Selective Laser Sintering Technique Research Articles

Mechanical Behavior of Additive Manufacturing (AM) and Wrought Ti6Al4V with a Martensitic Microstructure

Processing and microstructure are fundamental in shaping material behavior and failure characteristics. Additively manufactured materials, due to the rapid heating and solidification process, exhibit unique microstructures compared to their as-cast counterparts, resulting in distinct material properties. In this work, the response of the titanium alloy Ti6Al4V has been investigated for different processing conditions through quasi-static testing. AM Ti6Al4V was fabricated by employing Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) techniques. Both materials present a similar microstructure consisting of an acicular martensitic α′-phase. Commercial Ti6Al4V-grade 5 (supplied as bars) was also examined after heat treatment to achieve a microstructure akin to the AM material. The heat treatment involved rapid heating above the β-phase region and water quenching to obtain a full martensite microstructure. A similar constitutive behavior and tensile–compressive asymmetry in strength were noted for the investigated materials. However, AM alloys exhibited a significantly higher deformation at failure, reaching nearly 40%, compared to only 6.1% for the wrought martensitic material, which can be attributed to the dissimilar distribution of both α′ laths and prior-β grain boundaries in the investigated materials. The results indicate that AM can be implemented for the fabrication of martensitic microstructures with mechanical properties superior to those obtained with conventional water-quenching.

Powder Bed Fusion Techniques in Metal 3D Printing: A Review

The use of 3D printing (additive manufacturing) with metal has grown significantly in demand recently, greatly reducing the time and expense required to produce complex interconnected metal components. This method minimizes material wastage, facilitates material recycling, and eliminates the need for support materials. Among the various Metal Additive Manufacturing techniques, Powder Bed Fusion (PBF) processes stands out as the most prevalent for manufacturing parts. Within the realm of PBF, electron beam melting technique, selective laser sintering technique, and selective laser melting technique are the primary methods employed. Selective laser melting and selective laser sintering operate without the need for any special conditions, unlike EBM, which necessitates a vacuum environment. Regarding the choice of materials, laser melting/sintering processes are suitable for almost all types of metals except those which surpasses beam melting capabilities. While electron beam melting is constrained to a few materials such as titanium alloys, cobalt and chromium alloys, and nickel alloys, whereas selective laser melting and sintering allows for a broad range of materials, including iron and steel alloys. However, electron beam melting exhibit the ability to process brittle materials that would typically be challenging for melting and sintering through laser. Nevertheless, the ductility, yield testing, and ultimate testing of materials created through EBM are inferior to those processed by laser methods. Although all PBF techniques excel at creating complex structures, finishing products to have a smooth surface directly over a rough surface remains a subject of ongoing research. To attain suitable mechanical properties such as hardness, tensile strength, and endurance, critical process factors include power of laser or beam, speed for scanning, density for powder bed, thickness of laser or beam, and material characteristics. Inadequate material selection coupled with incorrect process settings can lead to issues such as porosity, slag formation, and other flaws.

Enhancing mechanical performance in SLS-printed PA12-slate composites through amino-silane treatment of mineral waste

The SLS additive manufacturing industry enables the development of products for diverse applications with distinct properties due to its excellent surface finish and ability to create varied part geometries, but it consumes high-performance materials with high acquisition costs. An extensive quarrying of stone leads to the accumulation of mineral residues, posing environmental hazards by contaminating soil and water when disposed of in landfills. The primary objective of the study was to incorporate mineral waste into the SLS technique and investigate the influence of its addition, along with a silane-based chemical treatment, on the mechanical performance of polymer-mineral composites (PA12-slate). Additionally, the feasibility of producing a highly loaded printed prototype, employing 50 wt% of mineral waste, was examined. Samples of PA12, PA12 blended with 50 wt% slate waste, and slate waste treated with silane underwent fabrication via selective laser sintering (SLS) and subsequent mechanical characterization, including tensile, flexural, and compressive tests. Additionally, the samples underwent accelerated aging using a QUV weathering tester, followed by mechanical characterization. The geometric accuracy, stability, and processing feasibility of these formulations were evaluated through SLS-printed composite prototypes utilizing PA12_50Sla_Si. It was found that the addition of 50% of slate to the PA12 presented mechanical properties decreasing compared to the printed PA12 only. However, an increase was verified when using silane-induced mineral bonding. The incorporation of mineral agents and silane enhanced the resistance of PA12 to aging. However, after aging, both tensile and flexural strength decreased across all printed samples. Nonetheless, this study showcased the feasibility of producing complex PA12-slate waste specimens containing up to 50 wt% of mineral waste using the SLS printing technique. Therefore, SLS presents itself as a viable means of adding value to this mineral waste.

Influence of various fabrication techniques and porcelain firing on the accuracy of metal-ceramic crowns

BackgroundThe fit of a metal-ceramic restoration is essential to its long-term durability. Regarding marginal and internal fit, there is not enough information about the technologies used in the production of metal-ceramic restorations. The aim of this in vitro study is to compare, both before and after porcelain firing, the marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic restorations manufactured using casting, additive or subtractive computer-aided design, and computer-aided manufacturing techniques (CAD/CAM).MethodsCAD/CAM were used to create 50 prepared maxillary first molar-shaped Co-Cr die models, which were randomly divided into 5 groups (n = 10). Cobalt-chrome copings were produced by casting (C), hard metal milling (HM), soft metal milling (SM), selective laser melting (SLM), and selective laser sintering (SLS) techniques. Before and after porcelain firing, discrepancies of the copings were measured using the silicone replica technique. The data obtained by measurements with a stereomicroscope at x80 magnification were analyzed statistically in the SPSS program. The ROBUST three-way analysis of variance (ANOVA) method was used to compare the discrepancy values.ResultsThere were statistically significant differences among fabrication methods (P < .001). The HM method showed the highest discrepancy (90.1 μm), and the C (63 μm) method showed the lowest discrepancy in terms of the die model- crown fit. The C, SLS, and SM methods (63 μm; 61.6 μm; 67.7 μm) were statistically similar (P > .001). The highest discrepancy was observed on the occlusal area (87.1 μm), and the lowest discrepancy was observed on the axial area (47.7 μm) of the coping. Porcelain firing had a decrease in the discrepancy values (P = .001).ConclusionAll CAD/CAM techniques are appropriate for clinical use; selective laser sintering and soft milling can be the more recommended methods for the compatibility of metal-porcelain restorations, as they have lower discrepancy values than the SLM and HM methods.

Comparative study on manufacturing of EDM electrodes by laser sintering process

The abstract aims to investigate the comparative performance of Electrical Discharge Machining (EDM) and Selective Laser Sintering (SLS) with unconventional machining processes. Unconventional machining processes have gained significant attention due to their versatility and capability to fabricate intricate components with high precision. This study focuses on assessing the efficacy of EDM and SLS techniques in terms of data removal rate and relative wear volume. Electrical Discharge Machining (EDM) is a thermal erosion process that utilizes electrical discharges to remove material from a workpiece. In contrast, Selective Laser Sintering (SLS) is an additive manufacturing technique that employs a laser to selectively fuse powdered material, layer by layer, to build up a three-dimensional object. Both methods offer unique advantages in terms of precision, speed, and material compatibility. The performance evaluation of these techniques involves analyzing key parameters such as data removal rate, which measures the volume of material removed per unit time, and relative wear volume, which quantifies the wear on the tool or workpiece during the machining process. By comparing these metrics, insights into the efficiency and effectiveness of EDM and SLS can be gained, aiding manufacturers and researchers in selecting the most suitable method for specific applications. Through experimental investigations and data analysis, this study aims to provide valuable insights into the capabilities and limitations of EDM and SLS in unconventional machining processes. The findings will contribute to advancing the understanding of these techniques and optimizing their utilization in various industrial sectors, including aerospace, automotive, and biomedical engineering. The experimental analysis examines the impact of the Direct Metal Laser Sintering (DMLS) process parameter on sintering depth. The optimized parameters for AlSi10Mg alloy powder sintering were obtained using laser power at 162 W, scanning speed at 156 mm s−1, porosity at 20%, laser area size of 0.2 mm, and layer thickness of 1 mm.

A novel straw structure sandwich hood with regular deformation diffusion mode

This work proposes an improved straw structure (ISS) sandwich hood (ISSH) to reduce the serious child head injuries caused by vehicle hood. The ISS sample is manufactured using the selective laser sintering (SLS) technique with nylon 11 material. A quasi-static compression experiment verifies the accuracy of the ISS in finite element analysis (FEA). The head injury criterion (HIC15) with the original hood and ISSH are then compared. The obtained results show that ISSH reduced the HIC15 by an average of 46.2 %. The ISSH has a regular deformation diffusion mode (RDDM), which helps to expand the energy absorption area. The ISS deformation mode is top-down layer-by-layer folding of structural layers. In addition, the impact of ISS geometric parameters on head injuries is studied. The thinner upper conical structures, larger layer heights, and material nylon 11 of the ISS contribute to the further improvement of protective effectiveness. The protective effectiveness of small-sized ISSs with connecting plates (SISC) against head injuries decreases with the increase of ISS quantity. In summary, this work provides new insights into the design of the sandwich hood for pedestrian protection, and the RDDM mechanism provides a novel direction for energy absorption.

Quasi-static compression and energy absorption behaviour of polymeric selective laser sintered open cell lattices under varying relative densities

PurposeThe purpose of this paper is to compare the influence of relative density (RD) and strain rates on failure mechanism and specific energy absorption (SEA) of polyamide lattices ranging from bending to stretch-dominated structures using selective laser sintering (SLS).Design/methodology/approachThree bending and two stretch-dominated unit cells were selected based on the Maxwell stability criterion. Lattices were designed with three RD and fabricated by SLS technique using PA12 material. Quasi-static compression tests with three strain rates were carried out using Taguchi's L9 experiments. The lattice compressive behaviour was verified with the Gibson–Ashby analytical model.FindingsIt has been observed that RD and strain rates played a vital role in lattice compressive properties by controlling failure mechanisms, resulting in distinct post-yielding responses as fluctuating and stable hardening in the plateau region. Analysis of variance (ANOVA) displayed the significant impact of RD and emphasised dissimilar influences of strain rate that vary to cell topology. Bending-dominated lattices showed better compressive properties than stretch-dominated lattices. The interesting observation is that stretch-dominated lattices with over-stiff topology exhibited less compressive properties contrary to the Maxwell stability criterion, whereas strain rate has less influence on the SEA of face-centered and body-centered cubic unit cells with vertical and horizontal struts (FBCCXYZ).Practical implicationsThis comparative study is expected to provide new prospects for designing end-user parts that undergo various impact conditions like automotive bumpers and evolving techniques like hybrid and functionally graded lattices.Originality/valueTo the best of the authors' knowledge, this is the first work that relates the strain rate with compressive properties and also highlights the lattice behaviour transformation from ductile to brittle while the increase of RD and strain rate analytically using the Gibson–Ashby analytical model.

Functionalization of recycled polymer and 3D printing into porous structures for selective recovery of copper from copper tailings

Selective copper recovery from copper tailings reduces environmental pollution caused by mining activities and provides a valuable source of copper. Furthermore, polymer waste accumulation and handling small functional materials like resins remains challenging. In this study, a 3D-printed adsorbent for selective copper recovery from copper tailings was designed by functionalizing recycled polymer with a chelating resin and 3D-printing using selective laser sintering technique. The 3D-printed adsorbent was characterized, and its adsorption performance examined under varying conditions. The adsorption kinetics and adsorption isotherm fitted well to the pseudo-second-order kinetics and Langmuir isotherm models, suggesting chemical and monolayer adsorption processes. FTIR indicated coordination as the possible adsorption mechanism. Thermodynamics revealed an endothermic process. The 3D-printed adsorbent demonstrated an excellent Cu(II) adsorption, high selectivity towards Cu(II), and reusability. This work offers a promising 3D-printed adsorbent for selective Cu(II) recovery, while also addressing polymer waste and particle handling issues.

Comparative Life Cycle Assessment of SLS and mFFF Additive Manufacturing Techniques for the Production of a Metal Specimen.

This work is part of a research project aimed at developing a bio-based binder, composed mainly of polylactic acid (PLA), to produce Ti6Al4V feedstock suitable for use in MAM (Metal Additive Manufacturing) via mFFF (metal Fused Filament Fabrication), in order to manufacture a titanium alloy specimen. While in Bragaglia et al. the mechanical characteristics of this sample were analyzed, the aim used of this study is to compare the mentioned mFFF process with one of the most used MAM processes in aerospace applications, known as Selective Laser Sintering (SLS), based on the Life Cycle Assessment (LCA) method. Despite the excellent properties of the products manufactured via SLS, this 3D printing technology involves high upfront capital costs while mFFF is a cheaper process. Moreover, the mFFF process has the advantage of potentially being exported for production in microgravity or weightless environments for in-space use. Nevertheless, most scientific literature shows comparisons of the Fused Filament Fabrication (FFF) printing stage with other AM technologies, and there are no comparative LCA "Candle to Gate" studies with mFFF processes to manufacture the same metal sample. Therefore, both MAM processes are analyzed with the LCA "Candle to Gate" method, from the extraction of raw materials to the production of the finished titanium alloy sample. The main results demonstrate a higher impact (+50%) process for mFFF and higher electrical energy consumption (7.31 kWh) compared to SLS (0.32 kWh). After power consumption, the use of titanium becomes the main contributor of Global Warming Potential (GWP) and Abiotic Depletion Potential (ADP) for both processes. Finally, an alternative scenario is evaluated in which the electrical energy is exclusively generated through photovoltaics. In this case, the results show how the mFFF process develops a more sustainable outcome than SLS.

Mechanical design and energy absorption performances of novel plate-rod hybrid lattice structures

Hybrid lattice structures, integrating diverse structural components from fundamental lattice topologies, have attracted significant attention for their exceptional mechanical properties encompassing elastic modulus, yield stress, and energy absorption. To amalgamate the lightweight characteristics of rod structures with the robust mechanical properties of plate structures, a novel plate-rod hybrid lattice (PRHL) with controllable geometrical parameters and higher energy absorption was proposed and fabricated via the Selective Laser Sintering technique. In the PRHL design, the hybrid rod structure, interlinked with the center of each surface of the semi-open Octet plate lattice (SOPL), mutually provides support and deformation constraints. To identify the mechanical properties of PRHL, quasi-static uniaxial compression tests of PRHL samples sintered by Polylactic Acid powder were carried out. In comparison to SOPL, the newly proposed PRHL demonstrates an approximate 13.4% improvement in initial crush stress and an 18.5% increase in specific energy absorption capacity. Furthermore, numerical simulations incorporating the effect of printing orientation were performed to analyze the deformation mechanism of the PRHL structures. The present study also underscores the capacity to fine-tune the mechanical properties of PRHLs by regulating the plate thickness, rod diameter and excavated hole diameter.

Novel approach to the 3D printing of biphasic calcium phosphate/molybdenum disulfide composite reinforced with polyamide12

In practical terms, the successful treatment of critical-sized bone defects remains a formidable obstacle. Among various options for bone regeneration, a customized 3D composite scaffold is widely acknowledged as the optimal choice. In the present study, we have developed a specialized composite scaffold utilizing biphasic calcium phosphate/molybdenum disulfide (BCp/MoS2) reinforced with polyamide12 (PA12) through the selective laser sintering (SLS) technique, employing different laser powers: 16W, 18W, 20W, and 22W. Notably, the BCp/MoS2/PA12 scaffold described in this research has not been explored in previous investigations. Analysis using a 3D profilometer reveals that the surface properties of the scaffold exhibit a robust mechanical interconnection between the 3-wt percent (Wt%) BCp/MoS2 composite within the PA12 matrix, particularly at a laser power of 22W. Remarkably, the mechanical properties of BCp/MoS2/PA12, including tensile strength (47.64 ± 0.42 MPa) and Young's modulus (2.31 ± 0.15 MPa), surpass those of pure PA12. These enhanced mechanical characteristics hold promising implications for the future advancement of bone tissue engineering. To comprehensively evaluate the composite scaffolds, we thoroughly investigated their thermal behavior and conducted morphological analysis. Moreover, after 21 days, in vitro live/dead results exhibited living cells along with their distinctive filopodia morphology, providing compelling evidence of the composite's non-toxicity. Further cell adhesion results showed enhanced growth, multiplication, and more reliable attachment and spreading across the composite surface. Encouragingly, the observed biological activity of the BCp/MoS2/PA12 scaffold with a 3 wt% concentration at a laser power of 22W suggests its significant potential for application in implant-related scenarios.

Selective laser sintered Pipe Ring Notched Tension specimens for examination of fracture properties of pipeline materials

In order to develop a non-standard method for determining the resistance to fracture and damage of pipeline materials, a new geometry of ring-shaped specimens with sharp notches or cracks has been defined. The need to develop a new method for testing of the specimens cut from the pipes arises due to the difficulties in determination of fracture mechanics parameters on thin-walled pressure pipelines, especially those with a smaller cross-section, by application of the standard procedures/specimens. Previous studies dealing with the topic of pipeline testing by non-standard methods are presented in the introductory part of the paper. In the experimental part of the research, tests on PRNT (Pipe Ring Notched Tension) and SENT (Single Edge Notched Tension) specimens are performed. Samples of these specimens were produced by SLS (Selective Laser Sintering) technique of additive production from PA12 (polyamide PA 2200) material. For the purpose of this study, a tool that is protected at the national level (in Serbia) as intellectual property is used for testing of the ring-shaped PRNT specimens. Tensile testing of both types of specimens is monitored by Aramis GOM 2M system; its operation is based on the method of digital image correlation, DIC. Additionally, finite element analyses are conducted on the PRNT and SENT geometries, enabling the calculation of the fracture mechanics parameter – Stress intensity factor K. It is concluded that the presented procedure based on the PRNT specimen has a good potential for use as a non-standard method for fracture resistance examination of pipeline materials. It can be performed on the specimens cut directly from the pipes (new or from exploitation). The dependence of the fracture resistance on the stress concentrator size is not pronounced, which means that the results depend dominantly on the material properties, rather than on geometry.

3D printing of carvedilol oral dosage forms using selective laser sintering technique

3D printing of carvedilol oral dosage forms using selective laser sintering technique

Influence of wall thickness on mechanical properties and porosity of additive manufactured polymer-based porous structures for fibula bone regeneration

In the recent past, Bone tissue engineering (BTE) has become a potentially effective solution for repairing bone defects. In the meantime, various fields, such as material science, additive manufacturing, and clinical medicine, are interlinked in the fast-emerging field of bone tissue engineering. Additive Manufacturing (AM) is a unique technology that accumulates content rather than waste materials in the form of chips. AM techniques like selective laser sintering (SLS), commonly used to create complex polymer structures, allow for the direct fabrication of complex structural implant components for use in BTE. However, the wall thickness of the product limits the SLS systems. In detail, research into the influence of wall thickness on mechanical properties and scaffold porosity is required to develop such lightweight and complex structures. In this study, Polyamide12-based bone Scaffolds were fabricated using the SLS technique by varying the wall thickness ranging from 0.9 mm to 1.10 mm in steps of 0.05 mm. Compression tests, porosity, scanning electron microscopy, and differential scanning calorimetry were conducted on the fabricated specimens. The studies demonstrated that the higher wall thickness benefits in reduction of porosity. The sample fabricated with a wall thickness of 1.1 mm has about 76% less porosity than the sample fabricated with a wall thickness of 0.9 mm. In addition, the study also found that compression strength decreases as porosity increases. The compressive strength of the scaffolds has been measured to be between 45.62 and 90.67 MPa for a wall thickness between 0.90 and 1.10 mm. The maximum compressive strength of a porous polyamide specimen is 90.67 MPa at a wall thickness of 1.10 mm. The fabricated samples with wall thicknesses of 0.9 and 0.95 mm were not mechanically stable, as their compressive strength values were lower than the compressive strength of human fibula bone (68 N/mm2).

Spherical porous structures for axial compression

Porous structures have attracted much attention because of the advantages of lightweight and strong energy absorption efficiency. This work proposes a spherical porous structure (SPS) and a square porous structure (SQPS), and the SPS sample is manufactured by selective laser sintering (SLS) technique with the material nylon 11. Their axial compression results of experiment and simulation show that the compressive strength of hollow cylinders is greater than that of porous spheres, and porous spheres are always crushed during compression. SPS exhibits the rapid collapse characteristics of porous spheres layer by layer, and it shows four sharp valley forces and significant negative stiffness characteristic. In addition, the specific energy absorption (SEA) value of SPS is higher than that of SQPS 30.84%. The compression capacity of porous spheres is stronger than that of porous cubes. This study furtherly discuss the mechanical behavior of SPS with different structural parameters. The negative stiffness characteristic, energy absorption efficiency and deformation mode of SPS depends on the strength combination of porous spheres and hollow cylinders, and smaller overall cell size, more cell layers, and thicker cells contribute to improving the anti-compression properties of SPS. The SEA values of SPS- T1.6 and SPS- F7 are 12.52% and 12.16% higher than that of SPS. In summary, SPS shows novel mechanical properties, providing a reference for the design of new energy absorbers.

Porous iron-reinforced polylactic acid TPMS bio-scaffolds: Interlocking reinforcement and synergistic degradation

Porous materials are expected to bring a positive impact on enhancing interfaces and mechanics due to their unique pore networks. Herein, porous iron (pFe) was used as the reinforcing phase to strengthen poly (lactic acid) (PLA) matrix, and PLA/pFe scaffolds were prepared via selective laser sintering (SLS) technique. Scaffold models were constructed using triply periodic minimal surfaces (TPMS) and the optimal porosity was obtained by mechanical evaluation. The results showed that pFe incorporation significantly improved mechanical properties, especially for PLA/5pFe scaffold, which was 121% higher than that of PLA scaffold. It may be that molten PLA molecules penetrate the pore network of pFe particles, forming spatial interlocks and encapsulations, thereby improving the efficiency of stress transfer. In addition, a chemical catalytic cycle is expected to be formed between PLA hydrolysis and pFe degradation to promote the degradation of composite scaffolds. Moreover, the composite scaffold also showed good biomineralization and cytocompatibility in vitro. These properties make the PLA/pFe composite scaffold promising for bone tissue engineering applications.

Novel 3D printable bio-based and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) microspheres for selective laser sintering applications

Selective laser sintering (SLS) has become the most popular additive manufacturing process due to its high accuracy, productive efficiency, and surface quality. However, currently there are still very few commercially available polymeric materials suitable for this technique. This research work focused on the fabrication and characterization of bio-based and biodegradable microspheres obtained by oil-in-water emulsion solvent evaporation, starting from a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) biopolymer matrix. First, the fabrication parameters were optimized to improve the morphological, thermal, and flowability properties of the synthetized microspheres. Once the best production conditions were established, the PHBH microspheres were further used to study their effective 3D printability on an SLS 3D printer using geometries varying from simple shapes to architectures with more complex internal patterns. The results of this research revealed that PHBH has promising applicability for the SLS technique. This study undertook the first step toward broadening the range of polymeric materials for this additive manufacturing technology. These findings will contribute to a greater and wider dissemination of the SLS technique in the future, as well as they will bring this manufacturing process closer to applications, such as the biomedical sector, where the use of biodegradable and biocompatible materials can add value to the final application.

Influence of Antibacterial Coating and Mechanical and Chemical Treatment on the Surface Properties of PA12 Parts Manufactured with SLS and MJF Techniques in the Context of Medical Applications

Additive manufacturing (AM) is a rapidly growing branch of manufacturing techniques used, among others, in the medical industry. New machines and materials and additional processing methods are improved or developed. Due to the dynamic development of post-processing and its relative novelty, it has not yet been widely described in the literature. This study focuses on the surface topography (parameters Sa, Sz, Sdq, Sds, Str, Sdr) of biocompatible polyamide 12 (PA12) samples made by selective laser sintering (SLS) and multi jet fusion (MJF). The surfaces of the samples were modified by commercial methods: four types of smoothing treatments (two mechanical and two chemical), and two antibacterial coatings. The smoothing treatment decreased the values of all analyzed topography parameters. On average, the Sa of the SLS samples was 33% higher than that of the MJF samples. After mechanical treatment, Sa decreased by 42% and after chemical treatment by 80%. The reduction in Sdq and Sdr is reflected in a higher surface gloss. One antibacterial coating did not significantly modify the surface topography. The other coating had a smoothing effect on the surface. The results of the study can help in the development of manufacturing methodologies for parts made of PA12, e.g., in the medical industry.

Direct Writing of Functional Layer by Selective Laser Sintering of Nanoparticles for Emerging Applications: A Review.

Selective laser sintering of nanoparticles enables the direct and rapid formation of a functional layer even on heat-sensitive flexible and stretchable substrates, and is rising as a pioneering fabrication technology for future-oriented applications. To date, laser sintering has been successfully applied to various target nanomaterials including a wide range of metal and metal-oxide nanoparticles, and extensive investigation of relevant experimental schemes have not only reduced the minimum feature size but also have further expanded the scalability of the process. In the beginning, the selective laser sintering process was regarded as an alternative method to conventional manufacturing processes, but recent studies have shown that the unique characteristics of the laser-sintered layer may improve device performance or even enable novel functionalities which were not achievable using conventional fabrication techniques. In this regard, we summarize the current developmental status of the selective laser sintering technique for nanoparticles, affording special attention to recent emerging applications that adopt the laser sintering scheme.

On the Reuse of SLS Polyamide 12 Powder.

In the Selective Laser Sintering (SLS) technique, the great majority of the powder involved is not included in the final printed parts, being just used as a support material. However, the quality of this powder is negatively affected during the process since it is subjected to high temperatures (close to its melting temperature) during a long time, i.e., the printing cycle time, especially in the neighborhood of the printed part contour. This type of powder is relatively expensive and large amounts of used powder result after each printing cycle. The present paper focuses on the reuse of Polyamide 12 (PA 12) powder. For this sake, the same PA 12 powder was used in consecutive printing cycles. After each cycle, the remaining non-used powder was milled and filtered before subsequent use. Properties of the powder and corresponding prints were characterized in each cycle, using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), computed tomography (CT), and tensile tests. It was concluded that subjecting the same powder to multiple SLS printing cycles affects the properties of the printed parts essentially regarding their morphology (voids content), mechanical properties reproducibility, and aesthetical aspect. However, post-processing treatment of the powder enabled to maintain the mechanical performance of the prints during the first six printing cycles without the need to add virgin powder.