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car
$2/lb
airliner
$200/lb
commercial,
military jets
$2,000/lb
rockets
$20,000/lb
Figure 6
Money savings per pound of lighter structure
The Airbus A380 is expected to be 10 to 15 tons lighter than the Boeing 747, implying fuel savings
of the order of $5 million over the lifetime of the aircraft. Laser welding is one of the new
techniques employed towards reaching this goal.
The use of FSW in the new Eclipse 500 commercial jet[6] saves an estimated 50 pounds, which
translate into an increase in range of operation of approximately 4%. Considering that the fuel
consumption rate of this airplane is $89 per hour, the savings per pound related to welding are
approximately $7,000 over 100,000 hours, in the same order of magnitude as military aircraft.
The use of aluminum-lithium alloys reduced 7,500 lb of the weight of the external tank of the Space
Shuttle. At $10,000 savings per pound, this represents savings of $75 million per launch in terms of
"New Trends in Welding in the Aeronautic Industry," P.F. Mendez and T.W. Eagar,
2nd Conference of New Manufacturing Trends, Bilboa, Spain, November 19 - 20, 2002.
5
increased payload capacity. Variable polarity plasma arc welding (VPPA) was developed to weld
this difficult-to-weld alloy. This process is now slated to be replaced by FSW.
While light weight is important for anything that moves, the faster the object moves, the greater is
the value of weight saved. In an aircraft, a pound of weight saved on a disk of a turbine engine can
be worth ten times the same weight saved on the fuselage. This is because a pound saved on the
engine can save 5 to 10 pounds on the wing structure. There is often a multiplier effect for rapidly
moving parts within the overall structure. This is the driving force behind the manufacture of
bladed disks or “blisks.” In a conventional turbine stage the blades are mechanically attached to a
hub. This attachment involves interlocking parts that add significantly to the total weight of the
rotating part. In a blisk, the blades and the hub are a single piece; the interlocking mechanism is
eliminated with significant weight savings. Linear friction welding and diffusion bonding are key
enabling technologies to manufacture blisks. The F119 (the engine used in the F-22) is believed to
contain blisks manufactured with this technique.
The material cost is a relatively small fraction of the fabricated cost, around 10% in the aeronautic
sector. Combining the materials costs with the value of a pound saved gives us the maximum
average cost of the material in a particular application. For example, for a commercial aircraft
where the value of a pound saved is $200, this figure times a 10% material cost as a fraction of the
total cost provides an upper limit (on average) of $20 per pound for the primary structural material.
Aluminum sheet is $1.50 per pound, while titanium sheet is $40. These figures indicate that
aluminum is a relatively inexpensive material for the aeronautic industry, while titanium is only
affordable for military applications or critical commercial structures. The different choice of
structural materials has an impact on the choice of welding processes. Since titanium must be
welded in vacuum, electron beam welding is the welding process of choice. Shielding gases are
adequate protection for aluminum; therefore, laser welding is the current choice of Airbus for
welding aluminum alloys. While FSW is replacing laser welding in aluminum, it is going to take
longer for it to replace EBW in titanium, a stronger metal. There is an important incentive for FSW
of titanium: since no melting is involved, it can be performed in the atmosphere, with the
consequent savings and freedom from the size restrictions imposed by vacuum chambers.
Economic trends in the U.S.
The American Welding Society and the Edison Welding Institute commissioned a report on
welding expenditures, investments, and productivity[7]. The following is a short analysis of the
data presented in that report.
The aeronautic/aerospace industry is relatively small compared to other industries such as
automotive, electronics, or construction. Revenues generated by the aerospace sector are only 1.5%
of the GDP, the lowest of all industries. The automotive sector is about four times larger, at 6%.
The GDP of the U.S. is about $10 trillion.
Total welding expenditures in the U.S. are around $30 billion, with only 1% related to the aerospace
sector. Welding accounts for 0.27% of the cost of production in aerospace, the lowest for all
industries, which have an average of 1.4%. This small incidence of welding in manufacturing costs
is probably related to the scarcity of welding in airplanes. The reason welding is scarce in airplanes
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