Researchers at the Department of Innovative Technologies of SUPSI in Switzerland presented a novel solution to 3D print bulk components by stereolithography with photosensitive ceramic-based slurries. Leveraging extensive experience in hybrid and ceramics materials research, the team from the University’s Institute of Mechanical Engineering and Materials Technology (MEMTi), composed by Alberto Ortona, Oscar Santoliquido, Francesco Camerota, Alice Rosa, designed, built and tested a system that is meant to reduce costs for 3D printing of bulk green ceramic components.
The research activities carried out at the Institute, primarily focusing on the development of products and processes, are characterized by relevant use of computational sciences. The experimental activities of the laboratories are therefore combined with those of modeling and simulation, using devices for the characterization of materials as well as dedicated software and high-performance computing tools for a multiscale and multidisciplinary approach. The introduction of additive manufacturing technologies a decade ago enabled the Institute to add a level of physicality to ongoing material, part and process research focusing on segments such as aerospace, industrial applications (heat management, advanced filtration) and energy.
The new ceramic 3D printing system is characterized by a UV transparent glass and a silicone flexible film under tension, which cures layers of ceramic slurries exploiting a top-down approach while also integrating some features of bottom-up stereolithography. This architecture guarantees a precise slice thickness between the transparent glass and the mating slice, allowing the precise building of bulk green ceramic components.
The device can 3D print viscous photosensitive ceramic slurries (i.e. viscosity up to 10 Pa s at 10 s−1 shear rate). Moreover, the apparatus allows for the production of complex bulk components where the layer separation forces are high. This permits to widen the range of geometrical features of 3D printed objects printable by common stereolithography. The work was published in the Open Ceramics journal.
In conventional “top-down” stereolithography, the object grows layer by layer on a build platform, which immerses progressively into the resin bath. To recoat the cured layer with fresh liquid resin and solidify it to form a new layer, the platform performs a vertical translation, moving downward first and then upward. When the platform is immersed, the fresh slurry flows by gravity on the previously cured layer.
Given a good wetting of the liquid resin on its solidified layer, the thickness uniformity of the new layer is significantly affected by the slurry’s viscosity. Defects can appear when the slurry is not deposited uniformly: one way to overcome these problems is to introduce a moving part (doctor blade) that spreads the slurry, which, however, adds complexity to the system because moving parts need to be controlled. In addition, the rheological behavior of the slurry in respect of the doctor blade speed has to be finely tuned.
Standard, low-cost stereolithographic systems cannot properly handle highly viscous ceramic slurries. Ceramic mixtures can be processed if doctor blades, wipers or similar systems are implemented. Few industrial highly sophisticated devices are available to handle such viscous pastes. Since this kind of slurry exhibits a shear-thinning behavior, the mechanical action performed by such devices introduces shear stresses which also helps in thinning the slurry. In the SUPSI approach, the fresh uniform layer is obtained without the introduction of additional movements in the machine, through the use of the flexible silicon film. The novel apparatus designed in this work was integrated into an existing commercial “top-down” 3D printer (GiziMate 130 basic, Gizmo 3D Printers) which was previously utilized to print the samples.
While not in direct competition with industrial-level ceramics stereolithography systems, the new set-up proposed by the SUPSI-MEMTi researchers is intended as an intermediate solution to successfully 3D print bulk ceramic components such as, for example, ceramic cores for investment casting.