The NCEMT's portfolio includes three recent Rapid Response projects-quick-turnaround initiatives that use the expertise of a Center of Excellence to insert technology to meet an immediate fleet need.
Stainless Steel Investment Casting
The Virginia-Class Submarine Program identified that at least 80% of the stainless steel investment castings for subassembly shock testing of a handling system required rework or repair due to micro-porosity defects. The NCEMT worked with Northrop Grumman Newport News, General Dynamics Electric Boat, Tech Cast, Inc. and a Critical Design Review (CDR) team to analyze and characterize the existing defects, provide simulation support and define an improved process to reduce or eliminate defects in future production castings. Through metallurgical examination of the existing castings, the team developed an improved casting process that uses a modified gating system to increase the pouring rate and sand packing to decrease the solidification rate. Twelve validation castings were produced utilizing the new casting process. No defective castings were found, a substantial improvement in surface quality and appearance was observed, and the tensile and Charpy V-no tch im pact energy properties were greatly improved. This technology will be used to support future production of saddle-castings for the Virginia-Class submarine.