ISBN 9783843945523

978-3-8439-4552-3, Reihe Werkstoffwissenschaften

Tobias Schlordt
Robocasting: From Solid Filaments to Hollow Filaments and Coextrusion

171 Seiten, Dissertation Universität Erlangen-Nürnberg (2020), Hardcover, A5

Zusammenfassung / Abstract

Extrusion freeforming (EFF) using a six-axis robot arm was applied to generate ceramic composite structures and structures consisting of hollow filaments. Starting with solid filaments, shape retaining, waterborne colloidal gels with volumetric solids contents of 48 % and 50 % were developed and modified to meet the demands of hollowly extruded filaments (Al2O3) and coextruded filaments (Al2O3 shell with carbon black core). While EFF of solid alumina filaments is well established, building 3D lattice truss structures consisting of hollowly extruded filaments and coextruded filaments could successfully be demonstrated. Coextrusion proved to be superior over hollowly extruded filaments as it facilitates higher deposition velocities of > 30 mm/s, smaller filament diameters, less difficult feedstock processing and the capability of generating extremely lightweight structures due to the thin alumina shell (~20 µm) on a carbon core that can be burned out without destroying the shell. Furthermore, the coextruded composites could be sintered in Ar atmosphere to result in electrically conductive C/Al2O3 core-shell structures. Rheological investigations of the colloidal gels under shear and oscillation were carried out to investigate the influence of dispersant, coagulant, and binder on viscosity, shear elastic modulus, and flow stress. The results also reveal that the ratio between flow stress and shear elastic modulus might be a crucial property of a feedstock governing the drawing of fibers upon filament interruption. Moreover, unexpected rheological behavior dependent on temperature was discovered in case of carbon black gels which emphasizes the necessity for investigating the interactions and properties of the polymers dissolved in the feedstocks. Based on thixotropy measurements simulating the first seconds after filament deposition, models describing the deformation (deflection, collapse and filament fusion) of robocast lattice truss structures are conceived.