Additive Manufacturing of Aerospace Ceramics – Aerospace Manufacturing and Design

The aerospike nozzle offers many advantages, including reduced fuel consumption and efficiency at a wide range of altitudes. Complex designs can be printed from a single piece of ceramic.

All photos credit Lithoz

Aerospace is the second industrial sector served by additive manufacturing (AM), after medicine, according to a manufacturing technology consultancy SmartTech. Yet, there remains a lack of awareness about the potential of AM with ceramic materials to rapidly fabricate aerospace components, with increased flexibility and cost-effectiveness. AM provides faster, more sustainable production of stronger, lighter ceramic parts, reducing labor costs, minimizing manual assembly, and reducing aircraft weight through modeling-developed designs that improve efficiency and performance. Additionally, AM ceramic technology provides dimensional control in finished parts for features below 100 µm.

However, the word ceramic can conjure up an erroneous idea of ​​fragility. In reality, AM ceramics create lighter, highly detailed components with tremendous structural strength, toughness, and resistance to wide temperature ranges. Forward-looking companies are turning to ceramics for components such as nozzles and thrusters, electrical insulators and turbine blades.

Materials

High purity aluminum oxides, for example, offer high levels of hardness combined with strong resistance to corrosion and temperature ranges. Alumina components are also electrically insulating at high temperatures often encountered in aerospace systems.

Zirconia-based ceramics meet many applications with extreme material requirements associated with high mechanical stresses, such as high-end metal forming, valves and bearings. Silicon nitride ceramics exhibit high strength, high toughness and excellent thermal shock resistance, as well as good chemical resistance to corrosion by many acids, alkalis and molten metals. Silicon nitride is used in high temperature low dielectric insulators, wheels and antennas.

Composite ceramics offer several desirable qualities. Silica-based ceramics with added alumina and zircon have proven to be exceptional for the manufacture of single crystal castings of turbine blades. Indeed, ceramic cores made from this material have very low thermal expansion up to 1500°C, high porosity, exceptional surface quality and good leaching. Printing these cores enables the production of turbine designs that can withstand higher operating temperatures and improve engine efficiency.

Various ceramic geometries and materials for aerospace applications, including silica-based ceramic cores for investment casting superalloy turbine blades, zirconia centrifugal turbine, and silicon nitride de Laval combustion nozzles .

Advantages of AM ceramics

Injection molding or machining ceramics is notoriously difficult, and machining provides limited access to a component being manufactured. Features such as thin walls are also difficult to machine.

The lithography-based ceramic fabrication (LCM) used at Lithoz, however, enables the fabrication of precise and complex-shaped 3D ceramic components.

From a CAD model, detailed specifications are digitally transferred to the 3D printer. A precisely formulated ceramic-based powder is then applied to a transparent tank. The mobile build platform is immersed in slurry and then selectively exposed to visible light from below. The image of the layer is generated via a digital micromirror device (DMD) coupled to a projection system. By repeating this process, a three-dimensional green part can be generated layer by layer. After thermal post-treatment, the binder is removed and the green parts are sintered – coalesced by a special heating process – resulting in fully dense ceramic components with exceptional mechanical properties and surface quality.

LCM technology provides an innovative, cost-effective, and faster process for investment casting of turbine engine components, avoiding the costly and labor-intensive mold making required for injection molding and investment casting.

LCM can also make designs that cannot be made any other way, while using far less raw material than other methods.

Lithoz ceramic 3D printers enable the manufacture of ceramics with high precision and reproducibility, from research to production.

Bridging the gap

Despite the enormous potential of ceramic materials and LCM technology, a gap exists between original equipment manufacturers (OEMs) and aerospace designers.

One reason may be resistance to new manufacturing methods in a sector with particularly strict safety and quality requirements. Aerospace manufacturing requires many validation and qualification processes, with extensive and rigorous testing.

Another hurdle is the perception that 3D printing is primarily only suitable for one-off rapid prototyping rather than anything that can be fielded in the air. Again, this is a misperception, as 3D printed ceramic components have already proven their reliability for mass production.

An example is the manufacture of turbine blades, where AM ceramic processes produce cores for single crystals (SX), as well as directionally solidified (DS) and equiaxed cast (EX) superalloy turbine blades. Cores with complex branching structures, multiple walls and trailing edges smaller than 200 µm can be produced quickly and economically, with the final components having consistent dimensional accuracy and excellent surface finish.

Greater communication can bring aerospace designers and AM OEMs closer together, with complete confidence in ceramic components made using technologies such as LCM. The technology and the expertise exist. This requires changing mindsets of AM for R&D and prototyping, to seeing it more as a way forward for large-scale commercial applications.

In addition to education, aerospace companies can invest time in human resources, engineering, and testing. Manufacturers should familiarize themselves with the different standards and methods for evaluating ceramics, as opposed to metals. Two key ASTM standards used by Lithoz for structural ceramics, for example, are ASTM C1161 for strength testing and ASTM C1421 for toughness. These standards are used for ceramics produced by all methods. In ceramic AM, the printing step is only a forming method and the parts undergo the same type of sintering as in conventional ceramics. Therefore, the microstructure of ceramic parts will be very similar to conventional processing.

Where will we be in 10 years?

Based on the continued advancements in materials and technology, we can say with some confidence that there will be a lot more data available to designers. New ceramic materials will be developed and adapted to specific technical requirements. Parts made with AM ceramics will have completed the qualification process for use in aerospace. And better design tools will be available, such as improved modeling software.

By collaborating with LCM technology experts, aerospace companies can integrate AM ceramic processes in-house, which shortens lead times, reduces costs and opens up opportunities to develop their company’s intellectual property. With long-term vision and planning, aerospace companies investing in ceramic technology can reap major benefits from their production portfolio over the next decade and beyond.

By forming collaborative partnerships with AM ceramic companies, aerospace OEMs will produce components previously unimaginable.

Lithoz

About the Author: Shawn Allan is Vice President of additive manufacturing specialist Lithoz. He can be contacted at [email protected]

Shawn Allan will speak on the challenge of effectively communicating the benefits of ceramic AM at Ceramics Expo in Cleveland, Ohio on September 1, 2021.

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