Ceramic materials

Components made of ceramic materials can be produced by all common additive processes, even from dense and porous ceramics, as current R&D projects show. With the exception of selective laser sintering, additive manufacturing is followed by a conventional thermal process for debinding and sintering. The additive manufacturing of ceramics serves particularly for the production of functional components in form of prototypes, small series or individual construction units. In comparison to polymers and metals, the production of ceramics is more challenging with respect to material and technology. The choice of materials depends on the respective requirements of the desired application: In addition to oxide ceramics (e.g. Al2O3, ZrO2), nitrides (e.g. Si3N4, AlN), carbides (e.g. SiC, TiC), silicate ceramic components (e.g. cordierite, porcelain) or bioactive ceramics (Ca-phosphates) as well as ceramic components can be produced by additive manufacturing from composite materials or with a graded material structure.

Shaped body made of bioactive ceramics

Using 3D powder printing processes, complex shaped, individual components are manufactured from hydroxyapatite (HAP). The prerequisites for the generation of HAP mouldings are the modification of the starting powder and the adaptation of the binder system or the hydraulic fluid. After sintering, the printed ceramics can be used as bioactive implants. The application-relevant shaped bodies in Figures 1 and 2 prove the efficiency of this generative process for the production of complex three-dimensional hydroxyapatite structures for bioactive implants. Channels and macropores can be realized by the printing process, while the microporosity can be adjusted by the starting powder and the sintering conditions. In the same way as for HAP, bioactive ceramic bodies can be produced from other calcium phosphates.

3DP-HAP	3DP-HAP MANDIBLES
Figure 1	Figure 2

Strength increase with laser-sintered SiC

A process chain is used for the SiSiC material, in which the shaped body is generated from the powder bed by selective laser sintering and the SiSiC material structure is then produced by pyrolysis and infiltration steps. As with all generative processes, laser sintering requires that the achievable material properties of the ceramics must withstand a critical comparison with the properties achieved with conventional manufacturing processes. If SiC starting powder mixtures adapted to the specific process are used and carbon powder is also added, then the material properties (strength, modulus of elasticity) that can be achieved with the above-mentioned process chain via laser sintering are at the same level as those achieved with conventional processes. This process and material development is the basis for the production of application-relevant SiC components by means of laser sintering.

Tool insert for plastic injection moulding

Internal cooling channels and a complex structured surface characterize an injection molding tool insert made of SiSiC, which was manufactured with selective laser sintering (SLS). The SiSiC ceramic does not shrink during the manufacturing process, so that high contour accuracy is achieved without reworking. A combination of the classic SLS process and laser microsintering (in cooperation with the Mittweida University of Applied Sciences) enables a hybrid construction of the component. Areas of the tool surface can be generated with a small layer thickness in such a way that they have a high surface quality, high strength and detail accuracy. The basic body, on the other hand, can be built up with greater layer thicknesses in a cost- and time-saving manner. The ceramic tool insert for the injection moulding of plastics is characterised by its high wear resistance and long service life.

Manufacturing processes of ceramic materials

The institutes of the Competence Field develop powder-based manufacturing processes for ceramic components and systems. In the lab and on testing facilities we work out prototypical solutions, produce small series and, if necessary, transfer it into pilot technology.

The benefit ranges from the processing of powders and raw materials to shaping, sintering, processing in green and sintered states as well as joining and integration techniques. In addition to direct additive manufacturing processes, shaping technologies such as powder injection moulding or vacuum casting are used in combination with rapid prototyping process chains.

Laser sintering of ceramic materials

Regarding laser sintering from powder bed, the Competence Field Additive Manufacturing, focuses on the development of functional patterns for selected ceramic materials as well as process and material feasibility studies. Laser sintering is particularly qualified for ceramic materials that can be further compacted after additive manufacturing by reaction sintering or glass infiltration.

Adapted process parameters enable the production of functional prototypes with high form accuracy and dimensional accuracy. The example of the SiSiC material shows, that the material properties of laser-sintered ceramic components can be on the same high level as those of conventionally produced ceramics.

Three-dimensional printing technology (3D printing) for ceramic materials

For 3D printing from the powder bed, we develop suitable binders as well as printing fluids and condition ceramic powders for the printing process. Process and material developments aim at the production of complex shaped bodies, which, after sintering, have a dense or porous material structure depending on the application requirements.

An innovative process and plant concept using highly dispersed ceramic suspensions will open up new application potential for 3D printing technology and produce dense ceramics with excellent material properties.