Computational Framework to Model the Selective Laser Sintering Process.

Selective Photo-Thermal Conversion of Tungsten Oxide Sol Precursor for Electrochromic Smart Window Applications

Lithium-ion Batteries Fabricated Entirely with Additive Manufacturing Craig Milroy1,2, Tim Phillips1, Abhimanyu Bhat1,3, David Bourell1, Joseph Beaman1 1Department of Mechanical Engineering, University of Texas, Austin; 2Texas Research Institute, Austin; 3Evonik/Structured Polymers, Inc.There is an immediate need for disruptive battery manufacturing technologies that enable novel architectures and improve energy density by reducing packaging, interconnect, and integration requirements. Most conventional batteries are packaged in rigid metal containers with a restricted range of cell geometries and form factors; this poses major challenges for minimizing footprint and integrating batteries into small spaces. Additive manufacturing (AM) methods fabricate parts layer-by-layer by precisely assembling materials according to digitized instructions, and offer a means for simplified, top-down battery production, which provides enormous freedom to create innovative two-dimensional (2D) and 3D electrode architectural designs, customize battery form factor, and enable on-demand manufacturing. As such, AM offers a paradigm shift in electrochemical device design and manufacturing to accommodate novel geometries, improve energy density, and reduce costs. However, AM is still an emerging field, and while there have been numerous reports describing the use of AM techniques to produce components for batteries and supercapacitors, the vast majority of these efforts have focused on single components (typically the electrodes), rather than on complete systems comprising printed electrodes, separators, and cases.In this presentation, we describe methods to fabricate all necessary components of coin and pouch cells for functional prototype lithium-ion (Li-ion) batteries, using a variety of AM techniques. For example, functional graphite anodes, and cathodes based on nickel-manganese-cobalt oxide (NMC) and lithium iron phosphate (LFP), were fabricated with pneumatic extrusion, screen printing, and selective laser sintering (SLS); polymeric separators were fabricated with SLS; cases/enclosures were fabricated with SLS and direct metal laser sintering (DMLS), and metal components (e.g., foils and tabs) were fabricated with DMLS.We also utilized AM as a rapid-prototyping tool to implement novel component design approaches that improve battery performance, for example:(1) we identified improved electrode configurations by fabricating a wide range of free-standing anodes and cathodes (i.e., electrodes that do not contain or require a metal current collector) using a range of SLS fabrication parameters, then quantified the internal electrode structure/porosity with X-ray computed tomography (XCT) analyses, and used the XCT data to investigate the relationship between AM build parameters and electrochemical performance;(2) we fabricated separators with SLS using a variety of materials (i.e., polypropylene, aluminum oxide, polypropylene-polyethylene copolymer, polyether ether ketone (PEEK), polyester, and blends of these materials). SLS is well-suited to producing porous films, since spherical particles can be lightly melted to create a continuous object with ample void space, minimal membrane thickness, and maximum planar uniformity by preconditioning the printing powders (to prevent clumping), and using a machined build-plate to limit powder depth.The cycle performance of NMC-based cathodes fabricated with extrusion/direct-write and screen-printing was essentially identical to tape-cast (control) cathodes; however, the extrusion-printed cathodes exhibited more pronounced capacity-fade, and there was evidence of electrode-maturation processes, indicating the need for further optimization. The electrochemical performance of LFP-based cathodes fabricated with SLS was found to depend strongly on build setpoints and discharge rate, but exhibited robust extended cycle performance for > 300 cycles.The capacity of graphite-based anodes increased steadily over the first ~20 cycles, and strongly depended on post-SLS processing methods and the charge/discharge rate. We attribute this to the properties of the binder used in the SLS process, and to electrode maturation processes.Printed separators were tested with either tape-cast NMC-based cathodes or additively manufactured anodes/cathodes, and were cycled continuously at rates between C/5 and 2C. Specific capacity was stable and consistent at all rates, and remained above 100 mAh g-1 with no observable capacity fade for any of the rates below 2C. Extended cycling at C/1.5 stable (or even increasing) capacity for approximately 85 cycles, at which point slight capacity fade began.We evaluated the cooperative functionality of printed components (i.e., printed electrodes and separators) in both half-cell and full cell configurations (this work is ongoing). Cells containing an SLS-fabricated separator and a screen-printed NMC cathode charged at C/10 and discharged at C/5 delivered reversible capacity ~160 mAh g-1 for 100 cycles.We will also present ongoing work that uses additive manufacturing to produce flexible batteries and batteries with conformal form-factors. Figure 1

An n-type Bi2Te3-based thermoelectric material Bi2Te2.85Se0.15 was prepared through an SLS (Selective Laser Sintering) process with E12/Bi2Te2.85Se0.15 as composite powder (weight ratio 1:7), from which E12 was degreased after the SLS process. It was studied the effect of laser power, scanning speed and scanning interval on the density and thermoelectric properties of the sintered samples. The laser power was found the most important influential factor, while the scanning interval was the second and the scanning speed the least. The maximum dimensionless thermoelectric figure of merit ZT is about 0.88 in the condition when the laser power, scanning interval and scanning speed were 20 W, 0.26 mm and 3000 mm s−1, respectively.

Cellular adhesion on surface structures from PA 2200 made through Selective Laser Sintering (SLS) process can be improved by modifying the parts surface. In this paper, different methods for surface modification are presented. The PA 2200 samples were immersed in six different solvents. SEM images and surface roughness tests were performed in order to evaluate the surface modification both for the control group and for the tested groups. The obtained results clearly show that there is a significant difference between the roughness of the control (untreated) surface and each of the treated surfaces. Modifying by immersion, of the PA 2200 structures produced by Selective Laser Sintering process, brings original approaches concerning the use of those procedures in the increase of the surfaces quality.

Two types of additive manufacturing (AM) techniques, fused filament fabrication (FFF) and selective laser sintering (SLS), were employed to fabricate specimens from three widely used AM polymers: polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyamide (PA): the first two using FFF and PA using SLS. The single‐edge notch bending (SENB) test was employed to measure the mode‐I fracture toughnesses of bulk and AM specimens in three directions relative to the printing direction. Unlike their bulk counterparts, AM polymers exhibited anisotropic fracture toughness. The degree of anisotropy in FFF‐PLA was much larger than FFF‐ABS and SLS‐PA. The smallest fracture toughness value for each AM polymer was achieved along the transverse printing direction. Different AM techniques affect fracture toughness differently. For instance, FFF is shown to increase PLA's plastic deformation, while SLS reduces PA's ductility. The decrease in fracture toughness is consistently observed when transitioning from bulk polymers to AM ones, reaching as much as 75%. This study provides insights into the fracture toughness of AM parts made via popular plastics, which are crucial for designing structural parts using FFF and SLS processes.

The potential advantages of pharmaceutical additive manufacturing (AM) are thoroughly described in the literature. Challenges related to pharmaceutical AM are less discussed. Selective laser sintering (SLS) is one of the AM methods possible for pharmaceutical applications. The article addresses aspects of SLS that are not typically explored in pharmaceutical studies. The literature research was conducted in parallel for both non-pharmaceutical (technical) and pharmaceutical SLS. As a result, in-depth studies on the temperature-dependent properties (rheological and optical) and thermal properties of powders for general technical printing are presented, along with the characterization of the laser sintering process. Special attention is given to the development of the "processing window" and "energy density" terms, as they continue to evolve. An application of a wide range of thermal analysis techniques is presented, including fast differential calorimetry, hot-stage microscopy, thermovision, and dielectric thermal analysis. Next, the complexity, regarding crystalline/semicrystalline/amorphous substances combination and their melt miscibility for pharmaceutical powders is marked. Pharmaceutical SLS studies are also analyzed, with emphasis on thermal aspects. Generally, pharmaceutical studies lack meaningful temperature-dependent and thermal analysis. The only significant exception is studies on drug substance amorphization during the SLS process. The main message is that pharmaceutical SLS should benefit from the methods and ideas developed for technical SLS. In particular, the research directions should include: (1) conscious powder design regarding the specificity of SLS manufacturing method, which completely different from powder compression (API - excipients matching), (2) extending the set of research methods, (3) consolidation process elucidation, (4) powder reusing or powder reusing avoiding, (5) searching for potential new carriers/excipients dedicated to pharmaceutical SLS process.

Purpose The purpose of this paper is to propose and develop PA2200-based composite powder containing 0-15 Wt.% magnesium oxide before directly using it in selective laser sintering (SLS) machine to produce end-use products for low-volume production in the engineering applications with keen focus to meet the functional requirements which rely on material properties. Design/methodology/approach The methodology reported emphasises PA2200-based composite powder containing 0-15 Wt.% magnesium oxide development for SLS process which starts with preparation and characterisation of composite material, thermal and rheological study of composite material to decide optimum process parameters for SLS process machine to get optimal part properties. Further, to verify composite material properties, a conventional casting methodology is used. The composition of composite materials those possessing good properties are further selected for processing in SLS process under optimal processing parameters. Findings The process parameters of SLS machine are material-dependent. The effect of temperature in X-ray diffraction profile is negligible in the case of magnesium oxide reinforced PA2200 composite material. The cyclic heating of material increases melting point temperature, this grounds to modify part bed temperature of material every time before processing on SLS machine to uphold build part properties, as well as material. With the rise in temperature, the Melt flow index and rheological property of materials change. The magnesium oxide reinforced PA2200 composite material has high thermal stability than pure PA2200 material. By the addition of small quantity of magnesium oxide, most of the mechanical property and flammability property improves while elongation at break (percentage) decreases significantly. Practical implications The proposed PA2200-based composite powder containing 0-15 Wt.% magnesium oxide material development system and casting metrology to verify developed material properties will be very useful to develop new composite material for SLS process with use of less material. The developed methodology has proven, especially in the case where non-experts or student need to develop composite material for SLS process according to the property requirement of applications. Originality/value Unlike earlier composite material development methodology, the projected methodology of polymer-based composite material and confirmation of material properties instead of commencing SLS process provides straight forward means for SLS process composite materials development with less use of the material and period of time.

As complex ceramic multicomponent materials, the lunar regolith and minerals still challenge people on onsite utilization technology limited to the lunar surface environment. In this paper, we investigate the suitability of lunar regolith simulants and ilmenite powders for 3D printing (aka Additive Manufacturing) of hypothetical brick aimed at lunar habitat construction. The first generation of laser 3D printing equipment (Lunar 1.0) for our experiments has been designed and assembled, which is suitable for selective laser sintering (SLS) process out of many kinds of ceramic powders to manufacturing samples with different geometrical shapes. The lunar regolith simulants and ilmenite powders are demonstrated obvious spectral absorbance from ultraviolet to near-infrared spectra, which are successfully performed during the SLS process in Lunar 1.0. The 3D printing technologies are constantly improved by adjusting the parameters of laser process and mechanical movement. The morphological features of 3D printed samples, including surface and porosity are investigated by using SEM. The evaluation of size and micro-hardness tests are also conducted to reveal the printing qualities of samples. The EDS and XRD results characterize the elements and components of 3D printed samples. Obviously, the strong heating process by laser source in Lunar 1.0 has a great impact on materials, because the complex multicomponent materials and solid state reaction in high temperature by SLS process for regolith simulants and ilmenite. However, this influence of heat treatment by laser source is quite different from continuously thermal treatment for ceramics such as normal high temperature furnace. In the future, the research for 3D printing of lunar regolith simulants and ilmenite powders for hypothetical brick in vacuum and low gravity will carry out for approaching the extreme manufacturing environment on lunar surface.

With the demand for complex, individualized and functionalized products with respect to constantly decreasing life cycles, additive manufacturing processes such as the process of selective laser sintering (SLS) has increasingly been of industrial interest. These processes are being used more and more to produce models, prototypes and partially finished products made of plastic, metal or ceramic and require neither a tool nor a form. Affected by decreasing installation spaces and increasing functional densities, flexible methods for circuit board application and their combination with additive manufacturing are in the focus of electronic industry research activities. In the context of this article both a thermoplastic polymer polybutylene terephthalate (PBT) which has been prepared to defined powder fractions with cryogenic milling, and the established and commercially available SLS material (PA12, PA2200) were the subject of a dry coating process with LDSadditives. Subsequently, these LDS-powders were processed with SLS to form test specimens. Finally their surface was structured and metallized through the LPKF-LDS-process (Laser-Direct- Structuring). Based on these metallized specimens, the metallization was studied as a function of an LDS-additive filling ratio. To uncover positive synergy effects from additively manufacturing the polymer body, the metallization was analyzed in terms of shape and adhesive strength.

Rapid manufacturing and high accuracy are very important factor in the Selective Laser Sintering (SLS) process, one of Solid Freeform Fabrication (SFF) system due to the life cycle of a product getting shorter. This paper addressed development of an industrial SFF system which employs the new laser scan path algorithm for more elaborate and speedy system for fabricating objects compared to existing SLS process. New laser scan path algorithm called Digital Mirror System (DMS). It contains variable beam expander for getting various laser beam spot size instead of the existing fixed beam expander. Also, experiments were performed to evaluate the effect of a new laser scanning path and fabrication parameters on sintering process and to fabricate the various 3D object using polymer power.

The process that combines selective laser sintering (SLS) and cold isostatic pressing (CIP) can manufacture nearly fully dense metal components with complex geometries. However, the SLS component will shrink to a significant extent during the CIP process. The modified cam-clay model was used to describe the constitutive equation of porous stainless-steel SLS components. The densification process of SLS porous components was simulated using the finite element method. The visual distributions of shape change, displacement, density, and stress were obtained, which showed that SLS components shrank with the same shape as the original design over the CIP process. In addition, a relative uniform density distribution appeared in cold isostatic pressed components. The experiment measurements displayed that the shrinkage rate of SLS components during the CIP process in height direction was a little higher than that on the forming plane due to the layer-by-layer manufacturing process of SLS. On the forming plane, the dimensional errors between simulations and experiments for the cuboid and the gear components are lower than 1% and 3%, respectively. However, the errors in height direction of the two components increase to the range of 6% and 9%.

Purpose Semi-crystalline polymers such as polyamide-12 can be used for selective laser sintering (SLS) to make near-fully dense plastic parts. At present, however, the types of semi-crystalline polymers suitable for SLS are critically limited. Therefore, the purpose of this paper is to investigate the processibility of a new kind of semi-crystalline polypropylene (PP) with low isotacticity for SLS process. Design/methodology/approach The SLS processibility of the PP powder, including particle size and shape, sintering window, degree of crystallinity and degradation temperature, was evaluated. Effects of the applied laser energy density on the surface micromorphology, density, tensile strength and thermal properties of SLS-built PP specimens were studied. Findings The results show that the PP powder has a nearly spherical shape, smooth surfaces, an appropriate average particle size of 63.6 μm, a broad sintering window of 21 oC and low crystalline degree of 30.4 per cent comparable to that of polyamide-12, a high degradation temperature of 381.8°C and low part bed temperature of 105°C, indicating a very good SLS processibility. The density and the tensile strength first increase with increasing laser energy density until they reach the maximum values of 0.831 g/cm3 and 19.9 MPa, respectively, at the laser energy density of 0.0458 J/mm2, and then decrease when the applied laser energy density continue to increase owing to the degradation of PP powders. The complex PP components have been manufactured by SLS using the optimum parameters, which are strong enough to be directly used as functional parts. Originality/value This paper provides a new knowledge for this field that low-isotacticity PPs exhibit good SLS processibility, therefore increasing material types and broadening the application of SLS technology.

The process of selective laser sintering (SLS) involves selective heating and fusion of powdered material using a moving laser beam. Because of its complicated manufacturing process, physical modeling of the transformation from powder to final product in the SLS process is currently a challenge. Existing simulations of transient temperatures during this process are performed either using finite-element (FE) or discrete-element (DE) methods which are either inaccurate in representing the heat-affected zone (HAZ) or computationally expensive to be practical in large-scale industrial applications. In this work, a new computational model for physical modeling of the transient temperature of the powder bed during the SLS process is developed that combines the FE and the DE methods and accounts for the dynamic changes of particle contact areas in the HAZ. The results show significant improvements in computational efficiency over traditional DE simulations while maintaining the same level of accuracy.

Selective Laser Sintering (SLS) is an Additive Manufacturing (AM) technology that is receiving considerable attention in the scientific and industrial communities due to its great ability to efficiently produce functional and complex parts. The present work aims to fabricate a real prototype via SLS, such as a hose reel for industrial applications, using polyamide 11 (PA11) as a starting material. Characterization of the PA11 powder properties was first carried out from a thermal and morphological viewpoint to determine the powder's thermal stability by TGA, the sintering window and degree of crystallinity by DSC, and the microstructure by SEM, PSD, and XRD analyses. The results revealed that PA11 has a 45-micron average particle size, circularity close to 1, and a Hausner ratio of 1.17. Together, these parameters ensure that PA11 powder flows smoothly, packs uniformly, and forms dense and defect-free layers during the SLS process, directly contributing to high part quality, dimensional precision, and stable process performance. The printability of the PA11 was optimized for the realization of 3D-printed parts for industrial applications. Finally, the quality of the printed samples and the mechanical and thermal performance were investigated. Several PA11-based parts were fabricated via SLS, showing a high level of complexity and definition, ideal for industrial applications, as confirmed by the predominantly green areas of the colored maps of X-CT. A complete prototypal case for a hose reel was assembled by using the parts realized, and it was chosen as a technological demonstrator to verify the feasibility of PA11 powder in the production of industrial professional components.

This study investigates the influence of tooth layer orientation on the bending fatigue behaviour of Nylon 12 spur gears manufactured by a selective laser sintering process in an ‘on-edge’ configuration. The test gears were submitted to single tooth bending fatigue tests, and the thermal response of gears was recorded using Infrared thermography. The surface morphology of failed teeth was examined using microscopy. The effect of tooth layer orientation on the fatigue strength of selective laser sintering gears was evaluated by testing each tooth configuration. The tooth configurations with the highest and lowest strength were 40° and 160°, respectively. The performance of selective laser sintering gears was compared with that of injection moulded Nylon 66 gears. The injection moulded, selective laser sintering 40°, and selective laser sintering 160° gear teeth were tested at multiple loads to investigate the high cycle fatigue and low cycle fatigue behaviour. The bending fatigue life was highest for the injection moulded gears in both low cycle fatigue and high cycle fatigue regimes. The surface temperature was higher in selective laser sintering gears, with 160° configuration exhibiting the highest temperature. The difference between the temperatures of selective laser sintering 40° configuration and injection moulded gear magnified as the applied load increased. Consequently, the strength of the selective laser sintering 40° configuration with respect to injection moulded gear deteriorated in the low cycle fatigue region. Fractography indicated that crack propagation in selective laser sintering 40° and selective laser sintering 160° configurations were cross-laminar and inter-laminar, respectively. In the cross-laminar mode of propagation, the crack propagation was impeded by the layer structure. However, the crack propagation was expedited in the inter-laminar mode, as the crack path was along the interlayer region, which presents a path of least resistance.