Selective Laser Melting Printing Research Articles

Enhanced thermoelectric properties of 3D printed Bi2Te2.7Se0.3 by atomic interface engineering

The performance of n-type Bi2Te3 materials prepared by selective laser melting (SLM) 3D printing technology tends to be lower than p-type materials. Herein, a bottom-up interface engineering strategy based on Atomic Layer Deposition (ALD) is presented to improve the properties of n-type Bi2Te2.7Se0.3 (BTS) materials prepared by SLM. To validate this strategy, a ZnO ultrathin layer was applied to the grain boundaries of BTS, synergistically optimizing carrier/phonon transport. In terms of electrical transport, the energy filtering effect triggered by the constructed ZnO/BTS interface effectively enhances the Seebeck coefficient of the Bi2Te3 material printed by SLM, substantially increasing the power factor. Additionally, the high thermal stability of the ALD-deposited ZnO ultrathin layer effectively suppresses the volatilization of Te in BTS, regulating the carrier concentration. Regarding thermal transport properties, the multiscale defects introduced by the non-equilibrium solidification process during SLM printing cause effective phonon scattering across a wide frequency range, which in turn reduces the thermal conductivity of the material. Atomic-level interface modification in SLM-printed BTS enhanced the ZT value to 1.25. Exploiting this superior thermoelectric performance, a thermoelectric module was constructed. It demonstrated a conversion efficiency of 5.7 % with a temperature difference of 200 K, comparable to the advanced Bi2Te3-based thermoelectric modules. The integration of an ALD interface modification strategy with SLM technology has not only demonstrated potential applications in Bi2Te3-based thermoelectric material development, but also bears significant importance for the accelerated advancement of high-performance thermoelectric materials in other systems.

Trueness of 3D-printed cobalt chromium versus titanium removable partial denture clasps.

The purpose of this in vitro study was to evaluate the trueness of removable partial denture clasps fabricated with titanium (Ti) through the selective laser melting (SLM) technique compared to cobalt-chromium alloys (CoCr). A virtual Aker clasp was designed on a scanned tooth, and SLM printers were used to print 20 claps using cobalt chromium (n = 10) and titanium alloy (n = 10). The deviation between the printed clasps and reference design was measured using the surface matching software (Geomagic control x) at rest, retentive tip, reciprocal tip, retentive shoulder, and reciprocal shoulder. An Independent t-test was used to determine the influence of 3D-printed material on the trueness (a = 0.05). The gap distance in mm between the reference design and printed in titanium showed an average of 0.0001 ±0.0544, 0.0256 ±0.1309, 0.0230 ±0.1028, 0.0701 ±0.1234, and 0.0013 ±0.0735mm in rest, reciprocal arm tip, retentive arm tip, retentive arm shoulder, and reciprocal arm shoulder, respectively. The gap distance in mm between the reference design and printed clasps in CoCr alloy showed an average of 0.0316 ±0.0692, 0.2783 ±0.1678, 0.1446 ±0.1528, 0.0315 ±0.0906, and 0.0419 ±0.1088mm in rest, reciprocal arm tip, retentive arm tip, retentive arm shoulder, and reciprocal arm shoulder, respectively. The difference between titanium and CoCr alloys at each observation site was significant. Clasps fabricated from titanium with SLM printing have the least deviation and better trueness compared to those fabricated from cobalt chromium.

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.

Effective heat conduction evaluation of lattice structures from selective laser melting printing

Lattice structures are promising for the applications as heat exchange media since additive manufacturing technology is able to prepare the parts in complex shapes. Thermal conduction performance is one of the key indicators evaluating the heat transfer capability of heat exchange media, and it is quantified by the effective thermal conductivity. The present study is to evaluate the heat conduction performance of lattice structures used as lightweight materials in industries. In order to design and fabricate lattice structures with controllable thermal conduction performance, the effects of structure design variables such as topology, porosity, specific surface area, and cross-section area on effective thermal conductivity of selective laser melting processed lattice structures are investigated systematically by experimental and numerical approaches. The results show that either decreasing the porosity or specific surface area increases the effective thermal conductivity of specific lattice structures. It is also found that the effective thermal conductivity increases up to 50.67% when the minimum cross-section area is enlarged along with the main heat conduction direction under the same porosity and specific surface area.

Current Status and Challenges of Powder Bed Fusion-Based Metal Additive Manufacturing: Literature Review

Powder bed fusion (PBF) is recognized as one of the most common additive manufacturing technologies because of its attractive capability of fabricating complex geometries using many possible materials. However, the quality and reliability of parts produced by this technology are observed to be crucial aspects. In addition, the challenges of PBF-produced parts are hot issues among stakeholders because parts are still insufficient to meet the strict requirements of high-tech industries. This paper discusses the present state of the art in PBF and technological challenges, with a focus on selective laser melting (SLM). The review work focuses mainly on articles that emphasize the status and challenges of PBF metal-based AM, and the study is primarily limited to open-access sources, with special attention given to the process parameters and flaws as a determining factor for printed part quality and reliability. Moreover, the common defects due to an unstrained process parameter of SLM and those needed to monitor and sustain the quality and reliability of components are encompassed. From this review work, it has been observed that there are several factors, such as laser parameters, powder characteristics, material properties of powder and the printing chamber environments, that affect the SLM printing process and the mechanical properties of printed parts. It is also concluded that the SLM process is not only expensive and slow compared with conventional manufacturing processes, but it also suffers from key drawbacks, such as its reliability and quality in terms of dimensional accuracy, mechanical strength and surface roughness.

Boosting thermoelectric performance of n-type Bi2Te2.7Se0.3 alloy by 3D printing induced in-situ texture engineering

Rational design of microstructure in thermoelectric materials is conducive to improve the thermoelectric properties. Bismuth telluride alloys are easy to form texture during sintering due to the weak van der Waals bonding between the Te-Te layers. However, high content of texture will greatly deteriorate the out-of-plane electrical properties and in-plane thermal properties. Herein, the bulk sample of n-type Bi2Te2.7Se0.3 with controllable texture degree was obtained by selective laser melting (SLM) 3D printing technology. By setting the appropriate laser power density, the epitaxial growth of some grains in the melt pool can be suppressed and controlled texturing of the material can be achieved. The printed Bi2Te2.7Se0.3 alloy shows texture-dependent thermoelectric properties by texture control ensuring that the Bi2Te2.7Se0.3 alloy has both high carrier mobility and strong phonon scattering, leading to a competitive ZT ∼ 1.21 at 373 K. Based on excellent thermoelectric properties, we have assembled a 127-pair thermoelectric module with a conversion efficiency of 6.2 % at a temperature difference of 213 K, and the corresponding output performance is comparable to that of state-of-art bismuth telluride thermoelectric modules. This study illustrates the potential of texture engineering based on SLM printing in developing high-performance thermoelectric materials.

Comparison on mechanical behavior and microstructural features between traditional and AM AISI 316L

AbstractThe aim of the present work is to investigate the difference in mechanical behavior between AISI 316L obtained by the turning process and that obtained by selective laser melting (SLM). To obtain a correlation between mechanical behavior and microstructure, static tensile and fatigue tests were performed, monitoring the energy release of the material adopting, respectively, the static thermographic method (STM) and the Risitano's thermographic method (RTM). Failure analysis was performed using optical and scanning electron microscopy. The corrosion resistance was evaluated by the double‐loop electropotential reactivation (DL‐EPR). Worst mechanical properties, both under static and fatigue loading conditions, loss of corrosion resistance, and heat dissipation compared to traditional stainless steel have been found. These findings can be attributed to microstructural defects typical of the SLM printing technology.

Effect of artificial aging on the strength, hardness, and residual stress of SLM AlSi10Mg parts prepared from the recycled powder

This study investigated the effect of artificial aging on the hardness, strength, and residual stress of SLM (Selective Laser Melting) AlSi10Mg parts prepared from recycled powder used for 30 SLM printing cycles. First, an analysis was conducted for a comparison of recycled and virgin powders; it revealed that the powders have the same shape and phase and chemical composition. The only significant differences were the slightly increased average particle size and higher oxygen content in the recycled powder, especially on the powder surface. Typical molten pools were found in the microstructure, and a fine cellular type of structure was observed. The peripheral areas of the molten pools contained coarser cells with an average size of 0.6 μm2, and the middle part of the molten pools contained finer cells with an average size of 0.17 μm2. Fine Si precipitates with an average size of 25 nm were observed inside the cells. In terms of microstructure, no significant differences were observed when compared to the published data relating to SLM using virgin powders. This suggests that recycled powder after 30 printing cycles can be utilized for SLM component preparation to achieve cost-effectiveness. However, comparison of products with the use of virgin and recycled powders showed that the use of recycled powder affects the submicron characteristics (precipitate size increase), density and the resulting mechanical properties. Artificial aging of samples from the recycled powder at 170 °C caused an increase in hardness, Young's modulus and strength, while ductility remained essentially the same after aging. Peak values of hardness and strength were determined after 6 h of artificial aging. The increase in strength of the prepared samples can be explained by the precipitation of fine Si particles and their coarsening inside the cells. However, after longer aging times, the precipitates continued to coarsen, coalesced and displayed a plate-like shape, which led to the reduction in strength. The residual stress measured by the bridge curvature method (BCM) showed a significant decrease with increasing artificial aging time. The lowest residual stress was determined for an aging time of 100 h; however, the difference between residual stress for 6–7 h and 100 h was not significant. In order to obtain higher strengths and remove internal stresses after SLM during one heat treatment, the most suitable time for artificial aging at 170 °C seems to be 6 h.

SLM printing of cermet powders: Inhomogeneity from atomic scale to microstructure

It is very challenging for 3D printing based on the selective laser melting (SLM) technology to obtain cermet bulk materials with high density and homogeneous microstructures. In this work, the SLM process of the cermet powders was studied by both simulations and experiments using the WC-Co cemented carbides as an example. The results indicated that the evolution of the ceramic and metallic phases in the cermet particle during the heating, melting and solidification processes were all significantly inhomogeneous from atomic scale to mesoscale microstructures. As a consequence, the microstructural defects were caused intrinsically in the printed bulk material. The formation and growth of the bonding necks between the particles were mainly completed at the later stage of laser heating and the early stage of solidification. Both simulations and experiments demonstrated that thin amorphous layers formed at the ceramics/metal interfaces. This work disclosed the mechanisms for the evolution from the atomic scale to microstructure during the SLM printing of cermet powders, and discovered the origin of the defects in the printed cermet bulk materials.

An Invar Alloy SLM Printed Diplexer With High Thermal Stability

This paper presents a selective laser melting (SLM) 3-D printed Ku-band diplexer using dual-mode resonators with high thermal stability. The diplexer is designed using dual-mode dimpled ellipsoid resonators which enables the diplexer mechanically self-supported in fabrication. Hence, the design has higher compatibility with the SLM printing process and the design can be extended to multiplexers with more channels. The excellent thermal stability is benefited from both the 4J36 invar alloy material with a lower coefficient of thermal expansion (C.T.E) as well as the tailored SLM printing process. Electrical and thermal performances of the diplexer are measured, showing that the fabricated diplexer is with average insertion losses of 0.69dB/0.42dB, return losses of >14dB, and centre frequency shifts of 5.62MHz/3.75MHz (<0.04%) in the two channels after copper plating. The measured frequency shift is less than 0.5 MHz over 100∘ temperature change, which is equivalent to a C.T.E of 0.5 ppm.

Laser Fusion of Aluminum Powder Coated with Diamond Particles via Selective Laser Melting: Powder Preparation and Synthesis Description

This work aims to study the possibility of obtaining Al–C composite from AlSi10MgCu aluminum matrix with the addition of 500 nm-sized diamond particles by selective laser melting (SLM) process. Al–C composite powder was prepared by mechanical mixing to form a uniform cover along the surface of aluminum particles. The diamond content in the resulting AlSi10MgCu-diamond composite powder was equal to 0.67 wt %. The selection of the optimal SLM parameters for the obtained composite material is presented. For materials characterization, the following methods were used: scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) was applied after SLM printing for a detailed investigation of the obtained composites. The presence of carbon additives and the formation of aluminum carbides in the material after the SLM process were demonstrated.

Mechanical properties and in vitro cytocompatibility of dense and porous Ti–6Al–4V ELI manufactured by selective laser melting technology for biomedical applications

The Ti–6Al–4V alloy is the most common biomaterial used for bone replacements and reconstructions. Despite its advantages, the Ti–6Al–4V has a high stiffness that can cause stress-shielding. In this work, we demonstrated that the selective laser melting (SLM) technology could be used to fabricate porosity in Ti–6Al–4V extra low interstitial (ELI) to reduce its stiffness while improving cell adhesion and proliferation. With a porosity of 14.04%, the elastic modulus of the porous Ti–6Al–4V ELI was reduced to 80 GPa. The compressive stress and the 3-point-bending flexural tests revealed that the porous Ti–6Al–4V ELI possessed a brittle characteristic. The additional pores within the beams of the lattice structures of porous Ti–6Al–4V ELI increased its surface arithmetic average roughness, Ra = 3.94 μm. The in vitro cytocompatibility test showed that the SLM printing process and the post-processes did not cause any toxicity in the MC3T3-E1 cells. The in vitro cell proliferation test also showed that the porous Ti–6Al–4V ELI increased the proliferation rate of osteogenic induced MC3T3-E1 cells on Day 7. The findings from this study would provide engineers and researchers with both the mechanical information and biological understanding of SLM printed porous Ti–6Al–4V ELI, and SLM printed dense Ti–6Al–4V ELI towards biomedical applications.

Variant selection during β to α transformation for Ti-6Al-4V alloy produced by Selective Laser Melting printing

During 3D printing by Selective Laser Melting (SLM) of the alloy Ti-6Al-4V, the phase transformation of BCC to HCP is associated with selection of particular crystallographic variants. In the present paper, the distribution of misorientation angle along grain boundaries was investigated by EBSd. It is revealed that the main misorientation pairs were located in the interval between 56° and 66°, which contains three theoretical misorientation angles, i.e. 60.00°, 60.83° and 63.26°. The observed misorientation axis/angle pairs were represented in the Rodrigues–Frank space with a certain tolerance angle, which illustrated clearly the distribution of the observed misorientations around the 5 theoretical values. The main peak of the misorientation pairs was observed for with 43.8% frequency, followed by with 21.8% population, whereas a distribution in the absence of variant selection would have produced values of 18.2% and 36.4%, respectively.

Nanoparticle Exposure and Workplace Measurements During Processes Related to 3D Printing of a Metal Object.

Metal 3D printing has many potential uses within prototyping and manufacturing. Selective laser melting (SLM) is a process that uses metal powders in the micrometer range as printing material. The particle release from the entire SLM printing process is not well-studied. While the 3D printing itself often occurs in a sealed chamber, activities related to the process can potentially release harmful metal particles to the indoor working environment through resuspension of the printing powder or via incident nanoparticles generated during printing. The objective of this study was to improve the understanding of particle exposure in work processes associated with 3D printing and potential needs for interventions by a case study conducted in a 3D printing facility. In this setting, direct release and dispersion of particles throughout the workspace from processes related to metal 3D printing was investigated. The release from five activities were studied in detail. The activities included post-printing cleaning, object annealing, and preparation of new base substrate for the next printing was. Three of the five measured activities caused particles number concentrations in the working environment to increase above background levels which were found to be 8·102 cm−3. Concentrations during chamber emptying and the open powder removal system (PRS) cleaning processes increased to 104 and 5·103 cm−3, respectively, whereas grinding activity increased number concentrations to 2.5·105 cm−3. Size distributions showed that particles were mainly smaller than 200 nm. Respirable mass concentrations were 50.4 μg m−3, collected on filters. This was corroborated by respirable mass measured with a DustTrak of 58.4 μg m−3. Respirable mass concentrations were below the occupational exposure limits in Denmark for an 8 h time-weighted average.

Optimal Design of Barrel Based on Selective Laser Melting

Selective Laser Melting (SLM) is an additive manufacturing technology based on melting layers of metal powder using powerful laser without traditional limits. SLM makes it possible to manufacture complex structures such as enclosed inner cavity and complex surface. However, most of the mechanical parts are designed according to the requirements of traditional processing technology. There is often material redundancy in these parts, which will seriously affect the speed of SLM printing and increase the cost of SLM printing. In this article, according to the actual working condition, the barrel of a grenade cartridge based on traditional process design was optimized using a method of interior lattice structure to achieve the goal of lightweight, to eliminate material redundancy as much as possible. Then the strength and printability of the optimized parts were verified.

Optimization of selective laser melting process parameters for Ti-6Al-4V alloy manufacturing using deep learning

Ti-6Al-4V products manufactured by selective laser melting (SLM) have been extensively used in biomedical, aerospace, and many other industries. However, SLM’s many process parameters and their vast range are barriers to efficiently printing desirable products. Because SLM requires so much time, expenditure, and expert knowledge about the process and materials, SLM printing of Ti-6Al-4 V products needs a pre-processing optimization system. In this paper, an SLM optimization system is developed based on a supervised deep neural network by applying the Python programming language and the TensorFlow library. The outputs of this optimization method are the optimal SLM process parameters, which can be used to produce a product that satisfies a user requirement. With this optimization system, an SLM operator does not need much experience or to spend much time on experimentation to print a desirable product. This system is a significant, important module for pre-processing SLM printing.

Influence of printing parameters on structures, mechanical properties and surface characterization of aluminium alloy manufactured using selective laser melting

The selective laser melting (SLM) technology, a 3D printing method, has been gaining more attraction recently due to its ability to fabricate highly complex and intricate featured medical, aerospace, automotive components. The extensive use of SLM in recent years has been augmented by readily available processing materials and distinct product features such as enhanced surface properties and improved mechanical strength of the printed products. This paper investigated the effects of support structures, building direction and post-processing on mechanical properties, surface roughness and microscopic analysis of parts printed by SLM. Support structures are required during the SLM printing process. It is desired to optimize the support structures, as this increases printing time and material consumption and reduces surface finish. Finite element analysis has been carried out prior to metal printing to optimize the support structure. It was found that the spider-cone line support shows efficient structure for this study. The mechanical properties of the fabricated specimen were studied, and experimental results were validated and compared with conventionally machined specimen. It was observed that the SLM printed parts have 20% increment in tensile strength as compared with conventionally cast specimen. However, the percent of elongation is low for SLM specimen due to large number of pores and un-melted powder presented in the printed part. In this study, the SLM specimens were subjected to heat treatment at the temperature of 550 °C for 2 h in order to achieve increment or optimal mechanical properties. The heat treatment demonstrated a 2-fold increment in elongation, as compared with the SLM as printed specimen. The present study is also aimed at evaluating the surface roughness of SLM printed specimen. It was observed that the surface roughness of SLM specimen ranged between ~ 0.3 and 3 μm. This demonstrated that SLM process is capable of providing the good surface quality component and considered an alternative process to conventional manufacturing process. The morphological studies have been carried out to support the results derived from the evaluation of mechanical properties and surface roughness. The morphological behaviour clearly shows the large pores and un-melted particles in fractured specimen. The results revealed that the support structure, build direction, orientation, surface finish and post-processing are important parameters to build a part using SLM effectively and efficiently.

Application of Selective Laser Melting Technology Based on Titanium Alloy in Aerospace Products

Selective laser melting (SLM) is a key technology for direct forming of metal parts in 3D printing technology. SLM technology can realize the direct forming of parts with complex shape, high dimensional accuracy and excellent mechanical properties. It is especially suitable for rapid manufacturing of personalized and customized structures of aerospace difficult-to-machine parts. SLM forming process involves complex physical and chemical behavior of materials. Forming mechanism is quite different from traditional casting processes. The process parameters are complex and difficult to control. In this paper, a set of SLM forming process parameters suitable for Ti6Al4V alloy has been explored through the development of a SLM forming equipment of ESO M290 in Germany. The innovation of this product application design is the SLM printing design and process of minimal size dual-antenna, and the process method and design idea are universal. SLM forming technology based on Ti6Al4V alloy will be more and more widely used in aerospace field.

MLCPM: A process monitoring framework for 3D metal printing in industrial scale

Abstract Metal 3D printing is one of the fastest growing additive manufacturing (AM) technologies in recent years. Despite much improvements in its technical capabilities, reliable metal printing is still not well understood. One of the barriers of industrialization of metal AM is process monitoring and quality assurance of the printed product. These barriers are especially much highlighted in aerospace and medical device manufacturing industries where the high reliable and quality products are needed. Selective Laser Melting (SLM) is one of the main metal 3D printing methods where more than 50 parameters may affect the quality of the print. However, current SLM printing processes only utilize a fraction of the collected data for quality related tasks. This study proposes a process monitoring framework named MLCPM (Multi-Layer Classifier for Process Monitoring) to predict the likelihood of successful printing at critical printing stages based on collective data provided by identical 3D printing machines producing the same part. The proposed framework provides a blueprint for control strategies during a printing process and aims to prevent defects using data-driven techniques. A numerical study using simulated data is provided to demonstrate how the proposed method can be implemented.