particularly true if the added time sig- nifi cantly aff ects the downstream pro- duction schedule. It becomes a critical issue that gets lots of attention.” T e Navy Metalworking Center
evaluated several potential methods to improve production of the wa- terjet inlet tunnel’s leading edge for future LCS hulls. T e project team agreed the best option was to cast the component separately into three seg- ments, each of which measure several feet long. T e molds were designed using casting simulation to minimize or eliminate porosity, distortion and cracking. T e sand mold segments were produced in two days using 3-D sand printing. T e segments were shipped to International Casting Corp., New Baltimore, Mich., where they were assembled and ready for pouring within two weeks from the date the design was fi nalized in cast- ing simulation. Using additive manu- facturing to print the molds allowed the team to produce a superior quality casting on a tight schedule at signifi - cantly lower cost than traditional 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 certifi ed by the American Bureau of Shipping for use on subsequent LCS platforms, starting with LCS-3, the USS Fort Worth. T e 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 turbulence, reduced ship power require- ments and minimal cavitation erosion.
Cast Stem T e design of the LCS includes
a sharp bow section. Connecting its forward edge (the stem) with the ad- joining hull plates is diffi cult because of the acute angle between the two structural members. In addition, the close proximity of the horizontal and
The cast waterjet inlet tunnel, shown here prior to the removal of gates and risers that fed metal into the part at the metalcasting facility, has saved many production labor hours since the second Freedom variant littoral combat ship was made.
vertical structural members (the breast hooks and frames) over the length of the stem makes welds diffi cult to complete and inspect. T e fi rst LCS ship, USS Freedom
(LCS-1), used a stem cut from a steel plate, which required a signifi cant amount of labor to shape properly. T is caused many schedule delays and increased fabrication cost due to rework and weld inspection. Fol- lowing this experience, Lockheed Martin and the shipyard, Marinette Marine Corp., sought an alternative stem design to reduce fi t-up labor and improve accessibility for welding and inspection. According to Akans, the new stem design was considerably more complex than the legacy design. T e V-shaped confi guration provided better access for the welder to join the stem to the hull plates. A team including the Navy Met-
alworking Center; Lockheed Martin; Marinette Marine Corp.; the Ameri- can Bureau of Shipping; Gibbs & Cox; Bollinger Shipyards Inc.; the Navy LCS program offi ce; Naval Surface Warfare Center, Carderock Division; and Newport News Industrial Prod- ucts worked to develop an optimized manufacturing solution involving a long cast stem that would ultimately meet the shipyards’ fi t-up and acces-
@
ONLINE RESOURCE
Take a look at more castings used in marine applications by viewing the Aquatic Castings gallery at
www.metalcastingdesign.com.
Jul/Aug 2014 | METAL CASTING DESIGN & PURCHASING | 21
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60