Laser Sintering Research Articles

3D Printing of a Tidal Turbine Blade Using Two Methods of SLS and FFF of a Reinforced PA12 Composite: A Comparative Study

This study scrutinizes the thermomechanical dynamics of 3D-printed hydrofoil blades utilizing a carbon and glass bead-reinforced thermoplastic polymer. Comparative analyses underscore the pivotal role of polymer reinforcement in augmenting mechanical strength and mitigating deformation and residual stress. The investigation elucidates the expeditious and cost-efficient manufacturing potential of low-cost Fused Filament Fabrication (FFF) printers for small-scale blades, revealing exemplary mechanical performance with nominal deflection and warping in the PA12-CB/GB printed blade. A comprehensive juxtaposition between Selective Laser Sintering (SLS) and FFF printing methods favors SLS due to its isotropic properties, notwithstanding remediable warping. Emphasizing the rigorous marine environment, the study cautions against the anisotropic properties of FFF-printed blades, despite their low mechanical warping. These discernments contribute to hydrofoil design optimization through numerical analysis, shedding light on additive manufacturing’s potential for small blades in renewable energy, while underscoring the imperative for further research to advance these techniques.

Energy absorption and low-velocity impact responses of the sandwich panels with lattice truss core

This study investigates the dynamic energy absorption performance of composite sandwich panels with two different configurations of lattice truss core. Two types of core structures were designed and created using polyamide 12 through the selective laser sintering (SLS) additive manufacturing method. These structures, with uniform and graded cell topologies, were created by changing the geometry and layer density of the body-centered cubic (BCC) unit cell. The cores were used to fabricate composite sandwich panels, which were made with E-glass/epoxy face sheets. Then, their ability to absorb energy during low-velocity impact and quasi-static compressive strength was tested using both experimental and numerical methods. It was found that the graded structure absorbed 10, 5, and 3% more energy than the uniform structure for the energy levels of 12.4, 16.5, and 17.9 J, respectively. It was also found that both structures could absorb at least 90% of the impact energy. In terms of strength, the uniform structure was able to tolerate 1.15 times larger impact loads, indicating its higher strength than the graded structure. The uniform structure had 8% more compressive strength.

Characterization of Microstructural and Mechanical Properties of 17-4 PH Stainless Steel by Cold Rolled and Machining vs. DMLS Additive Manufacturing

The 17-4 PH stainless steel is widely used in the aerospace, petrochemical, chemical, food, and general metallurgical industries. The present study was conducted to analyze the mechanical properties of two types of 17-4 PH stainless steel—commercial cold-rolled and direct metal laser sintering (DMLS) manufactured. This study employed linear and nonlinear tensile FEM simulations, combined with various materials characterization techniques such as tensile testing and nanoindentation. Moreover, microstructural analysis was performed using metallographic techniques, optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results on the microstructure for 17-4 PH DMLS stainless steel reveal the layers of melting due to the laser process characterized by complex directional columnar structures parallel to the DMLS build direction. The mechanical properties obtained from the simple tension test decreased by 17% for the elastic modulus, 7.8% for the yield strength, and 7% for the ultimate strength for 17-4 PH DMLS compared with rolled 17-4 PH stainless steel. The FEM simulation using the experimental tension test data revealed that the 17-4 PH DMLS stainless steel experienced a decrease in the yield strength of ~8% and in the ultimate strength of ~11%. A reduction of the yield strength of the material was obtained as the grain size increased.

Understanding the consolidation mechanism of selective laser sintering/powder bed selective laser process of ceramics: Hydroxyapatite case

PurposeThe consolidation process and morphology evolution in ceramics-based additive manufacturing (AM) are still not well-understood. As a way to better understand the ceramic selective laser sintering (SLS), a dynamic three-dimensional computational model was developed to forecast thermal behavior of hydroxyapatite (HA) bioceramic.Design/methodology/approachAM has revolutionized automotive, biomedical and aerospace industries, among many others. AM provides design and geometric freedom, rapid product customization and manufacturing flexibility through its layer-by-layer technique. However, a very limited number of materials are printable because of rapid melting and solidification hysteresis. Melting-solidification dynamics in powder bed fusion are usually correlated with welding, often ignoring the intrinsic properties of the laser irradiation; unsurprisingly, the printable materials are mostly the well-known weldable materials.FindingsThe consolidation mechanism of HA was identified during its processing in a ceramic SLS device, then the effect of the laser energy density was studied to see how it affects the processing window. Premature sintering and sintering regimes were revealed and elaborated in detail. The full consolidation beyond sintering was also revealed along with its interaction to baseplate.Originality/valueThese findings provide important insight into the consolidation mechanism of HA ceramics, which will be the cornerstone for extending the range of materials in laser powder bed fusion of ceramics.

A Photochemically Active Cu2O Nanoparticle Endows Scaffolds with Good Antibacterial Performance by Efficiently Generating Reactive Oxygen Species.

Cuprous oxide (Cu2O) has great potential in photodynamic therapy for implant-associated infections due to its good biocompatibility and photoelectric properties. Nevertheless, the rapid recombination of electrons and holes weakens its photodynamic antibacterial effect. In this work, a new nanosystem (Cu2O@rGO) with excellent photodynamic performance was designed via the in situ growth of Cu2O on reduced graphene oxide (rGO). Specifically, rGO with lower Fermi levels served as an electron trap to capture photoexcited electrons from Cu2O, thereby promoting electron-hole separation. More importantly, the surface of rGO could quickly transfer electrons from Cu2O owing to its excellent conductivity, thus efficiently suppressing the recombination of electron-hole pairs. Subsequently, the Cu2O@rGO nanoparticle was introduced into poly-L-lactic acid (PLLA) powder to prepare PLLA/Cu2O@rGO porous scaffolds through selective laser sintering. Photochemical analysis showed that the photocurrent of Cu2O@rGO increased by about two times after the incorporation of GO nanosheets, thus enhancing the efficiency of photogenerated charge carriers and promoting electron-hole separation. Moreover, the ROS production of the PLLA/Cu2O@rGO scaffold was significantly increased by about two times as compared with that of the PLLA/Cu2O scaffold. The antibacterial results showed that PLLA/Cu2O@rGO possessed antibacterial rates of 83.7% and 81.3% against Escherichia coli and Staphylococcus aureus, respectively. In summary, this work provides an effective strategy for combating implant-related infections.

Influence of build orientation on porosity, strength and dimensional accuracy of laser sintered polyamide porous bone scaffolds

Development of synthetic bone graft via bone tissue engineering involves seeding of patient’s stem cells onto a porous scaffold in presence of growth factors. Porosity, strength and dimensional accuracy of the porous scaffold play a vital role in this process. This work aims at ascertaining influence of build orientation on porosity, mechanical strength and dimensional accuracy of the selectively laser sintered polyamide porous scaffolds. Initially, CAD models of test specimens with pre-designed porosity were created in Solidworks® software. All the specimens were fabricated on EOSINT P395, a selective laser sintering machine, along various primary (Flat, Edge, Upright and Flat_diag) and secondary (0o, 30o, 45o, 60o and 90o) orientations. Results show that measured porosity of most of the specimens was (range: 42.89-35.26%) less than the designed porosity (41.71%). Maximum average tensile strength (16.84 MPa) was recorded for specimens printed along Flat_0o orientation. Specimens printed along Upright_90o orientation showed highest average compressive strength (8.26 MPa). Specimens printed along Flat orientation showed relatively better average impact strength. Best dimensional accuracy was obtained for specimens printed along Flat orientation.

Robust and Corrosion-Resistant Overall Water Splitting Electrode Enabled by Additive Manufacturing.

Electrolysis of water has emerged as a prominent area of research in recent years. As a promising catalyst support, copper foam is widely investigated for electrolytic water, yet the insufficient mechanical strength and corrosion resistance render it less suitable for harsh working conditions. To exploit high-performance catalyst supports, various metal supports are comprehensively evaluated, and Ti6Al4V (Ti64) support exhibited outstanding compression and corrosion resistance. With this in mind, a 3D porous Ti64 catalyst support is fabricated using the selective laser sintering (SLM) 3D printing technology, and a conductive layer of nickel (Ni) is coated to increase the electrical conductivity and facilitate the deposition of catalysts. Subsequently, Co0.8Ni0.2(CO3)0.5(OH)·0.11H2O (CoNiCH) nanoneedles are deposited. The resulting porous Ti64/Ni/CoNiCH electrode displayed an impressive performance in the oxygen evolution reaction (OER) and reached 30mAcm-2 at an overpotential of only 200mV. Remarkably, even after being compressed at 15.04MPa, no obvious structural deformation is observed, and the attenuation of its catalytic efficiency is negligible. Based on the computational analysis, the CoNiCH catalyst demonstrated superior catalytic activity at the Ni site in comparison to the Co site. Furthermore, the electrode reached 30mAcm-2 at 1.75V in full water splitting conditions and showed no significant performance degradation even after 60h of continuous operation. This study presents an innovative approach to robust and corrosion-resistant catalyst design.

Process Study of Selective Laser Sintering of PS/GF/HGM Composites.

To address the issues of insufficient strength and poor precision in polystyrene forming parts during the selective laser sintering process, a ternary composite of polystyrene/glass fiber/hollow glass microbeads was prepared through co-modification by incorporating glass fiber and hollow glass microbeads into polystyrene using a mechanical mixing method. The bending strength and dimensional accuracy of the sintered composites were investigated by conducting an orthogonal test and analysis of variance to study the effects of laser power, scanning speed, scanning spacing, and delamination thickness. The process parameters were optimized and selected to determine the optimal combination. The results demonstrated that when considering bending strength and Z-dimensional accuracy as evaluation criteria for terpolymer sintered parts, the optimum process parameters are as follows: laser power of 24 W, scanning speed of 1600 mm/s, scanning spacing of 0.24 mm, and delamination thickness of 0.22 mm. Under these optimal process parameters, the bending strength of sintered parts reaches 6.12 MPa with a relative error in the Z-dimension of only 0.87%. The bending strength of pure polystyrene sintered parts is enhanced by 15.69% under the same conditions, while the relative error in the Z-dimension is reduced by 63.45%. It improves the forming strength and precision of polystyrene in the selective laser sintering process and achieves the effect of enhancement and modification, which provides a reference and a new direction for exploring polystyrene-based high-performance composites and expands the application scope of selective laser sintering technology.

Gradual error detection technique for non-destructive assessment of density and tensile strength in fused filament fabrication processes

Fused filament fabrication (FFF) is a widely used additive manufacturing process for producing functional components and prototypes. The FFF process involves depositing melted material layer-by-layer to build up 3D physical parts. The quality of the final product depends on several factors, including the component density and tensile strength, which are typically determined through destructive testing methods. X-ray microtomography (XCT) can be used to investigate the pore sizes and distribution. These approaches are time-consuming, costly, and wasteful, making it unsuitable for high-volume manufacturing. In this paper, a new method for non-destructive determination of component density and estimation of the tensile strength in FFF processes is proposed. This method involves the use of gradual error detection by sensors and convolutional neural networks. To validate this approach, a series of experiments has been conducted. Component density and tensile strength of the printed specimens with varying extrusion factor were measured using traditional destructive testing methods and XCT. The cumulative error detection method was used to predict the same properties without destroying the specimens. The predicted values were then compared with the measured values, and it was observed that the method accurately predicted the component density and tensile strength of the tested parts. This approach has several advantages over traditional destructive testing methods. The method is faster, cheaper, and more environmentally friendly since it does not require the destruction of the product. Moreover, it facilitates the testing of each individual part instead of assuming the same properties for components from one series. Additionally, it can provide real-time feedback on the quality of the product during the manufacturing process, allowing for adjustments to be made as needed. The advancement of this approach points toward a future trend in non-destructive testing methodologies, potentially revolutionizing quality assurance processes not only for consumer goods but various industries such as electronics or automotive industry. Moreover, its broader applications extend beyond FFF to encompass other additive manufacturing techniques such as selective laser sintering (SLS), or electron beam melting (EBM). A comparison between the old destructive testing methods and this innovative non-destructive approach underscores the possible fundamental change toward more efficient and sustainable manufacturing practices. This approach has the potential to significantly reduce the time and cost associated with traditional destructive testing methods while ensuring the quality of FFF-manufactured products.

Simultaneous laser sintering and embedding of silver nanoparticles for highly flexible embedded electrodes

In manufacturing electronic devices embedded in flexible substrates, persistent technical challenges include process complexity, substrate damage, high surface roughness, and low mechanical flexibility. To address these challenges, this study proposes a method that involves simultaneously sintering silver nanoparticles (Ag NPs) and embedding them in polyethylene terephthalate (PET) substrates to fabricate flexible embedded electrodes. The proposed technique uses laser-generated high-intensity shock waves to compress Ag NPs coated on a PET substrate heated to its glass-transition temperature. The mechanical impact of the shock wave embeds the Ag NPs into the substrate while simultaneously sintering the particles. The thin-film Ag electrode fabricated using the proposed method exhibited outstanding electrical and mechanical properties. The electrical resistivity measured as low as 7.8 μΩ·cm, with a minimal increase of approximately 5 % after 2000 bending cycles at a bending radius of 1 mm. Furthermore, the fracture strength of the fully embedded electrode, as assessed through adhesive tape-peel tests, significantly surpassed that produced through conventional sintering methods. The proposed method has the potential to revolutionize conventional sintering methods in flexible substrate applications, offering a more efficient and reliable method for fabricating flexible embedded electrodes.

Architected flexible syntactic foams: Additive manufacturing and reinforcing particle driven matrix segregation

Polymer syntactic foams are transforming materials that will shape the future of next-generation aerospace and marine structures. When manufactured using traditional processes, like compression molding, syntactic foams consist of a solid continuous polymer matrix reinforced with stiff hollow particles. However, polymer matrix segregation can be achieved during the selective laser sintering process with thermoplastic polyurethane (TPU). It is uncertain what role hollow particles play in forming this matrix segregation and its impact on the corresponding mechanical properties of syntactic foams. We show that the size of the hollow particles controls the internal microscale morphology of matrix segregation, leading to counter-intuitive macroscale mechanical responses. Particles with diameters greater than the gaps between the cell walls of the segregated matrix get lodged between and in the walls, bridging the gaps in the segregated matrix and increasing the stiffness of syntactic foams. In contrast, particles with smaller diameters with higher particle crushing strength get lodged only inside the cell walls of the segregated matrix, resulting in higher densification stresses (energy absorption). We show that stiffness and densification can be tuned while enabling lightweight syntactic foams. These novel discoveries will aid in facilitating functional and lightweight syntactic foams for cores in sandwich structures.

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.

Exploring 3D printing with magnetic materials: Types, applications, progress, and challenges

3D printing, also known as additive manufacturing (AM), represents a rapidly evolving technological field capable of creating distinctive products with nearly any irregular shape, often unattainable using traditional techniques. Currently, the focus in 3D printing extends beyond polymer and metal structural materials, garnering increased attention towards functional materials. This review conducts an analysis of published data concerning the 3D printing of magnetic materials. The paper provides a concise overview of key AM technologies, encompassing vat photopolymerization, selective laser sintering, binder jetting, fused deposition modeling, direct ink writing, electron beam melting, directed energy deposition and laser powder bed fusion. Additionally, it covers magnetic materials currently utilized in AM, including hard magnetic Nd–Fe–B and Sm–Co alloys, hard and soft magnetic ferrites, and soft magnetic alloys such as permalloys and elect­rical steels. Presently, materials produced through 3D printing exhibit properties that often fall short compared to their counterparts fabricated using conventional methods. However, the distinct advantages of 3D printing, such as the fabrication of intricately shaped individual parts and reduced material wastage, are noteworthy. Efforts are underway to enhance the material properties. In specific instances, such as the application of metal-polymer composites, the magnetic properties of 3D-printed products generally align with those of traditional analogs. The review further delves into the primary fields where 3D printing of magnetic products finds application. Notably, it highlights promising areas, including the production of responsive soft robots with increased freedom of movement and magnets featu­ring optimized topology for generating highly homogeneous magnetic fields. Furthermore, the paper addresses the key challenges associated with 3D printing of magnetic products, offering potential approaches to mitigate them.

The effect of abrasive water jet peening and laser shock peening on the wear properties of direct metal laser sintered AlSi10Mg alloy

The present study explored the impact of laser shock peening (LSP) and abrasive water jet peening (WJP) on the physical, surface and wear properties of direct metal laser sintered (DMLS) AlSi10Mg alloy. The microstructure, phase composition, hardness, roughness, work of adhesion, residual stresses and wear properties of As-built AlSi10Mg, laser shock peened AlSi10Mg and water jet peened AlSi10Mg were evaluated. The results showed that both WJP and LSP could improve the hardness and wear resistance of DMLS AlSi10Mg alloy. Amongst, LSP was more effective than WJP in reducing the wear rate and coefficient of friction due to refined microstructure. Wear mechanisms were transformed from abrasive to fatigue after the LSP. Furthermore, the influences of roughness, residual stresses and hardness on the wear properties were discussed in detail.

Thermal and hydraulic performance of Al alloy-based 3D printed triangular microchannel heatsink governed by rough walls with graphene and alumina nanofluids as working liquid

Microchannel heat sinks (MCHS) are known for providing enhanced cooling performance but their fabrication requires complex and multi-step processes. The recent development of additive manufacturing has enabled the fabrication of state-of-art monolithic structures that had been impossible to build using conventional methods. In this work, a monolithic cross-flow triangular cross-section MCHS was fabricated from aluminum alloy (AlSi10Mg) using the Direct Metal Laser Sintering (DMLS) process. The microchannel wall surface roughness was measured and the cross-section shrinkage of the microchannels was compared with the initial design hydraulic diameter of 500 µm–1000 µm. The MCHS with an initial design hydraulic diameter of 750 µm possessed a relative wall surface roughness, R a of 7.7%. The triangular cross-section hydraulic diameter underwent a shrinkage of 15.2% and 5.3% in terms of the reduction in angle between adjacent side alloys. Experiments were conducted for Reynolds numbers between 50 and 275 with nanofluids containing graphene and Al2O3 nanoparticles in water/water +10% ethylene glycol; these were compared with their respective base fluids. The Poiseuille number indicated that flow was laminar developed with base fluid and laminar developing with nanofluid as coolant. Despite providing the lowest thermal resistance, the graphene nanoparticles in water created the greatest pressure drop leading to a reduced performance coefficient. Al2O3 nanoparticles in water/water +10% ethylene glycol were found to have 7.7% and 20% better performance coefficients than their respective base fluids.

3D printing modality effect: Distinct printing outcomes dependent on selective laser sintering (SLS) and melt extrusion.

A direct and comprehensive comparative study on different 3D printing modalities was performed. We employed two representative 3D printing modalities, laser- and extrusion-based, which are currently used to produce patient-specific medical implants for clinical translation, to assess how these two different 3D printing modalities affect printing outcomes. The same solid and porous constructs were created from the same biomaterial, a blend of 96% poly-ε-caprolactone (PCL) and 4% hydroxyapatite (HA), using two different 3D printing modalities. Constructs were analyzed to assess their printing characteristics, including morphological, mechanical, and biological properties. We also performed an in vitro accelerated degradation study to compare their degradation behaviors. Despite the same input material, the 3D constructs created from different 3D printing modalities showed distinct differences in morphology, surface roughness and internal void fraction, which resulted in different mechanical properties and cell responses. In addition, the constructs exhibited different degradation rates depending on the 3D printing modalities. Given that each 3D printing modality has inherent characteristics that impact printing outcomes and ultimately implant performance, understanding the characteristics is crucial in selecting the 3D printing modality to create reliable biomedical implants.

Investigation of a hybrid manufacturing method involving selective laser melting and sintering

Additive manufacturing (AM) has been widely used in the aerospace, automotive and medical fields. However, there are obstacles, such as long manufacturing times and high costs for large parts. This study focuses on the development of a new hybrid manufacturing technique to utilize both selective laser melting and traditional powder sintering together. The shell section and the lattice structures were produced by AM, and then the metal powders remaining in the closed volume were sintered. Ti6Al4V powders were preferred in the study. The specimens were subjected to scanning electron microscope microstructure examination, compression tests, crash tests, and damage analysis. Specimens have a hardness ranging from 184 to 971 HV, a relative density ranging from 81% to 100%, a compressive strength of up to 870 MPa and a crash strength of around 520 MPa.

Polystyrene powder materials for selective laser sintering

Polystyrene powder materials for selective laser sintering

Contact rheological DEM model for visco-elastic powders during laser sintering

Laser sintering is a widely used process for producing complex shapes from particulate materials. However, understanding the complex interaction between the laser and particles is a challenge. This investigation provides new insights into the sintering process by simulating the laser source and the neck growth of particle pairs. First, a multi-physics discrete element method (DEM) framework is developed to incorporate temperature-dependent contact rheological and thermal properties, incorporating heat transfer and neck formation between the particles. Next, energy transport by ray tracing is added to allow for computing the amount of laser energy absorbed during sintering. The DEM model is calibrated and validated using experimental data on neck growth and temperature evolution of particle pairs made of polystyrene and Polyamide 12. The findings show that the proposed DEM model is capable of accurately simulate the neck growth during the laser sintering paving the way for better controlling and optimizing the process.Graphical

Stiffness of Anatomically Shaped Lattice Scaffolds Made by Direct Metal Laser Sintering of Ti-6Al-4V Powder: A Comparison of Two Different Design Variants

The modern approach to the recovery of damaged and missing bone tissue is increasingly focused on the application of implants capable of supporting the growth and recovery of parent tissue, rather than replacing the tissue itself. In this regard, the primary task of modern bone implants is to enable the targeted deformation of the implant against the expected load that that piece of bone should bear. The paper presents research related to anatomically shaped lattice scaffolds (ASLSs) made by the direct metal laser sintering (DMLS) of Ti-6Al-4V powder, and refers to the influence of the crossing angle between the outer lattice struts on the rigidity of the scaffold structure. The study includes the measurement of the deformation of two ASLSs designed for the same missing piece of rabbit tibia; these differed in terms of the crossing angle of the struts in the outer lattice and were exposed to quasi-uniaxial compression. The results show that the ASLS with outer struts that intersect at 60° (the angle between the compression direction and the strut axes is 30°) is more flexible compared to the ASLS with outer struts that intersect at 90° (the compression direction and the strut axes are colinear), even though its porosity is lower and volume is bigger.