Laser Sintering Research Articles

A facile one step route that introduces functionality to polymer powders for laser sintering

Laser Sintering (LS) is a type of Additive Manufacturing (AM) exploiting laser processing of polymeric particles to produce 3D objects. Because of its ease of processability and thermo-physical properties, polyamide-12 (PA-12) represents ~95% of the polymeric materials used in LS. This constrains the functionality of the items produced, including limited available colours. Moreover, PA-12 objects tend to biofoul in wet environments. Therefore, a key challenge is to develop an inexpensive route to introduce desirable functionality to PA-12. We report a facile, clean, and scalable approach to modification of PA-12, exploiting supercritical carbon dioxide (scCO2) and free radical polymerizations to yield functionalised PA-12 materials. These can be easily printed using commercial apparatus. We demonstrate the potential by creating coloured PA-12 materials and show that the same approach can be utilized to create anti-biofouling objects. Our approach to functionalise materials could open significant new applications for AM.

Optimizing Surface Roughness of workpieces made of stainless steel 316L with DMLS technology: A Taguchi Method Approach

Abstract This study employs Direct Metal Laser Sintering (DMLS) technology to investigate surface roughness in stainless steel 316L 3D printing processes. Utilizing the Taguchi method in experimental design, we examine the influence of independent variables—laser power, scan speed, and hatch spacing - on surface roughness quality. Results indicate that laser power has the greatest impact, followed by scan speed and hatch spacing. Notably, both laser power and hatch spacing positively affect surface roughness, while scan speed adversely affects the top surface quality of printed components. This research enhances comprehension of the intricate relationship between process parameters and surface quality in DMLS-based 3D printing, offering insights for optimizing surface roughness in stainless steel 316L applications. The study holds practical significance for enhancing the quality and performance of 3D-printed components across diverse engineering and manufacturing sectors.

Design and Implementation of a Novel Fiber Deposition System to Enable Laser Sintering of Chopped Fiber Reinforced Polymers

Design and Implementation of a Novel Fiber Deposition System to Enable Laser Sintering of Chopped Fiber Reinforced Polymers

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.

Effect of laser etching on surface characteristics and porcelain bond to soft milled and direct metal laser sintered cobalt chromium alloys

Statement of problemThe surface topography of metal substrate can affect its bond to porcelain. A neodynium-doped yttrium aluminum garnet (Nd:YAG) laser has been introduced to modify the metal surface topography and improve porcelain bond strength. However, studies on the effect of laser etching on metal to porcelain bond strength are lacking. PurposeThe purpose of this in vitro study was to determine the effect of Nd:YAG laser etching on the surface roughness and wettability of and the porcelain bond strength to cobalt chromium (Co-Cr) substrate fabricated by milling and direct metal laser sintering (DMLS). Material and methodsThirty-two 0.5×3×25-mm Co-Cr specimens were fabricated by milling soft Co-Cr (M group) and DMLS Co-Cr metal powder (DML group). The surface topography of representative specimens from each study group was assessed under a scanning electron microscope (SEM) and an atomic force microscope (AFM). All specimens were assessed for surface roughness using a contact profilometer, and for wettability with a contact angle goniometer. Half of the specimens of each study group (n=8) were subjected to surface laser etching by using a Nd:YAG laser. The specimens subjected to etching were assessed again for surface topography and wettability. All specimens in both study groups were veneered with porcelain. The porcelain bond strength was tested with a 3-point bend test in a universal testing machine. The results were statistically analyzed with 2-way ANOVA test followed by the post hoc Tukey test for pairwise comparisons (α=.05). ResultsAfter etching, the M group had a higher mean ±standard deviation Ra and Rz of 2.9 ±0.6 and 17.7 ±3.2 µm and significantly better wettability and bond strength of 79 ±6 and 52 ±13 MPa. In contrast, after etching, the DMLS group had a significantly lower Ra and Rz of 7.9 ±2.4 and 41.8 ±9.3 µm and significantly lower wettability and bond strength of 87 ±4 and 70 ±10 MPa. The DMLS group had a significantly higher roughness and bond strength than the M group before and after laser etching. The SEM and AFM showed different surface topography in the study groups. ConclusionsThe manufacturing process of Co-Cr substrate had a significant effect on surface characteristics and porcelain bond strength. Laser etching improved the surface topography and bond strength of milled Co-Cr but not of DMLS Co-Cr.

Effect of graphite content on the microstructure and mechanical properties of SLS-based RB-SiC ceramics

In this study, reactive bonded (RB)-SiC ceramics were fabricated using a combination of selective laser sintering (SLS) and reactive melt infiltration (RMI). The microstructure and mechanical properties of RB-SiC ceramics were optimized by adjusting the graphite content. The sintered bodies were found to consist of α-SiC, β-SiC, Si and C. The addition of graphite prolonged the reaction time between carbon and silicon, resulting in a greater infiltration of molten silicon and an increased formation of β-SiC. Furthermore, a correlation was observed between the proportion of graphite content and the bulk density and bending strength of RB-SiC ceramics. In the range of 0–10 wt%, the bulk density initially increased and then decreased as the graphite content increased. The maximum density was found to be 2.74 ± 0.15 g/cm3. The flexural strength reached the maximum value at 217.9 ± 16.9 MPa when the graphite content was 5 wt%. However, beyond this point, the flexural strength decreased rapidly. The present research demonstrates the promising potential of utilizing SLS additive manufacturing to fabricate SiC ceramics with exceptional mechanical properties.

3D printing of low carbon steel using novel slurry feedstock formulation via material extrusion method

Conventional 3D metal printing methods, such as laser sintering and binder jetting are often associated with high initial capital costs that make them inaccessible to many consumers. In this article, an economical alternative approach to 3D metal printing is presented, which uses a slurry-based formulation with the material extrusion method. This method involves a novel slurry feedstock of metal powder and liquid binder, which can be printed at room temperature to form green samples without the need for equipment such as a laser source, binder jetting head, or heated nozzle. It is followed by a thermal treatment process to fuse the printed samples into a metal article. The slurry is prepared by blending carbon steel powder with a cellulose derivative binder and additives. Rheological behaviours of different metal contents and binder concentrations are being investigated to determine the optimum printable slurry formulation. It is found that the optimum slurry feedstock formulation comprises 45 vol% metal content, 54 vol% cellulose derivative binder solution at a concentration of 300 g/L, and 1 vol% defoamer. The resulting slurry has fast-drying shear-thinning behaviour and a high storage modulus of 4 × 107 Pa to sustain the printed article at room temperature. The printed articles exhibited an average linear shrinkage of 12.36%, with less than a 1% linear shrinkage difference between X, Y, and Z directions after thermal treatment. The measured densities of the sintered articles were 95% ± 2% compared to the ASTM B783 (material code F-0000). The sintered articles have a measured carbon content of 0.28 ± 0.02%, hardness of 64.15 ± 9 HV, ultimate tensile strength of 255.33 MPa and Young's modulus of 130.47 GPa. This work demonstrates the viability of this additive manufacturing method in producing metal parts with comparable properties to conventional manufacturing.

Research on improving the structural stability of surimi 3D printing through laser cooking techniques

At present, research on 3D printing technology for meat protein food is still in its early stages, and improving the molding stability and accuracy of products has always been a key challenge. Here, we take surimi protein as an example and achieve its localized thermal gelation quickly and precisely by incorporating laser sintering technology. And based on the thermal denaturation and solidification of proteins during the printing process, the structural instability problem of meat protein food 3D printing is solved. In this study, we used a CO2 laser with a power of 50 W to locally heat cure surimi during the printing process. The results show that under the conditions of 1 mm laser spot diameter, 500 mm/s scanning speed and 0.25 mm scanning interval, the shape accuracy and gel strength of surimi products with 1.5 mm layer thickness are significantly improved, and this combination parameter shows the best effect in the experiment. This study provides a theoretical basis and reference for real-time solidification in meat protein food printing.

DIRECT METAL LASER SINTERING TO DEVELOP COMPLEX CONTOURS OF AlSi10Mg ALUMINIUM ALLOY — BUILD PARAMETERS OPTIMIZATION

In the recent years, Additive Manufacturing (AM) has become a very demanding process utilized by majority of the manufacturing industries due to its complex geometrical capabilities, high accuracy, minimal material usage and better build quality. Among the various types of AM methods, Direct Metal Laser Sintering (DMLS) is a feasible method with many applications and a lot of scope for research. This paper focuses on optimizing the important parameters of DMLS process for better build quality of AlSi10Mg Aluminium alloy. The parameters identified are laser power, hatch distance, scanning speed, and layer thickness. Grey–Taguchi multi response optimization method has been used. Experimental specimens were fabricated and tested. Micro-Vickers hardness and average surface roughness were studied. Experiments were analyzed to determine the best combination of parameters of the DMLS process. A detailed micro-structural study was conducted on the specimens. Also, crystallographic study was made. The resultant specimen thus produced had a better build quality along with satisfying micro-structural characteristics.

Selective Laser Sintering PLA/Mg Composite Scaffold with Promoted Degradation and Enhanced Mechanical

Selective Laser Sintering PLA/Mg Composite Scaffold with Promoted Degradation and Enhanced Mechanical

Aortic Valve Engineering Advancements: Precision Tuning with Laser Sintering Additive Manufacturing of TPU/TPE Submillimeter Membranes.

Synthetic biomaterials play a crucial role in developing tissue-engineered heart valves (TEHVs) due to their versatile mechanical properties. Achieving the right balance between mechanical strength and manufacturability is essential. Thermoplastic polyurethanes (TPUs) and elastomers (TPEs) garner significant attention for TEHV applications due to their notable stability, fatigue resistance, and customizable properties such as shear strength and elasticity. This study explores the additive manufacturing technique of selective laser sintering (SLS) for TPUs and TPEs to optimize process parameters to balance flexibility and strength, mimicking aortic valve tissue properties. Additionally, it aims to assess the feasibility of printing aortic valve models with submillimeter membranes. The results demonstrate that the SLS-TPU/TPE technique can produce micrometric valve structures with soft shape memory properties, resembling aortic tissue in strength, flexibility, and fineness. These models show promise for surgical training and manipulation, display intriguing echogenicity properties, and can potentially be personalized to shape biocompatible valve substitutes.

Improving the Mechanical Properties of GlassFibre-Reinforced Laser-Sintered Parts Based on Degree of Crystallinity and Porosity Content Using a Warm Isostatic Pressing (WIP) Process

Additively manufactured fibre-reinforced polymers are gaining traction. After the development and optimisation of a novel fibre-deposition system in a laser sintering (LS) setup, polyamide 12 specimens were produced with and without glass fibres. In this study, the relation between the crystallinity, porosity, and mechanical properties of LS specimens with and without fibres is investigated. After testing as-built LS specimens, a detrimental effect of the fibres on the specimens’ performance was observed with a decrease in UTS of 6%. The degree of crystallinity remained the same; however, a porosity content of 2.6% was observed in specimens with fibres. These pores can have a negative influence on the bonding between the fibres and the matrix. To investigate the influence of the pores, warm isostatic pressing (WIP) was performed on LS specimens with and without fibres. The WIP process shows a positive influence on the specimens without fibres, resulting in an increase in UTS of 8.5%. The influence of the WIP process on specimens with fibres, however, is much less pronounced, with an increase in UTS of only 2%. Neither the crystallinity nor the porosity are the cause of the less-than-expected increase in UTS in LS specimens with fibres. A number of hypotheses and mitigation strategies are provided.

Thermal management with double layered heat sink produced by direct metal laser sintering

In this study, the thermal management of a heat sink which is the heart of a cold plate is investigated considering Additive Manufacturing (AM) technology. Although AM enables many flexibilities, it also brings some limits to design and manufacturing. In general, a cold plate is developed to cool many heat sources with an appropriate heat sink design just under the sources to have a maximum cooling rate. Due to the nature of Direct Metal Laser Sintering (DMLS) AM technology, we have to use some supports (used as pin fins in this study) to avoid material collapse to have a rugged and fine product. In this study, straight rectangular channels with the production limit of AM technologies have been investigated in detail and the results are compared to investigate the heat treatment effect for the same design. Due to its cooling advantages in a confined space, a double-layered heat sink is chosen as the heat sink geometry to reach the goals. In order to succeed in electronic performance requirements, two heat sources on each side of the plate (heat sink) must be so cooled that their temperatures are close to each other. This is one of the requirements in radar electronics to have higher performance and to decrease the necessary calibration efforts. Deliberately, the heat load is selected as 100W/cm2 using mini or smaller channel sizes to enforce the limits of AM technology. One of the most important aspects of a cold plate design is to distribute the fluid to the heat sources to collect it properly without sacrificing electronic components and use the space effectively. As a result; The Double Layered Heat Sink design allows temperature difference between the heat sources to be kept around 1°C with 100W/cm2 heat flux.

Hot isostatic pressing as an alternative thermo-mechanical treatment for metallic full-arch implant-supported frameworks obtained by additive and subtractive manufacturing technology: Vertical and horizontal fit, screw removal torque, and stress analysis.

To assess vertical and horizontal fit, screw removal torque, and stress analysis (considered biomechanical aspects) of full-arch implant frameworks manufactured in Ti-6Al-4V through milling, and additive manufacturing Direct Metal Laser Sintering (DMLS) and Electron Beam Melting (EBM), and the effect of the thermo-mechanical treatment Hot Isostatic Pressing (HIP) as a post-treatment after manufacturing. Maxillary full-arch implant frameworks were made by milling, DMLS, and EBM. The biomechanical assessments were screw removal torque, strain-gauge analyses, and vertical and horizontal marginal fits. The vertical fit was assessed by the single-screw test and with all screws tightened. All frameworks were submitted to a standardized HIP cycle (920°C, 1000bar pressure, 2h), and the tests were repeated (α = 0.05). At the initial time, milled frameworks presented higher screw removal torque values, and DMLS and EBM frameworks presented lower levels of strain. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally, higher fit values were found for milled frameworks, followed by DMLS and EBM. After HIP, milling and EBM frameworks presented higher screw removal torque values; the lowest strain values were found for EBM. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally no differences were found. DMLS and EBM full-arch frameworks presented adequate values of screw removal torque, strain, and marginal fit, although the worst values of marginal fit were found for EBM frameworks. The HIP cycle enhanced the screw removal torque of milled and EBM frameworks and reduced the strain values of milled frameworks. The HIP represents a reliable post-treatment for Ti-6Al-4V dental prostheses produced by milling and EBM technologies.

Optimization of a tetrahedron compliant spherical joint via computer-aided engineering tools

AbstractThis article focuses on enhancing the range of motion (ROM) of the Tetra II joint, a spherical compliant joint consisting of three internally interconnected tetrahedron-shaped elements that achieve motion through elastic deformation. Despite its excellent precision, this specific design is constrained in terms of ROM due to internal contacts among the tetrahedral elements. To overcome this limitation, this study utilizes a computer-aided engineering (CAE) framework to optimize the configuration of the Tetra II joint and enhance its ROM. The resultant optimized joint, referred to as Tetra III, is subsequently compared to Tetra II in terms of both ROM and center shift. Finite element models (FEM) are employed to validate the optimization results and examine how various tetrahedron-shaped geometries impact the joint’s performance. The newly optimized joint exhibits a significantly higher ROM compared to the previous version, while maintaining excellent precision and overall smaller dimensions. Finally, to demonstrate its manufacturability, the Tetra III joint is produced using selective laser sintering (SLS) technology, with Duraform PA serving as the construction material. The successful fabrication serves as a demonstrative example of the improved design of the Tetra III joint.

A review on natural fiber composites: Polymer matrices, fiber surface treatments, fabrication methods, properties, and applications

AbstractHigh performance and durability are essential for goods to satisfy the needs of the expanding worldwide market. Wood plastic composites (WPCs) are materials made from a combination of wood, polymers, and additives. WPCs can be extruded, injected, compressed, or thermoformed. Presently, WPCs are manufactured using sophisticated processes including as laser sintering, fused layer modeling, and additive manufacturing. Properly managing the melt temperature and pressure is crucial in the manufacturing process of WPCs to ensure effective polymer incorporation. Natural fibers have distinct benefits for polymer composites, but they also have some serious drawbacks, like lower strength properties—especially lower impact strength than synthetic fibers—poor compatibility with hydrophobic polymers, poorer dimensional stability and moisture absorption due to hydroxly groups, a maximum processing temperature that is limited, thermal degradation above 200–220°C, and lower biological durability. The modification of the surface of the fibers improves the mentioned disadvantages of the natural fibers. High‐quality WPCs require the application of chemical or physical treatment to the wood fibers. This extensive review focused on the modification techniques applied to the surface of wood, manufacturing processes, and properties and applications of WPCs.Highlights Modification methods used in surface treatment of natural fibers was explained. Properties and recent applications of wood polymer composites were given. Optimum requirements of natural fibers and polymer matrices are given. Fabrication methods of natural fiber composites are extensively given.

Shot Peening Effect on Sliding Wear in 0.9% NaCl of Additively Manufactured 17-4PH Steel.

The growing demand for modern steels showing corrosion and tribological resistance has led to their increased use in the production of medical devices. This study analyzed the effect of shot peening on wear resistance in 0.9% NaCl solution of 17-4PH steel produced by direct laser metal sintering (DMLS) technology. The study's novelty relies on revealing the effect of shot peening (SP) surface treatment on the wet sliding wear resistance of 17-4PH steel produced with DMLS. Moreover, in the context of 17-4PH steel application for medical devices, the 0.9% NaCl tribological environment were selected, and SP processes were conducted using steel CrNi shot and ceramic (ZrO2) beads. The up-to-date scientific literature has not identified these gaps in the research. DMLS technology makes it possible to obtain products with complex architectures, but it also faces various challenges, including imperfections in the surface layer of products due to the use of 3D printing technology itself. The chemical and phase composition of the materials obtained, Vickers hardness, surface roughness, and microscopic and SEM imaging were investigated. Tribological tests were carried out using the ball-on-disc method, and the surfaces that showed traces of abrasion to identify wear mechanisms were subjected to SEM analysis. The XRD phase analysis indicates that austenite and martensite were found in the post-production state, while a higher martensitic phase content was found in peened samples due to phase transformations. The surface hardness of the peened samples increased by more than double, and the post-treatment roughness increased by 12.8% after peening CrNi steels and decreased by 7.8% after peening ZrO2 relative to the reference surfaces. Roughness has an identifiable effect on sliding wear resistance. Higher roughness promotes material loss. After the SP process, the coefficient of friction increased by 15.5% and 20.7%, while the wear factor (K) decreased by 25.9% and 32.7% for the samples peened with CrNi steels and ZrO2, respectively. Abrasive and adhesive mechanisms were dominant, featured with slight fatigue. The investigation showed a positive effect of SP on the tribological properties of DMSL 17-4PH.

Post-Production Finishing Processes Utilized in 3D Printing Technologies

Additive manufacturing (AM) has revolutionized production across industries, yet challenges persist in achieving optimal part quality. This paper studies the enhancement of post-processing techniques to elevate the overall quality of AM-produced components. This study focuses on optimizing various post-processing methodologies to address prevalent issues such as surface roughness, dimensional accuracy, and material properties. Through an extensive review, this article identifies and evaluates a spectrum of post-processing methods, encompassing thermal, chemical, and mechanical treatments. Special attention is given to their effects on different types of additive manufacturing technologies, including selective laser sintering (SLS), fused deposition modeling (FDM), and stereolithography (SLA) and their dedicated raw materials. The findings highlight the significance of tailored post-processing approaches in mitigating inherent defects, optimizing surface finish, and enhancing mechanical properties. Additionally, this study proposes novel post-processing procedures to achieve superior quality while minimizing fabrication time and infrastructure and material costs. The integration of post-processing techniques such as cleaning, surface finishing, heat treatment, support structure removal, surface coating, electropolishing, ultrasonic finishing, and hot isostatic pressing (HIP), as steps directly within the additive manufacturing workflow can immensely contribute toward this direction. The outcomes displayed in this article not only make a valuable contribution to the progression of knowledge regarding post-processing methods but also offer practical implications for manufacturers and researchers who are interested in improving the quality standards of additive manufacturing processes.

Additively-manufactured gradient porous bio-scaffolds: Permeability, cytocompatibility and mechanical properties

The additive manufacturing technology enables the customization of artificial bone scaffolds, especially those with internal gradient porous structures (GS). It is of great significance to study the correlation between parametric design of GS and its properties. In this study, GS scaffolds were obtained by triply periodic minimal surfaces (TPMS) parametric design and fabricated by selective laser sintering. The stress distribution and permeability of GS scaffolds were elucidated by a combination of numerical simulation and experimental testing. Experimental tests indicated that the pore size of GS scaffold is in the range of 570 ∼ 1440 μm, corresponding to the average compressive strength of 3.0 ∼ 9.3 MPa, respectively. The test permeability of GS scaffolds ranged from 1.241 × 10-9 to 2.231 × 10-9 m2, all within the range of human bones (2.56 × 10-11 to 7.43 × 10-8 m2). Moreover, in vitro biomineralization and biological testing of GS scaffolds showed excellent calcium-phosphorus formation induction and biocompatibility. In summary, GS scaffold successfully realizes flexible control of structural parameters, especially GP-type scaffolds with radial gradient porous structures exhibit mechanical properties and permeability comparable to natural bone tissue, and even effectively regulate cell behavior. Therefore, the GS scaffolds proposed in this work is expected to exhibit great application potential in orthopedic implants.

Layered co-continuous structure in bone scaffold fabricated by laser additive manufacturing for enhancing electro-responsive shape memory properties

Porous scaffold based on electro-responsive shape memory polymers (ESMPs) possesses great potential applications in minimally invasive surgery for bone defect repair because it provides the ability for remote control and internal heating. However, it's difficult to obtain co-continuous structure in bone scaffold for achieving excellent electro-responsive shape memory properties. In this study, layered co-continuous structure with thermoplastic polyurethane (TPU) loaded with multi-walled carbon nanotubes (MWCNTs) (referred to as cTPU) layer and l-polylactic acid (PLLA) layer alternate stacking was obtained via layer-by-layer fabrication technology, and the porous scaffold was fabricated via selective laser sintering (SLS). The thermal and electrical shape memory properties of the scaffolds with different contents of MWCNT were evaluated by dynamic mechanical analysis (DMA) and U-bending experiments. The results indicated that the layered co-continuous structure improved phase continuity and confined MWCNTs to one side, enhancing the electrically driven properties and shape memory properties. The scaffold with 1.5 wt% MWCNTs achieved shape fixed and recovery rates of 95.6% and 90.2%, respectively. With the further increasing of MWCNTs content, the shape memory properties decreased due to the agglomeration of MWCNTs in the cTPU phase, which affected the phase continuity of cTPU. The DMA results confirmed the good mechanical properties of the scaffold, and the cell culture experiment results demonstrated excellent cytocompatibility for cell attachment and growth. This work provides a feasible method to fabricate electro-responsive shape memory bone scaffold with layered co-continuous structure, which exhibits great potential in applications of bone defect repair.