Additive Manufacturing

Fused Deposition Modeling (FDM) is a type of Additive Manufacturing (AM) technology that is becoming increasingly common in numerous applications thanks to its versatility and reduced material waste. However, the complex physical phenomena occurring during extrusion, including the dynamics of non-Newtonian fluids, viscoelastic behaviors and rheology, make the use of heuristic observations preferable to that of analytical approaches. Consequently, engineers have focused on optimizing materials and hardware rather than control algorithms. The limited knowledge about extrusion and deposition dynamics usually confines the control action to the motion of the printing head while keeping a constant flow rate. Existing attempts to synchronize motion and extrusion consists of open loop compensations, which, however, require identified transfer functions or need to be tuned manually. This article aims to compactly review FDM technologies from a control perspective by presenting (i) the models of extrusion and deposition and (ii) the control strategies currently adopted in industry. Full article

In the aerospace field, lightweight design is a never-ending pursuit. By integrating structural bionics and structural optimization, the vertical bracket of a wide angle auroral imager is designed and manufactured by additive manufacturing technology in this work. Initially, the classical topology optimization is utilized for the vertical bracket to find the optimal material layout and primary load carrying paths. Drawing on the width-to-diameter ratio and the bone mineral density distribution of human femur, the vertical support is designed as a bionic structure with a solid middle section and thin wall in other parts. Afterwards, size optimization is maintained for the bionic design model to obtain the optimal model. The simulation results show that the three-way eigenfrequencies of bionic optimized structure are 320 Hz, 303 Hz, and 765 Hz, respectively, which are closely approximate to the original structure. However, the mass of bionic optimized structure is reduced by 23%. Benefiting from Selective laser melting, the complex optimized design can be rapidly manufactured. The three-way eigenfrequencies of the optimized structure measured by the 0.2 g sweep tests are 307 Hz, 292 Hz, and 736 Hz, respectively. The vibration test of bionic optimized structure verifies the accuracy of the simulation results. This study indicates that the combination of structural bionics and structural optimization provides a powerful tool kit to the design of similar support structure for space applications. Full article

Despite the many benefits of additive manufacturing, the final quality of the fabricated parts remains a barrier to the wide adoption of this technique in industry. Predicting the quality of parts using advanced machine learning techniques may improve the repeatability of results and make additive manufacturing accessible to different fields. This study aims to integrate data extracted from various sources and use them to obtain accurate predictions of relative density with respect to the governing process parameters. Process parameters such as laser power, scan speed, hatch distance, and layer thickness are used to predict the relative density of 316L stainless steel specimens fabricated by selective laser melting. An extensive dataset is created by systematically combining experimental results from prior studies with the results of the current work. Analysis of the collected dataset shows that the laser power and scan speed significantly impact the relative density. This study compares ridge regression, kernel ridge regression, and support vector regression using the data collected for SS316L. Computational results indicate that kernel ridge regression performs better than both ridge regression and support vector regression based on the coefficient of determination and mean square error. Full article

Laser powder bed fusion (L-PBF)-processed 17-4 PH stainless steel (SS) generally exhibits a non-equilibrium microstructure consisting mostly of columnar δ-ferrite grains and a substantial fraction of retained austenite and martensite, contrary to 17-4 PH SS wrought with a fully martensite structure and coarse grains. Despite the different microstructures of L-PBF and wrought 17-4 PH SS, post-processing is typically performed using the conventional heat treatment method. The insufficient effect of the heat treatment on the L-PBF product produces a δ-ferrite phase in the microstructure. To obtain improved mechanical properties, the addition of a normalizing treatment to the conventional heat treatment after L-PBF in a nitrogen gas environment was investigated. The fully martensitic matrix developed by adding the normalizing treatment contained homogeneous Cu precipitates and exhibited a similar or improved strength and elongation to failure compared to the wrought SS. Full article

The study described in this contribution contains a fundamental strategy to select geometries for dry joint profiles in 3D-printed concrete constructions. A database, here called the ‘joint catalogue’, contains a variety of joint types adapted from timber, steel, and bionic connections. Weighting factors and different criteria evaluate and score the various joint profiles (e.g., manufacturability, duration of manufacturing, and mechanical behaviour). Therefore, an algorithm sums up the scores leading to the preselection of better suitable profiles. The preselected joint profiles were afterwards analysed by the finite element method, determining the load capacity of the joint in a unit specimen. According to the joint catalogue, a smooth, triangular, truncated cone and arc joint profile appeared to be the optimal combination for dry joints in additive manufacturing of construction (AMC). Full article

The semiconductor industry uses a physical vapor-deposition process, with a nickel-tantalum (NiTa) alloy-sputtering target, to apply an amorphous NiTa thin film layer between the magnetic soft underlayer and substrate of a heat-assisted magnetic-recording hard disk drive. Currently, the alloy-sputtering target is produced through a hot-pressing (HP) process followed by a hot isostatic pressing (HIP). In this study, we demonstrate a better process for producing the sputtering targets, using laser powder-bed fusion (L-PBF) followed by vacuum heat treatment (VHT), to produce alloy targets with superior microstructural characteristics that will produce better-quality thin films. We compare as-fabricated (just L-PBF) specimens with specimens produced by L-PBF and then annealed at different conditions. Where the as-fabricated specimens are characterized by columnar dendrites, annealing at 1275 °C for 4 h produces a uniform equiaxed grain microstructure and a uniformly dispersed fcc Ta precipitate. In addition, the average microhardness value is reduced from 725 ± 40 to 594 ± 26 HV0.2 and the maximum compressive residual stress is reduced from 180 ± 50 MPa to 20 ± 10 MPa as the result of dislocation elimination during the recovery and recrystallization process. Finally, due to microstructure recrystallization, the VHT-treated L-PBF NiTa specimens exhibit a smaller grain size (2.1 ± 0.2 µm) than the traditional HIP-treated HP specimens (6.0 ± 0.6 µm). Full article

The Directed Energy Deposition process is used in a wide range of applications including the repair, coating or modification of existing structures and the additive manufacturing of individual parts. As the process is frequently applied in the aerospace industry, the requirements for quality assurance are extremely high. Therefore, more and more sensor systems are being implemented for process monitoring. To evaluate the generated data, suitable methods must be developed. A solution, in this context, was the application of artificial neural networks (ANNs). This article demonstrates how measurement data can be used as input data for ANNs. The measurement data were generated using a pyrometer, an emission spectrometer, a camera (Charge-Coupled Device) and a laser scanner. First, a concept for the extraction of relevant features from dynamic measurement data series was presented. The developed method was then applied to generate a data set for the quality prediction of various geometries, including weld beads, coatings and cubes. The results were compared to ANNs trained with process parameters such as laser power, scan speed and powder mass flow. It was shown that the use of measurement data provides additional value. Neural networks trained with measurement data achieve significantly higher prediction accuracy, especially for more complex geometries. Full article

Laser Powder Bed Fusion (LPBF) is one of the most promising additive manufacturing (AM) technologies using metal powders. It has been increasingly applied in variety of industrial and engineering fields, including but not limited to aviation, aerospace, nuclear energy, automobiles, medical, molding, shipping, and so on. In this work, the influence of laser process parameters on the microstructure, textural features, and their resulting effect on the macroscopic mechanical properties of LPBF-manufactured K418 samples was investigated experimentally. OM, SEM, and X-ray diffraction were used to characterize the microstructure evolution, and EBSD was used to identify the crystal texture of the as-built K418 samples. The effect relationship between process, microstructure, and properties was investigated using mechanical property testing. Furthermore, the volumetric energy density VED was considered as a comprehensive evaluation index to reflect the effects of the main laser process parameters on the microstructure and mechanical behavior of LPBF-manufactured K418 samples, including scanning speed v, laser power P, layer thickness t, and hatch space H. The results show that as the volumetric energy density VED increases, the microstructure morphology of the LPBF-manufactured K418 sample evolves: clustered columnar grains → coarsened columnar grains → ultrafine columnar grains, and the mechanical properties of the LPBF-manufactured K418 sample improve, owing to the ultrafine elongated columnar grains and a strong {001} <100> cubic texture. Full article

Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geometrical and dimensional precision for polymeric materials. In recent years, a lot of studies have shown that the creation of ceramic resins, through a particular combination of monomeric components and ceramic powders, allows to obtain complex shape geometries thanks to the photopolymerization process. This review highlights the characteristics and properties of ceramic resins, peculiarities of the ceramic stereolithography processes, up to the relationship between the composition of the ceramic resin and the complexity of the post-processing phases. The comparison of different studies allows outlining the most common steps for the production of ceramic resins, as well as the physical and chemical compatibility of the different compounds that must be studied for the good feasibility of the process. Full article

Large structural parts manufactured by Extrusion Additive Manufacturing (EAM) are limited by strong anisotropy due to insufficient bond formation and reduced molecular entanglement along the layer interface. To understand the correlation between process and material parameters and to enable digital modeling of EAM, the effect of different substrate temperatures and layer heights on tensile strength was investigated. A simple testing methodology for pelletized carbon fiber-filled polyamide 6 was developed. Tensile tests were performed in a full factorial Design of Experiments (DoE) to determine the tensile properties. For bulk simulation, the nominal strength and modulus were also determined based on contact width obtained by optical microscopy. The results demonstrated high anisotropy, with the maximum transverse tensile strength reaching only 27% of the corresponding longitudinal results and the transverse tensile modulus reaching only 20% of its longitudinal value. The effects of varying layer height were less significant than varying substrate temperature. The results support the hypothesis that sufficient transverse tensile strength is achieved between the extrapolated crystallization onset and melt temperature. The methodology of this study can be used as a benchmark method to qualify new thermoplastic polymers for EAM processes and to determine optimal process parameters for improved fusion bonding. Full article

Layer times in large-scale Extrusion Additive Manufacturing (EAM) of carbon fiber-reinforced thermoplastics are often outside the recommended process window. Brief layer times of tall parts with short path lengths lead to high temperatures and thus to melting of the component. In contrast, the substrate temperature decreases too far at longer layer times to achieve sufficient fusion bonding through molecular diffusion across the interface. Heating by infrared emitters and cooling by compressed air were experimentally tested and evaluated as methods for temperature control. Assuming that bond formation is mainly temperature-controlled, mechanical properties were expected to be similar to those of non-manipulated samples at the same temperatures. Samples of short carbon fiber-filled polyamide 6 in pellet form were manufactured in three test series. Infrared heating resulted in comparable tensile properties to samples at the target temperature and in a significant increase compared to the base temperature without heating. Cooling proved to be more effective when closer to the deposition nozzle, with tensile results even exceeding the expected values at temperatures below 170 °C. Overall, the results support the potential for targeted temperature control in EAM and the hypothesis that comparable bond strength can be achieved in dependence of the final substrate temperature. Full article

A new method of controlling the residual stress in laser directed energy deposition additive manufacturing (DED AM) products proposed based on constraints used in manufacturing and the substrate design. The simulation results of the residual stress, which were validated with the experimental measured data, showed that weaker constraints on the substrate could greatly decrease the residual stress in the laser DED AM products. In addition, by designing local reduced thickness regions into the substrate, such as long strip holes or support legs, the residual stress in DED AM products could be further decreased. In this study, when long strip holes were designed in the substrate, the tensile residual stress was decreased by 28%. An even smaller amount of residual stress was achieved when the design structure was changed to support legs. The tensile residual stress decreased by more than 30%. The fewer support legs, the smaller the residual stress. The residual stress in DED AM products could be well-controlled by design, while the stiffness can be weakened with fewer constraints. Full article

Metallic additive manufacturing processes have been significantly developed since their inception with modern systems capable of manufacturing components for structural applications. However, successful processing through these methods requires extensive experimentation before optimised parameters can be found. In laser-based processes, such as direct energy deposition, it is common for single track beads to be deposited and subjected to analysis, yielding information on how the input parameters influence characteristics such as the output’s adhesion to the substrate. These characteristics are often determined using specialised software, from images obtained by cross-section cutting the line beads. The proposed approach was based on a Python algorithm, using the scikit-image library and optical microscopy imaging from produced 18Ni300 Maraging steel on H13 tool steel, and it computes the relevant properties of DED-produced line beads, such as the track height, width, penetration, wettability angles, cross-section areas above and below the substrate and dilution proportion. 18Ni300 Maraging steel depositions were optimised with a laser power of 1550 $\mathrm{W}$, feeding rate of 12 $\mathrm{g}$${\min }^{-1}$, scanning speed of 12 $\mathrm{mm} {\mathrm{s}}^{-1}$, shielding gas flow rate of 25 $\mathrm{L}$${\min }^{-1}$ and carrier gas flow rate of 4 $\mathrm{L}$${\min }^{-1}$ for a laser spot diameter of $2.1\mathrm{mm}$. Out of the cross-sectioned beads, their respective height, width and penetration were calculated with $2.71\%$, $4.01\%$ and $9.35\%$ errors; the dilution proportion was computed with $14.15\%$ error, the area above the substrate with $5.27\%$ error and the area below the substrate with $17.93\%$ error. The average computational time for the processing of one image was $12.7$$\mathrm{s}$. The developed approach was purely segmentational and could potentially benefit from machine-learning implementations. Full article

Metal additive manufacturing (AM) by Laser-Directed Energy Deposition (L-DED) usually results in the formation of textured columnar grains along the build direction, leading to anisotropic mechanical properties. This can negatively affect the intended application of the product. Anisotropy can be eliminated by modifying the material through an additional exposure to ultrasound (US-assisted) during the L-DED process. In this paper, a multi-track sample was manufactured from AISI H13 (TLS Technik, Bitterfeld-Wolfen, Germany) tool steel by a US-assisted (28 kHz) L-DED process using a specially designed cooling system. The study also included post-process annealing and quenching with the tempering heat treatment of the modified steel, resulting in the retention of the properties, as confirmed by hardness measurements. XRD analysis was used to measure the structural parameters of the unit cell, and the hardness properties were measured in two directions: longitudinally and parallel to the deposition direction. It was found that US-assisted L-DED allows us to obtain a more isotropic structure with an equal size of the coherent scattering region in two printing directions, and to reduce the residual stresses in the material. The anisotropy of the hardness was significantly reduced, with 636 and 640 HV found between the XY and XZ planes. Based on the obtained hardness data, it should be noted that some of the heat treatments studied herein can also result in a decrease in the anisotropy of the properties, similarly to the US-assisted effect. Full article

Wire and arc additive manufacturing (WAAM) employing a magnesium (Mg) alloy is superior in terms of safety, energy efficiency, and deposition rate when compared with a process that utilizes lasers and powder materials. However, problems with WAAM employing an Mg alloy include poor dimensional accuracy due to low viscosity of the molten Mg alloy. In addition, since Mg alloys cause a combustion reaction with water, an effective cooling method, such as direct water cooling, cannot be applied. In this study, a solid contact-based active cooling method employing copper blocks with high thermal conductivity was proposed to improve the dimensional accuracy and cooling efficiency of fabricated objects using AZ31. Moreover, the proposed method renders it possible to fabricate a wall structure with high flatness as the molten AZ31 solidifies upon direct contact with the flat surface of copper blocks. In addition, the copper blocks harboring an internal water circulation system achieved a higher cooling efficiency and shortened the interval cooling time between the deposition of subsequent layers. Meanwhile, it was discovered that the arc deflected toward the copper blocks, not onto the substrate or the previous layer when the wire tip approached too close to the blocks. Full article

Additively manufactured particle dampers can significantly improve component damping. However, if designed incorrectly, the damping can be worsened. For the design of additively manufactured particle dampers, there are not yet sufficient design rules and models to describe the effect due to numerous design parameters. The research question answered in this paper describes how the effect of particle damping can be characterised as a function of excitation force and excitation frequency for different cavity sizes. To characterise the effect of particle damping, a 3³ full factorial test plan is constructed, and the damping is determined experimentally. It is shown that the damping can be reliably evaluated with the circle-fit method. The effect of particle damping is investigated for beams made of AlSi10Mg, 1.2709 and Ti6Al4V. As a result, a positive effect of the particle damping in a frequency range from 500 to 30,000 Hz and partly up to the 9th bending mode can be proven. It is shown that, for the first bending mode, there is an optimum at approx. 2000 Hz. For the optimum, the increase of the damping for the tool steel 1.2709 to 28 and for the aluminium alloy AlSi10Mg to 18 can be proven. Full article

The advent of Additive Manufacturing (AM) is uncovering the limits of the current CAD systems and, at the same time, is highlighting the potentials of the Topology Optimization (TO) and Generative Design (GD) tools that had not been fully exploited until now. Differently from the traditional design approach in which designers occupy a predominant role in each stage of the design process, the introduction of such tools in the product development process pushes toward simulation-driven design approaches which imply a significant change in the role of the designer. To this end, the paper presents a comparison of two different design methods for Additive Manufacturing based on the adoption of TO and GD tools. The comparison aims to offer a reflection on the evolution of the traditional approach when TO and GD tools are used, and to highlight the potential and limitations of these optimization tools when adopted in an integrated manner with the CAD systems. Furthermore, this comparative study can be a useful and practical source for designers to identify the most appropriate approach to adopt based on their needs and project resources. The comparative study is carried out through the design study of a prototype of a rocker arm and a brake pedal for the Formula Student race car. Their results, compared in terms of mechanical performances, show that both TO and especially GD tools can be efficiently adopted early in a design process oriented to AM to redesign components to make them lighter and stronger. Full article

Lack of reinforcements is an existing drawback of 3D printed cementitious components, which is an urgent concern. A staple-inserting apparatus was developed and installed on a 3D printer and automatically fabricated 3D printed and staple-reinforced components with 98% successful insertion to achieve inner- and inter-reinforcement of the printed strips. The inserted staples inside the printed strips improved the compressive strength by 25% maximum owing to the inner locking effect by the staple pins, while the flexural strength did not increase because the scattered staples functioned separately. The staples over the strip interfaces remarkably increased the flexural stress by 46–120%. The inserted staples demonstrated a significant strip locking effect, but the unavoidable voids decreased the bonding between staples and the composite. The mechanical analysis concluded that the printing parameters considerably affected the reinforcing rate. The staple inserting technique proved the feasibility of automatic fabrication of fiber-reinforced and printed concrete structures. Full article

This paper aims to investigate the utilization of octet truss lattice structures in gas turbine blades to achieve weight reduction and improvement in vibration characteristics, which are desired for turbine blades to improve the efficiency and load capacity of turbines. A solid blade model using NACA 23012 airfoil was designed as reference. Three lattice-based blades were designed and manufactured via additive manufacturing by replacing the internal volume of solid blades with octet truss unit cells of variable strut thickness. Experimental and numerical vibration analyses were performed on the blades to establish their suitability for potential use in turbine blades. A maximum weight reduction of 24.91% was achieved. The natural frequencies of lattice blades were higher than those of solid blades. A stress reduction up to 38.6% and deformation reduction of up to 21.5% compared with solid blades were also observed. Both experimental and numerical results showed good agreement with a maximum difference of 3.94% in natural frequencies. Therefore, apart from being lightweight, octet-truss-lattice-based blades have excellent vibration characteristics and low stress levels, thereby making these blades ideal for enhancing the efficiency and durability of gas turbines. Full article

This paper aims to develop a reliable and effective model to investigate the behavior of micron-sized biological glue droplets impacting micron-sized bioceramic powder beds applied to the 3D printing process. It also endeavours to explore the common rules of droplet impact affected by particle size and the wettability of powder, which are supposed to provide process parameters guidance for the application of new materials in 3D printing. Firstly, based on the low impulse impact model, the simplified model was proposed. Then, the observation and simulation experiments of millimeter-scale droplet impacting were carried out under the same conditions to prove the effectiveness of the model. Furthermore, the characterization of a parametric experiment of a 3D printing practice was used to verify the significance and effectiveness of the simulation study method. Lastly, the method was performed to investigate the effect of wettability and particle size of the micron powder on the micron droplet impact. The results showed that the binder powder’s wettability and particle size could directly influence the droplet spreading behavior. The characterization results of samples printed in the simulation-predicted parameter showed that the amount of binder used could be reduced by 38.8~50.1%, while the green strength only lost 17.9~20%. The significance of this simulation method for prediction of 3D printing process parameters was verified. Full article

To make powder bed fusion (PBF) via laser beam (-LB) for metals (/M) available for highly regulated components such as pressure equipment according to the Pressure Equipment Directive, system-specific qualification methods need to be established to deal with process- and geometry-dependent inhomogeneous material behavior. Therefore, the material properties of austenitic stainless steel (316L) and their influences on normative acceptable qualification strategies were investigated in this study. Flat tensile test specimens were produced by two manufacturing systems identical in construction and were compared to specimens produced from conventionally rolled sheet material. Specimens were compared in the horizontal and vertical building directions in relation to different slope angles, wall thicknesses and cross-sectional areas. Despite identical process setups, parameters and powder feedstock, differences in mechanical behavior could be seen. Furthermore, the mechanical properties, surface roughness and density showed dependencies on the wall thickness and slope angle. In particular, the influence of wall thickness has not been covered in publications about PBF-LB/M before. These results suggest that geometry- and system-dependent components can be designed based on associated data from qualification processes. Therefore, a new qualification method based on wall structure properties is suggested for standard qualification processes of components with wall structures, such as pressure equipment. Full article

Tungsten (W) as a structural component has grown roots in many special applications owing to its radiation-shielding capabilities and its properties at elevated temperatures. The high ductile-brittle transition temperature (DBTT) and the very high melting point of tungsten however have limited its processability to certain technologies such as powder metallurgy. Laser powder bed fusion (LPBF) has been introduced in recent years as an alternative for manufacturing tungsten parts to overcome the design limitations posed by powder metallurgy technology. A review of the literature shows significant improvements in the quality of tungsten components produced by LPBF, implying a strong potential for manufacturing tungsten with this technology and a need for further research on this subject. This review paper presents the current state-of-the-art in LPBF of unalloyed tungsten, with a focus on the effect of process parameters on the developed structure/properties and identifies current knowledge gaps. Full article

Inconel 718 is a precipitation strengthened, nickel-based super alloy of interest for the Additive Manufacturing (AM) of low volume, complex parts to reduce production time and cost compared to conventional subtractive processes. The AM process involves repeated rapid melting, solidification and reheating, which exposes the material to non-equilibrium conditions that affect elemental segregation and the subsequent formation of solidification phases, either beneficial or detrimental. These variations are difficult to characterize due to the small length scale within the micron sized melt pool. To understand how the non-equilibrium conditions affect the initial solidification phases and their critical temperatures, a multi-length scale, multi modal approach has been taken to evaluate various methods for identifying the initial phases formed in the as-built Inconel 718 produced by laser-powder bed fusion (L-PBF) additive manufacturing (AM). Using a range of characterization tools from the bulk differential thermal analysis (DTA) and x-ray diffraction (XRD) to spatially resolved images using a variety of electron microscopy tools, a better understanding is obtained of how these minor phases can be properly identified regarding the amount and size, morphology and distribution. Using the most promising characterization techniques for investigation of the as-built specimens, those techniques were used to evaluate the specimens after various heat treatments. During the sequence of heat treatments, the initial as-built dendritic structures recrystallized into well-defined grains whose size was dependent on the temperature. Although the resulting strength was similar in all heat treated specimens, the elongation increased as the grain size was refined due to differences in the precipitated phase distribution and morphology. Full article

The main additive manufacturing (AM) methods to produce metal components are laser powder bed fusion and directed energy deposition, which are energy-intensive, time-consuming, and require high investment costs. An economical alternative is based on a new feedstock comprising a homogenous mixture of sinterable metal powders and a multi-component binder system. This feedstock enables the creation of metal components printed using the material extrusion (ME) technique. In this study, mechanical characterization of AISI 316L samples is conducted to identify the mechanical properties of parts printed using the metal ME process. The test results indicate an average maximum tensile stress of 426.6 ± 23.7 MPa and an elongation at break of 36%. Both the tensile and compressive yield stresses are approximately 150 MPa, demonstrating a symmetric response to the two opposite types of uniaxial loads. Rockwell B and Vickers hardness tests confirm the uniform behavior of the tested material. An X-ray diffraction analysis is conducted to assess the crystallographic structure of the ME 316L samples compared to that of the monolithic material. According to our study results, metal ME seems to be a promising technology to produce non-critical metallic parts that require good mechanical properties, good corrosion resistance, and complex shapes such as chemical tanks, heat exchangers, and medical instruments. Full article

Hot stamping uses boron (B) steel to simultaneously form parts at high temperatures while cooling the parts in a mold, which is advantageous because of the ability to freeze the forms. However, compared to conventional cold forming, this technique requires additional facilities that include heating devices and additional time for cooling after forming at high temperatures. Additionally, because of the high strengths of hot stamping parts, shear process operations after molding tend to be difficult to perform as a continuous operation via press processing; thus, most operations depend on separate laser processing, which results in lower productivity and increased manufacturing costs. This limitation continues to be the most significant problem with this technology, therefore, restricting its commercialization because of increased mold manufacturing costs and durability problems. This study investigated a low-cost, high-functionality shear mold manufacturing method for 1.5 GPa grade hot-stamped components using heterogeneous metal additive manufacturing. After the concentrated stress in steel during the shearing processes was analyzed using a multi-physical analysis, metal additive manufacturing was used to fabricate the shear mold. Its life was evaluated through trial molding and compared with that for conventional technology. Finally, the commercialization potential of the newly developed method was assessed. Full article

Direct-Powder Bed Selective Laser Processing (D-PBSLP) is considered a promising technique for the Additive Manufacturing (AM) of Silicon Carbide (SiC). For the successful D-PBSLP of SiC, it is necessary to understand the effects of process parameters. The process parameters are the laser power, scanning speed, hatching distance, and scanning strategies. This study investigates the effect of scanning strategies on the D-PBSLP of SiC and ensures that other process parameters are appropriately selected to achieve this. A numerical model was developed to obtain the proper process parameters for the investigation of scanning strategies in this work. Different scanning strategies available in the commercial Phoenix 3D printer manufactured by 3D Systems, such as concentric in–out, linear, inclined zigzag, and hexagonal, have been investigated. It was concluded that the zigzag strategy is the best scanning strategy, as it was seen that SiC samples could be printed at a high relative density of above 80% without a characteristic pattern on the layer’s top surface. SiC samples were successfully printed using different laser powers and scanning speeds obtained from the numerical model and zigzag strategy. Additionally, complex geometry in the form of triple periodic minimum surface (gyroid) was also successfully printed. Full article

In this study, we aimed to prepare and characterise hydrogel formulations using cellulose nanocrystals (CNCs), alginate (Alg), and polyethylene glycol diacrylate (PEGDA). The CNC/Alg/PEGDA formulations were formed using a double network crosslinking approach. Firstly, CNC was extracted from oil palm trunk, and the size and morphology of the CNCs were characterised using TEM analysis. Secondly, different formulations were prepared using CNCs, Alg, and PEGDA. The mixtures were crosslinked with Ca²⁺ ions and manually extruded using a syringe before being subjected to UV irradiation at 365 nm. The shear-thinning properties of the formulations were tested prior to any crosslinking, while the determination of storage and loss modulus was conducted post extrusion after the Ca²⁺ ion crosslink using a rheometer. For the analysis of swelling behaviour, the constructs treated with UV were immersed in PBS solution (pH 7.4) for 48 h. The morphology of the UV crosslinked construct was analysed using SEM imaging. The extracted CNC exhibited rod-like structures with an average diameter and length of around 7 ± 2.4 and 113 ± 20.7 nm, respectively. Almost all CNC/Alg/PEGDA formulations (pre-gel formulation) displayed shear-thinning behaviour with the power-law index η < 1, and the behaviour was more prominent in the 1% [w/v] Alg formulations. The CNC/Alg/PEGDA with 2.5% and 4% [w/v] Alg displayed a storage modulus dominance over loss modulus (G′ > G″) which suggests good shape fidelity. After the hydrogel constructs were subjected to UV treatment at 365 nm, only the F8 construct [4% CNC: 4% Alg: 40% PEGDA] demonstrated tough and flexible characteristics that possibly mimic the native articular cartilage property due to a similar water content percentage (79.5%). In addition, the small swelling ratio of 4.877 might contribute to a minimal change of the 3D construct’s geometry. The hydrogel revealed a rough and wavy surface, and the pore size ranged from 3 to 20 µm. Overall, the presence of CNCs in the double network hydrogel demonstrated importance and showed positive effects towards the fabrication of a potentially ideal 3D bioprinted scaffold. Full article

Powder Bed Selective Laser Processing (PBSLP) is a promising technique for the additive manufacturing of alumina. For the method’s success, PBSLP process parameters such as laser power, scanning speed, hatching distance, and scanning strategies need to be investigated. This paper focuses on studying the scanning strategies’ effects on the PBSLP of alumina numerically and experimentally. Scanning strategies such as linear with different orientation, concentric, and islands were investigated. A numerical model was developed in which the PBSLP parameters, scanning strategy effects, and interpreting the experimental results could be observed. The numerical model proved its ability to reach the proper process parameters instead of using experimental trails which are time and cost consuming. For relative density, the island strategy succeeded to print alumina samples with a high relative density reaching 87.8%. However, there are round passages formed inside the samples that remain a barrier for the island strategy to be effectively used in PBSLP of alumina. Both linear and concentric strategies achieved a relative density of 75% and 67%, respectively. Considering the top surface roughness, samples printed with linear strategies gave low top surface roughness compared to the island and concentric strategies. Linear-45° is considered the effective strategy among the studied strategies as it achieved good relative density and low roughness at top and side surfaces. For PBSLP of alumina, new scanning strategies should be considered, and this study presents a new scanning strategy that is mainly based on space filling mathematical curves and should be studied in future work. Full article

Constrained-surface-based stereolithography has recently attracted much attention from both academic and industrial communities. Despite numerous experimental, numerical and theoretical efforts, the fundamental need to reduce the separation force between the newly cured part and constrained surface has not yet been completely solved. In this paper, we develop a fluid dynamics approach, proposed in our previous work, to theoretically model the separation force in 3D printing of a cylindrical part for flat and patterned windows. We demonstrate the possibility of separation force reduction with an accelerated movement of the printing platform. In particular, we investigate behaviors of transient parameter, its reduction rate, and separation force reduction with respect to elevation speed and time. The proposed approach involves deceleration and acceleration stages and allows to achieve the force reduction for the entire printing process. Finally, we provide implicit analytical solutions for time moments when switching between the stages can be done without noticeable increase of separation force and explicit expression for separation force in case of patterned window. Full article

Due to their unique advantages over traditional manufacturing processes, metal additive manufacturing (AM) technologies have received a great deal of attention over the last few years. Using current powder-bed fusion AM technologies, metal components are very expensive to manufacture, and machines are complex to build and maintain. Wire arc additive manufacturing (WAAM) is a new method of producing metallic components with high efficiency at an affordable cost, which combines welding and 3D printing. In this work, gas tungsten arc welding (GTAW) is incorporated into a gantry system to create a new metal additive manufacturing platform. Design and build of a simple, affordable, and effective WAAM system is explained and the most frequently seen problems are discussed with their suggested solutions. Effect of process parameters on the quality of two additively manufactured alloys including plain carbon steel and Inconel 718 were studied. System design and troubleshooting for the wire arc AM system is presented and discussed. Full article

Laser powder bed fusion exhibits many advantages for manufacturing complex geometries from hard to machine alloys such as IN625. However, a major drawback is the formation of high tensile residual stresses, and the complex relationship between the process parameters and the residual stresses has not been fully investigated. The current study presents multi-scale models to examine the variation of process parameters on melt pool dimensions, cyclic temperature evolutions, cooling rate, and cyclic stress generation and how they affect the stress end state. In addition, the effect of the same energy density, which is often overlooked, on the generated residual stresses is investigated. Multi-level validation is performed based on melt pool dimensions, temperature measurements with a two-color pyrometer, and finally, in-depth residual stress measurement. The results show that scan speed has the strongest effect on residual stresses, followed by laser power and hatch spacing. The results are explained in light of the non-linear temperature evolution, temperature gradient, and cooling rate during laser exposure, cooling time, and the rate during recoating time. Full article

This paper is focused on the hybridization of additive manufacturing with single-point incremental forming to produce stiffening grooves in thin metal parts. An analytical model built upon in-plane stretching of a membrane is provided to determine the tool force as a function of the required groove depth and to estimate the maximum allowable groove depth that can be formed without tearing. The results for additively deposited stainless-steel sheets show that the proposed analytical model can replicate incremental plastic deformation of the stiffening grooves in good agreement with experimental observations and measurements. Anisotropy and lower formability caused by the dendritic-based microstructure of the additively deposited stainless-steel sheets justifies the reason why the maximum allowable depth of the stiffening grooves is approximately 27% smaller than that obtained for the wrought commercial sheets of the same material that are used for comparison purposes. Full article

Residual stresses are one of the primary causes for the failure of parts or systems in metal additive manufacturing (AM), since they easily induce crack propagation and structural distortion. Although the formation of residual stresses has been extensively studied, the core factors steering their development in AM have not been completely uncovered. To date, several strategies based on reducing the thermal gradients have been developed to mitigate the manifestation of residual stresses in AM; however, how to choose the optimal processing plan is still unclear for AM designers. In this regard, the concept of the yield temperature, related to the thermal deformation and the mechanical constraint, plays a crucial role for controlling the residual stresses, but it has not been duly investigated, and the corresponding approach to control stresses is also yet lacking. To undertake such study, a three-bar model is firstly used to illustrate the formation mechanism of the residual stress and its key causes. Next, an experimentally calibrated thermomechanical finite element model is used to analyze the sensitivity of the residual stresses to the scan pattern, preheating, energy density, and the part geometry and size, as well as the substrate constraints. Based on the numerical results obtained from this analysis, recommendations on how to minimize the residual stresses during the AM process are provided. Full article

Additive manufacturing (AM) is gaining significant importance, as demand for customized products is increasing nowadays. AM is one of the disruptive technologies of Industry 4.0, which can reduce waste generation, enabling sustainability. The adoption of sustainable practices in the manufacturing sector is due to the need of the current scenario to minimize harmful emissions and for human wellbeing. In this regard, AM technologies are integrated with sustainable manufacturing concepts to contribute toward sustainable AM (SAM), with various benefits from the design, manufacturing, use, and EoL perspectives. Still, many sustainability issues are associated with AM processes, namely limited speed and the uncertain performance of fabricated parts. From this viewpoint, it is essential to analyze the challenges associated with adopting SAM practices. This article presents identification and analysis of the potential challenges associated with adopting SAM practices. Fifteen SAM challenges have been identified from the literature survey and analyzed using the “Gray Technique for Order of Preference by Similarity to Ideal Solution” (G-TOPSIS) approach. The priority order of the challenges has been identified. The study identified that “training towards SAM benefits” and “limited materials recycling potential” were the significant challenges in adopting SAM practices in the manufacturing sector. The present study will help industry practitioners, decision makers, and researchers effectively analyze the challenges associated with SAM for its effective implementation. Researchers can utilize the findings of the study for establishing the guidelines for the adoption of SAM. Full article

One of the main issues hindering the adoption of parts produced using laser powder bed fusion (L-PBF) in safety-critical applications is the inconsistencies in quality levels. Furthermore, the complicated nature of the L-PBF process makes optimizing process parameters to reduce these defects experimentally challenging and computationally expensive. To address this issue, sensor-based monitoring of the L-PBF process has gained increasing attention in recent years. Moreover, integrating machine learning (ML) techniques to analyze the collected sensor data has significantly improved the defect detection process aiming to apply online control. This article provides a comprehensive review of the latest applications of ML for in situ monitoring and control of the L-PBF process. First, the main L-PBF process signatures are described, and the suitable sensor and specifications that can monitor each signature are reviewed. Next, the most common ML learning approaches and algorithms employed in L-PBFs are summarized. Then, an extensive comparison of the different ML algorithms used for defect detection in the L-PBF process is presented. The article then describes the ultimate goal of applying ML algorithms for in situ sensors, which is closing the loop and taking online corrective actions. Finally, some current challenges and ideas for future work are also described to provide a perspective on the future directions for research dealing with using ML applications for defect detection and control for the L-PBF processes. Full article

Laser powder bed fusion (LPBF) has indisputable advantages when designing new components with complex geometries due to toolless manufacturing and the ability to manufacture components with undercuts. However, fatigue properties rely heavily on the surface condition. In this work, in-process surface parameters (three differing contour parameter sets) and post-process surface treatments, namely turning and shot peening, are varied to investigate the influence of each treatment on the resulting fatigue properties of LPBF-manufactured specimens of the aluminium–magnesium–scandium alloy Scalmalloy^®. Therefore, metallographic analysis and surface roughness measurements, as well as residual stress measurements, computer tomography measurements, SEM-analyses, tensile and fatigue tests, along with fracture surface analysis, were performed. Despite the fact that newly developed in-process contour parameters are able to reduce the surface roughness significantly, only a minor improvement in fatigue properties could be observed: Crack initiation is caused by sharp, microscopic notches at the surface in combination with high tensile residual stresses at the surface, which are present on all in-process contour parameter specimens. Specimens using contour parameters with high line energy show keyhole pores localized in the subsurface area, which have no effect on crack initiation. Contours with low line energy have a slightly positive effect on fatigue strength because less pores can be found at the surface and subsurface area, which even more greatly promotes an early crack initiation. The post-process parameter sets, turning and shot peening, both improve fatigue behaviour significantly: Turned specimens show lowest surface roughness, while, for shot peened specimens, the tensile residual stresses of the surface radially shifted from the surface towards the centre of the specimens, which counteracts the crack initiation at the surface. Full article

PolyJet 3D printing can produce any color by mixing multiple materials. However, there are often large deviations between the measured color of printed samples and the target color (when the target color is used as the specified color in the printer software). Therefore, to achieve a target color on a printed sample, the specified color in the printer software should not be the same as the target color. This study applies response surface methodology (RSM) to determine the optimal color specification to compensate for color deviations of the measured color of printed samples from the target color in PolyJet 3D printing. The RSM has three steps. First, a set of experiments are designed for a target color according to central composite design. Second, the experimental data are used to develop a second-order multivariate multiple regression model to predict the deviation between the measured color and the target color. Third, the optimal color specification (often different from the target color) is determined by using the developed predictive model and the desirability function. When the optimal color specification is used as the specified color in the printer software, the deviation between the predicted color of the printed sample and the target color is minimized. The proposed method is applied to four target colors to demonstrate its effectiveness. The results show that the proposed method performs better than the conventional color specification method without compensation in achieving the four target colors by 33% on average. Full article

The wire laser additive manufacturing (WLAM) process is considered a direct-energy deposition method that aims at addressing the need to produce large components having relatively simple geometrics at an affordable cost. This additive manufacturing (AM) process uses wires as raw materials instead of powders and is capable of reaching a deposition rate of up to 3 kg/h, compared with only 0.1 kg/h with common powder bed fusion (PBF) processes. Despite the attractiveness of the WLAM process, there has been only limited research on this technique. In particular, the stress corrosion properties of components produced by this technology have not been the subject of much study. The current study aims at evaluating the effect of a slow strain rate on the stress corrosion resistance of 316L stainless steel produced by the WLAM process in comparison with its counterpart: AISI 316L alloy. Microstructure examination was carried out using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis, while the mechanical properties were evaluated using tensile strength and hardness measurements. The general corrosion resistance was examined by potentiodynamic polarization and impedance spectroscopy analysis, while the stress corrosion performance was assessed by slow strain rate testing (SSRT) in a 3.5% NaCl solution at ambient temperature. The attained results highlight the inferior mechanical properties, corrosion resistance and stress corrosion performance, especially at a slow strain rate, of the WLAM samples compared with the regular AISI 316L alloy. The differences between the WLAM alloy and AISI 316L alloy were mainly attributed to their dissimilarities in terms of phase compositions, structural morphology and inherent defects. Full article

A relatively static and unique bubble template is successfully realized on a microporous substrate by controlling the surface tensions of the electrodeposit solution, and a nickel layer containing macropores is prepared using this bubble template. When the surface tension of the solution is 50.2 mN/m, the desired bubble template can be formed, there are fewer bubbles attached to other areas on the substrate, and a good nickel layer is obtained. In the analysis of the macropore formation process, it is found that the size of the bell-mouthed macropores can be tailored by changing the solution stirring speed or the current density to adjust the growth rate of the bubble template. The size change of a macropore is measured by the profile angle of the longitudinal macropore, section. As the solution stirring speed increases from 160 to 480 r/min, the angle range of the bell-mouthed macropores cross-sectional profile is increased from 21.0° to 44.3°. In addition, the angle range of the bell-mouthed macropore cross-sectional profile is increased from 39.3° to 46.3° with the current density increasing from 1 to 2.5 A/dm². Different from the dynamic hydrogen bubble template, the bubble template implemented in this paper stays attached on the deposition and grows slowly, which is novel and interesting, and the nickel layer containing macropores prepared using this bubble template is applied in completely different fields. Full article

The clogging of piezoelectric nozzles is a typical problem in various additive binder jetting processes, such as the manufacturing of casting molds. This work aims at print head monitoring in these binder jetting processes. The structure-born noise of piezoelectric print modules is analyzed with an Artificial Neural Network to classify whether the nozzles are functional or clogged. The acoustic data are studied in the frequency domain and utilized as input for an Artificial Neural Network. We found that it is possible to successfully classify individual nozzles well enough to implement a print head monitoring, which automatically determines whether the print head needs maintenance. Full article

This paper examines the impact of oxide coatings on the surfaces of feedstock material used for Additive Friction Stir-Deposition (AFS-D). The AFS-D is a solid-state additive manufacturing process that uses severe plastic deformation and frictional heating to build bulk depositions from either metallic rod or powder feedstock. Since aluminum alloys naturally form an oxide layer, it is important to determine the influence of the feedstock surface oxide layer on the resultant as-deposited microstructure and mechanical properties. In this study, three AA6061 square-rod feedstock materials were used, each with a different thickness of aluminum oxide coating: non-anodized, 10-micron thick, and 68-micron thick. Macroscale depositions were produced with these feedstock rods using the AFS-D process. Optical and electron microscopy showed that the two oxide coatings applied through anodization were efficiently dispersed during the AFS-D process, with oxide particles distributed throughout the microstructure. These oxide particles had median sizes of 1.8 and 3 μm², respectively. The yield and tensile strengths of these materials were not measurably impacted by the thickness of the starting oxide coating. While all three feedstock material variations failed by ductile rupture, the elongation-to-failure did decrease from 68% to 55% in the longitudinal direction and from 60% to 43% in the build direction for the thickest initial oxide coating, 68 microns. Full article

Metal powders suitable for use in powder bed additive manufacturing processes should ideally be spherical, dense, chemically pure and of a specified particle size distribution. Ti6Al4V is commonly used in the aerospace, medical and automotive industries due to its high strength-to-weight ratio and excellent corrosion resistance properties. Interstitial impurities in titanium alloys have an impact upon mechanical properties, particularly oxygen, nitrogen, hydrogen and carbon. The plasma spheroidisation process can be used to spheroidise metal powder consisting of irregularly shaped particles. In this study, the plasma spheroidisation of metal powder was performed on Ti6Al4V powder consisting of irregularly shaped particles. The properties of the powder relevant for powder bed fusion that were determined included the particle size distribution, morphology, particle porosity and chemical composition. Conclusions were drawn regarding the viability of using this process to produce powder suitable for additive manufacturing. Full article

Wire and arc additive manufacturing has unique process characteristics, which make it have great potential in many fields, but the large amount of heat input brought by this feature limits its practical application. The influence of heat input on the performance of parts has been extensively studied, but the quantitative description of the influence of heat input on the surface quality of parts by wire and arc additive manufacturing has not received enough attention. According to different heat input, select the appropriate process parameters for wire and arc additive manufacturing, reversely shape the profile model, select the appropriate function model to establish the ideal profile model according to the principle of minimum error, and compare the two models to analyze the effect of heat input on the surface quality of the parts manufactured by wire and arc additive manufacturing. The results show that, when the heat input is high or low, the standard deviation value and the root mean square value reach 1.908 and 1.963, respectively. The actual profile is larger than the ideal profile. When the heat input is moderate, the standard deviation value and the root mean square value are only 1.634 and 1.713, respectively, and the actual contour is in good agreement with the ideal contour. Combined with the analysis of the transverse and longitudinal sections, it is shown that the heat input has a high degree of influence on the surface quality of the specimen manufactured by wire and arc additive manufacturing, and higher or lower heat input is disadvantageous to it. Full article

Cobalt superalloys such as Tribaloys are widely used in environments that involve high temperatures, corrosion, and wear degradation. Additive manufacturing (AM) processes have been investigated for fabricating Co-based alloys due to design flexibility and efficient materials usage. AM processes are suitable for reducing the manufacturing steps and subsequently reducing manufacturing costs by incorporating multi-materials. Laser directed energy deposition (laser DED) is a suitable AM process for fabricating Co-based alloys. T800 is one of the commercially available Tribaloys that is strengthened through Laves phases and of interest to diverse engineering fields. However, the high content of the Laves phase makes the alloy prone to brittle fracture. In this study, a Ni-20%Cr alloy was used to improve the fabricability of the T800 alloy via laser DED. Different mixture compositions (20%, 30%, 40% NiCr by weight) were investigated. The multi-material T800 + NiCr alloys were heat treated at two different temperatures. These alloy chemistries were characterized for their microstructural, phase, and mechanical properties in the as-fabricated and heat-treated conditions. SEM and XRD characterization indicated the stabilization of ductile phases and homogenization of the Laves phases after laser DED fabrication and heat treatment. In conclusion, the NiCr addition improved the fabricability and structural integrity of the T800 alloy. Full article

Multifunctional composites offer a higher strength to weight ratio, electrical properties, etc., thereby providing possible solutions for replacing the physical electrical wirings in aircraft. The lack of research on the coupled multifunctional characterization of 3D printed composites flexural-electrical properties is the main reason for its unsuitability in aerospace applications. The proposed method evaluates multifunctional flexural-electrical properties of 3D printed multifunctional carbon fiber composites. Traditional methods for conducting structural and electrical analyses for aircraft certification do not accommodate new technologies that are not yet proven. Such technologies are additive manufacturing (AM) techniques, multifunctional composite structures, and the certification requirements for 3D printed multifunctional carbon fiber composites for use in aircraft. In this study, the multifunctional 3D printed specimens were concurrently evaluated for flexural-electrical properties using three-point bending and electrical conductivity tests. The results showed that the multifunctional properties included the maximum flexural strength of 271 MPa and the maximum electrical resistance of 55.1 G Ohms, with the failure modes and mechanisms found to be consistent with the traditional composites. Due to its infancy, the existing AM techniques, and the use of the multifunctional carbon fiber composites manufactured using those AM technologies, are not implemented on a large commercial scale. Full article