Transcript MIG Welding

MIG Welding
Manufacturing and Materials Processes
(GMAW) MIG Welding
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Gas Metal Arc Welding (GMAW) is frequently
referred to as MIG welding.
MIG welding is a commonly used high
deposition rate welding process.
Wire is continuously fed from a spool.
MIG welding is therefore referred to as a
semiautomatic welding process.
MIG Welding Benefits
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All position capability
Higher deposition rates than SMAW
Less operator skill required
Long welds can be made without starts and
stops
Minimal post weld cleaning is required
MIG Welding Shielding Gas
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The shielding gas, forms the arc plasma,
stabilizes the arc on the metal being welded,
shields the arc and molten weld pool, and allows
smooth transfer of metal from the weld wire to
the molten weld pool.
The primary shielding gasses used
are:
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Argon
Argon – 95% to 5% Oxygen
Argon – 75% to 25% CO2
Argon/Helium
CO2 is also used in its pure form in some MIG
welding processes. However, in some
applications the presence of CO2 in the
shielding gas may adversely affect the
mechanical properties of the weld.
Welding Parameters and Techniques
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Welding current
Wire electrode extension
Welding voltage
Arc travel speed
WELDING CURRENT
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The welding current is the electrical amperage in
the power system as the weld is being made.
welding current is directly related to wire- feed
speed (if the wire extension beyond the guide
tip is constant). As the wire-feed speed is varied,
the welding current will vary in the same
direction. In other words, an increase (or
decrease) in the wire-feed speed will cause an
increase (or decrease) of the current.
WIRE ELECTRODE EXTENSION
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Wire extension or ”stick-out” is the distance
between the last point of electrical contact,
usually the end of the contact tip, and the end
of the wire electrode.
WIRE ELECTRODE EXTENSION
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Controlling tip-to-work distance is important.
Long extensions result in excess weld metal
being deposited with low arc heat. This can
cause poor bead shape and low penetration. In
addition, as the tip-to-work distance increases,
the arc becomes less stable.
WELDING VOLTAGE
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voltage setting directly controls the arc length.
In addition, a certain range is required to
maintain arc stability at any given welding
current level.
ARC TRAVEL SPEED
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As the material thickness increases, the travel
speed must be lowered.
For a given material thickness and joint design,
as the welding current is increased, so is the arc
travel speed. The converse is also true.
Higher welding speeds are attainable by using
the forehand welding technique.
WELDING TECHNIQUES
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Torch Position
Split the angle (90 degrees = 45 degree split)
 5 degree rake
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Good
Weld
Voltage to
High
Voltage to
Low
Too Fast
Too Slow
Less Stick
Out