Original Date: 07/21/2003
Revision Date: 01/18/2007
Best Practice : Virtual Fitting of Complex Castings to Optimize Machining
Electric Boat Corporation, Quonset Point Facility successfully developed its CATIA, Computer Aided Design/Computer Aided Manufacturing capabilities and used photogrammetric survey data to create a highly efficient and accurate process for machining, locating, and installing complex castings onto a ship’s hull. As the demand for increased modular designs and reduced delivery schedules continue to rise, the company’s virtual fitting of complex castings provides a clear, competitive advantage in the rapidly changing maritime and defense industries.
In virtual fitting of complex castings, Electric Boat Corporation, Quonset Point Facility’s (EBQP’s) Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) Engineering merged CATIA and photogrammetric survey capabilities. Historically, casting installations were performed on a trial-and-error basis requiring two or more attempts before final fitting. Machining lines were laid out to the as-built ship’s condition, castings were removed from location for final beveling after fit-up, part handling scenarios were undesirable, and optimal machine shop processing was rarely achieved. The casting location was determined with piano wire or fixturing, and hull weld build-ups were periodically required to complete an installation. This process was inaccurate, disruptive to work flow, and time consuming.
EBQP utilized its CATIA workstation capability and photogrammetric survey data to successfully resolve the casting installation dilemma. Employing CAD/CAM engineering capacity for design model overlay and manipulation, EBQP attained virtual hull fitting of complex castings prior to machining. This process was fully developed during machining and installation of the Virginia Class Weapons Shipping Trunk (WST), a large, complex casting. Photogrammetric survey data is collected during receipt and inspection of the rough casting, and is uploaded into CATIA and overlaid on the design model an example of virtual fitting of complex castings. The photogrammetric point cloud is then virtually fit to the model, and optimal machining coordinates are rendered. This information is then used to establish physical reference lines and working points for set up and machining, and define hull structure cuts and edge preps for welding. The results are less machining, less welding, a tighter fit of the WST casting to the ship’s structure, and improved hull fairness.
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