, different optical monitoring techniques are applied to detect flaws during the build process with the aim to detect and repair defects right away during the manufacturing process. However, optical monitoring system require a clear view of the melt pool and quite expensive equipment. Acoustic monitoring by AE sensors attached to the built plate would be a cheaper alternative which also can be used without visual contact to the building chamber. This paper shows a first approach of an AE based process monitoring. The build plate of a PBF-LB/M machine therefore was adapted to hold four AE sensors that are then used to monitor the process. The build process itself creates AE signals caused by the melting and cooling and the mechanical application of powder. The formation of pores and cracks is expected to create additional acoustic emissions that will be distinct from the AE pattern from the printing process. This AE signals can be linked to the different layers of the printed part or in the long run to the laser position. Results from the first tests in a customized LPBF machine will be shown as well as the implementation of AE into the PBF-LB/M machine.

Investigating Additive Manufacturing Possibilities for an Unmanned Aerial Vehicle with Polymeric Materials.

Fused filament fabrication, also known as fused deposition modeling and 3D printing, is the most common additive manufacturing technology due to its cost-effectiveness and customization flexibility compared to existing alternatives. It may revolutionize unmanned aerial vehicle (UAV) design and fabrication. Therefore, this study hypothesizes the 3D printing possibility of UAV using a simple desktop printer and polymeric material. The extensive literature analysis identified the acceptable prototyping object and polymeric material. Thus, the research focuses on applying polylactic acid (PLA) in manufacturing the flying wing-type UAV and develops a fabrication concept to replicate arial vehicles initially produced from a mixture of expanded polystyrene and polyethylene. The material choice stems from PLA's non-toxicity, ease of fabrication, and cost-effectiveness. Alongside ordinary PLA, this study includes lightweight PLA to investigate the mechanical performance of this advanced material, which changes its density depending on the printing temperature. This proof-of-concept study explores the mechanical properties of printed parts of the wing prototype. It also considers the possibility of fragmentation in fabricated objects because of the limitations of printing space. The simplified bending tests identified significant reserves in the mechanical performance regarding the theoretical resistance of the material in the wing prototype, which proves the raised hypothesis and delivers the object for further optimization. Focusing on the mechanical resistance, this study ignored rheology and durability issues, which require additional investigations. Fabricating the wing of the exact geometry reveals acceptable precision of the 3D printing processes but highlights the problematic technology issues requiring further resolution.

Activation of additively manufactured electrodes using methanol and ethanol solutions

AbstractThe use of polymer additive manufacturing to produce electrodes is an increasingly popular area of electrochemical research. However, one downside of additively manufactured electrodes is the frequent need to remove polymer from the electrode surface to reveal a triple‐phase boundary in order for improved electrode performance to be realized. A common way to achieve this, is surface activation via chronoamperometry within an aqueous sodium hydroxide solution. However, it has not been investigated whether the same activation can be carried out effectively in solutions of sodium hydroxide in simple alcohols. Therefore, in this work, we study the effect of performing common chronoamperometric additive manufacturing electrode activation methodologies in methanolic and ethanolic solutions of 0.05 M sodium hydroxide and compare these to activation carried out in standard aqueous solutions at concentrations of both 0.05 M and 0.5 M. We show that the alcoholic solutions are more effective in removing polymer from the additive manufacturing electrode surface, but that this does not lead to any improvement in electrode currents, and furthermore appears to hinder electron transfer kinetics at the additive manufacturing electrode surface, with the latter effect shown to be related to differences in the surface functionality of the exposed carbon black filler particles. As well as being interesting chemical experiments in their own right, these results may well be of interest to electrochemists who intend for their additive manufactured electrodes to be applied in these alcohols or indeed other non‐aqueous solvents.

On the fatigue behavior of a tool steel manufactured by powder bed based additive manufacturing—a comparison between electron- and laserbeam processed AISI H13

In recent years, additive manufacturing (AM) techniques have gained increased attention. The most common AM technologies to realize complex parts are powder bed-based fusion processes, especially electron beam powder bed fusion of metals (PBF-EB/M) and laser-based powder bed fusion of metals (PBF-LB/M). Focusing on industrial applications, cyclic loading scenarios and fatigue properties of components produced by such techniques came into focus of research. The present work deals with a comparison between microstructure, hardness, density and fatigue properties of a high-alloy tool steel AISI H13 (1.2344, X40CrMoV5-1) manufactured by PBF-EB/M and PBF-LB/M. The investigated specimens are characterized by a complex phase composition containing ferrite, perlite, bainite and martensite, eventually resulting in different hardness values depending on the used AM technology. Fatigue data for PBF-EB/M AISI H13 are reported for the first time in open literature. It is shown that the fatigue behavior is significantly influenced by the specimen density. Accordingly, parts with a high density are characterized by superior fatigue strength.

Advances in Fatigue Performance of Metal Materials with Additive Manufacturing Based on Crystal Plasticity: A Comprehensive Review.

Using metal additive manufacturing processes can make up for traditional forging technologies when forming complex-shaped parts. At the same time, metal additive manufacturing has a fast forming speed and excellent manufacturing flexibility, so it is widely used in the aerospace industry and other fields. The fatigue strength of metal additive manufacturing is related to the microstructure of the epitaxially grown columnar grains and crystallographic texture. The crystal plasticity finite element method is widely used in the numerical simulation of the microstructure and macro-mechanical response of materials, which provides a strengthening and toughening treatment and can reveal the inner rules of material deformation. This paper briefly introduces common metal additive manufacturing processes. In terms of additive manufacturing fatigue, crystal plasticity simulations are summarized and discussed with regard to several important influencing factors, such as the microstructure, defects, surface quality, and residual stress.

UV-assisted robotic arm freeforming of SiOC ceramics from a preceramic polymer

Material extrusion is a very common and facile additive manufacturing technique for ceramic materials, allowing for rapid design and fabrication of 3D structures without expensive tools. However, fabricating sophisticated structures with large spanning parts and overhanging features using this technology is still a challenge. Here, UV-assisted additive manufacturing is enabled by performing material extrusion with the assistance of UV light using mixture of a preceramic polymer and a photopolymer. The rheological properties of the ink were investigated under UV light radiation to optimize the printing parameters to achieve excellent printability. Complex ceramic structures were fabricated with this method, such as spiral and truss structures, which would be very difficult to obtain using traditional material extrusion without sacrificial supports. These structures have potential application in lightweight ceramic components, such as sandwich structures.

Optimization of 3D printing parameters in polylactic acid bio-metamaterial under cyclic bending loading considering fracture features

3D printing has become a crucial additive manufacturing technique with the applications in various industries. Fused deposition modeling (FDM) is a common additive manufacturing process that offers considerable flexibility in the component fabrication through multiple parameters, which strongly influence the properties of the produced parts. This study focused on the impact of different printing parameters on the fatigue behavior of polylactic acid (PLA). The standard samples were 3D-printed with varying speed (5, 10, and 15 mm/s), print temperature (180, 210, and 240 °C), and nozzle diameter (0.2, 0.4, and 0.6 mm). The fatigue properties were evaluated through rotating bending fatigue tests, and a model was developed based on the results with a statistical analysis. The model accuracy was validated and the interactions between the parameters were analyzed. The optimization study found that a print speed of 5 mm/s, print temperature of 210 °C, and nozzle diameter of 0.2 mm were optimal. The fracture surfaces were also examined using a scanning electron microscopy, revealing the presence of crazing despite the brittle behavior of PLA.

Thermo-mechanical properties of ABS/stainless steel composite using FDM

Fused deposition modelling (FDM) process is the most common and traditional additive manufacturing methods for producing complicated three-dimensional (3D) samples from computer-aided design data at a cheaper cost than alternative methods. However, when compared to other common plastic production processes, such as injection moulding, FDM produced parts results in low mechanical properties. Hence, the objective of this study is to produce composite filament using stainless steel (SS) as filler material to enhance the mechanical properties of ABS. ABS is a petroleum based thermoplastic that commonly used in FDM. The production of metal/polymer composites utilising ABS as the matrix and varied SS powder compositions was studied in this work. ABS/SS composite filaments containing 5, 10 wt% SS powder were developed in this experiment to compare with pure ABS for the FDM process. The result shows that the higher the composition of SS powder the lower the ultimate tensile strength and yield strength where 10 wt% SS shows 38.42 MPa in ultimate tensile strength while for yield strength it shows 24.32 MPa. Meanwhile, 10 wt% SS filament has better elongation which is 18.28 % compare to pure ABS that is 9.89 % and 13.3 % for 5 wt% SS. Thus, the percentage of filler plays an important role in determining the properties of ABS.

Shrinkage evaluation and geometric accuracy assessment on 17–4 PH samples made by material extrusion additive manufacturing

Material Extrusion Additive Manufacturing (MEX) is one of the most common Additive Manufacturing (AM) technology. The possibility to realize metal parts using this technology has several advantages and generates great costs reduction with respect to other metal Additive Manufacturing technologies. However, there are some disadvantages related to the design and production of these extrusion-based metal parts, especially when considering the fabrication of complex geometries. One of the main problems is related to the oversizing of the parts due to the shrinkage phenomenon occurring after the debinding and sintering steps.In this work, a comprehensive study about the shrinkage phenomenon was conducted on 17–4 PH stainless steel parts realized via MEX, analyzing the influence of printing and sintering orientation, infill strategy and aspect ratio. With this aim, by using the Design of Experiment approach, samples were analyzed in both as-printed and as-sintered conditions. Shrinkage percentage values, geometric accuracy and density were the main investigated outputs. A commercial 3D structured-light scanner was used to collect the dimensional and geometric data.Results showed a strong shrinkage anisotropy, more relevant for samples with different orientation during the printing and the sintering phase. Geometric accuracy, in terms of flatness, was also assessed comparing green and sintered parts.

Micromechanical Models for FDM 3D-Printed Polymers: A Review.

Due to its large number of advantages compared to traditional subtractive manufacturing techniques, additive manufacturing (AM) has gained increasing attention and popularity. Among the most common AM techniques is fused filament fabrication (FFF), usually referred to by its trademarked name: fused deposition modeling (FDM). This is the most efficient technique for manufacturing physical three-dimensional thermoplastics, such that FDM machines are nowadays the most common. Regardless of the 3D-printing methodology, AM techniques involve layer-by-layer deposition. Generally, this layer-wise process introduces anisotropy into the produced parts. The manufacturing procedure creates parts possessing heterogeneities at the micro (usually up to 1 mm) and meso (mm to cm) length scales, such as voids and pores, whose size, shape, and spatial distribution are mainly influenced by the so-called printing process parameters. Therefore, it is crucial to investigate their influence on the mechanical properties of FDM 3D-printed parts. This review starts with the identification of the printing process parameters that are considered to affect the micromechanical composition of FDM 3D-printed polymers. In what follows, their (negative) influence is attributed to characteristic mechanical properties. The remainder of this work reviews the state of the art in geometrical, numerical, and experimental analyses of FDM-printed parts. Finally, conclusions are drawn for each of the aforementioned analyses in view of microstructural modeling.

Surface Characterisation and Comparison of Polymeric Additive Manufacturing Features for an XCT Test Object

Additive manufacturing (AM) has experimented a huge development in recent years, improving the physical properties of parts produced by these technologies to the level of being capable of fabricating end-use functional products. High performance metals are widely used and studied; however, the reduction in material costs of polymers and their acceptable properties makes them suitable for common AM purposes. The intrinsic surface roughness of AM, as a consequence of the layer-by-layer technology, remains a challenge and its characterisation is necessary for quality control. X-Ray computed tomography (XCT), as a newly adapted evaluation technology for industrial applications, sets an opportunity for the dimensional measurement of AM parts, due to its capability of characterising the complex geometries that is possible to create with this manufacturing technologies. In this paper, a first approach to a surface characterisation of polymeric AM parts is presented. Several individual objects have been designed and manufactured using various polymeric AM technologies with different manufacturing principles (FDM, Polyjet, SLS) to build ramps with a range of surface roughness created by two main parameters (angle of inclination and layer thickness). Measurements have been carried out by an optical device (focal variation microscope, FVM), and a comparison with theoretical roughness values calculated following predictive models has been made, with the objective of analysing the behaviour of each surface. Results show that the influence of the angle of inclination is higher than the influence of layer thickness; post-processing, also, affects to the trueness of the real roughness comparing to the predicted one obtaining more unpredictable results.

Determination of Suitable Geometrical Ranges for the Manufacture of Microfluidic Channels by Low-Cost Additive Manufacturing Techniques

Additive manufacturing of microfluidic devices is a field of increasing interest due to the great variety of fields where they can be used, especially in physicochemical, biological and medical ones. These devices include internal channels whose manufacture can be challenging as it takes place close to or into the micro geometric scale. On the other hand, the use of low-cost techniques can provide access to certain services in depopulated areas in different fields, so this approach can be of interest in the development of new products under new production and living contexts. In this work, the geometrical ranges of practical application for the manufacture of microfluidic channels by two of the most common additive manufacturing techniques for polymeric materials (Fused Filament Fabrication and the Stereolithography) are analyzed by means of an evaluation of the dimensional accuracy obtained in samples with channels of circular section. The circular channels present diameters that vary from 2 mm to the minimal size feasible which each printer (a Markforged Onyx One, a Ultimaker S5 and a Formlabs Form3). The Ultimaker S5 (FFF) equipment is the one that presents the best results, being the dimensional deviations around 0.2 mm in a wide range 1 < dnom (mm) < 2; and contrary to the expectations, the SLA system provides the worst results, with a growing trend starting from deviations of 0.6 mm. An obturation effect in the channels has been also detected, being critical in the case of nominal diameters lower than 0.8 mm for the Ultimaker S5 system. In general, it can be concluded that the FFF technology is a more reliable option compared to SLA under the printing parameters considered in this work and for the materials used in this study.

Integrated deep learning-based online layer-wise surface prediction of additive manufacturing

Additive manufacturing (AM) is growing tremendously through its introduction into various industries over recent years, because of its capability of fabricating objects with complex designs. Despite its great successes, AM still has to deal with its main challenge, which is the quality assurance of the printed object. Although extensive studies have been conducted, there are still several critical gaps facing this technology. Due to layer-wise fabrication, one important aspect of quality assurance is to capture the surface morphology of the layer being printed online, which can help to better understand the process dynamics and greatly benefit the promotion of in-process quality control. Thus, this study developed an integrated deep learning model to achieve online layer-wise surface prediction of AM. The proposed deep learning model integrates the convolution autoencoder for surface representation learning and a long short-term memory (LSTM) network for layer-wise prediction. The proposed method is validated by a real-world case study in a common AM process, fused filament fabrication (FFF). The comparison with the benchmarks demonstrates that the developed method has great potential for online layer-wise prediction in AM.

Advancement of extreme environment additively manufactured alloys for next generation space propulsion applications

The National Aeronautics and Space Administration (NASA) has been involved in the development and maturation of metal additive manufacturing (AM) for space applications since the late 2000's. Several efforts have focused on the understanding of AM processes through material characterization and testing, standards development, component fabrication, and infusion into propulsion development and flight applications. NASA matured commonly used aerospace alloys from various alloy families (Nickel, Copper, Stainless and Steel, Aluminum, and Titanium-based) through detailed AM process and heat treatment characterization, in addition to mechanical and thermophysical testing. While these alloys are actively used in many propulsion applications, there is a need for ongoing AM optimized alloys using integrated computational materials engineering (ICME) and process development for high performance applications. The applications targeted are liquid rocket engines; advanced propulsion systems; and in-space propulsion with high heat fluxes, high pressure, and/or that use propellants that can degrade alloys (e.g., hydrogen). This paper highlights the characterization and physical properties of the more common AM alloys using laser powder bed fusion (L-PBF) and laser powder directed energy deposition (LP-DED) processes. Additionally, this paper discusses some of the ongoing novel alloy development and maturation using AM for use in these harsh environments, such as GRCop-42, GRCop-84, NASA HR-1, GRX-810, and C-103. The results from these processes demonstrated that AM could enable rapid development, and that optimized alloys could be developed using ICME, yielding higher performances. These alloys have undergone modeling, fundamental metallurgical evaluations, heat treatment studies, detailed microstructure characterization, and mechanical testing campaigns. This, combined with direct application-specific component fabrication and hot-fire testing, enabled the increase of the Technology Readiness Level (TRL) through high duty-cycle testing. A background and overview of these novel AM-enabled alloys and AM processing developments including metallurgical and mechanical property studies is presented here. The latest advancement in the parallel component development and hot-fire testing and future developments for these alloys is also discussed.

A Material-Recycling Unit for the Fused Deposition Modelling of Three-Dimensional Printing Systems

Fused deposition modelling (FDM) three-dimensional (3D) printing technology is one of the most common additive manufacturing (AM) technologies due to the relatively low cost of the printing units and materials. Although cost-effective, this technology is not conceived to convert 100% of the raw material into a complete product, creating a potential plastic waste problem. To recycle the plastic waste from the FDM machine into reusable filaments, the concept of a 3D printer material-recycling machine (3DP-MRM) was developed using CREO Parametric 9.0 software. A prototype with four systems, including a spooler system, extruder system, display system, and filament-positioning system, was manufactured in-house with complete run experiments. The tests of the 3DP-MRM were applied, and the machine worked successfully among all the designed functions with minor issues.

Performance of Additively Manufactured Fuels for Hybrid Rockets

Hybrid rocket engine (HRE) performance is dependent on fuel/oxidizer selection and fuel grain geometry. A literature review was performed to identify key trends and findings related to the application of the additive manufacturing (AM) of fuel systems for HREs. The effects of complex combustion port geometries, embedded structures, and end-burning systems, along with the use of metallic additives, turbulators, diaphragms, gel-like fuels, powdered fuels, liquid fuels, and liquifying fuels and their impact on regression rates, combustion efficiencies, and/or mechanical strength are thoroughly documented here. In general, the application of AM to HRE fuels can be implemented to increase regression rates and combustion efficiency, and tailor HRE designs. Chemical equilibrium analysis computations were completed to characterize the theoretical performance of HTPB and common AM fuels (ABS, PLA, PC, PMMA, Nylon 6, and a UV-based fuel) with common oxidizers (LOX and N2O). AM fuels exhibit a similar theoretical performance as the commonly used HTPB fuel, and proper selection of the fuel can yield improved performance and design metrics. Development of AM approaches for HRE fuel design have significantly expanded their design trade space and should enable the competitive application of HREs for future propulsion missions.

Differentiable Channel Design for Enhancing Manufacturability of Enclosed Cavities

Hollowing is a simple and effective method for achieving light-weighting by removing interior volume while maintaining the external shape of the model. However, the enclosed cavities created through hollowing can limit its applications due to the residual material restrictions of common additive manufacturing technologies, such as selective Laser Sintering (SLS) and Stereo Lithography Apparatus (SLA). To address this problem, we propose an efficient channel design framework to eliminate enclosed cavities and make the structures apply to common additive manufacturing technologies. The channels are treated as ideal objects with length and inclination angle. A differentiable channel planning is then devised to connect all enclosed cavities and make them manufacturable. An automatic optimization utilizing gradient-based optimization is applied to solve the problem, optimizing both the angles and positions of the channels to ensure the residual material can be discharged freely through the channels. Experiments and 3D printed models are carried out to demonstrate the effectiveness and feasibility of the proposed method.

Unraveling the failure mechanism of wire arc additive manufactured low carbon steel under tensile and high cycle fatigue loading

Wire arc additive manufacturing (WAAM) is one of the common additive manufacturing processes for efficiently building large components due to its high deposition rate and higher catchment efficiency with an easy and relatively simpler arrangement. However, WAAM components often observe defects that adversely affect some mechanical properties. The present work employs a two-camera digital image correlation (DIC)-based technique for simultaneous strain measurements on two mutually orthogonal surfaces to capture the strain accumulation due to defects and subsequent failure behavior under uniaxial tensile loading of WAAM deposited ER70S-6 low carbon steel samples. The elastic cyclic loading tests are also performed at different stress amplitudes, and their fracture surfaces are analyzed with scanning electron microscopy. Due to the weak interlayer consolidation, multiple delaminations and strain accumulation sites are observed. Propagation of delamination contributed towards the failure, and dimples as well as intergranular fractures are observed on failure surfaces. Premature failure with a reduced number of cycles to failure is observed during high cycle fatigue tests due to catastrophic fast failure in the neighborhood of the internal defects. While the fatigue crack initiation and propagation are distinctly observed on fracture surfaces, transition regions from fatigue fracture and fast fracture are mostly obscure.

Characterization of D2 Tool Steel fabricated thru Fused Filament Fabrication Process

Additive Manufacturing (AM) unlocked a new way of producing advanced structures that are stronger and use less material, enabling new possibilities due to design freedom, easiness of manufacturing complex parts, and mass personalization. One of the most common AM processes is Fused Filament Fabrication (FFF), which is mainly used to manufacture polymer parts. However, FFF can also produce metallic components, which is not as simple and direct since it requires debinding and sintering processes. This study was conducted to develop the knowledge of FFF using metal and aims to evaluate the characteristics of D2 tool steel. The mechanical and microstructural properties were evaluated, and the results were compared with the supplier's datasheets.

Surface Optimization of Components Obtained by Fused Deposition Modeling for Air-Plasma-Sprayed Ceramic Coatings

Additive manufacturing is an emerging disruptive 3D printing technology that is stimulating innovations in design and engineering, materials, and manufacturing thanks to the prospects of reducing cost and waste and increasing efficiency; in doing so, it presents the potential to have marked industrial, economic, and societal impacts. Thermoplastic polymers show some ideal characteristics for the most common additive manufacturing methods, and this aids in the improvement of the design accuracy and reliability and makes inroads for the customized manufacturing of high-design-flexibility polymer parts. Despite this, this material family is strongly sensitive to temperature, and one of the viable ways of limiting this weak point is surface coating with thermal barriers. The focus of this work was the optimization of an additive manufacturing process for producing thermoplastic components and to improve the adhesion of a thermal barrier coating on their surface. In detail, flat plate specimens of ULTEM 1010 were obtained by the fused deposition modeling technique by varying two significant surface parameters, the enhanced visible rasters and the visible raster air gap; then, their surfaces were covered by a thin ceramic coating by an air plasma spray system. A micro-geometric analysis that was conducted using a confocal microscope and the coating thickness measurements highlighted that a global larger roughness value, the presence of more flat peaks with a large area, and the complexity of the texture can be considered as supporting factors for improving the mechanical gripping and allowing a uniform adhesion of the coating powders on the thermoplastic substrate.