In recent years, casting molds made by additive manufacturing (AM) are increasingly applied to build prototypes and small quantity casting product. Devices and materials have been developed for accelerating the molding speed to achieve mass production using AM technology. Conventional AM molding methods using a furan type hardening system adopt a combination of a liquid catalyst and binder. The sand wet by the liquid catalyst makes it difficult to increase the molding speed and apply artificial sands which have excellent refractoriness to the sand molding using AM technology.

  This study developed a solid catalyst coated sand to improve the flowability of the sand and catalyst and to increase the binder hardening rate. The solid catalyst coated sand was made by covering sintered artificial sand with the solid catalyst of meta-xylene sulfonic acid after covering with the fine powder of anhydrous magnesium sulfate.

  First, this study confirmed that the solid catalyst coated sand has good fluidity in fluidity tests. The reduction of the surface tension by the bonding of the fine powder of anhydrous magnesium sulfate and the surface of the solid catalyst resulted in the dry state of the solid catalyst coated sand. Consequently, the catalyst coated sand showed good fluidity.

  Secondly, in mold hardening tests, the solid catalyst coated sand hardened the mold quicker than conventional methods. During the hardening reaction of the binder, water generated when furfuryl alcohols were bonded to each other was converted into a hydrate by anhydrous magnesium sulfate and absorbed. As a result, the reaction rate greatly improved compared with conventional methods that only release water outside the system.

  Finally, the ability to mold with this hardening system was tested with the AM molding apparatus using the binder jetting. The results of evaluating the characteristics of the mold showed that it has low thermal expansion and the unhardened part of the solid catalyst coated sand could be reused.

  In recent years, casting molds made by additive manufacturing (AM) are increasingly applied to build prototypes and small quantity casting products. Technological development aiming to use mass-produced castings is advancing with the emergence of high speed AM molding technology. Mass production is expected to improve the potentials of the entire casting product, such as the realization of more complicated internal structures, thinness and weight reduction by the improvement of cavity accuracy. Regarding binders applied to AM sand molding technology, so far organic self-hardening systems are mainly applied and their use is spreading. On the other hand, in the case of aluminum alloy castings, the application of a hardening system with an inorganic binder is required from the viewpoint of the casting working environment. The purpose of this study is to develop an AM sand molding technology utilizing a hardening system with an inorganic binder and artificial sand. The developed hardening system is composed of sand coated with an inorganic binder and inkjettable hardening catalyst. First, the hardening characteristics of the developed hardening system were evaluated using hand molded test pieces, and it was found that it is effective for increasing the initial hardening rate compared with conventional methods. Next, the ability to mold with this hardening system was tested using a binder jetting AM molding apparatus. The gas component generated by heating was measured and the coefficient of linear expansion by AM molded test pieces was tested to evaluate the characteristics of the molded test pieces as a casting mold. It was confirmed that harmful gas can be reduced and the mold has low thermal expansion.

  By combining 3D printed sand mold and counter pressure casting technology, we have succeeded in shortening the time for prototyping/producing aircraft parts that require high quality, such as nonferrous cast lightweight housing with complex hollow channel wrapped sterically around.