Wrinkle-free Ceramic From The 3D Printer

Additive manufacturing processes with plastics and metals as a material are state of the art today. However, if ceramics are to be processed additively, there are only a few methods to choose from. That is already in the nature of the material ceramic. The process requires high temperatures in order to fuse ceramic powder into a monolithic component - a component from a single cast. Nor can ceramics be crosslinked like resins or, like most polymers and metals, plastically deformed under heat.

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Professor Dr. Jens Günster, Head of Department 5.4 Ceramic Process Technology and Biomaterials at BAM and his team therefore rely on preceramic polymers in 3D powder printing. Pre-ceramic polymers are special polymers that can be converted into ceramics. They can be cross-linked, plastically deformed, melted or dissolved in many solvents. This is a clever way of dealing with the shaping problems with ceramics.

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“We use a commercial, very inexpensive powder that is used in industrial processes as well as in cosmetics production. We apply this layer by layer and glue it locally with a solvent until the desired structure is completed,”explains Günster. In this 3D printing process, the solvent is printed on the layers using a printhead, just like in inkjet printing. The polymer formed in this way is then fired in the absence of oxygen at temperatures above 1200 degrees Celsius: a ceramic made of glassy silicon oxycarbide (SiOC) is formed.

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The trick with the crosslinker

However, the process does not work without a trick, which, however, has brought the research group further with their development. The problem was that the printed polymer melts from 60 degrees Celsius and it is not possible to burn it. In order to nevertheless obtain a ceramic component, the scientists added a “crosslinker” to the dissolved powder. This crosslinker is then introduced into the polymer with the solvent during printing. When fired, it causes the printed structure to retain its shape.

“Inspired by the properties of the crosslinker, we have further developed the process. We now use two printheads like color printing on paper. Solvent with crosslinker leaves one printhead and pure solvent without crosslinker leaves the 3D printhead via the other printhead. With these two liquids we print the skeleton of a structure and the shell over it in one process. The skeleton retains its structure when it burns, since it contains the crosslinker. The shell applied above melts without a crosslinker. It wets the skeleton and, due to the interplay of viscosity, surface tension and gravity, also runs in its lattice structure. As a result, we get a ceramic whose surface contains no pores and is smooth, i.e. without sharp edges.The structure has been optimized through self-organization and is therefore more resilient to pressure,”Günster continues.

Technology transfer: Ceramic-compatible design through additive manufacturing

The research group at BAM developed this process together with Voxeljet AG, a market leader in Germany for the manufacture of platforms for powder-based 3D printing. With 3D printing as an additive manufacturing process, the material for the production of a component is added in layers. With this layer construction principle, geometrically complex structures that cannot be realized with conventional manufacturing processes or only with great effort can be produced. However, the limits and the associated technical reliability of these materials must be kept in mind: a task of BAM, which has decades of proven expertise in the field of materials research and testing. Questions of characterization, useful life, reliability and sustainability of materials,BAM bundles substances and materials in its subject area of ​​materials. (qui)

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