Friction stir welding (FSW) was invented by Welding Research Institute (TWI) in 199 1 year. Since then, based on the obvious advantages of this solid-state connection technology, such as excellent joint strength, no need to fill welding materials, no welding smoke and splash, small pre-welding preparation and welding deformation, a lot of research and development work has been carried out in international cooperation. In addition, friction stir welding can also weld aluminum alloy materials, such as 2000 series, 5000 series and 7000 series high-strength aluminum alloys used in aviation and aerospace fields, and high-quality connections can also be obtained by using this advanced welding method. Dave NICHOLAS of the Welding Research Institute believes that friction stir welding is the most striking welding method since the advent of laser welding, and its appearance will revolutionize the joining technology of non-ferrous metals such as aluminum alloy.
In April, 2002, Beijing Institute of Aeronautical Manufacturing Engineering signed a formal contract with TWI on the patented technology of friction stir welding, and obtained the exclusive second-class license of the patented technology of friction stir welding, which opened the door to the research and development and large-scale industrial application of friction stir welding technology in China market.
Second, the application status of aluminum alloy friction stir welding
Friction stir welding technology has many unique advantages. For the connection of light alloy materials (such as aluminum, copper, magnesium, zinc, etc.), it has incomparable advantages in welding methods, mechanical properties and production efficiency. Friction stir welding (FSW) is a solid-state joining method. The welded joint has excellent mechanical properties and small welding deformation. There is no need to add shielding gas and welding wire in the welding process, and there is no melting, smoking, splashing and arc light. It is an environmentally friendly new connection technology. The same is true in practice. In just a few years after the advent of FSW technology, great progress has been made in welding mechanism, applicable materials, welding equipment and engineering application. Friction stir welding technology was originally mainly used to solve the welding of aluminum alloy, magnesium alloy and zinc alloy. The welding institute has done a lot of research on the characteristics and application of friction stir welding technology, and applied for worldwide patent protection for 1993 and 1995. At present, the institute mainly cooperates with manufacturers of welding equipment such as aviation, aerospace, ships, high-speed trains and automobiles and major international companies, and develops friction stir welding technology in the form of group sponsorship or cooperation (TWI's GSP project), and continuously expands its application scope.
At present, the research projects sponsored by industrial enterprises include: friction stir welding of thick aluminum alloy, friction stir welding of steel, friction stir welding of titanium alloy and friction stir welding of automobile light components. The Edison Welding Research Institute (EWI) in the United States cooperates closely with TWI and is also conducting research on FSW technology. Lockheed company of the United States. Martin Aerospace, Marshall Space Flight Center, American Naval Research Year, Dartmouth University in Germany, Stuttgart University, Adelaide University in Australia, and Australian Welding Research Institute have all made special studies on friction stir welding from different angles.
Application of 1 aluminum alloy friction stir welding in aerospace field With the further development of friction stir welding research, friction stir welding equipment has gradually moved from laboratory to commercial use. TWI used this technology to produce three 2000 series aluminum alloy space shuttle fuel tanks for Boeing. Lockheed company of the United States. Martin Company, Boeing-McDonnell Douglas Company, Rockville Group, Edison Welding Research Institute and many other institutions are currently committed to the research, application evaluation and development of friction stir welding. Structures suitable for FSW welding in aerospace field include: skin of military or civil aircraft, cryogenic fuel tank in spacecraft, aircraft fuel tank, auxiliary fuel tank of military aircraft, military or scientific and technological exploration rocket, etc. Lockheed company of the United States. Martin Aerospace used this technology to weld a cryogenic container for storing liquid oxygen outside the space shuttle. This technology is also used by Marshall Space Center to weld large cylindrical containers.
Boeing invested millions of dollars to manufacture a large special friction stir welding machine for the large cryogenic fuel container of Delta launch vehicle. BAE Airbus is verifying the method, performance and feasibility of FSW technology in order to produce medium and large commercial passenger aircraft. The friction stir welding machine used is produced by GRAWFORD-SWIFT Company in Helivax, and it is said to be a power welding machine in Europe. ECLIPSE Airlines will use FSW to build a medium-sized aircraft, with a length of 10.86 m and a wingspan of11.88m. The company estimates that FSW can reduce the assembly time of stiffeners and frames on the fuselage wall by 80% and the aircraft cost to 837,000 US dollars. The main structural parts and skin of this aircraft are all manufactured by the latest international connection technology-friction stir welding technology, and the fuselage of passenger aircraft is basically manufactured by friction stir welding, including the assembly of aircraft skin, wing ribs, chord brackets, aircraft floor and structural parts.
The application of friction stir welding is mainly used to improve production efficiency and reduce manufacturing cost. Friction stir welding technology of aviation structural parts was jointly developed by TWI and ALCOA, and applied to the welding of ECLIPSE500 aircraft structural parts. In September 2000, the company passed the preliminary design review and certification of the Aircraft Safety Committee, and in June 20001year, the feasibility of friction stir welding aircraft manufacturing was determined. In June, 20001year, the company began to manufacture friction stir welding aircraft structural parts, and made its first flight in June, 2002. At present, hundreds of customers have rushed to order this new type of aircraft.
2 Application of Friction Stir Welding of Aluminum Alloy in Shipbuilding At present, friction stir welding has been deeply studied and developed in shipbuilding field because of its great advantages in welding methods, mechanical properties, manufacturing cost, environment and potential industrial application prospects. Shipbuilding requires not only the improvement of speed, but also the improvement of unit load performance, so shipbuilding should use aluminum alloy materials as much as possible to reduce the weight of the ship. The traditional connection methods of aluminum alloy materials are rivet connection and arc welding connection. Riveting increases manufacturing time, manpower and material consumption, while aluminum alloy is prone to deformation, defects and smoke during fusion welding, which also limits the use of arc welding in aluminum alloy components. Therefore, with the development of friction stir welding technology, it is an inevitable and revolutionary progress in the development of shipbuilding technology to realize high-integration prefabricated modular manufacturing by friction stir welding instead of the traditional ship plate-stiffened plate structure.
The application of friction stir welding in prefabricated light alloy structural parts of ships has obvious advantages in appearance, weight, performance, cost and manufacturing time. It can be used not only for manufacturing light alloy structural parts of ships, but also for field assembly. It provides a new connection mode for modern shipbuilding, and informs friction stir welding to replace fusion welding to realize the manufacture of light alloy structural parts, which is another leap in the development of modern welding technology.
FSW technology has broad application prospects in shipbuilding, marine industry and aerospace industry. The structures suitable for welding by FSW technology include: customized welding of deck, wallboard and partition, welding of aluminum extrusion, welding of hull and reinforcement, welding of helicopter landing platform, etc. At present, this technology has been used to weld aluminum alloy structural parts with a top length of 20 m in speedboats, and the total weld length is over 500 km.
Third, the development trend of aluminum alloy friction stir welding
In China, Beijing Institute of Aeronautical Manufacturing Engineering and China Friction Stir Welding Center-TWI Friction Stir Welding Technology Cooperation Center in the UK have made great progress in research on basic methods of friction stir welding, research and development of materials application, design, manufacture and sales of friction stir welding equipment.
(1) At present, the center is carrying out comprehensive research and engineering research on friction stir welding in the manufacture of space rocket barrel, friction stir welding of aircraft frame, skin and structure, manufacturing of light alloy for ships, and rapid manufacturing of aluminum alloy profiles for high-speed trains. In addition, while undertaking national defense scientific research and assembly projects, it has also strengthened horizontal cooperation and technical cooperation with enterprises and universities.
(2) In terms of friction stir welding equipment manufacturing, six kinds of friction stir welding equipment in three categories were designed, and two special friction stir welding equipment were manufactured and delivered for Harbin Institute of Technology and East China Institute of Shipbuilding Technology in March 2003.
(3) In engineering application, aluminum alloy friction stir welding will be first applied to power transmission and transformation, high-speed trains, new generation fighters and new launch vehicles.
Fourth, conclusion.
Friction stir welding, as a new welding technology, will have a revolutionary impact on the connection and manufacture of light alloy materials such as aluminum alloy. Based on the breakthrough of this connection technology in welding mode, it is expected that friction stir welding technology will fundamentally change the design and manufacturing baseline of military and civilian products such as aircraft, rockets, high-speed trains, missile speedboats and all-aluminum chariots.