Robocasting of 3D-ceramic macrocellular structures with tubular filaments

拟议的项目重点是调查机器人铸造过程的具体材料原理。该提案的主要目标是开发新型凝胶体系，负载Al_2O_3、SiC和Si3N_4，用于复杂三维结构的添加制造。方法上的创新之处在于应用了不同截面的管状长丝，这就需要特殊的高粘度凝胶和挤出机喷嘴。研究的重点是纤维在沉积过程中的变形，这主要是由外力和流变特性如粘度、剪切弹性模数和屈服应力决定的。对于高粘度凝胶而言，流变行为的研究是至关重要的；后者受挤出机喷嘴内的流型影响很大，在那里很容易发生壁面滑移和推流。另一个目标是减少由于外力(重力、毛细管中的负压)造成的细丝变形，以实现近乎净成形的能力。此外，凝胶应具有较高的固体含量(&gt；50vol%)，以导致较低的干燥收缩。挤压时形状演变的静态和动态模型需要验证并适用于管状纤维，重要的是阐述由管状纤维组成的结构与由块状纤维组成的结构在力学性能方面的差异。此外，还应根据单根烧结丝的力学性能，用有限元方法模拟陶瓷三维结构的力学性能。

The proposed project focuses on the investigation of material-specific principles of the robocasting-process. The main goal of the proposal is to develop novel gel-systems loaded with Al2O3, SiC und Si3N4 for additive manufacturing of complex 3D-structures. The methodical novelty is the application of tubular filaments of various cross-sections, which require special high-viscosity-gels and extruder-nozzle. The investigation concentrates on the deformation of the filaments while deposition, which is predominately determined by external forces and rheological characteristics such as viscosity, shear-elastic-modulus and yield-stress. For highly viscous gels the study of the rheological behavior is of crucial importance; the latter is strongly influenced by the flow-profile within the extruder-nozzle, where wall slip and plug flow are likely to occur. A further objective is to diminish the deformation of the filaments due to external forces (gravity, under-pressure in the capillary) to achieve near-net-shape capability. Furthermore a high solids content (> 50 vol%) of the gels shall be attained to induce a low drying-shrinkage. Static and dynamic models for shape-evolution while extrusion shall be verified and adapted to tubular filaments, It is important to elaborate the differences between structures composed of tubular filaments compared to structures composed of massive filaments concerning mechanical properties. In addition, the mechanical properties of ceramic 3D Structures shall be simulated using FEM based on mechanical properties of single sintered filaments.