Thermoplastic 3D Printing—An Additive Manufacturing Method for Producing Dense Ceramics Uwe Scheithauer,* Eric Schwarzer, Hans-Jurgen Richter, and Tassilo Moritz Fraunhofer Institute for Ceramic Technologies and Systems IKTS, Dresden 01277, Germany In our new approach—thermoplastic 3D printing—a high-filled ceramic suspension based on thermoplastic binder systems is used to produce dense ceramic components by additive manufacturing. Alumina (67 vol%) and zirconia (45 vol%) suspensions were prepared by ball milling at a temperature of about 100°C to adjust a low viscosity. After the preparation the suspension solidified at cooling. For the sintered samples (alumina at 1600°C, zirconia at 1500°C), a density of about 99% and higher was obtained. FESEM studies of the samples’ cross section showed a homogenous microstructure and a very good bond between the single printed layers. Introduction Today, additive manufacturing (AM) of polymers is state-of-the-art, see for example.1,2 In the field of metals, more and more materials can be processed as well.3 For producing ceramic components, the technical application of AM technologies is yet limited. However, ceramic materials have been studied in additive manufacturing processes ab initio with the development of the different AM technologies since about 25 years, see for exam- ple.4,5 All popular AM technologies—formerly referred as rapid prototyping (RP) or solid free form fabrication (SFF)—have been tested also for ceramic materials, which are shown subsequently. The conventional stereolithography (STL) process, for example, was applied for alumina,6 silicon nitride, and silica7 as well as for ZTA.8 In this STL-process, a photopolymerizable ceramic suspension is cured by an UV-laser. Based on the principal approach of using light-curable binders in the ceramic suspension or paste, specific AM techniques for the production of ceramic green bodies have been developed. So, UV curable inks with high Al2O3 loading are used in a robocasting pro- cess.9 Binders that are cured under visible blue light are applied in a DLP (direct light processing) process, which allows to produce complex-shaped dense alumina parts.10 Selective laser sintering (SLS) and 3D powder bed printing are typical AM powder-based processes. SLS was tested for a number of ceramic materials.11–15 A typ- ical application of 3D powder bed printing is focused on the production of porous ceramic components because of the powder layers, which are not compacted, and the green density is too low to reach high density ( 99%) after sintering. However, high densities are not required, for example for bioactive scaffold structures. So, complex individual bioactive components based on calcium phosphates have been produced by 3D powder bed printing.16–20 Another way to utilize the relative simple 3D-powder bed printing technique is the infiltration of the 3D printed and sintered porous ceramic component with liquid metal that was shown in.21 It is also possible to use a ceramic particle-filled ink in powder bed print- ing to adjust the composition and the green density of the printed sample.22 In general, when using AM methods for production of samples with high sinter density, it is necessary to use a suspension with a high powder volume content instead of a dry powder bed. This was shown, for example, in SLS process at which instead of powder layers a suspen- sion layers were deposited and consolidated (after short drying) by laser beam.23 The direct printing of suspensions is not only applied in combination with powder bed printing. High- filled ceramic suspensions have been also processed by direct ink-jet printing to fabricate complex-shaped cera- mic components.24 The conventional fused deposition modeling (FDM) uses a thermoplastic ceramic feedstock that is liquefied by heating and pressed through a fine nozzle—that means, in the physical sense a suspension is used too. For example, functional ceramic materials25 and alu- mina26 were processed using FDM. However, the efforts for the preparation of the thermoplastic ceramic feed- stock in the form of spooled filaments constrain the FDM application for ceramics. The robocasting process which is a computer-con- trolled deposition of colloidal pastes or slurries is similar *uwe.scheithauer@ikts.fraunhofer.de © 2014 The American Ceramic Society Int. J. Appl. Ceram. Technol., 12 [1] 26–31 (2015) DOI:10.1111/ijac.12306
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