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EML 2322L -- MAE Design and Manufacturing Laboratory

Welding

Intro to Welding
• A weld is made when separate pieces of material to be joined combine and form
one piece when heated to a temperature high enough to cause softening or
melting
...

• Welding is a dependable, efficient and economic method for permanently
joining similar metals
...

• Welding is used extensively in all sectors or manufacturing, from earth moving
equipment to the aerospace industry
...
These
processes differ greatly in the manner in which heat and pressure (when used)
are applied, and in the type of equipment used
...

• The most popular processes are shielded metal arc welding (SMAW), gas metal
arc welding (GMAW) and gas tungsten arc welding (GTAW)
...
The filler wire is then either
added automatically (GMAW) or manually (SMAW & GTAW) and the molten
pool is allowed to cool
...


Shielded Metal Arc Welding (SMAW)

Shielded Metal Arc Welding (SMAW)
SMAW is a welding process that uses a flux covered metal electrode to carry an
electrical current
...
The electric arc creates enough heat to melt both the
electrode and the base material(s)
...
As the arc
moves away, the mixture of molten metals solidifies and becomes one piece
...
Due to the
appearance of the electrodes, SMAW is commonly known as ‘stick’ welding
...
Moderate
quality welds can be made at low speed with good uniformity
...
Both the
equipment and electrodes are low in cost and very simple
...
It is a very portable process because all that’s required is a portable
power supply (i
...
generator)
...

Some of the biggest drawbacks to SMAW are (1) that it produces a lot of smoke &
sparks, (2) there is a lot of post-weld cleanup needed if the welded areas are to look
presentable, (3) it is a fairly slow welding process and (4) it requires a lot of
operator skill to produce consistent quality welds
...
Under the correct
conditions, the wire is fed at a constant rate to the arc, matching the rate at which
the arc melts it
...
Since molten metal is sensitive to oxygen in the air, good
shielding with oxygen-free gases is required
...
Consequently, GMAW
is commonly known as MIG (metal inert gas) welding
...
The filler material is usually the same
composition (or alloy) as the base metal
...
This process is easily used for welding
on thin-gauge metal as well as on heavy plate
...
It also requires a lower level of operator skill than the other two methods
of electric arc welding discussed in these notes
...


Gas Metal Arc Welding (GMAW) Photo

Gas Tungsten Arc Welding (GTAW)

Gas Tungsten Arc Welding (GTAW)
In the GTAW process, an arc is established between a tungsten electrode and the base
metal(s)
...
The filler metal is thin
wire that’s fed manually into the pool where it melts
...
The same inert gas
provides a stable, inert environment to protect the weld pool as it solidifies
...

Because fluxes are not used (like SMAW), the welds produced are sound, free of
contaminants and slags, and as corrosion-resistant as the parent metal
...
The arc temperature is typically around
11,000° F
...
As with
GMAW, the filler material usually is the same composition as the base metal
...
Virtually any metal that is
conductive lends itself to being welded using GTAW
...
This method produces the finest, strongest
welds out of all the welding processes
...


Gas Tungsten Arc Welding (GTAW) Photo

Selection of the welding process
The selection of the joining process for a particular job depends upon many
factors
...
A few of the factors that must be considered when
choosing a welding process are:
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•
•
•
•
•
•
•
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Availability of equipment
Repetitiveness of the operation
Quality requirements (base metal penetration, consistency, etc
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The following
figure shows the ideographs used most commonly

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