Welding Technology Fundamentals, 4th Edition Page 357 (357 of 463)

357
Chapter 29 Special Welding and Cutting Processes
Figure 29-12 shows a schematic of an ultrasonic
weld in process. The parts to be joined are placed
between two tips, as in resistance spot welding. An
electronic device called an ultrasonic transducer causes
either a wedge-reed or a lateral drive to vibrate
extremely fast. This, in turn, causes a sonotrode
(sound electrode) to vibrate. A slight force is applied
to the parts through the sonotrode. The vibrations
break up surface films, causing the parts to bond
together without heat. An ultrasonic weld is completed
faster than a resistance spot weld. Ultrasonic welds
can be made on similar or dissimilar metals.
Other Welding Processes
Other welding processes are those that do not
meet the definition of arc welding, oxyfuel gas welding,
resistance welding, or solid state welding. These other
welding processes are listed in Figure 2-6, Master
Chart of Welding, Joining, and Allied Processes. The most
common of these processes will be explained in the
following pages.
Laser Beam Welding (LBW)
A laser creates a beam of light with a high energy
density. This light energy is emitted from the laser
beam welding (LBW) machine as energy particles
called photons. The photons produce heat by striking,
and having their energy absorbed by, the base metal.
The most popular lasers include the Nd:YAG
(neodymium-doped yttrium aluminum garnet) crystal
laser and the CO2 gas laser. A schematic view of a CO2
laser is shown in Figure 29-13. Electrical energy is
Clamping
force
Reed
Sonotrode
tip
Anvil
Weldment
Vibration
Wedge
Ultrasonic
transducer
Figure 29-12. A schematic drawing of the wedge-reed ultra-
sonic welding principle. A small spot weld is made by vibrating
the reed while it is in contact with the base metal. (Sonobond
Ultrasonics, Inc.)
Full
reflecting
mirror
Partially
reflecting
mirror
Shutter
Laser
beam
Lens
Weld
Workpiece
Electrodes
Turning
mirrors
CO2 laser tube
Figure 29-13. A carbon dioxide (CO2) laser welding machine.
Mirrors reflect and aim the laser beam and a lens focuses it.
The beam is released to make the weld when the shutter opens.
A
B
Figure 29-11. A—A rapidly rotating tool with a large shoulder
and a probe to penetrate the parts being welded softens the base
metal. The base metals are welded together by stirring and
mixing. B—A completed friction stir weld is shown. (TWI)

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357
Chapter 29 Special Welding and Cutting Processes
Figure 29-12 shows a schematic of an ultrasonic
weld in process. The parts to be joined are placed
between two tips, as in resistance spot welding. An
electronic device called an ultrasonic transducer causes
either a wedge-reed or a lateral drive to vibrate
extremely fast. This, in turn, causes a sonotrode
(sound electrode) to vibrate. A slight force is applied
to the parts through the sonotrode. The vibrations
break up surface films, causing the parts to bond
together without heat. An ultrasonic weld is completed
faster than a resistance spot weld. Ultrasonic welds
can be made on similar or dissimilar metals.
Other Welding Processes
Other welding processes are those that do not
meet the definition of arc welding, oxyfuel gas welding,
resistance welding, or solid state welding. These other
welding processes are listed in Figure 2-6, Master
Chart of Welding, Joining, and Allied Processes. The most
common of these processes will be explained in the
following pages.
Laser Beam Welding (LBW)
A laser creates a beam of light with a high energy
density. This light energy is emitted from the laser
beam welding (LBW) machine as energy particles
called photons. The photons produce heat by striking,
and having their energy absorbed by, the base metal.
The most popular lasers include the Nd:YAG
(neodymium-doped yttrium aluminum garnet) crystal
laser and the CO2 gas laser. A schematic view of a CO2
laser is shown in Figure 29-13. Electrical energy is
Clamping
force
Reed
Sonotrode
tip
Anvil
Weldment
Vibration
Wedge
Ultrasonic
transducer
Figure 29-12. A schematic drawing of the wedge-reed ultra-
sonic welding principle. A small spot weld is made by vibrating
the reed while it is in contact with the base metal. (Sonobond
Ultrasonics, Inc.)
Full
reflecting
mirror
Partially
reflecting
mirror
Shutter
Laser
beam
Lens
Weld
Workpiece
Electrodes
Turning
mirrors
CO2 laser tube
Figure 29-13. A carbon dioxide (CO2) laser welding machine.
Mirrors reflect and aim the laser beam and a lens focuses it.
The beam is released to make the weld when the shutter opens.
A
B
Figure 29-11. A—A rapidly rotating tool with a large shoulder
and a probe to penetrate the parts being welded softens the base
metal. The base metals are welded together by stirring and
mixing. B—A completed friction stir weld is shown. (TWI)

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Solid-State Welding Processes
The American Welding Society lists nine processes
and four subprocesses in the solid-state welding
group. Refer to Figure 2-6. Solid-state welding (SSW)
may be defined as a group of welding processes that
produce a fusion weld by application of pressure at a
welding temperature below the melting temperature
of the base metal and filler metal. Solid-state welding
may be done cold, warm, or hot, but never above the
melting temperature of the base or filler metal. The
following sections describe some of the more common
solid-state welding processes.
Friction Welding (FRW)
When two objects are rubbed together, they gen-
erate heat. This principle is the basis of friction
welding (FRW). Figure 29-10 shows the steps in a fric-
tion weld. One part is held stationary, while the other
part is held in a chuck and rotated rapidly. The parts
are pressed tightly together. Friction heats the two
parts to their welding temperature. The welding tem-
perature is lower than the solidus of either part, but
high enough to allow fusion under pressure. When
the welding temperature is reached, the rotation is
stopped. The parts are then suddenly forced together
under heavy pressure. After the heavy pressure is
applied, the parts are held firmly until they cool. The
finished weld is strong, with complete fusion over
the entire joining surface. As shown in Figure 29-10,
the weld is upset (enlarged) where the parts meet.
Friction welds are often produced in less than
15 seconds. Friction welding has been used successfully
to join some dissimilar (unlike) metals that normally
cannot be welded by other processes.
Friction Stir Welding (FSW)
Friction stir welding (FSW) is similar to friction
welding except a rotating tool, not a rotating part,
creates the heat. This welding process was developed
at TWI, Cambridge UK in 1991.
A special rotating tool, firmly pressing on the
parts to be welded develops heat. The rotating tool
has a wide shoulder and a probe or pin that pene-
trates the parts along the weld joint. Friction created
by the rapidly rotating tool softens the base metals
and the base metals are mixed together. Full penetra-
tion welds can be made. Figure 29-11 shows a draw-
ing of the process and a completed butt weld.
Ultrasonic Welding (USW)
Sound waves can cause vibrations in objects. For
example, a loud stereo can make the walls vibrate. In
ultrasonic welding (USW), a very high-pitched sound is
used to vibrate the surfaces of the metals to be welded.
Ultrasonic welding has many advantages. Since
there is literally no heat, there is no metal distortion.
Fluxes and filler metal are not needed. Very thin metals
can be joined easily. Ultrasonic welds are normally
small welds like resistance spot welds. Seam welds
can also be made.
Welding Technology Fundamentals
356
Figure 29-9. Underwater welding electrode holder. Note that
the holder is well insulated, with no bare metal areas exposed.
(Broco, Inc.)
Figure 29-10. The steps in making a friction weld on two pieces
of 1″ (25.4 mm) diameter carbon steel. The rod at the left
is spun at a high speed. The rod at the right is then forced against
it. Friction creates enough heat to produce a strong weld.

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generally used to excite the lasing material in the laser
source, releasing photons. Photon energy is allowed to
build up in the laser or laser welding machine until the
desired level is reached. The energy is then released to
fuse the weld joint.
Fusion occurs at the point where the laser beam
strikes the weldment. Laser beams may be continuous
or pulsed. They can be focused with lenses to a very
small and accurate beam. Their direction can be
changed through the use of mirrors.
Electron Beam Welding (EBW)
Figure 29-14 shows the basic parts of an electron
beam welding (EBW) machine. Electrons are emitted
from the electron gun. They are then focused and
directed at the weld joint. The kinetic energy of the
electrons creates the heat for welding. Kinetic energy
is the energy of an object in motion. In this case, the
objects in motion are the electrons.
Electron beam welding may be done in a high vac-
uum, a partial vacuum, or under normal atmosphere
pressure. A vacuum is a condition in which atmos-
pheric pressure in a closed vessel has been decreased.
This is done by pumping out air. Figure 29-15 shows
an electron beam welder in use in industry. The
beam energy is easier to direct under high vacuum
conditions. Also, less energy is lost in a vacuum.
Advantages of Laser and Electron
Beam Welding
Laser and electron beam welding machines are
made in a variety of energy levels. The greater the elec-
trical energy input, the greater the energy output.
Nd:YAG lasers are produced in sizes from 100W–4000W
(watts). CO2 lasers are produced in sizes from
500W–25,000W. A 600W Nd:YAG laser will penetrate
steel .01″ (2.5 mm) in thickness.
Electron beam welding machines are produced in
sizes from 1kW–100kW (kilowatts). A 100kW EB
welding machine will produce 100% penetration on
steel 10″ (254 mm) thick. See Figure 29-16. Laser beam
and electron beam welding offer these advantages:
Welding Technology Fundamentals
358
Base metal Weld joint
High vacuum
Upper
column
Electron
gun
Column
valve
Optics
Magnetic lens
Deflection coil
Vacuum
chamber
3″
75 mm
Figure 29-14. The basic parts of an electron beam welding
machine shown in schematic form. Note that, in this machine,
the weldment is mounted in a vacuum chamber. (PTR-Precision
Technologies, Inc.)
Figure 29-15. This electron beam welding machine comes with
an optical viewing system, video, wire feed, vacuum chamber,
and CNC technology. (PTR-Precision Technologies, Inc.)
Figure 29-16. A cross section of an electron beam weld. Notice
how thin the weld is in relation to the metal thickness.
(PTR-Precision Technologies, Inc.)

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Page 12Section 1 Introduction to Welding click to expand contents

Page 50Section 2 Shielded Metal Arc Welding click to expand contents

Page 114Section 3 Gas Metal Arc Welding click to expand contents

Page 162Section 4 Gas Tungsten Arc Welding click to expand contents

Page 210Section 5 Plasma Arc Cutting click to expand contents

Page 224Section 6 Oxyfuel Gas Processes click to expand contents

Page 328Section 7 Resistance Welding click to expand contents

Page 350Section 8 Special Processes click to expand contents

Page 394Section 9 Technical Information click to expand contents

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