On Virginia Class Submarines, torpedoes like the one shown here are in weapons cradles from the time they arrive on the ship until they are launched. US Navy Photo
The objective of this project was to reduce the cost of each Virginia Class Submarine by improving the producibility of the submarine weapons cradles. The weapons cradles are used to secure weapons from the time they are loaded onto the ship until just prior to their launch. Because a large amount of welding is used to fabricate the long, thin assemblies, it is difficult to construct them and meet the precise dimensional tolerances.
Virginia Class (SSN 774) submarines use weapons cradles to handle 21” diameter weapons from the time they are loaded onto the ship until just prior to launch via the torpedo tubes. GDEB and NGSB-NN have encountered significant issues maintaining the very close dimensional tolerances for this long (approximately 21 feet), thin structure manufactured with a very large amount of welding. Any rework or scrapping is very costly to the program.
After studying the drawings, procedures and manufacturing areas, the IPT developed 15 recommendations. The necessary work instructions, design changes, and training or procedural changes have been developed for 10 of those recommendations. One recommendation is to initiate a full-scale Design for Manufacturing and Assembly Project. Two recommendations have been moved to that project due to their magnitude. Implementation of the remaining two will only be necessary if other recommendations are not successful.
By implementing the project’s results, the rejection rate and rework of weapons cradles will greatly decrease, leading to improved production costs and lead time. The Navy Metalworking Center examined the current weld processes, detailed drawings, and weld sequencing to identify ways to reduce weld-related distortion. NMC also provided recommendations to optimize welding fixtures to support the manufacturing process. The necessary work instructions, design changes, and training or procedural changes have been developed for 10 of the 15 recommendations identified. These recommendations are conservatively estimated to save $160K per ship set.
GDEB and NGSB-NN will partially implement the 10 recommendations for the weapons cradles being built for SSN 780 and fully implement those recommendations on cradles for SSN 781 in the spring of 2010.