Vol.11 No.2 2018

報告:Additive manufacturing of ceramic components (大司)−86−Synthesiology Vol.11 No.2(2018)selected in each of the technical items in order to obtain sound products through an AM approach, taking an example of PLM.[22] The total procedure of PLM can be roughly divided into three processes, including powder preparation, lamination (or PLM itself), and post process. Figure 5 shows technical processing items as well as evaluation items in each of these three processes.In the powder preparation, ceramic powder is mixed with polymer binder to be melted by laser heat as described above by some appropriate method. The mixed powder used in PLM should have sufficient flowability, which is generally obtainable with a spherical shape and size of ~50 µm. Therefore, when the powder size is below 10 µm which is typical for so called fine ceramics, granulation process including spray-drying is frequently used to produce Fig. 5 Technical processing items and evaluation items in starting powder preparation, lamination, and post-process Powder preparationPost processLaminationStarting powder evaluation: size & shape, owability*, packing density (static bulk density, tap density)Formed body evaluation: appearance (cracks, delamination, distortion, etc.), green density, strength, etc.Sintered body evaluation: appearance (cracks, delamination, distortion, etc.), sinter density, strength, etc. *Flowability: angle of repose, compression ratio, Hausnerratio, preliminary powder test for lamination, etc.EvaluationProcessingCeramic powder:type, size, additives, etc.Powder supply:layer-thickness, leveling (squeegee or roller), etc.Binder:type, size, melting point, cohesiveness, adhesiveness, wettability, burnability, etc.Pre-heating:depending on binder’s melting point. Debinding:heating schedule, pressure, atmosphere, etc.Inltration:melted metal, slurry, etc.Mixing:dry- or wet-mixing, granulation, drying, etc. Laser irradiation: laser type, power, scan spacing, scan speed, etc. Post sintering:heating schedule, atmosphere, pressure, etc. spherical granules of such a size. The mixed powder is evaluated in terms of owability including angle of repose, compression ratio, Hausner ratio as well as their size and shape, etc. Angle of repose is the angle measured in degrees between the horizontal plane and the steepest slope at which loose powder remains in place without sliding. Compression and Hausner ratios are given by (Dt-Db)/Dt and Dt/Db, respectively, where Dt is the tap density and Db is the static bulk density. When the flowability increases, these three indices all decrease. Suitability of powder to lamination of PLM is also examined in a simple preliminary powder test, where a lump of powder placed in the forming stage is leveled by using a squeegee. If the powder is flowable enough and not so cohesive, the surface becomes smooth without dimples and cracks, which appear with powder cohesive and less flowable, as shown in Fig. 6 (a) and (b),

元のページ  ../index.html#35