Selective Laser Sintering Technique Research Articles

Manufacturing processes for the development of engineered wood – A mini-review

In this article, various manufacturing processes for the production of engineered wood and wood based composites have been discussed. Most of the plastic material based industries were using these processes for a long time but now industries have found these methods suitable for wooden material as well. Some basic processes like extrusion and wet sheet formation are used to give shape and form to the product and the final shape is in the form of beam block or sheet generally. For complex profile and prototyping, injection moulding and 3D moulding processes are preferred. However, the selection of these methods may increase the production cost. Some other new technologies like selective laser sintering technique play a vital role in wooden prototyping and customized designing sector.

Selective laser sintering (SLS) technique for pharmaceutical applications—Development of high dose controlled release printlets

The paper presents the unique approach to 3D printing by Selective Laser Sintering of high dose controlled release pharmaceutical dosage form, which contains almost exclusively drug substance - just crystalline paracetamol as a model drug substance and small amount of dye were used. Comprehensive printlet characterization, that included pore space analysis, drug release and subsequent dissolution modeling as well as exploratory analysis, revealed various degrees of freedom for tuning its functional properties i.e. dissolution performance. Two degrees of freedom were found substantial for the proposed approach: (1) the macro structure shaping in terms of active surface to volume ratio; (2) microstructure shaping in terms of pore space structure. The latter was found to have a great potential and can be modified by the manufacturing parameters, e.g. hatch spacing. The simplicity of the preparation and flexibility to control the dissolution performance of the pharmaceutical dosage are the advantages of the proposed approach. • Pharmaceutical high dose oral administration. • Highly drug-loaded controlled release formulations by selective laser sintering • Macro and micro structure shaping for drug dissolution tuning. • Flexible dosage form design for personalized medicine. • Simple manufacturing and simple dissolution mechanism.

Towards selective laser sintering of objects with customized mechanical properties based on ANFIS predictions

Recently, the adaptive network-based fuzzy inference system (ANFIS) has been used extensively in modeling of manufacturing processes to save both optimization time and manufacturing costs. ANFIS is a powerful iterative tool for optimizing non-linear and multivariable manufacturing operations. In the present study, ANFIS is used to predict the optimum manufacturing parameters in selective laser sintering (SLS) of cement-filled polyamide 12 (PA12) composite. For this purpose, a set of cement-filled PA12 test specimens is manufactured by SLS technique with 8 different values of laser power (4.5–8 Watt) and 8 different weight fractions of white cement (5 %–40 %). Mechanical characterization of cement-filled PA12 is carried out to evaluate the ultimate tensile strength (UTS), compressive strength, and flexural properties. The experimental data are then divided into two groups; one group for training the ANFIS model and the other group for checking the validity of the identified model. The built ANFIS model was validated experimentally and comparison with experimental results revealed mean relative errors of 2.92 %, 3.84 %, 4.75 %, and 3.31 % in the predictions of UTS, compressive strength, flexural modulus, and flexural yield strength, respectively.

Biomaterials for Regenerative Medicine

Biomaterials for Regenerative Medicine

Oral preparations with tunable dissolution behavior based on selective laser sintering technique.

Selective laser sintering (SLS) sinters a powder layer by layer with a laser beam to prepare 3D printlets, which are widely used in the field of tissue engineering and personalized implants. To promote the SLS printing of oral solid preparations, the printability of commonly used drugs and excipients was evaluated using a 450nm low energy laser. It was found that yellow drugs could absorb laser energy and sinter, while white drugs and pharmaceutical excipients had SLS printability when tartrazine lake was added as a photoabsorber. The printing mechanism of non-crystalline and crystalline polymers was powder sintering and powder melting, respectively. Increasing the laser energy density was beneficial to the printing efficiency but reduced printing accuracy. To ensure the integrity of multilayer printlets, the sintered thickness of each layer should be greater than the layer thickness. Furthermore, ibuprofen immediate-release tablets and metoprolol tartrate sustained-release tablets were prepared. Using 10% carboxy methyl starch sodium as an additive, the shell tablets with a side thickness of 1.5mm had a good appearance and fast dissolution. Based on the optimized formulation, IBU preparations with various design shown good appearance and fast release property. There was no difference in the drug's crystalline state after SLS printing. Besides, the printed reservoir tablets with a sustained-released coating thickness of 3.5mm had a good appearance and allowed 12h sustained release. The results revealed that the SLS technique has great prospects in producing personalized oral preparations with immediate-release and sustained-release properties.

Effect of cable surface characteristics and flow turbulence on the aerodynamic behaviour of stay cables in dry conditions

This article describes a wind-tunnel study to evaluate the aerodynamic behaviour of stay cables of a bridge with various surface geometries in dry conditions. Nine cable models were fabricated and tested. Aerodynamic forces acting on the static models were measured for different wind speeds, cable-wind angles and cable axial rotation angles, in smooth and turbulent flow. The aerodynamic forces of bare, round cable models with different roughness levels were used as a baseline to compare the aerodynamic loading of the cables with surface geometry features. A comprehensive database of existing and emerging cable geometries in a wide range of flow conditions and cable-wind angles was generated. The trends exhibited by models with geometric features are similar to results available in the open literature. The aerodynamic drag coefficient was largely affected by the presence of cable surface geometry. The model with helical strakes had the lowest drag coefficient throughout the range of Reynolds numbers that was evaluated. It was observed that turbulence had a similar effect on all models, resulting in a reduction of the drag coefficient at lower Reynolds numbers and an earlier increase in drag that is associated with the supercritical Reynolds number regime. The presence of turbulent flow resulted in higher drag coefficients at high Reynolds numbers. An important secondary finding was that models fabricated with the Selective Laser Sintering (SLS) technique have a higher surface roughness than high-density polyethylene (HDPE) stay cable sleeves but when printed, they have a similar surface roughness.

Selective laser sintering of polyamide 12/flame retardant compositions

In this work, various flame retardants (FR) and clays were added to polyamide 12 (PA12). The processability by Selective Laser Sintering (SLS), thermal behaviour and flame retardancy of these compounds were evaluated. The observations show an important impact on powder flowability of some formulations containing melamine cyanurate and melamine polyphosphate leading to difficulties during SLS process. The incorporation of FRs also leads to changes in melting and crystallization temperatures of polyamide as a function of the FR type. Furthermore, in order to evaluate the influence of the process on thermal properties of samples, a comparison between thermocompression (TC) and SLS techniques was performed for the formulations containing the flame retardants alone. The addition of flame retardants impacts the porosity of the SLS samples as a function of the FR type. For the additives which are able to melt during SLS process, a lower porosity was observed. Samples made by TC containing 30 wt% of ammonium polyphosphate, zinc diethylphosphinate and a pentaerythritol ester of methane phosphonic acid showed a better thermal stability and flame retardancy compared to the ones made by SLS, probably due to the porosity of the SLS samples and some degradation of the flame retardant by the laser beam. For the formulation containing only zinc borate, no difference was observed between TC and SLS. In order to evaluate possibly synergistic effects between flame retardants, binary and ternary formulations were prepared by SLS. On the whole, these formulations led to an improvement of flame retardancy compared to neat PA12. Moreover, XRD results showed the formation of borophosphates for binary and ternary formulations, indicating interactions between flame retardants. EDX results showed that at least 95% of the phosphorus remained in the residue for the formulations containing zinc borate, thus corroborating the results obtained by XRD. The partial substitution of zinc borate by kaolinite led to a further improvement of flame retardancy at the expense of a porosity increase in the samples.

Delivering Proangiogenic Factors from 3D-Printed Polycaprolactone Scaffolds for Vascularized Bone Regeneration.

Natural bone is a highly vascularized tissue that relies on the vasculature for blood and nutrients supply to maintain skeletal integrity. Inadequacy of neovascularization may compromise the tissue ingrowth to the implanted scaffolds, and eventually results in failure for the repair. To tackle this issue and enhance self-vascularized bone regeneration, herein a 3D biomimetic selective lasersintering (SLS) derived scaffold, with an angiogenic growth factor immobilized on its surface, that can be released in a controlled manner is proposed. To this end, a porous polycaprolactone/hydroxyapatite (PCL/HA) scaffold is prepared via the SLS technique, which is further modified with vascular endothelial growth factor (VEGF) by coprecipitation with apatite. The resultant scaffold (PCL/HA/VEGF) has an excellent cytocompatibility, and subcutaneous implantation experiment shows that the VEGF-loaded scaffold significantly enhances the blood vessel formation compared with the VEGF-free control. It is further demonstrated that the PCL/HA/VEGF scaffold is able to enhance the in vivo bone regeneration in a rat cranial defect model. Taken together, the current study provides not only a feasible and promising scaffold candidate to enhance the vascularized bone regeneration, but also a general strategy to overcome the inadequate vascularization issue for the repair of other tissue and organs.

Enhanced Crystallinity and Antibacterial of PHBV Scaffolds Incorporated with Zinc Oxide

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has a great potential in bone repair, but unfortunately, the poor mechanical properties limit its further application. In this work, zinc oxide (ZnO) nanoparticles were incorporated into PHBV porous scaffold fabricated by selective laser sintering technique. It was because ZnO nanoparticles could provide nucleating sites for the orderly stacking of polymer chains, thereby enhancing the crystallinity of PHBV. It was well known that the mechanical properties of PHBV scaffold could be enhanced with the increase of crystallinity. More significantly, the released Zn2+ would combine negatively charged cell membranes of bacterial through electrostatic interaction and consequently destructed the protein structure and resulted in the death of bacterial, which was highly desired in reducing the risk of implant infection. Results indicated that the relative crystallinity of scaffold with 3 wt.% ZnO increased remarkably from 38% to 64% compared to pure PHBV scaffold, which effectively enhanced the compression strength and modulus by 56% and 51.5%, respectively. Moreover, the scaffold had a favorable antibacterial activity. Cell culture experiments proved that the scaffold could promote the cell behaviors. The positive results demonstrated the scaffold may serve as a potential replacement in bone repair.

Enhancement of mechanical properties of metamaterial absorber based on selective laser sintering and infiltration techniques

In this study, a 3D printing technology, selective laser sintering (SLS), and infiltration techniques were used to prepare a complex three-dimensional metamaterial absorber with high performance. The raw carbonyl iron (CI) powders were coated by polyamide12 (PA12), where the dissolution-precipitation method was used to improve their uniformity. The coated powders were then printed by SLS. The influence of laser power on the relative density of the composites was studied, where 18W was thought as the optimal laser power. And the SLS samples were infiltrated by thermosetting epoxy resin (EP, E−44) to increase their relative densities and strength. Mechanical tests showed that the infiltrated composites have an ultimate tensile strength of 41.98 MPa, almost 15 times higher than those without infiltration. The final metamaterial absorber (MMA) exhibited the reflection loss below −10 dB in 2.7–18 GHz. The above results indicate that the fabricated processes proposed in this paper have great potential for the preparation of three-dimensional metamaterial absorbers.

Selective laser sintered nano-HA/PDLLA composite microspheres for bone scaffolds applications

Purpose The main cause of aseptic inflammation after an in vivo implantation is that Poly(L-lactide) (PLLA) and Poly(D-lactide) have a slower degradation and absorption rate, while Poly(D, L-lactide) (PDLLA) has a much faster degradation rate than PLLA because of its amorphous structure. Also, the hydrolyzate of Hydroxyapatite (HA) is alkaline, which can neutralize local tissue peracid caused by hydrolysis of Polylactic acid. Design/methodology/approach In this study, the selective laser sintering (SLS) technique was chosen to prepare bone scaffolds using nano-HA/PDLLA composite microspheres, which were prepared by the solid-in-oil-in-water (S/O/W) method. First, the SLS parameters range of bulk was determined by the result of a single-layer experiment and the optimized parameters were then obtained by the orthogonal experiment. The tensile property, hydrophobicity, biocompatibility, biological toxicity and in vitro degradation of the samples with optimized SLS parameters were characterized. Findings As a result, the samples showed a lower tensile strength because of the many holes in their interior, which was conducive to better cell adhesion and nutrient transport. In addition, the samples retained their inherent properties after SLS and the hydrophobicity was improved after adding nano-HA because of the OH group. Furthermore, the samples showed good biocompatibility with the large number of cells adhering to the material through pseudopods and there was no significant difference between the pure PDLLA and 10% HA/PDLLA in terms of biological toxicity. Finally, the degradation rate of the composites could be tailored by the amount of nano-HA. Originality/value This study combined the S/O/W and SLS technique and provides a theoretical future basis for the preparation of drug-loaded microsphere scaffolds through SLS using HA/PDLLA composites.

Integrated Computation and Preparation Optimization of <i>In</i> S<i>itu</i> Ordered Porous Aluminum Filled Tubes

As a kind of structural and functional composite material, foam filled tubes have an application prospect in automobile industry because it meets the requirements of automobile light weight and safety performance. The traditional preparation method of foam filled tubes is ex-situ preparation and there is no metallurgical bonding between the ordered porous aluminum filler and the thin-walled tube. In this study, the in-situ ordered porous aluminum filled tubes were proposed and prepared by combining the additive manufacturing technique and infiltration casting technique. The sand preform fabricated by selective laser sintering technique was placed in the bottom of 6061 aluminum alloy thin-walled tube. ZL111 aluminum alloy was utilized to infiltrate the sand preform and expected to form a metallurgical bonding between the ordered porous aluminum filler and the thin-walled tube. The infiltration process of the in-situ ordered porous aluminum filled tube was optimized by integrated computation. The peak temperature of contact region on the thin-walled tube was obtained. The in-situ ordered porous aluminum filled tubes were successfully fabricated by utilizing the optimized parameters.

Investigation by Digital Image Correlation of Mixed Mode I and II Fracture Behavior of Metallic IASCB Specimens with Additive Manufactured Crack-Like Notch

This work investigates the fracture behavior of maraging steel specimens manufactured by the selective laser sintering (SLS) technology, in which a crack-like notch (sharp notch) was directly produced during the additive manufacturing (AM) process. For the evaluation of the fracture toughness, the inclined asymmetrical semi-circular specimen subjected to three points loading (IASCB) was used, allowing to cover a wide variety of Mode I and II combinations. The effectiveness of manufacturing crack-like notches via the SLS technique in metals was evaluated by comparing the obtained experimental results with the ones obtained with pre-cracks induced by fatigue loading. The investigation was carried out by using the digital image correlation (DIC) technique, that allowed the evaluation of the full displacement fields around the crack tip. The displacement field was then used to compute the stress intensity factors (SIFs) for various combinations of Mode I and II, via a fitting technique which relies on the Williams’ model for the displacement. The SIFs obtained in this way were compared to the results obtained with the conventional critical load method. The results showed that the discrepancy between the two methods reduces by ranging from Mode I to Mode II loading condition. Finally, the experimental SIFs obtained by the two methods were described by the mixed mode local stress criterium.

Emerging trend in manufacturing of 3D biomedical components using selective laser sintering: A review

Additive manufacturing (also known as 3D printing) process is an emerging technique for the fabrication of biomedical components. Selective laser sintering or melting is one of the widely used additive printing technology for manufacturing of metallic and non-metallic components used in the industry. This review paper presents, a summary of the published research papers on the fabrication of biomedical components using selective laser sintering technique. Therefore, author meticulously attempted to investigate individual biocompatible material-wise review which includes Ti6Al4V, Ti-7.5 Mo alloy, β-Ti35Zr28Nb, PEEK, PA2200, and Polyamide/Hydroxyapatite. In addition, this article also explores the effects of the various laser sintering process parameters such as laser power, scanning speed, density of the material on the mechanical properties, tribological properties, porosity and surface roughness of the fabricated alloy. Moreover, the author also investigated challenges and future prospective of the laser processing of biomedical implants.

Laser sintering of cryogenically ground polymer powders into high-performance parts: The role of dry particle coating with a conductive flow agent

The poor processability of cryogenically ground polymer powders rendered by their irregular shapes greatly hinders their applications in the selective laser sintering (SLS) technique. In this study, nonconductive silica (SiO2) nanoparticles and conductive carbon black (CB) nanoparticles were coated onto cryogenically ground polyamide 12 (PA12) powders and acted as flow agents to alleviate the flow problem. It was found that the addition of SiO2 or CB nanoparticles both greatly improved the flowability of cryogenically ground powders, thereby facilitating a successful sintering process. However, significantly improved mechanical performance and reduced structural defects were achieved only upon the addition of CB nanoparticles. The underlying mechanism was suggested to be related with the higher conductivity, lower friction, smaller adhesion energy and higher laser absorption efficiency of CB-coated powders. Therefore, conductive and radiation-adsorbing particles such as CB can serve as a multifunctional agent to enable the sintering of polymer powders with irregular shapes into parts with improved mechanical performance.

Elaboration of the measuring procedure facilitating precision assessment of the geometry of mandible anatomical model manufactured using additive methods

This article presents a procedure for minimizing ATOS II Triple Scan system measurement errors during the verification of geometrical accuracy of the final lateral-mandibular condyle model. The process of manufacturing a template geometrically similar to that of lateral-mandibular condyle was performed on the five-axis machining centre 100 DMU MonoBlock. The next stage of the research was related to the implementation of the measurement system procedure on the template model, and the 12 anatomical models of the mandibular body-condyle were manufactured using five different additive methods. As a result of the comparison of anatomical models of the mandibular body-condyle designed in reverse engineering/computer-aided design systems and manufactured using additive methods, the average results of histograms and parameters determining the accuracy of geometry of 12 models were obtained. In the case of models manufactured using fused deposition modelling, PolyJet and selective laser sintering techniques, a unimodal distribution was observed in the same way as in the template model. The best results were obtained in the case of models manufactured using selective laser sintering techniques (standard deviation = 0.06 mm). In the case of fused deposition modelling and PolyJet, a similar value of standard deviation (about 0.07 mm) was observed, despite the fact that the layer thickness for PolyJet technology was 0.016 mm. In the case of melted and extruded modelling and ColorJet Printing technologies, there was a bimodal distribution. Through the implementation of own template and measurement method, it will be easier to estimate errors in the manufacturing of anatomical models of lateral-mandibular condyle part. As a result, medical models, surgical templates and implants will be manufactured more accurately and precisely, which will significantly reduce intraoperative complications during the surgical procedure in this area.

Octacalcium phosphate coating for 3D printed cranioplastic porous titanium implants

In the present study, porous three-dimensional (3D) printed titanium (Ti) implants of complex shape and predefined architecture were produced by selective laser sintering (SLS) technique. Electrochemical deposition combined with biomimetic approach was applied to low-temperature coating of these implants with metastable octacalcium phosphate (OCP) achieved via chemical transformation of dicalcium phosphate dehydrate (DCPD). X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and compressive strength analyses were applied to study the chemical composition, morphology and mechanical properties of the final OCP coating on the titanium surface. In vivo comparative study of the porous 3D printed Ti and OCP coated Ti implants has been performed using critical-size crania model, porous 3D printed Ti and coated implants were compared. A statistically significant difference in the newly formed bone thickness for OCP coated Ti implants was detected already at 6 weeks after implantation. Our results provide an experimental proof of a new concept of OCP coating for cranioplasty clinical applications.

REDESIGN AND TOPOLOGY OPTIMIZATION OF AN INDUSTRIAL ROBOT LINK FOR ADDITIVE MANUFACTURING

Design optimization for Additive Manufacturing is demonstrated by the example of an industrial robot link. The part is first redesigned so that its shape details are compatible with the requirements of the Selective Laser Sintering technique. Subsequently, the SIMP method of topology optimization is utilized on commercially available software in order to obtain the optimum design of the part with restrictions applicable to Additive Manufacturing, namely member thickness, symmetry and avoidance of cavities and undercuts. Mass and strain energy are the design responses. The volume was constrained by a fraction of the initial mass. The desired minimization of maximum strain energy is expressed as an objective function. A 7% reduction in the mass of the part was achieved while its strength and stiffness remained unchanged. The process is supported by topology optimization software but it also involves some trial-and-error depending on the designer’s experience.

The Microstructural Revolution of Ti-6Al-4V Specimens Fabricated by Selective Laser Sintering of Pre-alloyed Powders

Selective laser sintering (SLS) is known as a cutting-edge technique to manufacture complex geometry products. Among various kinds of materials, Ti-6Al-4V is one of the most popular materials for the SLS process. The as-built Ti-6Al-4V products were widely applied in many applications such as aerospace, automobile, and especially in medical and implant parts. The purpose of this research is to investigate the microstructure and other properties of Ti6Al4V pre-alloyed powders produced by selective laser sintering technique. Through this research, the direct fabrication of Ti6Al4V metal object by SLS machine has been carried out using MetalSys250 machine. Different parameters of the SLS process were used to produce 1cm x1cmx1cm cubic samples and then microstructure, as well as mechanical properties of the as-built samples were investigated. Powder particles are fully dense, possess a spherical shape and are composed of acicular α phase. The as-build sample shows the oriented acicular martensitic phase with the defined columnar grain structures.

Isogeometric topology optimization for rational design of ultra-lightweight architected materials

Architected materials with the desirable properties, such as the lightweight and the superior stiffness, have accepted considerable attention in recent years. This paper aims to study the design of architected materials but with the ultra-lightweight using an effective and efficient Isogeometric Topology Optimization (ITO) method. An enough smooth and continuous Density Distribution Function (DDF) is constructed using the Shepard function and NURBS basis functions, to describe the topology of the micro-architecture. Later, the homogenization with a simple periodic boundary formulation is numerically implemented by isogeometric analysis (IGA) to predict effective macroscopic properties using the micro information. An ITO formulation with the specific objective function is developed to rationally design 2D and 3D architected materials with the extreme elastic properties using the DDF and IGA-based homogenization, in which the volume fraction needs to be very low to ensure the optimized micro-architectures with the ultra-lightweight. NURBS basis functions offer a unified formula for the structural geometry, the solution space and the micro topology in architected materials. Finally, several numerical examples are provided to display the effectiveness of the ITO method for the ultra-lightweight architected materials, particularly for 3D scenario. A series of novel and interesting 3D ultra-lightweight architected materials are found, which are also prototyped using the Selective Laser Sintering (SLS) technique.