Additive Manufacturing Technology Research Articles

Capturing Local Temperature Evolution during Additive Manufacturing through Fourier Neural Operators

Abstract High-fidelity, data-driven models that can quickly simulate thermal behavior during additive manufacturing (AM) are crucial for improving the performance of AM technologies in multiple areas, such as part design, process planning, monitoring, and control. However, the complexities of part geometries make it challenging for current models to maintain high accuracy across a wide range of geometries. Additionally, many models report a low mean square error (MSE) across the entire domain of a part. However, in each time step, most areas of the domain do not experience significant changes in temperature, except for the regions near recent depositions. Therefore, the MSE-based fidelity measurement of the models may be overestimated. This paper presents a data-driven model that uses the Fourier Neural Operator to capture the local temperature evolution during the AM process. Beside MSE, the model is also evaluated using the R2 metric, which places great weight on the regions where the temperature changes significantly than MSE. The model was trained and tested on numerical simulations based on the Discontinuous Galerkin Finite Element Method for the Direct Energy Deposition AM process. The results shows that the model maintains 0.983-0.999 R2 over geometries not included in the training data, which is higher than Convolutional Neural Networks and Graph Convolutional Neural Networks we implemented, the two widely used architectures in data-driven predictive modeling.

Comparison of CAD Software for Designing Cellular Structures for Additive Manufacturing

Additive manufacturing (AM) technologies provide significant design freedom, which is highly desirable in today’s fast-paced product design processes. However, most of the parametric CAD software tools used today do not fully utilize this potential for freedom of form and design. Design mechanisms, such as topology optimization (TO), generative design (GD), and lattice structures, are available on the market to help designers minimize weight and material cost while maximizing the stiffness and flexibility of planned designs. This paper proposes a benchmarking approach for designers and engineers to select a suitable software tool for lattice structure generation for their specific applications. The approach includes preselecting software tools based on a weighted point evaluation of seven significant criteria. The tools are then evaluated based on key metrics such as computing time and file size of exported structures, as well as the following six distinctive attributes: usability, reliability, availability, performance, support, and cost. The evaluation process considers a total of 32 defined features. The investigation produced clear recommendations regarding overall performance, reliability, and user experience. The findings indicate that the option of a comprehensive support offering, as well as the initial and operational costs, are significant drivers in the decision-making process.

Additive Manufacturing for Rapid Sand Casting: Mechanical and Microstructural Investigation of Aluminum Alloy Automotive Prototypes

The automotive industry is undergoing a rapid evolution to meet today’s challenges; therefore, continuous innovation and product development are needed. Validation tests on prototypes play a crucial role in moving new components into industrial production. There is also a pressing need for faster prototyping processes. In this context, rapid sand casting (RSC), based on additive manufacturing technology, offers a promising solution for a quick production of sand molds. While this technology is already employed in the industry, the need to deepen the general understanding of its impact on the casting properties is still a relevant item. In this study, different geometries of automotive prototypes made of aluminum EN AC 42100-T6 alloy were experimentally analyzed. Microstructural examinations, tensile tests, and fractography and porosity analyses were conducted. The findings demonstrate the considerable potential of RSC, giving, in general, high mechanical properties. A comparative analysis with prototypes produced through traditional sand casting revealed similar results, with RSC exhibiting superior yield strength and stress at brake. However, both technologies revealed a reduced elongation percentage, as expected. Future efforts will focus on standardizing the RSC process to enhance ductility levels.

The Three-Dimensional Printing of Composites: A Review of the Finite Element/Finite Volume Modelling of the Process

Composite materials represent the evolution of material science and technology, maximizing the properties for high-end industry applications. The fields concerned include aerospace and defense, automotive, or naval industries. Additive manufacturing (AM) technologies are increasingly growing in market shares due to the elimination of shape barriers, a plethora of available materials, and the reduced costs. The AM technologies of composite materials combine the two growing trends in manufacturing, combining the advantages of both, with a specific enhancement being the elimination of the need for mold manufacturing for composites, or even post-curing treatments. The challenge of AM composites is to compete with their conventional counterparts. The aim of the current paper is to present the additive manufacturing process across different spectrums of finite element analyses (FEA). The first outcomes are building definition (support definition) and the optimization of deposition trajectories. In addition, the multi-physics of melting/solidification using computational fluid dynamics (CFD) are performed to predict the fiber orientation and extrusion profiles. The process modelling continues with the displacement/temperature distribution, which influences porosity, warping, and residual stresses that influence characteristics of the component. This leads to the tuning of the technological parameters, thus improving the manufacturing process.

Additive Manufacturing of Rare Earth Permanent Magnetic Materials: Research Status and Prospects

With the rapid development of intelligent manufacturing, modern components are accelerating toward being light weight, miniaturized, and complex, which provides a broad space for the application of rare earth permanent magnet materials. As an emerging near-net-shape manufacturing process, additive manufacturing (AM) has a short process flow and significantly reduces material loss and energy consumption, which brings new possibilities and impetus to the development of rare earth permanent magnetic materials. Here, the applications of AM technology in the field of rare earth permanent magnets in recent years are reviewed and prospected, including laser powder bed fusion (LPBF), fused deposition modeling (FDM), and binder jetting (BJ) techniques. Research has found that the magnetic properties of AM Nd-Fe-B magnets can reach or even exceed the traditional bonded magnets. In addition, in situ magnetic field alignment, in situ grain boundary infiltration, and post-processing methods are effective in enhancing the magnetic properties of AM magnets. These results have laid a good foundation for the development of AM rare earth permanent magnets.

Mechanical behaviors and wear resistances of 3D-printed AISI 321 components for combustor swirler applications

This comprehensive study investigates the mechanical behaviors and wear characteristics of 3D-printed AISI 321, with a specific focus on its applicability in combustion swirler components for the power generation industry. Through meticulous exploration of various process parameters and postprocessing techniques, valuable insights were gained into the performance disparities between layered and cast specimens. Analyses revealed intriguing comparisons of key data points: while layered specimens exhibited higher surface roughness (4.37 μm), they demonstrated a lower friction coefficient (0.26) yet a higher wear rate (4.79 × 10−7 mm3/N·mm) compared to their cast specimens. Further investigation into the influence of layering direction unveiled that horizontally layered specimens presented smoother surfaces (0.26 μm), higher hardness (340 HV 1), and improved wear resistance (2.61 × 10−7 mm3/N·mm) compared to vertically layered specimens. Furthermore, the study examined the friction and wear characteristics of layered specimens based on the contact surface, including the top, side, and bottom surfaces. Lastly, a comparison of the mechanical behavior and friction/wear characteristics of layered specimens and cast specimens was conducted, demonstrating that the layered specimens fabricated using the Laser Powder Bed Fusion (LPBF) method exhibited superior performance. These findings underscore the significant potential of 3D-printed AISI 321 in enhancing performance and sustainability in power generation applications, while highlighting the ongoing need for continued research and development to fully exploit the capabilities of additive manufacturing technologies.

Structural design, interfacial behavior and mechanical properties of bimetallic nacre-like structures by laser powder-bed fusion

The nacre-like (NL) structure exhibits unique performance in preventing the catastrophic crack growth and improving the strengthening/toughening of the overall structure. In this study, the In718/316LSS bimetallic NL structures were first fabricated by a powder laying-absorption multiple-material additive manufacturing technology based on laser powder-bed fusion, and the stress release mechanism was revealed. The NL structures with optimal geometric parameters was obtained by calculation and simulation: the hard-phase inclination angle of 15 °, the hard-phase volume fraction of 70%, and the lamellar length-width ratio of 2. Due to the remelting effect, the same-layer bimetallic interfaces in NL structures showed strong metallurgical bonding with significantly grain refinement. The interlocking NL structure exhibited superior mechanical properties of 751.82 MPa in tensile strength and 25.14% in elongation, compared with the base alloys and the non-interlocking NL structure. Moreover, abnormal variation of work hardening rate in NL structures attributed to the stress concentration and release behavior, caused by the multi-cracks initiation and cracks deflection during deformation of the interlocking structure. By the stress concentration-release effect, the NL structure not only achieved the strengthening and toughening, but also improved the crack tolerance to avoid the sudden fracture failure.

Influence of part temperature on in-situ monitoring of powder bed fusion of metals using eddy current testing

AbstractPowder bed fusion of metals (PBF-LB/M) is currently the most widely adopted additive manufacturing technology for the fabrication of metal parts. However, the inconsistent quality of PBF-LB/M-manufactured parts and high costs for part certification are impeding wider industrial adoption. In-situ monitoring technologies are expected to enable process control in order to ensure consistent quality, and to replace some of the post-process inspection steps, therefore, reducing part certification costs. Eddy current testing (ECT) is a standardized nondestructive testing technique, which can be used as an in-situ monitoring technology to measure the part quality during the PBF-LB/M build cycle. However, the process-induced complex temperature fields in PBF-LB/M parts during the build cycle are among the most relevant disturbances due to the temperature dependence of the electrical conductivity. This study investigates the process-induced temperature influence on in-situ monitoring of relative density using ECT. Parts made from AlSi10Mg were manufactured on a PBF-LB/M machine and the build cycle was monitored using ECT and an infrared camera, which was used to extract the part surface temperature right before the ECT measurement. The results demonstrate that the temperature increase of the parts during the build cycle decreases the electrical conductivity independently of the relative part density, which was measured via micro-computed tomography. Therefore, a temperature compensation method was proposed and applied demonstrating that a layer-to-layer difference of 0.15 % relative density can be detected via ECT. Consequently, it has been demonstrated that ECT is an effective in-situ monitoring technology for PBF-LB/M, even in the presence of temperature disparities within parts.

Additive manufacturing of ultrahigh-resolution Poly(ε-caprolactone) scaffolds using melt electrowriting

Melt electrowriting (MEW) is an advanced additive manufacturing technology that produces high-resolution scaffolds for medical applications. Although there are many valuable parameter groups for MEW, the corresponding principles need to be clarified to improve the success of printing high-fidelity scaffolds. To this end, we investigate the print limit of MEW with respect to the minimum interfiber distance and the maximum print period based on a medical-grade poly(ε-caprolactone) material. The results indicate that relatively large turning loops and low turning speeds improve the print accuracy of the scaffolds; however, excessively large turning loops and low turning speeds result in fiber accumulation on the edge of the scaffolds, resulting in print failure. The turning loops with 500 μm in diameter and turning speeds of 0.625 × CTS (critical translation speed) can achieve well-defined MEW scaffolds with an interfiber distance down to 25 μm. For printing such high-resolution scaffolds, the constant printing process can last one week. Fiber placement gets random when the fiber diameter is larger than 2.5 μm, caused by the melt polymer degradation and shear thinning in the printing process. Additionally, we verify that the method of charge neutralization is not beneficial for improving the fiber overlay. This is a fundamental study clarifying the principles of printing high-resolution MEW scaffolds, being capable of extending the application of the MEW products.

Manufacturing-induced stochastic constitutive behaviors of additive manufactured specimens: testing, data-driven modeling, and optimization

Purpose Fused deposition modeling (FDM) is an extensively used additive manufacturing method with the capacity to build complex functional components. Due to the machinery and environmental factors during manufacturing, the FDM parts inevitably demonstrated uncertainty in properties and performance. This study aims to identify the stochastic constitutive behaviors of FDM-fabricated polylactic acid (PLA) tensile specimens induced by the manufacturing process. Design/methodology/approach By conducting the tensile test, the effects of the printing machine selection and three major manufacturing parameters (i.e., printing speed S, nozzle temperature T and layer thickness t) on the stochastic constitutive behaviors were investigated. The influence of the loading rate was also explained. In addition, the data-driven models were established to quantify and optimize the uncertain mechanical behaviors of FDM-based tensile specimens under various printing parameters. Findings As indicated by the results, the uncertain behaviors of the stiffness and strength of the PLA tensile specimens were dominated by the printing speed and nozzle temperature, respectively. The manufacturing-induced stochastic constitutive behaviors could be accurately captured by the developed data-driven model with the R2 over 0.98 on the testing dataset. The optimal parameters obtained from the data-driven framework were T = 231.3595 °C, S = 40.3179 mm/min and t = 0.2343 mm, which were in good agreement with the experiments. Practical implications The developed data-driven models can also be integrated into the design and characterization of parts fabricated by extrusion and other additive manufacturing technologies. Originality/value Stochastic behaviors of additively manufactured products were revealed by considering extensive manufacturing factors. The data-driven models were proposed to facilitate the description and optimization of the FDM products and control their quality.

Review on the Tensile Properties and Strengthening Mechanisms of Additive Manufactured CoCrFeNi-Based High-Entropy Alloys

The advent of high-entropy alloys (HEAs) provides new possibilities for the metallurgical community. CoCrFeNi-based alloys have been widely recognized to demonstrate superior mechanical properties, amongst the high-entropy alloy systems; in particular, they possess an outstanding tensile ductility and work-hardening capacity. Additive manufacturing (AM) uses a layer-by-layer material deposition approach to build parts directly from computer-aided design models, which are capable of producing near-net-shape HEAs with superior mechanical properties, surpassing traditional manufacturing methods that require a time-consuming post-treatment process, such as cutting, milling, and molding. Moreover, the rapid solidification inherent in AM processes induces the formation of high-density dislocations, which are capable of enhancing the mechanical properties of HEAs. This review comprehensively investigates and summarizes the diverse strengthening mechanisms within CoCrFeNi-based alloys produced using AM technologies, with a specific focus on their influence on tensile properties. A correlation is established between the AM processing parameters and the resultant phases and microstructures, as well as the mechanical properties of CoCrFeNi-based HEAs, which provide guidelines to achieve a superior strength–ductility synergy.

Performance evaluation of polymer-filled metal fused filament fabrication tooling for profile extrusion

AbstractThe application of additive manufacturing (AM) for tooling in the mould and die industry brings a disruptive potential in process performance, design flexibility and product enhancements. Maturing of existing AM technologies and emerging technologies such as metal-fused filament fabrication (metal FFF) can further support the applicability of AM tooling in polymer profile extrusion. This study provides a complete characterization of metal FFF 17–4 PH stainless-steel die inserts and evaluates their applicability in a polymer extrusion process chain. The presented experimental assessment pivots on the metrological characterization of the produced inserts and the impact of the insert characteristics on the final extrudates’ product. Considering a conventionally manufactured benchmark insert, produced via subtractive methods (CNC machining and electrical discharge machining), comparable results for AM tools in terms of extrudates’ quality and process repeatability are presented. It was found that despite significant higher average surface parameters for AM insert tools (Sa = 2–9 µm vs. Sa = 0.3–0.9 µm for dies manufactured by machining), a much smaller difference was observed in the resulting quality of polymer extrudates’ product. The roughness generation effect of polymer profile extrusion based on the different dies’ internal surface roughness topography and the effect on extrudates product was evaluated. Three-dimensional average roughness Sa on acrylonitrile butadiene styrene extrudate surfaces obtained from conventionally machined dies was in the range of 0.3 µm. For extrudates obtained from additively manufactured dies, their Sa was in the rage of 0.5 µm (despite the much higher surface roughness of FFF dies compared to machined dies). The results confirm that with suitable extrudates’ product requirement, it is feasible to apply metal FFF as the selected manufacturing method for tooling in polymer profile extrusion.

Achieving strong and ductile Ti-9Cr alloy with deformable TiCr2 nano-particles by direct energy deposition

Due to the strong segregation of Cr, the content of Cr was restricted in the commercial titanium alloy to avoid β-flecks and deterioration of mechanical performance. Here, we prepared a homogeneous Ti-9Cr alloy with uniform distribution of Cr element by additive manufacturing technology. Fine α laths and dispersed TiCr2 nano-particles were acquired in the alloy, generating a high ultimate tensile strength of 1000 MPa with elongation of 16 %. It was demonstrated that the TiCr2 nano-particles showed a face-centered cubic structure. Stacking faults occurred on the {111} plane of the TiCr2 during deformation, which relieved local stress.

Melting ceramic Al2O3 powder by electron beam powder bed fusion

AbstractElectron beam powder bed fusion (PBF-EB) is a known metal additive manufacturing (AM) technology. Processing non-conducting powders such as ceramics has so far been considered as not feasible because of the inherent problems with Coulomb repulsion due to insufficient electrical conductivity. In this study, a method for functionalizing ceramic powder is proposed where particles are electroless coated by a ~ 1 µm Ni layer to decrease the surface resistivity. The feasibility of the suggested approach is tested on Al2O3 powder, and the results show that the coated ceramic powder has a decreased surface resistivity, which enables processing by PBF-EB. Heating and melting parameters were investigated and samples were manufactured at ~ 1600 °C. Sintered and melted powders were analyzed by microscopy and micromechanically tested by nanoindentation. Calculations, visual observation and SEM–EDX suggest that the Ni coating is evaporated during the process, which suggests that the process could be feasible for the manufacturing of pure ceramic parts.

Compressive and flexural mechanical responses of components obtained through mSLA vat photopolymerization technology

In recent years, Additive Manufacturing (AM) has become an increasingly popular method in industrial applications for fabricating components with complex geometries, offering several benefits over traditional (subtractive) manufacturing methods. Among all available AM technologies, “vat photopolymerization” is still a reliable approach for manufacturing high-resolution components at relatively small costs. This particular AM technology is based on the photopolymerization process where 3D objects are created by light-induced solidification and it has been broadly developed and used in the past decades. Depending on the employed light source there are three different subtypes of this technology, namely: SLA, DLP, and mSLA. Among all three listed, the Masked Stereolithography Apparatus (mSLA) technology has emerged as a promising approach due to the much simpler AM machine construction compared to the other two. However, the mechanical properties of mSLA components have not been studied extensively, hence there is a lack of knowledge of how AM process parameters and post-processing treatments affect the final mechanical properties of mSLA components. This work presents an experimental investigation of the compressive and flexural mechanical responses of components produced through this relatively new AM technology. A series of static and cyclic tests were conducted with varying layer thickness and post-curing times. It is demonstrated that a thorough optimization of the mentioned variables is required to obtain parts with the desired mechanical properties.

Progress and challenges of the ECH transmission line design for DTT

The design of the Transmission Line (TL) as a part of the Electron Cyclotron Heating (ECH) system for Divertor Tokamak Test facility (DTT) is approaching the conceptual design maturity. With an ECH system of 16 MW installed for the first phase and with a total of 32 gyrotrons (170 GHz, ≥ 1 MW, 100 s) the TL design is undertaking the challenge of an evacuated Multi-Beam TL (MBTL) concept to deliver the large number of beam lines from the gyrotron hall to the torus hall buildings. The system is organized in 4 clusters, each of them including 8 beamlines. The routing consists of single-beam TL section used to connect the gyrotron output to a beam-combiner mirror unit for each cluster, a common MBTL running in a suspended corridor reaching the Tokamak building and a beam-splitter mirror unit to connect to the ex-vessel optics and launchers sections located in the equatorial and upper ports of one sector, for a total of 4 DTT sectors. The TL mirrors will be actively water cooled to cope with the heat load in long pulses due to the high power incident radiation, with the possibility to include advanced concepts for the cooling design compatible with additive manufacturing technology. The characteristics of the system and its components are presented, showing both the progress of the adopted solutions and the current design. Since the main challenge of this TL is to maintain the overall losses below 15%, in this paper we present the expected ohmic and spillover losses, including beam coupling simulations evaluating losses given by high order Transverse Electro-Magnetic modes (i.e. aberrations). We describe how the effects have been estimated with electromagnetic simulations and how losses could be mitigated, since TL efficiency could significantly drop due to the presence of non-idealities, like the deformations of mirrors surface ascribed to the microwaves heat loads and possible misalignments and aberrations effects occurring along the line.

A study on effects of curing and machining conditions in post-processing of SLA additive manufactured polymer

Stereolithography (SLA) is a promising additive manufacturing technology in terms of versatility and functionality. However, SLA-printed products lack mechanical properties and accuracy, so post-processing is essential. This study comprehensively contributes to a deeper understanding of influences of two types of post-processing [ultraviolet (UV) treatment and machining] and interactions between them. The effect of UV treatment was first investigated by evaluating properties of SLA specimens before and after UV curing. The UV curing greatly increased hardness by rearranging the molecular chains. The higher curing temperature, the denser and more uniform network was created; the surface hardness of the specimen cured at 80 °C increased by 208.30 % compared to the uncured specimen. Then, the interactions were analyzed by machining SLA specimens cured under different conditions. The pre-curing increased the hardness, molecular bonding, and brittleness. Thus, small surface roughness on the machined surface and small exit edge chipping were observed under the non-pre-curing conditions; the pre-curing increased the exit edge chipping size up to 48.21 %.

Developing Rib Bone Surrogates for High Dynamic Impact Assessment with Additive Manufacturing and Post-mortem Human Subjects (PMHS)-Based Evaluation

The conception of ballistic personal protective equipment requires a comprehensive understanding of the human body’s response to dynamic loads. The objective of this study is to develop rib bone surrogates enhancing new anthropomorphic test devices for personal protective equipment evaluation at high dynamic impacts. These are fabricated with additive manufacturing and compared to post-mortem human subjects (PMHS) data from literature. The 5th rib of the finite element Global Human Body Model Consortium (GHBMC) male 50th percentile (M50) model was extracted and transferred to a CAD model. This CAD model was divided into 30 sections with specific cortical bone thicknesses in all directions (caudal, cranial, cutaneous and pleural) from an equivalent rib of an M50 PMHS. Three different additive manufacturing technologies (direct metal laser melting, fused filament fabrication and multi jet modeling) were used to reproduce the M50 PMHS 5th rib surrogate. A total of 57 specimens were dynamically (500 mm/s) loaded to failure in a bending scenario imitating a frontal thoracic impact. Force, displacement, stiffness, and energy at failure were determined. Also, the strain distribution using 3D digital image correlation was recorded and compared to PMHS data from literature. The rib surrogates show deviations from the PMHS characteristic values. Nevertheless, there are also common characteristics in key variables to certain age groups of the PMHS data, which will facilitate the further development and improvement of adequate surrogates for a more realistic representation of the human body’s response to high dynamic loads.

Industry 4.0 and Sustainability: a Study on the Applicability of Additive Manufacturing as a Tool for Minimizing Environmental Impacts on Production Processes

Objective: The present research sought to analyze the applicability of additive manufacturing as a tool for minimizing environmental damage in production processes.
  
 Methodology: The research was conducted through an integrative literature review. Academic platforms such as SciELO and Google Academic were consulted, using specific keywords related to the theme. Inclusion criteria were established to select complete articles, in Portuguese and Brazilian languages, directly associated with the research theme, published between 2020 and 2024.
  
 Results and data analysis: The revised studies emphasize the growing importance of additive manufacturing (AM) and 3D printing technology in transforming production processes towards more sustainable and efficient practices. MA's ability to produce complex parts accurately and personalized, significantly reducing raw material waste through layer-by-layer manufacturing, stands out as a crucial tool to minimize environmental impacts on production. In addition, the integration of MA in the early stages of product development promotes efficiency in production, although more in-depth studies on its environmental and energy impacts are needed.
  
 Conclusion: It is therefore concluded that additive manufacturing is an essential tool for more sustainable and innovative practices in the industry, promoting the conservation of natural resources, the reduction of waste and the creation of adaptable and customized solutions. It is therefore up to companies and society to exploit and develop these technologies in search of a more sustainable and competitive future.

Gradient matters via filament diameter-adjustable 3D printing

Gradient matters with hierarchical structures endow the natural world with excellent integrity and diversity. Currently, direct ink writing 3D printing is attracting tremendous interest, and has been used to explore the fabrication of 1D and 2D hierarchical structures by adjusting the diameter, spacing, and angle between filaments. However, it is difficult to generate complex 3D gradient matters owing to the inherent limitations of existing methods in terms of available gradient dimension, gradient resolution, and shape fidelity. Here, we report a filament diameter-adjustable 3D printing strategy that enables conventional extrusion 3D printers to produce 1D, 2D, and 3D gradient matters with tunable heterogeneous structures by continuously varying the volume of deposited ink on the printing trajectory. In detail, we develop diameter-programmable filaments by customizing the printing velocity and height. To achieve high shape fidelity, we specially add supporting layers at needed locations. Finally, we showcase multi-disciplinary applications of our strategy in creating horizontal, radial, and axial gradient structures, letter-embedded structures, metastructures, tissue-mimicking scaffolds, flexible electronics, and time-driven devices. By showing the potential of this strategy, we anticipate that it could be easily extended to a variety of filament-based additive manufacturing technologies and facilitate the development of functionally graded structures.