Luzzi, Enrica (2024) Rational approaches and methodologies to study the printability of functional inks for Direct Ink Writing. [Tesi di dottorato]

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Abstract

Direct ink writing is a versatile additive manufacturing technique that is gaining lot of attention due to its high versatility and ability to process a wide range of materials, ranging from biopolymers to advanced ceramic materials. The increasingly growing topic-related literature proves the interest devoted to such approach, but, on the other hand, also testifies the spreading of conflicting knowledge about the technique. In fact, it has been noticed that there is still a huge debate around the requirements a material should possess to be defined printable and, moreover, there is a lack of standard to characterize a paste to determine its printability attitude. This results in the need to adopt a trial-and-error strategy to formulate a paste suitable for printing and to obtain a printed object with the desired quality, demanding to the operator expertise the task to optimize the ink properties and the printer settings before printing. With the aim to further develop the fundamental knowledge about this technique, this work focuses on, and try to systematize, the main approaches currently adopted to address these issues. Starting from an in-depth critical analysis of the literature regarding 3D printing of a wide range of materials, the main pitfalls in the currently adopted printability assessment methods and strategies have been identified, indicating that the meaning of printability itself is still fuzzy. To overcome these problems, standardized tests have been specifically conceived, developed and validated on several different systems. This approach fulfils two objectives: on the one hand, it sets geometrical requirements a printed trace should possess to define printable the material it is made of. On the other hand, it defines a rheological characterization protocol aimed at relating the paste properties and its printability, so to avoid the trial-and-error approach in finding the optimal formulation. Finally, with the aim of providing general guidelines to produce an object by direct ink writing, a test case-study has been conceived and followed from the formulation of the ink to the final assessment of the performance of the manufact. This work hope to be a systematic guide to the direct ink writing process, aiming at consolidating the existing knowledge and proposing novel, standardized approaches to widen the range of applications of this technology.

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