Laser Sintering Process Research Articles

Theoretical and experimental research on the quality of thermoformed foils using 3D-printed plastic moulds

An innovative approach to additive manufacturing consists in the possibility of producing moulds that can be used for traditional manufacturing processes such as thermoforming. The quality and dimensional precision of the interior surfaces of the plastic foils obtained after thermoforming is closely related to the used mould. The influencing factors considered are the different thermal and mechanical properties offered by the wide range of available plastic materials for additive manufacturing (AM), the multitude of printing parameters, and the technological process by means of which the mould was obtained. For the production of plastic moulds, Fused Filament Fabrication (FFF) and Selective Laser Sintering (SLS) processes, as well as materials specific to each technology, are used. This paper identifies and explains issues concerning the surface quality of the thermoformed foil through a systemic analysis approach and by conducting laboratory experiments. Optical 3D scanning equipment and software are employed to determine the proper additive process and materials for thermoforming process. The best quality of the finished product was obtained in the case of a male mould made by the SLS technology and PS foil with a thickness of 0.7 mm.

Investigations on Mechanical Properties of Polyamide Parts Fabricated by Selective Laser Sintering Process

Investigations on Mechanical Properties of Polyamide Parts Fabricated by Selective Laser Sintering Process

Performance Analysis of Conventional and DMLS Copper Electrode During EDM Process in AA4032-TiC Composite.

In recent days, the additive manufacturing process plays a vital role in the production of tool electrodes, which are used in the electrical discharge machining (EDM) process. In this work, the copper (Cu) electrodes prepared using the direct metal laser sintering (DMLS) process are used for the EDM process. The performance of the DMLS Cu electrode is studied by machining the AA4032-TiC composite material using the EDM process. Then the performance of the DMLS Cu electrode is compared with the conventional Cu electrode. Three input parameters, such as peak current (A), pulse on time (s), and gap voltage (v), are selected for the EDM process. The performance measures, which are determined during the EDM process, are material removal rate (MRR), tool wear rate, surface roughness (SR), microstructural analysis of machined surface, and residual stress. At a higher pulse on time, more material was removed from the workpiece surface and thus MRR is enhanced. Likewise, at a higher peak current, the SR is amplified and thus wider craters are formed on the machined surface. The residual stress on the machined surface has influenced the formation of craters, microvoids, and globules. Lower SR and residual stress are attained by using DMLS Cu electrode, whereas MRR is higher when using conventional Cu electrode.

Synthesis, structural, optical, and electrical properties of continuous wave and pulse laser sintered semiconductor Ge films

The crystallization process of Ge films by a continuous wave (CW) and a pulsed laser is very effective for producing smooth, homogeneous, and crack-free polycrystalline films to use in transistors, photodetectors, and photovoltaic applications. However, little progress has been made to directly crystallize Ge films based on micro/nanoparticles (NPs) using the laser sintering (LS) process. In this paper, a simultaneous LS and crystallization process of Ge micro/NPs to develop thick polycrystalline films on silicon substrates is demonstrated. Silicon substrates with a SiO2 insulating layer on top were considered for compatibility with complementary metal–oxide–semiconductor (CMOS) technology. The LS process was applied to solution deposited micro/NPs, 5 µm thick Ge films using both CW mode (infrared laser of wavelength 1070 nm) and pulse mode (UV laser of wavelength 355 nm) laser. After the LS process, around 2–2.5 µm thick film of polycrystalline Ge (pc-Ge) was achieved with optical and electrical properties comparable to traditionally developed chemical vapor deposited films. The crystallinity of the pc-Ge films was evaluated by Raman spectroscopy and x-ray diffraction (XRD). The laser-sintered films exhibited a Raman peak at 300 cm−1 and XRD 2θ peak at 27.35, which indicated the poly-crystalline structure. The fabricated film showed high hole mobility of 203 cm2 V−1 s−1, without any doping and film electrical resistivity value of 6.24 × 105 Ω-cm. The developed LS process allows the quick deposition of polycrystalline thick films, removing surface porosity and voids, increasing films adhesion with the substrate, and faster thermal annealing.

Effect of layer orientation on the single tooth bending fatigue strength of polymer gears manufactured by selective laser sintering

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.

Distinctive analysis of the shear bond strength of Porcelain Fused Metal substructure fabricated by conventional casting, direct metal Laser Sintering and CAD-CAM processing techniques

Background:The use of metal-ceramic restorations began in the late 1950’s allowing the development of prosthetic rehabilitation with better cosmetic results replacing previously in-demand precious metals. These restorations are commonly preparedusing conventional casting, Direct Metal Laser Sintering and CAD-CAM processing techniques. The present study has been attempted to perform a distinctive analysis of the shear bond strength of porcelain fused metal substructure fabricated by conventional casting, Direct Metal Laser Sintering and CAD-CAM processing techniques. Materials and Methods: The present study follows an in-vitro study design. A total of 45 samples were prepared and divided into 3 groups (n=15 in each group): conventional casting, Direct Metal Laser Sintering and CAD-CAM groups. The shear bond strength of all the specimens was measured using Universal Testing Machine. The specimens were subjected to shear load at the metal-porcelain interface with increasing load and the crosshead speed of 2 mm/sec till the disc debonded completely. The debonded samples were observed under Scanning Electron Microscope to assess the kind of failure. Results:The obtained data of three experimental group samples were analysed using the student’s t-test, One-way ANOVA test and Tukey’s Post-hoc test. Results of t-test showed that, of all the three techniques, Casting technique showshighest mean of force and shear bond strength, and this mean difference was significant. The same results were shown in One-way ANOVA test and Tukey’s Post-hoc test. Conclusion: From the observations of the present study, it can be stated that Casting technique showed highest mean of load and shear bond strength followed by the CAD/CAM method and DMLS technique, respectively. The results of this study ranged from 69-87MPa which is within the safety borders. Therefore, it can be concluded that allthree methods can be used to fabricate the metal substructure in metal-ceramic restoration.

Effect of Zircoat-M coating on SS304L for designing high temperature process chamber in selective laser sintering

Selective laser sintering (SLS) process is one of the most useful additive manufacturing techniques used, because it has the ability to readily generate complicated structures. The quality of parts made by SLS process directly depends on controlling heat transfer to powder bed. High temperature process chamber is specially designed for high temperature plastics and metal powders (PEEK and Aluminium). With the exception of aluminium, Zircoat - M is a Zirconia-rich refractory coating compound with a high proportion (63%) of Zirconia and is best suited for ferrous and non-ferrous metals and refractories. Metals and refractories are protected by Zircoat-M from corrosion erosion and flue gases escaping from heating chambers. An attempt was made to develop a high temperature build chamber and pre-heating system to manufacture prototypes using materials having maximum melting/ fuse temperature of 800°C. PEEK and Aluminium may be used to produce light weight products for multiple sectors such as bio-medical, automobile and aerospace. A high temperature resistant stainless steel 304L grade was chosen, along with SS304L coated with Zircoat-M for Build chamber and Pre-heating system. Experimental analysis such as Thermal Expansion, Thermal Conductivity and Corrosion resistance for the coated and uncoated specimen was carried out. Coefficient of Linear Thermal Expansion of uncoated specimen is 16 × 10-6 /°C and coated specimen is 14 × 10-6 /°C. Thermal conductivity for the Ceramic coated Zircoat-M on SS304L for 100 °C is 0.280 W/mK. Thermal conductivity of SS304L at 100 °C is 16.3 W/mK. Both the specimen has very good corrosion resistance.

Mixed modes crack paths in SCB specimens obtained via SLS

The paper presents experimental results of the crack path in Semi-Circular Bend (SCB) specimens obtained through additive manufacturing using Selective Laser Sintering (SLS) process. Determination of fracture parameters for components obtained via Additive manufacturing is a challenging topic, due to the influence of manufacturing parameters on the mechanical properties. Several researches provided the fracture toughness of SLS components, however there are not yet available results regarding the crack paths in such materials. The SCB specimens were designed with different crack orientations (0°, 15°, 30°, 45°, and 54°) and manufactured using EOS Formiga – SLS equipment (energy density 0.066 J/mm2, chamber temperature 169.5 °C, layer thickness 0.1 mm) using PA2200 material. The specimens were tested in symmetric three point bending configuration, creating 6 mode mixity from mode I (0° – crack orientation) to pure mode II (54° – crack orientation). Tests were performed at room temperature using 2 mm/min loading speed in a Zwick ProLine Z005 testing machine. For each crack orientation five specimens were tested. Crack initiation angle and crack propagation were measured by image digitization after the mechanical testing and presented in accordance to the initial orientation of the crack. Also, numerical simulation of crack path was conducted in the same way like the experiment and results were compared to the measured one.

Laser-sintering fabrication of integrated Al/Ni anodes for lithium-ion batteries.

Integrated Al/Ni electrodes of lithium-ion batteries (LIBs) with variant atomic ratios were successfully fabricated by a one-step laser-sintering process. The microstructure, phase composition, and pore structure were controlled by the raw material composition and laser parameters. The electrodes showed working merits without any conductive agent and binder, or even the collector used in a traditional battery. It was shown that the electrode consisted of multi-phases, i.e., Al, Al3Ni2, Al3Ni, and Ni, when the Al/Ni atomic ratio was higher than 5 : 5. A lower Al/Ni atomic ratio less than 5 : 5 favored the formation of a dual-phase electrode consisting of Al3Ni2 and Ni. As the Al content increased, the specific surface area of the as-sintered electrodes increased in the initial stage and then decreased. The formation of pores was closely related to the content of the residual Al phase after the laser sintering. The residual Al phase filled the pores when the Al content was high, leading to a lower pore size. In contrast, the liquid Al phase completely reacted with the Ni component, leaving a large number of pores at its original sites. The linked pores can serve as transport channels for Li+ ions, provide mass sites for electrochemical reactions, and also buffer huge volume changes of the active material. Among the electrodes, the one with an Al/Ni ratio of 3 : 7 showed the best cycling/rate performance, i.e., a capacity of 522.8 mA h g−1 by a current of 0.1 A g−1 after 200 cycles, even holding to 338.4 mA h g−1 by a big current impact at 2 A g−1. It formed a metallurgical combination between the conductive network and the active material with multiple porous structures, which is helpful for the electrodes to provide high capacity and maintain structural stability during cycling. In addition, the average laser-sintering time of a single electrode was within 10 s, which is suitable for industrial mass production.

Tensile testing on 3D-printed metallic specimens of CuZn28 at different planes and orientations

In this research paper, the mechanical properties of additive manufactured metallic specimens of CuZn28 at different manufactured/printed orientations were studied and analysed. Different mechanical properties like maximum strength, yield point, and relative strain were investigated as per the MSZEN 6892-1:2012 standard. This is the Hungarian and European standard for the tensile test. We analysed whether different printing/manufacturing orientations in the selective laser sintering process had any effect on the strength of the printed metallic specimens. Also, we concluded which printed orientation specimen was the best and worst in terms of strength behaviour pattern by analysing key mechanical properties obtained during tensile tests of the specimens.

Experimental characterization of 3D printed cellular structures

Due to the advancements in additive manufacturing the production of lattice structures has become feasible. These structures offer a higher design freedom than foams, which makes them interesting for lightweight applications, where an easy adaptation of the geometry is needed. To better understand the behavior of these structures several different unit cells are investigated. An octet-truss lattice, two types of auxetic structures and newly developed structures exhibiting anisotropic behavior are selected. Compression and tension tests are performed using 3D-printed specimens with different volume fractions. Two materials, polyamide and thermoplastic polyurethane, are selected, since they are suitable for the selective laser sintering process. The behavior of the structures depends on both the volume fraction and the bulk material properties. For the auxetic structures and the structures with anisotropic behavior the specific energy absorption was calculated, which also depends on the bulk material properties and is higher for the polyamide than for the thermoplastic polyurethane.While octet-truss structures have already been investigated, they still offer a good baseline for developing a test method. The behavior of 2D auxetic structures has been studied extensively, however, for 3D auxetic structures only little information is available. The novel anisotropic structures have not been examined in literature yet and are especially interesting for tailored mechanical behavior as the directional dependence can be used to better govern the local mechanical response.

A 3D model of the renal vasculature - a joined result of the corrosion casting technique, micro-CT imaging and rapid prototyping technology.

Three-dimensional (3D) printed model of the renal vasculature shows a high level of accuracy of subsequent divisions of both the arterial and the venous tree. However, minor artifacts appeared in the form of oval endings to the terminal branches of the vascular tree, contrary to the anticipated sharply pointed segments. Unfortunately, selective laser sintering process does not currently permit to present the arterial, venous and urinary systems in distinct colors, hence topographic relationship between the vascular and the pelvicalyceal systems is difficult to attain. Nonetheless, the 3D printed model can be used for educational purposes to demonstrate the vast renal vasculature and may also serve as a reference model whilst evaluating morphological anomalies of the intrarenal vasculature in a surgical setting.

Study of Microstructure and Mechanical Properties of As-built and Heat-treated Additive Manufactured Inconel 718 Alloy

Additive manufacturing technology is becoming popular in the industry because it allows the manufacturer to fabricate cost-effective, strong, lightweight, and complex-shaped parts directly from 3D design data as compared with the conventional manufacturing method. Inconel 718 alloy is the most demanding material in aviation as well as in the automobile industry, in terms of manufacturing high-performance parts. In this study, Inconel 718 samples were built using the direct metal laser sintering process, and standard heat treatment was performed on the samples to improve their microstructure and mechanical properties. The as-built samples exhibited good grain structure with fine laves phases, but the matrix was free from ?' and ?" phases. During the heat treatment, the strengthening phases ?' and ?" precipitated. The mechanical properties of as-built and heat-treated samples were analysed and compared. Tensile tests revealed that the direct-aged sample had the higher tensile strength compared with the other conditions, whereas the as-built samples had higher ductility. Finally, fractography and microstructure analysis were performed to measure the failure modes of tensile specimens.

Investigation of laser and thermal sintering processes of silver nanoparticles agglomerates synthesized by spark discharge

Changes in the shape and size of silver nanoparticles (NPs) during their laser and thermal sintering have been studied experimentally and theoretically. Aerosol silver NPs forming dendrid-like agglomerates 180 nm in size were synthesized by spark discharge and exposed to laser radiation and high temperature of 750 °C. The shape and size of the NPs were investigated depending on the power of the laser radiation and the temperature of the gas. It is estimated that, at a power density of laser radiation of the order of 103-104 W/cm2, the formation of spherical NPs with an average size of 140 nm is expected. Such particles turn out to be similar to NPs thermally heated in a gas flow at 750 °C for 6 seconds.

Numerical modeling and experimental verification of the composite material of PA12/HA with parameterized random distribution in selective laser sintering

PurposeThe purpose of this study is to establish a finite element (FE) model with the random distribution of the Nylon12/hydroxyapatite (PA12/HA) composite material in selective laser sintering (SLS) process for considering the material anisotropy, which aims to obtain the law of temperature and stress changes in PA12/HA sintering.Design/methodology/approachBy using python script in Abaqus, the FE model is established in which the two materials are randomly distributed and are assigned to their intrinsic temperature-dependent physical parameters. Molten pool sizes at various process parameters were evaluated in terms of numerical simulation and scanning electron microscope analysis, identifying a good agreement between them. Evaluation of temperature and stress distribution under the condition of different HA contents was also conducted.FindingsIt shows that the uneven distribution and quantity of HA powder play a vital role in stress concentration and temperature increase. Additionally, the influence of HA addition on the mechanical performance of SLS-fabricated parts shows that it is conducive to improve compressive strength when the HA ratio is less than 5% because an excess of HA powder tends to bring about a certain amount of microspores resulting in a decrease in part density.Originality/valueThe FE model of the PA12/HA composite material with parameterized random distribution in SLS can be applied in other similar additive manufacturing technologies. It provides a feasible guideline for the numerical analysis of properties of composite materials.

Combination of Laser and Thermal Sintering of Thermoelectric Ca3Co4O9 Films

AbstractThe manufacturing technology of thermoelectric materials is laborious and expensive often including complex and time‐intensive preparation steps. In this work, a laser sintering process of the oxide‐based thermoelectric material Ca3Co4O9 is investigated. Samples based on spray‐coated Ca3Co4O9 were prepared and subsequently sintered under various laser parameters and investigated in terms of the microstructure and thermoelectric properties. Here, the combination of laser sintering and subsequent thermal sintering proved to be a promising concept for the preparation of thermoelectric films. Laser sintering can thus make a great contribution in improving the processing of thermoelectric materials, especially when films are applied that cannot be sintered under pressure.

Numerical simulation of heat transfer in the selective laser sintering process of Polyamide12

Selective laser sintering (SLS) process is the most perfect seven three-dimensional printing processes that produces three-dimensional parts from a polyamide or metal powders in stratified, the need of this process is in all different fields, the medical field, art, aerospace and other industries. The thermal phenomena generated by SLS is essential to analysis the microstructure, mechanical properties, residual stress, and all deformation of produced parts. This study applied three-dimensional element finite (EF) method by COMSOL Multiphysics software to investigate the temperature evolution in SLS. The surface heat source and the dependence of material properties on temperature are considered. It is found that the developed element finite (EF) method is able to capture the high gradients of temperature in the center of the spot laser of polyamide powder 12 (heat affected zoon). The effects of physical proprieties and laser parameters are also investigated, it was observed in the polyamide 12 powder bed, the temperature increase with the increase of pre-heating temperature and also with increasing the power laser which sintered the polyamide powder bed, the temperature increases. Also, this simulation helps us to control all the parameters and optimize the SLS process of polyamide 12, to make a perfect polyamide part manufactured by this machine with excellent quality.

On three-dimensional printing of 17-4 precipitation-hardenable stainless steel with direct metal laser sintering in aircraft structural applications

The martensitic 17-4 precipitation-hardenable stainless steel is one of the commercially established materials for structural engineering applications in aircrafts due to its superior mechanical and corrosion resistance properties. The mechanical processing of this alloy through a conventional manufacturing route is critical from the dimensional accuracy (Δ d) viewpoint for development of innovative structural components such as: slat tracks, wing flap tracks, etc. In past two decades, a number of studies have been reported on challenges being faced while conventional processing of 17-4 precipitation-hardenable stainless steel for maintaining uniform thickness of aircraft structural components. However, hitherto little has been reported on direct metal laser sintering of 17-4 precipitation-hardenable stainless steel for development of innovative functional prototypes with uniform surface hardness (HV), Δ d, and surface roughness ( Ra) in aircraft structural engineering. This paper reports the effect of direct metal laser sintering process parameters on HV, Δ d, and Ra for structural components. The results of study suggest that optimized settings of direct metal laser sintering from multifactor optimization viewpoint are laser power 100 W, scanning speed 1400 mm/s, and layer thickness 0.02 mm. The results have been supported with scanning electron microscopy analysis (for metallurgical changes such as porosity (%), HV, grain size, etc.) and international tolerance grades for ensuring assembly fitment.

Pressure drop and fluid maldistribution analysis of a compact heat exchanger manufactured by 3D printing

The current work focuses on evaluating the pressure drop and fluid maldistribution in a compact heat exchanger produced by additive manufacturing. A polymer prototype was produced using the selective laser sintering process (SLS). Experimental tests were performed in order to evaluate the pressure drop in the system and the fluid maldistribution in the header. The pressure drop tests were carried out at room temperature over a wide range of Reynolds numbers, from laminar to turbulence flow, totaling 76 experimental tests. A theoretical model was presented and validated to predict the pressure drop in the heat exchanger, with an average error of approximately 21%. To evaluate the fluid maldistribution, the header outlet was divided into 9 sections and experimentally tested at 18 flow levels twice, totaling 36 experiments. A modified coefficient of variation (CoV) was applied to estimate the fluid distribution in the header, this model was based on the pressure difference between the header inlet and the section outlet pressure.

Relationships between porosity and mechanical properties of polyamide 12 parts produced using the laser sintering and multi-jet fusion powder bed fusion processes

Laser powder bed fusion (L-PBF, or Laser Sintering) and Multi-Jet Fusion (MJF) are two commercial powder bed fusion (PBF) additive manufacturing (AM) processes for polymers. While the strength of parts produced with polymer PBF processes is typically good, the toughness of AM parts is significantly reduced compared to traditional processes, such as Injection Molding (IM). This study evaluates the impact of residual porosity on the strength and ductility of polyamide-12 (PA-12) parts produced by powder bed fusion. Hot isostatic pressure (HIP) treatment is used to eliminate virtually all porosity from treated L-PBF and MJF parts. The relationship between porosity and mechanical properties (ultimate tensile strength, elongation at break, toughness) is evaluated for groups of parts with and without HIP treatment. For untreated parts, the thickness of the part was found to have a significant impact on mechanical properties, with 5 mm parts having more than 25% higher UTS, 39% higher maximum strains, and 21% higher Young's Moduli than 1 mm parts produced using the same process. In L-PBF parts, the HIP treatment greatly reduced porosity and increased ultimate tensile strengths by an average of 12% compared to parts that were not subjected to HIP, but they also exhibited reduced max strains. While HIP eliminated porosity in MJF parts, MJF parts did not exhibit any statistically significant improvements in mechanical properties from HIP. Though it was not possible to correlate the strength of an untreated part with density, a correlation does exist between density and some mechanical properties (UTS, Young's Modulus) as a result of a density change in L-PBF parts due to a post-processing HIP treatment. • No direct correlation between density and mechanical properties for L-PBF or MJF. • Hot isostatic pressure (HIP) treatment eliminated porosity in PA12 parts. • HIP increased tensile strength but reduced strain at failure. • Pore elimination did not improve ductility in PA12 AM parts.