Multi-scale simulation of molding materials for inorganic binders using binder-jet-3d-printing

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In recent years, 3D printing has been developed as a technology for producing sand cores for casting operations, especially for rapid prototyping and low-volume foundry applications. However, the layered structure of this process differs greatly from traditional core blowing, especially in terms of the density levels achieved. The goal of the proposed project is to understand the 3D printing process of sand cores in order to identify the influence of process variables on the final product. This should ensure the high quality of the printed sand cores in an application-specific manner, while minimizing the measurement effort required and the dependence on expert knowledge and experience. The following aspects are to be investigated in more detail: 1. Printed components generally have a much lower density than conventionally produced ones. In addition, this density is inhomogeneously and partially stochastically distributed over the installation space of a 3D printer. In addition, an anisotropy of different properties can be observed. 2. During the building process, a curling of already printed layers can be observed to an extent, that they are hit by the recoater and this causes the entire building process to be disturbed. 3. The building job's layer-by-layer structure increases the load on already printed areas. This leads to non-linear construction errors, which manifest themselves in defective layers or misalignment of the component. 4. If the coating speed is too high, components under construction are shifting their position in the build volume. Practical experience has shown that in addition to the powder composition, atmospheric conditions and the control of the coating process per se, the fact whether the substrate has already been printed or not is of utmost importance. In order to achieve the above-mentioned objectives, the project applied for is intended to create a digital model - closely accompanied by relevant experimental investigations - which depicts the layered structure of the sand core layers in 3D printing. Based on microcomputer tomography images of industrially used sands, the recoating of the sand grains under the influence of the binder on already printed layers is to be analyzed. Subsequently, a simulative and experimental evaluation of the mechanical, thermal and gas permeability properties of the printed sand cores is planned. The predecessor project µ-Core, which was financed by the DFG and dealt with the micromechanical modeling of the classical core blowing process, will serve as a starting point and will be substantially extended. A deeper understanding of the microscopic processes involved in the 3D printing of sand cores will serve as a basis for the further development of materials under environmental aspects and for optimizing the printing process itself.