Kosov, Mikhail E

Selective laser sintering (SLS) is one of the prominent methods of polymer additive manufacturing (AM). A low-power laser source is used to directly melt and sinter polymer material into the desired shape. This study focuses on the utilization of the low-power laser SLS system to successfully manufacture metallic components through the development of a metal–polymer composite material. In this study, 17-4 PH stainless powders are used and mixed with polyoxymethylene (POM) and high-density polyethylene (HDPE) to prepare the composite powder material. The polymeric mixture is removed during the thermal degreasing process and subsequent sintering results in a solid metallic component. Sinterit Lisa with a 5 W, 808 nm laser source is used to fabricate the green part. For the printing parameters of 140 °C, laser power of 35.87 mJ/mm2, and layer thickness of 100 μm, the printed samples achieved a maximum density of 3.61 g/cm3 and a complete shape. After sintering at 1310 °C for 180 min, the tensile strength of the shrunk sample is 605.64 MPa, the hardness is HRC 14.8, the average shrinkage rate is 22%, and the density is 7.57 g/cm3, which can reach 97% of the theoretical density. This process allows the use of a wide range of particle sizes that the usual AM technologies have, making it a low-cost, low-energy-consumption, high-speed AM technology.

The properties of each lattice structure are a function of four basic lattice factors, namely the morphology of the unit cell, its tessellation, relative density, and the material properties. The recent advancements in additive manufacturing (AM) have facilitated the easy manipulation of these factors to obtain desired functionalities. This review attempts to expound on several such strategies to manipulate these lattice factors. Several design-based grading strategies, such as functional grading, with respect to size and density manipulation, multi-morphology, and spatial arrangement strategies, have been discussed and their link to the natural occurrences are highlighted. Furthermore, special emphasis is given to the recently designed tessellation strategies to deliver multi-functional lattice responses. Each tessellation on its own acts as a novel material, thereby tuning the required properties. The subsequent section explores various material processing techniques with respect to multi-material AM to achieve multi-functional properties. The sequential combination of multiple materials generates novel properties that a single material cannot achieve. The last section explores the scope for combining the design and process strategies to obtain unique lattice structures capable of catering to advanced requirements. In addition, the future role of artificial intelligence and machine learning in developing function-specific lattice properties is highlighted.

Increased usage of selective laser sintering (SLS) for the production of end-use functional components has generated a requirement of developing new materials and process improvements to improve the applicability of this technique. This article discusses a novel process wherein carbon black was applied to the surface of TPU powder to reduce the laser reflectivity during the SLS process. The printing was carried out with a preheating temperature of 75 °C, laser energy density of 0.028 J/mm2, incorporating a 0.4 wt % addition of carbon black to the TPU powder, and controlling the powder layer thickness at 125 μm. The mixed powder, after printing, shows a reflectivity of 13.81%, accompanied by the highest average density of 1.09 g/cm3, hardness of 78 A, tensile strength of 7.9 MPa, and elongation at break was 364.9%. Compared to commercial TPU powder, which lacks the carbon black coating, the reflectance decreased by 1.78%, mechanical properties improved by 33.9%, and there was a notable reduction in the porosity of the sintered product.

Abstract Background The ethmoid sinus (ES) is a three-dimensional (3D) complex structure, a clear understanding of the ES anatomy is helpful to plan intranasal surgery. However, most prior studies use 2D measurements, which may not accurately depict the 3D structure. The current study measured the gender differences in ES morphology based on 3D reconstruction of computed tomography (CT) images. Methods The 3D models were reconstructed using CT images. Twenty-one males and 15 females were enrolled in the study. The ES dimensions, including width, height and aspect ratio (AR) of each cutting-plane section, were measured at 10% increments along with the anteroposterior axis of the ES. The gender differences in the above parameters were further evaluated by an independent t-test. Results The width of the ES for males is 12.0 ± 2.1 mm, which was significantly greater than that in females (10.0 ± 2.1 mm). The average height for males is 18.4 ± 3.5 mm, and 18.2 ± 3.4 mm for females. The AR of female (male) is around 0.56 (0.63) for the anterior ES and 0.66 (0.75) for the posterior. There are significant differences between genders in the parameters of width and AR (p < 0.05). Conclusion This study found that the aspect ratio greatly varies along the length of ES, indicating that the cross-section of the ES in the anterior is closer to an elliptical shape and turns closer to a circular shape near its posterior. There is a significant difference between genders in width and aspect ratio. The results would be helpful to know the complex anatomic details of the ethmoid sinus.

Powder-like g-C3N4 has been widely used as a photocatalyst but exhibits several drawbacks, including unrecyclable, high charge recombination, and limited light absorption. In this study, carbon-bridged g-C3N4 was successfully prepared and coated on a 3D-printed Al2O3 substrate for the photocatalytic oxidation of tetracycline. Oxamide (OD), malonamide (MD), and succinamide (SD) were used as carbon-containing linkers to react with precursors (melamine and urea) and produce carbon-bridged g-C3N4. Carbon substitution at the bridged N atoms of g-C3N4 improved light absorption, reduced charge recombination, and resulted in high photocatalytic tetracycline removal efficiency. Computational calculations were also employed, and Bader charge analysis supported the charge redistribution and transfer of the carbon-bridged g-C3N4 samples. Our results indicated that the degradation of tetracycline followed step-by-step oxidation, deamination, and mineralization to form CO2 and H2O. The 3D-printed Al2O3-supported carbon-bridged g-C3N4 exhibited a high removal rate of 85–90 % and stability for photocatalytic reactions and can be reused for at least 10 cycles. This study demonstrates that the 3D-printed Al2O3-supported carbon-bridged g-C3N4 catalyst is an efficient and effective catalyst support system for photocatalytic reactions.

This work addresses the issues of entrapment of polymer powder and the post-processing powder removal challenges in surface-based lattice structures 3D printed with powder bed-based additive manufacturing (AM) technology. A ventilation design approach has been proposed to enhance the powder removability from the widely researched three-dimensional gyroid and two-dimensional honeycomb lattice structure. The flow characteristics and mechanical behavior of the designed lattices were analyzed using computational fluid dynamics (CFD) and finite element analysis (FEA), respectively, followed by experimental powder flow and compression testing. HP jet fusion 4200® industrial 3D printer was used for printing the lattice structures for experimental validation. The results showed a 65–85% improvement in powder flowability, with a minimum to severe reduction in mechanical strength of different lattice structures. The study can be applied to designing products with multi-functional properties with surface-based lattice structures by employing the principle of design for additive manufacturing and post-processing (DfAM&PP).

ABSTRACT Image-based criteria have been adopted to diagnose femoroacetabular impingement (FAI). However, the overlapping property of the two-dimensional X-ray outlines and static and supine posture of taking computed tomography (CT) and magnetic resonance imaging images potentially affect the accuracy of the criteria. This study developed a CT image–based dynamic criterion to effectively simulate FAI, thereby providing a basis for physicians to perform pre-operative planning for arthroscopic surgery. Post-operative CT images of 20 patients with satisfactory surgical results were collected, and 10 sets of models were used to define the flexion rotation centre (FRC) of the three-dimensional FAI model. First, let these 10 groups of models simulate the FAI detection action and find the best centre offset, and then FRC is the result of averaging these 10 groups of best displacements. The model was validated in 10 additional patients. Finally, through the adjustment basis of FRC, the remaining 10 sets of models can find out the potential position of FAI during the dynamic simulation process. Rotational collisions detected using FRC indicate that the patient’s post-operative flexion angle may reach 120° or greater, which is close to the actual result. The recommended surgical range of the diagnostic system (average length of 6.4 mm, width of 4.1 mm and depth of 3.2 mm) is smaller than the actual surgical results, which prevents the doctor from performing excessive resection operations, which may preserve more bones. The FRC diagnostic system detects the distribution of FAI in a simple manner. It can be used as a pre-operative diagnosis reference for clinicians, hoping to improve the effect and accuracy of debridement surgery.

Additive manufacturing of metamaterial composites allows for lightweight structures with tunable mechanical and functional properties. This study achieves this using a Hybrid fused filament fabrication process where PU foam is injected inside the supportless closed cell lattice structure made of thermoplastic polyurethane (TPU). The process is based on the direct digital manufacturing concept, eliminating the need for post-processing. The resulting structures exhibited improved mechanical properties, including stiffness, energy dissipation, and damping capacity. Functionally grading the lattice structures further enhanced their properties, making them highly customizable for energy-absorbing and damping products such as protective and sporting goods.

The quest for obtaining lattice structures with mutually exclusive properties through morphological innovations has been rapidly increasing. Nowadays, lattice structures are not only meant for achieving lightweight components but also to deliver unique hybrid functionalities. In this context, the concept of tessellation is recently developed to obtain specific paths of stimulus (load, heat, fluid, vibration, etc.) transfer based on the required responses. The mechanical and functional properties of the lattice structures can be governed and manipulated by changing the path of stimulus transfer in it. In this study, the uniaxial load is considered as a stimulus to examine the load transfer mechanism and various properties of non-edge-to-edge tessellations. These tessellations were designed based on the principles of metallic crystal stacking systems. The designed tessellations were fabricated using HP multi-jet powder bed fusion technology. The deformation behavior, load transfer via stress contours, and equivalent plastic strain (PEEQ) were investigated using experimental compression and numerical analysis. The study reveals unique mechanical properties with changes in structural behavior upon changing the load transfer mechanism (i.e. tessellations). The study reveals radial, zig-zag, and S-shaped patterns of load transfers in BCC, FCC, and HCP tessellated lattice structures. As a result, both the BCC and FCC tessellated lattice structures are known for their load-bearing properties. FCC tessellation demonstrates the highest strength and specific energy absorption capacity. The PEEQ analysis shows extreme plastic deformation in many regions which is cross-validated by cracks in the experimental samples. Contrary to that, HCP is the only structure that shows a constant positive plateau slope until densification. The quasi-static crash force efficiency of the HCP structure outperforms its other counterparts. Moreover, the HCP lattice structure also shows very few locations of plastic deformation with a PEEQ value not exceeding 25%. These properties make HCP a suitable choice for generating cushioning effect. The real-time applications of these structures are presented in protective helmets which need high-strength strength outer covering and high cushioning inner liner. Similarly, the advantageous properties can also be exploited in customized athletic shoes.

This study introduces a novel design and additive manufacturing of technical textiles to achieve tunable mechanical properties through the tessellations of a singular material. The design of these chainmail fabrics was inspired by overlapping tessellation strategies found in biological structures. Two types of chainmail fabrics —BCC and FCC were designed to exhibit high flexibility and stretchability with two-dimensional degrees of freedom. The fabrics were designed to bend along two orthogonal axes and drape around curved surfaces. Furthermore, the relative placement of the unit cells was adjusted to selectively arrest the degrees of freedom, resulting in chainmail fabrics with tunable flexibilities and mechanical properties. Four fabrics for each design Fabric-A, Fabric-B, Fabric-C, and Fabric-D were developed with varying degrees of freedom. All the designed chainmail fabrics were additively manufactured using HP-MJF powder bed fusion technology with a polyamide-12 material. The mechanical properties of the fabricated samples were evaluated through experimental tension tests and numerical simulations. The fabricated BCC and FCC chainmail fabrics exhibited a stress-free zone, followed by an elastoplastic zone, with different mechanical properties observed at different orientations. The FCC fabrics outperformed the BCC fabrics with 45° orientation, exhibiting excellent load-bearing properties, and the 0° orientation showed superior energy absorption capacity. The numerical simulations accurately predicted the mechanical properties and failure locations. Fabric-A was highly flexible but had compromised load-bearing and energy-absorption abilities, whereas Fabric-D acted as a rigid lattice structure with exceptional load-bearing and energy-absorbing properties. FCC fabrics are easier to manufacture using various polymer additive processes owing to their supportless nature. Tunable technical fabrics such as these have potential applications in lightweight and adaptive spinal posture-correcting braces as well as in protective equipment.

In this paper, we accomplished the first 32-inch liquid crystal display (LCD) type vat photopolymerization 3D printing system based on the quasi-collimated visible backlight module with local dimming control. The large building area (40 × 70cm) of the 3D printing system can greatly increase the size of printing objects and the production rate. We focused on the design of quasi-collimated backlights and analyzed their optical properties and the appearance of 3D printing objects fabricated by them. The optical performances of the quasi-collimated backlight using stacks of optical films feature no large angle leakage light, 86 % intensity uniformity, and less than ±15° angular distribution of emitting light. After the optimization process by combining a variety of optical films, the uniformity, and collimation of the backlight module are greatly improved. Moreover, combining a local dimming algorithm with 3D printing technology can completely suppress unexpected photopolymerization residues, increase resin utilization rate, save energy, and greatly improve the probability of success in the 3D printing process, especially in large printing objects.