The ship building industry uses friction stir welding (FSW) for producing aluminium panels from aluminium extrusions.
The extrusions are light weight and corrosion resistant. They have integrated stiffeners resulting in a very attractive weight to strength ratio. Complete modules can be lifted by crane into the ship being built in a ship yard.
Friction stir welded aluminium panels in the X-Craft at Nicols Bros. Boat Builders in Freeland, Washington
The Sea Fighter (FSF-1) was built by Nichols Bros. Boat Builders, Freeland, Washington as an experimental littoral combat ship in service with the United States Navy. Its hull is of a small-waterplane-area twin-hull (SWATH) design, provides exceptional stability, even on rough seas. It All the flight decking and underbelly structure was made from prefabricated FSW panels, while the hull welds were all welded in the ship yard using MIG welding (GMAW). The friction stir welded panels were up to 13,75 m (45 ft) in length using 5000 and 6000 series aluminum with up to 9mm thickness. These were completed in 2003-2004.
The aluminum superstructure and the aluminum deckhouse of the 'USS Freedom (LCS-1)' has been friction stir welded. It is difficult to detect by radar systems because of its angular shape and the low distortion.
The ship has a semi-planing steel monohull and can achieve a top speed of over 40 knots (74 km/h; 46 mph). It was built by Lockheed Martin's LCS team (Lockheed Martin, Gibbs & Cox, Marinette Marine, Bollinger Shipyards) in Marinette, Wisconsin.
After being commissioned in Milwaukee, Wisconsin, on 8 November 2008, Freedom was assigned to Littoral Combat Ship Squadron One with its home-port in San Diego.It is planned to decomission and mothball the ship on 31 March 2021.
Friction stir welding was conducted at Friction Stir Link according to the “ANSI/AWS D1.2-XX Structural Welding Code - Aluminum” of the American Welding Society. The American Bureau of Shipping (ABS) was one of the certifying agencies, which signed off both the WPS and PQR for the production. A test specimen was initially removed from the end of a weld on every third panel and finally every fifth panel welded. The test specimen provided for a joint tensile and a root bend test with the specimen containing the FSW tool hole at end of the weld being discarded. Dye penetrant inspection of the weld root as well as radiographic inspection was required in some cases.
Marine Aluminium Aanensen, now a subsidiary of Norsk Hydro ASA, was the first company to prefabricate large ship building panels from aluminium extrusions. Due to the low distortion, these panels are very flat and have accurate dimensional tolerances.
The strength of friciton stir welds in artificially aged (T6) extrusions is higher than that of MIG welded extrusions, but ship building structures have to be designed with MIG welding values in mind, because this process is commonly used to attach the panels to the rest of the ship. As a consequence, the safety factor is higher than that of MIG welded panels.
Trendsetters were the Scandinavian aluminium extruders, who were in 1995 the first to apply the process commercially for the manufacture of hollow aluminium deep-freeze panels, and for ship decks and bulkheads. Friction stir welded structures are now revolutionising the way in which high-speed ferries, hovercraft and cruise ships are built from prefabricated lightweight modules.
Four inshore patrol vessels (IPVs) of the Royal New Zealand Navy (RNZN) were built in Whangarei by BAE Systems Australia (formerly Tenix Shipbuilding). Their design is based on a modified search and rescue vessel for the Philippine Coast Guard, with a different superstructure design made from friction stir welded aluminium panels, which were made by Donovan Group as the first New Zealand based company to use the technique, which is credited as having won them the contract for this part of the vessel's construction.
All four vessels were named after New Zealand lakes, thus they are known as Lake-class, Rotoiti class or Protector class. Due to political changes and their limited suitability for the sort of seas around New Zealand, the have seen only limited service, and two of them (Rotoiti and Pukaki) were decommissioned on 17 October 2019.
China FSW Center designed and produced the first large FSW machine for wide ship-panels in China in 2006 after considering production, weight and transport aspects. The CFSWT machine can be used for batch production of wide stiffened panels, which are used in high-speed aluminium alloy ships. Since the introduction of FSW panels, a new era started for the Chinese aluminium shipbuilding industry. First of all, batch production of panels by FSW helps to resolve on-site welding problems significantly. This technology has also simplified the design of ships. And most importantly naval architects have now more options, when they design new structures regarding material selection.
The Type 022 Houbei Class is the Chinese People's Liberation Army's new-generation stealth missile fast attack craft (FAC). The boat features a unique high-speed, wave-piercing catamaran hull with evident radar cross-section reduction design features. The futuristic design of this vessel has been admired internationally.
A number of Chinese shipyards across the country have been involved in the construction of the boat and it has been reported that FSW aluminium alloy panels have been used to produce this very advanced navy vessel in China. This military stealth catamaran is believed to be equipped with 4 anti-ship missiles, 12 surface-to-air missiles and a 30mm gun. It has great stealth capability, and can move very quickly in various sea conditions.