H. N. Chou, Boeing Phantom Works, St. Louis, MO

Summary:

The paper describes the permanent mold casting process, mold design, mold preparation and variables that may affect the casting product. Aluminum tail fairing castings manufactured from permanent mold process were submitted for Hot Isotatic Pressing (HIP) at 15 ksi and 960F for 4 hours. After HIP process the castings were solution heat treated and aged to -T6 temper. The static tensile properties of the final product exceeded those from baseline 6061-T6 machined aluminum forging tail fairing. The casting was 100% machined and submitted for component bending test at 150% Limit Load. Followed the successful bending test fatigue test specimens were extracted from the casting and specimens were submitted for vibration fatigue test in various strain and stress levels. The results from the fatigue test demonstrated that the HIPed casting had equivalent or better fatigue properties as the baseline 6061-T6 forging.

The paper investigated the benefits of various commercial HIP processes on aluminum permanent mold casting. The microstructure changes and porosity levels between non-HIP and HIPed castings were assessed in detail. Fatigue test results from 100% machined specimens and as-cast specimens were compared and found that the as-cast specimens had equivalent fatigue properties as the machined specimens. Based on this finding the paper recommends that the tail fairing casting can be used in as-cast condition without going through high cost machining process. Cost data for baseline 6061-T6 machined forging and D357 HIPed permanent mold machined casting were collected and evaluated. Significant amount of cost savings can be secured when the D357 tail fairing HIPed and selectively machined castings are appropriately implemented in weapon systems.