Application Of Selective Laser Melting Research Articles

Optimization design of support structure based on 3D printing technology

Parts are often warped and deformed when they are molded using selective laser melting (SLM) technology. Thus, it is necessary to study the addition support modes of parts molded using SLM. Consequently, we designed dendritic, E-stage and conical supports, having different structural parameters and different partitions using Magics, and then, we analyzed their performances using the finite element software Abaqus. The structural parameters of the supports were optimized and finally tested using SLM molding technology. The maximum stress concentration was found for dendritic supports, followed by E-stage supports, and then conical supports. The stress concentration and deformation level of Scheme 2 were less than those of Scheme 1. The stress intensity and deformation levels for two partitions were less than those for three partitions. For parts molded by SLM, the deformation was maximum for conical supports, followed by dendritic supports, and then E-stage supports. When gradient supports of similar volumes were added, additional partitions did not effectively improve the molding quality. When supports of similar volumes were added, adding gradient supports did not effectively improve the molding quality. The results provide a basis for the application of SLM in molding high-precision parts.

Structure and mechanical properties of PR-03N18K9M5TYu steel grade fabricated by selective laser melting and post-processing

We fabricate samples of PR-03N18K9M5TYu steel (equivalent to ChS4) using selective laser melting (SLM) in a nitrogen atmosphere. Our research focused on the influence of hot isostatic pressing (HIP) combined with heat treatment (HT), specifically hardening and aging, on the steel's structure and its physical and mechanical properties (σucs, σys, δ, ψ). Through tensile testing, we evaluated the impact of post-processing treatments (HIP followed by HT) on the material's strength. We also assessed how different post-processing protocols affected residual porosity. Our findings indicate that samples exhibiting the highest strength and plastic properties correspond to those with the least structural defects and minimal residual porosity. In-depth microstructural analysis revealed that the optimal structure–a fine-grained, homogeneous configuration–is achieved via the combined application of SLM, HIP, and subsequent HT. The improvement in mechanical properties can be primarily attributed to the dispersed hardening effect, which is a consequence of the precipitation of the superfluous Ni3Ti phase. Fractographic examination revealed that the post-processing leads to a ductile and dimple fracture, occurring through mechanisms of shearing and detachment, giving rise to mixed-type fractures. The samples that displayed superior mechanical properties were characterized by a homogenous ductile intergranular fracture surface with clear evidence of plastic deformation. We measured the hardness (Н), modulus of elasticity (Е), and elastic recovery via indentation methods. The post-processing treatments notably enhanced material hardness and elastic modulus, with an increase from H = 4.6 GPa and E = 194 GPa in the sample post-HIP to H = 8.5 GPa and E = 256 GPa following HIP coupled with hardening and aging.

Preparation and Performance Study of Titanium‐Based Nanocomposites in Selective Laser Melting: Microstructure Regulation and Optimization of Mechanical Properties

This study focuses on exploring the application of selective laser melting (SLM) technology in the preparation of titanium‐based nanocomposite materials. By introducing 0.5 wt% graphene oxide (GO) and 7.0% nanomolybdenum (Mo) powder, an attempt is made to improve the microstructure and mechanical properties of titanium alloy materials. The experimental results indicate that the microstructure of the titanium‐based nanocomposite material undergoes significant crystal refinement and phase transition behavior, suggesting a positive role of introducing nanoreinforcing phases in crystal structure regulation. Simultaneously, the introduction of GO significantly improves the thermal conductivity of the material, contributing to more uniform energy transfer and temperature distribution, thereby optimizing the process control of laser melting. In terms of mechanical performance, through microhardness and tensile performance tests, the microhardness of TC4–0.5GO–7Mo increases by ≈30.8% compared with pure TC4. This strengthening effect is primarily attributed to the uniform distribution of GO and Mo powder in the matrix, effectively hindering lattice slip and dislocation movement, enhancing the hardness and tensile properties of the material. Through a comprehensive analysis of microstructure and mechanical properties, not only the mapping relationship between the microstructure and mechanical properties of titanium‐based nanocomposite materials is clarified but also the strengthening mechanism is revealed.

Selective Laser Melting and Spark Plasma Sintering: A Perspective on Functional Biomaterials.

Achieving lightweight, high-strength, and biocompatible composites is a crucial objective in the field of tissue engineering. Intricate porous metallic structures, such as lattices, scaffolds, or triply periodic minimal surfaces (TPMSs), created via the selective laser melting (SLM) technique, are utilized as load-bearing matrices for filled ceramics. The primary metal alloys in this category are titanium-based Ti6Al4V and iron-based 316L, which can have either a uniform cell or a gradient structure. Well-known ceramics used in biomaterial applications include titanium dioxide (TiO2), zirconium dioxide (ZrO2), aluminum oxide (Al2O3), hydroxyapatite (HA), wollastonite (W), and tricalcium phosphate (TCP). To fill the structures fabricated by SLM, an appropriate ceramic is employed through the spark plasma sintering (SPS) method, making them suitable for in vitro or in vivo applications following minor post-processing. The combined SLM-SPS approach offers advantages, such as rapid design and prototyping, as well as assured densification and consolidation, although challenges persist in terms of large-scale structure and molding design. The individual or combined application of SLM and SPS processes can be implemented based on the specific requirements for fabricated sample size, shape complexity, densification, and mass productivity. This flexibility is a notable advantage offered by the combined processes of SLM and SPS. The present article provides an overview of metal-ceramic composites produced through SLM-SPS techniques. Mg-W-HA demonstrates promise for load-bearing biomedical applications, while Cu-TiO2-Ag exhibits potential for virucidal activities. Moreover, a functionally graded lattice (FGL) structure, either in radial or longitudinal directions, offers enhanced advantages by allowing adjustability and control over porosity, roughness, strength, and material proportions within the composite.

Improving the quality of AISI H13 tool steel produced by selective laser melting

AISI H13 tool steel is intended for making various tools and die-casting molds, which generally are of complex shapes. The application of selective laser melting (SLM) can significantly speed up their production, but it is accompanied by the appearance of various defects, such as high surface roughness, cracking, and reduced density. In particular, there is a fairly limited amount of data on the influence of SLM process parameters on the surface roughness of tool steels. The aim of this work is to study the possibility of improving the quality of AISI H13 steel by varying laser power and scanning speed during SLM. Optical profilometry and microscopy are used as methods of investigation, with statistical data analysis being carried out. It has been discovered that both surface roughness and porosity can be effectively influenced by varying the laser power and scanning speed during SLM. A direct relationship between surface roughness and porosity has been established, and this makes it possible to control effectively the quality of AISI H13 tool steel produced by selective laser melting. Steel of the highest quality with the lowest surface roughness and porosity has been obtained at a laser power of 250 W and a scanning speed of 350 mm/s. It has also been found that varying laser power and scanning speed does not prevent crack formation, and other technological solutions should be sought to eliminate cracking.

Coupling Analysis on Microstructure and Residual Stress in Selective Laser Melting (SLM) with Varying Key Process Parameters.

With the application of Selective Laser Melting (SLM) technology becoming more and more widespread, it is important to note the process parameters that have a very important effect on the forming quality. Key process parameters such as laser power (P), scan speed (s), and scanning strategy (μ) were investigated by determining the correlation between the microstructure and residual stress in this paper. A total of 10 group 316L specimens were fabricated using SLM for comprehensive analysis. The results show that the key process parameters directly affect the morphology and size of the molten pool in the SLM deposition, and the big molten pool width has a direct effect on the larger grain size and crystal orientation distribution. In addition, the larger grain size and misorientation angle also affect the size of the residual stress. Therefore, better additive manufacturing grain crystallization can be obtained by reasonably adjusting the process parameter combinations. The transfer energy density can synthesize the influence of four key process parameters (P, v, the hatching distance (δ), and the layer thickness (h)). In this study, it is proposed that the accepted energy density will reflect the influence of five key process parameters, including the scanning trajectory (μ), which can reflect the comprehensive effect of process parameters more accurately.

Characterisation of the multiple effects of Sc/Zr elements in selective laser melted Al alloy

The widespread application of selective laser melting (SLM) fabricated high performance lightweight Al components is hindered by the available commercial alloys due to their limited mechanical properties and processability. The introduction of Sc/Zr elements to the Al matrix for SLM provides conspicuous benefits, including grain refinement, precipitation strengthening and high thermal stability. In the present study, the multiple effects of Sc/Zr elements in SLM fabricated Al alloy are systematically investigated, using the recently developed Al-Mn-Sc alloy as an example. The application of Sc/Zr elements generated an unconventional heterogeneous grain structure characterised by the alternative growth of columnar-equiaxed grains in the molten pool, which effectively avoided the solidification cracks and alleviated the mechanical property anisotropy issues. The formation of the heterogeneous grain structure is mainly attributed to the precipitation of the primary Al3(Sc,Zr) particles which dependent on the local solidification conditions. The post heat treatment was also conducted to clarify the role of Sc/Zr additions on stress relieve effect and precipitation hardening effect. Moreover, the room temperature and elevated temperature mechanical properties of the SLMed Al-Mn-Sc alloy were also evaluated. The fundamental understanding of the Sc/Zr benefits in the SLM fabricated Al alloy is expected to shed light on future high performance Al alloy development specifically for the additive manufacturing process.

In situ monitoring methods for selective laser melting additive manufacturing process based on images — A review

Selective laser melting (SLM) has been widely used in the fields of aviation, aerospace and die manufacturing due to its ability to produce metal components with arbitrarily complex shapes. However, the instability of SLM process often leads to quality fluctuation of the formed component, which hinders the further development and application of SLM. In situ quality control during SLM process is an effective solution to the quality fluctuation of formed components. However, the basic premise of feedback control during SLM process is the rapid and accurate diagnosis of the quality. Therefore, an in situ monitoring method of SLM process, which provides quality diagnosis information for feedback control, became one of the research hotspots in this field in recent years. In this paper, the research progress of in situ monitoring during SLM process based on images is reviewed. Firstly, the significance of in situ monitoring during SLM process is analyzed. Then, the image information source of SLM process, the image acquisition systems for different detection objects (the molten pool region, the scanned layer and the powder spread layer) and the methods of the image information analysis, detection and recognition are reviewed and analyzed. Through review and analysis, it is found that the existing image analysis and detection methods during SLM process are mainly based on traditional image processing methods combined with traditional machine learning models. Finally, the main development direction of in situ monitoring during SLM process is proposed by combining with the frontier technology of image-based computer vision.

High‐Temperature Mechanical Behavior Assessment based on a Developed Constitutive Model of Inconel 718 Fabricated by Selective Laser Melting

Inconel 718, a typical nickel‐based superalloy, is widely used to fabricate high‐temperature components in aerospace and power industries. Conventional “subtractive” processes confront numerous problems due to the complicated structures. The application of selective laser melting (SLM), as one of the additive manufacturing (AM) techniques, is promising in part fabrication and repairment in the aerospace industry. Tensile tests with different strain rates and strain‐controlled cycling tests with different strain amplitudes are conducted in this study at a high temperature of 600 °C to assess the mechanical behavior of SLM‐built Inconel 718 and reinforce its application. Experimental data reveal that a relatively concise constitutive model incorporating damage is proposed on the basis of Chaboche's framework. Modifications to isotropic hardening and damage evolution rules are performed to embed lifetime prediction capacity. Simulated results achieve a good agreement with the experimental results. Microstructures of fatigue fracture surface are analyzed to further understand the fracture mechanism. The results show that both intergranular and intragranular fracture modes and the dimples signify ductility. Overall, this study presents significant techno‐economic implications in assessing the competence of SLM‐built Inconel 718 components used in real serving conditions and also provides a reference to improve the SLM preparation process.

Effect of atmosphere on the microstructure and properties of additively manufactured tungsten

The working atmosphere greatly affects the melting and solidification processes in powder-based additive manufacturing. In this work, pure tungsten components were fabricated by selective laser melting (SLM) under argon and nitrogen, respectively. The effects of the atmosphere and processing parameters on densification, microstructures, and phases were investigated. Tungsten processed under nitrogen exhibited a higher density, lower roughness, and superior mechanical performance than that processed under argon. The high dynamic viscosity of liquid tungsten in argon induced balling and pore formation during the laser melting process, leading to relatively low density and poor mechanical properties of the SLM-processed tungsten that was manufactured in argon. The results help to promote the practical application of SLM for complicated tungsten components in the nuclear and military industries.

Reduction in anisotropic response of corrosion properties of selective laser melted Co–Cr–Mo alloys by post-heat treatment

ObjectivesThe application of selective laser melting (SLM) to dentistry has been rapidly expanding; however, SLM-processed parts possess orientation-dependent properties (i.e., anisotropy) that can affect the long-term reliability of the dental prostheses. This study aimed to evaluate the anisotropic corrosion response of SLM-processed Co–Cr–Mo alloys under various heat treatments. MethodsSamples fabricated via SLM along the horizontal plane (x-y plane) and vertical plane (x-z plane), with respect to the build direction, were subjected to various heat treatments. The resulting microstructures of the samples were characterized, and their corrosion properties were evaluated using anodic polarization and immersion tests. ResultsAll samples showed similar transpassive behavior of the polarization curves. However, the immersion tests showed that the as-built x-z plane samples released significantly more metal ions than those fabricated on the x-y plane because of the larger area of preferentially corroded molten pool boundaries (MPBs) in the x-z plane samples. Our results further demonstrated that the heat treatments eliminated the MPBs, resulting in isotropic corrosion properties. However, excessive heat treatment at high temperatures induces the formation of coarse precipitates, resulting in a less-protective passive film. SignificanceThe post-build heat treatments at temperatures that eliminate the MPBs are effective in reducing anisotropic corrosion behavior, and the lowest possible temperature is suitable for reducing the amount of released metal ions. These findings are expected to facilitate the application of SLM in dentistry to allow fast and precise production of prosthetic devices.

The Influence of Process Parameters and Scanning Strategy on Lower Surface Quality of TA15 Parts Fabricated by Selective Laser Melting

With superior flexible manufacturing capability, selective laser melting (SLM) has attracted more and more attention in the aerospace, medical, and automotive industries. However, the poor quality of the lower surface in overhanging structures is still one of the factors that limits the wide application of SLM. In this work, the influence of process parameters and scanning strategy on the lower surface quality of SLMed TA15 (Ti-6Al-2Zr-1Mo-1V) titanium alloy parts were studied. The results showed that the laser surface energy density (EF) had a significant influence on the quality of the lower surface. Excessive EF led to obvious sinking of the molten pool and a serious slag hanging phenomenon. However, the too low EF easily contributed to the insufficient powder fusion in the lower surface area, which led to the agglomeration of a molten pool during core processing, resulting in slag hanging, pores, and powder spalling that reduced the quality of the lower surface. Moreover, the cross-remelting strategy and non-remelting strategy gained better surface quality at the low EF and high EF, respectively. In addition, it was found that the quality of the lower surface could be quickly and accurately evaluated by the cooling time of the molten pool during the processing of the lower surface. This research can increase the understanding of the forming mechanism of the lower surface and has certain guiding significance for the process optimization of the lower surface.

Compressive fatigue properties of additive-manufactured Ti-6Al-4V cellular material with different porosities

Selective laser melting (SLM) is a novel additive manufacturing (AM) technique for producing cellular metallic materials with designed pore structures. SLM Ti-6Al-4V cellular alloys have been extensively studied for biomedical and other applications. The objective of this study was to investigate the effects of porosity (33 vol%, 50 vol%, and 84 vol%) on the compressive fatigue performance and fracture mechanism of an SLM Ti-6Al-4V cellular material with a new cuboctahedron COH-Z unit cell. Furthermore, the influences of hot isostatic pressing (HIP) at 1000 °C/150 MPa on the fatigue properties and fracture were also examined in this study.The results showed that the fatigue strain slowly accumulated when the stress cycle was below the 70% fatigue life. After the 70% fatigue life, the ratcheting strain rate (dε/dN) gradually increased. A shear band along a direction inclined at ~45° to the stress axis could be definitely identified at about 95% fatigue life, as demonstrated by the digital image correlation technique. With further increases in the stress cycle, the shear band was intensified and finally led to rapid fatigue failure. The HIP process did not alter the fracture behaviors of the SLM cellular alloy, although the fatigue life was much improved by several times. On the other hand, the fatigue endurance ratio of the SLM cellular alloy with 33 vol% was 0.5. Raising the porosity from 33 vol% to 84 vol% reduced the endurance ratio from 0.5 to 0.15 due mainly to the high notch sensitivity of α′-martensite in the SLM cellular alloy. The HIP treatment changed the microstructure from α′-martensite to lamellar α+β phases and thus significantly improved the fatigue endurance performance. With the combination of the COH-Z unit cell and HIP treatment, the endurance ratios at 106 cycles of the Ti-6Al-4V cellular alloy with porosities of 33 vol% to 84 vol% were as high as 0.5. This superior endurance ratio is advantageous to the long-term application of SLM Ti-6Al-4V cellular alloy.

Enabling Electropolishing of Complex Selective Laser Melting Structures

Abstract In the last years the industrial application of selective laser melting (SLM) has been increased. Main advantages of SLM are the reduction of production time for small batches and the freedom to generate complex designs. However, the rough surface quality of SLM parts currently limits their use and hinders the application in several industry sectors such as the hygienic and food industry. Due to the high complexity of SLM parts, the application of conventional processes is limited. Electropolishing (EP) is a promising process for reducing the roughness of simple SLM parts. However, it has not yet been explored intensively on complex SLM parts. Additionally, design constraints for the design of SLM parts to enable post processing are not yet existent. This experimental study investigates the resulting roughness of EP on different SLM design elements. Three types of EP were investigated, direct current, pulse/pulse reverse current and pulsed current EP. Additionally, the current density and processing time were varied. The SLM test sample (316L) contains internal pipe surfaces with different diameters in different orientations, overhangs and a lattice structure. To analyze the surface roughness, the arithmetic mean height of the roughness (Sa) was measured. At the end of the paper the findings on the process and the design constraints for SLM parts are summarized. The results show a significant improvement of the roughness on the external surfaces of the test sample for all parameter sets. The orientation of the surfaces with respect to the build direction influences the reduction of Sa. Increasing the pipe diameter leads to an increasing effect of internal EP. Finally, the DC parameter set showed a significantly better improvement of the Sa value on the internal lattice structure.

Assessment of the Mechanical Properties of AlSi10Mg Parts Produced through Selective Laser Melting Under Different Conditions

Additive manufacturing technologies of metals are gaining increasing interest due to several advantages; among these processes the selective laser melting (SLM) is of particular interest for industrial applications. Despite the clear advantages related to this technique, there are some issues that still hamper a mainstream industrial application of SLM, one is the repeatability of the process. It is well known that varying, for instance, the building direction or the position in the building chamber the components obtained show different microstructures and mechanical properties, several authors are trying to develop processing routes aiming to increase the repeatability of the process. Another issue is the fact that different SLM equipment, produced by different manufacturers, even if the process parameters adopted are the same will lead to the production of components with slightly different properties. These differences are due to small differences among the different equipment, for instance the gas used in the chamber or the way the laser is delivered. The scope of this work is to investigate the mechanical properties of AlSi10Mg components produced with different SLM machines: EOS M400, SLM 280 and RENISHAW AM400. Aiming to assess which are the differences and try to find a range of properties that can be assumed for SLMelted parts. Tensile specimens, designed according to ASTM standard, were printed with the above-mentioned equipment and tensile tests were carried out. The results obtained showed that slight differences can be outlined among the different samples and a range of tensile properties has been also proposed.

3D Printing of Ion Optics for Electric Propulsion

Additive manufacturing is rapidly opening its way into many areas of the aerospace industry, where different 3D printing technologies are finding niche applications in which they do not only simplify the process and allow shorter lead times, but also the particularities of these new fabrication methods yield new material properties that enhance the component and can lead to higher performance and longer service life of an aerospace system. Although rapid manufacturing processes are being tested for in-space manufacturing and are commonly used to fabricate UAV parts and some spacecraft subsystems with 3D printed components have been tested in space, little research has been conducted on the potential application of these techniques to electric thrusters. This paper presents the study conducted on the application of selective laser melting, a powder bed fusion technology, to the fabrication of ion engine grids and the challenges faced during the process. The first proof of concept and its optimization are described. Later, the development of the selective laser melting process for molybdenum, the study of the 3D printed materials’ properties, their direct application to ion extraction systems, and the tests of additively-manufactured ion optics are described. It was found that 3D printed grids can be accurately fabricated with titanium and molybdenum, that they perform similar to conventional optics in short tests, that the selective laser melting process allows certain control of the coefficient of thermal expansion of the output and that this fabrication method allows the reproduction of sputtering erosion patterns. Future research in this direction will cover sputtering tests of selectively-laser-melted samples and the additive manufacturing of carbon-carbon grids.

Dynamic Loading of Lattice Structure Made by Selective Laser Melting-Numerical Model with Substitution of Geometrical Imperfections.

Selective laser melting (SLM) is an additive technology that allows for the production of precisely designed complex structures for energy absorbing applications from a wide range of metallic materials. Geometrical imperfections of the SLM fabricated lattice structures, which form one of the many thin struts, can lead to a great difference in prediction of their behavior. This article deals with the prediction of lattice structure mechanical properties under dynamic loading using finite element method (FEA) with inclusion of geometrical imperfections of the SLM process. Such properties are necessary to know especially for the application of SLM fabricated lattice structures in automotive or aerospace industries. Four types of specimens from AlSi10Mg alloy powder material were manufactured using SLM for quasi-static mechanical testing and determination of lattice structure mechanical properties for the FEA material model, for optical measurement of geometrical accuracy, and for low-velocity impact testing using the impact tester with a flat indenter. Geometries of struts with elliptical and circular cross-sections were identified and tested using FEA. The results showed that, in the case of elliptical cross-section, a significantly better match was found (2% error in the Fmax) with the low-velocity impact experiments during the whole deformation process compared to the circular cross-section. The FEA numerical model will be used for future testing of geometry changes and its effect on mechanical properties.

The influence of process parameters on vertical surface roughness of the AlSi10Mg parts fabricated by selective laser melting

In recent years, the aluminum alloys parts produced by Selective Laser Melting (SLM) are increasingly used instead of casting aluminum alloys parts in the automotive, aerospace and other fields. However, the high surface roughness of the vertical surfaces is a major issue influencing the application of SLM for aluminum. Moreover, most of the methods to reduce the surface roughness, such as polishing, bead blasting or machining, will increase the production delays and costs. The present study aims at evaluating the effect of linear energy density on the surface roughness of the vertical planes. Both deposited tracks and volumetric specimens were produced and the morphologies and the surface roughnesses were measured. The obtained results indicate that the surface roughness of the vertical planes was reduced to 4 μm from 15 μm when deposited a suitable linear energy density, reducing the surface roughness by more than 70%. The surface morphologies and the height change rate of the deposited tracks had a significant influence on the surface roughness. Furthermore, for experiments with the same linear energy density, the surface roughness was improved with higher laser power.

Parameters optimization for horizontally built circular profiles: Numerical and experimental investigation

Selective laser melting (SLM), a type of additive manufacturing (AM) process, is chosen for direct fabrication of powder-based functional metallic objects. The designing of small circular geometries or overhang surfaces built parallel to platform bed has been a subject of concern in the industrial application of SLM. This paper presents an attempt to design and fabricate horizontally built circular holes in a simple cubic model in SLM machine. The processing parameters for down-skin such as laser power, scan speed, and the number of scanned layers were found to play a significant role in the sustainability of small hole built without support structures. The lower incident energy in down-skin region prevents excess melting of powder particles. The Numerical study on ANSYS was first carried out to identify the melt pool depth with different processing parameters and later SLM machine was used to produce the specimens for visual inspection. The results were found satisfactory with the application of down-skin parameters (65 W, 1000 mm/s) subjected to scanning of 3–5 layers above the exposed surface.

Comparison of Vacuum Sintered and Selective Laser Melted Steel AISI 316L

AbstractThe paper presents the results of the basic mechanical properties determined in the static tensile test, impact un-notched Charpy test and hardness of austenitic stainless steel type 316L produced by two techniques: classical pressing and sintering in a vacuum with rapid cooling and selective laser melting (SLM). In this work fracture surface of Charpy test, samples were studied.The results indicate that application of selective laser melting (SLM) makes it possible to double increase the strength properties of components manufactured from austenitic stainless steel type 316L compared to sintering in a vacuum. Resulted in mechanical properties strongly depend on porosity characteristic and the presence of superficial oxides in the case of sintered steel and the character of observed microstructural defects deriving from non-fully melted powder particles and the formation of voids between subsequently melted pool tracks during the SLM.