Laser Sintering Process Research Articles

Metal additive manufacturing of damage-controlled elements for structural protection of steel members

This paper develops hybrid steel members by integrating additively manufactured, ultra-lightweight, damage-controlled elements (DCEs) into hot-rolled structural steel members. This approach relies on segmenting a structural member into distinct sections; one or two segments are enlarged to be capacity protected; however, anotherend or middle DCE segment is optimized to emulate theconventional member’s strength and stiffness. A small-scale DCE was topologically optimized and then additively manufactured using apowder bed fusion technique through adirect metal laser sintering process of 17-4PH stainless steel andthen was experimentally tested to study the buckling behavior under compression. The experimental testing of the optimized DCE shows acompressive strength of 81,000 times the specimen’s weight with stable post-peak buckling behavior. Numerical simulation confirms experimental results, showing agood correlation in fracture energy. A parametric study on four DCE specimens, scaled up by three, four, five, and six times, was performed and compared to hollow structural sections (HSS) of A500 Gr. C in tensile and compression strengths. The numerical simulation shows a linear relation between the weight ratio and HSS length. Additionally, numerical simulation of conventional member, DCE (scaled by three), and three hybrid members revealed that failure occurred in DCE as intended.

Study on the mechanical properties of PES-HmA samples printed by selective laser sintering under various pre-heating conditions

The purpose of this study is to investigate the influence of pre-heating characteristics on the mechanical properties and forming process of selective laser sintering (SLS) printed PES-HmA samples. An experimental setup with four heating tubes was designed to study the pre-heating temperature distribution on the powder bed. The pre-heating temperature distribution on the powder bed was captured using a thermal imaging camera. A method for evaluating pre-heating temperature distribution based on the average and standard deviation of surface temperature was proposed. The heating tube installation position was optimized using a response surface experiment study based on the temperature distribution evaluation. By optimizing the installation position of the tubes, the temperature distribution on the powder bed tends to become uniform. The effect of pre-heating temperature value and distribution on the mechanical properties of the SLS printed PES-HmA samples was also experimentally investigated. The cross sectional microstructure of the printed samples were examined by scanning electron microscope to analyze the layer formation process at different pre-heating temperature. By increasing the pre-heating temperature from 70°C to 100°C, the material diffusion at the layers interface was improved, which made the tensile strength of sample increased by 376%, and the flexural strength increased by 224%.

Enhanced SiC/NFG/Ni ternary composite microwave absorbing materials with micro-network structures produced by selective laser sintering

In this paper, a ternary composite wave-absorbing material consisting of silicon carbide (SiC), natural flake graphite (NFG) and nickel (Ni) has been successfully fabricated through a combined process of selective laser sintering (SLS) and vacuum pressure impregnation. The study investigated how the content of SiC powder affected the absorption capacity and mechanical performances of the composites. The findings indicate that as the proportion of SiC powder rises, the porosity of the composites diminishes, while the bending strength increases. As the content of SiC is 40 wt%, the porosity is 52.14 % and the flexure strength is 9.58 MPa, approximately five times greater than that of graphite-type ceramic preforms. The composite’s electromagnetic wave-absorbing capability initially improves and then declines with the increase of SiC content. When the SiC content is 10 wt% and the thickness is 1.5 mm, the composite absorbing material exhibits optimal electromagnetic absorption performance, with a minimum reflection loss (RLmin)of −44.04 dB and an effective absorption bandwidth (EAB) of 5.42 GHz (8.24–13.66 GHz). The composite material, characterized by its lightweight, high strength, and broad frequency range, shows promise for applications in microwave absorption technology.

Effects of heating rate and sintering temperature on the tensile properties of sintered γ-Ti/Al nanoparticle chains

Abstract This paper presents the results of molecular dynamics simulations that were performed to numerically study the laser sintering process and mechanical behavior of γ-Ti/Al bimetallic alloy nanoparticles (NPs). The study systematically investigates the effects of heating rate and sintering temperature on the resultant uniaxial tensile performances of the sintered NPs. A chain model was formed by connecting three pre-equilibrated Ti/Al NPs via necks during solid-state sintering. The solid-state sintered chain samples were heated to 1798 K using four different heating rates (0.04, 0.2, 0.5, and 1.0 K/ps). After high-temperature relaxation of selected sintering temperature cases (e.g., 398 K, 598 K, etc. with a 200 K interval) for 10 ns, the heat sintered chain samples underwent a solidification process with a cooling rate of 0.08 K/ps and maintained at 298 K for an additional 1 ns. The resulting sintered chain products were then subjected to uniaxial tension at a strain rate of 0.0001/ps. The thermodynamic properties and crystallographic deformation were investigated during the sintering and subsequent tension processes. Analysis of the yield strengths obtained from the tension tests revealed a statistically significant correlation between the tensile strength of the sintered NPs and the pre-established sintering temperatures at each temperature. This observation indicates that higher sintering temperatures strengthen the neck connections within the NP-chains, leading to greater tensile strength. The higher sintering temperatures can reinforce the neck during high-temperature relaxation. It is worth noting that the effect of heating rates on mechanical properties was less pronounced when the sintering temperature was constant.

A study on the machinability of DMLS In718 alloy using an electro-spark machining process

ABSTRACT The direct metal laser sintering process is used to develop the nickel base superalloy DMLS In718 for the experimentation. The DMLS In718 alloy is evaluated to ensure the metallurgical qualities and mechanical properties. Microstructure of the DMLS In718 alloy is anisotropic in nature and the hatch bands are clear to infer. The hardness of the DMLS In718 is 275 Hv which equivalent to the commercially available inconel718 material. the mechanical strength and density of the DMLS In718 alloy is justifiable to the commercial material. The machining studies are performed with electro spark erosion process to report on surface quality, kerf taper and material removal rate. the minimum pulse on time has produced a fine surface quality compared to the maximum process condition. The surface topography in terms of oxide scale and recast layers are identified during to inefficient process conditions. This paper was an opportunity to deliberate the machining quality of the wire electro spark process.

Study on the laser sintering process of veined red snail/polylactic acid composite powder

Drawing on the composition of shells and the microstructure of cross-laminated sheets, laser sintering technology was used to prepare laser-sintered fabrications of veined red snail powder as an inorganic material and polylactic acid (PLA) as an organic material. The process was optimized using the response surface method based on one-way experiments by adding veined red snail powder. At a 13.27 W laser power, 1.2 m/s scanning rate, 0.17 mm scanning spacing, and 0.23 mm delamination thickness, the bending strength of the veined red conch powder/PLA composite powder parts reached 8.53 ± 0.15 MPa, with an error of only 1.7% from the model’s predicted value. Under these process conditions, the characterization of laser-sintered parts with 0, 5, 10, 15, 20, and 25 wt% veined red snail powder revealed that parts with 15 wt% exhibited optimal mechanical properties, showing a 155.9% improvement over pure PLA parts.

Thermomechanical Assessment of Recovered PA12 Powders with Basalt Filler for Automotive Components

Additive manufacturing processes allow for precise and efficient production, but it is estimated that one-third of the materials used results in waste. Further improvement in a sustainable perspective could come from the ability to manage these scraps and from the exploration of different routes for recovery and reuse. The Selective Laser Sintering process is particularly sensitive to this issue due to the waste ratio which can reach a very high quantity of not-sintered virgin powders. In this research study, recovered PA12 powders, preliminarily characterized through thermal and mechanical analysis, were mixed with 15% basalt powder to improve their aspect and thermomechanical resistance. The influence of basalt powder (BP) on mechanical properties as well as on the thermal stability of polyamide12 (PA12) powder composites was investigated. A study conducted on mechanical properties showed that polymeric composites’ stiffness and hardness were influenced by adding filler, thus improving mechanical parameters. On the other hand, the application of thermogravimetric analysis allowed us to determine the composite’s thermal stability. The objective is to obtain a recovered fully biobased material that could be used to substitute the petroleum-derived polymeric ones currently employed in the production of interiors and shells in the automotive sector.

3D printing of high-stiffness and high-strength glass fiber reinforced PEEK composites by selective laser sintering

Glass fiber reinforced poly-ether-ether-ketone (PEEK) composites are emerging as structural materials of multifunctional devices in space applications, due to their outstanding mechanical properties, electrical insulating properties, and resistance to irradiation. Here, a new approach for preparing glass fiber/PEEK powders tailored for selective laser sintering (SLS) process is proposed. The surface of glass fiber is modified with the sulfonated PEEK following the designed procedure. The flowability of glass fiber/PEEK powders is also improved by adding the nano-scale SiO2 flow agent. The glass fiber reinforced PEEK composites are successfully 3D printed using the glass fiber/PEEK powders. Further, the enhancement of interfacial bonding between PEEK and glass fiber is analyzed through quasi-static tension tests and scanning electron microscopy (SEM) for the SLSed glass fiber reinforced PEEK composites. The average ultimate tensile strength reaches approximately 100 MPa using these optimal process parameters, while the average elastic modulus is around 7 GPa. Finally, the upper limit of fiber weight fraction is evaluated with the X-ray computed tomography (XCT) and the high-fidelity discrete element method (DEM) simulation.

Towards the Reuse of Fire Retarded Polyamide 12 for Laser Sintering.

The control of powder aging during Selective Laser Sintering (SLS) processing is one of the challenges to be overcome for the implementation of this technique in serial production. Aging phenomena, because of the elevated temperatures and long processing times, need to be considered when a fraction of the polymer powders present in the build chamber and not used to manufacture the parts are reused at various times. The aim of this study was to investigate the influence of successive reuse of blends of pure Polyamide 12 and its blends with two types of flame retardants (FR): ammonium polyphosphate (APP) and zinc borate (ZB). The composition of the blends was 70/30 (wt/wt) PA 12/FR. Four successive processing stages have been carried out by collecting the remaining powder blend each time. The powders were re-used using the same processing parameters after sieving. DSC measurements showed that the incorporation of FRs entailed a reduction in the processing window up to 4 °C; nevertheless, no further reduction was noted after aging. The TGA curves of aged blends of powders were also similar for pure PA 12 and PA 12 with FR. In addition, initial and reused powders presented a higher degree of crystallinity than the specimens processed from the powders. The heterogeneous character of the PA 12 after LS processing or reprocessing was shown through Pyrolysis Combustion Flow Calorimetry (PCFC) and cone calorimeter (CC) tests. FTIR analysis also showed that post-condensation reactions have occurred. The mode of action of the flame retardants was clearly seen on HRR curves at both tests. The first reuses of PA 12 powders entailed a significant reduction in time to ignition at the cone calorimeter (150 for the initial material to around 90 s for the reused material), indicating the formation of short polymer chains. Only in the case of zinc borate was it noticed that re-used powder was detrimental to the fire performance because of a strong increase in the value of pHRR (between 163 and 220 kW/m2 for reused material instead of 125 kW/m2 for the initial one).

Laser powder bed fusion sintering mechanism of phenolic resin investigated by ReaxFF molecular dynamics simulations

ABSTRACT This study presents an innovative approach utilising molecular dynamics simulations to elucidate the polymerisation and neck formation mechanisms of phenolic resin during laser powder bed fusion (L-PBF). By developing system and dual-particle models and employing infrared thermal imaging, we established a heat source model for phenolic resin under varying parameters. Our molecular dynamics simulations, using the ReaxFF reactive force field, indicate that high-power lasers significantly enhance cross-linking, achieving a peak polymerisation degree of 78.9% at 30W and 35W power levels. Conversely, increased scanning speed slows product degradation, reducing the polymerisation degree. The interplay of laser power and scanning speed influences polymerisation, with total input energy and heating rate impacting polymerisation and molecular size. Additionally, we investigated neck formation, revealing that small vortices evolve into larger ones during sintering, promoting neck formation. Optical microscopy confirmed diverse neck shapes under different conditions. Quantitative data showed that at a scanning speed of 1000 mm/s, the polymerisation degree reached 93%, with only 2 molecules remaining post-simulation. At 30W power, the largest individual molecule observed was C849H703O117. This research offers crucial insights for selective laser sintering processes, emphasising the importance of high energy input and optimal heating rates for well-formed necks.

3D printing of sustainable wood-based bio-composites for high-end custom carton

This research delves into an upscale, personalised packaging paradigm employing 3D printing and a bio-composite derived from esteemed rosewood. The study incorporates a design for additive manufacturing, enhancing designers’ flexibility, and fostering innovation. To address global sustainability imperatives, including efficiency, energy conservation, a low carbon footprint and ecological compatibility, a premium and sustainable rosewood/polyethersulfone (PES) composite is developed. Laser sintering (LS), renowned for its processing flexibility, is applied for crafting intricate packages. A weight ratio of 1:4 of rosewood to PES is highly suitable for LS processing. The resultant custom carton, embodying natural rosewood aesthetics and fragrance, exhibits commendable mechanical robustness and precision. Tensile and bending strengths reach peaks of 4.880 MPa and 7.870 MPa, respectively, under a 9-W laser power. Scanning electron microscope (SEM) analysis confirms the favourable dispersion of rosewood fibres in LS specimens, providing insights into the microstructure of the composite powder.

Carbon nanotubes/α-ZrP sheets for high mechanical performance and flame-retarding polyamides using selective laser sintering

ABSTRACT The current study presents a facile approach to synthesis carbon nanotube-anchor α-ZrP (CNT@α-ZrP) nanohybrid for multifunctional polyamide 12 (PA12) composites via ball-milling followed by selective laser sintering (SLS) process. Herein, CNTs serve dual roles; firstly, they act as a pigment, imparting black colouration to both PA12 powder and α-ZrP sheets, facilitating rapid light absorption and heating. Secondly, CNTs complement α-ZrP sheets to reinforce the PA12 matrix for strong and functional structures. The dominant filler content is α-ZrP nanosheets in PA12 powder to study the functionality of α-ZrP sheets in SLS-PA12 composites. CNT@α-ZrP hybrid enhances mechanical, tribological, corrosion resistance and flame-retarding properties of PA12 composite parts. PA12/CNT@α-ZrP composite exhibited 98.9%, 33.1%, and 34.6% increments in Young's modulus, tensile strength and impact strength, respectively. To predict the response of the composites across a range of applications, the constants for different hyperelastic models describing their mechanical behaviour were determined. The coefficient of friction and wear rate of the sintered composite parts were reduced significantly. Additionally, 1 wt% CNT@α-ZrP reduced smoke production rate and total smoke production by 36.5% and 13.8%, respectively along with a 2.2- fold increment in time-to-ignition. The work presents an industrial method to develop strong and functional intricate structures via SLS.

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.

Full-Field Strain and Failure Analysis of Titanium Alloy Diamond Lattice

The advancement in additive manufacturing has significantly expanded the use of lattice structures in many engineering fields. Titanium diamond lattice structures, produced by a direct metal laser sintering process, were experimentally investigated. Two cell sizes were selected at five different relative densities. Morphological analysis was conducted by digital microscopy. The compressive tests and digital image correlation technique allowed the evaluation of elastic moduli to be used in the Gibson–Ashby model. Failure mechanisms of the structures have been analysed by digital image correlation, which represents a promising technique for strain evaluation of such structures. A non-linear finite element model of the lattice structures was developed and validated using the experimental data. The analysis of the results highlights the good mechanical properties of the Ti6Al4V alloy lattice structures.

Evaluating the thermal, mechanical and swelling behavior of novel silicone and polyurethane additively manufactured O-rings in the presence of organic liquids and military fuels

This work investigates the physical properties and swelling behavior of additively manufactured (AM) and traditionally manufactured (TM) polyurethane (PU) and silicone O-rings when exposed to organic liquids and military fuels. Polymer properties were explored using differential scanning calorimetry, thermal gravimetric analysis, and tensile testing, and two AM print orientations (vertical and horizontal) were investigated. The AM polyurethane vertical and horizontal O-rings formed from a selective laser sintering (SLS) process had similar thermal features to each other and differed slightly from the un-sintered polymer in the temperature at which the greatest rate of mass loss occurred in the TGA analysis. The thermal features of the AM silicone O-rings formed using stereolithography (SLA) were more similar to those of a commercial soft silicone than to those of a commercial high purity silicone. The horizontal print orientation for each polymer had a higher tensile strength than its respective vertically oriented print. A 1-week exposure of the AM O-rings to the various organic liquids reduced the tensile strength of AM O-rings by as much as 80% (tensile strength exposed/tensile strength unexposed = 0.2). Polyurethane AM O-rings swelled from 3 to 74% with the greatest swelling occurring from exposure to acetone. Silicone AM O-rings swelled from 13 to 258% with the greatest swelling occurring from exposure to iso-octane. In general, the commercial O-rings swelled less than their AM counterparts, had higher tensile strengths, and had smoother surfaces. The maximum swelling for the PU O-rings occurred at an overall Hansen solubility parameter (HSP) between 18 and 20 MPa1/2, while the maximum for silicone occurred at an HSP of 14.3 MPa1/2. These values are consistent with literature values, which can vary widely.

Elasto-plastic residual stress analysis of selective laser sintered porous materials based on 3D-multilayer thermo-structural phase-field simulations

Residual stress and plastic strain in additive manufactured materials can exhibit significant microscopic variation at the powder scale, profoundly influencing the overall properties of printed components. This variation depends on processing parameters and stems from multiple factors, including differences in powder bed morphology, non-uniform thermo-structural profiles, and inter-layer fusion. In this research, we propose a powder-resolved multilayer multiphysics simulation scheme tailored for porous materials through the process of selective laser sintering. This approach seamlessly integrates finite element method (FEM) based non-isothermal phase-field simulation with thermo-elasto-plastic simulation, incorporating temperature- and phase-dependent material properties. The outcome of this investigation includes a detailed depiction of the mesoscopic evolution of stress and plastic strain within a transient thermo-structure, evaluated across a spectrum of beam power and scan speed parameters. Simulation results further reveal the underlying mechanisms. For instance, stress concentration primarily occurs at the necking region of partially melted particles and the junctions between different layers, resulting in the accumulation of plastic strain and residual stress, ultimately leading to structural distortion in the materials. Based on the simulation data, phenomenological relation regarding porosity/densification control by the beam energy input was examined along with the comparison to experimental results. Regression models were also proposed to describe the dependency of the residual stress and the plastic strain on the beam energy input.

Additive Manufacturing of Electrically Conductive Multi-Layered Nanocopper in an Air Environment.

The additive manufacturing (AM) of functional copper (Cu) parts is a major goal for many industries, from aerospace to automotive to electronics, because Cu has a high thermal and electrical conductivity as well as being ~10× cheaper than silver. Previous studies on AM of Cu have concentrated mainly on high-energy manufacturing processes such as Laser Powder Bed Fusion, Electron Beam Melting, and Binder Jetting. These processes all require high-temperature heat treatment in an oxygen-free environment. This paper shows an AM route to multi-layered microparts from novel nanoparticle (NP) Cu feedstocks, performed in an air environment, employing a low-power (<10 W) laser sintering process. Cu NP ink was deposited using two mechanisms, inkjet printing, and bar coating, followed by low-power laser exposure to induce particle consolidation. Initial parts were manufactured to a height of approximately 100 µm, which was achieved by multi-layer printing of 15 (bar-coated) to 300 (inkjetted) layers. There was no evidence of oxidised copper in the sintered material, but they were found to be low-density, porous structures. Nonetheless, electrical resistivity of ~28 × 10-8 Ω m was achieved. Overall, the aim of this study is to offer foundational knowledge for upscaling the process to additively manufacture Cu 3D parts of significant size via sequential nanometal ink deposition and low-power laser processing.

Computational Framework to Model the Selective Laser Sintering Process.

Selective laser sintering (SLS) is one of the most well-regarded additive manufacturing (AM) sub-processes, whose popularity has been increasing among numerous critical and demanding industries due to its capabilities, mainly manufacturing parts with highly complex geometries and desirable mechanical properties, with potential to replace other, more expensive, conventional processes. However, due to its various underlying multi-physics phenomena, the intrinsic complexity of the SLS process often hampers its industrial implementation. Such limitation has motivated academic interest in obtaining better insights into the process to optimize it and attain the required standards. In that regard, the usual experimental optimization methods are time-consuming and expensive and can fail to provide the optimal configurations, leading researchers to resort to computational modeling to better understand the process. The main objective of the present work is to develop a computational model capable of simulating the SLS process for polymeric applications, within an open-source framework, at a particle-length scale to assess the main process parameters' impact. Following previous developments, virgin and used polymer granules with different viscosities are implemented to better represent the actual process feedstock. The results obtained agree with the available experimental data, leading to a powerful tool to study, in greater detail, the SLS process and its physical parameters and material properties, contributing to its optimization.

A novel process study of biomass-based graphene-enriched body based on selective laser sintering technology

Laser-induced graphene (LIG) on natural wood is a novel method for producing porous graphene composite materials with low cost and high efficiency. However, the three-dimensional (3D) fabrication of biomass-derived LIG remains challenging, restricting its applications in various domains. This paper introduces a “SCG” (sintering, carbonization and grapheneization) preparation strategy, which integrates selective laser sintering and multiple laser processes to achieve rapid fabrication of graphene-enriched structures from natural biomass materials with complex shapes. The experiment demonstrates that the sintering necks are preserved during the carbonization and graphitization process, maintaining the original interlocking state of the upper and lower layers. The laser power and irradiation times for producing porous graphene have an optimal range, beyond which the quality of the synthesized graphene deteriorates. This study validates the effectiveness of this method and investigates the optimal process parameters and application directions. This method not only offers a 3D fabrication technique for biomass-derived LIG for the first time, but also enables 3D printing of biomass carbon electrodes, which have the benefits of wide applicability, no need for activators, low cost, and high efficiency.

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.