Modern ships consist of several complex components and sub-components which are held together by varied methods; with each method coming from their side effects on man hours in hull production and outfitting. However, due to heat distortion significant impact on nonproductive/nonmanufacturing operations such as straightening and fitting. Aside from that, the operations can also interfere with onboard outfitting and construction costs. Finally, those operations also impact material properties therefore on build quality and performance.
Modern ships, whether its a tanker, yacht or a cruise vessel have structural joint lengths from 400km; usually seen on cruise ships. Modern ships meaning modern joining techniques such as laser hybrid welding; comparable to arc welding and offering some advantages that arc welding doesn’t have. These advantages are faster welding speed, less heat distortion and rework, reduced consumption of filler material while improving quality of the output. Laser welding can be sustainable and economically-successful if the following factors are observed.
- Larger structures or thicker sections which are harder to access with standard equipment.
- Re-engineering of the entire shipbuilding process is necessary for exploitation of high productivity.
- Lacks of standard procedures or theoretical scenarios for operation and accidents leads to significant losses.
- Special skills and experiences in using new technology; on-occasion not available in smaller enterprises.
Leading onto the vessels themselves, flat components such as bulkheads and decks are a significant part of structure on modern ships; characterised by long straight butt and fillet welds; welded with CO2 lasers on pre-assembly stages. CO2 lasers require rigid mirror systems which are needed to guide the beam. Finally, regarding pre-assembly stages the gantries can be improved to reduce transport operations and increases in exploitation of equipment; those procedures are edge preparation and integrated peripheric work operations. However, re-engineering of the hull production chain is required.
An example of pre-assembly reworks is an investment by Meyer Werft in a new production facility which focuses on flat components in dimensions of 20mx20m. Hybrid welding was used exclusively for butt joints and long fillet welds. Justifying the cost of laser equipment, the entire process chain for deck and wall preassembly was redesigned and highly automated; laser welding and process control mechanism was integrated into the machines to reduce transport operations. Consistent usage of this method brought the following changes:
- Increased productivity through increased welding speed, reduced transport and setup operations.
- Reduced space in covered facilities.
- Increased flatness of the panels and decreasing efforts for straightening and fitting in later assembly stages.
- More efficient use of material.
- Decreased costs of edge preparation by using integrated milling tools instead of external services.
Lasers can also be modified for other purposes such as 3D welds with solid state lasers; where elements are combined to form another innovation. This is courtesy of Fincantieri, Italian shipbuilders who combined YAG (Yttrium Aluminium Garnet) lasers with a gas metal arc welding process for performing fillet welds in flat sub-assemblies and large panels common on passenger ship hulls. The conclusion that can be drawn from Fincantieri’s experiment is that YAG lasers have a less complex and more flexible therefore, more stable nature which fits on longer, precise welds.
The last example of contribution of laser technology is block and dock assembly which reduces rework and interference between various on-board operations. However, the drawbacks involve accessibility, external environment, large parts and thick plates. While such equipment is not yet on the market, the European DOCKLASER project is currently exploring variables for mobile laser processing. DOCKLASER consists of tractor systems for long structural butt and fillet welds in block and final assembly; tack welding tools to fix edges prior to welding of long joints and manually-guided tools for cutting and welding of short, non-structural welds in outfitting.
