Aerospace Expertise
technology, according to many industry experts, has reached a developmental limit. As a result, both increases in productiv- ity and structural weight saving will be minimal. Fiber laser welding of joints has a speed advantage over the
riveting process. Average laser welding speeds are 6–8 m/min, depending on the laser power, compared to 200–400 mm/min for riveting. While joining parts on a fuselage shell can take five hours using current riveting processes, laser welding can join the same components in just thirty minutes. Laser weld- ing is readily applied to a wide range of joint designs, includ- ing those requiring simultaneous welding of two sections of a joint such as T-joints and butt joints.
Power Savings Another reason fiber laser beam welding is replacing CO2
Fiber laser welding aerospace components provides very high strength mating components at high production speed and with consistent quality.
Many of these alloys currently are welded using tungsten inert gas (TIG) and electron beam (EB), in addition to laser welding. Tese alloys pose several welding challenges from heat-affected zone cracking to porosity formation in the weld fusion zone. Laser welding using high-power fiber laser has been shown through extensive testing to eliminate cracking and porosity formation. Fiber laser welding has been demonstrated to join Inconel
718 components in exhaust frame subassemblies in aero- engine hot sections. Reduced cracking and porosity formation using fiber laser welding is a result of the lower heat input and distortion compared to arc welding methods. For joint penetration up to 8 mm, laser welding has an
added advantage over electron beam welding. Fiber laser welding occurs at atmospheric pressure with inert gas shield- ing to protect the metal in the weld pool and the heat affected zone from contamination during the welding process. By comparison, electron beam welding occurs in a vacuum with the associated cost and complexity. Fiber laser welding has the advantage of being flexible. Set-
up changes for different parts are easier and can be performed more quickly than for arc and electron beam welding. Also, a fiber laser system oſten can be used for cutting and/or drilling, frequently for the same part in the same setup.
Alternative to Mechanical Joining Riveting is a standard mechanical joining process in aero-
space manufacturing. Approximately one million rivets are used to join components in a typical aircraſt fuselage. Te riv- eting rate for components 10.5 × 3.5 × 1.75 m is 4.4 rivets per minute using the most advanced, automated technology. Tis
128 Aerospace & Defense Manufacturing 2014
and Nd:YAG lasers is that the quality of the fiber laser beam means that it can be focused to give higher power density than from other types of lasers. Tis reduces power require- ments and costs. Te laser beam can be focused to submil- limeter diameters, which in combination with multikilowatt laser beams, produces power densities in the range 103–107 W/cm2
at the workpiece. Te high power densities produce a
“keyhole” weld with low heat input and fast welding speeds. Tis leads to higher aspect (high depth to width) ratio welds in many metals and alloys such as stainless steels, nickel, tita- nium, and aluminum-based alloys. Fiber lasers also offer the potential to reduce manufac-
turing costs through reduced operating costs. With its 1µm wavelength, the fiber laser has an absorption rate in metals at room temperature that is seven times higher than for the 10.6 µm wavelength of a CO2
laser which contributes to higher
welding speeds. Fiber laser also has a distinct advantage over other laser
sources in terms of operating cost. Te reduced operating cost of fiber laser is also due to the high energy efficiency of the pump source and of extraction from the gain medium that leads to a wall plug efficiency for the fiber laser that is typically around 25–30%, compared to less than 12% for a CO2
laser. Te higher efficiency leads to lower electrical energy consumption, the major cost factor in any high power laser system. Te higher efficiency also contributes to a more compact laser head. Compared to other solid state lasers, fewer mechanical components are needed in the laser con- struction. Recent trends indicate that as pump laser diode prices continue to decrease with increasing manufacturing volumes, fiber laser system prices will continue to decrease as well.
Welding Capability of Common Aerospace Materials Commercial aircraſt are getting larger (850 seats) and
laser and a few percent for a flashlamp pumped Nd:YAG
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