Selective Laser Melting Process Research Articles

EXPERIMENTAL AND NUMERICAL STUDY OF INCREASED CORE SURFACE AREA ON THE PERFORMANCE OF ADDITIVELY MANUFACTURED HONEYCOMB SANDWICH STRUCTURES

Abstract Sandwich composite structures have an efficient structural design that provides high bending stiffness and strength at low weight. However, these structures are plagued with weak core-to-facesheet bond strength. In this work, the effect of increasing the contact area between the composite facesheet and honeycomb core was studied. Sandwich panels were manufactured using two different honeycomb structures, a regular and a modified honeycomb, and their respective bond strengths were evaluated using the flatwise tension test (ASTM C297). The honeycombs were additively manufactured using selective laser melting (SLM) process. The modified honeycomb was designed to have a larger surface area while retaining the same relative density as the regular honeycomb. The facesheets were made out of carbon-fiber, while the core was additively manufactured using 304L stainless steel powder. Impact specimens were manufactured and tested for impact resistance. A finite element model was created to study the integrity of the sandwich structures subjected to localized impact damage. The finite element model of the damage resistance due to impact showed a good agreement with the experimental results. Samples with increased contact area showed higher impact resistance. The average impact strength of the modified samples was 41.3% higher than the average impact strength of the regular samples. Flatwise tension results showed that by increasing the contact area between the core and the facesheet the core-to-facesheet bond strength increased.

Numerical Simulation of the Evaporation Behavior of Fe-Mn Heterogeneous Powder in Selective Laser Melting Process

Multi-material additive manufacturing using heterogeneous powders as raw materials is one of the important development directions of metal additive manufacturing technology. The evaporation behavior of heterogeneous powders in the selective laser melting (SLM) process has a significant influence on the accuracy of chemical composition control and the quality of the final product. In this paper, the fusion process of Fe20Mn (80 wt.% Fe and 20 wt.% Mn) heterogeneous powder, Fe and Mn elemental powders, and Fe20Mn pre-alloyed powder is numerically simulated using FLOW-3D® software and partially validated through SLM experimental results. The morphology and the characteristics of the flow field and temperature field in the melt pool for four kinds of powder materials are analyzed. The influence of the elemental evaporation behavior of different powders on the mass loss of the Mn element is discussed. The results show that the excessive accumulation of heat increases the maximum temperature of the melt pool, thus increasing mass loss. The Fe20Mn heterogeneous powder has a wider heat-affected zone and a higher peak value of temperature, nearly 400 K higher than that of the Fe20Mn pre-alloyed powders, which exhibits an intensive evaporation behavior. The mass loss of the Mn element obtained from the SLM experiment for Fe20Mn heterogeneous powders forming parts is more than the Fe20Mn pre-alloyed powders’ forming parts for different laser powers, up to 17 wt.% at P = 120 W. This tendency is consistent with the numerical analysis of the effect of evaporation behavior of Fe–Mn heterogeneous powder during the SLM process. This study provides the necessary theoretical reference and process guidance for realizing the precise control of the SLM composition of a heterogeneous powder in multi-material additive manufacturing caused by evaporation behavior.

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.

Comparative study of Ti-6.5Al-2Zr-1Mo-1V (TA15) alloy fabricated by selective laser melting and laser metal deposition

In the present study, Ti-6.5Al-2Zr-1Mo-1V (TA15) alloy, one of the widely used near-α titanium alloys in the field of aeronautical and astronautical, was fabricated by two lasers additive manufacturing technologies, namely selective laser melting (SLM) and laser metal deposition (LMD). Microstructure, mechanical property, productivity, and forming cost of fabricated TA15 samples by these two processes were compared systematically. The results showed that the microstructure of the SLM-ed and LMD-ed samples exhibited differences in terms of crystallographic orientations, grain boundaries, and grain sizes, which was mainly attributed to the distinct thermal histories associated with each process. Such differences resulted in the LMD-ed sample presenting anisotropy, lower tensile strength, and higher elongation compared to the SLM-ed sample. Cost analysis indicated that the forming cost per unit volume of the LMD-ed sample was about half that of the SLM-ed sample. This difference was primally due to the higher productivity of the LMD process (226.1 cm3/h) compared to the SLM process (8.8 cm3/h), as well as the lower power cost of the powder materials (60 vs. 100 $/kg). Furthermore, the forming maximum volume of the LMD process (∼30.38 m3) was about 28 times than that of the SLM process (∼1.08 m3). In conclusion, this study provides a detailed comparison between SLM-ed and LMD-ed TA15 samples. The findings can act as a reference for selecting optimized fabrication methods for practical industrial applications, taking into consideration specific mechanical properties, forming size, and cost requirements.

Effect of remelting strategy on forming mechanism of selective laser melted AlSi10Mg

Selective laser melting (SLM) technology is widely used in various fields for manufacturing high-precision and complex parts. However, SLMed parts still exhibit some microstructural defects. The remelting strategy provides a new approach for defect elimination in SLM process, named as selective laser remelting (SLRM). In this study, the effects of remelting strategy on the melt pool were revealed through a finite element model. The porosity, microstructure, surface roughness, microhardness and tensile behavior of the specimens were also evaluated. The links between the formation mechanism of the melt pool and various experimental results were explored. The simulation results showed that the SLRMed melt pool had a significantly lower temperature and a shorter liquid phase time. The experimental results demonstrated that the remelting strategy effectively reduced the porosity, improved the density of the specimens, and provided a finer microstructure. The remelting strategy effectively reduced the surface roughness of the top surface of the specimens, while slightly adversely affecting the surface roughness of the side surface. Additionally, the microhardness and tensile properties of the specimens increased correspondingly due to the finer microstructure formed inside the SLRMed melt pool. These findings contribute to a better understanding and application of the remelting strategy for producing high-quality parts.

Effect of structural parameters on the surface roughness and mechanical properties of Ti-6Al-4 V alloy thin-walled structure fabricated by selective laser melting

Ti-6Al-4 V alloy (Ti64) thin-walled parts with different structural parameters including placement mode, tilt angle (θ), length and thickness were fabricated by selective laser melting (SLM). The effects of structural parameters on the surface roughness and mechanical properties were investigated to provide guidance for optimizing SLM process of thin-walled structures. Firstly, surface roughness on downdip plane is larger than that on updip plane. The thin-walled parts perpendicular to the scraper and increasing θ are beneficial for reducing surface roughness. Secondly, pores size is concentration below 50 μm, and the porosity is concentrated between 0.28% and 1.5%. The porosity shows a decreasing trend with increasing θ. Coarse columnar prior-β-Ti grains are parallel to building direction (BD), which is not affected by θ. α-Ti/β-Ti laths exhibit thickness less than 0.5 μm inside prior-β-Ti grains, and are refined with reducing thickness of the thin-walled parts. Finally, Ti64 thin-walled parts with different structure parameters exhibit relatively stable strength and plasticity, namely tensile strength of 1040–1130 MPa, yield strength of 1015–1145 MPa, and elongation of 7∼8.5%. In summary, placement mode and θ exhibit more significant impact on the final properties of the thin-walled parts, namely, perpendicular to the scraper and increasing θ are beneficial for reducing surface roughness and porosity. While the structural parameters show no significant effect on the mechanical properties.

Impact of Heat Treatment and Building Direction on Tensile Properties and Fracture Mechanism of Inconel 718 Produced by SLM Process

In the selective laser melting (SLM) additive manufacturing process of Inconel 718, the emergence of Laves and δ precipitate phases in the γ matrix during or after heat treatment is a critical consideration. This study comprehensively assesses the microstructures and mechanical properties of Inconel 718 alloy produced through SLM under varied conditions: as-built (AB), homogenization + solution + aging (HSA), homogenization + aging (HA), and solution + aging (SA). Additionally, the impact of building orientation, whether horizontal (H) or vertical (V), is investigated. The AB specimens oriented horizontally display a columnar melt pool structure, with dimensions roughly between 300 and 400 μm. In contrast, the AB specimens aligned vertically show an elongated river-like structure of melt pools, with their sizes approximately at 250 μm. From the detailed microstructural analysis, the findings reveal that the as-built specimens lack γ′ and γ″ precipitates in their microstructure. Conversely, in heat-treated specimens, both the γ′ and γ″ phases are evident. Notably, Inconel 718 alloy specimens subjected to SLM fabrication and SA heat treatment demonstrate optimal mechanical performance. Notably, SA exhibits an average hardness of 476 HV for the horizontal specimen, which is 51.1% higher than that of AB specimens. The morphology and distribution of the δ phase in the γ matrix emerge as decisive factors influencing high-temperature performance. In SA specimens, the dissolution of brittle Laves phases occurs, and the presence of the δ phase at the grain boundary imparts superior properties during high-temperature tensile testing, including excellent yield and ultimate tensile strength. The presence of the granular-δ phase in the SA specimens resulted in a tensile strength of 1422 MPa and a yield strength of 1236 MPa, which are the highest values among all the specimens. SA has a tensile strength of 1120 MPa and a yield strength of 974 MPa at 650 °C.

Influence of geometric imperfections on the mechanical behavior for Invar 36 alloy lattice structures fabricated by selective laser melting

The studies on the mechanical behavior of Invar 36 alloy lattice structures prepared by additive manufacturing process are limited. In this paper, the influence of geometric imperfections generated during the additive manufacturing process on the mechanical behavior of Invar 36 alloy lattice structures was investigated. To realize lightweight and high load-bearing capacity, lattice structures with different fillet radii were designed and subsequently fabricated by selective laser melting (SLM) process. Compression tests based on in-situ X-ray computed tomography (X-CT) were conducted to evaluate the manufacturing quality and corresponding mechanical behavior. Differences between design models and fabricated lattices were quantitatively compared. Various geometric imperfections, including strut waviness, varying cross-sections, visible surface defects, visible defects at strut intersections, and roughness on struts, were observed. Additionally, deformation patterns at different loading stages were also obtained, primarily manifesting as the yielding of the nodes and the buckling of the struts. Importantly, struts with varying cross-sections possess the most significant influence on the deformation behavior.

Multi-physics simulation of non-equilibrium solidification in Ti-Nb alloy during selective laser melting

This paper underscores the critical role of temperature distribution in the molten pool on the resulting solidification microstructure during selective laser melting (SLM) process. A powder-resolved computational fluid dynamics (CFD) model of Ti-Nb alloy is established to investigate heat transfer and fluid flow in the molten pool. When comparing the bulk model to the powder bed model, discrepancies in temperature gradient and cooling rate can reach up to 26.29% and 18.32%, respectively. Utilizing the powder bed CFD model, temperature gradient and cooling rate data at the molten pool boundary are integrated into the finite interface dissipation phase-field model. The simulation results illuminate the non-equilibrium solidification microstructure in the SLMed Ti-Nb alloy. Results indicate that the rapid solidification fosters a pronounced solute trapping effect, mitigating solute microsegregation. The microstructure manifests as cellular and dendritic structures, with Nb concentration in cellular cores and depletion in intercellular region. Predicted primary dendrite arm spacing (PDAS) or cell size range between 0.4 to 0.6 μm, consistent with experimental observations. In particular, the study reveals a transition from dendritic to cellular and from cellular to planar structures, with an accompanying analysis of the underlying mechanisms.

Multi-build orientation effects on microstructural evolution and mechanical behavior of truly as-built selective laser melting Ti6Al4V alloys

The unique combination of lightweight, strength, corrosion resistance, high-temperature resistance, and biocompatibility make Ti6Al4V alloy an important material in metal contact of solar cells, and selective laser melting (SLM) enables the production of Ti6Al4V parts complex geometries that would be difficult or impossible to produce using traditional manufacturing methods. The build orientation of SLM process presents an essential effect on the quality of the produced parts, and thus, in this study it investigates the impact of multi-build orientation (0°, 30°, 45°, 60°, 90°) on the microstructural evolution and mechanical behavior of truly as-built Ti6Al4V alloys produced by SLM. The microstructure analysis revealed the presence of ordered subsurface pores, located at a distance of about 50 μm–150 μm from the sample surface. The microstructure consisted primarily of α′ martensite with a small amount of β phase. Massive transformation was observed in the 30° and 45° samples, with corresponding grain sizes of 5 μm and 10 μm, respectively. To be specific, the content of β phase and ultimate tensile strength (UTS) varied with the sample orientation, and the 45° build orientation exhibited the highest content of β phase with value of approximately 2.8%, but also the lowest UTS and elongation, which were 1161 MPa and 3.99%, respectively.

Capillary effects and consolidation kinetics during selective laser melting of 316L powder

Selective laser melting (SLM) technology has the advantage of quickly producing complex-shaped parts. To achieve good mechanical properties, it's vital to minimize defects that can occur because of high residual porosity if incorrect processing techniques are used. One effective way to prevent defects is by using computer simulations of underlying processes before printing in the industry. This paper presents a reduced-order numerical model of SLM processing that accurately predicts material porosity by focusing on the key mechanisms that affect the melting and consolidation processes. The focus is on the formation of defects and the expected time that is required until the consolidation of a powder bed is completed. Then the elasticity of the SLM processed materials near defects is analyzed. The modeling results for powder consolidation are shown for comparison with experimental data on stainless steel 316L powder during SLM. This information can be further used for proper selection of SLM parameters such as the scanning speed and the power of the laser source.

A novel mathematical model for predicting a sustainable selective laser melting and controlled densification

ABSTRACT We introduce the innovative concept of Sustainable Laser Energy Consumption (SLEC, ε) that promotes sustainable metal additive manufacturing practices while maintaining productivity and tailored densification in the Selective Laser Melting (SLM) process. This study focuses on deriving analytical expressions through dimensional analysis and Buckingham’s π theorem to predict bulk density with high precision across studied materials: In718, W, AlSi10Mg, Ti6Al4V, and SS316L. This approach provides valuable insights and allows the setting of an appropriate combination of scanning speed and hatch distance for a range of laser power, enabling sustainable manufacturing of SLMed components with tailored density. Furthermore, the mathematical expression introduced as SLEC facilitates the tradeoff between energy consumption and productivity, promoting a greener and more sustainable future of metal additive manufacturing. Furthermore, the underlying fractal nature of SLM is explored through the investigation of the influence of fractal structures, present in the powder bed, on densification that provides information on how powder morphology and homogeneity (i.e. fractal dimension and lacunarity) of the powder bed are linked to a sustainable SLM process.

Porous Titanium/SF Sponge Composite Scaffold with Loads of Gentamicin and Small Extracellular Vesicles to Improve Antibacterial and Osteogenesis Properties

AbstractAdditive manufacturing has been widely used for producing porous titanium orthopedic implants. However, the higher surface area inherent to porous structures increases the risk of bacterial colonization. In this work, composite scaffolds with dual functions of the antibacterial and osteogenesis promotion properties are developed. The porous titanium is fabricated using a selective laser melting process to provide mechanical support. Silk fibrin (SF) sponge‐loading gentamicin and extracellular vesicles (EVs) are prepared in the pores of the porous titanium. The developed composite scaffolds are investigated for their antibacterial and osteogenesis effects. The samples exhibit well antibacterial activity against Escherichia coli. The samples also show good cytocompatibility, effectively promoting the adhesion and proliferation of the bone marrow mesenchymal stem cells (rBMSCs). EVs significantly promote the expression of osteogenesis‐related genes in rBMCSs and the superior extracellular matrix mineralization reveals that EVs have a remarkable role in enhancing osteogenic differentiation. Therefore, the composite scaffolds with dual functions of antibacterial and osteogenesis promotion properties have excellent potential for orthopedic implant applications.

3D printing of personalised stents using new advanced photopolymerizable resins and Ti-6Al-4V alloy

Purpose The development of new advanced materials, such as photopolymerizable resins for use in stereolithography (SLA) and Ti6Al4V manufacture via selective laser melting (SLM) processes, have gained significant attention in recent years. Their accuracy, multi-material capability and application in novel fields, such as implantology, biomedical, aviation and energy industries, underscore the growing importance of these materials. The purpose of this study is oriented toward the application of new advanced materials in stent manufacturing realized by 3D printing technologies. Design/methodology/approach The methodology for designing personalized medical devices, implies computed tomography (CT) or magnetic resonance (MR) techniques. By realizing segmentation, reverse engineering and deriving a 3D model of a blood vessel, a subsequent stent design is achieved. The tessellation process and 3D printing methods can then be used to produce these parts. In this context, the SLA technology, in close correlation with the new types of developed resins, has brought significant evolution, as demonstrated through the analyses that are realized in the research presented in this study. This study undertakes a comprehensive approach, establishing experimentally the characteristics of two new types of photopolymerizable resins (both undoped and doped with micro-ceramic powders), remarking their great accuracy for 3D modeling in die-casting techniques, especially in the production process of customized stents. Findings A series of analyses were conducted, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, mapping and roughness tests. Additionally, the structural integrity and molecular bonding of these resins were assessed by Fourier-transform infrared spectroscopy–attenuated total reflectance analysis. The research also explored the possibilities of using metallic alloys for producing the stents, comparing the direct manufacturing methods of stents’ struts by SLM technology using Ti6Al4V with stent models made from photopolymerizable resins using SLA. Furthermore, computer-aided engineering (CAE) simulations for two different stent struts were carried out, providing insights into the potential of using these materials and methods for realizing the production of stents. Originality/value This study covers advancements in materials and additive manufacturing methods but also approaches the use of CAE analysis, introducing in this way novel elements to the domain of customized stent manufacturing. The emerging applications of these resins, along with metallic alloys and 3D printing technologies, have brought significant contributions to the biomedical domain, as emphasized in this study. This study concludes by highlighting the current challenges and future research directions in the use of photopolymerizable resins and biocompatible metallic alloys, while also emphasizing the integration of artificial intelligence in the design process of customized stents by taking into consideration the 3D printing technologies that are used for producing these stents.

High-Strength 430 ferritic stainless steel fabricated by selective laser melting process

This study investigates the microstructure and mechanical properties of 430 ferritic stainless steel (FSS) fabricated via the selective laser melting (SLM) process. The mechanical properties and fracture morphologies of SLM-fabricated 430 FSS and conventional 430 FSS were compared in this paper. It was found that 430 FSS produced by SLM exhibits significant microstructural anisotropy, with higher dislocation density and the presence of oxides of silicon, manganese and aluminum. Regarding mechanical properties, 430 FSS fabricated via SLM process displays higher tensile strength and yield strength, as well as superior product of strength and elongation (PSE) and yield ratio, compared to those produced by conventional methods. Fracture morphology analysis revealed that SLM-fabricated 430 FSS primarily exhibited characteristics of cleavage fractures, whereas conventional 430 FSS showed typical features of ductile fractures.

Predictive Modeling of Fracture Behavior in Ti6Al4V Alloys Manufactured by SLM Process

This study focuses on ductile fracture behavior prediction for Ti6Al4V alloys fabricated via Selective Laser Melting (SLM). A modified Gurson-Tvergaard-Needleman (GTN) model characterizes void growth and shear mechanisms under uniaxial stress. The research explores the impact of Artificial Neural Network (ANN) architecture, specifically hidden layers and neurons, on predicting fracture parameters. Results reveal that increasing hidden layers substantially enhances accuracy, particularly for fracture displacement. Notably, predicting maximum force requires fewer layers than fracture displacement. Using selected layers and neurons, the system consistently achieved R2-values exceeding 0.99 for both maximum force and fracture displacement. The study identifies the initial void volume fraction (f0) parameter as having the most significant influence on both properties.

An experimental investigation of selective laser melting parameters effects on ferromagnetic properties of pure iron in both the as-built and annealed conditions

In this study, the effect of selective laser melting (SLM) parameters on the magnetic properties of pure iron has been experimentally extracted both in the as-built (A-Built) and stress-relieved (H-Treat) conditions, and the optimum levels of the parameters have been determined for optimum magnetic properties. The SLM process parameters include laser power, scanning speed, and hatch spacing, and the design of experiments was done by the Taguchi method. After manufacturing and preparing the specimens, their hysteresis curves were measured using vibrating-sample magnetometer (VSM), and the magnetic properties of the SLMed pure iron were calculated. Signal-to-noise analysis was used to determine the optimal levels of parameters for achieving the best magnetic properties. For samples’ permeability and coercivity, the best possible regression equations were extracted, and SOBOL sensitivity analysis was used to determine the most contributing input variable to the outputs. The results indicate that the laser power parameter has the most significant impact on the magnetic properties of the produced parts. Two of samples were annealed at 820 °C for 1 h, and then magnetic properties were remeasured. Although there was not a significant change in permeability, and magnetization saturation of the samples, coercive force has decreased approximately 60 %. This reduction in annealing is desirable for some AC electrical devices.

Effect of process parameters on residual stresses in SLM-formed bionic porous titanium alloy structures

Bionic porous titanium alloy structures have demonstrated broad application prospects in the field of biomedicine, and selective laser melting (SLM) has become one of the main methods for preparing porous titanium alloy structures due to its high degree of forming freedom. Residual stress is a crucial indicator for evaluating the forming quality of SLM parts, thus its control methods have garnered significant attention. Therefore, it is important to understand the process parameters' influence on the generation and regulation of residual stresses in SLM-formed bionic porous titanium alloy parts. In this paper, finite elements and experiments are employed to research the relationship between process parameters and residual stresses in the SLM process, and a method for controlling residual stresses in the key sensitive areas is proposed. It is found that increasing the laser scanning speed is conducive to reducing the residual stress of the porous structure and alleviating the phenomenon of stress concentration. Appropriately increasing the laser power can reduce the residual stress in the Z direction of the porous structure, with the optimal range being from 200 W to 250 W. Using a medium laying powder thickness (0.03 mm∼0.04 mm) results in uniformly distributed residual stress on the surface of the porous structure, leading to the attainment of maximum residual compressive stress. Building upon this foundation, the experimental verification of forming quality established stability, while the derived parameter optimization method and forming mechanism offered theoretical support for process optimization in fabricating porous titanium alloy structures through SLM.

Effects of selective laser melting process parameters on 3D-printing of Ti6Al4V/ST316L composite material and their optimization using response surface methodology

The mechanical properties of Ti6Al4V and ST316L bone implants make them superior to natural bone, which results in fewer contact points with the bone. Different manufacturing processes, such as selective laser melting (SLM), may result in different mechanical properties between Ti-6Al-4V and ST316L implants. Sustainable development for the composite implants was optimized (SLM) in this study to minimize their compressive strength and Young's modulus. A three-dimensional printing process using SLM was optimized based on laser power, hatch distance, laser velocity, and ST316L weight percentage. Composite implants made from titanium alloys and steel alloys were evaluated using response surface methodology (RSM). ST316L composition has been found to influence the mechanical properties of composites in a significant manner, based on the results of parameter optimization. Using Ti6Al4V/ST316L as a biomaterial in knee joint prostheses is possible.

Parametric Optimization of Selective Laser Melted 13Ni400 Maraging Steel by Taguchi Method

Parametric Optimization of Selective Laser Melted 13Ni400 Maraging Steel by Taguchi Method