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Smart structures of 4D printing are perhaps interdisciplinary research area with significant development and applicability future. The cornerstone of 4D printing is smart materials. When a stimulus is put in front of this structure, it changes into a different structure. This article initially provides a succinct insight of the aforementioned 4DP: SMs-SSs: 4D printing (4DP) technology imminent enlargements of smart material's (SMs) prospective to physique smart structure (SSs). Investigation into 4D printing has pulled in phenomenal enthusiasm. The research work of 4DP: SMs-SSs has stimulated promising future. The paper discusses smart materials and their potential towards mainstream 4D printing for smart constructions (4DP: SMs-SSs). Cursory research write-up on smart materials associated 4D printing approaches to process them based on adaptability to stimuli, fabrication, control mechanisms, multi physics modeling, and existing as well as emerging functionalities. Indeed, innovative structural initiatives could perhaps inspire new paradigms for stimulate positive structures. Novelty structures are being thoroughly researched, and new ideas will be incorporated. Programmability, reactivity toward and adaptability to their circumstances, and automation are all functionality of 4D-printed items. The article's conclusion is that 4DP: SMs that can create intelligent/smart structures (SSs) will even trigger a massive era of construction material. This article shows an insight into how quickly technology is changing, how some researchers and scholars are figuring out what it can do, and how engineers could use the ideas. The adoption of smart materials will assist in resolving the problem to a greater extent. 4D printing relies on shape memory alloys/polymers (SMAs/SMPs) as so forth organic materials. Imminent enlargements of smart materials prospective to physique smart structures are still being experimented with by scientists and engineers. [ABSTRACT FROM AUTHOR]

Uniform equal thickness layering is widely used in 3D printing, which cannot take into account the printing quality and printing efficiency. In this paper, a new adaptive layering algorithm based on multi-objective optimization is proposed for this problem. The algorithm comprehensively considers the surface features of the model, the slope and curvature of the contour, and establishes a multi-objective optimization model with print quality, print time, and feature constraints. And the Pareto optimal solution set of multi-objective optimization is solved by the improved non-dominated sorting genetic algorithm-II (NSGA-II), and the Pareto optimal solution that meets different printing requirements is selected by the Fuzzy-based weighted membership ranking method. Through comparative experiments, the method proposed in this paper reduces the volume error rate by 40.9% and the printing time by 33.3% compared with uniform layering, which can effectively improve the printing quality and printing efficiency. In addition, compared with the existing adaptive layering algorithms, it is also an algorithm with good comprehensive performance. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, the role of manufacturing parameters of fused deposition modeling (FDM) on the shape memory effect (SME) is investigated by design of experiments. PLA-TPU blend with a weight composition of 30:70% is processed by melt mixing and then extruded into 1.75 mm filaments for 3D printing via FDM. SEM images reveal that TPU droplets are distributed in the PLA matrix, and the immiscible matrix-droplet morphology is evident. Box-Behnken design (BBD), as an experimental design of the response surface method (RSM), is implemented to fit the model between variables and responses. The shell, infill density, and nozzle temperature are selected as variables, and their effects on loading stress, recovery stress, shape fixity, and shape recovery ratio are studied in detail. An analysis of variance (ANOVA) is applied to estimate the importance of each printing parameter on the output response and assess the fitness of the presented model. The ANOVA results reveal the high accuracy of the model and the importance of the parameters. Infill density and nozzle temperature had the greatest and least roles on shape memory properties, respectively. Also, the values of shape fixity and shape recovery were obtained in the ranges of 58–100% and 53–91%, respectively. Despite many researches on 4D printing of PLA, low ductility at room temperature and high stress relaxation rate are its weakness, which are covered by adding TPU in this research. Due to the lack of similar outcomes in the specialized literature, this paper is likely to fill the gap in the state-of-the-art problem and supply pertinent data that are instrumental for FDM 3D printing of functional shape memory polymers with less material consumption. [ABSTRACT FROM AUTHOR]

Compression mold tooling fabrication has been traditionally conducted via machining processes—for example, computerized numerical control machining, mill, or lathe operations. While subtractive manufacturing operations provide high-precision tooling, they have an extended lead time and generate material waste, which increases manufacturing costs. This paper analyzes direct metal laser sintering (DMLS) as a viable alternative to traditional compression mold manufacturing. DMLS is an additive manufacturing process that uses high-powered lasers to fuse metal powders in a layered approach to create high-precision metal components. Through layering materials, DMLS can produce complex geometries which can have features impossible to machine from traditional manufacturing methods. Additionally, DMLS uses less material for parts, reducing material costs and lead times. In this paper, DMLS manufactured mold was computationally studied against a traditional compression mold's thermal and pressure requirements. The DMLS mold was designed with a honeycomb structure to reduce material usage while maintaining structural integrity. Computational analysis showed that the production requirement, "maximum deflection of 0.001 inches," was achieved with the DMLS when pressures and temperatures were similar to those required for the tooling. In addition, DMLS-produced mold utilized 74% less material than a traditionally manufactured mold. [ABSTRACT FROM AUTHOR]

Determining the mechanical characteristics of additively manufactured materials has been an active topic of research in recent years. Many studies have been performed analyzing the impact of different 3D print parameters on the tensile properties of the printed material. However, compared to typical metals and polymers, there is no widely adopted standard for testing additively manufactured polymers. Consequently, the test results reported by the researchers in this field exhibit high amounts of variability between studies. A set of consistent experiments across five different printing parameters including build orientation, raster orientation, infill type, infill density, and layer thickness was carried out in the present paper. The results were analyzed to look at trends between the tested variables and the yield strength and elastic modulus of the resultant additively manufactured polyethylene terephthalate-glycol (PETG). Build orientation, raster orientation, infill type, and infill density all showed strong relationships with the tensile properties. Layer thickness showed little variation across the typical range for a given extrusion width. Previously developed experimental models were also checked and showed that even small variations in other parameters such as raster gap or extrusion factor could create significant enough variation to make the model inaccurate for a specific scenario. [ABSTRACT FROM AUTHOR]

This paper consists in a review of environmental issues of additive manufacturing technologies, mainly in those related to fused deposition modelling. The versatility, reduction of equipment costs due to patents expiring and the great flexibility offered by 3D printers have driven the amazing increase of these technologies in the last years. On the other hand, the democratization of additive manufacturing also poses some issues regarding environment; it is important to also have into account the potential effects of these technologies in the environment, coming from energy consumption, materials, and wastes produced. A review of different research works dealing with environmental impact of additive manufacturing, such as products' life cycle assessment, energy and materials consumption, and particles and gases releases (mainly due to health issues), has been performed. The assessment performed has helped highlighting the importance of environmental issues in additive manufacturing, according to the number of published papers. The main findings are the importance of establishing a method for applying eco-design principles taking into account the specific features of additive manufacturing. [ABSTRACT FROM AUTHOR]

3D printing is an emerging technology that revolutionizes the traditional construction industry. Although it has gained wide attention, implementing the state of the art of 3D printing in construction has remained limited. Since the technology has been developing very fast and many innovations have been made public by nonacademic sources, excluding them would inevitably result in an incomplete picture. Therefore, in this review, we aimed to fill this gap by including all the construction 3D printing projects and studies performed from nonacademic sources as well as academic articles. Apart from evaluating the current progress, we also examined the readiness of 3D printing applications in construction, both from technical and nontechnical aspects. As reflected by various printing products and applications, this technology can offer much for the construction industry. However, the current printing technology cannot yet produce products for the construction sector due to limited printing materials, methods, and systems. Many projects have been performed by self-developed printing setups, which are technically similar. In addition, the impacts of the technology have never been quantified. Researchers and practitioners dive into technological developments without knowing whether they would bring benefits to the construction industry. Whether following this new trend and reinventing 3D printing setups a waste of resources remains a question. For its applications in construction, more government support and official national and international building codes can be expected. [ABSTRACT FROM AUTHOR]

A prediction-based multi-objective optimization (PBMO) method is proposed in this paper to forecast and reduce 3D printing (3DP) resources on demand, including time, energy, and material. In the authors' previous research work, a hybrid code-based and data-driven modeling (HCDM) scheme was proposed to customize the predictive models based on process parameters, material deposition paths, and machine behaviors. This study further utilizes the models as multi-objectives to be minimized, aiming at the appropriate solution of process parameters that consume the least resources. Non-dominated sorting genetic algorithm II (NSGA-II), one of the commonly used metaheuristic algorithms, is adopted to construct the PBMO framework, where the HCDM process is embedded in the fitness evaluation step. The corresponding computing program is compiled and then validated on two material extrusion (MEX) machines. Based on the optimization results, hypervolume, as a Lebesgue measure, is used to evaluate the superiorities of all near-optimal solutions, thereby recommending the best-performing solutions for real 3DP. Apart from the 3DP process, the proposed optimization method is adaptable to other mainstream computer numerical control (CNC) manufacturing processes and will guide process design to promote resource conservation for cleaner production. [ABSTRACT FROM AUTHOR]

Recently, because of the complex international situation and combat environment in the future, the development and application of new concept weapons have raised higher performance requirements for manufacturing technologies. However, at present, most weapons are still prepared using traditional charging methods (cast curing, pressure casting, and melt casting), which require subtractive manufacturing (SM) treatments before use. At present, the demand for weapon products is shifting towards reactive micro structures, high preparation efficiency, miniaturization, and controllable energy release. Besides, the modern "energetic-on-a-chip" trend was expected to reduce size and cost while increasing safety and maintaining performance. In this case, the traditional charging methods were not preferred due to their inherent drawbacks, such as being limited to the model, requiring long solvent drying times and recycling required and pores/cracks caused by the shrinkage of slurry, and so on. Therefore, it is necessary to innovate the processing and manufacturing technology of weapons and address the boundaries of existing charging methods, and this will enable the precise customization of high-quality energetic materials and avoid many defects. Additive manufacturing (AM), or 3D printing technology, has been booming recently. The application of additive manufacturing technology in the field of energetic materials (EMs) can promote the innovation of manufacturing technology for EMs and regulate the microstructure. Additionally, 3D printing technology can break through the existing design and development mode, expand explosive charging technology, and enable the distribution of different types of explosives and explosive density in a specific space area. Besides, 3D printing can fabricate "reactive microstructures" (RMS), which offer a deeper understanding of the EMs' combustion and detonation phenomena at the micro- and nanoscale. Thus, the explosive/propellant grains with multiple damage modes can be designed and manufactured. This paper aims to summarize the current progress in the 3D printing of EMs, analyze the corresponding mechanisms, and provide guidance for future research. [ABSTRACT FROM AUTHOR]

As a promising technology capable of transforming the conventional manufacturing techniques, the use of additive manufacturing (AM) has span beyond the prototyping it was initially known for, and its use is currently revolutionising the future of the manufacturing and research world. A review of some of the advances made in the additive manufacturing of polymers and their composites is presented in this paper. Some of the advantages and disadvantages of the different AM techniques used in polymer composites (PC) fabrications are presented, and the different areas of applications of the AM fabricated PC are highlighted. Also highlighted are some of the potentials and challenges associated with the fabrication of components using 4D printing. Finally, the paper presents the prospects and the endless opportunities that abound with the AM of polymeric materials. [ABSTRACT FROM AUTHOR]

3D printing, specifically fused deposition modeling (FDM) of poly-ether-ether-ketone (PEEK), is one of the most powerful and efficient state-of-the-art manufacturing techniques. However, FDM of PEEK is challenging. Indeed, it is critical to consider specific 3D printing parameters and filament feedstock quality to achieve optimum mechanical properties in the 3D-printed PEEK parts. In this paper, we investigate the effect of specific 3D printing parameters such as nozzle and chamber temperature, print speed, and layer height on the mechanical properties of 3D-printed PEEK. Moreover, we explore the effect of filament quality on the structures' mechanical properties. In that regard, we developed PEEK filaments using a customized extruder setup in-house and used those laboratory-developed filaments (LD) to 3D print PEEK structures suitable for mechanical testing (tensile, compression, and flexural testing) and compared them to the mechanical properties of 3D-printed parts that were developed using commercially available (CA) filaments. Results indicate that an optimum combination of a nozzle and chamber temperature, print speed, and layer height is appropriate to achieve 3D-printed parts with optimum mechanical properties. Notably, results confirmed no significant differences between the specimen groups developed using LD and CA filaments, highlighting that the LD filaments were of comparable quality to the CA ones. The highest mean strengths recorded for the parts printed with the LD filaments were 106.45 MPa (compressive), 85.43 MPa (tensile), and 102.63 MPa (flexural). This paper confirms that high-quality PEEK-based filaments can be developed in-house to yield 3D-printed PEEK parts with optimum mechanical properties. [ABSTRACT FROM AUTHOR]

3D printing is a constantly expanding technology that represents one of the most exciting and disruptive production possibilities available today. This technology has gained global recognition and garnered considerable attention in recent years. However, technological breakthroughs, particularly in the field of material science, continue to be the focus of research, particularly in terms of future advancements. The 3D printing techniques are employed for the manufacturing of advanced multifunctional polymer composites due to their mass customization, freedom of design, capability to print complex 3D structures, and rapid prototyping. The advantages of 3D printing with multipurpose materials enable solutions in challenging locations such as outer space and extreme weather conditions where human involvement is not possible. Each year, numerous research papers are published on the subject of imbuing composites with various capabilities such as magnetic, sensing, thermal, embedded circuitry, self-healing, and conductive qualities by the use of innovative materials and printing technologies. This review article discusses the various 3D printing techniques used in the manufacture of polymer composites, the various types of reinforced polymer composites (fibers, nanomaterials, and particles reinforcements), the characterization of 3D printed parts, and their applications in a various industries. Additionally, this review discussed the limitations of 3D printing processes, which may assist future researchers in increasing the utility of their works and overcoming the shortcomings of previous works. Additionally, this paper discusses processing difficulties, anisotropic behavior, stimuli-responsive characteristics (shape memory and self-healing materials), CAD constraints, layer-by-layer appearance, and void formation in printed composites. Eventually, the promise of maturing technology is discussed, along with recommendations for research activities that are desperately required to realize the immense potential of operational 3D printing. [ABSTRACT FROM AUTHOR]

Heat staking is a joining technology by which thermoplastic pins are formed by force and temperature to create a form- and force-fitting connection between components. This paper examines the characteristics of 3D printed pins in comparison to conventionally turned pins for heat staking applications. The 3D printed pins are created using fused layer modeling, with variations in horizontal and vertical building directions, as well as different layer thicknesses. The study investigates the impact of significant factors on the heat staking process, including the forming force and temperature. Tensile tests, micrographs, and micro-CT measurements were conducted to determine the properties of the heat-staked joints. Additionally, a stage plan was developed to enhance the understanding of the forming process of both printed and conventionally turned materials. The findings suggest that, under specific process parameters, 3D printed pins exhibit comparable strength to conventionally manufactured pins. The research also demonstrates that the anisotropy resulting from the layer-by-layer construction of the pins significantly influences the strength of the connection. Furthermore, the study reveals that 3D printed pins exhibit good forming accuracy during the heat staking process, and the cavities formed during printing can be substantially reduced. [ABSTRACT FROM AUTHOR]

This paper explores the possibility of applying reverse engineering to flexible coupling spare parts through additive manufacturing. Although couplings' simplicity makes them go unnoticed, they connect elements that transmit power between two shafts, thus being an essential component for most of the machinery currently used in the industry. In this study, flexible couplings with different infill density (60% and 80%) were 3D printed by the fused filament fabrication technique. The original and the additive manufactured couplings were modelled to compare their compressive response and energy-absorbing characteristics, and experimental tests were performed to validate finite element analysis. To derive an optimal material distribution within coupling structure, a generative design approach was conducted through nTopology software. With this novel simulation-driven design, it is possible to reduce the weight of the redesigned part up to 15.8% by defining the wall thickness of the internal structure based on the results of finite element simulation, while maintaining its functionality. Moreover, an economic-environmental study was carried out. Results ensure that the 3D printed prototypes are suitable for replacing the original one under its current operating conditions. Additionally, the economic study shows that the redesigned couplings allow companies to save more than €2700 per coupling in relation to CO2 emission payments. [ABSTRACT FROM AUTHOR]

The paper is devoted to studying two different ways of obtaining the complex-shaped bell-type samples from the titanium alloy Ti-6Al-4V. It is shown that the process of obtaining the samples on a three-axis table is sensitive to the wire feed geometry as depended on four such geometry zones. These zones are characterized by the angles between the wire feed direction and the tangent to the printing path. On the contrary, samples obtained on a rotary four-axis table are not sensitive to the wire feed geometry. Each of the two ways provides formation of its own specific types of the structure and different mechanical characteristics. In this paper, the structure of geometry affected zones is determined and the most optimal way for obtaining the samples is selected. [ABSTRACT FROM AUTHOR]

This paper proposes a 3D nesting algorithm which combines the flower pollination algorithm (FPA) with the oriented bounding box (OBB) collision detection to solve the 3D packing of irregular shaped objects for powder-based additive manufacturing. In the powder-based 3D printing process, stacking multiple models most compactly in the build volume is an important task because no support structure is needed. Given a fixed printing area, the post-nesting build height directly impacts the printing cost and efficiency. To reduce the printing cost, 3D models must be packed as closely as possible and the build height must be minimized. This has been found to be a combinatorial optimization and an NP-hard problem. We propose to use the most recent and effective meta-heuristic optimization algorithm FPA, combined with the collision detection of printed objects set up as the optimization constraint using the OBB tree, to find the near-optimal 3D nesting solution. In FPA optimization, a significant amount of time is spent on collision detection. This paper uses the safety clearance distance to adaptively reduce the OBB tree subdivision, hence significantly reducing the computation of collision detection. As a result, the proposed method finds the model positions and rotations of the global solution, and generates the near-optimal solution in reasonable time. Finally, our method is compared with state-of-the-art commercial softwares. The results show that the proposed method produces lower build height with better efficiency. For real-world complex engine parts (30 different STL models and a total of 192,018 triangles), the computation time is only 160 s, and the build height is 12.4% and 13% better than the results from Netfabb and Magics, respectively. [ABSTRACT FROM AUTHOR]

High-resolution 3D printing technologies can print thin films; however, they are not commonly available because of their high initial cost, and the majority of them employ a pneumatic-driven printing technique that hinders retraction, which is crucial for printing complex geometries. The main objective of this paper is to modify an extrusion-based 3D printing technology and investigate its potential for thin-film printing for electronic device applications like perovskite solar cells (PSCs). The modification is done by replacing the filament extrusion system with a liquid extrusion system using a syringe pump. CAD software, CATIA V5R20, is used to model the parts of the syringe pump, which are then 3D printed from polylactic acid (PLA) filaments. To validate the functionality of the modified 3D printer for thin-film printing, a physical experiment is conducted to print a poly 3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) solution, a widely used conductive polymer, by varying the 3D printing parameters, namely; print speed, bed temperature, nozzle diameter, and x-distance offset. Based on the experiment, a thin PEDOT:PSS film was successfully printed with a thickness of 142 nm and a notable level of surface uniformity when compared to the spin coating. Further, the modified 3D printer is utilized to print a PEDOT:PSS and a perovskite methylammonium leadtriiodide-chloride (CH3NH3PbI3 − xClx) solution in a layer-by-layer fashion sequentially and tested for validity for perovskite solar cell (PSC) application by printing other layers of PSC on top of the perovskite layer using the spin coating method. Based on the test conducted, a competitive open-circuit voltage of 740 mV was successfully generated from the printed PSC. Finally, it has been observed that extrusion-based 3D printing technology can be modified and optimized to print thin films for PSC applications. This has tremendous advantages for rapidly printing and testing electronic devices in general, and PSCs in particular. [ABSTRACT FROM AUTHOR]

Due to easy access, faster production, and on-demand printing, the applications of 3D printing are proliferating and reaching the mass customization level where individuals can print their self-design products. Many service providers emerge and supply 3D printers to allow mass customization within their specific service areas. Along with the technological advancement, these distributed 3D printers can be integrated and shared via a cloud-based platform for the manufacture of customized products in a dynamic and cost-effective environment. However, the 3D printing service allocation is a key challenge for the platform, especially when customers have specific time requirements for production. This paper investigates a 3D printing service allocation problem with optimization-based and real-time allocation strategies. The workflow of 3D printing service allocation is first analyzed in a cloud-based platform. Subsequently, a binary integer linear programming model is developed to allocate the 3D printing services to tasks given global demand information. A real-time allocation model is then developed on a first-come-first-serve basis to match 3D printing services with tasks. The objective is to maximize the net revenue of the platform. Numerical studies are conducted to compare the performance of two proposed models. The results show that the optimization model can increase the profit by approximately 100% on average, which implies the optimization-based strategy is superior to the real-time strategy in a metropolitan city; and because of the penalty mechanism, the acceptance rate can be increased by 5%. The results also show that the operators can find the optimal ratio of supply and demand to maximize the net revenue of the platform through historical data. [ABSTRACT FROM AUTHOR]

Cellular infill structures such as honeycomb have been widely used in the field of light weighting. In recent years, the emergence of additive manufacturing technologies has provided a new solution to fabricate complicated cellular infill structures. This paper presents a continuous printing path planning method for gradient honeycomb structures. Given a 2D filling region represented by a polygon, a honeycomb graph that covers the filling area is trimmed to generate an infill pattern. Then an algorithm is proposed to transform the honeycomb filling pattern into an Eulerian graph, which can be traversed by a single-stroke printing path. For each honeycomb, double-spiral paths are used to generate gradient honeycomb structures with varying wall thicknesses. Later, the 2D honeycomb infills are generalized to 3D cases that are suitable for multi-axis printing. First, three mutually orthogonal vector fields that are embedded on the tetrahedral mesh of the printed part are generated by considering the support-free condition. Then the three vector fields are used to calculate three monotonically increasing scalar distance fields, which span a non-Euclidean space. Finally, the 2D honeycomb infills are generated in the non-Euclidean space with parallel sliced layers, which are then mapped back to the Euclidean space to obtain the real self-supporting 3D honeycomb infills. The proposed 2D/3D honeycomb infill structures generation algorithms have been verified by both simulation and experimental tests. [ABSTRACT FROM AUTHOR]

The delta robot can reach higher speeds than traditional serial-axis machines used in fused filament fabrication 3D printing. However, like serial machines, delta printers suffer from undesirable vibration at high speeds which degrades the quality of fabricated parts. This undesirable vibration has been suppressed in serial printers using linear model-inversion feedforward control methods like the filtered B-splines (FBS) approach. However, techniques like the FBS approach are computationally challenging to implement on delta 3D printers because of their coupled, position-dependent dynamics. In this paper, we propose a methodology to address the computational bottlenecks by (1) parameterizing the position-dependent portions of the dynamics offline to enable efficient computation of the model online, (2) computing models at sampled points (instead of every point) along the given trajectory, and (3) employing QR factorization to reduce the number of floating-point arithmetic operations associated with matrix inversion. In simulations, we report a computation time reduction of up to 23× using the proposed method when compared to using the computationally expensive exact LPV model—all while maintaining high tracking accuracy. Accordingly, we demonstrate significant quality improvements on parts printed at various positions on a commercial delta 3D printer using our proposed controller compared to a baseline alternative, which uses an LTI model from one position. Acceleration measurements during printing show that the improvement in print quality of the proposed controller is due to vibration reductions of up to 39% when compared to the baseline controller. [ABSTRACT FROM AUTHOR]

Material extrusion (MEX), frequently known as fused filament fabrication (FFF), is a material extrusion 3D printing process for fabricating cost-effectively functional polymeric parts. Even if the MEX process fabricates fully dense or lightweight specimens with a relatively complex geometry in a reduced time and cost, it presents some drawbacks in shape accuracy, surface roughness, and anisotropic mechanical response. Herewith, the interaction between material design, 3D printing, and laser post-processing is investigated for efficient printable nanocomposite materials. Polylactic acid (PLA)/carbon black (CB) nanocomposites were prepared with a thermomechanical process and characterized for their mechanical and electrical properties. Then, they were processed with a low-cost CO2 laser, to assess their behavior in the process. Critical geometrical characteristics were measured, and results were analyzed with statistical modeling, to optimize the process and evaluate the effect of the laser cutting parameters on the quality of the samples. This paper points out new data on low-cost CO2 laser cutting of MEX thin plates fabricated using PLA/CB nanocomposite filament and an affordable material extrusion MEX 3D printing process. The data produced are helpful for the improvement of the shape accuracy and surface roughness of parts and components used in nanocomposite-based innovative assemblies and systems. [ABSTRACT FROM AUTHOR]

Many studies have shown that the mechanical properties and geometric accuracy of additive manufacturing parts are dependent of many factors such as laser energy density, build orientation, and heat transfer histories. Amongst the factors, heat transfer histories are highly dependent on the geometry of a part, resulting in influencing the mechanical properties and microstructure evolution due to the repeated heating and cooling process. Heat transfer histories are associated with material thermal properties which include thermal conductivity, thermal diffusivity, specific heat capacity, and temperature gradient. The objective of this paper is to understand and observe the microstructure evolution process and microhardness based on variation in geometrical characteristic of the laser-based powder bed fusion (L-PBF). This paper presents the effect of the geometric factors on the mechanical properties and geometric accuracy during the L-PBF process, which benefit future process optimisation and modelling. In this study, samples with varying wall thickness are fabricated in TI6AL4Vand AlSi10Mg alloys by L-PBF. The samples are systematically evaluated by the optical microscope and the Vickers hardness tester. Microstructural characterisation of these samples is further evaluated via scanning electron microscopy. The results show that there is a signification relationship between material thermal properties, microstructure evolution, and mechanical properties with respect to the variation in wall thickness. These results can be used to understand the material thermal behaviour in lattice structures with a thin or small-sized feature and serve as a design guideline to indirectly control the microstructure of a L-PBF part. [ABSTRACT FROM AUTHOR]

Multi-material fused deposition 3D printing has the unique ability to maintain complex shapes and add special properties. However, the narrow selection of consumable materials, low printing efficiency, and poor performance of the finished products limit the application scope of this technology. In this paper, we propose a twin-screw extrusion 3D printing system that can print a variety of powdered or granular materials, including environmentally friendly biomass particles, metal particles, and thermoplastics, and that enables the mixing of heterogeneous materials. Then we investigate the heat transfer and rheological properties of the system's material extrusion process. Through the coupled thermal-fluid-solid multi-physical field simulation of the nozzle system, we qualitatively and quantitatively study the transport law and thermal flow field distribution characteristics of the material within the extrusion system, analyze the transport and melting mechanism of the hot melt in the runner during the extrusion process, and obtain the mechanism of the influence of the structural design parameters and the 3D printing process parameters on the transient flow field characteristics and mixing performance. When the screw's outer diameter is 20 mm and the speed range is 5–25 r/min, the nozzle extrusion flow rate is 2.45–20.15 mm3/s, and the printing efficiency is 3–4 times that of traditional wire printing. The flow field characteristic parameters are optimal when the screw lead is 24–36 mm, and the material extrusion effect is best when the rotational speed is 8–15 r/min. The heat flow field distribution in the extrusion system is stable, the speed distribution is reasonable, and the temperature field distribution is uniform. There is no solution reflux or overflow at the nozzle, the nozzle is not blocked, and the material can be extruded at constant temperature and pressure. The strength of the twin-screw is within the allowable range, the mixing performance is good, and the material can be transported forward with positive displacement. The maximum thermal deformation of the nozzle is 0.09861 mm, which is much smaller than the maximum deformation precision of 0.2 mm, indicating that the screw and nozzle are reasonably designed. The simulation proves the reasonableness of the calculation results. [ABSTRACT FROM AUTHOR]

A widespread problem of manufacturing processes is represented by the occurrence of tool wear that can lead to both poor surface finish and poor mechanical properties in the workpiece. This issue affects also additive manufacturing technologies such as the material extrusion technique. In this process, the wear mechanisms of the extrusion nozzle can be severe, in particular when materials with a high abrasive capacity, such as carbon fiber-reinforced polymers, are 3D printed. Despite the significance of this problem, scientific literature lacks systematic evaluations of nozzle wear and its correlation with parts mechanical properties. In this framework, the present paper aims at investigating the effect of the nozzle wear evolution on the mechanical properties of additively manufactured parts in short carbon fiber-reinforced polyamide. To this purpose, 3D printing processes were performed. The time dependence of the nozzle wear was analyzed by interrupting the additive manufacturing process at fixed time intervals. To analyze the effect of nozzle wear on the mechanical performances of printed parts, tensile specimens were 3D printed and tested at room temperature. A reduction in mechanical performances of the printed samples and a worsening in the surface quality were observed with increasing the nozzle wear. Optical microscopy investigation and X-ray computed tomography were used to monitor the external and internal nozzle wear evolution. The surface roughness measurements were performed to evaluate the surface quality of the 3D printed parts. Furthermore, the scanning electron microscopy was used to observe the three-dimensional topography of the longitudinal sections of filament in Carbon PA, at different printing time values, and fractured surfaces of tensile samples. This study can help to better understand nozzle wear and to predict tool service life for industrial applications. In addition, it can prompt future studies focused on the reduction of tool wear. [ABSTRACT FROM AUTHOR]

3D printed polymer composite materials offer a cost-effective and rapid tooling option for prototyping, and low-cost, low-volume sheet metal forming applications. Due to the high anisotropy in mechanical properties of 3D printed composites, accurate characterization and finite element modeling of the material become paramount for successful design and application of these forming tools. This paper presents experimental characterization of 3D printed fiber–reinforced polymer composite material at various strain rates. A homogenized material model with orthotropic elasticity and the Hill 1948 anisotropic yield criterion were then calibrated based on these experimental data. Finite element simulations of the stamping of high-strength steel sheets using composite tooling were performed, and tool deformation was predicted and compared with experimental measurements. FE simulation results were in good agreement with stamping experiments performed with polymer tooling. It was found that the anisotropy and strain rate sensitivity of 3D printed polymer composites play a significant role in their performance as tooling materials. [ABSTRACT FROM AUTHOR]

Polycaprolactone (PCL)-based scaffolds have great potential in various tissue engineering applications because of their biodegradability, high mechanical strength, and easy fabrication using different 3D printing methods. However, previous research has only focused on developing and examining each PCL-based scaffold printing method's merits and limitations separately. Thus, the lack of a systematic comparison of the various methods to recommend the most appropriate one for each application remains. This paper provides an overview of different PCL-based scaffold printing methods. Four typical 3D printing methods for fabricating PCL-based scaffolds and five important evaluation criteria including quality, usage, productivity, cost, and flexibility are identified. The integrated fuzzy-analytical hierarchy process (i-FAHP) and sensitivity analysis are proposed as multi-criteria decision-making methods for selecting the most appropriate scaffold printing method (SPM) under constrained construction and material types. Customized software based on a flexible fuzzy-AHP expert system is built to support decision-makers in determining the optimal SPM quickly and effectively. The result shows that the melt-based extrusion method is optimal for different scaffold types. This study's findings will be useful for developing biomaterial and multi-head 3D bioprinters for customized and commercial tissue engineering applications. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is an important, rapidly emerging, manufacturing technology that takes the information from a computer-aided design (CAD) and builds parts in a layer-by-layer style. Thus, since the development of 3D printing, the fused deposition modeling (FDM) is one of the most promising and inexpensive techniques for shaping free-form parts. It used a thermoplastic filament as a starting material to extrude, layer by layer, the suitable 3D object. It is assisted by a large community of developers, searchers, and users and with multiple free hardware and software open sources expanding the scope of its applications. However, in this process, printing objects with multi-materials and multicolors becomes a major challenge for most extrusion system of printing platforms. For example, in case it is required to print multi-material and multicolored parts, a high-quality head extruder should be used. The main objective of this work is to show the importance of proposing a new extruder system of printing parts with multicolors and materials. For this purpose, in the present paper, the different extrusion systems capable of printing parts with multicolors and materials were presented. The operating principle of each extrusion system is well explained through functional diagrams. Then, its advantages and disadvantages are cited. Finally, some prospects for improving these systems are presented and that will be the work of the next paper. [ABSTRACT FROM AUTHOR]

The selection of printing parameters for 3D printing can dramatically affect the dynamic performance of components such as polymer spur gears. In this paper, the performance of 3D printed gears has been optimised using a machine learning process. A genetic algorithm (GA)–based artificial neural network (ANN) multi-parameter regression model was created. There were four print parameters considered in 3D printing process, i.e. printing temperature, printing speed, printing bed temperature and infill percentage. The parameter setting was generated by the Sobol sequence. Moreover, sensitivity analysis was carried out in this paper, and leave-one cross validation was applied to the genetic algorithm-based ANN which showed a relatively accurate performance in predictions and performance optimisation of 3D printed gears. Wear performance of 3D printed gears increased by 3 times after optimised parameter setting was applied during their manufacture. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) or 3D printing is a manufacturing technique where successive layers of material are layered to produce parts. The design freedom afforded by AM is ideal for the space industry, where part production is low volume and highly customized. The objective of this paper is to review research in the area of additive manufacturing for space (AMFS) in all areas, from propulsion to electronics to printing of habitats, and to identify the gaps and directions in the research. In this paper, we investigate the AMFS research by splitting it into two domains: space and ground-based. Space-based AMFS has been performed on the International Space Station using polymers, and we also discuss the future of in space AM, a subject closely related to more general in space manufacturing. The ground-based research is split into three categories based on the printing material: metal, polymer, and others. The last category includes regolith, cement, and ceramic. This paper explores AMFS by bringing together as much research information as possible using a combination of papers, presentations, and news articles. We expect that the paper will allow the reader to gain an understanding of the current status of AMFS research and will contribute to the field as a reference and research guidelines. [ABSTRACT FROM AUTHOR]

Since the advent of 3D printing in the mid-1980s, additive manufacturing has grown steadily and found numerous applications across all types of industries. More recently, the industry has seen a spur of growth as the terms of the original patents expired and new companies entered the market. While there exist several different methods of additive manufacturing, polymer-based material extrusion 3D printing (also known as fused filament fabrication) has become one of the most widely used ones due to its lower cost, ease of use, and versatility. While development has greatly expanded the material availability and improved the quality of prints, material extrusion 3D printers have often faced a challenge in physical scaling. There are inherent design hurdles to the extrusion process when the print starts to grow larger. This paper aims to study the market landscape of extrusion-based 3D printing technology for polymer-based material as well as challenges faced in upscaling this technology for industrial applications. A prototype large-scale material extrusion 3D printer has been designed, constructed, and then tested to gain experimental data on large-scale 3D printing using thermoplastic polymers as a printing material. Results of testing and experimentation verified certain key design elements and how they can improve large-scale 3D printing. Testing also revealed how large diameter nozzles for the hot end introduce challenges not seen in small-scale 3D printers. This paper also seeks to consolidate available information pertaining to large-scale 3D printing into one comprehensive document. [ABSTRACT FROM AUTHOR]

The objective of this paper is to determine the impact of density fraction on the mechanical properties of 3D printed thermoplastic materials to maximize the mechanical strength of parts through a combination of topology optimization and tailored density fraction. The results obtained reveal a significant finding of the applicability of the strategy for improving additive manufacturing processes, design automation, and manufacturing of high-strength components. The effect of infill density and print orientation on the mechanical properties of PLA-based 3D-printed parts are quantified by ultimate strength and Young's modulus in two material orientations (in the printing direction and out of the printing plane), employing both experimental and simulated uniaxial tensile tests, a polynomial relationship as a function of density fraction is determined. These data are then used in a series of successive topological optimizations of a part subjected to operational loads that maximize strength with a targeted reduction in the overall mass. The resulting optimized part exhibits a discrete density fraction distribution from the overlapped topologies that allows the total mass of the original part to be maintained with a 258% increase in load-carrying capacity before failure and a mere 23% increase in fabrication time by fused deposition modeling. These findings underscore the promise of leveraging advanced 3D printing methods and topology optimization to enhance the strength and efficiency of manufactured components. [ABSTRACT FROM AUTHOR]

Notably, despite the widespread application of 3D printing technology across diverse industries, issues like dimensional variations continue to limit its full-scale production potential. In this research, the dimensional variation between the CAD model and a 3D printed specimen by extrusion technique is investigated by a developed software algorithm. In contrast to previously employed techniques such as coordinate measuring machines, laser scanning, optical profilometry, and CT scanning, which have been highlighted in the literature, the developed software algorithm is cheap and stands out by relying on computer vision for the assessment of dimensional deviations in the printed model. The proposed software algorithm assesses the dimensional quality of 3D printed components through a comprehensive three-step methodology: preparation, measurement, and analysis. The software scrutinizes both the CAD model and the G-code-sliced model, extracting crucial dimensional data that serves as a reference for monitoring deviations during the actual 3D printing process. The software is fully tested across a diverse 3D geometry, capable of predicting real-time dimensional variances that could otherwise result in printing failures. The solution not only ensures the preservation of economic and human resources in additive manufacturing but also enhances the overall efficiency of the process. The paper concludes that the choice of the appropriate method should be contingent on the specific part type and the level of accuracy required. [ABSTRACT FROM AUTHOR]

Advancements in additive manufacturing (AM) have allowed for a transition in the manufacturing industry. The ability to print solid metal parts for use in prototypes, custom tooling, and fast replacement parts has driven advancements in the manufacturing sector. Material extrusion additive manufacturing processes such as fused deposition modeling (FDM) is a common AM processes in the world of thermoplastics and it is being developed in the field of metal additive manufacturing. Metal FDM (FDMm) process provides a low cost, customizable, and user-friendly printing experience while still delivering high printing tolerances. While there are many materials that can be printed using FDM technologies, process parameters vary across materials resulting in inconsistent process parameters across the industry. This review paper focuses on the techniques and parameters performed by various researchers for the printing, debinding, and sintering of FDM printed 316L Stainless Steel, 17-4PH Stainless Steel and high melt Iron alloy filaments. [ABSTRACT FROM AUTHOR]

In recent years, 3D printing technology has played an essential role in fabricating customized products at a low cost and faster in numerous industrial sectors. Fused deposition modeling (FDM) is one of the most efficient and economical 3D printing techniques. Various materials have been developed and studied, and their properties, such as mechanical, thermal, and electrical, have been reported. Numerous attempts to improve FDM products' properties for applications in various sectors have also been reported. Still, their applications are limited due to the materials' availability and properties compared to traditional fabrication methods. In 3D printing, the process parameters are crucial factors for improving the product's properties and reducing the machining time and cost. Researchers have recently investigated many approaches for expanding the range of materials and optimizing the FDM process parameters to extend the FDM process's possibility into various industrial sectors. This paper reviews and explains various techniques used in 3D printing and the various polymers and polymer composites used in the FDM process. The list of mechanical investigations carried out for different materials, process parameters, properties, and the FDM process's potential application was discussed. This review is expected to indicate the materials and their optimized parameters to achieve enhanced properties and applications. Also, the article is highly anticipated to provide the research gaps to sustenance future research in the area of FDM technologies. [ABSTRACT FROM AUTHOR]

Fused deposition modelling (FDM) 3D printing, as a supporting technology in social manufacturing and cloud manufacturing, is a rapidly growing technology in the era of industry 4.0. It produces objects with a layer-by-layer material accumulation technique. However, qualitative uncertainties are the common challenges yet. In order to assure print quality, studying the error causing parameters and minimizing their effects are important. This paper presents a feedback-based error compensation strategy, which integrates a fuzzy inference system and a grey wolf optimization algorithm. The objectives are twofold. First, the possible errors in FDM 3D printing are discussed in detail and optimal error causing parameters are obtained in percentage. This is used to understand the effects of the printing errors in every phase of the 3D printing process. From the nine optimization configuration trials used, Config-6 that has 100 number of iterations and 60 wolves is selected due to its higher convergence speed and best fitness value. The integral absolute error (IAE) is used as an objective function and the global minimum is achieved in the iteration interval 86 , 100 . The outputs of this optimization problem are used to achieve the next objective. Second, a closed-loop quality monitoring approach comprising of inner-loops and an outer-loop is taken. The three inner-loops are used to monitor the errors during pre-printing, printing, and post-printing, respectively. The outer-loop, on the other hand, is responsible for monitoring the aggregated errors in all the three 3D printing phases. The error compensation system simulation in Matlab is run for 10 s, and the results show that the "normal" range deformation factors are reached within less than 2 s for the inner-loops, whereas the outer-loop deformation factor is achieved within 2 s. The responses are within the acceptable time range. [ABSTRACT FROM AUTHOR]

Robotics and 3D printing are becoming more widely used in the field of construction industry. This paper reviews the work focused on the robotics technologies that aided for 3D printing in construction. Several aspects of them can be summarized as follows: (1) system composition and information flow, (2) robot workspace and motion planning, (3) control system and optimization of control strategy, (4) precision measurement and optimization, (5) quality assessment of 3D printing, (6) others, such as stability and interoperability. The challenge of every aspect is analyzed, and the correspondingly technical characteristics and methods are discussed in detail. The differences between robotics and construction mechanisms for 3D printing are analyzed and compared. Also, the robotics are further classified based on the workpiece size and their configurations. Finally, a brief description of future work to the robotics that suitable for 3D printing in construction is prospected. [ABSTRACT FROM AUTHOR]

Three-dimensional printing (3DP) is an evolutionary solution for making customize items for all sectors, but it has become more prominent in the healthcare sector. In this field, some solutions have to be adapted to patients. This is especially true for dentistry, where all the patients have their own unique mouth and tooth structure. It is now possible to provide an accurate model of the patient's mouth and teeth with solutions that are perfectly compatible with them, leading to the provision of a dental service with a high success rate. Even if there is a problem, it is enough to change the three-dimensional design. Therefore, it is a time-saving method, too. The purpose of this study is to investigate the role of 3DP in dentistry and to identify the processes and procedures resulting from the use of this technology. To do so, with the help of a case study, a 3DP-based dental clinic that provides implant, orthodontics, restoration and dentures services is simulated in Arena software. The current state of the system is assessed by defining appropriate evaluation criteria including net profit, utilization, waiting time, patients makespan and laboratory makespan. The simulation model is then developed with innovations such as adding an inventory control policy, creating rest time for resources and controlling the policy of sending products from laboratory to the clinic. After an extensive sensitivity analysis, improving the performance of the system is on the agenda of this paper by examining various scenarios. Results show that scenarios such as reducing some resources of the system or considering rest time in exchange for increasing the duration of the work shift can have a significant impact on clinic performance. [ABSTRACT FROM AUTHOR]

The advent of the Three-Dimensional (3D) printing technique, as an Additive Manufacturing technology, made the manufacture of complex porous scaffolds plausible in the tissue engineering field. In Fused Deposition Modeling based 3D printing, layer upon layer deposition of filaments produces voids and gaps, leading to a crack generation and loose bonding. Cohesive zone model (CZM), a fracture mechanics concept, is a promising theory to study the layers bond behavior. In this paper, a combination of experimental and computational investigations was proposed to obtain bond parameters and evaluate the effect of porosity and microstructure on these parameters. First, we considered two different designs for scaffolds beside a non-porous Bulk design. Then, we performed Double cantilever beam and Singe Lap Shear tests on the 3D printed samples for Modes I and II, respectively. Afterward, we developed the numerical simulations of these tests using the Finite element method (FEM) to obtain CZM bond parameters. Results demonstrate that the initial stiffness and cohesive strength were pretty similar for all designs in Mode I. However, the cohesive energy for the Bulk sample was approximately four times of porous samples. Furthermore, for Mode II, the initial stiffness and cohesive energy of the Bulk model were five and four times of porous designs while their cohesive strengths were almost the same. Also, using cohesive parameters was significantly enhanced the accuracy of FEM predictions in comparison with fully bonded assumption. It can be concluded that for the numerical analysis of 3D printed parts mechanical behavior, it is necessary to obtain and suppose the cohesive parameters. The present work illustrates the effectiveness of CZM and FEM combination to obtain the layer adhesive parameters of the 3D printed scaffold. [ABSTRACT FROM AUTHOR]

Although the literature is abundant with the experimental methods to characterize mechanical behavior of parts made by fused filament fabrication 3D printing, less attention has been paid in using computational models to predict the mechanical properties of these parts. In the present paper, a numerical homogenization technique is developed to predict the effect of printing process parameters on the elastic response of 3D printed parts with cellular lattice structures. The development of finite element computational models of printed parts is based on a multi scale approach. Initially, at the micro scale level, the analysis of micro-mechanical models of a representative volume element is used to calculate the effective orthotropic properties. The finite element models include different infill densities and building/raster orientation maintaining the bonded region between the adjacent fibers and layers. The elastic constants obtained by this method are then used as an input for the creation of macro scale finite element models enabling the simulation of the mechanical response of printed samples subjected to the bending, shear, and tensile loads. Finally, the results obtained by the homogenization technique are validated against more realistic finite element explicit microstructural models and experimental measurements. The results show that, providing an accurate characterization of the properties to be fed into the macro scale model, the use of the homogenization technique is a reliable tool to predict the elastic response of 3D printed parts. The outlined approach provides faster iterative design of 3D printed parts, contributing to reducing the number of experimental replicates and fabrication costs. [ABSTRACT FROM AUTHOR]

Utilization of laser powder deposition (LPD) as an innovative repair tool for damaged steel components is increasingly growing in recent years. This paper investigates repairing a standard US light rail using LPD. No study has focused on repairing standard US rails thus far. Besides, this is the first time that a three-dimensional finite element model is developed where element-birth-and-kill technique is employed to study thermal-kinetic-mechanical evolutions during the LPD rail repair process. Exploration of hardness versus microstructure yielded a reverse correlation between hardness level and austenite volume fraction. The maximum hardness was found near rail-deposition interface with the minimum austenite concentration, while the topmost deposition layer with the highest austenite concentration showed the minimum hardness. Longitudinal residual stresses at the rail-deposition interface were significantly more than that of transversal and normal. Comparing the residual stress against deposition material yield strength showed a slight exceedance (~5%) of transversal stress from the maximum limit, no exceedance for normal stress, but an extreme exceedance of 50% for longitudinal stress. This fact suggested a high risk of cracking along longitudinal direction at the rail-deposition interface, while there existed only a minor risk of transversal cracking and almost no chance of layer delamination. The simulated results were compared against experimental results obtained via optical and scanning electron microscopy, hardness test, and X-ray diffraction stress measurement, where a maximum deviation of 10% proved the model accuracy. The validated model in this study would be a great backbone for future studies on different process parameters to increase hardness and reduce stress in an LPD repaired rail. [ABSTRACT FROM AUTHOR]

Specialty thermoplastic materials based on fluoropolymer polyvinylidene fluoride (PVDF) became commercially available to the 3D printing community only recently. Additive manufacturing of PVDF-based structural components suited for harsher operational conditions is important for more demanding industrial sectors such as biomedical/chemical, aerospace, or automotive. Such components must ensure adequate mechanical performance in diverse deformation cases. Hence, this paper reports on fused filament fabrication (FFF) and quasi-static tensile, flexural and compressive testing of PVDF homopolymer, biocompatible PVDF-co-hexafluoropropylene (PVDF-HFP) copolymer, and static-dissipative PVDF-HFP/graphene composite specimens, which were printed with triangular lattice infill of variable density for addressing the influence of lightweighting. Printability in an open-chamber-based FFF machine is discussed in terms of part warpage and adhesion issues, which aggravate FFF process because of the higher degree of crystallinity, larger coefficient of thermal expansion, and hydrophobicity of PVDF. It was found that these printing complications are alleviated by applying lower printing speed and temperature together with the use of wider brims and a specialized FFF-tailored adhesive. The measured stress–strain curves are examined to analyze changes in strengths and moduli of elasticity of the specimens as a function of infill density including comparisons in ductility, failure mode, and anisotropic mechanical behavior such as tension–compression asymmetry. The presented results serve as a guideline for additive manufacturing of functional PVDF-based load-bearing components that are intended for service in different loading regimes. [ABSTRACT FROM AUTHOR]

Grinding performance-oriented proactive design is hard to realize by conventional hot-pressing sintered grinding wheel, because the internal micro-structure of grinding wheel is relatively enclosed, resulting in wheel clogging and surface burn of workpiece. This paper adopts triply periodic minimal surfaces (TPMS) to design the controllable micro-structure of the grinding wheel, and numerous interconnected pores and liquid channels can be constructed with the novel design method and 3D printing to control the grinding performance. The grinding performance is comprehensively evaluated based on the grinding experiment of BK7 glass. By comparative analysis of the novel and conventional electroplated grinding wheels in grinding force, specific grinding energy, workpiece surface morphology, and wheel wear, the influence mechanisms between the micro-structure design parameters and grinding performance are investigated. The experimental results indicate that the shape scale of the micro-structure is the main factor that affects the fluctuation of grinding force and surface roughness, and the stiffness and effective area of the micro-structure are the main factors that affect average grinding force and specific grinding energy. Compared with the electroplated grinding wheel, the proposed novel grinding wheel has smaller grinding force, specific grinding energy, and has obvious superiority in wear resistance and self-sharpening capability. [ABSTRACT FROM AUTHOR]

Sintering is a key step that determines the mechanical performances and shape quality of 3D printed ceramics. In this domain, there is an increasing interest in complex thin structures and low fill density shapes. However, these complex structures may suffer from distortions by gravity forces developed on the light structure, friction with supports, shrinkage anisotropy, or thermal gradients. Finite element simulation of the sintering process is then of high importance for predicting the specimens distortions. This paper focuses on the identification of the model parameters in the special case of anisotropic sintering of porcelain with final stage swelling. This study points out the printed specimen high resistance to high temperature shear deformation due to the alignment of the printed rods. A mesoscale simulation has been carried out to explain this mechanism. The resulting model was tested for the sintering of a thin wall cup shape. [ABSTRACT FROM AUTHOR]

Feedrate optimization (FO) and servo error pre-compensation (SEP) are often performed independently to improve the accuracy and speed, respectively, of computer-controlled manufacturing machines. However, this independent approach leads to excessive tradeoff between speed and accuracy. To address this issue, the authors have proposed a new concept of simultaneous FO and SEP (or FOSEP) where SEP is integrated into FO, yielding large reductions in motion time without sacrificing positioning accuracy relative to independent FO and SEP. However, in their prior work, the authors used linear programming to achieve FOSEP resulting in the following: (i) inaccuracy in enforcing nonlinear constraints and (ii) poor computational efficiency for long toolpaths. To address these two problems, this paper proposes a new approach for FOSEP using windowed sequential linear programming (SLP). The use of SLP improves the accuracy of FOSEP in enforcing nonlinear constraints; however, it lowers the computational efficiency of FOSEP. Windowing addresses the problem of low computational efficiency by applying SLP to FOSEP in small overlapping batches. A downside of windowed SLP is that it may lead to infeasibility in the optimization. This problem is resolved by smoothly switching between the optimal solution obtained using windowed SLP and a backup conservative solution in case of impending infeasibility. The proposed windowed SLP with smooth switching approach for FOSEP is validated in simulations where it significantly improves the accuracy and computational efficiency of FOSEP while guaranteeing feasibility. The practical benefits of the proposed approach for FOSEP is demonstrated in experiments on a 3D printer where it achieves up to 25% reduction in cycle time without sacrificing printing quality relative to the conventional approach of independent FO then SEP, both applied to a long toolpath. [ABSTRACT FROM AUTHOR]

The 3D printing technology used for small tidal and wind turbines has great potential to change and overcome certain weaknesses in traditional manufacturing techniques. In rural areas and isolated communities, small turbine systems could be locally fabricated and assembled by using additive manufacturing machines and also can be employed to decrease residential energy consumption. The objective of the paper is to study the thermomechanical performance of 3D printing of a small-scale tidal turbine blade and their process using Digimat-AM because more research efforts are needed in this area. In this work, the tidal turbine blade is printed by using the selective laser sintering (SLS) method with polyamide 12 (PA12) and polyether ether ketone (PEEK) polymers reinforced by carbon beads (CB) and glass beads (GB). This research examines conceptual considerations of small tidal turbines including material properties and aerodynamic parameters. Once the finite element evaluation has been completed, the deflection, residual stresses, temperature distribution, and the deformed blade or warpage can be obtained. It is concluded that PA12-CB has warpage higher than PA12-GB by 3.78%, and PEEK-CB has warpage lower than PEEK-GB by 8.4%. Also, the warpage of PA12-CB is lower than PEEK-CB by 10.31%, and the warpage of PA12-GB is lower than PEEK-GB by 20.95%. Therefore, the lowest warpage is observed for PA12-GB. Finally, the results showed that 3D printing presents an excellent opportunity in the design and development of tidal energy systems in the future. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has emerged in the last decades as an alternative to traditional subtractive and forming manufacturing processes. AM is a process where 3D objects are built by adding material in consecutive layers. Typical AM is characterized by four processing stages: model orientation, creation of supports, slicing, and path planning. In this paper, we will focus on how to use mathematical optimization to address some limitations that arise from the model orientation, creation of supports, and slicing processing stages. Model orientation and creation of supports are usually related, since the best orientation of the object to be built can result in lower building time and lower need for creation of supports, leading to an improvement of the surface quality. Slicing comprises the object division by layers and the major difficulty is the staircase effect, which becomes more critical for objects with high slopes and curvatures, resulting in high roughness surfaces. In this paper, we show how to take advantage of a state-of-the-art optimization solver to optimize object building orientation and the need for supports generation in additive manufacturing, thus leading to better object surface accuracy and smoothness. [ABSTRACT FROM AUTHOR]

Traditional fused deposition modeling (FDM) additive manufacturing technologies usually fabricate a 3D physical model layer by layer. However, support structure under cantilever geometry and model unloading are two major drawbacks of the FDM technology that waste material and hamper the automation of FDM. This paper designs a kind of flexible support platform for assisting FDM to avoid waste and promote automation of FDM, which consists of basic units controlled to rise and fall by the computer. During the printing process, the platform can form different support structures using basic units for different models. When the printing process is finished, basic units rise to unload the model from the platform. Typical models were printed to verify efficiency of support structure reduction, and effects of the model’s position on reduction were studied. The automatic unloading of the flexible platform was simulated to study the stress state and then the mechanical test was put into effect to measure the actual value of pressure. In the last part, parameters of unloading successfully are given to guide the unloading process. [ABSTRACT FROM AUTHOR]

The development of information, materials science, and technology has led to profound changes in manufacturing. Many new ideas and technologies have emerged in recent years, such as cloud manufacturing and 3D printing. Cloud manufacturing (CM) is a new type of networked manufacturing mode proposed in 2010, and 3D printing is an example of new manufacturing methods. CM and 3D printing both have significant influence in the manufacturing mode and manufacturing method and are already research hotspots in the field of advanced manufacturing technology. What kind of innovations will be produced when they integrate? To explore this issue, this paper first analyses the characteristics of cloud manufacturing and 3D printing. Second, the combination research of cloud manufacturing and 3D printing in recent years is studied, including 3D printing cloud platform (3D-PCP) service architectures, 3D printing resource access technology, 3D printing service optimized configuration technology, 3D printing service control and monitoring technology, and 3D printing service evaluation technology. There are several research achievements and commercial application cases of 3D-PCP, but a true sense of 3D printing cloud ecology from the perspective of a manufacturing system has not been formed to date. On the basis of the survey and analysis, this paper highlights the shortcomings in current research and proposes development suggestions of the combination of 3D printing and cloud manufacturing, including the potential research direction of 3D-PCP system modes, the Internet of Things in 3D printing, and the 3D printing service process control and evaluation. [ABSTRACT FROM AUTHOR]

Additive manufacturing is the process of building a three-dimensional object from a computer-aided design model, by successively adding material layer-by-layer. This technology allows to print complex shape objects and is being rapidly adopted throughout the aircraft industry, medical implants, jewelry, footwear industry, automotive industry, and fashion products. The build orientation of 3D objects has a strong influence on many quality characteristics. In this paper, a many-objective approach is applied to the Fin model, using the NSGA-II algorithm to optimize four conflicting objective functions regarding the need for support structures, the build time, the surface roughness, and the overall quality of the surface. First, a bi-objective optimization is performed for each couple of two objectives and some representative solutions are identified. However, when applying many-objective optimization to the four objective functions simultaneously, some more orientation angles are found as good optimal solutions. Visualization tools are used to inspect the relationships and the trade-offs between the objectives. Then, the decision-maker can choose which orientation angles are more favorable according to his/her preferences. The optimal solutions found confirmed the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

The fourth industrial revolution (Industry 4.0) is transforming industries all around the world focusing on areas including advanced robotics and automation, sensor technology and data analytics. The authors are involved in a project developing a multi-robot material extrusion 3D printer to print a gravity separation spiral (GSS), an instrument used in the mining industry to separate mineral slurry into different density components. Compared with traditional mould-based manufacturing, this new additive manufacturing method will significantly reduce manufacturing tooling costs, improve the customisation to enable the production of bespoke GSS that each processes different minerals and reduce worker exposure to hazardous materials. Slicing and printing large-scale helical objects in conventional horizontal layer addition would result in an unreasonable amount of waste material from support structures, and poor surface quality due to step-wise bumps. This paper presents a novel slicing algorithm using concentric vertical ray lines to slice objects radially, enabling layers to be deposited progressively in the same fashion. This method can be applied in large-scale additive manufacturing where objects are printed by a robot in a radial direction, which is different from layered vertical printing in conventional additive systems. An example GSS is sliced to generate motion plans for a print head affixed to the end effector of a robot arm. Then through simulations, it is shown how a robot's expected manipulability measure can be used to predict and ensure the successful completion of the print. [ABSTRACT FROM AUTHOR]