of the edge became costly and required more production time than expected. Shipbuilders spent many hours grind- ing the welded structure into the acceptable hydrodynamic shape. “Generally, the shipyard has tar-
geted fabrication times and labor costs planned for the fabrication/installation of critical components,” Akans said. “When these targets are significantly exceeded beyond what was planned, the ‘red flag’ is generally raised. Tis is particularly true if the added time sig- nificantly affects the downstream pro- duction schedule. It becomes a critical issue that gets lots of attention.” Te Navy Metalworking Center
evaluated several potential methods to improve production of the waterjet inlet tunnel’s leading edge for future LCS hulls. Te project team agreed the best option was to cast the component separately into three segments, each of which measure several feet long. Te molds were designed using casting simulation to minimize or eliminate porosity, distortion and cracking. Te sand mold segments were produced in two days using 3-D sand printing. Te segments were shipped to Interna- tional Casting Corp., New Baltimore, Mich., where they were assembled and ready for pouring within two weeks from the date the design was finalized in casting simulation. Using additive manufacturing to print the molds allowed the team to produce a superior quality casting on a tight schedule at significantly lower cost than tradi- tional sand casting methods. Now, 3-D printing the sand molds
for the cast steel leading edges of the waterjet inlet tunnel is Marinette Marine Corp.’s preferred produc- tion method. It was certified by the American Bureau of Shipping for use on subsequent LCS platforms, starting with LCS-3, the USS Fort Worth. Te three-piece cast steel leading
edge has resulted in: • 75% reduction in construction labor hours.
• 23% reduction in weld length. • 30% reduction in weight. • Reduced production cycle time. Additionally, the increased accuracy of
the contoured shape improved the hydro- dynamic performance, leading to reduced
The U.S. Navy and Lockheed Martin intentionally built the first littoral combat ship based on immature ship designs with the purpose of using the first experience building and operating the ship to improve future designs.
The cast stem (the curved piece making the edge of the upside down bow) allows for improved fit-up and accessibility to adjoining structural members. The bow module shown here was installed on the LCS-3.
turbulence, reduced ship power require- ments and minimal cavitation erosion.
Cast Stem Te design of the LCS includes a
sharp bow section. Connecting its for- ward edge (the stem) with the adjoin- ing hull plates is difficult because
of the acute angle between the two structural members. In addition, the close proximity of the horizontal and vertical structural members (the breast hooks and frames) over the length of the stem makes welds difficult to complete and inspect. Te first LCS ship, USS Freedom
August 2014 MODERN CASTING | 51
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