One of the main priorities of the aircraft industry today is to design and produce more efficient engines, which consume less fuel and are thus better for the environment and more cost-effective. A key part in achieving these improved engine models is the ceramic investment casting process used in the production of turbine blades, which enables complex designs through the sacrificial nature of foundry cores.
However, foundry cores with the complexity needed for efficient new generation turbine blades—which integrate internal cooling channels—are time consuming and expensive to make using traditional manufacturing processes such as ceramic injection molding, because they must be fabricated in several pieces and assembled. The lead times associated with traditional means have also meant that few modifications (with high cost impact) can be made to foundry core designs throughout the production process.
Enter 3D printing. France-based ceramic 3D printing expert 3DCeram has developed a process for producing complex foundry cores for engine turbine blades that leverages its laser stereolithography (SLA) 3D printing process and innovative SILICORE material. This approach was recently validated through a partnership with Design Bureau Ivchenko, a state design service provider based in Zaporizhia, Ukraine that specializes in designing and developing aircraft engines.
To the core
At the foundation of 3DCeram’s foundry core production process is its laser SLA technology, which builds parts by selectively curing a photopolymerizable ceramic suspension using a computer-controlled UV laser beam. In the production of foundry cores, material is also a critical factor: ceramic types vary depending on the type of alloy being used in foundry production so that there is no chemical reaction between the core and the metal in the casting stage. The selected ceramic must also have the heat and mechanical resistance to withstand the metal casting, have a low coefficient of thermal expansion (CTE), high dimensional stability during the process and have good leachability after the metal cooling process.
For this application—the production of foundry cores for turbine blades—3DCeram developed the silica-based SILICORE material. The material is not unlike other silica-based compositions, which have been used in the casting of nickel-based turbine blades for decades, in that it is characterized by excellent thermal stability resulting from a low CTE (about 0.6×10-6K-1) and good thermal shock resistance. Further, the silica-based core has high leachability and can be easily removed post-casting using a soda or potash solution, both of which are harmless to alloys. Finally, 3DCeram emphasizes that the sintering of a silica core leads to the formation of cristobalite through a devitrification process, ensuring the core’s temperature resistance and high dimensional stability.
Overall, 3DCeram’s process offers a range of benefits for the investment casting process, including more design flexibility, a higher degree of core complexity, faster iteration of new designs and increased profitability, due to lower investments in tool maintenance and storage.
Last year, 3DCeram partnered with Design Bureau Ivchenko to validate the SILICORE formulation on the CERAMAKER 900 3D printer for turbine blade production. Together, the partners set out to achieve optimal 3D printing results for the foundry cores and guarantee a level of quality equal to that of traditional methods. Ultimately, the 3D printed foundry core made from SILICORE was tested and validated using an SX investment casting process.
In the first stage, the companies combined ceramic 3D printing with an established core measurement method using mechanical gauges. This enabled them to successfully 3D print the core and embed it within a wax casting. The wax mold (with internal ceramic core) underwent X-ray control which showed that the ceramic cores were intact and suffered no cracking or damage.
In the next stage, Design Bureau Ivchenko assembled casting blocks and casted the foundry molds using a nickel-based alloy. After leaching the ceramic core from the cast metal turbines, each blade underwent additional controls, including X-ray control and Ultrasonic control. The former proved that the ceramic material had successfully been removed in the leaching process, while the latter was used to measure the thickness of different sections of the blade.
In the end, 3DCeram’s ceramic 3D printing process and SILICORE material were implemented successfully for the production of foundry cores for aerospace turbine blades. Throughout the SX-casting process, industrial tests confirmed that SILICORE’s properties met the required specifications, leading Design Bureau Ivchenko to qualify the material as compliant for the production of foundry cores.
This article was published in collaboration with 3DCeram.