Ceramic laser stereolithography (SLA) is a top-down additive manufacturing method requiring a photopolymerizable paste that have self-standing properties at rest. A scraper/doctor blade is used to deposit thin layers (25 to 100µm) of paste that are successively photopolymerized. Importantly, the paste must exhibit shear-thinning behaviour to ensure a regular layer surface and a high enough solid loading to achieve dense ceramic sintered parts with controlled grain size. Several technical solutions have been implemented in the stereolithography machines to enhance paste spreadability, without being fully rationalized, e.g.: the disposition of rotating cylinders behind the blade, the scraping with two blades or the blade vibration [1]. In this presentation, we will discuss these solutions from a rheological point of view to clarify their impact on the processing route.
 
First, we will present sequential rheometric steady and oscillatory shear measurements showing two stable states on several homemade and commercial pastes: (1) an homogeneous structure after high amplitude shear favouring flowability by lowering shear moduli at rest, and (2) a structure containing clusters of particles leading to higher moduli at rest when the material is sheared with moderate amplitude [2]. Second, Orthogonal Superposition Rheometry experiments have been performed on different printable pastes in order to understand the evolution of their dynamical response under steady shear and their reaction to multiaxial solicitation and its possible benefits for the spreading process, being reminiscent of blade vibration. Finally, we will highlight the interest of combining rheometry and scattering methods to optimize the formulation of “homemade” stereolithography pastes. We will notably underline the impact of the powder functionalization prior to its incorporation into the organic phase.
 
[1] V. Pateloup, V. Chartier, C. Chaput. (2017). Method for manufacturing pieces by the technique of additive manufacturing by pasty process and manufacturing machine for implementing the method (United States Patent No. 20170355100), https://www.freepatentsonline.com/y2017/0355100.html
[2] N. Koumakis, E. Moghimi, R. Besseling, W. Poon, J. Brady, G. Petekidis. 2015. Tuning Colloidal Gels by Shear. Soft Matter 11: 4640–48. https://doi.org/10.1039/C5SM00411J