摩擦攪拌焊接

Friction stir welding is a variant of friction welding that produces a weld between two (or more) workpieces by the heating and plastic material displacement caused by a rapidly rotating tool that traverses the weld joint. Heating is believed to be caused by both frictional rubbing between the tool and workpiece and by visco-plastic dissipation of the deforming material at high strain rates. Like conventional friction welding processes, the friction stir welding process is solid state in nature.

The process has been in existence since the early 1990s and was developed mainly for the welding of aluminum alloys. The significant benefits of this process were quickly recognized, motivating considerable research and development that expanded the technology to other materials during the next decade.

Friction stir welding has focused mainly on aerospace and marine applications, with a growing number of applications in the automotive, marine, and rail transportation industries. Some of the aerospace and aircraft projects include construction of the main fuel tank of the space shuttles, the booster core tanks of Delta rockets, floor decking for the C-17 Globemaster cargo aircraft and the fuselage and wing sections of the Eclipse 500 business-class jet. Marine and rail transportation applications include the welding of fast-ferry decking and sections of subway and rail cars.

Figure 1: Friction stir welding of 7?8-in.-thick 2014-T6 aluminum alloy panels for the booster core tank of a space launch vehicle. Source: BoeingThe first commercial application of friction stir welding was the joining of 65.6 ft aluminum sheets for the construction of fast ferries in Norway. In the United States, Boeing was the first to use the friction stir welding process, developing its own technology and standards and cooperating with government, university and industry resources to implement the construction of the Delta series of aerospace launch vehicles. The booster core of the Delta IV, or first-stage launch vehicle, includes a 44 ft high liquid oxygen tank, 28 ft high fuel tank, and 216 ft high inter-stage cylinder welded with friction stir welding.

Friction stir welding on a booster core tank of a space launch vehicle is shown in Figure 1. The tanks are formed using three sheets of 7?8 in thick 2014-T6 aluminum alloy.

Several aircraft builders use friction stir welding, including Airbus and Eclipse Aviation. Airbus used the friction stir process for its A350, A340-500 and A340-600 models. As shown in Figure 2, Eclipse Aviation utilized the process to attach the circumferential aluminum fuselage stiffeners and door doublers of its business-class jet.

Figure 2: Pictured is the Eclipse jet with circumferential aluminum fuselage stiffeners and door doublers that were attached with friction stir welding. Source: Eclipse Aviation

Automotive applications of friction stir welding include suspension components and auto body weldments. Friction stir welding is used for these weldments because it does not react adversely to the coating used for this type of assembly. For example, the Ford Motor Co. has used the process to weld the central tunnel assembly of several thousand Ford GT automobiles. Additionally, the Mazda Motor Corp. has utilized friction stir spot welding to manufacture the automobile doors (Figure 3).

Figure 3: Friction stir spot welds in an automobile door: A — Door structure spot welded for impact stability; B — construction detail of a spot-welded door. Source: Mazda Motor Corp.

This article was excerpted from the Welding Handbook, Ninth Edition, Volume 3, Welding Processes, Part 2.