Vol.11 No.2 2018

報告:Additive manufacturing of ceramic components (大司)−83−Synthesiology Vol.11 No.2(2018)PM. Examples are semiconductor production parts, plasma-resistant parts and ceramic cores of gas-turbine blades in the industrial eld; water-purifying lters and portable toilets in areas related to everyday life; bone prostheses and ceramic heads for hip joints in the medical eld (Fig. 1, bottom).Figure 2 also shows the participating organizations of the HCMT project.[1] The core R&D sites are placed at the National Institute of Advanced Industrial Science and Technology (AIST) and Osaka University for intensive R&D using common research facilities and equipment. TOTO Ltd., NGK Insulators, Ltd., NGK Spark Plug Co., Ltd. and Noritake Co., Limited dispatch their researchers to core R&D sites for developing platform technologies in collaboration as well as product manufacturing for their own targets. These four companies are known as the “Morimura” Group which has established the foundation of modern ceramic industries of Japan since the beginning of the 20th century. In addition, Japan Fine Ceramics Center (JFCC), Kyushu University and Tohoku University are in charge of R&D on CLS. 3 R&D strategies for AM of ceramicsAM (additive manufacturing), also known as 3D printing, is a process by which a three-dimensional body is built through point, line or planar deposition of material typically using a print head, a nozzle, or another appropriate equipment. Objects are produced by not subtracting but adding material, based on computer-aided design (CAD) files or 3D model data, without using machining tools or forming dies and molds. The advantages include the following: (1) Realizing complex-shaped or integral-structured bodies which are never attainable by conventional molding approaches (this enables us to make totally new design of products enhancing their performance and durability), (2) Saving production time and cost due to a moldless process (this is particularly true for large variety-small amount production such as for new product prototypes and articial bones and teeth), and (3) Saving raw materials since only a necessary amount is consumed while substantial amount of machining loss is generated in subtractive manufacturing, (4) Actualizing unique material structures including compositionally or functionally gradient layer textures. There are a variety of AM methods, which are classified into seven categories according to ASTM F2792-12a, “Standard Terminology for Additive Manufacturing Technologies.” Table 1 shows this classication with illustrations.AM has been well developed in the field of polymers and already has been widely used for fabricating 3D products of this sort of material to such an extent that household 3D printers for resin have been commercially available for some time.[5] Some key metal parts have also been successfully produced by AM;[6]-[8] for example, GE Aviation has introduced the additive-manufactured metal fuel nozzles in combustion systems of aircraft engines that could not be made conventionally.[8] The benefits include “25 % lighter weight than its predecessor part,” “the number of parts of the nozzle reduced from 18 to 1,” and “5 times higher durability due to more intricate cooling pathways and support ligaments.”Regarding AM of ceramics however, though some complex-shaped 3D bodies have been prepared with relatively high precision using vat photo-polymerization (stereolithography), etc.,[9]-[18] their product size has been generally limited, typically to a few centimeters or less, and the status is far from manufacturing technologies to be used in industries. Hence, comprehensive R&D efforts on manufacturing processes including powder preparation, lamination, and post-process suitable for ceramics are crucially required to grow AM of ceramics to the level of industrial application, and this has triggered the HCMT project.[1]-[3]When applying AM methods, which have been used in the fields of polymers and metal, to ceramics, because of the difficulty in directly obtaining sintered bodies due to their intrinsic nature such as high refractoriness and less-sinterability, it is general to produce green or formed bodies instead, which are to be sintered in a conventional furnace afterwards. For example, in powder bed fusion, laser heat melts polymer binder which is mixed with ceramic powder to form green bodies. The HCMT project employs PLM and SLM for forming green bodies as stated above; the former is categorized into powder bed fusion (also called “indirect selective laser sintering”) of the ASTM F2792-12a classification (Table 1), and the latter into vat photo-polymerization thereof. This is because these two approaches are known to be superior to the others in terms of homogeneous microstructure, good properties of

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