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Development of 3D printing ceramics for investment casting shells and cores

In a joint tailoring project, Japanese ceramics expert AGC Ceramics Co, Ltd (AGCC) and voxeljet AG have qualified the high-performance ceramic material Brightorb™ for 3D printing. In addition to potential applications in the production of structural components and works of art, the material is particularly suitable for 3D printing of highly complex moulds and cores for metal casting.

To develop the new high-performance ceramic material set Brightorb™ for 3D printing, AGC Ceramics entered into a co-operation with voxeljet AG from Friedberg in Bavaria, Germany. Brightorb was developed on a VX1000 with a build volume of 1000 x 600 x 500mm. The 3D printing system works layer-based and bonds the ceramic particles with an inorganic binder. Targeted applications for the new, ceramic material set include high-performance cores for sand and investment casting, ceramic filters, structural components, as well as art and product design.

Environmental benefits

The ceramics material with its brand name Brightorb is composed of spherical sand with the main components aluminium oxide (Al2O3) 80 per cent, zirconium oxide (ZrO2) 10 per cent, silicon oxide (SiO2) 9 per cent, the minerals corundum, baddeleyite and kinds of cement. During 3D printing, Brightorb is applied to the build platform with average grain sizes of 50μm and layer thicknesses of 100μm and selectively bonded with an inorganic binder. The inorganic binder is characterised by its high environmental compatibility as only water vapour is produced during moulding. This greatly improves environmental and working conditions in foundries. To subsequently prepare the printed ceramic for the final application, the printed components get impregnated by a silica-based liquid and have to be fired in a sintering furnace for their final strength. Most of the unprinted powder can be reprocessed, recycled and fed back into the printing process.

“We have been noticing a growing demand for increasingly complex component geometries among our customers for a long time,” explains Dr Ingo Ederer, CEO at voxeljet. “The great advantage of the geometric freedom of 3D printing is that geometric adjustments can significantly optimise the efficiency and effectiveness of, for example, engines or turbine wheels. It is rare that such complex components can still be produced using conventional moulding processes. Together with AGCC, we have been able to optimise a VX1000 for ceramic powder in close co-operation, so that it is ideally suited for the challenging demands of metal casting – both in terms of strength and surface quality.”

The 3D-printed ceramics are used, for example, as cores for the investment casting process to reproduce complex and filigree cavities within castings. In this process, the filigree cores are combined with conventional wax patterns. These are coated with a ceramic slurry and burned out before casting. What remains is a hollow ceramic mould in which the printed core is still inserted. Molten metal is then poured into the mould. After cooling, both the mould and the core are removed. This process makes it possible, for example, to integrate internal cooling channels in turbine blades, thus increasing turbine efficiency and reducing downtimes to a minimum.

Mr Ushimaru, additive manufacturing director from AGCC is also satisfied: “Brightorb is a high-performance ceramic that is extremely well suited for metal casting due to its high chemical stability, heat resistance, thermal conductivity and low thermal expansion. We were able to optimise the material set in such a way that the shrinkage factor of the printed components during the downstream sintering process at 1,400°C is less than one per cent. This means that the components are also suitable for filigree core designs. Thanks to the high fire resistance, it is possible to cast alloys with melting points beyond 1,600°C. Overall, ceramics will continue to gain importance as a material in the future, and the same applies to 3D printing as a manufacturing technology. We are pleased to have embarked on this path together with voxeljet and look forward to further close co-operation.”

Brightorb was qualified in voxeljet’s material certification lab in Friedberg, Bavaria, Germany. The powder was developed by AGCC and adapted to 3D printing together with voxeljet. Commercial availability of Brightorb is scheduled for July 2021 onwards, both for printing systems and as an on-demand service.

For more information, visit www.voxeljet.com or follow voxeljet on YouTube, LinkedIn, Facebook and Instagram.