Promising Manufacturing Technology Research Articles

Analysis of Microstructure and Mechanical Properties of CoCrMo Alloys Processed by Metal Binder Jetting Multi-Step Technique

Metal Binder Jetting (BJT/M) has emerged as a promising additive manufacturing (AM) technology for the realization of complex parts using a wide range of metal alloys. This technology offers several advantages, such as design flexibility, reduced lead times, a high building rate, and the ability to fabricate intricate geometries that are difficult or impossible to achieve with conventional manufacturing methods. Cobalt Chromium Molybdenum (CoCrMo) alloys are particularly suitable for demanding applications in the aerospace, biomedical, and industrial sectors that require high strength and hardness, corrosion resistance, and biocompatibility. In this work, ten cubic and ten tensile samples were printed with a layer height of 50 µm using the shell printing method, debound and sintered at 1325 °C for 4 h, with the aim of investigating the properties of CoCrMo parts made using BJT technology. A density of 7.88 g/cc was obtained from the Archimede’s test. According to the printing and sintering parameters, an average hardness of 18.5 ± 1.8 HRC and an ultimate tensile strength of 520.5 ± 44.6 MPa were obtained. Finally, through a microstructure analysis, an average grain size of 182 ± 14.7 µm was measured and the presence of an intergranular Cr-rich phase and Mo-rich carbides was detected.

In-situ visual monitoring for multi-scale defects detection in laser powder bed fusion

Laser powder bed fusion (PBF-LB) is a promising metal additive manufacturing technology. However, ensuring consistent quality remains a pressing challenge due to defects that arise during the PBF-LB process. These defects significantly impede subsequent molding procedures, emphasizing the urgent need for real-time monitoring technology to steer part production effectively. Present monitoring techniques are limited, typically addressing specific defect types or contour deformations individually and lacking a simple and effective method to achieve multi-scale defects detection for PBF-LB parts. This study aims to pioneer a method that can detect defects and part contour deformations during the PBF-LB process using only an industrial camera as the monitoring device. The proposed method consists of two key components: a semantic segmentation model based on deep transfer learning (SS-DTF model) and a contour deformation detection module. To begin with, an off-axis in-situ monitoring system is deployed with an industrial camera to capture powder bed images for each layer after laser scanning and powder spreading. This enables the production of datasets for post-scanning and post-spreading anomalies. The SS-DTF model is trained on the above two datasets respectively to achieve segmentation for multi-category defects. The contour deformation detection module provides automatic early warning by comparing the true contour of the part with the nominal contour layer-by-layer, using statistical process monitoring method. The proposed method is then used to monitor parts with various geometries under real processing conditions, aiming to clarify the potential correlation between monitoring outcomes and the parts’ multi-scale defects in PBF-LB. The results show that the proposed method provides a promising solution for in-situ monitoring of the PBF-LB process.

Thermal characterization of Xenon-Arc flash lamp heating system for automated fiber placement (AFP) of thermoplastic composites

In this study, a systematic experimental and simulations-based characterization of key thermal aspects of the arc-flash lamp based AFP heating is presented. Ex-situ measurements of heat flux output from the flash lamp as well as the resulting temperature field on a material sample are carried out in a geometry representative of actual manufacturing conditions, using a heat flux sensor and infrared thermography. A thermal simulation model is developed to predict the temperature field resulting from the measured heat flux data. Good agreement is found between experimental data and simulation predictions. This work contributes towards developing a fundamental understanding of heat transfer processes during AFP manufacturing. Data presented here may be of broad benefit to AFP-related research, and may contribute towards process design and optimization in order to further expand the capabilities of this promising additive manufacturing technology.

Mechanical and Corrosion Behaviour in Simulated Body Fluid of As-Fabricated 3D Porous L-PBF 316L Stainless Steel Structures for Biomedical Implants.

Laser powder bed fusion (L-PBF) is one of the most promising additive manufacturing technologies for creating customised 316L Stainless Steel (SS) implants with biomimetic characteristics, controlled porosity, and optimal structural and functional properties. However, the behaviour of as-fabricated 3D 316L SS structures without any surface finishing in environments that simulate body fluids remains largely unknown. To address this knowledge gap, the present study investigates the surface characteristics, the internal porosity, the corrosion in simulated body fluid (SBF), and the mechanical properties of as-fabricated 316L SS structures manufactured by L-PBF with rhombitruncated cuboctahedron (RTCO) unit cells with two distinct relative densities (10 and 35%). The microstructural analysis confirmed that the RTCO structure has a pure austenitic phase with a roughness of ~20 µm and a fine cellular morphology. The micro-CT revealed the presence of keyholes and a lack of fusion pores in both RTCO structures. Despite the difference in the internal porosity, the mechanical properties of both structures remain within the range of bone tissue and in line with the Gibson and Ashby model. Additionally, the as-fabricated RTCO structures demonstrated passive corrosion behaviour in the SBF solution. Thus, as-fabricated porous structures are promising biomaterials for implants due to their suitable surface roughness, mechanical properties, and corrosion resistance, facilitating bone tissue growth.

Reducing Laser Exposure Time of PBF-LB/P by Providing High Energy Without Thermal Degradation and Its Effect on Part Strength and Process Time

Abstract One of the most promising additive manufacturing technologies for the production of end-use parts is powder bed fusion of polymer with laser beam (PBF-LB/P). This technology can reduce production costs by increasing process efficiency and production speed. As PBF-LB/P is a layer-wise additive manufacturing process, the production speed can be increased by reducing the layering time. Although some operations such as recoating are performed during the layering process, considerable time is spent on laser scanning. To reduce the laser exposure time while maintaining proper powder melting, a high-power beam should be irradiated to the powder layer to prevent energy shortage. However, as the laser beam power increases, the irradiance at the beam center increases significantly, causing powder degradation such as thermal decomposition or sublimation. In this study, an appropriate input energy range was determined by obtaining an input energy limit that does not cause powder deterioration via experimental observations and temperature estimations during the process. Furthermore, the influence of the scanning parameters on the mechanical properties of built specimens was investigated to reduce the layering time within an indicated range. Results show that the mechanical strength of the built parts decreases slightly as the scan spacing increases following the expansion of the beam diameter. This study also validated the effects of scanning parameters on layering time. As a result, by doubling the scan speed and spacing, the layering time can be reduced by up to 1/3.

3D Printing of Liquid Crystal Polymers for Space Applications

AbstractFused Filament Fabrication is a promising manufacturing technology for the circularity of space missions. Potential scenarios include in‐orbit applications to maximize mission life and to support long‐term exploration missions with in situ manufacturing and recycling. However, its adoption is restricted by the availability of engineering polymers displaying mechanical performance combined with resistance to space conditions. Here, a thermotropic Liquid Crystal Polymer (LCP) is reported as a candidate material with extrusion 3D printing. To expand its scope of applicability to structural parts for space applications, four different exposure conditions are studied: thermal cycling under vacuum, atomic oxygen, UV, and electron irradiations. While 1 MeV‐electron irradiation leads to a green coloration due to annealable color centers, the mechanical performance is only slightly decreased in dynamic mode. It is also found that increased printing temperature improves transverse strength and resistance to thermal cycling with the trade‐off of tensile stiffness and strength. Samples exposed to thermal cycling and the highest irradiation dose at lower printing temperatures still display a Young's modulus of 30 GPa and 503 MPa of tensile strength which is exceptionally high for a 3D‐printed polymer. For the types of exposure studied, overall, the results indicate that LCP 3D‐printed parts are well suited for space applications.

Design and batch fabrication of anisotropic microparticles toward small-scale robots using microfluidics: recent advances.

Small-scale robots with shape anisotropy have garnered significant scientific interest due to their enhanced mobility and precise control in recent years. Traditionally, these miniature robots are manufactured using established techniques such as molding, 3D printing, and microfabrication. However, the advent of microfluidics in recent years has emerged as a promising manufacturing technology, capitalizing on the precise and dynamic manipulation of fluids at the microscale to fabricate various complex-shaped anisotropic particles. This offers a versatile and controlled platform, enabling the efficient fabrication of small-scale robots with tailored morphologies and advanced functionalities from the microfluidic-derived anisotropic microparticles at high throughput. This review highlights the recent advances in the microfluidic fabrication of anisotropic microparticles and their potential applications in small-scale robots. In this review, the term 'small-scale robots' broadly encompasses micromotors endowed with capabilities for locomotion and manipulation. Firstly, the fundamental strategies for liquid template formation and the methodologies for generating anisotropic microparticles within the microfluidic system are briefly introduced. Subsequently, the functionality of shape-anisotropic particles in forming components for small-scale robots and actuation mechanisms are emphasized. Attention is then directed towards the diverse applications of these microparticle-derived microrobots in a variety of fields, including pollution remediation, cell microcarriers, drug delivery, and biofilm eradication. Finally, we discuss future directions for the fabrication and development of miniature robots from microfluidics, shedding light on the evolving landscape of this field.

Progress in the Study of Quality and Mechanical Properties of Selective Laser Melting Molded Parts

Abstract: Selective laser melting (SLM) is considered to be a widely promising additive manufacturing technology with the advantages of high machining precision, high manufacturing freedom, and short cycle time, which is widely used in aerospace, the integration of medicine, and industry, chemical, and other fields. The research progress on the temperature field, stress field, forming quality, and mechanical properties during the SLM manufacturing process is reviewed. The study aims to systematically analyze how SLM process parameters affect the temperature field, stress field, forming quality, and mechanical properties, and to discuss the importance of the selection of process parameters and performance regulation to achieve high-quality, highperformance metal parts. The effects of SLM process parameters on temperature field, stress field, surface roughness, densification, hardness, strength, and fatigue properties are analyzed and summarized. The importance of process parameters in the SLM forming procedure in the quality of formed components is emphasized, and conducting an in-depth study on the optimization and performance regulation of the process parameters is of great significance in achieving the high quality and performance of metal parts. With the rapid advancement of technology, the potential of SLM technology in terms of molding quality and mechanical performance has become increasingly significant, heralding significant breakthroughs. These potential breakthroughs will greatly promote the widespread application of SLM technology in various industries, thus more efficiently meeting the growing needs and expectations of industries such as petrochemicals, transportation, aerospace, nuclear energy, as well as food and medical sectors.

Dynamic formation of gradient structure by microparticle impact — A crystal plasticity material point method study

Metallic materials with unique microstructure can achieve desirable strength-ductility synergy. However, effectively fabricating and precisely controlling microstructure distribution in metals remain challenging. Microparticle impact, the key process of cold spray technique, can lead to a gradient structure in the particle, which may also serve as a promising additive manufacturing technology. To investigate the dynamic formation mechanism of heterogeneous microstructure and its significant influencing factors, the crystal plasticity material point method (CPMPM) is developed, especially for microstructure formation under a high strain rate and large deformation. Our work provides a quantitative analysis of evolution of structural gradient during impact. It is found that decreasing grain size can afford a larger structural gradient and there is negligible influence on the compression ratio of particles. It suggests that microstructure distribution can be tailored by optimizing the impact process without influencing vertical deformation of particles.

A microscale cellular automaton method for solid-state phase transformation of directed energy deposited Ti6Al4V

Directed energy deposition is a promising additive manufacturing technology that fabricates complex geometries by fusing feed material layer-by-layer. However, the formation mechanism of the directed energy deposited Ti6Al4V solid-state phase transformation process, which is crucial for understanding the process-structure–property relationship, has remained unclear. In this study, a microscale cellular automaton method is proposed to simulate the microstructure evolution process for Ti6Al4V, specifically the β→α/α′ phase transformation process within a few β grains. The method is further integrated with the mesoscale cellular automaton method, which predicts the prior β grain structure, the solid-state phase transformation kinetics model for the prediction of the phase volume fractions, and the finite volume method, which is used for the thermal-fluid flow modelling, providing a temperature field to the former. The integrated numerical framework not only links the thermal history with the phase volume fractions but also provides the columnar β grain structures and acicular α/α′ grain structures in satisfying agreement with the available experimental observation. Moreover, the predictions shed some light on the formation mechanism of the hierarchical α/α′ structure and their particular clusters. The influence of the cooling rate on the α/α′ grain formation is illustrated via the three-layer case simulation. The findings on the formation mechanism of α/α′ are beneficial in tailoring the microstructure of Ti6Al4V for excellent mechanical properties in directed energy deposited Ti6Al4V.

A Statistical Investigation and Prediction of the Effect of FDM Variables on Flexural Stress of PLA Prints

Due to its many engineering applications, low manufacturing costs, and environmental friendliness, 3D printing is considered one of the most promising manufacturing technologies. The quality of printed parts will inevitably be affected by the controllable variables used in the 3D printing process. The present study aims to investigate how different printing process parameters affect the bending strength of PLA prints. The ASTM D790 standard was used to fabricate the samples in this work, while the Taguchi principle was used to design the experiments. The following values were chosen: shell width (0.8, 1.2, 1.6, and 2 mm), layer thickness (0.15, 0.2, 0.25, and 0.3 mm), and infill density (40%, 60%, 80%, and 100%). The results showed that fill density is the most effective variable for improving bending strength. Measurements of infill density (100%), layer thickness (0.15 mm), and shell width (2 mm) gave the best results, which were calculated to be 83.1479 MPa in bending test. The mathematical model in this study was developed using linear regression analysis, and the residuals confirmed that the model fit the data well, with a maximum error of 6.1%.

Powder movement rules of laser powder bed fusion additive manufacturing aluminum alloy based on discrete element method

Laser Powder Bed Fusion (LPBF) is a promising metal additive manufacturing technology based on layer by layer powder spreading, and powder bed uniformity has a great influence on the forming quality. By Discrete Element Method and powder spreading experiment, the interaction and movement between powder were studied during powder spreading, including powder jamming, rebound, splash, eddy, and empty powder area. Additionally, five kinds of powder spreading schemes were explored, and the new process of one-way reciprocating with tri-splint blade was designed to change the motion state of powder spreading from “blade pushing powder” to “blade holding powder.” By increasing the distance between the blade and the working platform form 0 to 20 µm with the distance between the upper surface of the substrate and the working platform 50 µm, defects such as powder splash and empty powder decreased. And the uniform powder bed of aluminum alloy powder was achieved with the new process of one-way reciprocating with tri-splint blade structure.

Ray tracing heat source model for polymer powder bed fusion considering laser energy absorption and multiple reflection

Powder bed fusion is considered one of the most promising additive manufacturing technologies, but the generation and evolution of volumetric heat source involved in the powder bed fusion process remain unclear as laser-powder bed interactions has not been fully developed. In this work, a ray tracing model is established to simulate the laser-powder bed interaction during the powder bed fusion process. Five types of powder beds with homogeneous and non-homogeneous particle radius distributions are generated using the discrete element method, and then the energy distributions in the ray tracing heat source are explored by considering laser energy absorption and multiple reflection. The results indicate that the energy distribution in the ray tracing heat source basically exhibits a Gaussian-like trend in the horizontal plane and an exponential decay in the vertical direction. The fitting coefficients Z0 (related to laser power) and η2 (related to laser radius) of the ray tracing heat source for different powder beds show maximum differences of 21.87 % and 72.22 %, respectively, compared to conventional Gaussian volumetric heat sources. The deviation between the fitting coefficient η3 (related to laser energy attenuation) and the corresponding fitted attenuation coefficient of the powder bed is related to the overall uniformity of the powder bed. Due to multiple reflections of the laser within the powder bed, the ray tracing heat source has larger width and depth as compared to Gaussian volumetric heat source. This study is significant because it provides a more accurate heat source model for the reliable prediction and safe operation of powder bed fusion process.

Enriching Laser Powder Bed Fusion Part Data Using Category Theory

Laser powder bed fusion (LPBF) is a promising metal additive manufacturing technology for producing functional components. However, there are still a lot of obstacles to overcome before this technology is considered mature and trustworthy for wider industrial applications. One of the biggest obstacles is the difficulty in ensuring the repeatability of process and the reproducibility of products. To tackle this challenge, a prerequisite is to represent and communicate the data from the part realisation process in an unambiguous and rigorous manner. In this paper, a semantically enriched LPBF part data model is developed using a category theory-based modelling approach. Firstly, a set of objects and morphisms are created to construct categories for design, process planning, part build, post-processing, and qualification. Twenty functors are then established to communicate these categories. Finally, an application of the developed model is illustrated via the realisation of an LPBF truncheon.

Solar-driven hydrogen production based on moisture adsorption-desorption cycle

Photocatalytic hydrogen production by water splitting is considered one of the most promising green hydrogen manufacturing technologies, but the actual outdoor deployment of this technology is limited by the availability of water feedstocks in geographical locations. An integrated device consisting of a photocatalytic layer and an atmospheric water harvesting material that can achieve in-situ photocatalytic water vapor splitting for hydrogen production by spontaneously capturing moisture from the air as a water feedstock is proposed herein. The integrated system has excellent photocatalytic and photothermal synergistic ability, low hydrogen diffusion resistance by interfacial photocatalysis, and high stability by isolating salts contamination. The system can achieve a hydrogen production rate of 425.4 μmol g−1 h−1 and a water vapor supply rate of 0.121 kg m−2 h−1 under one sun illumination, and has a water vapor adsorption rate of 0.03 kg m−2 h−1 under dark conditions in the laboratory. Furthermore, this hybrid device obtains a total hydrogen production of up to 3963.1 μmol g−1 in the real outdoor daytime and accomplishes water regeneration within 10 hours by capturing environmental moisture at night. This work provides a suitable solution for hydrogen production in areas with water scarcity or drought.

Microstructure and mechanical properties of IN718 on 42CrMo for repair applications by laser directed energy deposition

Laser Directed Energy Deposition (LDED) has gained significant attention as a promising additive manufacturing technology for the repair and restoration of worn parts. The objective of this study is to assess the feasibility and performance of repairing 42CrMo substrates using Inconel 718(IN718) powder. In this study, the LDED process was employed to investigate the influence of varying laser power, scanning speed, and feed rate on a single track study. The optimal process parameters for trapezoidal groove repair were determined by comparing and evaluating factors such as dilution, aspect ratio, track continuity, and molten pool shape. Furthermore, the effects of different repair strategies (X-, Y-, Cross-paths) on the microstructure and mechanical properties were investigated. The results indicate that by using suitable process parameters, successful deposition of IN718 on 42CrMo is achieved. The investigation reveals elemental diffusion between the two materials, quenching phase transition on the substrate surface, and the formation of intermetallic compounds in the fusion zone. The fusion zone(FZ) and heat-affected zone(HAZ) exhibited the highest microhardness compared to the substrate. Significant changes in molten pool shape and arrangement were observed using different repair strategies, while the effect on grain size was not significant. Due to the high directionality of the samples fabricated using the LDED process, the samples of the X-path demonstrated the highest ultimate tensile strength and elongation compared to the other two repair strategies. The ultimate tensile strength after repair is comparable to that of the substrate, while the elongation is reduced.

Evaluation of tensile properties of ABS material specimen using commercial and manufactured filaments in FDM process

Acrylonitrile butadiene styrene (ABS) is the most common of engineering plastic materials; it is copolymer of Styrene-Acrylonitrile and butadiene styrene in special form. It is widely used in substantive and Additive Manufacturing (AM) applications. AM is a promising manufacturing technology that can fulfill future needs as products and their configurations are changing day by day. Fused Deposition Modeling FDM is an AM technique that fabricates parts layer upon layer. This paper analyses the effect of different process variables and orientations on the tensile properties of the FDM manufactured specimens. Standard specimens are printed using commercial ABS and manufactured ABS filaments for analysis of tensile properties. The ABS filament is fabricated using a mini filament extruder. After modeling, the specimens are printed using an FDM printer. The tensile testing of specimens is carried out on the Instron 3360 table frame UTM machine. Tensile properties obtained for different specimens are presented.

Effect of solid-solution treatment on high-temperature properties and creep fracture mechanism of laser powder bed fused Inconel 625 alloy

Laser powder bed fusion (LPBF) has been widely used for fabricating Inconel 625 (IN625) alloy, and it is widely regarded as a promising manufacturing technology. However, during high-temperature service, the γ″ strengthening phase of LPBFed IN625 gradually transforms into the detrimental δ phase. Controlling the morphology and distribution of precipitates is necessary for optimizing high-temperature performance. This study compared the as-built and 1090 °C solution-treated LPBFed IN625 alloy and investigated the microstructure evolution, tensile properties, and creep fracture behavior at a high temperature of 815 °C. The results show that the solid-solution treatment improves the creep ductility of LPBFed IN625 alloys at 815 °C by forming a high percentage of twinned boundaries and eliminating dislocations. The formation of coarsened needle-like δ phases and carbides during creep reduces the strength of the grain boundaries and is responsible for creep fracture failure. During creep of the as-built samples, the irregular Laves phase between the columnar dendrites gradually transforms into plate-like δ phases and M6C carbides uniformly and densely distributed within the columnar grains. The precipitation-strengthening effect of these fine precipitates, combined with the initial high density of dislocations and strong texturing effect, brings favorable high-temperature strength and creep fracture life but consequently leads to low creep ductility.

3D bioprinting in otorhinolaryngology: from bench to clinical application

Three-dimensional (3D) bioprinting is a promising additive manufacturing technology that uses imaging data and computer-assisted deposition of biological materials or cells to reconstruct complex 3D structures accurately. This technology has progressed rapidly, in part because of its integration across multiple disciplines and combination with other technologies for clinical applications. Advances in experimental research and clinical applications related to otorhinolaryngology have led to the development of diagnostic and treatment methods based on 3D bioprinting, including the development of tissue engineering scaffolds, biosensors, organ chips, and organoids, surgical planning, graft construction, and medical education. Additionally, otorhinolaryngologists will be better equipped to treat tissue function defects with personalized printed graft implants. It is also expected that 3D printing can be used to build ideal in vitro models in the future to help solve existing research challenges. This article briefly introduces the relevant 3D bioprinting technologies and bioinks that can be used by otorhinolaryngologists and discusses their potential applications in otorhinolaryngology.

A Real-Time Monitoring Method for Selective Laser Melting of TA1 Materials Based on Radiation Detection of a Molten Pool.

Selective laser melting (SLM) technology is a promising additive manufacturing technology. However, due to the numerous influencing factors in this complex process, a reliable real-time method is needed to monitor the forming process of SLM. The molten pool is the smallest forming unit in the SLM process, the consistency of which can effectively reflect the quality of the printing process. By using a coaxial optical path structure and a compound amplifier circuit, high-speed acquisition of molten pool radiation can be realized. Next, single factor analysis and orthogonal experimentation were used to investigate the influence levels of key process parameters on the radiation of molten pool. In addition, numerical simulation was carried out with the same parameter setting schemes, the results of which are consistent with those in radiation detection experiments. It is shown that the laser power has the greatest effect on the radiation of the molten pool, while the scanning speed and the hatch spacing have little effect on the radiation. Finally, the positioning experiment involving the small hole structure was carried out, and the experimental results showed that the device could accurately locate the position coordinates of the given hole structure.