Original Date: 02/10/2003
Revision Date: 01/18/2007
Best Practice : Advanced Steel Joining Processes
Bender Shipbuilding and Repair Company, Inc. installed a new steel fabrication process that utilizes lasers for cutting and marking steel up to three inches thick. It implemented a new tab and slot method for fitting and aligning steel components without the need for tack welding. Significant savings in assembly man hours have already been realized. Bender has also developed a laser welding system that uses the same lasers.
In the past, Bender Shipbuilding and Repair Company, Inc. used traditional shipyard processes for cutting, marking, fitting, and welding steel fabrications. These included using plasma and/or oxy-fuel for cutting parts; manually placing punch marks to identify where stiffeners, webs, and bulkheads would be placed; using a combination of tack welding and brute force to align these items to the punch marks, then using traditional processes for welding the steel components together. In order to dramatically improve productivity and reduce the cost of the steel fabrication process, Bender developed and implemented a laser cutting and marking system, and a new tab and slot system for rapid alignment and fitting parts together without the need for tack welding and force fitting. Bender also developed a laser welding system that revolutionizes shipyard welding.
Bender installed Tanaka 6KW and 4KW lasers, which are used for cutting steel up to 1.25 inches thick using laser only, and three inches thick with Laser Assisted Oxygen Cutting (LASOX). The laser provides very accurate, clean cutting of steel plates, an etching layout, and reference lines. This also minimizes heat distortion providing more accurate parts for later fit-up. Because of the accuracy of laser cutting, Bender has been able to adopt a new fitting and joining technique called tab and slot. In essence, the laser cuts tabs on a piece of steel that will be joined with appropriate slots in another piece, allowing the two pieces to be joined by fitting the tabs into the slots. The tabs protrude from the backside of the slot and can be twisted to lock the pieces in place. This process eliminates the need for tack welding pieces in place prior to final welding. It also assures accurate steel assemblies, which greatly reduces later fit-up problems.
Bender has developed a laser welding system to augment its conventional welding system. The new process utilizes the same lasers used for cutting. Laser welding has the potential for almost zero distortion welding. It also has the potential for eliminating the use of traditional weld wire, which provides significant savings in material cost. Laser welding also facilitates the construction of lightweight sandwich panels that are currently impossible to fabricate using traditional methods. These sandwich panels are 40% lighter, 50% stronger, and take up 60% less volume than traditionally stiffened panels. They offer significant opportunities for building lighter and stronger ships for both commercial and military use.
Bender’s new tab and slot alignment and fit-up process has resulted in a 40% reduction in fitting and welding steel T-Beam girders to flanges. Bender has documented a 60% reduction in the man-hours for the fitting and welding of an uptake trunk using the new tab and slot methods. Laser welding, when it is implemented, will significantly reduce man-hours and material cost, and offer the opportunity for new ship design and construction using sandwich panels.
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