Issue No 2, August

Abstract

Stereolithographic additive manufacturing was developed to create bulky ceramic components with functionally geometric structures. In this process, two-dimensional (2D) cross sectional patterns were created through photo-polymerization with an ultraviolet laser drawing on spread resin paste. Ceramic nanoparticles and three-dimensional (3D) composite models were sterically printed by layer lamination though chemical bonding. The created precursor was dewaxed and sintered in an air to yield full ceramic components. This review describes the computer aided design, manufacture, and evaluation of artificial dendrite structures called photonic crystals with spatially ordered micro cavities. A periodic arrangement in dielectric constants can exhibit forbidden regions called photonic band gaps in the transmission spectra through electromagnetic wave diffraction. The permitted modes of transmission peaks at theoretically calculated frequencies can be selected via the introduction of point, linear, and planar structural defects into the artificial crystals. Ceramic processing using stereolithographic additive manufacturing with high accuracy on the micrometer scale will be presented in this paper.

Abstract

Technological progress in the field of additive manufacturing (AM) as a shaping method is inexorably advancing. In particular, AM provides the possibility to manufacture functionally graded components using a voxel model method. In medical technology, especially in implantology, these new structures can open new applications. In order to increase the ingrowth of cells into an implant, a function-optimized structure with a defined porosity gradient seems to be advantageous. In addition, ceramic implants are known for their excellent biocompatibility. From the material side, alumina toughened zirconia is a particularly interesting material. In combination with AM processes, completely new possibilities arise for the production of novel implants. Vat photo polymerization of ceramics (CerAM VPP), also known as lithography-based ceramic manufacturing (LCM), is suitable to realize defined and filigree structures. This article will show results from the process development for CerAM VPP of ATZ components with a defined graded porosity.

Abstract

Direct ink writing (DIW) facilitates the fabrication of three-dimensional (3D) green structures through the layer-by-layer deposition of colloidal gel-based inks. Several gel designs have been developed for aqueous systems. Here, we report a facile gelation method for a non-aqueous system: Y2O3-stabilized ZrO2 (YSZ) particles dispersed in ethanol. First, fluidic and concentrated YSZ colloids were prepared using polyethyleneimine (PEI) as a dispersant. Then, a fluid-to-gel transition was triggered by adding polyvinyl butyral (PVB) as a free polymer. The resulting colloidal gels had a viscoelastic response adequate for DIW. Further analysis revealed that the depletion flocculation mechanism plays an important role on this gelation. Moreover, using the non-aqueous colloidal gel, a helical coil structure of ~100 µm dimeter was patterned via the deposition of a continuous filament extrusion through a cylindrical nozzle in a water reservoir. During the deposition, a PVB film was formed in situ on the surface of the filament because of the poor solubility of PVB in water, which was used to avoid variations in the ink rheology owing to unexpected ethanol evaporation. The present methodology may be a useful route for the engineering of 3D green structures.

Abstract

In general, micromilled mould inserts made of steel, aluminum or brass are used today for ceramic injection moulding (CIM) processes. However, tool making via mechanical subtractive manufacturing processes as micromilling is time- and cost-effective and the use of 3D printed mould inserts becomes an attractive alternative to metal mould inserts. In this paper, we report about the use of 3D printed mould inserts for CIM of alumina microreactor parts. It was observed that mould inserts printed using the Polyjet technology were very well suited for functional prototyping via CIM. The mould inserts surface was found without visible thermally introduced damage after twenty CIM process cycles. In contrast to the high quality of mould inserts printed using the PolyJet technology, mould inserts made via fused deposition modeling (FDM) technology revealed as not applicable for the purpose of this study. The mould inserts manufactured using FDM-printer exhibit significantly higher surface roughness, larger longitudinal deflection and manufacturing-related undercuts along the edges of the 3D printed microstructure.

Abstract

Additive Manufacturing methods offer groundbreaking new opportunities for geometrical complexity such as for personalization and individualization of ceramic components. Moreover, several AM processes suited for ceramic powders can also be applied to other materials like hard metals, metals or glasses. Two AM methods, one suspension-based (CerAM VPP – Ceramic Vat Photo Polymerization) and one feedstock-based (CerAM T3DP – Ceramic Thermoplastic 3D Printing) will be introduced in this article for making novel sintered glass components. The article will show results of process development as well as glass powder compositions with new functionalities.

Abstract

Mechanical behaviour of ceramic materials shaped by robocasting additive manufacturing and traditional extrusion processes has been compared with the aim of analysing the suitability of printing 3D traditional ceramic artefacts to withstand high mechanical strengths as traditional ceramic tiles show. Extruded artefacts by both methodologies were characterized using X-ray diffraction, mercury porosimetry and mechanical strength tests. Although traditional extruded samples presented higher mechanical strength and lower global porosity when comparing similar compositions and shaping techniques, 3D printed artefacts by robocasting showed interesting mechanical properties within the range of the extrusion process. This feature along with their characteristic closed porosity make them be considered as light ceramic artefacts with a remarkable hardness to withstand specific designs in which moderated mechanical resistance could be required.

Abstract

The outstanding versatility shown by Inkjet printing has turned it into a leading technology in several industrial manufacturing fields of which ceramic tile decoration is a good example. Several papers in literature have set the rheological and fluid dynamics characteristic of the inks and the process parameters required for an optimum ink deposition for ceramic tile decoration. However, there is a lack of studies investigating the conditions for the deposition of glass-ceramic glazes. The glazes considered in the present study are intended for digital injection devices using printheads working in the Drop On Demand (DOD) mode based on piezoelectric elements or other digital injection techniques such as continuous ink jet (CIJ), electrovalves, pistons or others. The purpose of this work is to study experimentally the influence of chemical composition and mineralogy acting on the jettability of a range of glass-ceramic glazes. Relevant parameters like viscosity, surface tension and process parameters such as applied pressure, are discussed on the basis of fluid mechanics parameters and printing diagrams. The specific characteristics of digital glaze deposition technologies (continuous jetting and drop on demand) are discussed and the remaining challenges for future applications of the technology are outlined.

Abstract

Additive manufacturing of alkali-activated materials currently attracts a lot of attention, because of the possibility to produce customized high-performance elements for a range of applications, potentially being more resource-efficient than conventionally produced parts. Here, we describe a new additive manufacturing process for alkali-activated materials that is based on selective laser-heating of lithium aluminate/microsilica slurries. The new process-material combination allows to manufacture elements with complex geometries at high building rates and high accuracy. The process is versatile and transferrable to structures of sizes differing by orders of magnitude. The mechanical strength of the obtained materials was in the range of values reported for conventional metakaolin-based geopolymers, and superior to what has been hitherto reported for alkali-activated materials produced by additive manufacturing. This mechanical performance was obtained despite the fact that the degree of reaction of the lithium aluminate and the microsilica was low, suggesting that significant reactions took place only at the surface of the microsilica particles.

Abstract

Porous alumina parts were prepared using a lithography-based ceramic manufacturing process (Lithoz CF7500). Green parts were subjected to debinding and sintering processes to produce mechanically strong parts. The photopolymer binder was found to be highly sensitive to heating rate. The primary alumina particles contained within the binder were quasi-spherical and >100 nm diameter. By deliberately under-sintering it was possible to produce porous structures with up to 45% open porosity, and sharp, unimodal pore size distributions, with pores in the range 40-70 nm. When no sintering dwell time was used, the porosity-type was almost exclusively open. However, when a sintering dwell was employed at 1500°C, the percentage of closed porosity increased at the expense of open porosity. Such regularly-shaped parts with open, interconnected porosity are candidates as monoliths for separation science applications.

Abstract

3D printing is the iconic technology of the fourth industrial revolution, characterized by a merger of diverse technologies that is blurring the boundaries between physics, digital technology and biology. Previously associated with prototyping only, additive manufacturing has won acclaim by adapting to a wide variety of materials and industrializing its processes. But what about the most technically challenging materials such as ceramics? Technical ceramics take benefit of this new technology also: 3D printing enables new innovative development in various market field, the production of Solid Oxide Fuel Cells (SOFC) being the most meaningful use case.