Improving ceramic additive manufacturing via machine learning-enabled closed-loop control

Advanced ceramic products are widely used in aerospace, automotive, electronic, laboratory equipment, and other industries. To achieve the geometric complexity and desirable properties that are difficult to obtain by conventional manufacturing methods, ceramic additive manufacturing (AM) methods have been studied intensively in recent years. However, the adaptive control with feedback is not currently implemented in any commercially available ceramic three-dimensional printer. Robocasting is one of the most widely utilized constant-volumetric-flow AM processes for creating various ceramic materials at a low cost. This study employed robocasting as a model to implement an adaptive control with a feedback loop in the ceramic AM process. In this research, processing load that was proportional to the processing pressure, width of the print, and length of extrusion were selected to be representative of process signal, quality signal, and control parameter, respectively. First, a database of the load and extrusion length was established. An artificial neural network model was created using that established database. The data-driven, closed-loop control was integrated into the robocasting process. Finally, the improvement was validated by comparing the quality of the prints produced by both the closed-loop process with the adaptive control and the open-loop process without the adaptive control.     

Lithography-based ceramic manufacturing (LCM) – Viscosity and cleaning as two quality influencing steps in the process chain of printing green parts

The advantages of suspension based Additive Manufacturing (AM), e.g. the lithography-based ceramic manufacturing (LCM), are high structural resolution, and compared to other available AM techniques, the manufacturing of dense (>99%) ceramic components with high performance. This novel manufacturing technique permits innovative designs, new types of ceramic components, and offers a range of new applications; like micro reactors, catalyst supporting structures or heat exchangers, as well as cutting edge biomedical devices and personalized medical products. Some examples of personalized medical products are customised ceramic knee implants or custom spinal fusion implants. Producing these implants using LCM would allow product offerings not possible before. However, the LCM process chain includes several open points, which have to be solved, in order to get high quality end results. In this paper, the development of suspensions (curable slurries) based on different binders, and the procedures for cleaning printed parts are thoroughly considered.     

Additive Manufacturing of Ceramics: Issues,Potentialities, and Opportunities

Additive manufacturing (AM) is a technology which has the potential not only to change the way of conventional industrial manufacturing processes, adding material instead of subtracting, but also to create entirely new production and business strategies. Since about three decades, AM technologies have been used to fabricate prototypes or models mostly from polymeric or metallic materials. Recently, products have been introduced into the market that cannot be produced in another way than additively. Ceramic materials are, however, not easy to process by AM technologies, as their processing requirements (in terms of feedstock and/or sintering) are very challenging. On the other hand, it can be expected that AM technologies, once successful, will have an extraordinary impact on the industrial production of ceramic components and, moreover, will open for ceramics new uses and new markets.     

Additive Manufacturing of Dense Alumina Ceramics

In this study, a new process for additive manufacturing (AM) of dense and strong ceramic objects is described. The lithography‐based ceramic manufacturing (LCM) technique is based on the selective curing of a photosensitive slurry by a dynamic mask exposure process. The LCM technique is able to produce strong, dense and accurate alumina ceramics without virtually any geometrical limitations. With over 99.3% of a theoretical alumina density, four‐point bending strength of 427 MPa, and very smooth surfaces, the LCM process distinguishes itself from other AM techniques for ceramics and provides parts with very similar mechanical properties as conventionally formed alumina.     

Additive manufacturing of ceramic materials for energy applications: Road map and opportunities

Among engineering materials, ceramics are indispensable in energy applications such as batteries, capacitors, solar cells, smart glass, fuel cells and electrolyzers, nuclear power plants, thermoelectrics, thermoionics, carbon capture and storage, control of harmful emission from combustion engines, piezoelectrics, turbines and heat exchangers, among others. Advances in additive manufacturing (AM) offer new opportunities to fabricate these devices in geometries unachievable previously and may provide higher efficiencies and performance, all at lower costs. This article reviews the state of the art in ceramic materials for various energy applications. The focus of the review is on material selections, processing, and opportunities for AM technologies in energy related ceramic materials manufacturing. The aim of the article is to provide a roadmap for stakeholders such as industry, academia and funding agencies on research and development in additive manufacturing of ceramic materials toward more efficient, cost-effective, and reliable energy systems.     

Materials research & measurement needs for ceramics additive manufacturing

We report on a recent workshop dedicated to additive manufacturing (AM) of ceramics that was held at the National Institute of Standards and Technology (NIST) in November 2019. This two-day all-invited meeting brought together experts from industry, government agencies and academia to review the state of the field and identify the most pressing applied materials research and metrology issues which, if addressed, could accelerate the incorporation of AM methods into commercial ceramic manufacturing. Besides the AM technologies, the discussions included consideration of the necessary post-processing steps. We highlight some of the successes and challenges for the adoption of ceramics AM on an industrial scale, as viewed by the workshop participants. We also propose actions for the ceramic community to facilitate the wider commercialization of these fabrication methods.     

Additive manufacturing of fiber reinforced ceramic matrix composites: Advances,challenges, and prospects

Fiber reinforced ceramic matrix composites (FRCMCs) have been used in various engineering fields. Additive manufacturing (AM) technologies provide new methods for fabricating FRCMCs and their structures. This review systematically reviews the additive manufacturing technologies of FRCMCs. In this review, the progress for additive manufacturing of FRCMCs were summarized firstly. The key scientific and technological challenges, and prospects were also discussed. This review aims to motivate the future research of the additive manufacturing of FRCMCs.     

Additive manufacturing of Al2O3 ceramic core with applicable microstructure and mechanical properties via digital light processing of high solid loading slurry

Ceramic cores are essential intermediate mediums in casting superalloy hollow turbine blades. The developing of additive manufacturing (AM) technology provides a new approach for the preparation of ceramic cores with complex structure. In this study, alumina oxide (Al₂O₃) ceramic cores with fine complex geometric shapes were fabricated by digital light processing (DLP) in high resolution. The maximum solid content of 70 vol% of ceramic slurry was adopted in the printing process, which is important for the regulation of deformations and mechanical properties. The effects of the printing parameters, including exposure intensity, printing layer thickness and sintering temperature on the microstructures and mechanical properties of printed samples were investigated. The decrease of residual stress and similar shrinkage in X, Y, and Z directions could be obtained by adjusting the printing parameters, which are crucial to prepare complex ceramic cores with high quality. Besides, the flexure strength and open porosity of ceramic cores reached 34.84 MPa and 26.94%, respectively, which were supposed to meet the requirement of ceramic cores for the fabrication of superalloy blades.     

Additive manufacturing of ceramics: Advances,challenges, and outlook

Additive manufacturing (AM) of ceramics is relatively more challenging with respect to polymers and metals, owing to their high melting temperatures and inherent brittleness. Thus, this review aims to provide a comprehensive survey of recent AM technologies successfully employed to produce net shape ceramic components. In recent years, several techniques have been developed and the latest progress in this field are highlighted, as well as the current challenges in the complex shaped ceramic parts production via AM technologies. The state of the art concerning the various 3D printing processes applied to the fabrication of ceramic components is discussed with, for each method, the presentation of its advantages, disadvantages, and possible applications. The potential of AM for producing complex shape ceramic components and the challenges to overcome are discussed as well.     

CerAMfacturing of silicon nitride by using lithography-based ceramic vat photopolymerization (CerAM VPP)

Hardness, high mechanical strength, wear and corrosion resistance, for instance, are the most important properties of silicon nitride. Next to technical application, the material becomes more and more important for medical applications, especially for implants and the focus in research for this increase steadily. Up to now, the demands on the geometry of silicon nitride-based components could largely be met by using conventional shaping methods such as pressing and green machining or injection moulding. However, requirements in terms of complexity and function are constantly increasing. By using additive manufacturing (AM) technologies, the complexity of components can be significantly increased and additional functions such as transport channels or features like triple periodic minimal surfaces (TPMS), which seem to be advantageous for osseointegration can be integrated, for instances. High-resolution AM processes such as stereolithography enable the production of very accurate and complex ceramic components. In this work a silicon nitride suspension suitable for biomedical applications was developed and the influence of the formulation on the properties (especially flow and curing behavior) were analyzed. Afterwards, various test samples were generated by ceramic additive manufacturing via vat photopolymerization (CerAM VPP), thermally processed and the sintered parts were characterized with common ceramic methods, like mechanical tests and microstructure analyses, showing satisfying results for the described development state.     

中国传统陶瓷的雕塑性造型特质研究

随着人民生活水平的提高,人们对陶瓷以实用功能为主的物质文化需求逐渐转变为以审美功能为主的精神文化需求。表面平滑、规则、单纯的陶瓷造型已不能满足人们的审美需求,立体化的雕塑性陶瓷造型以其自身巨大冲击力、震撼力和感染力开始吸引人们的注意力。在陶瓷造型的设计中,雕塑性技法发挥着重要的作用,即有利于塑造陶瓷精美的外形,给人呈现视觉上的完美效果;又能丰富人们的内心世界,满足人们的审美需求。本文主要以中国传统雕塑性的陶瓷造型为分析对象,分析传统陶瓷造型的雕塑性及其特质。     

A review on laser deposition-additive manufacturing of ceramics and ceramic reinforced metal matrix composites

Ceramics and ceramic reinforced metal matrix composites (MMCs) are widely used in severe working conditions and have been applied in biomedical, aerospace, electronic, and other high-end engineering industries owing to their superior properties of high wear resistance, outstanding chemical inertness, and excellent properties at elevated temperatures. These superior properties, on the other hand, make it difficult to process these materials with conventional manufacturing methods, posing problems of high cost and energy consumptions. In response to this problem, direct additive manufacturing (AM), which is equipped with a high-power-density laser beam as heat source, has been developed and extensively employed for processing ceramics and ceramic reinforced MMCs. Compared with other direct AM processes, laser deposition-additive manufacturing (LD-AM) process excels in several aspects, such as lower labor intensity, higher fabrication efficiency, and capabilities of parts remanufacturing and functionally gradient composite materials fabrication. Besides these benefits, problems of poor bonding, cracking, lowered toughness, etc. still exist in LD-AM fabricated parts. This paper reviews developments on LD-AM of ceramics and ceramic reinforced MMCs in both bulk parts fabrication and cladding. Main issues to be solved, corresponding solutions, and the trend of development are summarized and discussed.     

Fractography of zirconia-specimens made using additive manufacturing (LCM) technology

A relatively new method to manufacture complex ceramic prototypes and components is additive manufacturing (AM). With the LCM (Lithography-based Ceramic Manufacturing)-technology the green body is manufactured layer-by-layer using selective curing of light-sensitive ceramic slurry by a mask exposure process. After curing by blue light the component is removed from the building platform and the green body is sintered to a ceramic component.The aim of this work is to investigate the influence of processing and layer architecture on the mechanical properties of an Yttria-stabilized zirconia ceramic. Strength tests were performed by uniaxial bending tests and by biaxial Ball-on-three Balls (B3B) tests. To identify typical fracture initiating flaws a systematic fractographic investigation was performed on different batches of Ball-on-three Balls-test and bending test specimens, respectively.Through additional investigations it was found that hardness and fracture toughness were independent on the layer architecture. But an extensive fractographic analysis showed that the strength was limited by flaws, which were introduced by processing and handling. If these flaws can be avoided by optimisation of the process the strength should be equal to that of conventional processed ceramics.     

用于摩托车尾气净化催化剂的金属蜂窝载体

由金属薄片或丝网制成的蜂窝状载体是继陶瓷载体之后用于制备汽车尤其是摩托车尾气净化催化剂的又一新型载体。与陶瓷载体相比较,由金属载体制成的催化剂具有起燃温度低。净化效率高。处理能力大。排气背压小。抗振性强和催化剂寿命长等优点,因而为开发符合越来越严格的摩托车排放法规的催化转化器提供了可靠的技术支持。     

Three-dimensional complex construct fabrication of illite by digital light processing-based additive manufacturing technology

Illite is a group of clay minerals that are expected to be widely used in catalyst fabrication, radioactive element adsorption, and so forth, due to its excellent adsorption properties. However, the shape control limitation of the illite product should be overcome to maximize its utilization and properties. We herein propose additive manufacturing (AM) as one of the best solutions to solve this structural drawback. Digital light processing (DLP) technology with the film-type of the material supplying system was adapted instead of the general vat-type DLP system to increase illite printability. The photo-curability and printability of illite-contained photocurable suspension were optimized. The color effect due to different ferric oxide content in yellow- and white-illite which influence the photopolymerization process also adjusted thoroughly. White illite showed better photo-curability and could be increased solid loading than yellow illite. The defect-free illite products with three-dimensional complex structures, which cannot be produced by typical ceramic processes, were obtained by DLP technology for both yellow- and white-illite after sintering at 1100°C. The overcoming of shape control limitation of illites by ceramic AM proved in this study has excellent potential for expanding illite utilities in various applications.     

Additive manufacturing of green ceramic by selective laser gasifying of frozen slurry

The slurry-based additive manufacturing (AM) of ceramics involves a drying process to form solid support; however, the drying process is time-consuming, and the support is not easily removed. We propose a new AM process for green ceramic that includes freezing a layer of aqueous ceramic slurry, laser gasifying of the frozen-layer ice to process 2D green ware, and removing the support in water to release the 3D ceramic part. With a suitable laser power and scanning speed, this approach can yield a layer that has a thickness of 90 μm, a cantilever structure with a wall thickness of 115 μm and a span of 30 mm without deflection. The casting layer cannot be damaged by using a cryopanel to rapidly freeze the slurry, and redundant frozen materials can be melted in water without swelling. Therefore, this new process can rapidly form a solid support and has a high removal efficiency.     

Additive manufacturing of silicon nitride ceramics: A review of advances and perspectives

Silicon nitride (Si₃N₄) ceramic has been widely applied in various engineering fields. The emergence of additive manufacturing (AM) technologies provides an innovative approach for the fabrication of complex-shaped Si₃N₄ ceramic components. This article systematically reviews the advances of the AM of Si₃N₄ ceramic in recent years and forecasts the potential perspectives in this field. This review aims to motivate future research and development for the AM of Si₃N₄ ceramic.     

New observations on wear characteristics of solid Al2O3/Si3N4 ceramic tool in high speed milling of additive manufactured Ti6Al4V

Additive Manufacturing (AM) technologies applied to the titanium alloys have attracted attention from industries in recent years. Despite one of the main goals of AM is the reduction of manufacturing steps, semi-finish/finish machining operations are still required so as to obtain the desired geometrical tolerance and surface features. In this study, the solid end mill was manufactured by Al₂O₃/Si₃N₄ (Sialon) ceramic materials and employed in high-speed slot milling of Ti6Al4V alloy fabricated by the Direct Metal Laser Sintering (DMLS) AM technology to study the tool wear characteristics during processing. The Raman spectroscopic method was employed to characterize the molecular structures of Sialon ceramics for the manufacturing of the cutting tool. The morphologies and elemental maps of wear region of the ceramic tool were examined by scanning electron microscope and energy dispersive spectroscopy techniques. The results show that the adhesion wear and diffusion wear are the dominant wear mechanisms, and the chemical stability of Al₂O₃/Si₃N₄ (Sialon) ceramics fabricated as the solid ceramic tool to the attack of the atoms from additive manufactured Ti6Al4V is relatively weak under the atmosphere. The difference of thermal expansion coefficients of diffusion layer and tool substrate accelerates the initiation and propagation of thermal cracks formed on the diffusion interface. Moreover, fracturing and crater-like groves near the tool edge were finally formed due to the removal of adhered workpiece material.     

Binder-free additive manufacturing of ceramics using hydrothermal-assisted jet fusion

Ceramic additive manufacturing (AM) typically uses a high fraction of organic binders to form pre-sintered green parts that require a post de-binding process to remove. The de-binding process inevitably results in severe gas expansion and residual chars, leading to structural defects, accumulated stress, and compromised material properties in the final parts. Here we report a binder-free additive manufacturing process named hydrothermal-assisted jet fusion (HJF) that utilizes a hydrothermal method to create geometrically and compositionally complex ceramics under mild temperatures. The HJF process employs a selectively deposited volatile dissolving ink, high pressure, and mild heat to strategically fuse a ceramic powder bed into complex geometries. Compared to traditional AM methods for ceramics, the HJF process eliminates the need for organic binders in green part fabrication and offers the potential to directly co-print ceramics with other dissimilar materials, such as polymers and metals, enabling the development of novel multi-functional ceramic composites.     

Fabrication of dense SiSiC ceramics by a hybrid additive manufacturing process

In this work, we report the fabrication of Silicon infiltrated Silicon Carbide (SiSiC) components by a hybrid additive manufacturing process. Selective laser sintering of polyamide powders was used to 3D print a polymeric preform with controlled relative density, which allows manufacturing geometrically complex parts with small features. Preceramic polymer infiltration with a silicon carbide precursor followed by pyrolysis (PIP) was used to convert the preform into an amorphous SiC ceramic, and five PIP cycles were performed to increase the relative density of the part. The final densification was achieved via liquid silicon infiltration (LSI) at 1500°C, obtaining a SiSiC ceramic component without change of size and shape distortion. The crystallization of the previously generated SiC phase, with associated volume change, allowed to fully infiltrate the part leading to an almost fully dense material consisting of β-SiC and Si in the volume fraction of 45% and 55% respectively. The advantage of this approach is the possibility of manufacturing SiSiC ceramics directly from the preceramic precursor, without the need of adding ceramic powder to the infiltrating solution. This can be seen as an alternative AM approach to Binder jetting and direct ink writing for the production of templates to be further processed by silicon infiltration.