As high-strength thin-steel usage in ship design increases, dimensional management becomes very critical to control rework costs and schedule delays in ship production. Prior Office of Naval Research (ONR) and National Shipbuilding Research Program (NSRP) projects have helped Ingalls Shipbuilding to emphasize dimensional control for thin steel structures. Huntington-Ingalls (previous Northrop Grumman Shipbuilding) has, in recent years, substantially increased its emphasis on dimensional management as an enabler to achieving its aggressive goals for the future. These goals include cost and lead time reduction for hull erection and increasing early-stage outfitting.
Nevertheless, improvements to shipbuilding facilities and process technology have not kept pace with the rate of change in ship design. Worse, new designs using thinner steels are subject to legacy weld size requirements. These two factors result in widespread overwelding. Severe plate buckling in naval vessels has been attributed to oversized welds in thin plate ship structures. The problem of overwelding has two distinct sources:
- The weld sizing method developed in the 1980s is still used in most shipbuilding specifications regardless of ship class. This prevents the incentive of application of latest technologies that can make strong, precision fillet welds for modern lightweight thin steel naval surface combatants.
- Shipyard welders tend to make welds even larger than design requirement in order to satisfy Quality Assurance (QA) inspection. In a number of investigations, fillet welds requiring a leg size of 5mm are typically found to have an average size of 8mm, resulting in more than double the heat input and distortion. The approach to the solution of this overwelding problem will be described in detail in this paper:
- Develop appropriate weld sizing criteria for thin plate structures-this can be facilitated by numerical modeling to ensure adequate static shear, tensile, bending, fatigue and dynamic impact capacity of structural welds;
- Perform a robust designed experiment to confirm the models and establish confidence that precision weld sizes can provide necessary performance and strength throughout the design service life of the vessel.