Product
Spotlight
3D Printing Casting Cores for Aircraft and Industrial Gas Turbines
by Isabel Potestio, Lithoz GmbH, Vienna, Austria; Shawn Allan, Lithoz America, Troy, New York
• Lithography-based manufacturing enables printing of complex core geometries not possible by injection molding
• 3D Printing accelerates product development cycle through rapid-prototyping
• Increased build volume size and serial printer designs enable the transition to core production using 3D-printing
A
s gas turbine inlet temperatures continue to rise, in the quest for more thrust and greater
efficiency, the cooling of turbine blades to prevent them from melting presents a major challenge to both designers and manufacturers. The internal passageways and cavities within the blades that allow cooling air to circulate become more complex and dimensionally critical. Turbine blades are traditionally manufactured by investment casting, beginning with a ceramic core to form the internal cooling structure. New designs for multivane, complex,
16 ❘ March 2020 ®
narrow feature cores push the limits of mold and tooling based processes. Additive manufacturing offers a tool-free solution for increased complexity from prototyping to production. This is where a ceramic 3D printed core becomes necessary. Direct 3D printing of cores is
possible with Lithography-based Ceramic Manufacturing (LCM). In LCM, ceramic powder is blended with a photocurable resin to produce a slurry. This slurry is then cured one layer at a time in the LCM 3D printer. Lithoz CeraFab LCM printers produce features down to and below 200 µm through tailoring core and resin formulations and using highly accurate and reproducible digital light projection (DLP). Cores can be produced with complex branching, multiple walls, fine trailing edges, and thru-holes. After printing, the cores are sent through thermal debinding and sintering processes similar to non-AM processes. The material that Lithoz developed
to additively manufacture these casting cores is known as LithaCore 450. This is a silica-based high-performance
Photo above: Cores and technical ceramics printed using LCM.
ceramic material that, when sintered, has properties that make it perfect for casting core applications. These cores have low thermal expansion, high porosity, outstanding surface quality, and exceptional leachability. Lithoz’s LithaCore material has been verified in production conditions such as directionally solidified (DS), equiax-cast (EX), and single-crystal (SX) casting of nickel-based alloys. On top of this, the composition of the photosensitive slurry that eventually becomes the ceramic core can be tailored to the individual needs of the customer, allowing them to use their own powders and therefore successfully integrate their know-how developed through years of research. LCM technology can handle the
printing of smaller cores for aircraft engine turbines, as well as much larger cores needed for industrial gas turbines. Lithoz’s newest 3D printer release, the CeraFab System S230 is capable of producing cores over 450 mm in length on a build platform measuring 192 x
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