Develop, calibrate, upgrade and validate fabrication parameters that will produce CVN-78 foundation assemblies that meet flatness requirements.
The CVN-21 class of aircraft carriers is constructed using different grades and gauges of steel than the CVN-68 class of aircraft carriers. Because the inner bottom assemblies provide the foundation for many compartments, maintaining flatness is a CVN-21 fabrication requirement. Fabrication parameters derived from CVN-68 class carrier measurements are not directly applicable to the CVN-21 foundation assemblies due to the change in plate grade. If unacceptably large distortions occur during production, the assemblies must be reworked, and construction delays will occur.
The Navy Metalworking Center (NMC) is working closely with Northrop Grumman Newport News (NGNN) shipyard production personnel, the PMS 378 Program Office, and appropriate NAVSEA Technical Codes to establish the transverse and longitudinal unit pre-cambers and directions to be applied to the CVN-21 production foundation assemblies. This will be done by building a mock-up foundation assembly with no initial pre-camber, then measuring the resultant cambers during assembly. Regression and correlation analysis will be used to define the pre-camber and direction to be initially applied in the CVN-21 production units to meet flatness requirements once the internal welding is completed. A secondary objective is to assess the applicability of weld distortion modeling for predicting distortion in large structures of interest to the shipbuilding industry. To accomplish this, NMC is building the CTC Innerbottom, a test article which represents a generic scaled-down ship’s innerbottom and comparing it to software predictions.
This technology will reduce weld distortion and minimize any subsequent required rework, which will lead to cost avoidance and minimized schedule impact. The technology may be applicable to other Navy surface ships that contain High-Strength Low-Alloy Steel welded structures, resulting in additional benefits to the Navy.
By working closely with NGNN and PMS 378, the technology developed under this project will be directly implemented in the production of CVN-78, with the fabrication of the first production units beginning in January 2007. The mock-up foundation assembly produced in this project is a deliverable to the Navy and will be available for future testing.
StakeholderDidier J. LeGoff