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1
Introduction
In our previous paper at this conference[1], we focused on welding fundamentals and the trends in
the aerospace industry that can be expected from progress at a fundamental level. We ranked the
welding processes by the intensity of the heat (Figure 1). This ordering revealed many important
trends. In this paper, we introduce cost as a driving force behind new welding processes.
102 103 104 105 106 107
Air/fuel gas flame
Electroslag, oxyacetylene
flame, thermite
Friction
Arc welding
Resistance welding
Oxygen cutting
Plasma Arc Welding
Electron beam
Laser beam
W/m2
practical range for welding
d/w
efficiency
HAZ size
interaction
max speed
cost
-
%
cm
s
cm/s
$
.2
1
1-10
10-100
0.1
103
10
99
.01-.1
10-4 - 10-3
1000
106
0.1-1
104
Figure 1
Welding processes ranked according to heat source intensity[2].
Welding fundamentals
For fusion welding, the ratio of depth to width of the weld increases dramatically with the intensity
of the heat source, making the welding process faster, more efficient, and stronger, as indicated in
Figure 2. A smaller heat source moving at a faster speed also implies a much reduced dwell time at
any particular point. High intensity processes, such as laser and electron beam welding, have a
dwell time smaller than the human time of reaction (approximately 0.3 seconds) and require
automation, as shown in Figure 3. Concentrated heat sources create a smaller heat affected zone
with lower post-weld distortions, as indicated in Figure 4. The benefits brought by a more
concentrated heat source come at a price: the capital cost of the equipment is roughly proportional
to the intensity of the heat source as can be deduced from Figure 5.
"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.
2
Figure 2
Relation between effective heat input and weld strength for fusion welding[3]
human response time
manual processes automatic processes
Figure 3
Maximum weld travel velocity, heat source spot, and interaction time as a function of intensity of
the heat source[2].
"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.
3
Figure 4
Cross sections of welds performed with electron beam (left) and GTA (right). The higher heat
intensity of the electron beam creates a much smaller fusion zone and HAZ[4].
In solid-state joining processes such as FSW, there is no melting and solidification of the metal,
thus the geometry and properties of the weld are determined by the tool used, not by heat transfer
considerations as in fusion welding. This sets these processes apart from fusion welding processes.
Considering that Eclipse Aviation spent one million dollars on a FSW gantry with welding speeds
of about 1 cm/s, Figure 5 shows that capital investment for FSW is much higher than that for
traditional welding processes.
Friction
stir
Figure 5
Capital cost of welding equipment as a function of productivity[2].
The nature of welding in the aeronautical industry is characterized by low unit production, high unit
cost, extreme reliability, and severe operating conditions[5]. These characteristics point towards the
more expensive processes such as FSW, plasma arc, laser beam and electron beam welding as the
processes of choice for welding of critical comp
onents.
4
Money and weight savings drive innovative welding processes
The main force for the use of welding in aeronautical components is weight savings, which translate
directly into better economics. The faster a vehicle moves, the bigger the potential savings by
reducing weight. Figure 6 shows the potential savings obtained by removing a pound from moving
vehicles. This table considers the savings in fuel at one to two dollars per gallon over the 100,000-
mile life of a car. For a commercial aircraft the fuel savings are estimated over the 100,000-hour
life of a fuselage. For spacecraft, the cost per pound of payload in orbit is $20,000. For the
reusable Space Shuttle, the cost drops to around $10,000 per pound, still far from the goal of $1,000
per pound for single stage to orbit vehicles such as the cancelled X-33 space plane.
1
10
100
1000
10000
100000
10 100 1000 10000 100000
Velocity [km/h]
Savings per pound lighter [$/lb]
　
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