Stereolithography Technique Research Articles

Analysis of Geometrical Accuracy and Surface Quality of Threaded and Spline Connections Manufactured Using MEX, MJ and VAT Additive Technologies

This paper presents the process of manufacturing mechanical joint components using additive manufacturing (AM) techniques such as Material Extrusion (Fused Deposition Modelling (FDM)), Material Jetting (PolyJet), and Vat Photopolymerization (VAT)/Stereolithography (SLA). Using the PolyJet technique and a photopolymer resin, spline and threaded joint components were produced. For comparative analysis, the threaded joint was also fabricated using FDM and SLA techniques. PLA material was used for the FDM technique, while photopolymer resin was utilized for the SLA process. The components produced underwent a surface analysis to evaluate the accuracy of the dimensions in relation to the nominal dimensions. For the spline connection components, the dimensional deviations recorded by a 3D scanner ranged from −0.11 to +0.18 mm for the shaft and up to 0.24 mm for the sleeve. Measurements of screw and nut diameters showed the highest accuracy for screws produced using the PolyJet technique, while the nuts exhibited the best accuracy when fabricated with the SLA method. The profile of the screw threads using a contour gauge revealed the most accurate thread profile on the screw manufactured with the PolyJet technique.

Design and parametrization of TPMS lattice using computational and experimental approach

Triply periodic minimal surface (TPMS) based lattices are extensively explored as a scaffold design for bone regeneration. TPMS maintains zero mean curvature at each point and offers a large surface area comparable to a trabecular bone. The best four TPMS minimal surfaces (IWP. Neovius, primitive, and F-RD) were selected, designed, and fabricated using acrylonitrile butadiene styrene (ABS) resin through the stereolithography (SLA) technique. The results indicate that small changes in unit cell dimensions do not significantly alter the structure topology, which ensures stress distribution within the lattice remains relatively uniform across different unit cell sizes when the porosity level is constant. The optimal unit cell size (2 to 5 mm) and porosity (70 to 80%) significantly affect the compressive strength and surface area to volume (SA/V) ratio due to a unique arrangement of the internal architecture of each TPMS unit cell. The lattice structure (formed by stacking unit cell) of unit cell size 2.11 mm with 70% porosity exhibited a maximum compressive strength of 39.8 MPa in IWP, followed by Neovius, primitive, and F-RD-based lattice structures. Moreover, the lattice showed more stability under compression force, minimized stress concentration compared to a unit cell, and exhibited distinct deformation patterns at different strain levels during compression.

Integration of soft tooling by additive manufacturing in polymer profile extrusion process chain

Integrating additive manufacturing (AM) into polymer extrusion offers process chain flexibility and design freedom. It reduces the need for time-consuming iterations and trial-and-error in the die design process. Consequently, polymer AM of extrusion (i.e., soft tooling) allows for a shorter product development cycle and cost-effectiveness for small-scale production and highly customized products. In this study, carbon fibre (CF)-polyether-ether-ketone (PEEK) dies were manufactured using the fused filament fabrication (FFF) AM process, employing a streamlined die design achieved through freeform transition planes. Calibration slides were produced using masked stereolithography (MSLA), FFF, and conventional manufacturing techniques (i.e., machining) to preserve the final product’s cross-section during the cooling process. The dimensional and surface characteristics of these calibration slides were evaluated to assess the dimensional accuracy and surface topography of various materials and manufacturing processes. The dimensional evaluation reveals that MSLA-printed parts exhibit deviation from the nominal dimension closer to the conventionally manufactured part. The integrated soft tooling in the polymer extrusion line was tested with polypropylene (PP) and acrylonitrile butadiene styrene (ABS) as extruded materials. The surface topography of the CF-PEEK die displays distinctive ripple features resulting from the FFF process, identified by relatively flat peaks and deep valleys. The overall surface texture parameter values of CF-PEEK were higher due to the presence of deep valleys. Considering that the areas around the peaks interacted more with polymer molecules during the extrusion, the surface texture parameters of the extrudates were closer to the value observed in 90 µm region areas around the peaks. Notably, extrudates of AM calibration slides have lower surface texture parameters than extrudates of conventionally manufactured calibration slides, even though surface defects in the form of dimple sink marks were observed in extruded material of PP from extrudates using AM calibration slides.

Stereolithographic Rapid Prototyping of Clear, Foldable, Non-Refractive Intraocular Lens Designs: A Proof-of-Concept Study

Purpose A cataract is a cloudy area in the crystalline lens. Cataracts are the leading cause of blindness and the second cause of severe vision impairment worldwide. During cataract surgery, the clouded lens is extracted and replaced with an artificial intraocular lens, which restores the optical power. The fabrication of intraocular lenses using existing molding and lathing techniques is a complex and time-consuming process that limits the development of novel materials and designs. To overcome these limitations, we have developed a stereolithography-based process for producing models of clear lens designs without refractive function, serving as a proof of concept. This process has the potential to contribute toward new lens development, allowing for unlimited design iterations and an expanded range of materials for scientists to explore. Methods Lens-like 3D objects without refractive function were fabricated by using stereolithography. A photopolymerizable resin containing 2-phenoxyethyl acrylate, poly (ethylene glycol) dimethacrylate, and a suitable photoinitiator was developed for the production of lens-like 3D object prototypes. The morphology of the printed devices was characterized by scanning electron microscopy. The transparency and thermal properties were analyzed using spectrophotometry and differential scanning calorimetry, respectively. The biocompatibility of the devices was investigated in a cultured human lens cell line (FHL-124), using a standard lactate dehydrogenase assay, and the lenses were folded and implanted in the human capsular bag model. Results One-piece lens-like 3D objects without refractive function and with loop-haptic design were successfully fabricated using Stereolithography (SLA) technique. The resulting 3D objects were transparent, as determined by UV spectroscopy. The lactate dehydrogenase test demonstrated the tolerance of lens cells to the prototyping material, and apparent foldability and shape recovery was observed during direct injection into a human capsular bag model in vitro. Conclusions This proof-of-principle study demonstrated the potential and significance of the rapid prototyping process for research and development of lens-like 3D object prototypes, such as intraocular lenses.

Rapid non-destructive inspection of sub-surface defects in 3D printed alumina through 30 layers with 7 μm depth resolution

The use of additive manufacturing (AM) processes has grown rapidly over the last ten years like fused deposition modelling and stereolithography techniques. 3D printing offers advantages in ceramic component production due to its flexibility. To enhance quality and reduce resource consumption in ceramics industry, fast, integrated, sub-surface and non-destructive inspection (NDI) with high resolution is needed. This study demonstrates sub-surface monitoring of 3D printed alumina parts to a depth of ∼0.7 mm in images of 400 × 2048 pixels with a lateral resolution of 30 μm and axial resolution of 7 μm, using mid-infrared optical coherence tomography (MIR OCT) based on a 4 μm center wavelength MIR supercontinuum laser. We detected individual printed ceramic layers and tracked predefined defects through all four processing steps and demonstrated how a defect in the green phase could affect the final product. This research sets the stage for NDI integration in AM.

Mechanically induced long period gratings in different silica multi-layered optical fibers

This work presents a thorough comparative investigation of mechanically induced long period gratings (MILPGs) realized in different unconventional multi-layered silica optical fibers: two double cladding fibers (DCF), with progressively three layered (PTL) and W-type structures, and a solid core photonic crystal fiber (PCF). A periodic interdigitated grooved structure, based on the stereo-lithography 3D printing technique, is developed for the grating formation in these fibers with simplicity and cost-effectiveness. Multiple grating periods are developed in the range 480–660 μm, resulting in attenuation bands with depth within 15–25 dB and wide range of tunability over the wavelength range of 1100–1700 nm. The results demonstrate effective management of transmission spectra evolution as a function of the applied weight, with minimal alteration in wavelength position when testing the fiber with or without its coating. Polarization dependent properties of these gratings are also investigated demonstrating a negligible impact. This is the first time that such a broad investigation is conducted about MILPGs in the fibers mentioned earlier with broad scouting in fabrication parameters, opening to the application of such devices for sensing and communication purposes.

Design, Validation, and Fabrication of a Tailored Electrochemical Reactor Using 3D Printing for Studies of Commercial Boron-Doped Diamond Electrodes.

Boron-doped diamond (BDD) electrodes are the most effective and resistant electrodic materials to perform advanced oxidation processes. Having a reactor that can provide adequate hydrodynamic conditions is mandatory to use these electrodes effectively. In this work, the diamond anode electrochemical reactor (E3L-DAER) is designed to fulfill this necessity. Several features are included to improve its efficiency, like conic inlet/outlet, flow enhancers, and a reduced interelectrode gap. The fluid dynamic validation has been performed using computer fluid dynamics (CFD) calculations, residence time distribution (RDT) curves, and mass transfer analysis. The reactor has been made using a three-dimensional (3D) printing stereolithography (SLA) technique, which allows us to build chemical-resistant reactors with nonstandard and tailored features in a cheap and fast way. The obtained results demonstrate that the designed reactor has the required fluid dynamics properties to perform reliable BDD electrode studies and applications. Finally, a BDD electrode was used to test the production of different oxidants such as persulfate, peroxophosphate, and chlorine-derived species.

One-step preparation of silver nanoparticle containing polymer nanocomposites via stereolithography technique

As a technique that uses ultraviolet light to cure photo-polymers layer by layer with high spatial resolution and surface quality, stereolithography (SLA) allows for precise process control and optimization for various UV-curable polymers and their nanocomposites with various nanoparticles. In this study, UV-curable polymer nanocomposites were prepared with the addition of different contents of silver nitrate via SLA technique for use in antibacterial applications. In-situ synthesis of AgNPs was achieved during the SLA process without any additional treatments. The effect of AgNO3 addition on the curing of the resin and the mechanical properties of the nanocomposite specimens were investigated. To understand the fracture mechanism of the nanocomposite samples, the fractured surfaces of the samples were evaluated by SEM, and the AgNO3 content of the nanocomposite was evaluated by EDX. The nanocomposites containing 0.3 wt. % AgNO3 exhibited improved mechanical properties. Further increasing the AgNO3 content to 3 wt. % led to deterioration in the physical and mechanical properties of the polymer nanocomposites.

Evaluation on Surface Characteristics, Accuracy, and Dimensional Stability of Tooth Preparation Dies Fabricated by Conventional Gypsum and 3D-Printed Workflows.

To evaluate the surface characteristics, accuracy (trueness and precision), and dimensional stability of tooth preparation dies fabricated using conventional gypsum and direct light processing (DLP), stereolithography (SLA), and polymer jetting printing (PJP) techniques. Gypsum preparation dies were replicated according to the reference data and imported into DLP, SLA, and PJP printers, and the test data were obtained by scanning after 0, 1, 3, 7, 14, 28, and 42 days. After analyzing the surface characteristics, a best-fit algorithm between the test and the reference data was used to evaluate the accuracy and dimensional stability of the preparation dies. The data were analyzed by one-way analysis of variance and Tukey test or Kruskal-Wallis H test (α = .05). Compared with the gypsum group (3.61 ± 0.59 μm), the root mean square error (RMSE) values of the SLA group (5.33 ± 0.48 μm) was rougher (P < .05), the PJP group (2.43 ± 0.37 μm) was smoother (P < .05), and the DLP group (2.92 ± 0.91 μm) had no significant difference (P > .05). For trueness, the RMSE was greater in the PJP (34.90 ± 4.91 μm) and SLA (19.01 ± 0.95 μm) groups than in the gypsum (16.47 ± 0.47 μm) group (P < .05), and no significant difference was found between the DLP (17.10 Å} 1.77 μm) and gypsum groups. Regarding precision, the RMSE ranking was gypsum = DLP = SLA < PJP group. The RMSE ranges in the gypsum, DLP, PJP, and SLA groups at different times were 6.79 to 8.86 μm, 5.44 to 10.17 μm, 10.16 to 11.28 μm, and 10.94 to 32.74 μm, respectively. Although gypsum and printed preparation dies showed statistically significant differences in surface characteristics, accuracy, and dimensional stability, all tooth preparation dies were clinically tolerated and used to produce fixed restorations.

3D printed piezoelectric focused element for ultrasonic transducer

Bulk 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-29PT) piezoelectric ceramics are prepared using 3D printing stereolithography (SLA) technique. The crystal strcture and microstructure of the 3D printed green bodis and sintered ceramics were analyzed. The 3D printed samples exhibit prospective dielectric, piezoelectric and ferroelectric performance. The dielectric constant and piezoelectric coefficient d33 of the sintered PMN-29PT ceramics reach 2698 and 487 pC/N, respectively. Furthermore, focused piezoelectric element with bowl-like structure was designed and prepared using SLA. The ultrasonic transducer based on the 3D printed focused element presents promising performance with center frequency of 2.85 MHz and 45% −6 dB bandwidth. These results demonstrate the potential of fabricating piezoelectric ceramics with complex structure by 3D printing for the application in piezoelectric devices.

3D printing PMN-PT textured ceramics for transducer applications

3D printing stereolithography (SL) technique were successfully applied in the preparation of <001>-textured 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-29PT) ceramics in this work. The as-sintered textured ceramics show obvious grain orientation control effects, and the relative density reaches 93% of the theoretical density. The obtained ceramics demonstrate typical dielectric/ferroelectric/piezoelectric properties, enabling the device applications. The ultrasonic transducer with the center frequency of 6.7 MHz and the −6 dB bandwidth of 25% are designed and prepared based on the obtained textured ceramic. This work signifies the great potential of 3D printing SL technology on the fabrication of piezoelectric ceramic elements for advanced applications.

Strain-rate-dependent behavior of additively manufactured alumina ceramics: Characterization and mechanical testing

This study experimentally investigates the mechanical behavior of additively manufactured (AM) alumina ceramics by stereolithography technique. The AM alumina specimens with two different printing orientations (POs) are tested under quasi-static and dynamic loading rates. The material shows a quasi-static (i.e., a strain rate of 10−3 s−1) compressive strength of 1640.54 ± 99.33 MPa and 1494.25 ± 260.08 MPa for the PO1 and PO2, respectively, and a dynamic (i.e., a strain rate of 640–730 s−1) compressive strength of 3077.25 ± 174.07 MPa and 3107.33 ± 97.03 MPa for the PO1 and PO2, respectively, which are among the highest reported values for AM alumina due to the higher density and finer grain size. The strain-rate-dependent compressive strength of the material is slightly affected by the PO which is alleviated with the increase in strain rate from quasi-static to dynamic loading conditions. In contrast, the PO noticeably affects the macro-scale failure pattern. The fractography analysis shows the dominant contribution of the intergranular failure mechanism and a combination of intergranular and transgranular mechanisms under quasi-static and dynamic loading, respectively. The crack speed propagation is found to be 785 ± 174 m/s on average which is ∼68% less than that of conventional ones in the literature. The current AM alumina shows a hardness of 24.45 ± 0.88 GPa which is higher than that of the majority of other AM alumina. Overall, this study discusses the potentiality of using AM ceramics in engineering fields replacing the conventionally-made counterparts, and provides implications for designing better-performing AM ceramics.

On the understanding of bubble dynamics through a calibrated textile-like porous medium using a machine learning based algorithm

In this work, we present a proof of concept for both 3D-printed media and a machine learning analysis methodology to investigate void formation and transport during liquid filling. Through a series of experiments, we characterized void formation and transport at constant flow rates using two calibrated fabric-like porous geometries created by Stereolithography and Multi Jet Fusion 3D printing techniques. Our findings highlight the significance of porous medium geometry and void size, in addition to the capillary number, in characterizing void formation and mobility during resin flow into a mold containing a fibrous preform. Notably, the paper's strength lies in the presentation of advanced bubble analysis methods, including frame-by-frame high-resolution video analysis, enabling the identification of individual bubbles and the extraction of their statistics, such as count, size, and velocity throughout the experiment. These insights contribute to the design of more efficient processes, resulting in composite parts with reduced void content.

Light-oriented 3D printing of liquid crystal/photocurable resins and in-situ enhancement of mechanical performance

Additive manufacturing technology has significantly impacted contemporary industries due to its ability to generate intricate computer-designed geometries. However, 3D-printed polymer parts often possess limited application potential, primarily because of their weak mechanical attributes. To overcome this drawback, this study formulates liquid crystal/photocurable resins suitable for the stereolithography technique by integrating 4’-pentyl-4-cyanobiphenyl with a photosensitive acrylic resin. This study demonstrates that stereolithography facilitates the precise modulation of the existing liquid crystal morphology within the resin. Furthermore, the orientation of the liquid crystal governs the oriented polymerization of monomers or prepolymers bearing acrylate groups. The products of this 3D printing approach manifest anisotropic behavior. Remarkably, when utilizing liquid crystal/photocurable resins, the resulting 3D-printed objects are approximately twice as robust as those created using commercial resins in terms of their tensile, flexural, and impact properties. This pioneering approach holds promise for realizing autonomously designed structures that remain elusive with present additive manufacturing techniques.

Effect of debinding on alumina specimens and ultra-thin veneer fits using solvent-based stereolithography

The solvent-based ceramic slurry stereolithography (3S) technique offers a novel approach to fabricating complex structures, yet its potential in the realm of alumina specimens and ultra-thin veneers remains underexplored. The present study assessed the impact of the debinding process on the microstructure and mechanical properties of 3S-fabricated alumina specimens, while also evaluating the fit of ultra-thin veneers with a thickness of just 0.3 mm. The results indicated that variations in debinding parameters—such as different rates and holding times—do not significantly affect surface morphology, density, Vickers hardness, or flexural strength. Additionally, the cell viability of 3S-fabricated specimens exceeded 90% for both MG-63 and NIH-3T3 cells, suggesting excellent biocompatibility. The mean marginal and internal gaps of the 3S-fabricated veneers were within clinically acceptable ranges, measuring 93.38 ± 29.53 μm and 130 ± 46.1 μm, respectively. These groundbreaking insights not only validate the robustness of the 3S fabrication technique but also highlight its promising potential for biomedical applications, distinguishing this research in the field.

Developing a New Flow Cell for Electrochemical Machining Anodic Dissolution Investigations by Simulation-Based Design and 3D Printing

Abstract Electrochemical machining (ECM) is an essential non-traditional industrial shaping technology. An in-depth understanding of ECM anodic dissolution is fundamentally important for process parameter design and optimization. However, the existing electrochemical setups face challenges in achieving efficient analysis of these processes. In this work, a new flow cell has been developed via simulation-based design and 3D printing that demonstrates comprehensive advantages in terms of improved electric and flow conditions, measurement technique versatility, and production simplicity at low cost. Simulations are performed to reveal particular characteristics of the proposed cell in terms of physical distributions and to determine its key dimensions with high efficiency. The stereo lithography technique is used to realize the complex design and fabricate the proposed flow cell, thus ensuring ease of accessibility. Furthermore, the effectiveness of the developed cell is verified experimentally by examining the anodic behavior of typical metals in common ECM electrolytes, using Fe and SS304 stainless steel as examples. Test results show that information on the polarization behavior, current efficiency, anodic interface structure, and surface finish can be obtained conveniently and the results agree with previous findings, demonstrating the potential of the developed cell to perform high throughput tests to study ECM fundamentals.

An Ex Vivo Pilot Study to Assess the Feasibility of 3D Printing of Orbital Implants in Horses.

Severe ophthalmic conditions such as trauma, uveitis, corneal damage, or neoplasia can lead to eye removal surgery. Poor cosmetic appearance resulting from the sunken orbit ensues. The aim of this study was to demonstrate the feasibility of manufacturing a custom-made 3D-printed orbital implant made of biocompatible material for the enucleated horse and usable in conjunction to a corneoscleral shell. Blender, a 3D-image software, was used for prototype design. Twelve cadaver heads of adult Warmbloods were collected from the slaughterhouse. On each head, one eye was removed via a modified transconjunctival enucleation while the contralateral eye was kept intact as control. Ocular measurements were collected on each enucleated eye with the help of a caliper and used for prototype sizing. Twelve custom-made biocompatible porous prototypes were 3D-printed in BioMed Clear resin using the stereolithography technique. Each implant was fixated into the corresponding orbit, within the Tenon capsule and conjunctiva. Heads were frozen and thin slices were then cut in the transverse plane. A scoring system based on four criteria (space for ocular prosthesis, soft-tissue-coverage, symmetry to the septum, and horizontal symmetry), ranging from A (proper fixation) to C (poor fixation), was developed to evaluate implantation. The prototypes reached our expectations: 75% of the heads received an A score, and 25% a B score. Each implant cost approximately 7.30€ and took 5 hours for 3D-printing. The production of an economically accessible orbital implant made of biocompatible porous material was successful. Further studies will help determine if the present prototype is usable in vivo.

Effect of geometrical defects on the acoustical transport properties of periodic porous absorbers manufactured using stereolithography

Additive manufacturing allows the fabrication of acoustical materials with previously unrealizable micro- and macrostructural complexities. However, the still nascent understanding of various geometrical defects occurring during the additive process remains a barrier to accurately predicting the acoustical behavior of such complex absorbers. In this study, we present the results from our efforts on numerically modeling the absorption behavior of periodic porous absorbers fabricated using the stereolithography (SLA) technique using the hybrid micro-macro multiphysics approach. Specifically, we focus on understanding the role played by the expansion or shrinkage of the solid ligaments during the SLA process on the acoustical properties of the final printed samples. First, the periodic absorbers are modeled using COMSOL multiphysics, where the transport properties are derived using the micro-modeling method and sound absorption behavior using the Johnson-Champoux-Allard-Lafarge-Pride semi-empirical model. Then, results from the expansion study guide the changes in the ligament sizes in the unit cell modeling. Finally, the fabricated samples are tested using an impedance tube, and the measured absorption properties are compared to the a priori numerical predictions. Results indicate that accounting for fabrication defects within the numerical modeling schema can provide reliable sound absorption predictions for additively manufactured porous absorbers.

Performance optimization of Si/SiC ceramic triply periodic minimal surface structures via laser powder bed fusion

AbstractSiC ceramic lattice structures (CLSs) via additive manufacturing (AM) have been recognized as potential candidates in engineering fields owing to their various merits. Compared with traditional SiC CLSs, SiC triply periodic minimal surface (TPMS) CLSs could possess more outstanding properties, making them more promising for wider applications. Since SiC CLSs are hard to be fabricated through stereolithography techniques because of inferior light performance, the laser powder bed fusion (LPBF) process via selective sintering is an effective method to prepare near‐net‐shaped SiC TPMS lattices. As the mechanical performances of lattice structures are the foundation for future practical applications, it is of great significance to optimize the preparation process, thus improving the mechanical properties of SiC TPMS structures. In this work, the optimal printing parameters of the LPBF and liquid silicon infiltration process for SiC ceramic TPMS CLSs with three different volume fractions were systematically illustrated and analyzed. The effects of the printing parameters and carbon densities on the fabrication accuracy, microstructure, and mechanical performance of SiC TPMS CLSs were defined. The mechanism of the reactive sintering process for the SiC TPMS lattice structure was revealed. The results reveal that Si/SiC TPMS CLSs with optimum preparation have superior manufacturing accuracy (most less than 6%), relatively high bulk densities (about 2.75 g/cm3), low residual Si content (6.01%), and excellent mechanical properties (5.67, 15.4, and 44.0 MPa for Si/SiC TPMS CLSs with 25%, 40%, and 55% volume fractions, respectively).

3D printed Er3+ doped KNNLN piezoelectric ceramics for transparent ultrasonic transducer application

The transparent [Li0.04(K0.5Na0.5)0.96]NbO3+0.5mol% Er2O3 (KNNLN-Er) lead-free piezoelectric ceramics were prepared by stereolithography technique. The influence of different sintering holding time (4h∼8h) on the micromorphology, relative density, shrinkage, electric properties, and photoluminescence properties were systematically investigated. The KNNLN-Er ceramics show the coexistence of orthorhombic and tetragonal structures. The grain size increases obviously and then decreases slightly with the holding time increasing. The KNNLN-Er ceramics exhibit good piezoelectric performance (piezoelectric constant d33∼97 pC/N, electromechanical couple coefficient kt∼0.36) and the moderate transparency of 34% when the holding time is 6h during sintering at 1120°C. Besides, the intensity of the photoluminescence emission spectra increases with the holding time increasing. Furthermore, in order to estimate the properties of the KNNLN-Er transparent ceramics, an ultrasonic transducer with a center frequency of 10.5 MHz was fabricated, which can be used for photoacoustic and fluorescence imaging. The results indicate that the KNNLN-Er ceramics have potential for multimode imaging applications.