Selective Laser Melting Metal Research Articles

Design of nonlinear gradient sheet-based TPMS-lattice using artificial neural networks

Gradient triply periodic minimal surface (TPMS) structures are renowned for lightweight design and enhanced performance, but their complex and nonlinear configurations pose challenges in achieving targeted design goals. A new design methodology for the nonlinear gradient structure was proposed in this study, with the aim of achieving efficient and accurate modeling of complex and gradient sheet-based TPMS structures under specific performance objectives. This method utilized automated finite element (FE) simulations to obtain structure topology element densities under various boundary conditions. An artificial neural network (ANN) was then employed to efficiently predict the correspondence between these boundary conditions and topology element densities. A mapping was established between topology element densities and TPMS structural parameters, and the gradient structure was accurately constructed by using the voxel modeling technique. Taking a typical cantilever beam TPMS structure as an example of nonlinear gradient design, the results indicate that the error between the ANN-predicted and FE-simulated structure topology element densities is only 2.73 %, with prediction time being only 0.15 % of the simulation time. The thin regions of the gradient structure align with those geometrically removed in regular topology optimization scheme, achieving up to 65.45 % weight reduction, a 28.72 % improvement over the regular scheme, along with uniform structural stress transition and maximum stress reduction. TC4 alloy nonlinear gradient TPMS structures, printed by metal selective laser melting (SLM) technique, confirm the practical application value of this design method.

Analysis of printing time components and powder utilisation efficiency of metal selective laser melting process in case of 316L and Ti6Al4V materials

ABSTRACT In selective laser melting technology, the productivity and the efficiency of powder utilisation were examined. Individual components of the printing time were determined by developing a specially designed model. Two main components of the powder recoating and the laser exposure time were given as a function of the filling ratio of the cross-section. Based on the results, the spreading time can increase the printing time by several hours, depending on the filling factor of the cross-section. In the case of a sampling of 70 prints, the individual elements and process of the powder usage were determined, as well as the mass measurement of the different amounts of powder in the case of 316L and Ti6Al4V materials. It turned out that 45–80% of the powder amount is not used to build the model, which is an essential for both printer users and equipment developers for material cost prediction.

Reactor design via scan line patterning: An implicit approach to create scalable microstructured parts in selective laser melting

The adaptation of additive manufacturing for chemical flow reactors has recently gained momentum as the methods become more advanced and equipment is increasingly affordable. With the design of periodic open cellular structures (POCS) from metal selective laser melting (SLM), structured catalyst substrates can be realized in a much more ordered fashion than well-established metal foams with a random structure. Hence, tailored transport properties are achieved and flow profiles are homogenized, eliminating flow channeling and stagnant flow zones.However, with current SLM methods, the minimal achievable feature size and therewith the specific surface area is still limited. Moreover, the size of finely resolved STL files that define the structure grows exponentially with decreasing feature sizes, further limiting the scalability of methods with direct structure definition.In this work, we present a method for implicit structure design by metal SLM with specific surface areas and porosities that compete with established catalyst substrates. The definition of the microstructure is realized by control of the laser scan lines, where single scan lines create fine struts. The general applicability of our method to various metal materials is demonstrated by production from stainless steel and copper. In a numerical study for a model steam reforming application, we show that the POCS provide mass transfer coefficients and volumetric reaction rates that compete with benchmark substrates.Scan line patterning therefore provides a promising method to create highly ordered, well-scalable substrates for heterogeneous catalysis from a wide range of materials, e.g., for the application in highly efficient small-scale reactors.

Compressive Behavior of Various BCC Lattice Structure

The lattice structures are a particular type of structures made by the multiply of a unit cell. In addition, their structure is close to some physiological tissues and bone structure, which can allow their use to develop prostheses needed to the rehabilitation or replacement of a body part. Lattice structures are widely used in various engineering applications due to their high weight-to-strength ratio and exceptional energy absorbing performance. The feasibility of using different base materials to fabricate these cellular structures with complex geometries has been significantly widen with the development of additive manufacturing (AM) technology. Additive manufacturing in particular metal selective laser melting (SLM) processes are rapidly being industrialized. In this work, samples with different lattice structures were manufactured by SLM technique using CoCr powder alloy. Compression tests were carried out to characterize their mechanical behavior. Starting from a BCC lattice cell measuring 5x5x5mm and 1mm diameter of the strut, were designed using Catia V5 R19 software. The BCC lattice unit cell consists of 4 solid struts with circular cross-section by which they intersected at 45°angle and modify by adding radius at the intersection of all four struts, furthermore the empty space is filled with BCC cell to increase the stiffens of the structure. The BCC cell was duplicate in three directions (X, Y, Z) measuring 20mm in each direction. To obtain the final part the BCC structure ware intersected with a cylindrical part measuring 20mm in Z direction, 15mm diameter and 1mm wall thickness, resulting a cylindrical part with three different BCC lattice structure inside.

Применение SLM-технологии для изготовления деталей оборудования нефтеперерабатывающих предприятий

The paper presents the results of work on re-engineering of safety critical parts of imported equipment, including the selectionof parts optimally suited for manufacturing by the additive technology (AT) method using additivity coefficient calculations, creation of 3D-models and design documentation, material execution of parts, construction by the selective laser melting of metals (SLM) method. The paper comprises of analysis of the structure on different axes of construction, mechanical characteristics and hardness of the material obtained by the AT method. In the study of the structure and strength characteristics, anisotropy associatedwith layer-by-layer growth of the part is revealed. The main disadvantage of the structure obtained by the SLM method is porosity, but with the developed printing modes, this parameter can be controlled and a quality structure with a minimum porosity size(up to 2 μm) can be guaranteed.

An improved high order smoothed particle hydrodynamics method for numerical simulations of selective laser melting process

Metal selective laser melting (SLM) is an important Additive Manufacturing (AM) technology, which directly melts and solidifies metal parts by heating metal or alloy powder with laser. High-fidelity numerical simulations could provide tools for insight investigations of the SLM processes. In this study, an improved high order smoothed particle hydrodynamics (SPH) method was developed to simulate the melting and solidification process of metal selective laser melting. In the improved high order SPH model, the improved kernel gradient correction (KGC) is developed to overcome the non-conservation problem of traditional KGC. And an improved surface tension model is developed to improve the stability and accuracy of modeling the surface tension. In order to establish the numerical model for simulating the SLM forming process, the Gaussian heat source model and melting latent heat model are introduced. Moreover, particle shifting technology integrated with X-SPH technology are applied to improve the uniform of particle distributions stability of calculation. A number of test examples are investigated with the improved high order SPH, and compared with results from other approaches including traditional SPH. From the obtained numerical results, we can conclude the improved high order SPH is effective in modeling the melting and solidification process of SLM.

Effect of SiC Addition on Microhardness and Relative Density during Selective Laser Melting of 316L Stainless Steel

The utilization of 316L stainless steel has been very common in marine, automotive, architectural, and biomedical applications due to its adequate corrosion resistance to cracks after the completion of welding process. However, there has been ongoing attempts to investigate the potential enhancement in the strength and durability of 316L stainless steel by reinforcing it with silicon carbide (SiC). The present work adopts the selective laser melting (SLM) technique to fabricate SiC-reinforced 316L steel to boost its microhardness and strength properties. The methodology involved the addition of 1% wt. silicon carbide with particle sizes <40 μm to reinforce the stainless steel matrix. An SLM metal printing machine equipped with a continuous wave of 300 W fiber laser is employed to form the specimens. To measure the properties of the final product, EDX, XRD, FESEM, and universal tensile test machines have been used. The maximum value of 296 HV was obtained for a 1% volume of SiC compared to the 285 HV microhardness of pure stainless steel 316L. FESEM examination showed that the SiC microparticles were dissolved completely and they were randomly distributed in the melting basin. The samples were dissolved entirely, and the best porosity was obtained at 0.4% with influential parameters of 200 W laser power, 70 µm hatching distance, 30 µm layer thickness, and 700 mm/s velocities. The results also revealed that the microhardness at these parameters is the best compared to the samples produced with different values. The volumetric energy density was also considered. The findings can be informative to the researchers and manufacturers interested in 316L steel industry.

Expert consensus for selective laser melting metal prostheses

Having been widely reviewed and revised, a recommended clinical expert consensus based on the results of experimental and clinical studies for selective laser melting (SLM) metal prostheses was released by the Society of Maxillofacial Prosthetics, Chinese Stomatological Association. This expert consensus formulates the standardized operation procedures for SLM metal restoration and is aimed at standardizing the clinical application of SLM metal restoration and improving the quality and long-term success rate of SLM metal prostheses. At the same time, this expert consensus will help to widely promote the clinical usage of this technique.

Prediction model of surface roughness of selective laser melting formed parts based on back propagation neural network

AbstractIn this article, selective laser melting (SLM) equipment is used to print 316L stainless steel parts under different process parameters, and the surface roughness of the parts is measured. Based on back propagation neural networks (BP neural networks, BPNN), the upper surface roughness prediction model is established. The laser power, scanning speed, and scanning interval are used as model input, and the surface roughness of the workpiece is output. This model can easily and quickly predict the surface roughness of SLM metal printing, with high prediction accuracy, and can provide a basis for the optimization of SLM process parameters.

Quantitative simulation of selective laser melting of metals enabled by new high-fidelity multiphase, multiphysics computational tool

Laser powder bed fusion represents the future for metal additive manufacturing. Advance of this emerging technology is bottlenecked by the unavailability of high-fidelity prediction tools for cost-effective optimization on printing design. Simulations of selective laser melting of metals must tackle a complex granular solids and multiphase fluids system that undergoes intra- and inter-phase interactions and thermal-induced phase changes, including melting, vaporization, and solidification, which are challenging to model. We develop a high-fidelity computational tool to provide high-resolution simulations of the multiphase, multiphysics processes of selective laser melting (SLM). Key to this tool is a multi-phase, semi-coupled resolved Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). It contains innovative features including (1) a fully resolved immersed boundary CFD with fictitious particle domain coupling with DEM for resolving mechanical interactions and heat transfers between solid particles and surrounding fluid; (2) An evaporation model in consideration of the Knudsen layer implemented in the volume of fluid (VOF) method which is enriched by two sharp interface capture schemes, isoAdvector and MULES, for accurate identification of the vaporization process and phase boundaries of fluids with different Courant numbers; and (3) a ray tracing model compatible with the VOF method for high-resolution of absorbed laser energy. We demonstrate the proposed method can quantitatively reproduce key observations from synchrotron experiments and captures critical interdependent physics involving melt pool morphology evolution, vapor-driven keyhole dynamics and powder motions. This new computational tool opens a new avenue for quantitative design and systematic optimization of laser powder bed fusion and may find wider engineering applications where thermal induced phase changes in a multi-phase system are important.

Modeling and simulation of metal selective laser melting process: a critical review

Modeling and simulation of metal selective laser melting process: a critical review

Investigation of the effect of lattice structure on the fluid flow and heat transfer of supercritical CO2 in tubes

• Combined experimental and numerical methods to study supercritical heat transfer. • Effects of composite vortex on supercritical fluid and heat transfer were studied. • BCC lattice was used for supercritical CO 2 heat transfer experiment. • Experimental section was fabricated by SLM metal additive manufacturing. • The heat transfer deterioration was suppressed with an acceptable pressure drop. Under specific conditions of low mass flux and high heat flux, heat transfer deterioration (HTD) occurs in tubes, which is detrimental to the supercritical CO 2 heat exchanger. To suppress the HTD and promote the overall heat transfer capability of supercritical CO 2 in a vertical heated tube, the effect of the body-centered cubic (BCC) lattice structure on the fluid flow and heat transfer characteristics were studied. The BCC lattice structure was applied to a supercritical heat transfer experiment by exploiting selective laser melting (SLM) metal additive manufacturing. The results of the experimental and numerical studies indicate that the BCC lattice structure can effectively suppress the HTD by generating a composite vortex composed of a horseshoe vortex at the leading edge of the lattice ligaments, the streamwise vortex at the trailing edge of the ligaments, and the counter-rotating longitudinal vortex at the center of the ligaments. The vortex system strengthens the local turbulence intensity and enhances flow mixing, thus weakening the buoyancy effect and suppressing the HTD. Compared with the smooth tube, the average heat transfer coefficient of the tube with BCC lattice structure increased by up to 100%, whereas the pressure drop increased by 13.5%.

Force and Microstructure Variation of SLM Prepared AlMgSc Samples during Three-Point Bending.

Lightweight parts manufactured by metal selective laser melting (SLM) are widely applied in machinery industries because of their high specific strength, good energy absorption effect, and complex shape that are difficult to form by mechanical machining. These samples often serve in three-dimensional stress states. However, previous publications mainly focused on the unidirectional tensile/compressive properties of the samples. In this paper, AlMgSc samples with different geometric parameters were prepared by the SLM process, and the variation of force and microstructure during three-point bending were systematically investigated. The results demonstrate that the deformation resistance of these samples has good continuity without mutation in bending, even for brittle materials; the bending force-displacement curves exhibit representative variation stages during the entire bending process; the equivalent bending strength deduced from free bending formula is not applicable when compactability is less than 67%. The variations of grain orientation and size of the three representative bending layers also show regularity.

Advancing of Additive-Manufactured Titanium Implants with Bioinspired Micro- to Nanotopographies.

There is an increasing demand for low-cost and more efficient titanium (Ti) medical implants that will provide improved osseointegration and at the same time reduce the likelihood of infection. In the past decade, additive manufacturing (AM) using metal selective laser melting (SLM) or three-dimensional (3D) printing techniques has emerged to enable novel implant geometries or properties to overcome such potential challenges. This study presents a new surface engineering approach to create bioinspired multistructured surfaces on SLM-printed Ti alloy (Ti6Al4V) implants by combining SLM technology, electrochemical anodization, and hydrothermal (HT) processes. The resulting implants display unique surfaces with a distinctive dual micro- to nano-topography composed of micron-sized spherical features, fabricated by SLM and vertically aligned nanoscale pillar structures as a result of combining anodization and HT treatment. The fabricated implants enhanced hydroxyapatite-like mineral deposition from simulated body fluid (SBF) compared to control. In addition, normal human osteoblast-like cells (NHBCs) showed strong adhesion to the nano-/microstructures and displayed greater propensity to mineralize compared to control surfaces. This engineering approach and the resulting nature-inspired multiscale-structured surface offers desired features for improving osseointegration and antibacterial performance toward the development of next-generation orthopedic and dental implants.

Laser line scanner aptitude for the measurement of Selective Laser Melting parts

When looking for any metrological verification of parts manufactured by metal laser printing with optical equipment, it is necessary to ensure the traceability of the measurements that can be obtained. The difficulty of this process lies in the fact that these measurements are obtained on point clouds captured from surfaces with high form errors and poor surface finishes, even when this type of surface usually undergoes processes to improve the surface finish, such as sandblasting. This research focuses precisely on the analysis of the metrological suitability of a laser line scanner (laser triangulation sensor) on parts manufactured by Selective Laser Melting (SLM).The study starts from the design of a test part specifically oriented to the printing process with SLM metal powder bed. This test part was printed in 17-4PH stainless steel and then sandblasted. The test part was measured in a Coordinate Measuring Machine (CMM), obtaining reference GD&T values. The measurement was carried out under pre-sandblasting ("as built") and post-sandblasting conditions, thus providing interesting information about the erosion rate of this post process. A state-of-the-art laser sensor was employed for the metrological comparison, mounted on the same available CMM that was used for contact measurements.In this research three analyses were carried out: the quality of 3D metal printed parts with respect to CAD model, the effect of the sandblasting post-process, and the accuracy of the measurements obtained with the laser line sensor. In addition, this work conducts an in-depth study about the influence of point cloud treatment and filtering procedures, by comparing the filtering methods applied by different reverse engineering software packages. The study leads to the conclusion that filters based on the standard deviation of the point cloud are the best candidates in order to obtain laser measurements closer to the contact measurements.

Finite element modeling of residual stress and geometrical error formations in selective laser melting of metals

Recent works, both numerical and experimental, on residual stress and geometrical errors in selective laser melting-produced parts highlighted the preponderance of these phenomena. However, their mechanisms of appearance are not yet fully explained. An in-house finite element model was developed and implemented to reproduce their formations. The consistence of the model with existing simulation results and with respect to experimental observations was checked. Simulations were then performed using a computational design of experiments to better comprehend the underlying phenomena and the influence of the laser speed and power. Relationships between process parameters and residual stress, plastic strain, and geometrical errors formations have been put into evidence which can support optimization procedures at design stage.

Inoculation treatment of an additively manufactured 2024 aluminium alloy with titanium nanoparticles

Considerable studies on metal selective laser melting (SLM) have proved the necessity to refine microstructure parts fabricated by SLM in order to eliminate property anisotropy, hot-tearing and to increase the SLM-processability. In the present work, Ti nanoparticles, at the first time, were discovered to be an extremely effective inoculant for an SLMed 2024 aluminium alloy. 0.7 wt% addition of Ti nanoparticles was capable of substantially eliminating the hot-tearing cracks and columnar structure, and refining the grains in the SLMed 2024 alloy in a broad processing window. The substantial grain refinement in the Ti-inoculated 2024 alloy was attributed to the in-situ formation of Al3Ti nanoparticles with a L12 ordered structure, which formed a coherent interface with Al matrix and therefore significantly promoted the heterogeneous nucleation of the α-Al during solidification of melt pools in the SLM process. After a conventional T6 heat treatment, this SLMed alloy exhibited a superior balance of strength and ductility (tensile strength was up to 432 ± 20 MPa and elongation of 10 ± 0.8%), which was comparable to its wrought counterpart. This work can be considered as a breakthrough in research of fabricating high-strength aluminium alloys using SLM.

Inoculation Treatment of an Additively Manufactured 2024 Aluminium Alloy with Titanium Nanoparticles

Considerable studies on metal selective laser melting (SLM) have proved the necessity to refine microstructure parts fabricated by SLM in order to eliminate property anisotropy, hot-tearing and to increase the SLM-processability. In the present work, Ti nanoparticles, at the first time, were discovered to be an extremely effective inoculant for an SLMed 2024 aluminium alloy. 0.7 wt.% addition of Ti nanoparticles was capable of substantially eliminating the hot-tearing cracks and columnar structure, and refining the grains in the SLMed 2024 alloy in a broad processing window. The substantial grain refinement in the Ti-inoculated 2024 alloy was attributed to the in-situ formation of Al3Ti nanoparticles with a L12 ordered structure, which formed a coherent interface with Al matrix and therefore significantly promoted the heterogeneous nucleation of the α-Al during solidification of melt pools in the SLM process. After a conventional T6 heat treatment, this SLMed alloy exhibited a superior balance of strength and ductility (tensile strength was up to 432 ± 20 MPa and elongation of 10 ± 0.8%), which was comparable to its wrought counterpart. This work can be considered as a breakthrough in research of fabricating high-strength aluminium alloys using SLM.

选区激光熔化激光功率对316L不锈钢熔池形貌及残余应力的影响

选区激光熔化激光功率对316L不锈钢熔池形貌及残余应力的影响

Revealing hot tearing mechanism for an additively manufactured high-entropy alloy via selective laser melting

Hot tearing mechanisms of a high-entropy alloy CoCrFeNi additively manufactured by selective laser melting have been investigated. Intergranular hot cracks are present regardless of various parameters used, suggesting poor laser-based printability for the alloy. Elemental segregation does not exist at the grain boundary that favours the hot cracking. We find that severe residual stress induced by the large grain size is the root cause for the intergranular cracking. The classic Rappaz-Drezet-Gremaud model is used to predict the characteristic depression pressure limit beyond which hot tearing will occur for the selective laser melting of metals and alloys.