Shipbuilder Boosts Welds with Lasers
Brent D. Johnson
With Lindbergh's trans-Atlantic flight in 1927, it appeared that the days of the ocean liner were numbered and that floating palaces like Olympic and Aquitania that had once ruled the seas might forever pass into oblivion. And so they nearly did.
Increased demand for cruise ships has led to modernized shipbuilding techniques, including using prefabricated steel panels to reduce time in the building dock.
However, the phenomenon of the cruise vacation has largely reinvigorated the great ships, and passengers with the means to do so can spend days or weeks lounging in Caribbean sanctuaries while being ferried between ports of call by vessels that dwarf their predecessors. In the golden age of ocean travel, the goal was speed, and the trim hulls of the Cunard and White Star lines dueled for supremacy by setting and then breaking speed records. With today's behemoths, the design concept is primarily focused on capacity and comfort, as the ships themselves have become the destination.
An innovative technique combines metal inert gas torch welding with laser welding to create surface and deep welds simultaneously. Seams can be welded from only one side, which reduces material consumption and production time.
Currently, 49 cruise ships are under construction, with dates of completion scheduled between 2002 and 2005. Twenty-eight of those ships weigh in at more than 81,000 tons, making them heavier than the Queen Mary. This demand for larger and larger ships requires some updated building methods.
Meyer Shipyard, on the Ems River in Germany, has collaborated with Schuler Inc. to develop a welding system that could revolutionize the shipbuilding industry.
The hybrid technique combines laser welding with standard torch welding in one focal point. It uses a radio-frequency-excited CO2 laser, with a peak output of 12 kW, from Schuler Held Lasertechnik GmbH & Co. KG of Heusenstamm, Germany, and a metal inert gas welding current source of 450 A. The system's designer, Hermann Lembeck, said that the quality of the welds produced this way meets the normal shipbuilding standards and has less ductility, increased hardness and better joint properties.
The system joins prefabricated steel panels up to 65 square feet in area and from 5 to 15 mm thick. The metal inert gas welder fuses filler metal to the seam edge of the panel, while the laser tracks behind it, melting through the seam root and penetrating deeply into the metal.
The chief advantage of the system is that the panels can be welded from only one side instead of from both sides simultaneously. The result is a significant savings in time and reduced use of welding material. The machine completes a 20-meter-long weld in less than 10 minutes. In the past, when the company used a submerged arc welding process, the welding length was limited to 10 meters, and there was higher distortion and more shrinkage of the workpieces. The new process makes pieces fit better and enables more efficient pre-outfitting. The company says the hybrid system has upped its productivity by 60 percent.
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