Ceramic Stereolithography Research Articles

Ceramic Stereolithography of Li7La3Zr2O12 Micro-Embossed Sheets for Solid Electrolyte Applications

Ceramic Stereolithography of Li7La3Zr2O12 Micro-Embossed Sheets for Solid Electrolyte Applications

Production of ceramic alumina scaffolds via ceramic stereolithography with potential application in bone tissue regeneration

Scaffolds are devices that mimic the characteristics of the extracellular matrix; they are highly porous, with well-distributed and interconnected pores. Tissue engineering proposes scaffolds as an alternative treatment for different diseases and injuries affecting bone tissue. Triply periodic minimal surfaces (TPMS) are geometric structures whose characteristics fit well with the scaffold’s requirements. Ceramic stereolithography enables the production of these complex geometries with high precision using ceramic materials. Alumina (Al2O3) is a well-known ceramic material appreciated for its chemical and mechanical stability properties. The biomedical use of alumina as an alternative to replace metallic parts in bone components has been increasing. In this work, a suspension of alumina particles in a photopolymerizable resin is developed in order to be implemented in the printing of ceramic scaffolds with TPMS-type geometries by ceramic stereolithography for potential biomedical applications. The resin used was characterized in a different work by TGA and FTIR (Duque et al., 2023) and is acrylic in nature, also the alumina particles were characterized by DTP and XRD, these are micrometer sized and a showed an α-alumina phase with a high degree of crystallinity. The rheological behavior of the suspension was studied with ceramic load percentages of 35, 40, and 50 vol% in order to choose the most favorable conditions for piece printing. The three suspensions presented low viscosities, being the 50 vol% sample the one that presented the highest viscosity, with an average value of 0.77 Pa s. These viscosities were suitable for the ceramic stereolithography printing process. The 50 vol% suspension was characterized by TGA and DSC and did not show any difference compared to the resin without particles. Scaffolds with TPMS Gyroid and Schwartz P geometry were obtained by ceramic stereolithography and characterized morphologically and mechanically before and after sintering. The thermal treatment was successful. The polymer-ceramic scaffolds before sintering exhibited better compression resistance than the sintered ones. Fully ceramic scaffolds with gyroid geometry showed compressive strength values of 0.4 MPa, which is comparable to human trabecular bone. The best compression resistance was for the samples with the gyroid geometry. Since the 50 vol% sintered scaffolds with gyroid geometry showed better mechanical results, they were impregnated with propolis extracts from the Arauca region of Colombia in order to evaluate their antimicrobial activity against the standard strains Staphylococcus aureus (ATCC 29212) and Escherichia coli (ATCC 25922). The evaluated scaffolds exhibited better antibacterial activity against the S. aureus strain. After sintering, the 50Al scaffolds were submitted to a degradation test in phosphate-buffered saline (PBS) to assess the chemical stability of the alumina. The results indicated that the samples maintained their initial weight throughout the testing period, with measurements taken on days 1, 5, 8, and 12 showing no significant changes in weight loss percentage. This stability suggests that the alumina scaffolds possess robust chemical resistance under the tested conditions.

A study on the control of the printing accuracy in alumina parts by ceramic stereolithography

The printing accuracy in ceramic stereolithography is deteriorated by shrinkage due to photopolymerization of monomers and broadening owing to scattering of light. To improve the accuracy of printed alumina parts, a series of experiments involving the reduce of shrinkage and broadening were conducted. Firstly, the dependence of conversion of monomers, shrinkage of suspensions and warpage of parts on energy doses was quantitively investigated and correlated, with which the shrinkage was well controlled through optimization. Besides, the warpage problem was effectively resolved when adding 30 wt% PEG-200 in the suspensions to release the accumulated internal stress. Next, the broadening under different energy doses was observed and reduced by addition of absorbers, after which a self-defined parameter Cd/We was applied to suggest strategies in the selection of appropriate processing parameters and absorber content. On this basis, the holes with a diameter ranging from 50–200 μm were successfully printed.

Spreading ceramic stereolithography pastes: Insights from shear- and orthogonal-rheology

We study the shear rheological behavior of a commercial stereolithography paste containing ≈50 vol. % of zirconia particles (diameter ≈ 100 nm) with the aim to clarify physical mechanisms occurring during the “scraping” step of this yield stress fluid. Beyond a flow curve characterized by a high zero-shear viscosity accompanied with an overall shear-thinning behavior, we investigate in a systematic way the transient regime through start-up experiments. We demonstrate that a structural transition occurs between 10−2 and 10−1 s−1, resulting in an apparent interruption of the shear-thinning. The corresponding transient response presents a pronounced extra-growth of the shear stress before to stabilize at high strain amplitude and a negative first normal stress difference peak, both effects become stronger at higher shear rates. These observations are rationalized based on the high interparticle friction owing to the polyhedral shape and the roughness of the particles. In addition, relaxation tests following the start-up experiments reveal that the samples submitted to shear rates higher than 10−1 s−1 cannot relax the shear stress to the same level as in low shear rate experiments, suggesting a durable structural modification likely to impact the quality of the parts prior to their debinding and densification. Finally, we utilize orthogonal superposition rheology to illustrate how the application of an oscillatory deformation during the scraping procedure could help to reduce the shear-thinning interruption and improve the stereolithography processing as already observed empirically during scraping.

Additive manufacturing of composite glass/ceramic structures with self-similar geometries

The Hilbert curve fractal pattern was used to create a self-filling structure with designed porosity that would be ideal for applications such as biomedical components, circuit boards, and building materials. 3-Dimensional Hilbert curve structures were designed and analysed by Finite Element Analysis for various functions in fluid transport, heat transfer, and structural applications. A bespoke glass/zirconia composite paste was optimised for the fabrication of these structures by ceramic stereolithography, achieving a thixotropic photosensitive paste with a high solid loading of 69 %. Optimisation of process parameters and sintering schedule was carried out to allow accurate fabrication of the composite glass/zirconia structures. 3-Dimensional Hilbert curve structures were successfully fabricated by stereolithography and the designed structures have potential uses as highly efficient components in various industries.

3D‐printed heterogeneous isotropic–anisotropic dielectric resonator for singly fed dual‐band circularly polarised antennas

AbstractThe design of three‐dimensional (3D)‐printed heterogeneous ceramics exhibiting isotropic and anisotropic dielectric permittivities at microwave frequencies is studied for dielectric resonator antenna (DRA) applications. The heterogeneous ceramics are engineered by using periodic structures made up of subwavelength unit cells filled with zirconia ceramic and air. Ceramic stereolithography (CSLA) allows the 3D printing of a one‐piece ceramic block mixing isotropic and anisotropic dielectric regions. In order to demonstrate the possibility of exploiting such 3D‐printed ceramics, a singly fed dual‐band circularly polarised DRA is presented. To achieve circular polarisation at both bands, the relative permittivity of the dielectric resonator is locally controlled by introducing anisotropic dielectric regions. The 3D‐printed DRA is finally measured, and its results agree well with the simulations.

Local flow assisted platelet template alignment and corresponding alumina texturing in ceramic stereolithography process

Using local slurry laminar flow to align alumina platelet in the slurry and fabricate textured alumina by ceramic stereolithography has been shown with potential. However, the alignment process of alumina platelet and the corresponding texturing of alumina based on this method have not yet been revealed. This study systematically analyzed the mechanism of aligning alumina platelet in the local flow and the evolution of the microstructure of textured grain. The results showed that with the increase of the alumina platelet content in the slurry, the thickness of the grains gradually decreased. After sintering at 1600 °C for 2 h, textured alumina had mainly the crystal plane of (1010). The textured alumina with 15 vol% alumina platelet addition had the highest Lotgering factor (65 %) of (1010). The alumina platelet located in the middle and bottom of the local flow field aligned slower during the flow process. The distribution of flow velocity gradient was the main factor determining the alignment of alumina platelet.

Shrinkage Compensation and Effect of Building Orientation on Mechanical Properties of Ceramic Stereolithography Parts.

Stereolithography additive manufacturing (SLA-AM) can be used to produce ceramic structures by selectively curing a photosensitive resin that has ceramic powder in it. The photosensitive resin acts as a ceramic powder binder, which is burned, and the remaining ceramic part is sintered during post-processing using a temperature-time-controlled furnace. Due to this process, the ceramic part shrinks and becomes porous. Moreover, additive manufacturing leads to the orthotropic behavior of the manufactured parts. This article studies the effect of the manufacturing orientation of ceramic parts produced via SLA-AM on dimensional accuracy. Scaled CAD models were created by including the calculated shrinkage factor. The dimensions of the final sintered specimens were very close to the desired dimensions. As sintering induces porosity and reduces the mechanical strength, in this study, the effect of orientation on strength was investigated, and it was concluded that the on-edge specimen possessed by far the highest strength in terms of both compression and tension.

A Novel Approach Toward the Integration of Fully 3-D Printed Surface-Mounted Microwave Ceramic Filters

A first approach toward the integration of heterogeneous electronic circuit technologies and fully 3-D printed ceramic microwave devices is discussed in this work. Additive manufacturing (AM) capabilities are explored for the development of multifunction surface-mount compact components used in different RF front-ends’ scenarios. Monolithic ceramic bandpass filters (BPFs) are designed to operate in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$</tex-math> </inline-formula> -Band and to assess the typical limitations of ceramic stereolithography (SLA) processes. A post-fabrication tuning method based on a laser engraving strategy is presented to overcome the manufacturing constraints and carry out the filters’ correction. 2.5-D and 3-D printed four-pole filters were fabricated and tuned using the proposed methodology.

Binder removal from ceramic stereolithography green bodies: A neutron imaging and thermal analysis study

AbstractStereolithography of ceramics remains one of the most powerful additive manufacturing routes for the creation of intricate ceramic parts. Despite its utility as a forming tool, ceramic stereolithography requires a challenging debinding stage due to the requisite high polymeric loading. Earlier research has identified both the polymeric resin composition and debinding atmosphere to be crucial factors in improving debinding performance. Here, we use a combination of thermogravimetric analysis and neutron imaging to examine samples of different compositions printed using the same processing and exposure parameters. We quantify the influence of both polyethylene glycol addition and the use of different debinding atmospheres (argon and vacuum) on the debinding behavior of ceramic pellets. Specifically, we demonstrate a method for examining the concentration gradients that develop during thermal debinding with the aid of neutron tomography. We find that at a constant heating rate of 1°C/min up to 500°C, vacuum atmosphere appears to result in a greater number of cracks as compared to the use of argon. The vacuum atmosphere led to the development of lower concentration gradients in the samples on average. The greatest improvement resulted with the addition of polyethylene glycol to the samples. This addition led to significantly less cracking and much lower concentration gradients in samples during debinding. These results prompt us to conclude that while keeping printing and exposure parameters constant, composition modification has a more significant effect on the debinding improvement than heating atmosphere.

Sintering behavior of ultra-thin 3D printed alumina lattice structures

Ceramic stereolithography or vat photopolymerization is a process allowing the fabrication of ceramic objects with highly complex shapes. Lattices structures are particularly used together with advanced optimization topology tools for the design of printable lightweight shapes with optimized mechanical resistance. If the mechanical resistance of these lattices structures is well controlled at the polymeric state, they can be severely deformed at high temperatures during the sintering stage. The deformation sensitivity of the lattices structures during the sintering should then be determined to include this aspect at the conception stage. The finite element (FEM) simulation of lattices sintering is an interesting solution to anticipate numerically the deformation sensitivity of the lattices and determine their minimum wall thickness. This requires to determine the sintering behavior of the printed green specimens and to take into account the sintering anisotropy, which involves weaker resistance between the layers. In this study the sintering behavior is first determined by multiple-axis dilatometry, modeled analytically and then simulated by the FEM method. Afterward, the sintering simulation of lattices with different wall thicknesses is conducted. This allows testing the simulation tool predictability for each lattices wall thickness and to compare their deformation sensitivity at high temperatures.

Additively-Manufactured All-Dielectric Microwave Polarization Converters Using Ceramic Stereolithography

We report a class of all-dielectric, additively-manufactured polarization converters with tailored temporal frequency responses within the Ku and Ka microwave bands (15 – 40 GHz). These multi-layer devices consist of cascaded, subwavelength, high-contrast gratings with different fill fractions and orientations, providing control over the effective anisotropic properties of each layer. In design, the subwavelength gratings are modeled as homogeneous anisotropic layers. This allows the overall metastructure to be treated as a stratified dielectric medium. Therefore, it can be analyzed and optimized using plane-wave transfer matrix techniques that fully account for multiple reflections between layers. Using this cascaded grating geometry, a variety of high-efficiency microwave polarization converters can be realized with broadband, multiband, or multifunctional behavior. The transmissive metastructures do not require anti-reflection layers since impedance matching is incorporated into their design. Three example devices based on alumina/air gratings have been monolithically fabricated using ceramic stereolithography: a broadband reflective half-wave plate, a broadband isotropic polarization rotator, and a dual-band linear-to-circular polarization converter.

Non-contact/contact hybrid support based on the slice for ceramic stereolithography

Ceramic stereolithography (CSL) technology can produce parts with complex structures, high precision and excellent mechanical properties. However, to ensure printability, dense and massive contact supports of the suspension part for better performance reduce the surface quality of parts and increase the cost of post-treatment. The shrinkage caused by the photopolymerization of the resin in the slurry and the time asynchrony from the layer-by-layer mode lead to the edge warping of the printed objects. Based on the yield stress of ceramic paste, a new mixed support form combining non-contact support and contact support (NCC) is designed in this paper. The non-contact support and the narrow slurry layer under it provide support for the gravity of the upper part and ensure surface quality. The slight contact support of the boundary is used to limit the curing warpage caused by the resin. What's more, an automatic generation algorithm based on slices for NCC support is designed. The k-neighborhood expansion method is proposed to identify the support demand of each pixel in the slice. The effectiveness of the NCC supports and generation algorithm is proved by the case on the sinking digital light procession (DLP) equipment with alumina ceramic slurry. NCC support can solve the problem of warping while maximizing the surface accuracy, ensuring the stability of printing which represents great industrial value.

Simulation and experimental analysis on the deformation rate on slender rod parts during the recoating process in high viscosity ceramic stereolithography

Simulation and experimental analysis on the deformation rate on slender rod parts during the recoating process in high viscosity ceramic stereolithography

Study of alumina ceramic parts fabricated via DLP stereolithography using powders with different sizes and morphologies

AbstractSelecting suitable ceramic powders for the preparation of UV‐curable ceramic suspensions, which are well suited for printing processes and production of high‐performance ceramic components, is a crucial factor in the practical industrial application of digital light processing (DLP) stereolithography. Therefore, this study aims to provide a comprehensive evaluation of alumina ceramic parts fabricated via DLP stereolithography using a variety of alumina powders with varying sizes and morphologies. Experiments were conducted to examine the rheological response, recoating performance, and curing behavior of UV‐curable alumina suspensions. Additionally, the thermal decomposition behavior of three‐dimensional (3D)‐printed green‐bodies, as well as the physical and mechanical properties of 3D‐printed sintered alumina components were thoroughly investigated. The best physical and mechanical performances were achieved by printing 55 vol% suspensions prepared using near‐spherical AA04 alumina powders (median diameter .4 μm). This study elucidates the effects of ceramic particle size and morphology on the entire technological process of DLP‐based ceramic stereolithography, thereby establishing the guidelines for the fabrication of high‐performance 3D‐printed ceramic objects in industrial and engineering production by selecting appropriate ceramic powders.

A comprehensive evaluation of vat-photopolymerization resins and alumina slurries for ceramic stereolithography

Ceramic slurries play an essential role in the fabrication of complex ceramic parts in ceramic stereolithography (CSL), in which photosensitive monomer is the focus. In this study, the comprehensive properties of commonly used monomers were quantitatively studied by a new evaluation system. As a result, ACMO, PONPGDA and EOTMPTA were selected as the final three monomers with better properties. On this basis, an optimal combination of the above monomers with the best comprehensive performance was obtained by blending them at a ratio of 60:60:40. Next, the influence of different resins on the properties of alumina slurries was investigated. It was found that using the mixture of the above three monomers, an excellent as-prepared slurry with low viscosity, small shrinkage and good photo-curable ability was obtained.

Reduction of Dewaxing and Sintering Time by Controlling the Particle Size of YSZ Particles for Stereolithography

In ceramic stereolithography, composite “green” bodies must be thermally processed to de-bind organic content and sinter the material. The conventional process for dewaxing and sintering of yttria stabilized zirconia stereolithography components is typically very long. The time and energy cost of thermal treatment of these components can be reduced by controlling the size of the solid particles in the photosensitive material. The Discrete Element Method was used to model the number of particle contacts per mass using particles of various median diameter, and a three-dimensional curved surface graph was generated. Ceramic slurries were prepared using powders that fulfilled the conditions of various calculated data points from the DEM model analysis. The prepared slurries were processed by stereolithography additive manufacturing and fabricated precursors were thermally processed to dewax and sinter the parts. The relationship between the particle size and the occurrence of crack formation after heat treatment was investigated. Heat treatment parameters were further investigated using the predicted slurry composition that was optimal for crack prevention. The required time for dewaxing and sintering of yttria stabilized zirconia components was reduced to one tenth of the conventional time through optimization of slurry composition and thermal treatment schedule.

High-Speed Alumina Stereolithography

The additive manufacturing of ceramics offers a reliable and repeatable method for fabricating parts with complex geometries. To compete with conventional ceramic forming methods, the time and cost associated with material and process optimization for ceramic stereolithography should be improved. Computational analysis methods can be utilized to reduce the number of experimental steps required for material and process optimization. This work used the discrete element method and ray tracing analyses to predict suitable material parameters and processing conditions for ceramic stereolithography. The discrete element method was used to create alumina particle dispersion models to predict suitable paste compositions, and ray tracing was used to predict suitable laser power and scan speed to achieve a sufficient curing depth for stereolithography processing. The predicted conditions of paste composition and processing parameters were comparable to experimental values, reducing the number of experimental iterations required for process optimization. Furthermore, suitable processing parameters for high-speed fabrication by stereolithography was predicted, achieving a processing speed much faster than previously reported ceramic stereolithography. The reduction in process optimization timeline, and the increase in fabrication speed, could increase the appeal of ceramic stereolithography to industry.

Theoretical and experimental research on the coating process of ceramic stereolithography

The coating process in ceramic stereolithography is one of the principal sources of inaccuracy in the height dimension. The coating in stereolithography is a layer-by-layer build-up process, so the thickness of one layer coated is influenced by the previous layer and affects the thickness of the next layer. If inconsistent layer thicknesses exist, they will result in the poor quality of the final product. This paper analyzes the coating process of the slurry-separated system based on a simple 2D model and Navier-Stokes equations, presenting the theoretical equations of layer thickness for the commonly used blade types. Given the characteristics of layer-by-layer coating in stereolithography, the theoretical equations should be constantly iterated to obtain the thickness of each layer. This paper discovers the initial blade gap has a significant impact on the layer thicknesses by theoretical analyses. With the verification of experiments, the results shows that the presence of the unreasonable initial blade gap may lead to large fluctuations in layer thicknesses of the first few layers, and the coating in stereolithography is a "self-regulating" process with a tendency to the desired thickness. The larger the desired layer thickness, the worse this "self-regulating ability" is. This paper defines a coefficient of blade gap and proposes that using the coefficient of blade gap to determine a reasonable initial blade gap based on different working conditions can effectively control the consistency of each layer thickness.

Fabrication of silica-based ceramic cores with internal lattice structures by stereolithography

Ceramic cores are widely used in investment casting, and ideal properties of cores are essential for high-quality castings. Under the circumstances requiring thick cores, solid cores are likely to encounter deformation and cracking defects due to the accumulation of shrinkage. Therefore, with the superiority of ceramic stereolithography in producing complex ceramic parts, hollow cores with lattice structures were designed and fabricated. The dimensional accuracy and properties of the green and sintered bodies were evaluated. Results show the dimensional accuracy of sintered cores is controlled within ±0.25 mm benefited from the precise green bodies. The mechanical properties are not obviously deteriorated. The bending strength reaches 11.94 MPa at room temperature and 12.87 MPa at 1,500 °C with a creep deformation of 0.345 mm. Furthermore, casting verifications prove that the hollow cores meet the requirements of investment casting. Smooth casting surfaces are obtained, at the same time, the core-removal efficiency is improved by over 3 times.