Fig. 4.36. Gas Metal Arc Welding (GMAW) Schematic and clean welds since the welding is conducted in a vacuum chamber. The biggest disadvantage of EB is the high capital equipment cost. EB welding has been successfully used on two major fighter programs to make large unitized structures. In the late 1960s, Grumman Aerospace used EB welding on the F-14 aircraft to weld the folding wingbox. Since computer controls were not available at that time, almost every weld was made through constant thickness material with the beam perpendicular to the surface. In addition, a separate set-up was required for almost every weld. Nevertheless, Grumman successfully delivered over 700 production units. More recently, Boeing is using EB welding extensively on the aft fuselage of the F-22 aircraft. The four major assemblies being welded are the aft and forward booms (two each), which are fabricated from beta annealed Ti-6-4. This amounts to over 3000 linear inches of weldment which requires many less set-ups due to improvements in computer controls.31 Weld thickness ranges from 1/4 in. to slightly more than 1 in. Gun-to-work distances vary from 10 to 25 in. with beam swings of more than 130°.32 Both of these applications avoided the costly and error-prone process of installing thousands of mechanical fasteners.
Laser beam (LB) welding uses a high intensity coherent beam of light, which, like EB, results in a very narrow HAZ. However, LB welding is limited to sheet and plate up to about 0.50 in. One big advantage of LB is that it can be conducted in the open atmosphere with appropriate shielding while EB requires a vacuum chamber.
Titanium alloys can be readily resistance welded using both spot and seam welding. As with all titanium welding, cleanliness of the material to be welded is mandatory. Due to the rapid thermal cycles experienced with resistance welding, inert gas shielding is not required.
Diffusion bonding is a solid state joining process that relies on the simultaneous application of heat and pressure to facilitate a bond that can be as strong as the parent metal. DB, as shown in Fig. 4.37, occurs in four steps: (1) development of intimate physical contact through the deformation of surface t t
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