Ceramic Additive Manufacturing Research Articles

Investigating Defect Detection in Advanced Ceramic Additive Manufacturing Using Active Thermography

Additive manufacturing of advanced materials has become widespread, encompassing a range of materials including thermoplastics, metals, and ceramics. For the ceramics, the complete production process typically involves indirect additive manufacturing, where the green ceramic part undergoes debinding and sintering to achieve its final mechanical and thermal properties. To avoid unnecessary energy-intensive steps, it is crucial to assess the internal integrity of the ceramic in its green stage. This study aims to investigate the use of active thermography for defect detection. The approach is to examine detectability using two benchmarks: the first focuses on the detectability threshold, and the second on typical defects encountered in 3D printing. For the first benchmark, reflection and transmission modes are tested with and without a camera angle to minimize reflection. The second benchmark will then be assessed using the most effective configurations identified. All defects larger than 1.2 mm were detectable across the benchmarks. The method can successfully detect defects, with transmission mode being more suitable since it does not require a camera angle adjustment to avoid reflections. However, the method struggles to detect typical 3D-printing defects because the minimum defect size is 0.6 mm, which is the size of the nozzle.

Interlaboratory study of flexural strength in additively manufactured alumina

AbstractWe report the results of an international interlaboratory study of the flexural strength of alumina fabricated across six laboratories using the vat photopolymerization ceramic additive manufacturing (AM) technology. The mechanical testing of all the specimens, 142 in total, was performed at the National Institute of Standards and Technology (NIST) according to the well‐established four‐point bending method standardized for traditional ceramics. Overall, the existing ASTM standard for the four‐point bend testing proved adequate for AM ceramics, with several modifications to the specimen requirements to account for the specifics of AM processes. Critical flaws that caused failure were identified in all but two cases using optical fractography augmented with the imaging of fracture surfaces in a scanning electron microscope. The flexural strength data, analyzed following the Weibull statistics, exhibited considerable variation among the specimen sets manufactured by different laboratories. This variability correlated with the presence of many distinct critical flaws. We identified seven types of flaws that accounted for the failure of 94% of specimens. The prevalent flaws depend on the printing direction relative to the specimen's geometry. We discuss the nature of these flaws and their relation to the printing and post‐processing conditions. Removal of several types of critical flaws will significantly improve mechanical properties of ceramic parts built using vat‐photopolymerization AM.

Microstructure formation mechanisms and property regulation methods during ceramic additive manufacturing

Anisotropic surface lamellar defects, dimensional shrinkage, and bending strength are important scientific issues that constrain vat photopolymerization additive manufacturing of biological, electronic, and core ceramics with high precision and complex structures. Through the single-factor experiment of photoinitiator concentration, average particle size, volume fraction, and refractive index constant in ceramic-resin slurry, this work studies the photopolymerization characteristics and profile curves, surface lamellar defects, and crosslinking density, verifies the reliability of the photopolymerization profile equations affected by the slurry composition, and acquires the anisotropic property formation mechanisms and control methods. The single-point scanning photopolymerization profile shape is parabolic, resulting in x-, y-, and z-direction lamellar defects before and after sintering (1550 °C), with no obvious weakening. After the quantitative description of the lamellar defects, the average surface roughnesses before and after sintering of the green body are 6.82 and 4.92 μm, respectively. Additionally, the laser energy attenuation along the penetration direction induces a gradient distribution of crosslinking density in the photopolymerization profile region. The crosslinking density gradient distribution of the decay from the slurry surface toward the depth direction is influenced by the slurry component concentration, leading to a gradient of cured powder concentration, which induces anisotropic behaviors. Through the crosslinking density controlling, the average bending strength in x(y) and z directions is increased by 63.19 % (46 %), the difference in anisotropic strength is reduced by 22.55 %, and the dimensional shrinkage difference of x and z directions is reduced by 48.32 %. This provides a theoretical and experimental research basis for ceramic vat photopolymerization with high dimensional accuracy, excellent performance, and morphology control.

Novel 3D printed bioactive SiC orthopedic screw promotes bone growth associated activities by macrophages, neurons, and osteoblasts.

Ceramic additive manufacturing currently relies on binders or high-energy lasers, each with limitations affecting final product quality and suitability for medical applications. To address these challenges, our laboratory has devised a surface activation technique for ceramic particles that eliminates the necessity for polymer binders or high-energy lasers in ceramic additive manufacturing. We utilized this method to 3D print bioactive SiC orthopedic screws and evaluated their properties. The study's findings reveal that chemical oxidation of SiC activated its surface, enabling 3D printing of orthopedic screws in a binder jet printer. Post-processing impregnation with NaOH and/or NH4OH strengthened the scaffold by promoting silica crystallization or partial conversion of silicon oxide into silicon nitride. The silica surface of the SiC 3D printed orthopedic screws facilitated osteoblast and neuron adhesion and extensive axon synthesis. The silicate ions released from the 3D printed SiC screws favorably modulated macrophage immune responses toward an M1 phenotype as indicated by the inhibition of TNFα secretions and of reactive oxygen species (ROS) expression along with the promotion of IL6R shedding. In contrast, under the same experimental conditions, Ti ions released from Ti6Al4V discs promoted macrophage TNFα secretion and ROS expression. In vivo tests demonstrated direct bone deposition on the SiC scaffold and a strong interfacial bond between the implanted SiC and bone. Immunostaining showed innervation, mineralization, and vascularization of the newly formed bone at the interface with SiC. Taken altogether, the 3D printed SiC orthopedic screws foster a favorable environment for wound healing and bone regeneration. The novel 3D printing method, based on ceramic surface activation represents a significant advancement in ceramic additive manufacturing and is applicable to a wide variety of materials.

In-situ monitoring of multi-physical dynamics in ceramic additive manufacturing

Ceramic additive manufacturing is an innovative technology for developing complex ceramic structures, while a direct understanding of the physical phenomena occurring in sequential layers remains challenging, affected by the material design such as the presence of inorganic particles and their contents. This study provides a direct analysis of how the ceramic particles influence fabrication behavior utilizing an in-situ monitoring system. The force profile provides immediate feedback on fractures and geometric design, with the fluctuation in force directly corresponding to specific structural characteristics and stability during the fabrication. Furthermore, the multi-physical dynamics was investigated with a unit signal based on the effect of ceramic on the rheological-curing-mechanical behavior. For example, the mechanical behavior was characterized in real-time, as shown through an intensified peak of 6.6 kPa during the manufacturing of a ceramic composite, a 5.6 times increase compared to pure resin. The monitored data quantified the geometric dynamics and the multi-physical mechanism in real-time, achieved from the data on the overall fabrication status and the unit signal analysis of continuous manufacturing. This method can improve the reliability of ceramic additive manufacturing by providing insight into how ceramics impact fabrication behavior on sequential layers in real-time.

Effect of sintering temperature on feature resolution and flexural strength of ceramics fabricated through vat photopolymerization additive manufacturing

PurposeAlthough ceramic additive manufacturing (AM) could be used to fabricate complex, high-resolution parts for diverse, functional applications, one ongoing challenge is optimizing the post-process, particularly sintering, conditions to consistently produce geometrically accurate and mechanically robust parts. This study aims to investigate how sintering temperature affects feature resolution and flexural properties of silica-based parts formed by vat photopolymerization (VPP) AM.Design/methodology/approachTest artifacts were designed to evaluate features of different sizes, shapes and orientations, and three-point bend specimens printed in multiple orientations were used to evaluate mechanical properties. Sintering temperatures were varied between 1000°C and 1300°C.FindingsDeviations from designed dimensions often increased with higher sintering temperatures and/or larger features. Higher sintering temperatures yielded parts with higher strength and lower strain at break. Many features exhibited defects, often dependent on geometry and sintering temperature, highlighting the need for further analysis of debinding and sintering parameters.Originality/valueTo the best of the authors’ knowledge, this is the first time test artifacts have been designed for ceramic VPP. This work also offers insights into the effect of sintering temperature and print orientation on flexural properties. These results provide design guidelines for a particular material, while the methodology outlined for assessing feature resolution and flexural strength is broadly applicable to other ceramics, enabling more predictable part performance when considering the future design and manufacture of complex ceramic parts.

Multi-Image Fusion-Based Defect Detection Method for Real-Time Monitoring of Recoating in Ceramic Additive Manufacturing

Multi-Image Fusion-Based Defect Detection Method for Real-Time Monitoring of Recoating in Ceramic Additive Manufacturing

Mechanical properties of additively manufactured lattice structures composed of zirconia and hydroxyapatite ceramics

Ceramic lattices hold great potential for bone scaffolds to facilitate bone regeneration and integration of native tissue with medical implants. While there have been several studies on additive manufacturing of ceramics and their osseointegrative and osteoconductive properties, there is a lack of a comprehensive examination of their mechanical behavior. Therefore, the aim of this study was to assess the mechanical properties of different additively manufactured ceramic lattice structures under different loading conditions and their overall ability to mimic bone tissue properties.Eleven different lattice structures were designed and manufactured with a porosity of 80% using two materials, hydroxyapatite (HAp) and zirconium dioxide (ZrO2). Six cell-based lattices with cubic and hexagonal base, as well as five Voronoi-based lattices were considered in this study. The samples were manufactured using lithography-based ceramic additive manufacturing and post-processed thermally prior to mechanical testing. Cell-based lattices with cubic and hexagonal base, as well as Voronoi-based lattices were considered in this study. The lattices were tested under four loading conditions: compression, four-point bending, shear and tension.The manufacturing process of the different ceramics leads to different deviations of the lattice geometry, hence, the elastic properties of one structure cannot be directly inferred from one material to another. ZrO2 lattices prove to be stiffer than HAp lattices of the same designed structure. The Young’s modulus for compression of ZrO2 lattices ranges from 2 to 30GPa depending on the used lattice design and for HAp 200MPa to 3.8GPa. The expected stability, the load where 63.2% of the samples are expected to be destroyed, of the lattices ranges from 81 to 553MPa and for HAp 6 to 42MPa.For the first time, a comprehensive overview of the mechanical properties of various additively manufactured ceramic lattice structures is provided. This is intended to serve as a reference for designers who would like to expand the design capabilities of ceramic implants that will lead to an advancement in their performance and ability to mimic human bone tissue.

Towards a debinding-free additive manufacturing of ceramics: A development perspective of water-based LSD and LIS technologies

Ceramic additive manufacturing (AM) requires a complex process chain with various post-processing steps that require expensive machines and special expertise. The key to further market penetration is AM that makes it possible to integrate into an already established ceramic process chain. Most successful AM technologies for ceramics are, however, based on processes that initially have been developed for polymeric materials. For ceramics AM, polymers or precursors are loaded with ceramic particles. This strategy facilitates the entry into AM, however the introduction of organic additives into the ceramic process chain represents a considerable technological challenge to ultimately obtain a ceramic component after additive shaping. In the present communication, two technologies based on ceramic suspensions will be introduced, the “layerwise slurry deposition” (LSD) and “laser induced slip casting” (LIS) technology. Both technologies take advantage of the high packing densities reached by conventional slip casting and moreover enable the processing of fines, even nanoparticles.

Ceramic additive manufacturing and microstructural analysis of tricalcium phosphate implants using X-ray microcomputed tomography

Additive manufacturing (AM) of ceramic bone implants from tricalcium phosphate (TCP) offers several benefits for bone regeneration and defect treatment. TCP scaffolds, e.g. featuring lattice or gyroid geometries, can effectively induce bone ingrowth and integration, showing a high potential in the treatment of large bone defects, e.g. as filler material for large bone defects. A major advantage of TCP is its osteoconductivity making it an effective choice for a broad range of orthopedic and dental applications. In addition, AM allows for the possibility to create precise, patient-specific implants with controllable mechanical properties. Those properties can be controlled by the implants' microstructure, e.g. in relation to bulk density and internal porosity. In this contribution, eleven resorbable bone implants were produced from β-tricalcium phosphate (β-TCP) in order to quantify the internal porosity in three dimensions using microcomputed tomography (μ CT). All components were manufactured using an extrusion-based process and scanned using an industrial μCT system at a voxel size of 10 μm. Two samples were physically prepared to allow a high-resolution μCT analysis at a voxel size of 1 μm. Results show that post-processed image data enables the non-destructive inspection of highly complex ceramic AM implants. Using μCT we were able to quantify internal porosity in β-TCP bone implant and quantify the geometry and distribution of wall thicknesses in the gyroid geometry. However, a detailed microstructural analysis is only possible using high-resolution μCT volume data, e.g. in relation to internal porosity. The findings emphasize that ceramic AM is able to produce complex components. However, NDT using μCT is crucial in the development of new materials and geometries. μCT provides high-resolution insights into the internal and external structure of ceramic AM components. It plays a critical role in detecting internal features, including small-scale porosity and delamination which are crucial for the integrity and functionality of medical implants. Moreover, μCT provides volumetric data that supports the design and manufacturing process at various stages, enabling an iterative approach of continuous improvement in mechanical performance and osseointegration.

Vat photopolymerization based Photoinhibition aided Ceramic additive manufacturing (PinCAM)

Vat photopolymerization (VPP) in ceramic additive manufacturing (CAM) faces challenges due to high viscosity from ceramic powder loading, necessitating interruptive recoating steps. Ceramic particles also attenuate and divert irradiated light, causing reduced cure depth and over-curing, leading to slow print, weak interlay adhesion, and dimensional errors. This study introduces photo inhibition-aided CAM (PinCAM) using dual-wavelength digital light processing to mitigate these issues. PinCAM employs two optical masks for initiation and inhibition at different wavelengths. While previous research focused on polymers, this work evaluates inhibition's effects in suspension-based VPP-CAM. Modeling and experiments examine inhibition and curing characteristics, print speed, dimensional accuracy, surface roughness, and microstructure. Preliminary results suggest that photoinhibition has the potential to enhance geometrical and surface properties as well as particle distribution homogeneity of green ceramic components without significantly compromising print speed. Understanding inhibition's impact will aid further research in PinCAM optimization for rapid and precise ceramic manufacturing.

Potential and challenges for Powder Bed Fusion – Laser Beam (PBF-LB) in industrial ceramic additive manufacturing

In recent years, ceramic 3D printing has proven its potential for increasing the cost and time efficiency of ceramic manufacturing, especially for customizable products, small series production and for (multi-material) parts with complex design. This work gives an overview of the methods for ceramic additive manufacturing that are currently available for industrial production with their advantages and disadvantages. Ceramic Powder Bed Fusion- Laser Beam (PBF-LB) or also known as selective laser sintering or melting (SLS/SLM) is introduced, using a ceramic powder as starting material for shaping by selective laser irradiation. Amongst others, the technique offers a superior productivity, which might be the central argument in the future for evaluating the applicability of PBF-LB for industrial manufacturing. Additionally, a novel approach to ceramic PBF-LB is presented, using a thermoset binder for incorporating ceramic particles in the starting material that, due to the non-meltable nature of the binder, improve the dimension stability of the green parts during thermal debinding and sintering. The production of large, complex structures opens up a wide range of applications. One promising application for porous structures made of photocatalytic titanium oxide is water treatment. Such printed, debinded and sintered filter modules enable the degradation of organic residues in water, thus contributing to safer and higher water quality. Furthermore, high-resolution printing can be realized via micro-PBF-LB (μ-PBF-LB, also known as μ-SLS).

Evolution of ceramic additive manufacturing: A comprehensive survey for high-performance and dental applications

The manufacturing landscape has been altered by additive manufacturing (AdMa), which has surfaced as a versatile and adaptive technology. Notable advancements have been made in the creation of ceramic substances for AdMa procedures. The ceramic components made using AdMa processes show deficiencies concerning their overall performance and mechanical properties. More recently, research has concentrated on improving mechanical properties and effectiveness by optimizing the fabrication procedure by integrating additional post-processing methods and using a material pre-treatment approach. The advancements in AdMa methods for producing high-performance ceramic (H-Perform-C) materials, referred to as advanced ceramics, are reviewed and examined in this article. AdMa methods are classified based on the ASTM's standards and the particular technology used in these procedures is further explained. A comprehensive review is provided, explaining the fundamental principles, mechanical characteristics, merits, drawbacks, practical implementations and constraints associated with each respective technological approach.

Advancements in multi-material additive manufacturing of advanced ceramics: A review of strategies, techniques and equipment

Ceramics possess notable attributes including excellent wear resistance, exceptional high-temperature strength, superior hardness, and outstanding biocompatibility, rendering them indispensable for the fabrication of key industrial components. Additive manufacturing presents significant benefits such as precise fabrication, design flexibility, and the ability for mass customization. This technology facilitates the creation of intricate structural or functional ceramic components with complex geometries, effectively addressing issues that are inadequately managed by conventional methods, such as the inherent brittleness of ceramics and challenges associated with ceramic machining. As advancements in aerospace, special industry, and biomedical sectors progress, the performance limitations of uniform ceramic materials and structures have emerged as a bottleneck constraining the broadening of their application range. There is a pressing need to transition from single-material ceramic additive manufacturing to multi-material printing. This paper highlights and compares various notable advancements in typical single-material ceramic additive manufacturing. In addition, it delves into the present status of multi-material ceramic additive continuous forming and the development of associated equipment, focusing on different forming mechanisms. Finally, the paper concludes by identifying the primary challenges and research priorities in multi-material ceramic additive manufacturing, and suggests potential directions for future development.

Slurry-based photoinitiator jetting process for ceramic additive manufacturing

This study proposes a novel additive manufacturing (AM) process called Slurry-Based Photoinitiator Jetting Process (SPJ) for high-volume or large-size precision ceramics fabrication. The SPJ process draws inspiration from vat photopolymerization and binder jetting processes, using ceramic slurries containing photosensitive resins as the feedstock. The process involves first spreading ceramic slurry on a platform, followed by selectively jetting photoinitiator into the slurry layer by printheads, and finally light curing. This innovative SPJ process achieves simultaneous advantages in large build area, high-speed, and high-quality ceramic AM. By employing silicon carbide as the typical printing feedstock for SPJ, this study meticulously analyzed the jettability of the photoinitiator ink and focused on assessing the impacts of various factors on curing depth and the occurrence of tailing phenomena. Ultimately, high green density ceramic parts with exceptional homogeneity and a minimum designed pore size of 200 μm were obtained. The SPJ method demonstrates significant potential for the efficient manufacture of large or mass-produced precision ceramic components.

Forming ability and quality of fine ceramic structure fabricated by vat photopolymerization

In recent years, ceramic additive manufacturing technology based on vat photopolymerization has been widely used in various fields. This technology has amazing structural design freedom and forming precision. However, the printed structure can't be regarded as a simple reproduction of the virtual model. In our work, by analyzing the characteristic edge structure caused by the uneven propagation of exposure energy in ceramic slurry, we explore the manufacturing limits of fine structure in ceramic vat photopolymerization and the reasons for the decline in fine structure printing quality. The ability of ceramic vat photopolymerization to construct fine structures was improved by personalized selection of exposure energy. This work plays an important role in studying and expanding the ability of ceramic vat photopolymerization to construct fine structures.

High-Performance Defect Detection Methods for Real-Time Monitoring of Ceramic Additive Manufacturing Process Based on Small-Scale Datasets

Vat photopolymerization is renowned for its high flexibility, efficiency, and precision in ceramic additive manufacturing. However, due to the impact of random defects during the recoating process, ensuring the yield of finished products is challenging. At present, the industry mainly relies on manual visual inspection to detect defects; this is an inefficient method. To address this limitation, this paper presents a method for ceramic vat photopolymerization defect detection based on a deep learning framework. The framework innovatively adopts a dual-branch object detection approach, where one branch utilizes a fully convolution network to extract the features from fused images and the other branch employs a differential Siamese network to extract the differential information between two consecutive layer images. Through the design of the dual branches, the decoupling of image feature layers and image spatial attention weights is achieved, thereby alleviating the impact of a few abnormal points on training results and playing a crucial role in stabilizing the training process, which is suitable for training on small-scale datasets. Comparative experiments are implemented and the results show that using a Resnet50 backbone for feature extraction and a HED network for the differential Siamese network module yields the best detection performance, with an obtained F1 score of 0.89. Additionally, as a single-stage defect object detector, the model achieves a detection frame rate of 54.01 frames per second, which meets the real-time detection requirements. By monitoring the recoating process in real-time, the manufacturing fluency of industrial equipment can be effectively enhanced, contributing to the improvement of the yield of ceramic additive manufacturing products.

Fabrication of highly transparent yttria by DLP-based additive manufacturing

High-quality transparent yttria (Y2O3) is produced using various shaping techniques; however, the geometric control limits of shaping processes hinder its utilization and application. Thus, this study proposed digital light processing (DLP)-based additive manufacturing (AM). Although popular, transparent ceramic AM faces issues owing to limited transparency and simple shapes. This study fabricated a three-dimensional-structured transparent Y2O3 ceramic using DLP-based AM assisted by vacuum sintering and revealed the critical factors governing its transparency. Zirconia and lanthana were utilized as sintering additives to regulate grain growth. Slurry conditions (dispersant concentration and solid loading) were optimized to control the homogeneity and density of the green body. After pre-sintering and vacuum sintering, the transparent Y2O3 ceramics exhibited a transmittance of 94.86 % of the theoretical limit and a relative density of 99.89 % owing to a fine-grained dense microstructure. The fabricated lens array structures of Y2O3 demonstrated a notable level of transparency and satisfactory optical imaging capabilities.

Machine learning assisted material development for lithography-based additive manufacturing of porous alumina ceramics

The transition of applying ceramic additive manufacturing (AM) from prototyping to mass production and from monolithic to multi-material (MM) components can be supported by continual development in materials and processes. Lithography-based ceramic manufacturing (LCM) can be used for MM printing of ceramics with high accuracy by introducing different approaches that enable discrete/smooth multidirectional material transitions. Adaptation of ceramic slurries plays important role for the successful printing and co-sintering. Especially for co-sintering, the shrinkage of the materials must be adapted so that no internal residual stresses occur. Machine learning (ML) offers promising opportunities for development of new materials and optimization of processes in AM by introducing relations between input features and output responses. In this article, ML algorithms were used for the prediction of shrinkage and porosity of alumina samples dependent on input features including material, printing, and thermal processing parameters so that defect-free porous/dense alumina combination can be achieved.

Initiation and evolution of systemic innovations: Patterns and interactions in the emergence of additive manufacturing technologies

AbstractTechnological innovations are becoming increasingly systemic in the complex and interconnected world. The initiation and evolution of systemic innovations take time and include numerous challenges, and the mechanisms through which systemic innovations emerge in the interaction between different technologies represent a research gap. This paper explores the emergence of ceramic additive manufacturing as an example of a systemic manufacturing technology innovation. We implemented an event history analysis of four ceramic‐material additive manufacturing technologies. We traced the initiation and evolution paths of each of the four technologies over time and showed a pattern of activities within and across the technologies. The study contributes by revealing that systemic innovations emerge as a result of parallel and sequential development paths of within‐technology system components as well as the interaction between multiple technologies. The timing of the coalescing development paths of the system components and technologies appears crucial but serendipitous instead of coordinated. The findings open new pathways for speeding up the emergence of systemic innovations and forthcoming research to support the evolution of additive manufacturing.