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Light-Based Printing of Leachable Salt Molds for Facile Shaping of Complex Structures

Cyril Dénéréaz

3D printing is a powerful manufacturing technology for shaping materials into complex structures. While the palette of printable materials continues to expand, the rheological and chemical requisites for printing are not always easy to fulfill. Here, a universal manufacturing platform is reported for shaping materials into intricate geometries without the need for their printability, but instead using light-based printed salt structures as leachable molds. The salt structures are printed using photocurable resins loaded with NaCl particles. The printing, debinding, and sintering steps involved in the process are systematically investigated to identify ink formulations enabling the preparation of crack-free salt templates. The experiments reveal that the formation of a load-bearing network of salt particles is essential to prevent cracking of the mold during the process. By infiltrating the sintered salt molds and leaching the template in water, complex-shaped architectures are created from diverse compositions such as biomedical silicone, chocolate, light metals, degradable elastomers, and fiber composites, thus demonstrating the universal, cost-effective, and sustainable nature of this new manufacturing platform.

WILEY-V C H VERLAG GMBH2022

3D metal freeform micromanufacturing

Yves Bellouard, Luciano Borasi, Enrico Casamenti, Raphaël Charvet, Léa Deillon, Cyril Dénéréaz, Fatmah Ebrahim, Andreas Mortensen, Sacha Jérémy Florentin Pollonghini, Tao Yang

Despite remarkable progress made in recent years, producing freeform three-dimensional micro-components out of copper, silver or gold and their alloys remains an engineering challenge: current processes are either too slow to be economically viable, or produce porous or otherwise imperfect metal microstructures. Here we introduce an alternative, faster approach for the freeform fabrication of metal micro-components amenable to the processing of noble metals. The process begins with the 3D, micron-resolution, carving of arbitrarily shaped interconnected molds into amorphous silica using femtosecond laser micromachining and selective etching. This is followed by pressure infiltration of the mold with the molten metal, which is subsequently solidified. Metal architectures produced by this process have micron-scale resolution, are fully freeform and multiscale in geometry, and are made of dense metal, while the process speed largely exceeds what is achieved in current alternative metal microfabrication approaches. The resulting glass/metal combinations enable new micro-device architectures. Alternatively, by mold dissolution, self-standing micron-scale 3D metal parts are produced, of high metallurgical quality and with features sizes down to ~2 μm.

2021

Compression testing spherical particles for strength: Theory of the meridian crack test and implementation for microscopic fused quartz

Raphaël Charvet, Cyril Dénéréaz, Andreas Mortensen, Václav Pejchal, Goran Zagar

We show that uniaxial compression testing of spherical particles can give unambiguous access to their tensile strength as governed by surface flaws if one uses pairs of elasto-plastic platens, tailoring their hardness in order to control the relative area of particle-to-platen contact during the test. This eliminates the development of contact microcracks that are typically found to govern particle fracture when hard platens are used. We show that, if the platen materials are well chosen, one can probe a range of stress states for which it is known that particle failure was initiated along the surface, under elevated hoop stress within a region situated remote from the points of load application. Specifically, platens must be chosen such that particles tend to fracture when the ratio of projected contact area radius to particle radius exceeds a specific value that depends on the Poisson ratio of the particles. With fused quartz of Poisson ratio 0.17, this specific ratio value equals 0.65. We demonstrate the approach using microscopic fused quartz spheres 40 +/- 20 gm in diameter as a testbench material; with those particles hardened steel serves as an appropriate platen material. Their strength values are statistically distributed; this is addressed using several platen materials. The resulting bank of data is interpreted using established survival-analysis methods, namely the non-parametric product-limit estimator. We also give a maximum likelihood estimation of the particle strength Weibull distribution parameters derived from the ensemble of data after left-truncation and/or right-censoring of data points situated inside of the range of unambiguous surface fracture strength measurement for each platen material. This gives a Weibull modulus of 6.3 and characteristic strength of 890 MPa for the fused quartz particles. These values are significantly lower than what is produced in high-strength fused quartz fibers of comparable diameter; the difference is most likely a result of surface damage caused during powder storage and manipulation in the absence of a protective coating.

2017