Selective Laser Melting Process Parameters Research Articles

Experimental Study of Performance of Ti-6Al-4V Femoral Implants Using Selective Laser Melting (SLM) Methodology

Selective laser melting (SLM) technology used for the design and production of porous implants can successfully address the issues of stress shielding and aseptic loosening associated with the use of solid implants in the human body. In this paper, orthogonal experiments were used to optimize the process parameters for SLM molding of Ti-6Al-4V (TC4) material to investigate the effects of the process parameters on the densities, microscopic morphology, and roughness, and to determine the optimal process parameters using the roughness as a judging criterion. Based on the optimized process parameters, the mechanical properties of SLM-formed TC4 alloy specimens are investigated experimentally in this paper. The main conclusions are as follows: the optimal combination of roughness is obtained by polar analysis, the microhardness of SLM-molded TC4 alloy molded specimens is more uniform, the microhardness of specimens on the side and the front as well as the abrasion resistance is higher than that of casting specimens, the yield strength and tensile strength of specimens is higher than that of ASTM F136 standard and casting standard but the elongation is not as good as that of the standard, and the elasticity and compressive strength of porous specimens are higher than that of casting specimens at different volume fractions. The modulus of elasticity and compressive strength are within the range of human skeletal requirements. This work makes it possible to fabricate high-performance porous femoral joint implants from TC4 alloy SLM-molded materials.

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.

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.

Selective laser melting and mechanical behavior of Mo-coated diamond particle reinforced metal matrix composites

Defects, such as pores, microcracks, and thermal damage, pose significant challenges in the selective laser melting (SLM) process of diamond reinforced metal matrix composites. To address these issues, this study utilizes Mo-coated diamond particles prepared via salt bath plating for SLM processing of CoCr-diamond composites. The SLM process parameters including laser power, scanning speed, and hatch spacing were systematically optimized using the response surface method (RSM). Subsequently, the microstructure and mechanical properties of the SLMed CoCr-diamond composites were thoroughly investigated. Notably, a protective layer of Mo2C is formed on the surface of diamond particles during the salt bath plating process. When compared to the SLMed CoCr-15 vol% Mo-uncoated diamond composite, the Mo coating significantly enhances the compressive strength by 69 % and flexural strength by an impressive 345 % for the CoCr-15 vol% Mo-coated diamond composite.

Study on the effects of the processing parameters on the single tracks and the block support structures fabricated by selective laser melting

In order to prevent the deformation of the part, enhance heat conduction, and establish a stable foundation, additional support structures are typically incorporated beneath the parts during the selective laser melting (SLM) process. These structures are subsequently eliminated once the SLM process is completed, thereby facilitating the attainment of near-net forming. Therefore, their SLM processing parameters should be different from those of the solid parts to obtain the desirable functions and removability. However, there is so far very little research focusing on the optimization of the SLM processing parameters of the support structures compared with the solid objects. In this work, the widely used block support was illustrated as an instance, and an optimization strategy of its SLM processing parameters was provided. The effects of laser power, scanning speed, and layer thickness on the morphology and qualities of single track, support sample, and support tensile sample were systematically investigated. The results showed that the SLM processing parameters have a significant impact on the properties of the block support by regulating the qualities of the single tracks. At last, a group of optimal SLM processing parameters (80 W of laser power, 400 mm/s of scanning speed, 60 μm of layer thickness) was determined for the Ti-6Al-4V titanium alloy, and the corresponding ultimate tensile strength of the support structure reached 416 MPa.

Enhancing mechanical properties of selective-laser-melting TiN/AISI 420 composites through Taguchi GRA and PCA multi-response optimization

The enhancement of mechanical properties in martensitic AISI 420 stainless steel is realized through the incorporation of TiN ceramic particles using the selective laser melting (SLM) method. This study introduces an innovative hybrid mixing method designed to uniformly disperse TiN within the AISI 420 matrix, ensuring the absence of agglomerations and contaminations in the feedstock for the SLM process. Employing a combined approach involving the Taguchi method, Grey Relational Analysis, and Principle Component Analysis, optimal processing parameters and TiN content are identified, encompassing a laser power of 350 W, laser speed of 370 mm/s, hatch distance of 0.07 mm, layer thickness of 0.05 mm, and one percent by weight of TiN particles. The optimized SLM sample showcases exceptional characteristics with a hardness of 743 ± 20 HV, tensile strength of 1822 ± 21 MPa, and a modulus of toughness of 99.7 ± 3.0 J/m3, surpassing existing results. Introducing TiN particles into the AISI 420 matrix with suitable SLM processing parameters induces significant microstructural alterations, reinforcing the matrix and elevating the mechanical properties. These results mark a substantial advancement in metal matrix composite materials by applying cutting-edge manufacturing techniques.

Process parameter effects estimation and surface quality prediction for selective laser melting empowered by Bayes optimized soft attention mechanism-enhanced transfer learning

Additive Manufacturing (AM), particularly Selective Laser Melting (SLM), has revolutionized the industrial manufacturing sector owing to its remarkable design flexibility and precision. However, it is well known that slight changes in SLM process parameters may highly affect the surface quality of the as-built product. In this paper, we investigate the influence of SLM printing parameters (laser power, laser scanning speed, layer thickness, and hatch distance) on surface quality and develop a predictive model for surface quality based on the given printing parameters. The developed model is constructed by a Bayesian Optimization and soft Attention mechanism-enhanced Transfer learning (BOAT) framework with superior domain adaptability and generalization capability. Through experimental validation, the effectiveness of the BOAT approach in estimating printing parameters and correlating them with surface quality has been verified. The comprehensive methodology, experimental configurations, prediction results, and ensuing discussions are all presented. This study contributes to providing valuable insights and practical implications for improving the competitiveness and impact of SLM in advanced manufacturing by accurately predicting surface quality with specified printing parameters.

Phase Composition, Microstructure and Mechanical Properties of Zr57Cu15Ni10Nb5 Alloy Obtained by Selective Laser Melting

Zr57Cu15Ni10Nb5 (more known as Vit-106) is a promising zirconium-based alloy with a high glass-forming ability, and belongs to the so-called bulk metallic glasses (BMG). Workpieces with a size of around one centimeter in all three dimensions can be obtained from a BMG alloy by casting. However, further increasing the cast size decreases the cooling rate and thus induces crystallization. Selective laser melting (SLM) is a well-known technique to overcome size limitations for BMGs because a workpiece is built by the addition of multiple melt portions in which the cooling rate is kept above the critical one. Currently, BMG parts obtained by SLM suffer from partial crystallization. The present work studies the influence of SLM process parameters on the partial crystallization of Vit-106 by metallography and the influence of the microstructure on mechanical properties by microhardness and wear resistance testing. Submicron crystalline inclusions are observed in an amorphous matrix of a Vit-106 alloy obtained by SLM. The size and the concentration of the inclusions can be controlled by varying the laser scanning speed. It is shown that submicron crystalline inclusions formed in the amorphous matrix during SLM can favorably affect microhardness and wear resistance.

Comprehensive optimization of selective laser melting process parameters for microstructure, density, hardness, and tribological performance of pure copper

This study is concerned with the optimisation of the processing parameters for the selective laser melting (SLM) of pure copper. The influence of these parameters on the microstructure, density and mechanical properties of copper samples produced by SLM is investigated in detail. Taguchi analysis is used to assess the importance of key building parameters including layer thickness, laser spot size and hatch distance on density. In addition, ANOVA is used to describe the contribution of each parameter to the density. The results reveal that layer thickness is the most effective parameter on density with an impact rate of 88.86%. Contrary to this situation, it appears that the effect of laser spot size and hatch distance on the density is quite limited, with an impact rate of 2.57% and 0.10%, respectively. Optimum results, including a relative density of 95.4% and a hardness of 63 HV, are achieved under specific parameters: a layer thickness of 0.03 mm, a hatch distance of 110 mm and a laser spot size of 70?m. This study provides a valuable insight into SLM processing of pure copper and offers practical recommendations for optimising the parameters used.

In situ TiC reinforced Ti6Al4V matrix composites manufactured via selective laser melting

PurposeCurrent methods for the preparation of composite powder feedstock for selective laser melting (SLM) rely on costly nanoparticles or yield inconsistent powder morphology. This study aims to develop a cost-effective Ti6Al4V-carbon feedstock, which preserves the parent Ti6Al4V particle’s flowability, and produces in situ TiC-reinforced Ti6Al4V composites with superior traits.Design/methodology/approachTi6Al4V particles were directly mixed with graphite flakes in a planetary ball mill. This composite powder feedstock was used to manufacture in situ TiC-Ti6Al4V composites using various energy densities. Relative porosity, microstructure and hardness of the composites were evaluated for different SLM processing parameters.FindingsHomogeneously carbon-coated Ti6Al4V particles were produced by direct mixing. After SLM processing, in situ grown 100–500 nm size TiC nanoparticles were distributed within the α-martensite Ti6Al4V matrix. The formation of TiC particles refines the Ti6Al4V β grain size. Relative density varied between 96.4% and 99.5% depending on the processing parameters. Hatch distance, exposure time and point distance were all effective on relative porosity change, whereas only exposure time and point distance were effective on hardness change.Originality/valueThis work introduces a novel, cost-effective powder feedstock preparation method for SLM manufacture of Ti6Al4V-TiC composites. The in situ SLM composites achieved in this study have high relative density values, well-dispersed TiC nanoparticles and increased hardness. In addition, the feedstock preparation method can be readily adapted for various matrix and reinforcement materials in future studies.

Quality assurance thermophysical aspects of highly porous implants with cellular structure obtained by selective laser melting

Selective laser melting (SLM) is an additive manufacturing process that involves the layer-by-layer construction of a three-dimensional object by local melting of a powder layer based on a prepared CAD model. This technology makes it possible to manufacture products of complex configuration, including internal channels of complex geometry. Such products include personalized highly porous implants, which are subject to very strict requirements in the field of elastic and strength properties, ensuring their compliance with the properties of the biological objects being replaced. The quality of highly porous cellular products formed by the selective laser melting method based on metal powder compositions is determined by a significant number of factors, the combined influence of which is difficult to control. At the same time, the structure and mechanical properties of highly porous cellular materials (HPCM) obtained by laser synthesis are largely determined by the melt bath shape stability, which depends on the ability of local heat dissipation, which in turn is determined by the fused product geometry. Under these conditions, simulation of thermal processes, including the prediction of the part fusion temperature modes, is of paramount importance. This study focuses on the numerical analysis of the powder layer thermophysical parameters during the laser melting process, which is difficult to analyze by direct measurements, and a computational model based on COMSOL Multiphysics has been created to predict the melt bath temperature field. The numerical model made it possible to quantify the influence of the selective laser melting process parameters (laser power and scanning speed) in combination with the choice of material and topology of the part on the temperature fields formation to determine the process technological parameter and the features of creating geometry for additive manufacturing, which make it possible to obtain products of proper quality. Cellular implants based on Ti6Al4V powder have been grown by selective laser melting.

Multi-objective optimization to specify optimal selective laser melting process parameters for SS316 L powder

PurposeThis paper adopts a modified Taguchi approach to develop empirical relationships to the performance characteristics (output responses) in terms of process variables and demonstrated their validity through comparison of test data. The method suggests a few tests as per the orthogonal array and provides complete information for all combinations of levels and process variables. This method also provides the estimated range of output responses so that the scatter in the repeated tests can be assessed prior to the tests.Design/methodology/approachIn order to obtain defect-free products meeting the required specifications, researchers have conducted extensive experiments using powder bed fusion (PBF) process measuring the performance indicators (namely, relative density, surface roughness and hardness) to specify a set of printing parameters (namely, laser power, scanning speed and hatch spacing). A simple and reliable multi-objective optimization method is considered in this paper for specifying a set of optimal process parameters with SS316 L powder. It was reported that test samples printed even with optimal set of input variables revealed irregular shaped, microscopic porosities and improper melt pool formation.FindingsFinally, based on detailed analysis, it is concluded that it is impossible to express the performance indicators, explicitly in terms of equivalent energy density (E_0ˆ*), which is a combination of multiple sets of selective laser melting (SLM) process parameters, with different performance indicators. Empirical relations for the performance indicators are developed in terms of SLM process parameters. Test data are within/close to the expected range.Practical implicationsBased on extensive analysis of the SS316 L data using modified Taguchi approach, the optimized process parameters are laser power = 298 W, scanning speed = 900 mm/s and hatch distance = 0.075 mm, for which the results of surface roughness = 2.77 Ra, relative density = 99.24%, hardness = 334 Hv and equivalent energy density is 4.062. The estimated data for the same are surface roughness is 3.733 Ra, relative density is 99.926%, hardness is 213.64 Hv and equivalent energy density is 3.677.Originality/valueEven though equivalent energy density represents the energy input to the process, the findings of this paper conclude that energy density should no longer be considered as a dependent process parameter, as it provides multiple results for the specified energy density. This aspect has been successfully demonstrated in this paper using test data.

The effect of selective laser melting process parameters and remelting scanning strategy on relative density and surface hardness of stainless steel 316L

Selective laser melting (SLM) process is the foremost metal additive manufacturing (AM) technology that precisely generates complex geometries from CAD files. Mechanical behavior of printed parts is greatly affected by printing parameters and defining the optimal values of the process parameters to enhance the mechanical properties of components is highly regarded. In this work, four different SLM parameters including scanning speed, laser power, hatch spacing and scan pattern angle were applied to manufacture SS316L parts. For investigating the effect of each parameter and their interactions on hardness and relative density, Taguchi L16 orthogonal array was employed. The influence of part geometry and remelting is also evaluated in order to optimize the hardness and relative density of components. The results exhibited that the laser scanning speed was the most predominant SLM parameter for investigated mechanical properties. Analyzing the regression formula obtained from the results showed that the optimum laser energy density resulted in a 0.37% and 5.38% increase compared to the lowest relative density and hardness, respectively. High remelting energy associated with low remelting scanning speed, caused an 8.5% and 17.9% rise in hardness of squares and triangles, respectively; however, it led 12.5% reduction in hardness for circles. Remelting caused a 2.32% reduction, 2.1% increase and 5.3% rise on relative density for circles, squares and triangles, respectively.

Recommendation of SLM Process Parameters Based on Analytic Hierarchy Process and Weighted Particle Swarm Optimization for High-Temperature Alloys.

Selective laser melting (SLM) of high-temperature alloys involves intricate interdependencies among key process parameters, such as laser power and scanning speed, affecting properties such as density and tensile strength. However, relying solely on experiential knowledge for process parameter design often hampers the precise attainment of target requirements. To address this challenge, we propose an innovative approach that integrates the analytic hierarchy process (AHP) and weighted particle swarm optimization (WPSO) to recommend SLM process parameters for high-temperature alloy fabrication. Our proposed AHP-WPSO model consists of three main steps. First, a comprehensive historical database is established, capturing the process parameters and performance metrics of high-temperature alloy SLM parts. Utilizing an AHP framework, we compute the performance similarity between target and historical cases, applying rational thresholds to identify analogous cases. When suitable analogs are elusive, the model seamlessly transitions to the second step. Here, the WPSO model optimizes and recommends process parameters according to target specifications. Lastly, our experimental validation of the GH4169 high-temperature alloy through SLM experiments corroborates the effectiveness of our AHP-WPSO model in making process parameter recommendations. The outcomes underscore the model's high accuracy, attaining a recommendation precision of 99.81% and 96.32% when historical analogs are present and absent, respectively. This innovative approach offers a robust and reliable solution to the challenges posed in SLM process parameter optimization for high-temperature alloy applications.

Towards Selective Laser Melting of High-Density Tungsten

Selective laser melting (SLM) of tungsten (W) is challenging due to its high melting point and brittleness, resulting in defects including balling phenomenon, porosity and cracks. In this work, high-density crack-free SLM W was fabricated by employing cost-effective powders modified through air jet milling. The influence of the SLM processing parameters on microstructure, density, crack formation and the resulting mechanical properties of SLM W was investigated. Laser energy density and hatch distance were found to be the most important parameters in controlling porosity and crack formation of SLM W. The check-like microstructure in horizontal plane was induced by the difference in thermal gradients, which were caused by the movement of the heat source between overlapping regions and central regions of the molten pool. Combined efforts including powder modification through air jet milling, a 67° rotation scanning strategy, a hatch distance of 0.08 mm and a laser speed of 450 mm/s result in dense crack-free SLM W with relative density of 99.3%, microhardness of 403 HV50, and bending strength of 154 MPa. Additionally, the microstructure changed upon annealing at 1200 °C, accompanied by the reduced anisotropy of mechanical properties on both horizontal and vertical plane.

Topological design and high-performance additive manufacturing of porous femoral implants

The use of porous implants can successfully address the issues of stress shielding and sterile loosening associated with the use of solid implants in the human body. Implant structures can be designed and produced using topology optimization (TOP) and selective laser melting (SLM). In this paper, a unit-optimized structure with better mechanical properties is obtained by topology optimization as the femoral implant constitutive unit. The orthogonal experiment is used to optimize the process parameters of SLM molding Ti-6Al-4 V material to determine the optimal process parameters based on the judging criterion of density. Finally, the SLM technique is used to mold the optimized porous femoral implants. The results of the above study are found as follows: The volume fraction of the optimized cell structure is effectively reduced to 30%, effectively solving the stress shielding problem. Based on the optimal process parameters, the surface of the SLM molded porous femoral implant is clear, with good connection to adjacent unit structures and no overhang on the surface, indicating good molding quality. The application of high-performance porous femoral implants is made possible by this work.

Predictability assessment of as-built hardness of Ti-6Al-4V alloy fabricated via laser powder bed fusion

Evaluating the predictability of selective laser melting (SLM) process has been a persistent endeavor in the manufacturing community since the technique’s inception. The ability to accurately predict the as-built hardness of fabricated parts is critical to judge its serviceability for specific applications. This investigation aims at achieving such predictability with as little as experimentation possible. In this research, reliable historical SLM data was mined on as-built Ti-6Al-4V alloy, from technical articles published over the past fifteen years. Three predictive models of Gaussian Process Regression (GPR), Neural Network (NN) and parametric Multiple Linear Regression (MLR) were built for as-fabricated bulk hardness of Ti-6Al-4V alloy manufactured via SLM. Ten-fold cross-validation training of the models involved a substantial 1,284 spatial datapoints of major SLM process parameters such as laser power, scanning speed, hatch spacing, layer thickness and volumetric energy density. Ultimate assessment of hardness predictability was performed by making predictions on ten cubic Ti-6Al-4V test coupons fabricated using a SLM machine. The GPR model stood out amongst other models, yielding a mean absolute prediction error of 6.12 HV over all samples. The overall predictability of these models came out to be in declining order of GPR > NN > MLR. Rudimentary characterization of test coupons revealed variation in observed hardness. Two tiers of robust validations, comprehensive dataset, statistical insights, actual experimental validation and material characterization make this study extremely unique for as-fabricated hardness of SLM-ed Ti-6Al-4V alloy.

Selective Laser Melting Process Parameter Optimization on Density and Corrosion Resistance of 17-4PH Stainless Steel

Selective Laser Melting Process Parameter Optimization on Density and Corrosion Resistance of 17-4PH Stainless Steel

Magnetic and mechanical properties of additive manufactured Fe-3wt.%Si material

In this work, the Fe-3wt.%Si soft magnet with a very low porosity was obtained successfully via additive manufacturing of selective laser melting (SLM) after optimizing the SLM processing parameters. The magnetic properties under different conditions and the mechanical performances including microhardness, tensile properties and tribological behavior were investigated and described in detail. The results showed that the soft magnet exhibited a typical columnar structure with an oriented growth of building direction (BD) and a 〈001〉 texture along the BD. The selective laser melted (SLM) Fe-3wt.%Si magnet showed a typical soft magnetic property with a very low ratio between magnetization saturation (Ms) and residual magnetization (Mr). The power loss (P) at excitation frequency f = 50 Hz and maximum flux density B = 1 T in alternating current (AC) condition under the condition was 18.8 w/kg. Due to the relatively low microhardness, the magnet showed good mechanical performance with an elongation of 8.8%, ultimate tensile strength, yield strength of 562 MPa, 445 MPa, respectively. A mixed-mode of ductile and brittle failure was the dominant rupture mechanism. This SLM Fe-3wt.%Si magnet showed a good wear resistance with a relatively low wear rate of 5.3 × 10-5 mm3/(N•m). The adhesive wear and abrasive wear are the dominant wear mechanisms.

A short review on SLM-processed Ti6Al4V composites

The advancements in computer-aided design, manufacturing, and additive manufacturing techniques attracted the researcher to apply various new methods with the unique combination of alloys and composites to design and develop complex parts. Among them the selective laser melting (SLM) process, a branch of additive manufacturing, and Ti6Al4V (Ti64) composite. Due to the better mechanical and corrosion resistance characteristics of Ti64 and its composites, they have been utilized for making various engineering parts related to jet engine fans of aero-engine, engine valves of automobiles, knee and hip joint endoprosthesis in the biomedical field, and corrosion resistance pipes in chemical industries. Also, more complex, net-shaped, and lattice-structured components can be fabricated by advancing the SLM process. The final quality of the parts manufactured from the SLM technique will depend on the fabrication process parameters followed. Many researchers have done research work on metal additive manufacturing by changing and optimizing the SLM process parameters such as laser power ( P), scanning speed ( v), hatch spacing ( d), and layer thickness ( h). Also, they have studied the effect of changes on the feedstock preparation, SLM process parameters, milling time of composite and post-heat treatment on the quality of Ti6Al4V composites. Therefore, a detailed review is needed to study the effect of the abovementioned parameters on the quality of metal additively manufactured parts through SLM. Hence, a short review is done on future challenges and opportunities of SLM-processed Ti6Al4V composites and reported in this article.