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
© U.S. Navy photo by Jesse Praino
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.
The roots of the friction stir welded panels are clearly visible on USNS 'Yuma' (T-EPF-8)
The aluminium catamarans of the Spearhead-Class of the US Navy were initially called Joint High Speed Vessel (JHSV), because they were used by the Navy and the Army, but have subsequently been re-classed as Expeditionary Fast Transport (EPF).
The catamarans are assembled from friction stir welded aluminium panels using TIG and MIG processes at Austal USA in Mobile, Alabama. They are unpainted above the waterline, so that the roots and edges of the FSW panels are clearly visible. To prevent fouling, the hull is painted below the waterline.
USNS 'Spearhead' (T-EPF-1), USNS 'Choctaw County' (T-EPF-2) and USNS 'Fall River' (T-EPF-4)
FSWed deck of the interior of USNS 'Millinocket' (T-EPF-3)
"Click on the photo to enlarge"
Approximately 700 tonnes of aluminum are used as sheets, plates, extrusions and forgings in the Module Manufacturing Facility (MMF). They are subsequently assembled in the Final Assembly and and finally completed in the Vessel Completion Yard (VCY).
Friction stir welded panels in the bow section of the USNS 'Carson City' (T-EPF-7)
The aluminium caramarans are 103 m long and can transport 600 tonnes over 1,200 nautical miles at an average speed of 35 knots. Important technical data are as follows:
So far 12 of these ships have been built and are currently(2021) in active service. Two more have been ordered. Their names and numbers are as follows:
Friction stir welded USNS 'Newport' (T-EPF-12)
© Commander Naval Sea Systems Command/Austal USA
Guided missile cruiser 'USS Vicksburg' (CG 69)
© US Navy , Michael Sandberg, ID 041110-N-4374S-010
Concurrent Technology Corporation (CTC) developed a portable FSW machine to repair cracks or damage in aluminium vessels in-situ, i.e. on the spot, avoiding a time-consuming and therefore costly removal and replacement process.
Sensitisation in 5000-series aluminium alloys is a problem characterised by the gradual formation and growth of the beta phase Al2Mg3 at the grain boundaries, which increases the susceptibility of the alloys to intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC).
A CTC team repaired sensitised aluminium on the USS Vicksburg (CG 69) at BAE Systems in Norfolk, Virginia, in late 2020 or early 2021. They repaired a hole in a bulkhead using a portable friction
stir welding (PFSW) machine.
The on-site repair saved the US Navy about US$250,000 in two days. Normally, a hole in the superstructure is repaired by either removing the entire section of the bulkhead and replacing it with new aluminium material, or installing a temporary eight-layer fibreglass patch, which must then be repaired during a shipyard stay.
The cost of removing and replacing the entire section is between US$300,000 and US$500,000. In comparison, the successful PFSW and reverse sensitisation repair cost only US$22,000. This new repair approach is applicable in principle to all aluminium ships, with particular emphasis on the CG 47 (Ticonderoga-class) cruisers.
Concurrent Technology Corporation implemented the ASMC programme under the Ingalls Shipbuilding CG 47 Class Planning Yard contract, which supports the modernisation of the CG 47-class cruisers.
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.
Friction stir welded aluminium panels made by Norsk Hydro ASA in Norway
© Norsk Hydro ASA, CC BY-NC-SA 2.0
Hydro's FSW are very flat, have high strength and acccurate tolerances
© Norsk Hydro ASA, CC BY-NC-SA 2.0
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.
The module with the circular portholes below the chimney has been made using FSW panels in Haugesund, Norway
The strength of stir welds in artificially aged (T6) extrusions is higher than that of MIG-welded extrusions, but shipbuilding structures must be designed with MIG weld values in mind, as this process is commonly used to attach panels to the rest of the ship. As a result, the safety factor is higher than that of MIG-welded panels.
Friction stir welded aluminium modul of 'Finnmarken' at Marine Aluminium in Haugesund, Norway
© Marine Aluminium
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.
HMNZS Hawea (P 3571), HMNZS Pukaki (P 3568), HMNZS Rotoiti (P 3569) and HMNZS Taupo (P 3570)
© New Zealand Defence Force, CC BY 2.0
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.
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.
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. China FSW Center could produce up to 5 x 12 m large aluminium panels by friction stir welding at the time, when they were built.
In the second half of the 1990s, Kawasaki Heavy Industries (KHI) introduced the FSW technology invented at TWI to Japan and investigated its potential applications for its own products. After its own application studies, it was able to use friction stir welding as the first company in Japan with a maximum plate thickness of 50 mm for the double-sided construction of 5083 alloy for aluminium high-speed vessels and for the LNG tank, although the seawater-resistant 5083 alloy is more difficult to process with friction stir welding than the heat-treated 6000 series alloys used for rail vehicles.
Based on this development result, FSW was to be applied to the new construction of aluminium alloy ships, such as the ultra-high-speed passenger ship "Jet Foil" (「ジェットフォイル」) for the Kyushu region and the Izu Islands, and the ultra-high-speed car ferry "Jet Piercer" (「ジェットピアサー」). In addition, FSW has been widely used for the production of aluminium LNG tanks in the manufacture of KHI's liquefied natural gas tankers, which require a high level of safety.
In June 2002, KHI we signed an agreement to provide Mitsui Shipbuilding with some of the FSW know-how. KHI and Mitsui Zosen had previously entered into business alliances in the general merchant shipping sector, during which time they deepened cooperation in all areas such as design, production and procurement.
As a result, Mitsui Zosen started a technical study to apply FSW to the ultra-high-speed freighter "Techno Super Liner" (「テクノスーパーライナー」). The implementation of this plan, was the first holistic application of FSW for ships in Japan.
In addition to the thin sheet processing technology for aluminium alloys, which KHI had already owned since the beginning of the technology introduction through research and development, this technology licensing agreement was part of the development results of that time as well as the technology for the production of FSW machines and the manufacturing technology for medium-thickness plates.
KHI then continued to engage in research and development of design and manufacturing technologies for various vessels and was actively involved in the construction of various gas tankers and LNG carriers, for which there was an ever-increasing demand at the time, as gas is more environmentally friendly than oil and coal.
In this 3½ min video, Chris Moyle, Hydro's Marine & Offshore Market Manager, shows how versatile aluminium is, as its alloy composition can be changed to give it unique properties, be it more strength, better corrosion properties, better surface treatment.
Experts agree: The advantages of using aluminium in marine and offshore
3:25 © Norsk Hydro, 19. Juni 2019
Stefano Ferraris (Fincantieri Cantieri Navali Italiani S.p.A.,Italy) und Luis Mario Volpone (Istituto Italiano della Saldatura, Genoa,
Italy): Aluminium Alloys in Third Millennium Shipbuilding: Materials, Technologies,
Perspectives. The Fifth International Forum on Aluminum Ships Tokyo, Japan 11.-13. Oktober 2005.