Additive Manufacturing Promises Engine Cost and Weight Reductions Published March 4, 2010 By Heyward Burnett Materials and Manufacturing WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- Work performed as part of the Air Force Research Laboratory-managed Metals Affordability Initiative demonstrated the value of superalloy additive manufacturing in reducing jet engine cost and weight. The use of laser powder deposition and electron-beam wire deposition enabled layer-by-layer deposit of nickel superalloy engine case attachment features--surface points for attaching fuel lines, generators, and cables--to the surface of a representative forged ring. The preliminary results indicate that incorporating superalloy additive manufacturing methods into the production process will meet quality standards and, more specifically, will potentially reduce the cost (and weight) of forged engine cases and the weight of cast cases. This project also established a cost model for measuring savings and comparing the respective benefits of LPD and EBWD in particular applications. The high temperatures and stresses encountered by a jet engine casing demand its forging or casting from superalloy metals. Meanwhile, the case surface features (attachment points) must withstand the same harsh environment. In a conventional production scenario, these features are machined from the excess material remaining after case forging or casting. Thus, the forging or casting process itself must employ enough material so that whatever remains can support the additional machining needed for maintaining attachment point integrity. Overall, this translates to a time-consuming machining process and, further, yields a heavier-than-necessary engine case, since all extra metal is not removed. Conversely, additive manufacturing builds surface attachment features by depositing material a layer at a time instead of machining away excess material from a larger piece. Attachment features generally fall into one of three different geometries: rectangular pad; thin-walled flange; or thick-walled, hollow cylinder (called a boss). Accordingly, these shapes represent the ones chosen by the researchers to demonstrate LPD and EBWD feasibility. LPD uses 1) a laser to melt superalloy metal powder and 2) computer-numerical-control (CNC) software to precisely deposit the melt on the case exterior so that the required feature is built one layer at a time. EBWD uses an electron beam as its heat source for melting a superalloy metal wire; it too relies on CNC to determine and control the layer-by-layer deposition path. The demonstration showed that both methods attain the desired rough shapes. After deposition, the ring structures underwent heat treating; nondestructive inspection; microstructural examination; and, finally, mechanical test (including tensile strength at room temperature and elevated temperatures, creep stress rupture, and some low-cycle fatigue testing). Having been successfully validated against quality standards, these processes are now ready for demonstration on actual noncritical production parts. Simultaneous development of the cost model enabled the researchers to capture potential cost savings and assess the benefits associated with each process. This model not only compares the new processes to the old, but also aids in determining which deposition process--LPD or EBWD--is best for specific applications. The cost model reveals that additive-manufacturing-based production generates upwards of a 30% savings over traditional forged-and-machined engine cases; the initial forging requires less material, which saves money and time and ultimately creates a lighter case as well. The model also shows that while additive manufacturing does not cut costs for a cast engine case, it nonetheless achieves significant weight reduction (up to 10%) by producing thinner case walls.