Abstract: Water-soluble calcia ceramic core prepared by extrusion 3D printing technology is used to form complex internal cavity casting components with high quality and efficiency, and the residual cores after casting are quickly removed by dissolving with water, which possesses a large potential for application in precision casting of complex internal cavity components. A four-factor, three-level orthogonal experiment is conducted with four key process parameters: needle diameter, layer height/needle diameter ratio, printing speed, and internal filling direction. By measuring and counting the surface roughness of 3D printed forming green bodies with different process parameters, the influences of each printing parameter on the surface quality of the printed green bodies are determined using extreme difference analysis, and the optimal printing parameters for extrusion 3D printing of calcia ceramic cores were obtained. The results show that the internal filling direction has a significant effect on the surface-forming quality of the green bodies. When the internal filling direction is 45 ° and 90 ° to the outer contour, there are many inflection points between the internal filling slurry and the outer contour layer, and the forming direction at the inflection point changes suddenly, resulting in sudden changes in the direction of the extrusion pressure and acting on the outer contour layer, the outer contour layer becomes uneven, and the surface roughness of the green body formed layer by layer by layer is large poor surface quality. When the needle inner diameter is 0.41 mm, the layer height/needle diameter ratio is 70% , the printing speed is 20 mm/s, and the internal filling direction is parallel to the outer contour layer, the surface roughness of the green body is the minimum, and the surface quality of the core green body is the best. By increasing the number of layers of the outer profile, the influence of the filling direction on the surface roughness of the blank can be effectively reduced or even eliminated, when the outer profile is increased to two layers, the surface roughness of the core blank is reduced by about 22%, which is important for the rapid and accurate forming of water-soluble ceramic cores.

Key words: calcia ceramic cores, extrusion 3D Printing, internal filling direction, number of outer profile layers