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Training Objective Welding
Fundamental Manufacturing Processes Video Series Study Guide
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Training Objective
After watching this video and reviewing the printed material, the
student/trainee will gain a knowledge and understanding of the role of
various welding processes used in industry today.
A guide to process selection is presented
Fusion welding methods are explained
Solid state welding methods are detailed
The operative aspects of the processes and their applications are given.
Welding Processes
The selection of a specific welding process is dependent upon many factors.
The geometric shape of the weldment itself is the result of joint designs
which, in several forms, is central to the issue of process applicability.
Additionally, alloys to be welded, size and thickness, costs, portability,
and skills needed, are among the many important weld process characteristics
to be considered.
The two basic forms of joining, or the coalescing of metals, are by fusion
and solid state welding. The principle fusion welding processes include:
arc welding
resistance welding
laser beam welding
electron beam welding
Common to these methods is the melting of the base metal and, though not
always, the addition of a filler metal.
Electric arc welding, in general, will use a consumable electrode to create
the arc and then as melting occurs, the rod itself becomes part of the fused
joint. Some arc welding methods use a tungsten electrode which is non-
consumable and if a filler metal is required, it is added separately as a
bare wire. The major arc welding processes are:
shielded metal arc welding
submerged arc welding
gas metal arc welding
flux-cored arc welding
gas tungsten arc welding
plasma arc welding
Shielded metal arc welding uses a flux covered consumable electrode which in
the heat of the arc forms a gaseous shield to protect the weld puddle from
the atmosphere. Welding current is either AC or DC and the process is used
primarily on the ferrous metals.
Submerged arc welding is a semi or fully automatic process in which the arc
takes place under or submerged in a blanket of granular flux. Equipment
includes weld wire feeding devices and joint-tracking mechanisms which move
either the welding head or the work. Welding
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Gas metal arc welding uses a bare wire fed through a manually manipulated gun
or torch. Weld shielding is obtained from a flow of inert gas, usually argon
or argon mixtures. Weld characteristics are largely determined by the actual
mode of metal transfer across the arc. The three basic modes are short
circuiting, spray transfer, and globular transfer.
Flux-cored arc welding is essentially a variation of the gas metal arc
welding process. The principle difference is in the use of weld wire that
is tubular and contains within its core a granulated flux.
Gas tungsten arc welding uses a non-consumable tungsten electrode along with
argon, helium, or mixtures of the two to shield the weld. Weld filler rod is
usually manually added and depending on the type of metal being welded will
use either AC or DC straight polarity current.
Plasma arc welding utilizes a constricted arc made up of a high velocity
stream of ionized gas or plasma. Additionally, there is a separate shielding
gas of argon or argon mixtures used. The plasma arc process affords very deep
penetration at higher welding speeds.
Resistance welding includes the spot, seam, and projection welding processes.
Spot welding occurs when the work is squeezed between two copper electrodes
which have an electric current flowing between them. In seam welding, the
electrodes are in the form of opposing wheels which effect a continuous fused
joint or seam. In projection welding, fusion occurs at predetermined
locations characterized by embossments, projections, or joint intersections.
Most resistance welding methods are semi-automatic and manually operated or
may be fully automatic.
Laser beam welding uses a focused beam of light as a heat source. The two
most common types are the gas or CO
2
laser and the solid state or YAG
laser. The more powerful gas laser can weld thick as well as very thin
workpieces, while the solid state laser is used only for the thinner work.
Laser welding is particularly useful in joining dissimilar metals and in
welding the refractory metals. Welding may take place in a high or partial
vacuum or at atmospheric pressures.
Solid State Welding
The two most used solid state welding processes are friction welding and
ultrasonic welding. Friction welding is accomplished by the action of
friction and axial force. Usually appearing as either butt or T-joints, one
rapidly rotating member is brought into contact with a stationary member.
When, through friction, the proper surface temperature is reached, an
upsetting action or motion completes the weld. Friction welding is used to
join many combinations of metallic and non-metallic materials.
Ultrasonic welding occurs when two pieces, in a lap joint configuration, are
subjected to a high frequency vibratory energy with the same amount of force
or pressure. There is relatively little heat generated by the process. The
workpieces are clamped between two welding tips called sonotrodes. Vibrating
energy passes through one or both which oscillate laterally as a
perpendicular force maintains contact between the work surfaces. Such
interfacing generates temperatures reaching only 35 to 50 percent of the
workpieces melting temperature. Basic equipment includes a power supply and
a frequency generator which increase line frequency to generally 15,000 to Welding
Fundamental Manufacturing Processes Video Series Study Guide
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75,000 hertz. There are also transducers that convert that power to an
acoustical power of the same frequency.
Ultrasonic welding usually requires that one of the workpieces be thinner
than its mating piece. The usual weld joints are spot or straight and
circular seams. Metals welded are commonly the more ductile types, either
similar or dissimilar. The principle users of the process are the electrical
and electronic industries. Welding
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Review Questions
1.
Weld process applicability is most dependent upon:
a. portability
b. size
c. cost
d. joint design
2.
A consumable electrode is one which:
a. is replaceable
b. becomes part of the weld
c. generates a shield
d. is made of tungsten
3.
Submerged arc welding takes place:
a. underwater
b. in a cloud of gas
c. between work surfaces
d. under a blanket of granular flux
4.
A principle shielding gas is:
a. oxygen
b. helium
c. nitrogen
d. argon
5.
Plasma arc welding requires:
a. consumable electrode
b. a separate gas shielding system
c. AC current
d. slower welding speeds
6.
Resistance welding is:
a. non-fusing or melting
b. suitable for non-ferrous metals only
c. uses copper electrodes
d. requires full automation
7.
Laser beam welding usually takes place in:
a. a high vacuum
b. a partial vacuum
c. the atmosphere
d. all of the above
8.
Friction welding joints are:
a. usually lap joints
b. butt or T-joints
c. always T-joints
d. applicable to any joint type
9.
Ultrasonic welding uses:
a. high frequency energy
b. intense heat
c. high compression forces
d. radiation Welding
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10.
Ultrasonic welding usually requires:
a. workpieces of equal thickness
b. workpieces of unequal thickness
c. very thin workpieces
d. very thick workpieces Welding
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Answer Key
1.

d
2.

b
3.

d
4.

d
5.

b
6.

c
7.

d
8.

b
9.

a
10.

b