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The feasibility of friction stir welding (FSW) of steel is demonstrated. Tensile and bend testing have confirmed that the mechanical properties of friction stir welded 12% chromium alloy and low carbon steel joints compare favourably with the properties of the parent metal. Some initial feasibility studies of FSW of both 12% chromium alloy and low carbon steel are described. Although more development work is needed, particularly to improve tool materials, the prognosis for continued developments in FSW of steel is shown to be good.

Friction stir welding (FSW) was invented by TWI in 1991 [1] and substantial development has been conducted subsequently. It allows metals, including aluminium, [2±12] lead, [13] magnesium, [14] steel, [15] titanium, [16] zinc, copper, [17] and metal matrix composites [18,19] to be welded continuously. Many alloys, which are regarded as difficult to weld by fusion processes, may be welded by FSW. The basic principle of the FSW process is shown in Figure 1.A non-consumable rotating tool is employed of various designs, which is manufactured from materials with superior high temperature properties to those of the materials to be joined. Essentially, the probe of the tool is applied to the abutting faces of the workpieces and rotated, thereby generating frictional heat, which creates a softened plasticized region (a third-body) around the immersed probe and at the interface between the shoulder of the tool and the workpiece. The shoulder provides additional frictional treatment to the workpiece, as well as preventing plasticized material from being expelled from the weld. The strength of the metal at the interface between the rotating tool and the workpiece falls to below the applied shear stress as the temperature rises, so that plasticized material is extruded from the leading side to the trailing side of the tool. The tool is then steadily moved along the joint line giving a continuous weld.Although incipient melting during welding has been reported for some materials, FSW can be regarded as a solid state, autogenous keyhole joining technique. The weld metal is thus free from defects typically found when fusion welding, e.g., porosity. Furthermore, and unlike fusion welding, no consumable filler material or profiled edge preparation is normally necessary.The process has already made a significant impact on the aluminium-producing and user industries worldwide and FSW is now a practical technique for welding aluminium rolled and extruded products, of thickness ranging from 0.5 to 75 mm. The present paper describes recent developments in FSW tool design, as this is the key to the successful application of the process.Tools and Techniques: Conventional Rotary Welds: Although FSW consistently gives high quality welds, proper use of the process and control of a number of parameters is needed to achieve this. A key factor in ensuring weld quality is the use of an appropriate tool and welding motion.The importance of the tool is illustrated in the following recent example involving the lap welding of 6 mm 5083-O, aluminium alloy wrought sheet. In preliminary trials a conventional cylindrical threaded pin probe tool was used which gave a good as-welded appearance. A typical pin type probe is shown in Figure 2.However, bend testing showed the weld to be weak due to excessive thinning of the top sheet and thickening of the bottom sheet caused by a pressure differential during welding (see Fig. 3).The failure followed the original interfacial surface oxide layers, which in 5083-O condition aluminium alloy, are known to be pa...

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Considering the stringent regulations, manufacturing of aircraft parts is often quite complex and time consuming. The multi-million components, multi-tier manufacturing systems and the severe constraints surrounding the sector lead to heavy inventory investments to achieve the just-in-time supply of parts often needed to reduce the airplane ground times. Additive manufacturing evolved allowing for the direct production of complex parts based on digital data with no complex tooling or machinery, a messiah of true just in time production. Appropriate integration of additive manufacturing with the aircraft industry could resolve some of the supply chain and inventory hurdles. Significant progress is already evident in these lines, but the lack of quality assurance attributes and certification standards is hampering the progress. The state-of-the-art of the application of additive manufacturing in the aircraft industry is reviewed in this paper. The supply chain configurations of the aircraft industry, the possible roles of additive manufacturing in relaxing the pressures in the system are evaluated. The application areas, enhanced attributes, and certification standards are critically reviewed and classified. The overall growth in the application of additive manufacturing in the aircraft industry, the main hurdles, and the future possibilities are evaluated and presented systematically, clearly portraying the developments.